Mitochondrial transcription factor B2 overexpression increases M2 macrophage infiltration via cytosolic mitochondrial DNA-stimulated Interleukin-6 secretion in ovarian cancer

Abstract

Mitochondrial transcription factor B2 (TFB2M) is a protein modulating both mitochondrial DNA (mtDNA) transcription and compacting. In this study, we explored the expression profile of <i>TFB2M</i> in ovarian cancer, its association with infiltration of tumor-associated macrophages (TAMs), and its influence on macrophage polarization. Serial sections of ovarian cancer tissue arrays were stained to detect TFB2M and CD163 expression. Epithelial ovarian cancer cell line OVISE and CAOV4 were used to assess the influence of TFB2M on IL-6 expression. THP-1 cells were utilized as an <i>in vitro</i> model for macrophage migration and polarization. Results showed that higher <i>TFB2M</i> expression is associated with poor survival in ovarian cancer patients. IHC staining confirmed a moderately positive correlation between <i>TFB2M</i> expression and the infiltration of CD163-positive cells in 68 primary ovarian cancer cases. <i>TFB2M</i> overexpression was associated with increased mtDNA outside the mitochondria and elevated IL-6 expression in ovarian cancer cells. When cytosolic mtDNA was selectively inhibited by DNase I, <i>TFB2M</i>-induced IL-6 upregulation was canceled. <i>TFB2M</i> overexpression could activate the nuclear factor kappa-B (NF-κB) signaling pathway via promoting nucleus entry of p65 and p-p65, which was abrogated by inhibiting cytosolic mtDNA, TLR9, or NF-κB signaling pathway. Conditioned medium from OIVSE cells with <i>TFB2M</i> overexpression could induce macrophage migration and M2 polarization. However, these inducing effects were abrogated by DNase I, TLR9 inhibitor, and anti-IL-6 R pretreatment. In conclusion, this study showed a novel role of TFB2M in the immunosuppressive tumor microenvironment. It promotes M2 macrophage infiltration via a cytosolic mtDNA/TLR9/NF-κB/IL-6 pathway in ovarian cancer.