Roles of β‑catenin protein in non‑small cell lung cancer (Review)

Introduction

Lung cancer is the most common malignancy worldwide in terms of incidence and is also the leading cause of cancer-related death (1), with non-small cell lung cancer (NSCLC) accounting for ~89% of all lung cancer cases (2). Although chemoradiotherapy and targeted therapy have improved survival, patients with NSCLC ultimately develop resistance to these treatment regimens (3). Metastatic lung cancer is considered incurable (4); therefore, understanding the signal transduction pathways that drive lung cancer progression and metastasis is essential for developing effective treatment strategies. The Wnt/β-catenin pathway has a key role in embryonic development and tissue homeostasis (5). Abnormal activation of this pathway, which is essential for maintaining cellular homeostasis, has been observed in breast, prostate, gastrointestinal and lung cancer (6–9). The β-catenin protein is a central component of the Wnt/β-catenin signaling pathway and plays a critical role in maintaining cell-cell adhesion (10). Abnormal β-catenin expression promotes the proliferation, metastasis and drug resistance of NSCLC cells (11). The present review examines the role of β-catenin protein in epithelial-mesenchymal transition (EMT) and the tumor microenvironment (TME), discusses the mechanisms regulating its nuclear translocation and its contribution to the resistance against EGFR-tyrosine kinase inhibitors (TKIs) and explores its potential (alongside that of its coding gene) as a prognostic biomarker.

Wnt signaling pathway

The Wnt signaling pathway is a highly conserved pathway that is notably comparable in humans and insects; it plays a crucial role in regulating cell growth, division and carcinogenesis (12). The Wnt protein family comprises cysteine-rich secreted glycoproteins that are widely distributed in both vertebrates and invertebrates (13). These proteins bind to the extracellular domains of Frizzled receptors (14). Based on its dependence on β-catenin, the Wnt signaling pathway is classified into two types: canonical and non-canonical (15,16).

The canonical pathway plays a critical role in cell division and proliferation, making it an important biological target for cancer treatment (12). The β-catenin protein, a key intracellular signaling molecule, participates at every stage of this process (5). The adenomatous polyposis coli (APC)-Axin-GSK-3β-casein kinase-1 (CK1) complex, which comprises APC, Axin, CK1, protein phosphatase 2A and GSK-3β, facilitates β-catenin degradation (17). This canonical pathway functions in two states depending on the presence or absence of the Wnt ligand. In the absence of Wnt, β-catenin binds to the destruction complex, where phosphorylation of its N-terminal serine or threonine residues triggers ubiquitination and subsequent proteasomal degradation (17). In the absence of nuclear β-catenin protein accumulation, T-cell factor/lymphoid enhancer factor (TCF/LEF) transcription factors remain bound to corepressor proteins, thereby inhibiting transcription (18,19). Wnt ligands can bind to Frizzled receptors and, with the co-receptor assistance of low-density lipoprotein receptor-related proteins 5/6 (LRP5/6), activate the cytoplasmic Dishevelled (Dvl) protein (20,21). Ligand-receptor binding also activates protein kinases (PKA, PKB and PKC), as well as the PI3K and MAPK signaling pathways, which inhibit GSK-3β phosphorylation. Concurrently, Dvl inactivates the destruction complex, thereby preventing β-catenin phosphorylation and subsequent degradation (22). As β-catenin accumulates in the cytoplasm, it translocates into the nucleus, where it binds to TCF/LEF transcription factors. This interaction activates the transcription of Wnt target genes, including c-MYC, Cyclin D1 gene (CCND1) and Dickkopf-1, which regulate cell growth and development (23) (Fig. 1).

