ASF1A: A versatile histone chaperone bridging chromatin dynamics, disease mechanisms and clinical potential (Review)

1. Introduction

Histone chaperones regulate chromatin assembly and epigenetic homeostasis (1). The anti-silencing function 1 (ASF1) family is highly conserved among eukaryotes. Humans encode two paralogs of this family, ASF1A and ASF1B (1,2). ASF1A is a conserved histone H3-H4 chaperone with a bipartite architecture that supports histone binding and post-translational regulatory modification (2-4). Canonically, ASF1A participates in two independent chromatin assembly pathways and maintains genome stability via the DNA damage response (5).

Accumulating evidence has revealed its pathogenic roles in a broad range of diseases (1). In malignant tumors, aberrantly upregulated ASF1A drives tumor proliferation, metastasis and drug resistance through multiple oncogenic signaling cascades. In non-neoplastic disorders including atherosclerosis and embryonic developmental defects, dysregulated ASF1A expression disrupts epigenetic modifications and cell fate programming. Notably, most early functional experiments failed to separate the distinct biological functions of ASF1A and ASF1B. Furthermore, translational research targeting ASF1A interventions remains limited to preclinical studies only. The present narrative review integrates current available evidence to elaborate on the physiological functions and pathogenic mechanisms of ASF1A, and further discusses its translational prospect as a clinical prognostic biomarker and therapeutic target.

2. Molecular characteristics and physiological functions of ASF1A

Literature inclusion criteria and isoform distinction

The present narrative review compiles published literature on ASF1A biology and disease associations. Given that several foundational studies in the field predate the widespread use of isoform-specific reagents, findings that reflect pan-ASF1 or combined ASF1A/B perturbation rather than ASF1A-specific manipulation are explicitly noted.

Molecular characteristics of ASF1A

ASF1A, a highly conserved histone chaperone encoded by human chromosome 6, consists of ~204 amino acids and is the mammalian homolog of yeast anti-silencing factor ASF1 (1,2). The N-terminal region of ASF1A consists of 155 amino acids and forms a highly conserved core domain with a typical immunoglobulin-like β-sandwich fold (3). The surface of this domain contains not only a deep hydrophobic binding groove but also a strongly negatively charged region, whose unique physicochemical properties enable it to specifically recognize and bind to positively charged histone H3-H4 dimers with high affinity (4,5). Structural biological studies have further revealed that ASF1A extensively interacts with the α2 helix of histone H3 and key regions of H4 through its hydrophobic groove, and competitively occupies the H3-H3 dimerization interface spatially, thereby effectively preventing the spontaneous assembly of (H3-H4)2 tetramers and ensuring the precise delivery of histones in the form of dimers (3,4,6) (Fig. 1).

Figure 1 Domain architecture and post-translational regulation of human ASF1A. The N-terminal core (1-155 aa) binds H3.1-H4 and H3.3-H4 dimers and mediates mutually exclusive delivery to the CAF-1 and HIRA complexes, respectively. The intrinsically disordered C-terminal region (156-204 aa) integrates regulatory inputs from TLK1/2-mediated phosphorylation, USP52-dependent deubiquitination and p300/CBP-associated acetylation. Ac, acetylation; P, phosphorylation; Ub, ubiquitination; ASF1A, anti-silencing function 1A; aa, amino acids; CAF-1, chromatin assembly factor 1; CBP, CREB-binding protein; CDAN1, congenital dyserythropoietic anemia type 1; IDR, intrinsically disordered region; HIRA, histone regulator A; TLK1/2, Tousled-like kinase 1/2; USP52, ubiquitin-specific peptidase 52.

Flexible C-terminal regulatory hub

In addition to the core domain, the C-terminal region of ASF1A is an intrinsically disordered region (IDR) rich in acidic amino acids with high conformational flexibility (7). This region demonstrates notable interspecies differences (for example, certain protozoan homologs can form dimers, while human ASF1A mainly exists as a monomer) and acts as a key regulatory hub in human cells (8). The presence of IDR endows ASF1A with the ability to participate in several transient or regulated protein-protein interactions and dynamically modulates its histone-binding activity through allosteric effects. Furthermore, this region is the key target for post-translational modifications (PTMs), especially serving as the phosphorylation site of Tousled-like kinases (TLK)1/2. The chaperone activity of ASF1A and the efficiency of chromatin assembly are finely regulated through cell cycle-dependent phosphorylation modifications (9).

Precise ‘traffic commander function’. Functionally, ASF1A acts as a ‘molecular traffic commander’ for the distribution of newly synthesized H3-H4 dimers, achieving precise trafficking of histones by constructing a dynamic interaction network (10).

In the replication-dependent pathway, ASF1A recognizes and binds to newly synthesized H3.1-H4 dimers with specific modifications (such as histone H4 lysine 5 acetylation/K12 acetylation), promotes their nuclear import in coordination with the nuclear import protein importin-4, and then delivers them to the chromatin assembly factor-1 (CAF-1) complex (composed of p150, p60 and p48) to complete nucleosome assembly after S-phase DNA replication (11,12).

In the replication-independent pathway, ASF1A specifically binds to the histone regulator A (HIRA) complex (containing ubinuclein-1 and calcineurin-binding protein 1), mediates the deposition of variant histone H3.3-H4 in transcriptionally active regions, enhancers and DNA damage sites and participates in transcriptional regulation and chromatin remodeling (13-15).

Notably, ASF1A is involved not only in nucleosome assembly but also in disassembly. During the differentiation of mouse embryonic stem cells, ASF1A activates the expression of lineage-specific genes by regulating the disassembly of bivalent chromatin domains (16).

Multilevel regulation of PTMs and protein stability. The function of ASF1A is strictly controlled by a sophisticated multilevel regulatory network. First, it is involved in the recruitment of histone-modifying enzymes: In yeast, ASF1 cooperates with the Rtt109-Vps75 complex to promote histone H3 lysine 56 acetylation (H3K56ac) through allosteric regulation of its acidic C-terminal region; in human cells, this function is mainly compensated by p300/CREB-binding protein (CBP) to maintain replication fork stability (17). Second, the protein stability of ASF1A is strictly regulated by the ubiquitin-proteasome system. The deubiquitinase ubiquitin-specific peptidase 52 (USP52) can directly remove the ubiquitination modification of ASF1A, enhance its stability and chromatin assembly function and thus promote cell cycle progression (18). Studies have reported that the expression of USP52 is positively associated with that of ASF1A in tumors such as breast cancer, and inhibition of USP52 accelerates ASF1A degradation and notably suppresses tumor proliferation, suggesting the important pathological significance of this axis (19,20). In addition, ASF1A can interact with proteins such as TLK1/2 kinases to further integrate cell cycle signals with chromatin assembly processes (10,21,22).

