The regulation of STAT5 by C/EBPa, C/EBPb, and PPARr in adipogenesis

Abstract

Adipogenesis is a complex process that includes the proliferation of precursor cells, their commitment to the adipogenic lineage, and terminal differentiation. During the differentiation of preadipocytes, the expression of adipocyte-specific genes depends on the transcriptional activation and the expression of families of transcription factors, C/EBPs and PPARs. In addition, adipogenesis is largely dependent on the STAT (Signal Transducer and Activator of Transcription) pathway. However, the molecular mechanism of the STAT pathway’s role on the adipogenesis of human bone marrow derived-stromal cells (BMSCs) is still not well known. In this study, we investigated transcriptional regulation involved in the expression of STAT5A and STAT5B during adipogenesis.We determined that the expression of STAT5A and STAT5B increases from the onset of adipogenesis of hBMSCs and 3T3-L1 cells and is maintained throughout adipogenesis. In addition, we successfully determined that STAT5A is regulated at the transcriptional level by PPAR? and RXR?, whereas STAT5B is regulated by C/EBP? and C/EBP?. The PPRE regulatory element of STAT5A exists at a promoter region ranging from nucleotides -346 to -101, and the C/EBP regulatory element was located at the -196 to -118 nucleotide region of the STAT5B promoter. We determined that C/EBP? and C/EBP? collectively bind to the STAT5B promoter region, whereas PPAR? binds to that of STAT5A using EMSA and ChIP assays. RNA interference with STAT5A resulted in a complete blockage of the differentiation, whereas inhibition of STAT5B only partially blocked the differentiation. We propose that C/EBP?, C/EBP? and PPAR? control adipogenesis by regulating STAT5B and STAT5A, respectively, and that STAT5A is absolutely necessary; STAT5B only plays a supplemental role during adipogenesis. Furthermore, PPAR?-STAT5 regulation by C/EBP?

signaling seems to be crucial in the adipogensis pathway-initiating cascade of various adipogenic genes.