Figure 1. Role of β-catenin in the canonical Wnt signaling pathway. In the absence of the Wnt ligand, cytosolic β-catenin binds to the destruction complex, leading to its degradation. During this state, TCF/LEF transcription factors are bound to co-repressor proteins and cannot initiate transcription. When Wnt ligands bind to Frizzled receptors and LRP5/6, Dvl is activated, which inactivates the destruction complex. This inhibits β-catenin phosphorylation and degradation, allowing cytoplasmic β-catenin to accumulate and translocate into the nucleus. There, it can bind TCF/LEF transcription factors, thereby activating the transcription of Wnt target genes and promoting cell proliferation and epithelial-mesenchymal transition. TCF/LEF, T-cell factor/lymphoid enhancer factor; LRP5/6, low-density lipoprotein receptor-related protein 5/6; Dvl, Dishevelled; co-repressor pro, co-repressor protein; EMT, epithelial-mesenchymal transition; CK1, casein kinase-1; APC, adenomatous polyposis coli; βTrCP, β-transducin repeat-containing protein; DKK1, Dickkopf-1.

Non-canonical Wnt pathways regulate downstream effects through alternative signaling molecules. Key pathways include the Wnt/planar cell polarity (24), Wnt/Ras-related protein 1 signaling (25), Wnt/PKA (26), Wnt/PKC (27) and Wnt/Ca2+ (28) pathways. These pathways exhibit overlapping activities and are not entirely independent.

The Wnt signaling pathway plays a central role in the initiation and progression of lung cancer; it regulates stem cell renewal, migration, apoptosis and proliferation (29). Cancer development is associated with aberrant Wnt signaling, particularly abnormal activation of the canonical pathway driven by elevated β-catenin levels (30). Kren et al (31) reported that β-catenin protein expression is correlated with tumor grade, stage and size, with 71% of NSCLC cases showing upregulation of β-catenin in the cytoplasm and plasma membrane.

β-catenin

Structurally, β-catenin comprises three primary domains: A central armadillo (ARM) repeat region of ~550 amino acids, an N-terminal domain of 150 amino acids and a C-terminal domain containing 100 amino acids (32,33). The N-terminal domain is the site of phosphorylation by GSK-3β and CK1, whereas the C-terminal domain interacts with nuclear TCF/LEF transcription factors. On the cell membrane, β-catenin forms a complex through ARM domain binding to E-cadherin (34–36) (Fig. 2).

Figure 2. Primary structure of β-catenin protein. The β-catenin protein consists of three main domains: The N-terminal, ARM repeat and C-terminal domains. The N-terminal domain can bind to GSK-3β and CK1 for phosphorylation, a process that regulates the degradation of β-catenin. The ARM repeat domain binds to E-cadherin on the cell membrane, which enhances cell-cell adhesion. The C-terminal domain binds to nuclear TCF/LEF transcription factors, initiating the transcription of target genes. ARM, A central armadillo; GSK-3β, glycogen synthase kinase-3β; CK1, casein kinase-1; TCF/LEF, T-cell factor/lymphoid enhancer factor.

Cytoplasmic β-catenin serves multiple functions (37). Two main factors underscore the significance of the β-catenin protein. First, it establishes and maintains specific intercellular adhesion (38). Second, it regulates target gene expression through the Wnt signaling pathway (32,39). The function of β-catenin varies depending on its subcellular localization. When located on the cell membrane, the strong attachment of β-catenin to E-cadherin helps regulate cell-cell connections (40). Under normal conditions, β-catenin is predominantly found on the membrane (17). However, when the β-catenin protein levels are abnormally elevated in the cytoplasm and nucleus, it can form co-transcriptional complexes with TCF/LEF transcription factors. This process activates target gene transcription, which controls tissue structure and cell movement (41,42). Research has demonstrated that in patients with NSCLC, increased levels of cytoplasmic β-catenin protein or nuclear positivity is correlated with reduced overall survival (43). Additionally, low levels of β-catenin in the membrane are associated with a poor prognosis in patients with NSCLC (44).

