MicroRNA-19a-3p inhibits breast cancer progression and metastasis by inducing macrophage polarization through downregulated expression of Fra-1 proto-oncogene

Abstract

One of the hallmarks of malignancy is the polarization of tumor-associated macrophages (TAMs) from a pro-immune (M1-like) phenotype to an immune-suppressive (M2-like) phenotype. However, the molecular basis of the process is still unclear. MicroRNA (miRNA) comprises a group of small, non-coding RNAs that are broadly expressed by a variety of organisms and are involved in cell behaviors such as suppression or promotion of tumorigenesis. Here, we demonstrate that miR-19a-3p, broadly conserved among vertebrates, was downregulated in RAW264.7 macrophage cells of the M2 phenotype in conditoned medium of 4T1 mouse breast tumor cells. This downregulation correlated with an increased expression of the Fra-1 gene, which was reported to act as a pro-oncogene by supporting the invasion and progression of breast tumors. We found significant upregulation of miR-19a-3p in RAW264.7 macrophages after transfection with a miR-19a-3p mimic that resulted in a significant suppression of the expression of this gene. In addition, we could measure the activity of binding between miR-19a-3p and Fra-1 with a psiCHECK luciferase reporter system. Further, transfection of RAW264.7 macrophage cells with the miR-19a-3p mimic decreased the expression of the Fra-1 downstream genes VEGF, STAT3 and pSTAT3. Most importantly, the capacity of 4T1 breast tumor cells to migrate and invade was impaired in vivo by the intratumoral injection of miR-19a-3p. Taken together, these findings indicate that miR-19a-3p is capable of downregulating the M2 phenotype in M2 macrophages and that the low expression of this miRNA has an important role in the upregulation of Fra-1 expression and induction of M2 macrophage polarization.

MicroRNAs as mediators and communicators between cancer cells and the tumor microenvironment

“…TNF α , IL-12, IFN γ , CCL5) 58, 60, 61 . Several other miRNAs were also found to be downregulated within TAMs, including miR-142-3p 62 , miR-125b 63 , and miR-19a-3p 64 . Downregulation of miR-142-3p limited the tumor infiltration of macrophages and reduced the therapeutic effect of adoptive T cell transfer 62 .…”

“…Restoring miR-125b expression in macrophages promoted an anti-tumor response by targeting IRF-4, a known promotor of the M2 macrophage phenotype 63, 65 . Macrophages have been found to downregulate miR-19a-3p within the TME, possibly through a cancer derived soluble factor 64 . The downregulation of miR-19a-3p promoted STAT3 signaling, because miR-19a-3p directly targets Fra-1 (Fos-related antigen), a member of the AP1 family involved in macrophage polarization and the upstream regulation of STAT3 64, 66 .…”

“…Macrophages have been found to downregulate miR-19a-3p within the TME, possibly through a cancer derived soluble factor 64 . The downregulation of miR-19a-3p promoted STAT3 signaling, because miR-19a-3p directly targets Fra-1 (Fos-related antigen), a member of the AP1 family involved in macrophage polarization and the upstream regulation of STAT3 64, 66 . STAT3 expression in macrophages, which promotes immune suppression, was rescued upon overexpression of miR-19a-3p 64 .…”

MicroRNAs in breast cancer: oncogene and tumor suppressors with clinical potential

“…Down-regulated miR-19a in TAMs, induced by the TME, is able to maintain the phenotype of TAMs by targeting Fos-related antigen 1 (Fra-1) and other genes in its downstream signaling pathway. The reintroduction of miR-19a to this kind of macrophage can promote transformation of M1 to M2, resulting in the enhancement of migration and invasion of breast cancer cells (Yang et al, 2014).…”

Harnessing the immune system for the treatment of breast cancer

“…Suppressing the signal transducer and activator of transcription 3 (STAT3) signaling pathway by hydrazinocurcumin converts the TAM phenotype from M2 to M1 and inhibits breast cancer progression and metastasis (Zhang X. et al, 2013). Inhibition of cyclooxygenase (COX)-2 or enhanced expression of microRNA miR-19a-3p also suppresses breast cancer metastasis by preventing M2 phenotype polarization (Na et al, 2013;Yang et al, 2013a). Anti-angiogenic treatment has also been shown to reprogram TAMs from the M2 to the M1 phenotype and enhance immunotherapy (Huang et al, 2012).…”