Physiological functions of ASF1A

As a key histone chaperone, ASF1A is widely involved in basic biological processes such as chromatin assembly, DNA replication, DNA damage repair, embryonic development and cellular senescence. In addition to these canonical roles, ASF1A participates in innate immune responses and vascular homeostasis (Fig. 2).

Figure 2 Context-dependent physiological functions of ASF1A. ASF1A participates in replication-coupled and replication-independent chromatin assembly, DNA damage repair via homologous recombination and non-homologous end joining, HIRA-mediated transcriptional regulation, embryonic development, cellular senescence, innate immune responses and vascular homeostasis. ASF1A, anti-silencing function 1A; ac, acetylation; CAF-1, chromatin assembly factor 1; CBP, CREB-binding protein; DSB, double-strand break; EndMT, endothelial-mesenchymal transition; HIRA, histone regulator A; HR, homologous recombination; H3K18la, histone H3 lysine 18 lactylation; H3K56ac, histone H3 lysine 56 acetylation; IPO4, importin 4; IRF3, interferon regulatory factor 3; MDC1, mediator of DNA damage checkpoint 1; Oct4, octamer-binding transcription factor 4; RAD51, RAD51 recombinase; RIF1, replication timing regulatory factor 1; ROS, reactive oxygen species; SAHF, senescence-associated heterochromatic foci; TONSL, Tonsoku-like DNA repair protein; 53BP1, p53 binding protein 1.

ASF1A is a core regulator in chromatin assembly and DNA replication: It promotes nucleosome formation and chromatin stability by binding to H3-H4 dimers and delivering them to the corresponding complexes, thus maintaining genomic integrity (13). Furthermore, it cooperates with the CAF-1 complex to deposit newly synthesized histones onto post-replicative DNA to complete replication-coupled chromatin reconstruction (7). In addition, ASF1A can work with the HIRA complex to mediate H3.3 deposition and participate in the dynamic renewal of chromatin in transcriptionally active regions (14).

ASF1A exerts multi-dimensional regulatory effects in DNA damage repair: It mediates histone replacement at damage sites, recruits the MMS22-like DNA repair protein, Tonsoku-like DNA repair protein complex and promotes RAD51 recombinase loading to drive homologous recombination repair (13); in double-strand break (DSB) repair, ASF1A not only activates ATM kinase to transduce damage signals by promoting H4K16 acetylation (22,23), but also finely regulates the local level of histone ubiquitination through interaction with mediator of DNA damage checkpoint 1, thereby affecting p53 binding protein 1 (53BP1) recruitment and balancing the classical non-homologous end joining (NHEJ) pathway (24). Meanwhile, ASF1A can also be recruited to break sites by the 53BP1-replication timing regulatory factor 1 (RIF1) complex, which protects DNA ends by promoting heterochromatinization and maintains the NHEJ-dominated repair mode in BRCA1-deficient cells (25).

ASF1A is essential for embryonic development and cellular senescence. After mouse fertilization, it mediates H3.3 deposition and rapid nucleosome assembly in the paternal pronucleus, and its knockdown leads to decreased levels of H3K56ac and octamer-binding transcription factor 4 (Oct4) expression in embryos, impairing pre-implantation developmental potential (13). In somatic cells, ASF1A promotes the formation of senescence-associated heterochromatic foci and drives cell cycle exit, thereby regulating the process of cellular senescence (7).

In addition, ASF1A has also been implicated in immune and vascular biology. Upon viral infection, ASF1A binds to CBP to promote H3K56ac, enhance IFN regulatory factor 3 dependent IFN-β expression and participate in the innate immune response (25). In atherosclerosis, ASF1A acts as a cofactor of P300 to promote histone H3 lysine 18 lactylation (H3K18la), drive epithelial-mesenchymal transition (EMT) and accelerate disease progression (26).

ASF1A and ASF1B

ASF1A and ASF1B share notable core commonalities: Both participate in histone H3-H4 dimer binding and nucleosome assembly (6), can be phosphorylated by TLK2 to regulate DNA replication-coupled nucleosome assembly and cell proliferation, and both can interact with congenital dyserythropoietic anemia type 1 (CDAN1) (27). Furthermore, both are essential for early embryonic development, as demonstrated by their distinct but complementary roles during mouse fertilization and pre-implantation development (28), and both are overexpressed in acute myeloid leukemia (AML) and can serve as potential therapeutic targets (29). However, it is important to note that pan-cancer expression analyses establishing prognostic value have largely focused on ASF1B in solid tumors (30-35), whereas ASF1A-specific expression data in cancer are derived from individual disease studies rather than comprehensive pan-cancer surveys (35,36).

The functional and disease-associated differences between ASF1A and ASF1B are distinct. ASF1A focuses on regulating histone H3.3 assembly, H3K56ac modification and embryonic epigenetic reprogramming (28), acts as a Notch transcriptional coactivator to promote disease progression in blast crisis of chronic myeloid leukemia (CML-BC) (36) and has a causal association with alcoholic hepatocellular carcinoma (HCC) (37). ASF1B has cell-cycle promotion as its core function, serves as an independent prognostic factor in the majority of solid tumors and its silencing can induce S-phase arrest, DNA damage and apoptosis of tumor cells, as well as enhance chemosensitivity (38-41). ASF1B can also regulate tumor progression through specific signaling pathways such as AKT/forkhead box P3 and CBP/c-Myc (42-44).