The β-catenin protein is encoded by the CTNNB1 gene (11). Common mutation sites in CTNNB1, including Ser33, Ser37, Ser45, Thr41, Asp32 and Gly34, alter the N-terminal phosphorylation-dependent degradation domain of the β-catenin protein (45–47). Consequently, β-catenin produced from mutated CTNNB1 can no longer bind to the destruction complex, leading to its accumulation in the cytoplasm. A study has demonstrated that CTNNB1 mutations activate the canonical Wnt signaling pathway, thereby accelerating NSCLC progression (48). Overall, β-catenin and its coding gene, CTNNB1, are essential for gene transcription, extracellular signaling and various other cellular processes.

Regulatory mechanisms of β-catenin nuclear trans-location

Nuclear translocation of β-catenin is essential for initiating the expression of proliferation-related genes (49). Theoretically, sufficient production of stable β-catenin protein enables its entry into the cell nucleus, where it can activate proliferative programs (50). This nuclear transport is not a process of simple free diffusion but is instead governed by precise and complex regulatory mechanisms (50).

Cytoplasmic regulation and stability

Cytoplasmic regulatory mechanisms play a crucial role in determining the stability and accumulation of the β-catenin protein, which is essential for its nuclear transport (23). In normal cells, β-catenin is primarily localized at the cell membrane and is degraded in the cytoplasm by the destruction complex (17). Mutations in the CTNNB1 gene impair β-catenin phosphorylation and ubiquitination, resulting in its cytoplasmic accumulation (51). Additionally, various factors can increase cytoplasmic β-catenin levels through upregulation of CTNNB1 transcription. For example, FLVCR1-AS1 and LINC01006 are associated with high levels of CTNNB1 mRNA in lung adenocarcinoma (LUAD) cells, thereby promoting the activation of the canonical Wnt pathway (52–54). The transcription of CTNNB1 is regulated by eIF3a and WD repeat and SOCS box-containing protein 2 (53,55), while cold-inducible RNA-binding protein binds to CTNNB1 mRNA to modulate its expression (56). In addition, cytoplasmic β-catenin protein is regulated by the destruction complex, which, as aforementioned, consists of GSK-3β, APC, Axin and CK1. Aquaporin-3 (57), microRNA (miR)-1246 (58) and long non-coding RNA (IncRNA) PHLDA3 (59) downregulate GSK-3β expression at the transcriptional, translational and protein levels, respectively, thereby disrupting the function of the destruction complex. Zbed3 (60) and IncRNA DLX6-AS1 (61) downregulate Axin expression; however, the expression of APC is regulated by multiple miRNAs (62,63). These regulatory abnormalities collectively promote the accumulation of β-catenin in the cytoplasm, providing sufficient substrate for its nuclear translocation.

Nuclear import

The mechanism by which β-catenin is transported from the cytoplasm to the nucleus remains a subject of debate. Early studies suggested that β-catenin lacks a classical nuclear localization signal, does not bind to the nuclear transport receptor Importin-β1 (64) and is independent of the Ran-mediated classical nuclear import pathway. Instead, its ARM structure was thought to enable selective passage through the nuclear pore complex (65). However, more recent studies indicate that the nuclear translocation of β-catenin is Ras-related nuclear protein-dependent, with nuclear transport proteins such as KPNA2 (66) and Importin-11 (67) facilitating its nuclear import.

Nuclear retention

Once inside the nucleus, β-catenin binds with the cofactors BCL9 and Pygo to form a complex that anchors it within the nuclear space. This BCL9/Pygo complex significantly enhances the affinity of β-catenin for the TCF/LEF transcriptional complex, thereby preventing its nuclear export (68).

Other regulatory mechanisms can also influence pathway activity. Beyond the classical Wnt pathway, the nuclear translocation of β-catenin is affected by additional pathways. For instance, the amplification or mutation of the EGFR gene can activate AKT, which in turn stabilizes β-catenin by inhibiting GSK-3β or directly phosphorylating the Ser552 residue, thereby facilitating its nuclear entry (69).

