Osteosarcoma is the most common bone tumor affecting both adolescents and children. Early detection is critical for the effective treatment of the disease. Derived from cancer cells, miR-21 contained within exosomes in the tumor microenvironment may act on both cancer cells and the surrounding tumor microenvironment (TME), including immune cells, endothelial cells and fibroblasts. In human serum and plasm, the level of exosomal miR-21 between osteosarcoma patients and healthy controls differs, supporting the role of miR-21 as a biomarker for osteosarcoma. The involvement of a number of miR-21 target genes in tumor progression suggests that miR-21 may significantly affect the plasticity of cancer cells, leading to tumor progression, metastasis, angiogenesis and immune escape in osteosarcoma. Understanding the biogenesis and functions of exosomal miR-21 is of great value for the diagnosis and therapy of cancer, including osteosarcoma. The present review discusses the role of miR-21 in the tumor microenvironment, and in the development and progression of osteosarcoma, with an aim to summarize the functions of this miRNA in cancer.
Osteosarcoma is the most common human primary malignant bone tumor affecting children and young adults (1), and is usually located in the distal femur, the proximal tibia, or the proximal humerus (2). The tumor is evolved from mesenchymal cells and is characterized by spindle cells and aberrant osteoid formation pathologically (3). The survival of patients with localized disease is increased with aggressive, multi-agent, neo-adjuvant chemotherapy and limb-salvage surgery. However, despite aggressive therapies, the long-term survival rate of patients with metastatic or recurrent disease however is <20% (2,4,5). Although several genes have been reported to be involved in osteosarcoma tumorigenesis and therapeutic resistance (6-11), the precise molecular mechanisms involved in these processes remain unclear. The identification of clinically relevant diagnostic and prognostic biomarkers, such as circulating or cellular/tissue biomarkers, is, therefore, urgently required.
2. Exosomes
Exosomes are lipid bilayer membrane bound, nano-sized extracellular vesicles that are 40-100 nm in diameter (12-14). The exosomes are formed by pinching off of multivesicular endosomes (MVEs) on the membrane in the form of small intraluminal vesicles within the MVE and packing with cytoplasmic contents, including proteins, mRNAs and microRNAs (miRNAs or miRs) (15,16). The secretion of exosomes occurs when MVEs fuse with the plasma membrane, and thus release the contents in exosomes into the extracellular environment. According to the exosome content database, ExoCarta, 9,769 proteins, 1,116 lipids, 3,408 mRNAs and 2,838 miRNAs have been identified in exosomes of different cell types in multiple organisms (17,18).
Exosomes were first described as vesicles released from reticulocyte MVEs for the removal of obsolete transferrin receptors (19,20). However, in recent years, exosomes have been considered to be important mediators of cellular communication in both normal physiological processes, and in the development and progression of diseases, such as cancer. Exosomes have been identified in the majority of bodily fluids, including the serum, urine, amniotic fluid, saliva, breastmilk, cerebrospinal fluid and nasal secretions (21,22). Importantly, cancer cells secrete a greater number of exosomes compared to healthy cells (23), indicating their potential for use as diagnostic biomarkers.
3. Exosomal miRNAs and cancer
miRNAs are a class of small non-coding endogenous RNAs (18-24 nucleotides in length). miRNAs can act as post-transcriptional gene regulators by pairing with complementary sequences in the 3′ untranslated region (3′ UTR) of target mRNAs, leading to mRNA degradation or translational repression (24,25). miRNAs regulate a variety of cellular processes associated with carcinogenesis, such as cell proliferation, cell cycle, apoptosis, angiogenesis, invasion and metastasis (26-31).
The expression of miRNAs is altered in a variety of cancer types and is associated with the disease stage in some cases. Some specific miRNAs may contribute to tumor growth, progression, metastasis and drug resistance (32-35). Among these, miR-21 is most notable, since it has been extensively studied in various types of cancer. The majority of miRNAs detectable in serum and saliva is concentrated within exosomes (23). The level of miRNAs is similar in both circulating exosomes from cancer patients and tumor cells (22,36). In a number of studies, the high expression of circulating miR-21 has been used to differentiate cancer patients from healthy individuals and predict disease outcomes (37 and refs. therein), suggesting that circulating exosome miRNAs, such as miR-21 can be utilized as for liquid biopsy miRNA profiling.
4. Exosomal miR-21 and osteosarcoma
hsa-mir-21 or miR-21 is an abundantly expressed miRNA in different types of mammalian cells (38-40), indicating its importance among miRNAs. miR-21 regulates biological processes, such as osteoclastogenesis, osteoclast differentiation, etc. Thus, miR-21 plays an essential role in the development of diseases, such as cancer, cardiovascular diseases and inflammation (41-43) The hsa-miR-21 gene is located on chromosome 17q23.2. Pri-miR-21 (primary transcript containing miR-21) is located within the intronic region of the tmem49 gene. Even though pri-miR-21 and tmem49 genes overlap in the same direction of transcription, pri-miR-21 is transcribed by its own promoter and is terminated with its own poly(A) tail. The pri-miR-21 transcript is subsequently processed into mature miR-21 (44,45).
The expression of miR-21 has been found to be increased in the majority of cancer types analyzed, rendering it an established oncogenic miRNA (44-54). Functional analyses in epithelial-, hepatocyte- and glial cell-derived cell lines support the regulatory role of miR-21 in cell growth, migration and invasion (46,47,55-57). Moreover, miR-21 and its associated pathways play a critical role in the pathogenesis of osteosarcoma and act as a therapeutic target for this tumor type (58). miR-21 exhibits a significantly higher expression in osteosarcoma tissues compared to adjacent normal tissues (59-61). miRNA expression has been shown to be positively associated with Enneking clinical staging and lung metastasis (62). Moreover, serum miR-21 has been reported to be a biomarker for chemosensitivity and the prognosis of human osteosarcoma (63). Additionally, circulating miR-21 levels are higher in patients with osteosarcoma than in healthy individuals. Studies have demonstrated that the detection of plasma miR-21 together with miR-143 and miR-199a-3p in patients with osteosarcoma can discriminate between the presence or absence of this tumor (62,64). The evaluation of tumor metastasis and histopathological subtype from tumors of patients with osteosarcoma has revealed a higher level of miR-21 in patients with metastatic compared to non-metastatic disease (62).
5. Exosomal miR-21 and tumor microenvironment
The tumor microenvironment (TME) differs from that of normal tissues. The TME is composed of cellular and extracellular components. The cellular components of the TME involve cancer-associated fibroblasts (CAFs), myofibroblasts, adipocytes, endothelial cells, epithelial cells and immune inflammatory cells, such as T lymphocytes, B lymphocytes, natural killer cells and natural killer T-cells, and tumor-associated macrophages (65). Cells in the TME are in constant autocrine and paracrine communication, which contributes to tumor development, progression, drug resistance and metastasis (66-70).
