Identification and characterization of novel gene involved in insulin action

点击翻译按钮获取中文摘要

For better understanding of intracellular signaling involved in insulin's metabolic actions, I have attempted to identify novel signaling molecules that contribute to insulin action. I first tried to purify novel insulin-induced phosphorylated proteins with the use of metal-chelating affinity chromatography. Although Ga-chelating affinity column was found to absorb phosphorylated proteins with high efficiency ; we could not identify any novel protein that is phosphorylated in 3T3-L1 adipocytes in response to insulin with this method. As a second approach, with the use of Gene Chip analysis, I next attempted to identify novel genes of which expression is induced by insulin. We analyzed the alteration of hepatic gene expression during a fast-feeding cycle in normal mice, in insuhn-administered STZ-diabetes mice, and in mice that express a dominant negative mutant of PI 3-kinase (Δp85) specifically in the liver. We picked up genes of which expression are upregulated in a fast-feeding cycle and by insulin administration in STZ mice and are downregulated by Δp85 expression. Among such genes, Stra13, a basic helix-loop-helix transcription factor, was found to be upregulated by insulin in primary cultured hepatocyte both in protein and mRNAlevels. Insulin-induced expression of Stra13 was attenuated by an inhibitor of PI 3-kinase, and an active form of the kinase induced its expression in the absence of insulin, indicating that Stra13 is an insulin-induced gene. We also identified several more transcription factors whose expression is suppressed by insulin or induced by glucocorticoid or cAMP. These transcription factors may be involved in metabolic regulation in the liver.