Effects of β-catenin on EMT

The invasion and metastasis processes of malignant cells rely on EMT, a key driver of cancer-related mortality (70,71). EMT refers to the transformation of epithelial cells into mesenchymal-like phenotypes. This process has an important role in various biological processes, including embryonic development, tissue regeneration and tumor invasion and metastasis (72). During EMT, cells acquire mesenchymal characteristics, such as cytoskeletal alterations, loss of polarity and reduced intercellular adhesion. These changes enhance the invasiveness, resistance to apoptosis and migration ability of cells (73).

E-cadherin is essential for maintaining cell-cell adhesion and polarity (74). EMT occurs when the intercellular adhesion connections are disrupted and E-cadherin expression is lost (75). E-cadherin contains two conserved domains that bind β-catenin and p120, separately (76). The strong association between membrane-bound β-catenin and E-cadherin helps stabilize cell junctions (77). E-cadherin expression can be suppressed by three distinct families of transcription factors: Snail (Snail1, Snail2 and Snail3), Twist (Twist1 and Twist2) and Zeb (Zeb1 and Zeb2) (78). Among these, Snail1 can be activated transcriptionally by various signaling pathways, thereby initiating EMT (79).

EMT is regulated by the Wnt signaling pathway. When extracellular Wnt proteins bind to Frizzled receptors and LRP5/6, they form trimeric complexes that activate the Dvl protein (20). This activation inhibits GSK-3β phosphorylation, leading to the accumulation of cytoplasmic and intranuclear β-catenin, thereby promoting the transcription of Wnt target genes, such as Snail (78). This process accelerates EMT by inhibiting the E-cadherin protein (5).

In addition to its role in cell adhesion, E-cadherin inhibits β-catenin, thereby negatively regulating the classical Wnt pathway (80). By forming a complex with β-catenin, E-cadherin prevents the nuclear translocation of β-catenin and helps maintain the cell-cell link. The nuclear translocation of β-catenin, which stimulates transcriptional activity and promotes EMT, is facilitated by both the stimulation of the Wnt pathway and reduced E-cadherin protein expression (81).

Additionally, Wnt regulators can modulate EMT by affecting the transcriptional and translational levels of the Wnt/β-catenin signal transduction pathway (82). Among these, miRNAs are key regulators of Wnt signaling. These small molecules, typically 18–24 nucleotides in length, bind complementarily to the 3′ untranslated region (UTR) of target mRNAs, leading to their degradation or translational inhibition (83). Through this mechanism, miRNAs play a notable regulatory role in tumorigenesis (84). A number of miRNAs have been implicated in tumorigenesis, acting either as oncogenes or tumor suppressors. Specifically, miRNAs can directly regulate EMT-promoting signaling pathways and major transcription factors involved in E-cadherin expression (74). Notably, the miR-200 family, along with miR-101, miR-506, miR-155, miR-31 and miR-214, serves critical roles in controlling both EMT and mesenchymal-epithelial transition, thereby enabling cellular flexibility between the epithelial and mesenchymal states during transition (84,85). For example, in meningiomas, miR-200 suppresses the Wnt pathway by blocking the translation of CTNNB1 mRNA (86). Similarly, miR-34 inhibits both the Wnt/β-catenin/TCF signaling cascade and EMT by targeting conserved regions within the WNT1, WNT3, CTNNB1, AXIN2, LRP6 and LEF1 genes (87). Furthermore, miR-214 interacts with β-catenin as a hetero-transcriptional complex and negatively regulates the transcription of downstream target genes (88). In NSCLC cells, miR-214 inhibits the transmission of the Wnt signaling pathway by directly targeting the 3′-UTR of CTNNB1 (84).

Overall, alterations in the E-cadherin protein expression levels, certain miRNAs and the CTNNB1 gene can each regulate β-catenin protein expression, modulate the canonical Wnt pathway and drive the progression of EMT.