Exosomes provide a unique method of information transfer both locally and globally by releasing their contents into the target cell, e.g., miRNAs. By releasing exosomes, tumor cells reprogram their surroundings in the TME into a tumor-permissive or tumor-promoting environment (71-74). mir-21 present in osteosarcoma cell-derived exosomes may affect the TME (75,76), mediating the crosstalk between cancer cells, endothelial cells, immune cells, and fibroblasts in the TME to promote osteosarcoma development by i) the stimulation of tumor angiogenesis; ii) the inhibition of the immune response by acting directly on effector cells; iii) interfering with the regulation of stromal cell activation; and iv) the promotion of cancer progression by preparing the metastatic niche (Fig. 1).
miR-21 promotes cancer progression and metastasis (crosstalk among cancer cells)
Cancer is a highly heterogeneous disease. A single tumor is composed of groups of genetically clonal cells that have different growth rates, metastatic potential, invasion potential and sensitivities to chemotherapy and radiotherapy. Individual malignant tumor cells can affect the invasion and migration of surrounding tumor cells by releasing exosomal miRNAs. In contrast to exosomes released from healthy cells, exosomes derived from patients with osteosarcoma have been shown to significantly increase the adhesion, migration and viability of MG63 human osteosarcoma cells (77). Synthetic miR-143 introduced into osteosarcoma cells is released via exosomes. The delivery of exosome-contained miR-143 significantly reduces the migration of osteosarcoma cells, suggesting that miRNAs in exosomes regulate the function of cancer cells (78).
miR-21 is suggested to function as an oncogene, since it promotes the growth and development of osteosarcoma and other cancer types. In MG-63 cells, the downregulation of miR-21 results in decreased proliferation and invasion. By contrast, the elevation of miR-21 by using a mimic increases cell proliferation and invasion (79). The phosphoinositide 3-kinase (PI3K)/ R AC-α ser ine/th reon ine-protein k inase (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is one of the important pathways dysregulated in osteosarcoma (80-82). miR-21 may regulate the expression of the tumor suppressor phosphatase and tensin homolog (PTEN). The downregulation or deletion of PTEN activates the PI3K/AKT (phosphoinositide 3-kinase/RAC-α serine/threonine protein kinase) signaling pathway, leading to cancer development, invasion and metastasis (83,84).
In addition to PTEN, miR-21 is suggested to target the TGF-β1 signaling pathway to promote cell proliferation in osteosarcoma. miR-21 knockdown inhibits the proliferation of osteosarcoma and promotes the expression of PTEN and TGF-β1 proteins in MG63 and U2OS human osteosarcoma cell lines (85). Moreover, it has been demonstrated that treatment with a TGF-β1 inhibitor countered the inhibitory effects of miR-21 knockdown on osteosarcoma cell proliferation (86).
Caspase-8 is a direct target of miR-21; miRNA negatively regulates the expression of caspase-8. The overexpression of miR-21 has been shown to enhance cell viability and survival, whereas it suppresses the apoptosis of the human osteosarcoma cell line, SAOS-2. In a subsequent study, miR-21 suppression was shown to increase caspase-8 expression and decrease apoptosis (60).
miR-21 is a regulator of drug resistance in osteosarcoma. The suppression of miR-21 activity has been shown to enhance the resistance of U2OS cells to cisplatin, while the ectopic expression of miR-21 in MG-63 cells reduces the resistance. Elevated miR-21 levels suppress the expression of Sprouty2. On the other hand, the ectopic expression of Sprouty2 has been shown to rescue the miR-21-mediated suppression of resistance to cisplatin, but not doxorubicin or methotrexate in osteosarcoma cells (87).
The process of metastasis is considered to be initiated in the majority, if not all, by an epithelial-to-mesenchymal transition (EMT) of the tumor cells. This allows them to migrate to and enter the vascular or lymphatic vessels, resulting in either local or distant metastasis (88,89). miR-21 has been revealed to be an important miRNA associated with cancer invasion and metastasis. The study by Yan et al (90) demonstrated that miR-21 enhanced the invasion and migration of human breast cancer MCF7 and MDA-MB-231 cells, whereas cancer cell invasion was inhibited by the knockdown of miR-21. The mechanism of metastasis regulation by miR-21 is highly complex. miR-21 targets PDCD4, tropomyosin and PTEN that are known to modulate cancer cell invasion and metastasis (91-94). Moreover, miR-21 can inhibit PTEN expression and activate AKT signaling, inducing EMT, and promoting the invasion and migration of cancer cells (95-97). Furthermore, miR-21 can trigger the interleukin (IL)-6/signal transducer and activator of transcription (STAT)3/nuclear factor (NF)-κB-mediated signaling loop for the maintenance of EMT in cancer cells (98).
miR-21 induces tumor angiogenesis (crosstalk between tumor cells and endothelial cells)
Tumor angiogenesis refers to the ability of tumor cells to recruit their own vasculature, which is critical for cancer progression. Several studies have demonstrated that exosome-encapsulated miRNAs secreted from tumor cells are able to induce angiogenesis in different cancer types (99-102). Exosomal miR-21 released by transformed lung cancer cells has been shown to induce vascular endothelial growth factor (VEGF) production and angiogenesis in nearby normal bronchial cells in a STAT3-dependent manner (99). In another study, the overexpression of miR-21 in the human prostate cancer cell line, DU145, was shown to increase the expression of Hypoxia-inducible factor (HIF)-1α and VEGF, and induce tumor angiogenesis. The miR-21-mediated activation of the AKT and extracellular signal-regulated kinase (ERK)1/2 signaling pathways enhances HIF-1α and VEGF expression (103).
miR-21 activates cancer-associated fibroblasts (CAFs; crosstalk between tumor cells and fibroblasts)
CAFs become 'activated' during the neoplastic process. CAFs are capable of accelerating the growth and promoting the invasion of tumor cells (104-109). Cancer exosomes trigger the transformation of fibroblasts through the transforming growth factor (TGF) β/Smad pathway and elicit unique effects from soluble TGFβ. The depletion of miR-21 blocks TGF-β1-induced CAF formation, whereas the overexpression of miR-21 promotes CAF induction, independent of TGF-β1. These findings clearly demonstrate that miR-21 is a critical regulator of TGF-β1 signaling induction of CAF formation (110). The conditioned medium from human lung cancer A549 cells has been shown to increase miR-21 expression and thus, through the TGF-β pathway, induce migration, CAF-like morphology and CAF markers [periostin, α-smooth muscle actin (α-SMA) and podoplanin] in human lung fibroblast MRC-5 and IMR-90 cells (111).
