Induction of the SHARP-2 mRNA level by insulin is mediated by multiple signaling pathways

The rat enhancer of split- and hairy-related protein-2 (SHARP-2) is an insulin-inducible transcription factor which represses transcription of the rat phosphoenolpyruvate carboxykinase gene. In this study, a regulatory mechanism of the SHARP-2 mRNA level by insulin was analyzed. Insulin rapidly induced the level of SHARP-2 mRNA. This induction was blocked by inhibitors for phosphoinositide 3-kinase (PI 3-K), protein kinase C (PKC), and mammalian target of rapamycin (mTOR), actinomycin D, and cycloheximide. Whereas an adenovirus infection expressing a dominant negative form of atypical PKC lambda (aPKC lambda) blocked the insulin-induction of the SHARP-2 mRNA level, insulin rapidly activated the mTOR. Insulin did not enhance transcriptional activity from a 3.7kb upstream region of the rat SHARP-2 gene. Thus, we conclude that insulin induces the expression of the rat SHARP-2 gene at the transcription level via both a PI 3-K/aPKC lambda- and a PI 3-K/mTOR- pathways and that protein synthesis is required for this induction.