Influence of β-catenin on the tumor immune microenvironment

The widespread use of immune checkpoint inhibitors (ICIs) has provided significant clinical benefits for patients with NSCLC (89). However, the combination of pembrolizumab and chemotherapy achieves only a ~45.7% 2-year overall survival rate in these patients (90). Resistance to ICIs is commonly associated with three mechanisms: Deficiency of major histocompatibility complex class I (91), β-2-microglobulin gene deletions (92) and mutations in the IFN-γ signaling pathway (93). Studies have also indicated that activation of the Wnt/β-catenin pathway in tumors contributes to ICI resistance in lung cancer. This pathway promotes immune evasion, supports carcinogenesis, facilitates cancer progression and plays a role in shaping the TME (94–96).

The Wnt/β-catenin pathway promotes the expression of activating transcription factor 3 (ATF3), which in turn suppresses the expression of C-C motif chemokine ligand 4 (CCL4) (97). Reduced CCL4 expression leads to decreased infiltration of antigen-presenting cells, impairs lymphocyte homing to tumors and enables cancer cells to evade the immune surveillance more effectively (98). Beyond inhibiting CCL4 synthesis through ATF3, the Wnt/β-catenin pathway also exerts multiple additional effects that promote immune evasion. In NSCLC, activation of this pathway is associated with a higher tumor mutational burden, suggesting that these cancer cells are likely to be highly immunogenic (94). Consequently, immune editing may be required for their survival. Immune editing driven by the Wnt/β-catenin pathway involves three primary mechanisms. First, the Wnt/β-catenin pathway modulates tumor-associated macrophages (TAMs), which are typically classified as M1 and M2. The M2 subtype promotes tumor proliferation, migration and immune escape (99). IL-1β generated by TAMs can phosphorylate GSK-3β, stabilizing β-catenin and Snail and activating the Wnt/β-catenin pathway. This activation, in turn, stimulates macrophages to produce additional IL-1β, thereby enhancing tumor survival and metastatic potential (100). Second, tumor cells with activated β-catenin produce elevated levels of IL-10, which impairs dendritic cells (DCs) and inhibits their maturation (101). Third, the Wnt/β-catenin pathway reshapes tumor metabolism, contributing to an immunosuppressive TME. Activation of the Wnt/β-catenin signaling pathway can increase the expression of pyruvate dehydrogenase kinase 1 and monocarboxylate transporter 1 (102), shifting cancer cell metabolism from oxidative phosphorylation to aerobic glycolysis and creating a more acidic TME. Collectively, these mechanisms facilitate tumor cell evasion of the immune response. In addition to preventing the activation of T cells and DCs, the lactic acid-rich microenvironment can also stimulate the polarization of TAMs toward the M2 subtype, as well as the expression of VEGF and hypoxia-inducible factor-1α (103). This microenvironment, shaped by aerobic glycolysis, further suppresses T-cell activity, resulting in resistance to ICIs (104).

In summary, tumor immune escape is closely associated with hyperactivation of the Wnt/β-catenin pathway and aberrant β-catenin production. Moreover, research has indicated that patients with NSCLC who are β-catenin-positive generally experience a poorer prognosis when treated with anti-programmed cell death protein 1 (PD-1) monotherapy (95). These findings suggest that β-catenin expression may serve as a prognostic marker for the efficacy of anti-PD-1 therapy in patients with NSCLC.

Mechanisms by which β-catenin induces resistance to EGFR-TKIs

In EGFR-mutated NSCLC, β-catenin plays a pivotal role in inducing drug resistance (105); it primarily mediates EGFR-TKI resistance through several mechanisms including EGFR signaling activation, cooperation with bypass signaling pathways, regulation of nuclear transcription and remodeling of the immune microenvironment (Fig. 3).