Exosomes from the multiple myeloma cell line, OPM2, have been showon to contain high levels of miR-21. The Co-culture of OPM2 exosomes with CAFs has also been shown to significantly increase the proliferation of and induce the CAF transformation of mesenchymal stem cells, demonstrated by the increased expression levels of fibroblast-activated protein (FAP), α-SMA and stromal-derived factor 1 (SDF-1), and the secretion of IL-6 (112). In another study, miR-21 was demonstrated to induce the metabolic alteration of CAFs and to affect the development of the human pancreatic cancer cell line, BxPC-3. Compared to normal fibroblasts, CAFs exhibited an increased miR-21 expression, glucose uptake and lactic acid production. Treatment with a miR-21 inhibitor reduced glycolysis in CAFs. The co-culture of BxPC-3 cells with CAFs treated with the miR-21 inhibitor reduced oxidative phosphorylation and the invasion of BxPC-3 cells (113).
Exosomal miR-21 suppresses the immune system (crosstalk between tumor cells and immune cells)
Exosomes secreted by tumor cells are able to inhibit the immune system by acting directly on effector cells or indirectly through their regulation (114-120). Tumor cells secrete miR-21 together with miR-29a to communicate with macrophages, eliciting a pro-inflammatory pro-metastatic response. miR-21 is a paracrine agonist of Toll-like receptor-8 (TLR-8). The activation of TLR-8 in immune cells triggers a pro-inflammatory response, that may lead to tumor growth and metastasis (121). miR-21 induces tumor-associated macrophage reprogramming through STAT3, and thereby facilitates growth, intravasation and the spread of tumor cells (122,123).
Myeloid-derived suppressor cells (MDSCs) are the major myeloid cells responsible for the immune evasion of cancer. They are composed of a heterogeneous population of immature myeloid cell progenitors, macrophage precursors, granulocytes and dendritic cells. MDSCs can promote tumor growth by the promotion of angiogenesis or the suppression of innate and adaptive immune responses. miR-21 has been shown to be upregulated in bone marrow-derived and splenic MDSCs, and increases MDSC survival and proliferation by targeting PTEN and thus, STAT3 activation (112,124).
miR-21 expression is higher in effector and memory CD8+ T-cells than in naïve CD8+ T-cells. Memory CD8+ T-cells are emerging as a key player in tumor immunosurveillance (125), and recent evidence suggests that they can control tumor growth. miR-21 negatively regulates TCR signal transduction to modulate the sensitivity of memory T-cells (118,119). Moreover, miR-21 may be involved in tumor-mediated immu-nosuppression (120,126). miR-21 from C666-1 nasopharyngeal cancer cells has been shown to activate nuclear factor 1 A-type (NF1-A) and induce IL-10 in B cells, which inhibits cytotoxic CD8+ T-cells (127).
6. Perspectives
Biogenesis of exosomal miR-21: Loading, release, and uptake. The majority of serum miRNAs is concentrated in exosomes. The loading of miRNAs into exosomes is dependent mainly on the surface molecules of exosome membranes, the endosomal sorting complex required for transport (ESCRT), and the specific binding motifs of the miRNAs themselves. A previous study demonstrated that miRNAs in exosomes are released through a ceramide-dependent secretory mechanism (128). Notably, exosomes secreted by cancer cells contain miRNAs associated with the miRNA-processing machinery RNA-induced silencing complex (RISC), and therefore, have the ability to process precursor miRNAs into mature miRNAs in a cell-independent manner, resulting in efficient and rapid reprogramming of transcriptome of the target cells (129).
Certain miRNAs are secreted selectively into exosomes. For example, the let-7 miRNA family in certain metastatic gastric cancer cell lines is secreted selectively to extracellular environment via exosomes (130). Breast cancer cell lines release the majority of miR-451 and miR-1246 selectively via exosomes, whereas both miRNAs are retained inside the non-malignant mammary epithelial cells and normal fibroblasts (131). Additionally, the TME may influence exosome release and uptake. The acidic microenvironment of tumors increases the rate of exosomal release and uptake by cancer cells (132). Furthermore, the aberrant exosome biogenesis and secretion in cancer cells, as compared with normal cells, may cause the differences in receptor recycling/degradation, plasma membrane remodeling, and the ability of endosomes to function as a signaling entity (133). In a number of types of cancer, aberrant p53 activity may result in the overexpression of the tumor suppressor-activated pathway 6 (TSAP6), through which it increases exosome production (134,135). Furthermore, heparanase, an enzyme upregulated in numerous cancer cell lines, has been shown to regulate exosome secretion in cancer cells (136).
The level of exosomal miR-21 in serum is higher in patients with osteosarcoma than in healthy individuals, which is also reflected by the high levels of miR-21 found in tumor tissue (61-64). The molecular mechanisms of exosome sorting and release have been studied extensively recently. However, the differences in miRNA content between cancer- and healthy cell-derived exosomes, the differences in exosome biogenesis between cancer and healthy cells, and the reasons why cancer cells release more exosomes with distinct content, such as miR-21, remain unclear. Additionally, whether the release of miR-21 in exosomes occurs through a distinct secretary pathway remains to be elucidated. Further investigation into the distinct exosome cargo loading mechanisms for miR-21 and other miRNAs in osteosarcoma and other cancers may aid in the identification of specific therapeutic targets related to exosome biogenesis. Further research may facilitate the use of exosomes as delivery vehicles for drugs, antigens, etc., for cancer treatment in the future.
Exosomal miR-21 as a cancer biomarker
Exosomal miR-21 is detected in human serum and plasma. Differences in miR-21 expression have been found in serum or plasma from patients with osteosarcoma and in healthy controls, supporting the role of miR-21 as a biomarker for osteosar-coma (61-64). The advantages of using exosomal miR-21 as a non-invasive biomarker are that miRNAs in blood are persistent and are highly stable against destruction by ribo-nucleases (137,138). The current methods used for exosome isolation include ultracentrifugation, size exclusion or precipitating with reagents (139). Ultracentrifugation is the commonly used method for exosome isolation. However, it is a lengthy process, which requires a large volume of samples and costly reagents and equipment. Thus, the method is impractical for clinical diagnosis. The size exclusion method uses columns to separate extracellular vesicles based on size and requires only a small amount of samples. However, the exosomes collected have heterogeneous sizes, curtailing the use for cancer diagnosis. The precipitation of exosomes with reagents not only pulls down miRNAs, but also protein aggregates that complicate the analysis for disease-specific markers.
In order to implement miR-21 as a biomarker for osteo-sarcoma, along with more effective methods for the isolation of cancer exosomes and exosomal miR-21, additional clinical trials are required to validate its use in the diagnosis of osteosarcoma and other types of cancer. Most importantly, miR-21 needs to be profiled together with other miRNAs or biomarkers specific to osteosarcoma to improve the reliability and specificity of miR-21 as a biomarker.
