Transcriptional analysis of transcription factor c-Maf as a molecular switch that controls immune suppression by programming macrophages in lung cancer

To investigate c-Maf-controlled gene expression, M2-like bone marrow-derived macrophages (BMM) were transfected with c-Maf or control siRNA. Knockdown of c-Maf significantly decreased c-Maf protein and mRNA expression levels. In addition, IL-10 and arginase mRNA levels were significantly decreased while IL-12 was increased. In contrast, ectopic expression of c-Maf in the M1-like BMM significantly upregulated IL-10 and arginase mRNA expression levels while downregulated IL-12 expression level, suggesting an M2-like phenotype. These data indicate that c-Maf may be a critical controller in regulating M2-related gene expression. To further determine which part of the M2 macrophage transcriptomic profile is controlled by c-Maf, we performed microarray analysis using polarized M2-like BMM from WT or c-Maf KO fetal liver chimeric mice. Notably, many M2 genes were differentially regulated by c-Maf. Further real-time PCR (qPCR) analysis confirmed that the mRNA expression levels of IL-12, IL-1β, IL-6, arginase, IL-10, VEGF, TGF-β, IRF-4, and CCR2 were significantly altered in c-Maf-deficient M2 BMM. Since M2-like macrophages have a potent immunosuppressive function on T cell activation, we next determined whether deficiency of c-Maf in M2 BMM would reverse such effect. M2 BMM from WT mice exhibited potent immunosuppressive activity as IFN-γ production from antigen (Ag)-specific CD4 and CD8 T cells was significantly diminished. In contrast, c-Maf deficiency in M2 BMM significantly increased IFN-γ production by CD4 and CD8 T cells compared to WT M2 BMM. These data suggest that c-Maf not only controls many M2-related gene expression but also is critical in regulating M2-like macrophage-mediated T cell immunosuppression. Gene expression of polarized M2-like BMM from WT or c-Maf KO fetal liver chimeric mice was compared using 3 replicates in each group.