Figure 3. Mechanisms by which β-catenin induces resistance to EGFR-TKIs. β-catenin contributes to EGFR-TKI resistance through several mechanisms including activation of EGFR signaling, cooperation with bypass signals, regulation of nuclear transcription and alteration of the tumor immune microenvironment. ITGB1, β1 integrin; SRPK1, serine-arginine protein kinase 1; PAK2, p21-activated kinase 2; CK1, casein kinase-1; APC, adenomatous polyposis coli; βTrCP, β-transducin repeat-containing protein; TCF/LEF, T-cell factor/lymphoid enhancer factor; CCND1, Cyclin D1 gene; EMT, epithelial-mesenchymal transition.

EGFR phosphorylates β-catenin at tyrosine residues rather than at serine/threonine sites. This tyrosine phosphorylation causes β-catenin to dissociate from the α-catenin/E-cadherin complex, leading to increased intranuclear β-catenin and activation of the Wnt/β-catenin signaling pathway (106). EGFR can also bind directly to β-catenin, transactivating the classical Wnt pathway through PI3K signaling (107). Activation of the EGFR/PI3K/AKT signaling pathway inhibits GSK-3β activity, preventing β-catenin phosphorylation and degradation. Consequently, the β-catenin protein accumulates in the cytoplasm and initiates the classical Wnt pathway (108). These interactions demonstrate a close connection between β-catenin and EGFR, with the Wnt and EGFR signaling pathways functioning cooperatively. Therefore, β-catenin can influence the effectiveness of EGFR-TKIs by activating its signaling independently of direct EGFR interaction.

Furthermore, β-catenin mediates EGFR-TKI resistance through synergistic interactions with bypass signaling pathways. In the NOTCH3-dependent β-catenin resistance pathway, EGFR-TKI treatment rapidly activates NOTCH3, which physically binds to the β-catenin protein. This interaction increases the stability and activation of β-catenin, promoting EMT and cell stemness and ultimately driving EGFR-TKI resistance (109). Another critical mechanism involves the HER3/p21-activated kinase2 (PAK2)/β-catenin signaling pathway, which plays a significant role in osimertinib resistance (110). This pathway is activated in osimertinib-treated cells, where PAK2 increases the phosphorylation of β-catenin at Ser552, preventing its ubiquitination and proteasomal degradation. This allows β-catenin to translocate into the nucleus, where it upregulates the expression of the target gene, SOX2, enhancing tumor stem cell-like characteristics and contributing to osimertinib resistance. The membrane β1 integrin/AKT/β-catenin signaling pathway is associated with erlotinib resistance. In erlotinib-resistant cells, the Rab25 protein is highly expressed, mediating the recycling of ITGB to the plasma cell membrane, activating AKT and phosphorylating GSK-3β. This results in β-catenin accumulation and enhanced tumor cell proliferation (111). Similarly, the serine-arginine protein kinase 1 (SRPK1)/GSK-3β axis promotes gefitinib resistance. In gefitinib-treated cells, highly expressed SRPK1 binds to Ser9 of GSK-3β, promoting GSK-3β autophosphorylation and activating the Wnt pathway. SRPK1 also promotes the binding of LEF1, β-catenin protein and the EGFR promoter, leading to an increase in EGFR expression and contributing to drug resistance (112).

β-catenin protein mediates EGFR-TKI resistance through nuclear transcriptional regulation. Upon entering the nucleus, β-catenin binds to TCF4, forming a complex that activates genes associated with multidrug resistance. This includes the activation of Snail transcription, which downregulates E-cadherin expression and promotes EMT and tumor metastasis (113). This complex also triggers the transcription of CCND1, relieving cell cycle arrest and sustaining tumor cell proliferation under TKI stress (114). Additionally, β-catenin activates MYC transcription, promoting tumor cell growth and helping cells evade immune surveillance (115). Furthermore, this complex induces Twist1 transcription, which directly binds to the intron and promoter regions of BCL2L11 (BIM), inhibiting BIM transcription and conferring resistance to TKI-induced apoptosis (116).