7. Conclusions
Exosomal miR-21 is detected in human serum and plasma. miR-21 expression in serum or plasma from patients with osteosarcoma differs from that in healthy controls, supporting the use of miR-21 as a biomarker for osteosarcoma. Exosomal miR-21 promotes cancer progression and development by mediating the crosstalk among cells in the TME. Larger-scale studies are warranted to further validate the sensitivity, specificity and applicability of circulating miR-21 as a biomarker for osteosarcoma in the future. Furthermore, extensive efforts need to be made to identify the specific cargo-loading mechanisms for exosomal miR-21. These studies will be critical for targeting miR-21 in cancer therapy to improve early-stage exosome- and miRNA-based therapeutics.
Funding
This study was supported by the National Natural Science Foundation of China (grant nos. 81672176, 81871783 and 81702582).
Availability of data and materials
Not applicable.
Authors' contributions
SW and TL wrote the manuscript. SW performed the literature search for this review article. FM and YF revised and corrected the manuscript. FM and YF assisted in the literature search for this review article and also contributed to the conception and design of the study. FM contributed to processing of the figure. TL and SH conceived and designed the study. All authors read and approved the final manuscript.
Ethics approval and consent to participate
Not applicable.
Patient consent for publication
Not applicable.
Competing interests
The authors confirm they have competing interests.
ReferencesMeyersPAGorlickROsteosarcomaPediatr Clin North Am44973989199710.1016/S0031-3955(05)70540-X9286295OttavianiGJaffeNThe epidemiology of osteosarcomaCancer Treat Res152313200910.1007/978-1-4419-0284-9_1GillJAhluwaliaMKGellerDGorlickRNew targets and approaches in osteosarcomaPharmacol Ther1378999201310.1016/j.pharmthera.2012.09.003OstenfeldMSJeppesenDKLaurbergJRBoysenATBramsenJBPrimdal-BengtsonBHendrixALamyPDagnaes-HansenFRasmussenMHCellular disposal of miR23b by RAB27-dependent exosome release is linked to acquisition of metastatic propertiesCancer Res7457585771201410.1158/0008-5472.CAN-13-351225261234ChouAJGellerDSGorlickRTherapy for osteosarcoma: Where do we go from here?Paediatr Drugs10315327200810.2165/00148581-200810050-0000518754698SadikovicBYoshimotoMChilton-MacNeillSThornerPSquireJAZielenskaMIdentification of interactive networks of gene expression associated with osteosarcoma oncogenesis by integrated molecular profilingHum Mol Genet1819621975200910.1093/hmg/ddp11719286668LiZDouPLiuTHeSApplication of Long Noncoding RNAs in Osteosarcoma: Biomarkers and Therapeutic TargetsCell Physiol Biochem4214071419201710.1159/00047920528715796ZhouJLiuTWangWPrognostic significance of matrix metalloproteinase 9 expression in osteosarcoma: A meta-analysis of 16 studiesMedicine (Baltimore)97e13051201810.1097/MD.0000000000013051LiuTYanZLiuYChoyEHornicekFJMankinHDuanZCRISPR-Cas9-Mediated Silencing of CD44 in Human Highly Metastatic Osteosarcoma CellsCell Physiol Biochem4612181230201810.1159/00048907229672299DengLLiuTZhangBWuHZhaoJChenJForkhead box C1 is targeted by microRNA-133b and promotes cell proliferation and migration in osteosarcomaExp Ther Med1428232830201710.3892/etm.2017.4870289128455585732LiuTLiZZhangQDe Amorim BernsteinKLozano-CalderonSChoyEHornicekFJDuanZTargeting ABCB1 (MDR1) in multi-drug resistant osteosarcoma cells using the CRISPR-Cas9 system to reverse drug resistanceOncotarget78350283513201610.18632/oncotarget.13148278358725347784SimonsMRaposoGExosomes - vesicular carriers for inter-cellular communicationCurr Opin Cell Biol21575581200910.1016/j.ceb.2009.03.00719442504RaposoGNijmanHWStoorvogelWLiejendekkerRHardingCVMeliefCJGeuzeHJB lymphocytes secrete antigen-presenting vesiclesJ Exp Med18311611172199610.1084/jem.183.3.116186422582192324LeeTHD'AstiEMagnusNAl-NedawiKMeehanBRakJMicrovesicles as mediators of intercellular communication in cancer--the emerging science of cellular 'debris'Semin Immunopathol33455467201110.1007/s00281-011-0250-321318413KahlertCMeloSAProtopopovATangJSethSKochMZhangJWeitzJChinLFutrealAIdentification of double-stranded genomic DNA spanning all chromosomes with mutated KRAS and p53 DNA in the serum exosomes of patients with pancreatic cancerJ Biol Chem28938693875201410.1074/jbc.C113.532267243986773924256Villarroya-BeltriCBaixauliFGutiérrez-VázquezCSánchez-MadridFMittelbrunnMSorting it out: Regulation of exosome loadingSemin Cancer Biol28313201410.1016/j.semcancer.2014.04.009247690584640178MathivananSFahnerCJReidGESimpsonRJExoCarta 2012: Database of exosomal proteins, RNA and lipidsNucleic Acids Res40D1D1241D1244201210.1093/nar/gkr8283245025MathivananSSimpsonRJExoCarta: A compendium of exosomal proteins and RNAProteomics949975000200910.1002/pmic.20090035119810033PanBTTengKWuCAdamMJohnstoneRMElectron microscopic evidence for externalization of the transferrin receptor in vesicular form in sheep reticulocytesJ Cell Biol101942948198510.1083/jcb.101.3.94229933172113705HardingCHeuserJStahlPReceptor-mediated endocytosis of transferrin and recycling of the transferrin receptor in rat reticulocytesJ Cell Biol97329339198310.1083/jcb.97.2.32963098572112509KellerSRuppCStoeckARunzSFogelMLugertSHagerHDAbdel-BakkyMSGutweinPAltevogtPCD24 is a marker of exosomes secreted into urine and amniotic fluidKidney Int7210951102200710.1038/sj.ki.500248617700640TaylorDDGercel-TaylorCMicroRNA signatures of tumor-derived exosomes as diagnostic biomarkers of ovarian cancerGynecol Oncol1101321200810.1016/j.ygyno.2008.04.03318589210GalloATandonMAlevizosIIlleiGGThe majority of microRNAs detectable in serum and saliva is concentrated in exosomesPLoS One7e30679201210.1371/journal.pone.0030679224278003302865BartelDPMicroRNAs: Genomics, biogenesis, mechanism, and functionCell116281297200410.1016/S0092-8674(04)00045-514744438BartelDPChenCZMicromanagers of gene expression: The potentially widespread influence of metazoan microRNAsNat Rev Genet5396400200410.1038/nrg132815143321ChenLTXuSDXuHZhangJFNingJFWangSFMicroRNA-378 is associated with non-small cell lung cancer brain metastasis by promoting cell migration, invasion and tumor angiogenesisMed Oncol2916731680201210.1007/s12032-011-0083-xIvanovskaIBallASDiazRLMagnusJFKibukawaMSchelterJMKobayashiSVLimLBurchardJJacksonALMicroRNAs in the miR-106b family regulate p21/CDKN1A and promote cell cycle progressionMol Cell Biol2821672174200810.1128/MCB.01977-07182120542268421LuYThomsonJMWongHYHammondSMHoganBLTransgenic over-expression of the microRNA miR-17-92 cluster promotes proliferation and inhibits differentiation of lung epithelial progenitor cellsDev Biol310442453200710.1016/j.ydbio.2007.08.007177658892052923TakamizawaJKonishiHYanagisawaKTomidaSOsadaHEndohHHaranoTYatabeYNaginoMNimuraYReduced expression of the let-7 microRNAs in human lung cancers in association with shortened postoperative survivalCancer Res6437533756200410.1158/0008-5472.CAN-04-063715172979WangZXBianHBWangJRChengZXWangKMDeWPrognostic significance of serum miRNA-21 expression in human non-small cell lung cancerJ Surg Oncol104847851201110.1002/jso.2200821721011WangXLingCBaiYZhaoJMicroRNA-206 is associated with invasion and metastasis of lung cancerAnat Rec (Hoboken)2948892201110.1002/ar.21287FerracinMVeroneseANegriniMMicromarkers: miRNAs in cancer diagnosis and prognosisExpert Rev Mol Diagn10297308201010.1586/erm.10.1120370587Nana-SinkamPCroceCMMicroRNAs in diagnosis and prognosis in cancer: What does the future hold?Pharmacogenomics11667669201010.2217/pgs.10.5720415558FanHLuSWangSZhangSIdentification of critical genes associated with human osteosarcoma metastasis based on integrated gene expression profilingMol Med Rep209159302019311732066625205GulinoRForteSParentiRMemeoLGulisanoMMicroRNA and pediatric tumors: Future perspectivesActa Histochem117339354201510.1016/j.acthis.2015.02.00725765112RabinowitsGGerçel-TaylorCDayJMTaylorDDKloeckerGHExosomal microRNA: A diagnostic marker for lung cancerClin Lung Cancer104246200910.3816/CLC.2009.n.00619289371WangYGaoXWeiFZhangXYuJZhaoHSunQYanFYanCLiHDiagnostic and prognostic value of circulating miR-21 for cancer: A systematic review and meta-analysisGene533389397201410.1016/j.gene.2013.09.038Lagos-QuintanaMRauhutRLendeckelWTuschlTIdentification of novel genes coding for small expressed RNAsScience294853858200110.1126/science.106492111679670Lagos-QuintanaMRauhutRYalcinAMeyerJLendeckelWTuschlTIdentification of tissue-specific microRNAs from mouseCurr Biol12735739200210.1016/S0960-9822(02)00809-612007417LandgrafPRusuMSheridanRSewerAIovinoNAravinAPfefferSRiceAKamphorstAOLandthalerMA mammalian microRNA expression atlas based on small RNA library sequencingCell12914011414200710.1016/j.cell.2007.04.040176047272681231KumarswamyRVolkmannIThumTRegulation and function of miRNA-21 in health and diseaseRNA Biol8706713201110.4161/rna.8.5.16154217126543256347HuCHSuiBDDuFYShuaiYZhengCXZhaoPYuXRJinYmiR-21 deficiency inhibits osteoclast function and prevents bone loss in miceSci Rep743191201710.1038/srep43191282402635327426LiXGuoLLiuYSuYXieYDuJZhouJDingGWangHBaiYMicroRNA-21 promotes osteogenesis of bone marrow mesenchymal stem cells via the Smad7-Smad1/5/8-Runx2 pathwayBiochem Biophys Res Commun493928933201710.1016/j.bbrc.2017.09.11928943430KrichevskyAMGabrielyGmiR-21: A small multi-faceted RNAJ Cell Mol Med133953200910.1111/j.1582-4934.2008.00556.x191756993823035PanXWangZXWangRMicroRNA-21: A novel therapeutic target in human cancerCancer Biol Ther1012241232201010.4161/cbt.10.12.1425221139417AsanganiIARasheedSANikolovaDALeupoldJHColburnNHPostSAllgayerHMicroRNA-21 (miR-21) post-transcriptionally downregulates tumor suppressor Pdcd4 and stimulates invasion, intravasation and metastasis in colorectal cancerOncogene2721282136200810.1038/sj.onc.1210856FrankelLBChristoffersenNRJacobsenALindowMKroghALundAHProgrammed cell death 4 (PDCD4) is an important functional target of the microRNA miR-21 in breast cancer cellsJ Biol Chem28310261033200810.1074/jbc.M707224200LiTLiDShaJSunPHuangYMicroRNA-21 directly targets MARCKS and promotes apoptosis resistance and invasion in prostate cancer cellsBiochem Biophys Res Commun383280285200910.1016/j.bbrc.2009.03.07719302977LuZLiuMStribinskisVKlingeCMRamosKSColburnNHLiYMicroRNA-21 promotes cell transformation by targeting the programmed cell death 4 geneOncogene2743734379200810.1038/onc.2008.7218372920ZhuSSiMLWuHMoYYMicroRNA-21 targets the tumor suppressor gene tropomyosin 1 (TPM1)J Biol Chem2821432814336200710.1074/jbc.M61139320017363372ZhuSWuHWuFNieDShengSMoYYMicroRNA-21 targets tumor suppressor genes in invasion and metastasisCell Res18350359200810.1038/cr.2008.2418270520ZhengJXueHWangTJiangYLiuBLiJLiuYWangWZhangBSunMmiR-21 downregulates the tumor suppressor P12 CDK2AP1 and stimulates cell proliferation and invasionJ Cell Biochem112872880201110.1002/jcb.2299521328460XuJWuCCheXWangLYuDZhangTHuangLLiHTanWWangCCirculating microRNAs, miR-21, miR-122, and miR-223, in patients with hepatocellular carcinoma or chronic hepatitisMol Carcinog50136142201110.1002/mc.2071221229610SchramedeiKMörbtNPfeiferGLäuterJRosolowskiMTommJMvon BergenMHornFBrocke-HeidrichKMicroRNA-21 targets tumor suppressor genes ANP32A and SMARCA4Oncogene3029752985201110.1038/onc.2011.15213179273134876GabrielyGWurdingerTKesariSEsauCCBurchardJLinsleyPSKrichevskyAMMicroRNA 21 promotes glioma invasion by targeting matrix metalloproteinase regulatorsMol Cell