Novel roles for Maf1 in embryonic stem cell differentiation and adipogenesis

2016-09-21Maf1 represses transcription from select RNA Polymerase (Pol) II‐ and RNA Pol III‐dependent genes. Our previous studies demonstrated that Maf1 functions as a tumor suppressor and it negatively regulates intracellular lipid accumulation. Together, these results identify Maf1 as an important link in between metabolism and cancer. However, a potential biological role for Maf1 in early development and cellular differentiation has not yet been examined. ❧ Maf1 expression was analyzed in human and mouse embryonic stem (ES) cells and as they differentiate into embryoid bodies (EBs). Maf1 protein expression is high in ES cells, and markedly reduced during their differentiation into EBs. This corresponded with a reciprocal change in the amounts of RNA Pol III‐dependent transcripts. We further examined whether Maf1 was required for the two properties of ES cells, self‐renewal and pluripotency. Maf1 knockdown did not affect ES cell self‐renewal or proliferation. However, analysis of markers associated with the three germ layers in EBs showed that alterations in Maf1 expression significantly affected the expression of mesoderm‐associated genes. These results indicate that Maf1 is important for driving ES cell induction into mesoderm. As Maf1 negatively regulates intracellular lipid accumulation, and adipocytes are one of the derivatives of mesoderm, we examined whether Maf1 is required for adipogenesis. Mouse ES cells, 3T3‐L1 preadipocytes, and Maf1-/- mouse embryo fibroblasts (MEFs) were terminally differentiated into mature adipocytes. Reduced Maf1 expression in either mouse ES or 3T3‐L1 cells resulted in enhanced RNA Pol III‐dependent transcription, reduced expression of key adipogenic genes, PPARγ, C/EBPα, and FABP4, and compromised adipocyte formation. Ectopic expression of Maf1 in Maf1-/- MEFs enhanced adipocyte differentiation, correlating with an increase in adipogenic gene expression and a decrease in RNA Pol III‐dependent transcription. Given that Maf1 is an established repressor of RNA Pol III‐dependent transcription, we examined whether this Maf1 function contributes to the ability of Maf1 to induce adipogenesis. Repression of RNA Pol III‐dependent transcription in 3T3‐L1 cells by either treatment of a RNA Pol III inhibitor, ML‐60218, or knockdown of the RNA pol III‐specific transcription factor, Brf1, resulted in a significant increase in adipogenic gene expression and adipocyte differentiation. However, treatment with the RNA Pol III inhibitor in Maf1‐knockdown 3T3‐L1 cells or Maf1-/- MEFs did not lead to induction of adipogenic gene expression or adipogenesis. Together, our findings reveal a novel and unexpected role for Maf1 and RNA Pol III‐dependent transcription in lineage specification and differentiation. Our results support a model in which Maf1 promotes formation of mesoderm and it also drives the terminal differentiation of adipocytes. These results further reveal that repression of RNA Pol III‐dependent transcription contributes to Maf1‐mediated induction of adipogenesis