NSCLC resistance to EGFR-TKIs is associated with the upregulation of programmed death-ligand 1 (PD-L1) expression (117,118). Recent research indicates that β-catenin contributes to EGFR-TKI resistance by promoting the upregulation of PD-L1 in NSCLC (119). As noted earlier, EGFR signaling activates the AKT/β-catenin pathway, and nuclear β-catenin can increase PD-L1 levels while reducing CD8+ T cell recruitment in tumors, thereby inducing drug resistance (97). The mechanism by which β-catenin upregulates PD-L1 involves two pathways: First, nuclear β-catenin forms a complex with TCF/LEF, increasing the transcriptional activity of the CD274 promoter and upregulating PD-L1 expression (120); and second, the same complex activates the target gene MYC, which further stimulates PD-L1 transcription (115). Together, these processes promote tumor immune escape, ultimately contributing to EGFR-TKI resistance.

Mechanisms of chemoradiotherapy resistance mediated by β-catenin

Chemotherapy and radiation resistance are associated with aberrant β-catenin levels. For instance, in lung carcinoma cells, the transfer of exosomal targeting protein for Xenopus kinesin-like protein 2 promotes docetaxel resistance and cell migration by increasing β-catenin expression and activating downstream Wnt signaling (121). In vitro experiments indicate that elevated β-catenin levels can reduce the effect of cisplatin in lung cancer cells, potentially contributing to cisplatin resistance (122). Additionally, Yin et al (123) demonstrated through bioinformatic analyses that ubiquitin-conjugating enzyme E2T promotes β-catenin upregulation by facilitating the ubiquitin-dependent degradation of FOXO1, thereby driving EMT and conferring radioresistance in NSCLC. Tumor cell resistance to chemotherapy and radiation is associated with the characteristics of cancer stem cells (CSCs) (124). Tumor stemness, a key biological feature regulated by the CSC signaling network, describes the ability of CSCs to self-renew and promote tumor formation (125). CSCs exhibit self-regeneration, differentiation and dedifferentiation capacities, as well as participate in the reprogramming of epithelium-mesenchymal, immune-mediated, metabolic and epigenetic systems. These adaptations enable them to survive the TME and resist host defenses and therapeutic interventions (125). Furthermore, the expansion and maintenance of CSCs are influenced, directly or indirectly, by the classical Wnt pathway (126,127).

β-catenin protein and its coding gene, CTNNB1, as prognostic indicators and therapeutic targets in NSCLC

The intracellular localization and expression level of β-catenin protein can be assessed using immunohistochemistry. Tumor prognosis is negatively affected by both increased and decreased membrane expression of β-catenin. In addition, increased levels of cytoplasmic β-catenin protein or nuclear positivity are correlated with reduced overall survival (43). This suggests that β-catenin levels in the cytoplasm, nucleus and cell membrane can serve as important prognostic indicators in patients with NSCLC (128). Elevated β-catenin levels are also correlated with poorer immunotherapy results, suggesting its potential as a predictor of the effectiveness of immunotherapy (95). However, the commonly used methods to determine β-catenin protein, such as western blotting, immunohistochemistry and reporter gene plasmid assays, have specific requirements regarding experimental conditions, pathological tissues and cell states, which limits their clinical applicability. By contrast, gene mutation data can be more readily obtained through next-generation sequencing. For instance, ~6% of LUADs harbor CTNNB1 mutations, which can be used in predicting the postoperative recurrence of EGFR-mutated LUAD (129). Moreover, CTNNB1 co-mutations may serve as potential predictors of the efficacy of EGFR-TKIs in treating NSCLC, as patients with EGFR and CTNNB1 co-mutations exhibit reduced responses to EGFR-TKIs (130).

