miR‐21a negatively modulates tumor suppressor genes PTEN and miR‐200c and further promotes the transformation of M2 macrophages

Abstract

miR-21a is well-known to inhibit PTEN expression. We have previously shown that PTEN suppressed the transformation of M2 macrophages in the tumor microenvironment. Therefore, we hypothesized that miR-21a could influence M2 macrophage transformation by regulating PTEN expression. In this study, we identified how miR-21a reduced the expression of both PTEN mRNA and protein in murine macrophage cell lines and primary macrophages. Moreover, opposite effects were identified upon the use of a miR-21a inhibitor. Using a cytokine array, we identified the cytokines closely associated with miR-21a-mediated macrophage transformation to the M2 phenotype. miR-21a mimics could also enhance the migratory ability of murine breast cancer 4T1 cells, the growth of breast cancer in vivo and CD206 intratumor expression. In addition, quantitative PCR (qPCR) and methylation-specific PCR analysis showed that miR-21a enhanced miR-200c methylation and then decreased miR-200c and PTEN expression. These effects could be reversed by treatment with 5'-Aza, a DNA-demethylating agent. MiR-200c was predicted to target the PTEN 3'UTR, but qPCR illustrated the miR-200c mimic that increased PTEN expression, and 5'-Aza could enhance its effect. The above results indicate that miR-21a negatively modulates two tumor suppressor genes, miR-200c and PTEN, thereby promoting M2 macrophage transformation. This demonstrates that miR-21a represents a novel target for improving the overall tumor microenvironment.

The emerging role of microRNA in regulating the mTOR signaling pathway in immune and inflammatory responses

“…82 miR-21a overexpression in macrophages can promote the switch to the anti-inflammatory M2 phenotype via downregulation of PTEN tumor suppressor gene and improve the migration capacity of breast cancer cells. 83 Moreover, the AKT/mTOR signaling pathway has been found to have a critical role in M2 macrophage proliferation in response to IL-4. R€ uckerl et al 84 demonstrated that miR-378-3p was specifically induced by IL-4 and confirmed the IL-4Ra/PI3K/AKT signaling pathway as a target.…”

PTEN Function at the Interface between Cancer and Tumor Microenvironment: Implications for Response to Immunotherapy

“…Supernatants derived from human glioblastoma cells upregulated miR-32, which in turn interacts and suppresses PTEN in an in vitro model of human monocytes, thus promoting the M2 phenotype and resulting in an enhanced cell proliferation [ 85 ]. miR-21 reduces the expression of PTEN and its upstream positive regulator miR-200c in primary macrophages, promoting their differentiation into M2 [ 86 ]. Exosomes derived from pancreatic cancer cells promote hypoxia-inducible factors (HIF)-1 α /HIF-2 α -dependent M2 phenotype through PTEN regulation: miR-301a-3p converts stromal macrophages into M2 macrophages and promotes lung metastases formation by blocking PTEN transcription [ 87 ].…”

MicroRNAs in tumor immunity: functional regulation in tumor-associated macrophages

“…A recent study has proved that the tumor suppressor genes phosphatase and tensin homologue (PTEN) and miR-200c are also targets of miR-21a. Upregulation of miR-21a in macrophages can promote transformation to the anti-inflammatory phe-notype through downregulation of PTEN and enhance the migratory ability of breast cancer cells (Li N et al, 2018). Consistent with these findings, a genetic deficiency of miR-21 can promote the polarization of macrophage to the M1 phenotype in the presence of tumor cells through the IFN-γ/signal transducer and activator of transcription 1 (STAT1) pathway.…”