ASF1A and ASF1B also exhibit specificity in protein interaction and clinical notability. The structural domain requirements for binding to CDAN1 are different (6), as ASF1B can interact with CDK9 to regulate the cell cycle (33), while ASF1A specifically participates in the formation of the Notch signaling complex. In terms of disease research, studies on ASF1A are focused on CML-BC and alcoholic HCC (36,37), while those on ASF1B have a broader pan-cancer coverage, and the expression of ASF1B is associated with tumor mutational burden, microsatellite instability and immunotherapy response (30,34,35). The Arabidopsis thaliana model also suggests that they may have functional divisions in the selection of histone variants (14).

Given the substantial sequence identity within the histone-binding surface and the partial functional redundancy between ASF1A and ASF1B, phenotypes observed upon combined depletion or pan-ASF1 perturbation cannot be unambiguously assigned to either paralog alone. Therefore, the present review distinguishes ASF1A-specific findings from ASF1B-specific observations and explicitly label shared or compensatory mechanisms derived from co-depletion studies as ‘ASF1 family’ or ‘ASF1A/B’ effects, rather than attributing them solely to ASF1A.

3. Role and molecular mechanisms of ASF1A in diseases

Malignant diseases

This section summarizes the oncogenic roles and underlying molecular mechanisms of ASF1A in leukemia, breast cancer, colorectal cancer, hepatocellular carcinoma, gastric cancer and prostate cancer.

Leukemia. Leukemia is a type of cancer originating from the bone marrow hematopoietic system. The main characteristics of leukemia are impaired differentiation and abnormal proliferation of hematopoietic stem cells or progenitor cells, leading to the massive accumulation of immature leukemia cells in the bone marrow and peripheral blood, thus inhibiting normal hematopoietic function (45,46). Studies have shown that abnormal chromatin regulation and epigenetic imbalance serve important roles in the occurrence and development of leukemia, among which histone chaperones are considered important regulatory factors (1,47). As a key H3/H4 histone chaperone, ASF1A maintains chromatin stability by participating in nucleosome assembly and DNA replication processes and sustains the uncontrolled proliferation of leukemia cells (36).

Both ASF1A and its homolog ASF1B are overexpressed in AML. Studies have demonstrated that the TLK-ASF1 signaling pathway can promote the proliferation of leukemia cells by regulating cell cycle progression and DNA damage response, and depletion of ASF1 proteins (ASF1A/B) can markedly inhibit the growth of leukemia cells, suggesting that this pathway may be a potential therapeutic target for AML (27,29). In addition, the expression of ASF1A is notably elevated in CML-BC. ASF1A can act as a coactivator of the Notch transcription complex and enhance RBPJ binding by promoting H3K56ac modification in the promoter region of Notch target genes, thereby activating the Notch signaling pathway and causing myeloid cell differentiation arrest. This accelerates the progression of the disease to blast crisis (36). Given the key roles of Notch, Wnt and PI3K/Akt signaling pathways in the maintenance of leukemia stem cells, chromatin regulation mediated by the ASF1 family may serve an important role in leukemia progression (48,49) (Fig. 3).

Figure 3 Mechanistic roles of ASF1A across malignant and non-neoplastic disorders. Dysregulated ASF1A drives leukemogenesis, tumor proliferation, EMT and therapeutic resistance through distinct signaling axes in a tissue-specific manner, while its perturbation in non-neoplastic contexts disrupts embryonic development and promotes vascular pathology. ASF1A, anti-silencing function 1A; Ac, acetylation; CRPC, castration-resistant prostate cancer; EMT, epithelial-mesenchymal transition; EndMT, endothelial-mesenchymal transition; H3K56ac, histone H3 lysine 56 acetylation; H3K18la, histone H3 lysine 18 lactylation; ICB, immune checkpoint blockade; NHEJ, nonhomologous end-joining; PARPi, poly (ADP-ribose) polymerase inhibitor; ZEB1, zinc finger E-box binding homeobox 1.

Breast cancer. Breast cancer is one of the most common malignant tumors in women worldwide and a key cause of cancer-related mortality in women (50). Although molecular subtyping and targeted therapy have improved the prognosis of certain patients, tumor metastasis, drug resistance and recurrence remain challenges in treatment. Therefore, it is key to analyze the molecular mechanisms of breast cancer and explore new therapeutic targets (51).

The histone chaperone ASF1A serves a key role in the occurrence and progression of breast cancer, involving chromatin structure maintenance, gene expression regulation, DNA damage repair and tumor cell proliferation (12). ASF1A silencing can be achieved through epigenetic modifications, RNA polymerase II transcription inhibition and post-transcriptional regulation of microRNAs, and restoration of its expression can effectively inhibit tumor cell proliferation and induce cell death (52).

In terms of molecular mechanisms, ASF1 family members, including ASF1A and ASF1B, coordinate replication-coupled histone supply at replication forks (12). ASF1A specifically delivers H3-H4 dimers to the CAF-1 and HIRA complexes, thereby regulating chromatin structure and gene transcription (53,54). Upon DNA damage, ASF1 proteins, particularly ASF1A through its interaction with RIF1, promote chromatin remodeling and local heterochromatinization at damage sites, maintain the stability of DNA break ends and facilitate NHEJ repair (55). ASF1A and ASF1B exhibit partially redundant functions in DSB repair, although ASF1A shows a stronger association with the RIF1-53BP1 complex (53). In BRCA1-deficient breast cancer cells, ASF1A deletion markedly affects DNA end resection and homologous recombination processes, suggesting it has a key role in regulating the sensitivity of breast cancer to DNA damage therapies such as poly(ADP-ribose) polymerase inhibitors (53). In addition, the function of ASF1A is regulated by the TLK signaling axis, and TLK1/2 modulates the activity of ASF1A through phosphorylation, participating in DNA replication and chromatin assembly processes (27,56). Studies have reported that TLK inhibitors can reduce the phosphorylation level of ASF1A, interfere with DNA replication and trigger the DNA damage response, thereby inhibiting the growth of triple-negative breast cancer cells, suggesting the potential targeting value of the TLK-ASF1 signaling axis in breast cancer therapy (29,57).