Despite extensive efforts to develop drugs targeting the Wnt/β-catenin signaling pathway, to the best of our knowledge, no effective treatments currently exist that directly target the β-catenin protein. Recent clinical investigations indicate that 5 µM berberine liquid crystalline nanoparticles efficiently target the Wnt signal by suppressing the production of CTNNB1 and its corresponding protein, reducing both the gene and protein levels in the human lung tumor cell line, A549 (131). The CTNNB1 gene can be specifically targeted using RNA interference triggers incorporated into the nanoparticle-based therapeutic known as Dicer-substrate small interfering RNA targeting CTNNB1 (DCR-BCAT). DCR-BCAT effectively suppresses β-catenin protein expression, significantly increases T-cell infiltration and enhances tumor susceptibility to ICIs, as demonstrated in a mouse tumor model (132). The nuclear localization inhibitor of β-catenin, IMU-1003, significantly reduces colonies resistant to osimertinib, suggesting that blocking intranuclear β-catenin can overcome transgenerational EGFR-TKI resistance (133). Triptolide has also been reported to reverse paclitaxel resistance and EMT in LUAD cells while suppressing tumor progression by blocking the p70S6K/GSK3/β-catenin pathway (134). Through its interaction with β-catenin, ubiquitin-specific peptidase 5 (USP5) helps to deubiquitinate, stabilize and activate the classical Wnt pathway. When the small molecule WP1130 binds to USP5, it increases β-catenin breakdown, which markedly lowers lung cancer cell migration and infiltration (135). Additionally, fucoxanthin exhibits antitumor potential in LUAD by reversing EMT, limiting proliferation, inducing apoptosis and downregulating the expression of TGF-β1, which can induce β-catenin expression (136). Asiaticoside, a triterpenoid saponin with antitumor properties, has been observed to reduce intranuclear β-catenin levels and inhibit the Wnt/β-catenin pathway by promoting GSK-3β phosphorylation, increasing APC expression and lowering Axin levels. This blockade of EMT suppresses NSCLC growth and metastasis (137). In conclusion, various experimental approaches primarily focus on directly targeting the CTNNB1 gene or lowering β-catenin levels to modulate the TME, reverse EMT, suppress treatment resistance and inhibit tumor growth.

Conclusion and perspectives

NSCLC development and progression are driven by the β-catenin protein. Elevated nuclear β-catenin levels activate the Wnt/β-catenin pathway, leading to aberrant cell division and promoting carcinogenesis. This process induces EMT, remodels the TME and facilitates cancer migration and immune evasion.

Several clinical investigations have demonstrated that CTNNB1 mutations and upregulated β-catenin protein levels are associated with poor treatment outcomes and survival in NSCLC (48,95,129). However, notable challenges remain before these factors can be used reliably as prognostic indicators for NSCLC treatment. First, the mutation rate of the CTNNB1 gene in NSCLC is relatively low and detection methods are not standardized. Second, there is currently no consensus on measuring β-catenin protein expression, and its prognostic effects can vary depending on its intracellular localization. Future research should prioritize additional clinical trials and detailed patient stratification to establish unified standards for using CTNNB1 gene mutations and β-catenin protein levels as predictors. For instance, a prospective study on immunotherapy that includes patients with untreated NSCLC could be conducted. Before treatment, the CTNNB1 gene status in pathological tissues should be assessed, as well as the expression levels of β-catenin protein in the cell membrane, cytoplasm and nucleus. Progression-free survival, overall response rate and overall survival should then be monitored to evaluate whether CTNNB1 mutations and β-catenin protein levels in these cellular compartments could serve as predictors of immunotherapy outcomes. Additionally, the cut-off values for β-catenin protein levels that impact prognosis should be determined. Finally, targeting β-catenin protein and its encoding gene may represent a promising strategy for optimizing lung cancer therapy. However, significant research efforts will be required in the coming decades to advance the development of β-catenin-targeted drugs.

Acknowledgements

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Authors' contributions

LP wrote the manuscript and prepared the figures. RG and LH assisted with the literature search and manuscript revision. TF and CB provided guidance and assisted in revising and correcting the manuscript. Data authentication is not applicable. All authors have read and approved the final version of the manuscript.

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Competing interests

The authors declare that they have no competing interests.

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References