Biol2853695380200810.1128/MCB.00479-08185912542519720MengFHensonRWehbe-JanekHGhoshalKJacobSTPatelTMicroRNA-21 regulates expression of the PTEN tumor suppressor gene in human hepatocellular cancerGastroenterology133647658200710.1053/j.gastro.2007.05.022176811834285346SiMLZhuSWuHLuZWuFMoYYmiR-21-mediated tumor growthOncogene2627992803200710.1038/sj.onc.1210083SekarDManiPBirunthaMSivagurunathanPKarthigeyanMDissecting the functional role of microRNA 21 in osteosarcomaCancer Gene Ther26179182201910.1038/s41417-019-0092-z30905966HuaYJinZZhouFZhangYQZhuangYThe expression significance of serum MiR-21 in patients with osteosarcoma and its relationship with chemosensitivityEur Rev Med Pharmacol Sci2129892994201728742209XuBXiaHCaoJWangZYangYLinYMicroRNA-21 Inhibits the Apoptosis of Osteosarcoma Cell Line SAOS-2 via Targeting Caspase 8Oncol Res2511611168201710.3727/096504017X1484169839682928109080RenXShenYZhengSLiuJJiangXmiR-21 predicts poor prognosis in patients with osteosarcomaBr J Biomed Sci73158162201610.1080/09674845.2016.122071027922432ZhaoHYanPWangJZhangYZhangMWangZFuQLiangWClinical significance of tumor miR-21, miR-221, miR-143, and miR-106a as biomarkers in patients with osteo-sarcomaInt J Biol Markers34184193201910.1177/172460081984353731084400YuanJChenLChenXSunWZhouXIdentification of serum microRNA-21 as a biomarker for chemosensitivity and prognosis in human osteosarcomaJ Int Med Res4020902097201210.1177/030006051204000606OuyangLLiuPYangSYeSXuWLiuXA three-plasma miRNA signature serves as novel biomarkers for osteosarcomaMed Oncol30340201310.1007/s12032-012-0340-7WhitesideTLThe tumor microenvironment and its role in promoting tumor growthOncogene2759045912200810.1038/onc.2008.271188364713689267CretuABrooksPCImpact of the non-cellular tumor micro-environment on metastasis: Potential therapeutic and imaging opportunitiesJ Cell Physiol213391402200710.1002/jcp.2122217657728HartmannSBholaNEGrandisJRHGF/Met Signaling in Head and Neck Cancer: Impact on the Tumor MicroenvironmentClin Cancer Res2240054013201610.1158/1078-0432.CCR-16-0951273706076820346GuFHuCTaiZYaoCTianJZhangLXiaQGongCGaoYGaoSTumour microenvironment-responsive lipoic acid nanoparticles for targeted delivery of docetaxel to lung cancerSci Rep636281201610.1038/srep36281278050515090365FriedlPAlexanderSCancer invasion and the microenvi-ronment: Plasticity and reciprocityCell1479921009201110.1016/j.cell.2011.11.01622118458WuTHongYJiaLWuJXiaJWangJHuQChengBModulation of IL-1β reprogrammes the tumor microenvironment to interrupt oral carcinogenesisSci Rep620208201610.1038/srep20208MaiaJCajaSStrano MoraesMCCoutoNCosta-SilvaBExosome-Based Cell-Cell Communication in the Tumor MicroenvironmentFront Cell Dev Biol618201810.3389/fcell.2018.00018295159965826063HuCChenMJiangRGuoYWuMZhangXExosome-related tumor microenvironmentJ Cancer930843092201810.7150/jca.26422302106316134819WangZChenJQLiuJLTianLExosomes in tumor microenvironment: Novel transporters and biomarkersJ Transl Med14297201610.1186/s12967-016-1056-9277564265070309MilaneLSinghAMattheolabakisGSureshMAmijiMMExosome mediated communication within the tumor microenvi-ronmentJ Control Release219278294201510.1016/j.jconrel.2015.06.02926143224RaimondiLDe LucaAGalloACostaVRusselliGCuscinoNMannoMRaccostaSCarinaVBellaviaDOsteosarcoma cell-derived exosomes affect tumor microenvironment by specific packaging of microRNAsCarcinogenesisJul102019Epub ahead of print10.1093/carcin/bgz13031294446JerezSArayaHHeviaDIrarrázavalCEThalerRvan WijnenAJGalindoMExtracellular vesicles from osteo-sarcoma cell lines contain miRNAs associated with cell adhesion and apoptosisGene710246257201910.1016/j.gene.2019.06.005311767326684290ShenRKZhuXYiHWuCYChenFDaiLQLinJHProteomic identification of osteosarcoma-derived exosomes and their activation o f pentose phosphate pathwayInt J Clin Exp Pathol9414041482016ShimboKMiyakiSIshitobiHKatoYKuboTShimoseSOchiMExosome-formed synthetic microRNA-143 is transferred to osteosarcoma cells and inhibits their migrationBiochem Biophys Res Commun445381387201410.1016/j.bbrc.2014.02.00724525123LvCHaoYTuGMicroRNA-21 promotes proliferation, invasion and suppresses apoptosis in human osteosarcoma line MG63 through PTEN/Akt pathwayTumour Biol3793339342201610.1007/s13277-016-4807-626779632GrazianoACCardileVAvolaRVicarioNParentiCSalvatorelliLMagroGParentiRWilms' tumor gene 1 silencing inhibits proliferation of human osteosarcoma MG-63 cell line by cell cycle arrest and apoptosis activationOncotarget81391713931201710.18632/oncotarget.14715281071965355150WangLTangBHanHMaoDChenJZengYXiongMmiR-155 Affects Osteosarcoma MG-63 Cell Autophagy Induced by Adriamycin Through Regulating PTEN-PI3K/AKT/mTOR Signaling PathwayCancer Biother Radiopharm333238201810.1089/cbr.2017.230629412697ZhangJYuXHYanYGWangCWangWJPI3K/Akt signaling in osteosarcomaClin Chim Acta444182192201510.1016/j.cca.2014.12.04125704303WuYRQiHJDengDFLuoYYYangSLMicroRNA-21 promotes cell proliferation, migration, and resistance to apoptosis through PTEN/PI3K/AKT signaling pathway in esophageal cancerTumour Biol371206112070201610.1007/s13277-016-5074-227188433XueRLeiSXiaZYWuYMengQZhanLSuWLiuHXuJLiuZSelective inhibition of PTEN preserves ischaemic post-conditioning cardioprotection in STZ-induced Type 1 diabetic rats: Role of the PI3K/Akt and JAK2/STAT3 pathwaysClin Sci (Lond)130377392201610.1042/CS20150496LiCXuBMiuXDengZLiaoHHaoLInhibition of miRNA-21 attenuates the proliferation and metastasis of human osteosarcoma by upregulating PTENExp Ther Med15103610402018294346945772948HuXLiLLuYYuXChenHYinQZhangYmiRNA-21 inhibition inhibits osteosarcoma cell proliferation by targeting PTEN and regulating the TGF-β1 signaling pathwayOncol Lett16433743422018302505376144926VanasVHaiglBStockhammerVSutterlüty-FallHMicroRNA-21 Increases