Colorectal cancer (CRC). CRC is the third most common malignant tumor worldwide and the second leading cause of cancer-related mortality (58). The occurrence of CRC is closely associated with genetic variations (such as inactivating mutations of the APC regulator of Wnt signaling pathway gene leading to the activation of the Wnt/β-catenin signaling pathway and abnormal lipid metabolism), lifestyle (high-calorie diet, red meat intake, smoking, obesity and alcohol consumption) and intestinal flora imbalance (elevated serum D-lactic acid and endotoxin levels, and abnormal flora distribution in patients) (59-61). The occurrence of CRC and its development are often accompanied by several genetic and epigenetic abnormalities (62). Previous studies have reported that ASF1A is notably highly expressed in CRC tissues and is closely associated with enhanced proliferation and invasion abilities of tumor cells. As a key chromatin assembly factor, ASF1A promotes malignant proliferation of CRC cells when abnormally expressed by regulating gene transcription programs (63,64).

In terms of molecular mechanisms, ASF1A is mainly involved in the occurrence and development of CRC by maintaining chromatin structure stability and regulating DNA replication. ASF1A delivers histone H3-H4 dimers to the chromatin assembly complex, promotes nucleosome reconstruction after DNA replication and thus maintains chromatin structure stability (12). In addition, ASF1A is also involved in the DNA damage repair response, helping tumor cells survive under genomic stress by regulating the homologous recombination repair pathway (63). In colon cancer cells, ASF1A can directly bind to histone H4 and positively regulate H4 expression, thereby activating autophagy-related genes (ATG) and promoting the cellular autophagy process (65). Functional experiments have shown that knockdown of ASF1A can markedly reduce autophagosome formation and decrease the microtubule-associated protein light chain 3-II/I ratio, suggesting that the ASF1A-H4 axis serves an important role in the regulation of autophagy in CRC (64). Meanwhile, the high expression of ASF1A in gastrointestinal tumors is also closely associated with the abnormal activation of the Wnt/β-catenin signaling pathway, further promoting the malignant progression of CRC (62,64).

HCC. HCC is the most common type of primary liver cancer (accounting for ~90%), originating from hepatocytes and belonging to digestive system malignant tumors (66). The global incidence ranks sixth, and it is the third or fourth leading cause of cancer-related mortality. The global number of cases is expected to exceed 1 million in 2026, with a rising mortality rate year by year (67-69). A total of ~80% of HCC cases are associated with chronic liver disease and cirrhosis. The traditional etiologies are mainly hepatitis B virus (HBV) and HCV infection (abnormal genes such as cytoplasmic polyadenylation element binding protein 3 and RAB26, member RAS oncogene family exist in HBV-related HCC) and long-term alcohol abuse (no safe threshold) (70-73). In recent years, non-alcoholic fatty liver disease, metabolic dysfunction-associated steatohepatitis and metabolic dysfunction-associated steatotic liver disease have become the main etiologies in Western countries and are expected to become the major driving factors worldwide (74). In addition, exposure to aflatoxin is also a risk factor, and the proportion of HCC in non-viral and non-cirrhotic settings is increasing (75).

The Cancer Genome Atlas (TCGA) multi-omics analysis combined with functional experiments revealed that ASF1A is notably upregulated in HCC tissues, and its high expression can markedly promote the proliferation, migration and colony-forming abilities of liver cancer cells (37). In addition, Mendelian randomization analysis incorporating ASF1A as a key node within the telomere maintenance signature further demonstrated a causal association between high ASF1A expression and increased risk in alcohol-associated HCC, suggesting its role in the occurrence and development of alcohol-related HCC. In addition, relevant mechanistic studies have reported that knockdown of ASF1A can notably activate the p53-p21 signaling pathway and induce senescence of liver cancer cells (37,76). Furthermore, clinical correlation analysis indicated that high expression of ASF1A is associated with low expression of p21, and combined detection of the two can be used as a potential predictive indicator for worse prognosis of patients with HCC.

Gastric cancer. Gastric cancer is one of the common malignant tumors of the digestive system, whose occurrence and development involve multi-factor etiologies and complex molecular mechanisms. Epidemiological and etiological studies have reported that Helicobacter pylori infection can activate the NF-κB pathway by upregulating steroid receptor RNA activator 1, promoting the proliferation and migration of gastric mucosal epithelial and gastric cancer cells (77,78). Epstein-Barr virus infection is also associated with ~10% of gastric cancers, and its encoded latent membrane protein 2A can upregulate programmed death-ligand 1 through the NF-κB/transporter 1, ATP binding cassette subfamily B member 1/JNK/STAT1 axis to mediate immune evasion (79). The A allele of the upstream transcription factor 1 (USF1)-202 G/A polymorphism site is associated with an increased risk of gastric cancer and decreased serum USF1 levels (80). At the clinical and molecular levels, gastric cancer can be divided into early and metastatic gastric cancer. Blue laser imaging endoscopy is helpful for the precise identification of early lesions, and the hemoglobin, albumin, lymphocytes and platelets score can be used to evaluate the prognosis of patients with advanced disease (81). Tumor progression is often accompanied by abnormal activation of signaling pathways such as EMT, Wnt/β-catenin, PI3K-AKT and Hippo/Yes-associated protein, as well as epigenetic regulatory disorders (82-86).

As a key histone chaperone, ASF1A is highly expressed in gastrointestinal tumors and serves an important oncogenic role in gastric cancer. ASF1A can promote cell proliferation and invasion by interacting with β-catenin, and induce EMT to enhance migration ability by upregulating zinc finger E-box binding homeobox 1 and downregulating E-cadherin (64). In addition, high expression of ASF1A is closely associated with resistance to immune checkpoint blockade therapy in gastric cancer and can serve as an immune microenvironment marker and a target for combination therapy (87). ASF1A also maintains the integrity of extrachromosomal DNA hubs and affects oncogenic transcription by regulating H3K56ac and interacts with molecules such as bromodomain containing 4, ubiquitin-specific peptidase 7 and CBP (88), participating in the regulation of chromatin accessibility in the context of SET domain containing 2 (SETD2) deficiency (24). CDAN1 can bind to and inhibit the activity of ASF1A (6), while ASF1A can also mediate the delivery of H3.3/H4 to the HIRA complex (89). The aforementioned mechanisms collectively contribute to the malignant progression of gastric cancer. Notably, while ASF1A has been implicated in gastrointestinal malignancies through β-catenin interactions (64), its paralog ASF1B is also upregulated in gastric cancer tissues and is associated with worse prognosis via PI3K/AKT/mTOR signaling (86), suggesting potential functional redundancy or paralog-specific oncogenic programs that warrant further dissection.

