Implication of activin E in glucose metabolism: Transcriptional regulation of the inhibin/activin βE subunit gene in the liver

Activin E is a newly identified member of the transforming growth factor-β superfamily. To assess the role of activin E in glucose/energy metabolism, we investigated the transcriptional regulation of activin E in the liver. Northern blotting, Western blotting, quantitative real-time polymerase chain reaction (PCR), reporter assays and chromatin immunoprecipitation assays were used in this study. Insulin up-regulated activin E expression at the mRNA and protein level in HepG2 cells. Reporter assays revealed that the putative, functional, promoter sequence of human activin E gene was responsible for the effect of insulin. Mutational analysis of the promoter revealed that CCAAT/enhancer-binding proteins (C/EBPs) play a key role in regulating activin E expression and in the stimulatory effect of insulin on activin E transcription. Chromatin immunoprecipitation assays revealed that the C/EBPs can bind to the activin E promoter in HepG2 cells. The expression of activin E mRNA was up-regulated in the liver of diet-induced obese mice. These observations suggest that activin E plays a pathophysiological role in glucose metabolism.