Proliferation and Cisplatin Sensitivity of Osteosarcoma-Derived CellsPLoS One11e0161023201610.1371/journal.pone.0161023275134624981312HeerbothSHousmanGLearyMLongacreMBylerSLapinskaKWillbanksASarkarSEMT and tumor metastasisClin Transl Med46201510.1186/s40169-015-0048-3258528224385028KarlssonMCGonzalezSFWelinJFuxeJEpithelial-mesenchymal transition in cancer metastasis through the lymphatic systemMol Oncol11781791201710.1002/1878-0261.12092285900325496496YanLXWuQNZhangYLiYYLiaoDZHouJHFuJZengMSYunJPWuQLKnockdown of miR-21 in human breast cancer cell lines inhibits proliferation, in vitro migration and in vivo tumor growthBreast Cancer Res13R2201110.1186/bcr2803212196363109565ZhaoMYWangLMLiuJHuangXLiuJZhangYFMiR-21 Suppresses Anoikis through Targeting PDCD4 and PTEN in Human Esophageal AdenocarcinomaCurr Med Sci38245251201810.1007/s11596-018-1872-730074182LiaoJLiuRShiYJYinLHPuYPExosome-shuttling microRNA-21 promotes cell migration and invasion-targeting PDCD4 in esophageal cancerInt J Oncol4825672579201610.3892/ijo.2016.345327035745MelnikBCMiR-21: An environmental driver of malignant melanoma?J Transl Med13202201510.1186/s12967-015-0570-5261163724482047JiangLHGeMHHouXXCaoJHuSSLuXXHanJWuYCLiuXZhuXmiR-21 regulates tumor progression through the miR-21-PDCD4-Stat3 pathway in human salivary adenoid cystic carcinomaLab Invest9513981408201510.1038/labinvest.2015.10526367487BeraADasFGhosh-ChoudhuryNKasinathBSAbboudHEChoudhuryGGmicroRNA-21-induced dissociation of PDCD4 from rictor contributes to Akt-IKKβ-mTORC1 axis to regulate renal cancer cell invasionExp Cell Res32899117201410.1016/j.yexcr.2014.06.022250162844177976ZhaoMAngLHuangJWangJMicroRNAs regulate the epithelial-mesenchymal transition and influence breast cancer invasion and metastasisTumour Biol391010428317691682201710.1177/101042831769168228222665HanMWangYLiuMBiXBaoJZengNZhuZMoZWuCChenXMiR-21 regulates epithelial-mesenchymal transition phenotype and hypoxia-inducible factor-1α expression in third-sphere forming breast cancer stem cell-like cellsCancer Sci10310581064201210.1111/j.1349-7006.2012.02281.x22435731De Mattos-ArrudaLBottaiGNuciforoPGDi TommasoLGiovannettiEPegVLosurdoAPérez-GarciaJMasciGCorsiFMicroRNA-21 links epithelial-to-mesenchymal transition and inflammatory signals to confer resistance to neoadjuvant trastuzumab and chemotherapy in HER2-positive breast cancer patientsOncotarget63726937280201510.18632/oncotarget.5495264520304741929LiuYLuoFWangBLiHXuYLiuXShiLLuXXuWLuLSTAT3-regulated exosomal miR-21 promotes angio-genesis and is involved in neoplastic processes of transformed human bronchial epithelial cellsCancer Lett370125135201610.1016/j.canlet.2015.10.011MaoGLiuYFangXLiuYFangLLinLLiuXWangNTumor-derived microRNA-494 promotes angiogenesis in non-small cell lung cancerAngiogenesis18373382201510.1007/s10456-015-9474-526040900UmezuTTadokoroHAzumaKYoshizawaSOhyashikiKOhyashikiJHExosomal miR-135b shed from hypoxic multiple myeloma cells enhances angiogenesis by targeting factor-inhibiting HIF-1Blood12437483757201410.1182/blood-2014-05-576116253202454263983LinXJFangJHYangXJZhangCYuanYZhengLZhuangSMHepatocellular Carcinoma Cell-Secreted Exosomal MicroRNA-210 Promotes Angiogenesis In Vitro and In VivoMol Ther Nucleic Acids11243252201810.1016/j.omtn.2018.02.014298580595992447LiuLZLiCChenQJingYCarpenterRJiangYKungHFLaiLJiangBHMiR-21 induced angiogenesis through AKT and ERK activation and HIF-1α expressionPLoS One6e19139201110.1371/journal.pone.0019139BrentnallTAArousal of cancer-associated stromal fibroblasts: Palladin-activated fibroblasts promote tumor invasionCell Adhes Migr6488494201210.4161/cam.21453OrimoAGuptaPBSgroiDCArenzana-SeisdedosFDelaunayTNaeemRCareyVJRichardsonALWeinbergRAStromal fibroblasts present in invasive human breast carcinomas promote tumor growth and angiogenesis through elevated SDF-1/CXCL12 secretionCell121335348200510.1016/j.cell.2005.02.03415882617CampsJLChangSMHsuTCFreemanMRHongSJZhauHEvon EschenbachACChungLWFibroblast-mediated acceleration of human epithelial tumor growth in vivoProc Natl Acad Sci USA877579199010.1073/pnas.87.1.75229660653202GleaveMHsiehJTGaoCAvon EschenbachACChungLWAcceleration of human prostate cancer growth in vivo by factors produced by prostate and bone fibroblastsCancer Res513753376119911712249KanekuraTChenXKanzakiTBasigin (CD147) is expressed on melanoma cells and induces tumor cell invasion by stimulating production of matrix metalloproteinases by fibroblastsInt J Cancer99520528200210.1002/ijc.1039011992541SameshimaTNabeshimaKTooleBPYokogamiKOkadaYGoyaTWakisakaSGlioma cell extracellular matrix metalloproteinase inducer (EMMPRIN) (CD147) stimulates production of membrane-type matrix metalloproteinases and activated gelatinase A in co-cultures with brain-derived fibroblastsCancer Lett157177184200010.1016/S0304-3835(00)00485-710936678LiQZhangDWangYSunPHouXLarnerJXiongWMiJMiR-21/Smad 7 signaling determines TGF-β1-induced CAF formationSci Rep32038201310.1038/srep02038KunitaAMoritaSIrisaTUGotoANikiTTakaiDNakajimaJFukayamaMMicroRNA-21 in cancer-associated fibroblasts supports lung adenocarcinoma progressionSci Rep88838201810.1038/s41598-018-27128-3ChengQLiXLiuJYeQChenYTanSLiuJMultiple Myeloma-Derived Exosomes Regulate the Functions of Mesenchymal Stem Cells Partially via Modulating miR-21 and miR-146aStem Cells Int20179012152201710.1155/2017/9012152MaceTACollinsALWojcikSECroceCMLesinskiGBBloomstonMHypoxia induces the overexpression of microRNA-21 in pancreatic cancer cellsJ Surg Res184855860201310.1016/j.jss.2013.04.061237264313773267MullerLMitsuhashiMSimmsPGoodingWEWhitesideTLTumor-derived exosomes regulate expression of immune function-related genes in human T cell subsetsSci Rep620254201610.1038/srep20254268426804740743GreeningDWGopalSKXuRSimpsonRJChenWExosomes