Prostate cancer (PC). PC is the second most common malignant tumor worldwide and one of the most common malignant tumors in men. It originates from prostate glandular epithelial cells, and it was associated with ~396,792 mortalities in 2022(90). The clinical phenotypes of PC are markedly different, ranging from indolent and slowly progressive to highly aggressive metastatic castration-resistant PC (91). Disease progression is often accompanied by an increase in the Gleason score, indicating decreased differentiation and worse prognosis; age is an important risk factor, and for each 1-year increase, the risk of high-risk PC with a Gleason score ≥3+4 increases by ~11% (92). Early diagnosis and therapeutic strategies are key for curbing disease progression, and research focuses on exploring tumor molecular mechanisms, the immune microenvironment and new therapeutic targets (93).

ASF1A is highly expressed in PC and may reduce immune checkpoint blockade efficacy by remodeling the tumor immune microenvironment and inhibiting antitumor immune responses (87). ASF1A is also notably associated with the unrestricted proliferative capacity of tumor cells (87). The oncogenic effect of ASF1A is partially dependent on the inhibition of the p53-p21 pathway: In the context of wild-type p53, ASF1A deletion can activate this pathway and trigger cell cycle arrest. TCGA data analysis reported that high expression of ASF1A is negatively associated with low expression of p21, suggesting that ASF1A can promote the progression of prostate cancer by interfering with the p53 signaling pathway (76).

Non-neoplastic disorders

This section discusses the roles of ASF1A in atherosclerosis and reproductive/developmental disorders, focusing on its metabolic-epigenetic interactions and epigenetic reprogramming functions.

Atherosclerosis (AS). AS is a chronic inflammatory vascular disease involving multiple processes such as lipid deposition, endothelial dysfunction, inflammatory response and phenotypic transformation of smooth muscle cells (94). In recent years, studies have reported that epigenetic regulation serves a key role in the progression of AS. Among them, ASF1A has been demonstrated to promote disease development through a metabolic-epigenetic interaction mechanism. In the blood vessels of patients with AS, lipid peroxidation can induce EMT of endothelial cells, a process driven by lactate-mediated H3K18la. ASF1A, as a cofactor of P300, precisely regulates the enrichment of H3K18la in the promoter region of specific genes, thereby activating transcription and promoting EMT. Endothelial-specific knockout of ASF1A can notably inhibit EMT, improve endothelial function and alleviate atherosclerotic lesions in mouse models. In addition, inhibition of glycolysis can suppress ASF1A-mediated transcriptional activation and EMT by reducing the level of H3K18la, suggesting that metabolic intervention may exert a therapeutic effect by regulating the function of ASF1A (26,94).

Reproductive and developmental disorders. ASF1A serves a core role in epigenetic regulation in multiple key links of reproductive development, and its abnormal expression or function can trigger a series of problems such as fertilization disorders, embryonic development arrest, reproductive toxicity and impaired fertility. During early embryonic development, ASF1A is indispensable for mouse fertilization and pre-blastocyst embryonic development and can coordinately regulate of histone H3.3 in the paternal pronucleus, while participating in the regulation of H3K56ac modification and the expression of the pluripotency gene Oct4. Deletion of ASF1A directly leads to mouse embryonic development arrest (28). In environmental toxin-induced reproductive toxicity, monobutyl phthalate, an environmental endocrine disruptor, can notably upregulate the expression of ASF1A mRNA in porcine oocytes, accompanied by a decrease in histone H3 lysine 36 trimethylation levels, reduced SETD2 expression and abnormal DNA methylation patterns, ultimately leading to embryonic developmental disorders, suggesting that ASF1A is involved in mediating reproductive system damage induced by environmental toxins (95).

In oocyte reprogramming disorders, the expression of ASF1A in bovine oocytes is markedly downregulated under low-calcium culture conditions, and this change is closely associated with decreased oocyte maturation ability and impaired epigenetic reprogramming function, further confirming the key regulatory role of ASF1A in the epigenetic reprogramming process of oocytes (96). Regarding male infertility, a study using Arabidopsis thaliana reported that histone H3.3 deposition mediated by the ASF1A/1B-HIRA complex is necessary for normal male gametophyte development (97). In the process of human spermatogenesis, ASF1 can bind to the histone variant H3T and participate in the chromatin remodeling process during spermatogenesis, and its functional abnormalities may affect sperm maturation, thus affecting male fertility (97,98).

Methodological considerations for ASF1A/ASF1B attribution

A key limitation in interpreting the literature is that several functional studies employ pan-ASF1 antibodies or combined ASF1A/B depletion. Given their shared histone-binding surface and redundant roles in S-phase histone deposition and DNA replication-coupled chromatin assembly, phenotypes from such studies cannot be unambiguously assigned to ASF1A alone. The seminal study by Groth et al (12) utilized combined small interfering (si)RNA depletion of ASF1A and ASF1B to demonstrate replication fork regulation, and TLK-ASF1 pathway study in AML revealed that ASF1B is the dominant driver of leukemic progression while ASF1A may provide compensatory function (29). Similarly, peptide inhibitors targeting the ASF1-histone interface (99) exhibit nanomolar affinity for both ASF1A and ASF1B. Future studies using isoform-specific genetic ablation (such as CRISPR-Cas9 knockout or paralog-specific siRNA) are required to resolve the individual contributions of ASF1A and ASF1B in specific malignancies and to validate whether ASF1A-targeted therapeutics can achieve sufficient specificity without disrupting ASF1B-dependent physiological processes.

