The Roles Of Secreted MicroRNA-214 And MicroRNA-150 In Tumor-immune System Interaction

microRNAs?miRNAs?are a class of small non-coding RNAs that regulate gene expression at post-transcriptional level.With the introduction of circulating miRNAs,miRNAs are not only intracellular regulatory molecules but also cell signaling molecules in intercellular communication.Secreted miRNAs,a type of actively secreted circulating miRNAs,serve as mediators of a new form of intercellular communication.Intensive studies have provided evidence that microvesicles?MVs?released from various cell types transfer miRNAs into neighboring or distant cells,where these exogenous miRNAs function as endogenous miRNAs to regulate the target gene expression and function of recipient cells.The immune system plays a key role in tumor progression,during which tumor cells and immune cells interact via various types of signals.In the tumor microenvironment,tumor cells not only provide antigenic stimulation for T cell activation but also release crucial cytokines for T-cell differentiation and proliferation,when interacting with tumor-infiltrating innate immune cells.The expansion of regulatory T cells?Tregs?can cause immune suppression and immune tolerance,ultimately leading to tumor immune escape.The nature of signals,which released by tumor cells to induce Treg expension,is poorly understood.Macrophages are a fundamental part of the innate defense mechanisms,which can promote specific immunity by inducing T cell recruitment and activation.However,their presence within the tumor microenvironment has been associated with enhanced tumor progression and shown to promote cancer cell growth and spread,angiogenesis and immunosuppression.The underlying mechanism remains to be elucidated.Considering that secreted miRNAs mediate intercellular communication,we ask if secreted miRNAs bridge the interactions between tumor and the immune system,and lead to tumor progression and immune escape.We first investigated the role of tumor-secreted miRNAs in T cell modulation.We found that miR-214 expression and secretion were increased in human cancer patients and tumor-implanted mice,and secreted miR-214s were mainly delivered via MVs.We also found that LLC-secreted miR-214 induced the expansion of CD4⁺CD25^high Foxp³⁺Tregs by targeting the CD4⁺ T-cell PTEN in vitro and in vivo.In conclusion,our findings illustrate that the delivery of secreted miR-214 from tumor cells to CD4⁺ T-cells via MVs could expand the population of CD4⁺CD25^high Foxp³⁺Tregs by decreasing the level of CD4⁺ T-cell PTEN,and cause immunosuppression.These results suggest a novel mechanism of Tregs expansion and immune evasion in tumor progression.We also investigated the role of macrophage-secreted miRNAs in tumor progression.We found differential expression of miRNAs in macrophages during M1 and M2 polarization,and secretion of these highly expressed miRNAs may affect the physiological and pathological conditions.A higher level of miR-150 was found in M2 macrophages and tumor-associated macrophages.It is reported that secreted miR-150 derived from human monocyte?THP-1?can induced the migration of endothelial cells?HMEC-1?,which prompts the initial speculation that miRNAs secreted by macrophages may affect tumor growth by promoting angiogenesis.We found that THP-1 cell-derived MVs with abundant miR-150 dramatically promoted angiogenesis and growth in tumor.The secreted miR-150 can initiate capillary tube formation in vitro and enhance angiogenesis in vivo.By depleting miR-150 from THP-1 MVs and enhancing miR-150 in 293T MVs,we demonstrated that it was miR-150 in the MVs that accounted for the pro-angiogenic properties.Furthermore,the MV delivery of anti-miR-150 into tumor-implanted mice significantly reduced angiogenesis and tumor progression.Taken together,our findings demonstrate that secreted miR-150 from macrophages can promote angiogenesis in vitro and cause angiogenesis in tumor progression in vivo.These results demonstrate that immune cell-secreted miRNAs involve in tumor development,and raise the possibility to develop a novel miRNA-based therapeutic approach for disease treatment.In summary,we found that the secreted miRNAs as mediators of a new form of intercellular communication between tumor and the immune system.This may herald a new era in our understanding of signal and molecule transfer between cells.The elucidation of this novel information transfer system will be important in understanding many biological processes including immune response and tumorigenesis.