and their roles in immune regulation and cancerSemin Cell Dev Biol407281201510.1016/j.semcdb.2015.02.00925724562KurywchakPTavorminaJKalluriRThe emerging roles of exosomes in the modulation of immune responses in cancerGenome Med1023201810.1186/s13073-018-0535-4295802755868069RobbinsPDMorelliAERegulation of immune responses by extracellular vesiclesNat Rev Immunol14195208201410.1038/nri3622245669164350779WangLHeLZhangRLiuXRenYLiuZZhangXChengWHuaZCRegulation of T lymphocyte activation by microRNA-21Mol Immunol59163171201410.1016/j.molimm.2014.02.00424631982CarissimiCCarucciNColomboTPiconeseSAzzalinGCipollettaECitarellaFBarnabaVMacinoGFulciVmiR-21 is a negative modulator of T-cell activationBiochimie107Pt B319326201410.1016/j.biochi.2014.09.02125304039SheedyFJTurning 21: Induction of miR-21 as a Key Switch in the Inflammatory ResponseFront Immunol619201510.3389/fimmu.2015.00019256882454310327FabbriMPaoneACaloreFGalliRGaudioESanthanamRLovatFFaddaPMaoCNuovoGJMicroRNAs bind to Toll-like receptors to induce prometastatic inflammatory responseProc Natl Acad Sci USA109E2110E2116201210.1073/pnas.1209414109227534943412003WangZBrandtSMedeirosAWangSWuHDentASerezaniCHMicroRNA 21 is a homeostatic regulator of macrophage polarization and prevents prostaglandin E2-mediated M2 generationPLoS One10e0115855201510.1371/journal.pone.0115855257066474338261CurtaleGMiRNAs at the Crossroads between Innate Immunity and Cancer: Focus on MacrophagesCells7E12201810.3390/cells7020012294197795850100LiLZhangJDiaoWWangDWeiYZhangCYZenKMicroRNA-155 and MicroRNA-21 promote the expansion of functional myeloid-derived suppressor cellsJ Immunol19210341043201410.4049/jimmunol.130130924391219KlebanoffCAGattinoniLRestifoNPCD8+ T-cell memory in tumor immunology and immunotherapyImmunol Rev211214224200610.1111/j.0105-2896.2006.00391.x168241301501075CereghettiDMLeePPTumor-Derived Exosomes Contain microRNAs with Immunological Function: Implications for a Novel Immunosuppression MechanismMicroRNA2194204201410.2174/2211536611302999001225069443MiaoBPZhangRSLiMFuYTZhaoMLiuZGYangPCNasopharyngeal cancer-derived microRNA-21 promotes immune suppressive B cellsCell Mol Immunol12750756201510.1038/cmi.2014.129KosakaNIguchiHYoshiokaYTakeshitaFMatsukiYOchiyaTSecretory mechanisms and intercellular transfer of microRNAs in living cellsJ Biol Chem2851744217452201010.1074/jbc.M110.107821203539452878508MeloSASugimotoHO'ConnellJTKatoNVillanuevaAVidalAQiuLVitkinEPerelmanLTMeloCACancer exosomes perform cell-independent microRNA biogenesis and promote tumorigenesisCancer Cell26707721201410.1016/j.ccell.2014.09.005254468994254633OhshimaKInoueKFujiwaraAHatakeyamaKKantoKWatanabeYMuramatsuKFukudaYOguraSYamaguchiKLet-7 microRNA family is selectively secreted into the extracellular environment via exosomes in a metastatic gastric cancer cell linePLoS One5e13247201010.1371/journal.pone.0013247209490442951912PigatiLYaddanapudiSCIyengarRKimDJHearnSADanforthDHastingsMLDuelliDMSelective release of microRNA species from normal and malignant mammary epithelial cellsPLoS One5e13515201010.1371/journal.pone.0013515209760032958125BoussadiaZLambertiJMatteiFPizziEPuglisiRZanettiCPasquiniLFratiniFFantozziLFelicettiFAcidic micro-environment plays a key role in human melanoma progression through a sustained exosome mediated transfer of clinically relevant metastatic moleculesJ Exp Clin Cancer Res37245201810.1186/s13046-018-0915-zHessvikNPLlorenteACurrent knowledge on exosome biogenesis and releaseCell Mol Life Sci75193208201810.1007/s00018-017-2595-95756260LespagnolADuflautDBeekmanCBlancLFiucciGMarineJCVidalMAmsonRTelermanAExosome secretion, including the DNA damage-induced p53-dependent secretory pathway, is severely compromised in TSAP6/Steap3-null miceCell Death Differ1517231733200810.1038/cdd.2008.10418617898YuXHarrisSLLevineAJThe regulation of exosome secretion: A novel function of the p53 proteinCancer Res6647954801200610.1158/0008-5472.CAN-05-457916651434ThompsonCAPurushothamanARamaniVCVlodavskyISandersonRDHeparanase regulates secretion, composition, and function of tumor cell-derived exosomesJ Biol Chem2881009310099201310.1074/jbc.C112.444562234307393617250WangKZhangSMarzolfBTroischPBrightmanAHuZHoodLEGalasDJCirculating microRNAs, potential biomarkers for drug-induced liver injuryProc Natl Acad Sci USA10644024407200910.1073/pnas.0813371106192463792657429MitchellPSParkinRKKrohEMFritzBRWymanSKPogosova-AgadjanyanELPetersonANoteboomJO'BriantKCAllenACirculating microRNAs as stable blood-based markers for cancer detectionProc Natl Acad Sci USA1051051310518200810.1073/pnas.0804549105186632192492472GreeningDWXuRJiHTauroBJSimpsonRJA protocol for exosome isolation and characterization: Evaluation of ultra-centrifugation, density-gradient separation, and immunoaffinity capture methodsMethods Mol Biol1295179209201510.1007/978-1-4939-2550-6_15
Exosomal miR-21 regulates the tumor microenvironment in osteosarcoma by targeting specific molecules in tumor cells, endothelial cells, cancer-associated fibroblasts and immune cells. The pathways depicted herein were deduced from studies focusing only on a specific cell type (75,76,83,85,86), and miR-21 is originated from other sources in addition to osteosarcoma. AKT, RAC-alpha serine/threonine-protein kinase; BTG, B-cell translocation gene; FASL, Fas ligand; NF1A, nuclear factor 1 A-type; PDCD4, programmed cell death 4; PTEN, phosphatase and tensin homolog; HIF-1α, hypoxia-inducible factor 1α; RECK, reversion-inducing-cysteine-rich protein with Kazal motifs; STAT3, signal transducer and activator of transcription 3; TCR: T-cell receptor; PGE2, prostaglandin E2; TLR8; Toll-like receptor 8; TPM1, tropomyosin 1; VEGF, vascular endothelial growth factor.