Critical appraisal of ASF1A-centric pathological models

Despite the expanding body of literature implicating ASF1A in diverse malignancies and non-neoplastic disorders, several conceptual and experimental limitations constrain the robustness of current disease models. First, much of the evidence linking ASF1A to tumor progression derives from correlative analyses, most notably pan-cancer transcriptomic datasets, rather than from prospective, isoform-specific functional studies. While expression profiling consistently associates high ASF1A with adverse outcomes (65,76), these observations do not establish causality; they merely identify ASF1A as a passenger or facilitator of oncogenic chromatin states. Second, the mechanistic narratives remain fragmented across disease types. ASF1A has been reported to activate Notch signaling in CML, Wnt/β-catenin in gastrointestinal cancers (GICs) and p53-p21 in liver cancer and PC, yet no unified framework explains how the same histone chaperone selectively couples to distinct oncogenic pathways in different cellular contexts. This disconnect suggests that certain pathway assignments may reflect secondary or compensatory effects rather than direct, primary regulatory roles. Third, the functional duality of ASF1A, which can be oncogenic in most tumors yet potentially protective in DNA damage repair and innate immunity (22,25), remains poorly understood at the molecular level. The absence of tissue-specific or temporally controlled genetic models (such as conditional knockout mice or patient-derived organoids) means that cell-autonomous requirements cannot be confidently distinguished from systemic or microenvironmental adaptations. Finally, nearly all therapeutic hypotheses rest on cell-line-based perturbation studies and syngeneic mouse models with limited translational fidelity. Collectively, these gaps indicate that the role of ASF1A in pathogenesis remains a plausible but still largely hypothetical one, as the available knowledge does not yet constitute a mechanistically resolved or clinically actionable knowledge base. The expression characteristics, molecular mechanisms and supporting experimental evidence of ASF1A in different diseases are summarized in Table I.

Table I Expression profile, potential mechanisms and experimental evidence of ASF1A in different diseases.

Table I

Expression profile, potential mechanisms and experimental evidence of ASF1A in different diseases.

A, Neoplastic disease
Disease	ASF1 expression change	Core mechanism of action	Key experimental evidence/clinical relevance	(Refs.)
Acute myeloid leukemia	Marked overexpression of ASF1A (with concomitant ASF1B upregulation)	TLK-ASF1 axis regulates cell cycle progression and DNA damage response, providing epigenetic support for leukemic cell proliferation	Knockdown of ASF1 markedly inhibits leukemia cell proliferation and high ASF1 is closely associated with abnormal proliferation of leukemic cells	(29)
Chronic myeloid leukemia blast crisis	Markedly elevated	ASF1A acts as a coactivator of the Notch complex, promotes H3K56ac modification, enhances RBPJ binding and activates Notch signaling to block myeloid differentiation	High ASF1A expression accelerates progression to blast crisis and H3K56ac at Notch target gene promoters is notably enhanced	(36)
Breast cancer	Markedly overexpressed	ASF1A participates in nucleosome assembly and balances NHEJ/HR repair, activity is modulated by TLK1/2-mediated phosphorylation and regulates PARP inhibitor sensitivity in BRCA1-deficient cells	ASF1A silencing induces breast cancer cell death via epigenetic and transcriptional regulation, TLK inhibition reduces ASF1A phosphorylation and suppresses triple-negative breast cancer growth	(12,27,29,53,55-57)
Colorectal cancer	Markedly overexpressed	Maintains chromatin stability and regulates DNA replication and homologous recombination, is associated with Wnt/β-catenin pathway hyperactivation and binds histone H4 to upregulate ATG genes and promote autophagy	High ASF1A is associated with enhanced proliferation, invasion and shorter overall survival, serving as an independent prognostic factor, and ASF1A knockdown reduces autophagosome formation and the LC3-II/I ratio	(12,64,65)
HCC	Markedly upregulated	Inhibits p53-p21 pathway to confer cancer cell senescence resistance and is causally linked to alcohol-associated HCC	High ASF1A promotes proliferation, migration and colony formation of HCC cells, combined detection of ASF1A, and p21 predicts worse prognosis and Mendelian randomization suggests a causal role in alcoholic HCC	(37,76)
Gastric cancer	Overexpressed	Interacts with β-catenin to trigger EMT via upregulation of ZEB1 and downregulation of E-cadherin, modulates H3K56ac to maintain ecDNA hub integrity and interacts with BRD4/USP7/CBP to regulate chromatin accessibility	ASF1A facilitates tumor proliferation, invasion and immune escape and high expression is closely associated with resistance to immune checkpoint blockade therapy	(65,87,88)
Prostate cancer	Overexpressed	Represses p53-p21 signaling to drive cell cycle progression, remodels tumor immune microenvironment and suppresses antitumor immunity	High ASF1A is negatively associated with p21 expression and uncontrolled tumor growth and elevated ASF1A predicts worse response to ICB therapy	(76,87)
B, Non-neoplastic disease
Disease	ASF1 expression change	Core mechanism of action	Key experimental evidence/clinical relevance	(Refs.)
Atherosclerosis	Functionally recruited as a P300 cofactor	ASF1A serves as a P300 cofactor to enrich H3K18la at specific gene promoters, thereby activating transcription and driving EndMT	Endothelial-specific ASF1A knockout suppresses EndMT and alleviates atherosclerotic lesions in mice and glycolysis inhibition reduces H3K18la and blocks ASF1A-mediated EndMT	(26)
Reproductive and developmental disorders	Abnormal expression upon toxin exposure or low-calcium culture	Mediates H3.3 deposition, H3K56ac and Oct4 expression during early embryonic development, regulates oocyte epigenetic reprogramming and male gametophyte development, and binds histone variant H3T during human spermatogenesis	ASF1A deletion leads to mouse preimplantation embryonic arrest, MBP exposure upregulates ASF1A and causes epigenetic disturbance and embryonic developmental defects, low-calcium induced ASF1A decline impairs oocyte maturation and reprogramming and ASF1A-H3T binding participates in chromatin remodeling during human spermatogenesis	(28,95-98)

[i] AML, acute myeloid leukemia; ASF1, anti-silencing factor 1; ASF1A, anti-silencing function 1A; ATG, autophagy-related gene; BRD4, bromodomain-containing protein 4; CBP, CREB-binding protein; ecDNA, extrachromosomal DNA; EMT, epithelial-mesenchymal transition; EndMT, endothelial-mesenchymal transition; HCC, hepatocellular carcinoma; H3K56ac, histone H3 lysine 56 acetylation; H3K18la, histone H3 lysine 18 lactylation; ICB, immune checkpoint blockade; LC3-II/I, microtubule-associated protein light chain 3-II/I; MBP, monobutyl phthalate; NHEJ/HR, nonhomologous end-joining/homologous recombination; Oct4, octamer-binding transcription factor 4; PARP, poly(ADP-ribose) polymerase; RBPJ, recombination signal binding protein for immunoglobulin κ J region; TLK, Tousled-like kinase; USP7, ubiquitin specific peptidase 7; ZEB1, zinc finger E-box binding homeobox 1.

