Analysis of Induction Mechanisms of an Insulin-lnducible Transcription Factor SHARP-2 Gene by (-)-Epigallocatechin-3-gallate

摘要

The rat enhancer of split- and hairy-related protein-2 (SHARP-2) is an insulin-inducible transcription factor. In this study, we examined the mechanism(s) involved in the regulation of the rat SHARP-2 gene expression by (-)-epigallocatechin-3-gallate (EGCG). The induction of SHARP-2 mRNA by EGCG was repressed by pretreatments with inhibitors for either phosphoinositide 3-kinase (PI3K.) or RNA polymerase II. Then, we examined a biological relationship between EGCG and transcription factor NF-kB interfering with the insulin action. The protein levels of the NF-kB were rapidly decreased by an EGCG treatment. Finally, the mechanism(s) of transcriptional activation of the rat SHARP-2 gene by both NF-kB and EGCG was analyzed. While overexpression of the NF-/cB p65 protein decreased the promoter activity of the SHARP-2 gene, EGCG did not affect it. Thus, we conclude that EGCG induces the expression of the rat SHARP-2 gene via both the PI3K pathway and degradation of the NF-kB p65 protein.