4. Clinical translation of ASF1A

Application as a biomarker

The clinical utility of ASF1A as a biomarker is primarily evident in prognostic assessment and prediction of therapeutic response, whereas evidence supporting its diagnostic value remains insufficient. Regarding prognosis, the role of ASF1A is well-established in retrospective datasets. Pan-cancer analyses [such as TCGA/Genotype-Tissue Expression (GTEx) datasets (100)] demonstrate notable ASF1A overexpression in solid tumors such as HCC, CRC and GICs. This overexpression is strongly associated with worse overall survival, establishing ASF1A as an independent prognostic factor for adverse outcomes (65,76). In CML, ASF1A levels are markedly elevated in the blast crisis phase compared with those in the chronic phase, serving as a negative predictor of disease progression (36).

The prognostic importance of ASF1A is mechanistically associated with specific regulatory pathways. In HCC and PC, it promotes proliferation and senescence resistance by suppressing the p53-p21 pathway (76); in GIC, it drives stemness and invasiveness via β-catenin-mediated activation of c-MYC and leucine-rich repeat-containing G-protein coupled receptor 5(64); and in CML, it acts as a co-activator of the Notch transcriptional complex, inducing H3K56ac to block differentiation (36). Furthermore, Mendelian randomization analysis has demonstrated a causal link between high ASF1A expression and increased risk in alcohol-associated HCC (37). Notably, the robust prognostic value of ASF1A has facilitated its integration into multi-gene predictive models. For instance, a dual-gene risk signature comprising ASF1A and Holliday junction recognition protein effectively predicts survival and immunotherapy sensitivity in HCC (101). Additionally, as a core component of a phosphatase and tensin homolog-autophagy risk score, ASF1A has been demonstrated to outperform the Tumor Immune Dysfunction and Exclusion score in predicting responses to immune checkpoint blockade (12).

In terms of therapeutic response monitoring, ASF1A shows promise. The expression levels of ASF1A are closely associated with the tumor immune microenvironment (TIME), serving as a characteristic marker (87). A preclinical study using an ASF1A-targeted immuno-PET tracer (68Ga-AP1, a 68Ga-labeled ASF1A-binding peptide) revealed that signal intensity was negatively associated with the response to anti-programmed cell death-1 (PD-1) therapy. This suggests that ASF1A could serve as a non-invasive, dynamic tool for assessing the TIME and guiding patient stratification for immunotherapy (87). Conversely, the specific genetic status of ASF1A also holds predictive value: Homozygous deletion of ASF1A, occurring in 10-15% of tumors, impairs NHEJ repair. Consequently, this deficiency serves as a biomarker for heightened sensitivity to radiotherapy or DNA double-strand break-inducing chemotherapies (24).

However, it is important to acknowledge that all current prognostic data are derived from retrospective bioinformatic analyses (such as TCGA/GTEx) rather than prospectively validated assays with predefined cutoffs. Direct clinical evidence supporting ASF1A for early screening or pathological differentiation (such as sensitivity, specificity and area under the curve in prospective cohorts) is currently unavailable. Similarly, experimental evidence directly linking ASF1A expression levels to efficacy or resistance to conventional chemotherapy remains limited (36,37,65,76,87).

Development of therapeutic targets

By regulating chromatin assembly, DNA repair and key signaling pathways, ASF1A has emerged as a novel therapeutic target. Current strategies focus on direct inhibition, function-state-guided personalized therapy and combination interventions (Table II).

Table II Clinical translational applications of ASF1A (biomarkers and therapeutic targets).

Table II

Clinical translational applications of ASF1A (biomarkers and therapeutic targets).

A, Biomarker application
Disease	Biological type	Molecular mechanism/cell/animal/clinical evidence	(Refs.)
HCC	Tissue mRNA + multigene prognostic model	High ASF1A expression is associated with worse prognosis, ASF1A-HJURP signature predicts patient survival and immunotherapy responsiveness and combined detection with p21 improves prognostic accuracy	(76,101)
Colorectal cancer	Tissue mRNA	High ASF1A is associated with shortened overall survival and acts as an independent prognostic factor validated by independent cohorts and drives tumor progression by activating β-catenin target transcription	(64)
Gastrointestinal cancer	Tissue protein/mRNA	Interacts with β-catenin to upregulate stemness-related genes (c-MYC, CCND1, ZEB1 and LGR5), and high expression is closely associated with tumor metastasis	(64)
Prostate cancer	Tissue mRNA + immune microenvironment marker	High ASF1A is negatively associated with p21 level, tumor iPET enables non-invasive detection and ASF1A over-expression mediates ICB resistance	(76,87)
B, Therapeutic target application
Disease	Biological type	Molecular mechanism/cell/animal/clinical evidence	(Refs.)
Various solid tumors	ASF1A-H3/H4 targeting peptide inhibitor	Bakail peptide inhibitor binds ASF1A at nanomolar affinity and disrupts histone interaction, suppresses tumor proliferation, migration and induces cell cycle arrest in vitro, and intra-tumoral injection inhibits xenograft tumor growth in mice	(99)
Tumors with ASF1A homozygous deletion (10-15%)	Functional molecular marker	ASF1A deficiency impairs NHEJ repair and confers high sensitivity to radiotherapy and DSB-inducing chemotherapy	(24)
Colorectal cancer	ASF1A-H4 autophagy axis	ASF1A binds histone H4 and modulates H4Y72 phospho-rylation to activate ATG genes; ASF1A knockdown reduces autophagosome formation and LC3-II/I ratio and targeting this axis suppresses tumor-protective autophagy	(65)
HCC/prostate cancer	p53-p21 signaling axis	ASF1A inhibition activates the p53-p21 pathway and induces cancer cell senescence and TCGA data demonstrates negative associations between ASF1A and p21 expression	(76)
ASF1A-high prostate cancer	Radionuclide-labeled targeting peptide (Ga/Lu/Ac-AP1)	The peptide specifically targets ASF1A-overexpressing tumors, improves antitumor efficacy and prolongs survival in animal models and combination with a PD-1 antibody reverses immune resistance	(87)
Drug-resistant residual tumors	Evolutionary game theory-based sequential strategy	After conventional chemotherapy eliminates most tumor cells, ASF1A-targeted therapy may eliminate residual resistant clones and enhance clonal competition to achieve tumor controla	(102)

[i] ^aBased on evolutionary game theory modeling; whether ASF1A-targeted therapy can leverage such dynamics remains speculative. ASF1A; anti-silencing function 1A; CCND1, cyclin D1; HCC, hepatocellular carcinoma; HJURP, Holliday junction recognition protein; ICB, immune checkpoint blockade; iPET, immune positron emission tomography; LC3-II/I, microtubule-associated protein light chain 3-II/I; LGR5, leucine-rich repeat-containing G-protein coupled receptor 5; NHEJ, nonhomologous end-joining; PD-1, programmed cell death protein-1; TCGA, The Cancer Genome Atlas; ZEB1, zinc finger E-box binding homeobox 1; AP1, ASF1A-binding peptide 1.

The most advanced progress involves peptide inhibitors targeting the ASF1-histone interaction interface. A structural study indicated that these inhibitors exhibit nanomolar affinity for both ASF1A and ASF1B (dissociation constant of ~3 and 2 nM, respectively) in vitro, effectively disrupting ASF1 binding to histones H3/H4(99). Functionally, they dose-dependently suppress proliferation, migration and invasion while inducing cell cycle arrest. In syngeneic mouse models, intratumoral injection of these lead peptides notably inhibited tumor growth, providing proof-of-concept for ASF1-targeted therapy (99). Furthermore, leveraging ASF1A overexpression, radioligand therapy strategies have been developed. Peptides AP1 labeled with Lutetium-177 (177Lu) or Actinium-225 (225Ac) specifically accumulate in ASF1A-high tumors. In animal models, these agents, either as monotherapy or combined with anti-PD-1 antibodies, markedly suppressed tumor growth and overcame immune resistance, demonstrating substantial potential for precision medicine (87).

The functional status of ASF1A (overexpression vs. homozygous deletion) guides distinct therapeutic approaches. In HCC and PC, where ASF1A overexpression drives uncontrolled proliferation, its inhibition induces DNA damage and activates the p53-p21 pathway, leading to senescence (76). Analysis of TCGA data has demonstrated a negative association between high ASF1A and low p21; combined detection of these markers enables more precise identification of high-risk patients, providing a rationale for targeted intervention (76). Conversely, ASF1A deficiency indicates heightened sensitivity to DNA-damaging therapies (such as radiotherapy and platinum-based chemotherapy), offering a basis for precision treatment via synthetic lethality (24).

Mechanistic insights support novel combination and sequential therapies. First, in GIC, β-catenin inhibitors completely abrogate pro-tumorigenic effects driven by ASF1A overexpression, highlighting the potential of combining ASF1A inhibitors with Wnt/β-catenin pathway blockers (64). Second, ASF1A promotes protective autophagy by positively regulating ATG family genes via the ASF1A-H4 axis (65); targeting this axis may synergize with chemotherapy by inhibiting tumor-protective autophagy. Additionally, evolutionary game theory models suggest that sequential therapy strategies exploiting inter-clonal competition may enhance therapeutic efficacy (102). However, whether ASF1A-targeted therapy could leverage such dynamics remains speculative.

Despite these advances, the clinical translation of ASF1A targeting remains entirely hypothetical. All current studies, including peptide inhibitors and radioligands, are confined to preclinical models. There are no registered trials for ASF1A-targeted agents on ClinicalTrials.gov (accessed July 2024), to the best of our knowledge, underscoring the gap between preclinical promise and clinical reality. Furthermore, no ASF1A-targeted agent has entered phase I-III clinical trials, to the best of our knowledge, and human efficacy and safety data are entirely lacking (36,76,87,101). Notable challenges persist, particularly the potential toxicity arising from the critical role of ASF1A in normal development (such as in embryogenesis) (28,103) and innate immunity (25). Thus, while literature posits that targeting ASF1A represents a promising therapeutic strategy (36), its clinical translation remains constrained by unresolved safety and efficacy barriers.

5. Conclusions and perspectives

As an evolutionarily highly conserved H3-H4 histone chaperone, ASF1A serves a central role in maintaining genomic stability and cell fate determination by regulating nucleosome assembly, DNA repair and epigenetic modifications. The present review summarizes the mechanisms by which ASF1A drives proliferation and immune evasion by activating pathways such as Notch and Wnt in several malignant tumors, including leukemia and breast cancer, and reveals its new function in regulating disease progression through metabolic-epigenetic interactions (such as H3K18la) in non-neoplastic disorders such as AS. These findings establish the important position of ASF1A as a potential prognostic indicator and exploratory therapeutic target in preclinical models.

Despite the broad prospects, the clinical translation of ASF1A still faces challenges: Its tissue-specific interaction network is not yet clear and its functional heterogeneity in different disease settings limits the development of universal therapeutic strategies. Future research should focus on the following: i) Resolving the high-resolution structure of key ASF1A complexes to facilitate the design of small molecule inhibitors; ii) performing multicenter cohort studies to assess the reliability of its use as a prognostic biomarker; and iii) developing targeted delivery systems to explore the synergistic effect of ASF1A inhibitors with chemotherapy and immunotherapy. Addressing these challenges will promote the translation of ASF1A from basic research to precision medicine and provide a new therapeutic paradigm for tumors and refractory non-neoplastic disorders.

Acknowledgements

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Funding

Funding: No funding was received.

Availability of data and materials

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Authors' contributions

JY was responsible for conceptualization, writing the original draft and resources. XZ contributed to writing the original draft, data curation and resources. LW participated in writing the original draft, data curation and investigation. XW was involved in writing the original draft, investigation and validation. TL contributed to visualization, writing the original draft and data curation. QW was responsible for conceptualization, supervision and writing-review and editing. All authors have read and approved the final version of the manuscript. Data authentication is not applicable.

Ethics approval and consent to participate

Not applicable.

Patient consent for publication

Not applicable.

Competing interests

The authors declare that they have no competing interests.

References