Insulin Stimulates the Expression of the SHARP-1 Gene via Multiple Signaling Pathways

Abstract

The rat enhancer of split- and hairy-related protein-1 (SHARP-1) is a basic helix-loop-helix transcription factor. An issue of whether SHARP-1 is an insulin-inducible transcription factor was examined. Insulin rapidly increased the level of SHARP-1 mRNA both in vivo and in vitro. Then, signaling pathways involved with the increase of SHARP-1 mRNA by insulin were determined in H4IIE rat hepatoma cells. Pretreatments with LY294002, wortmannin, and staurosporine completely blocked the induction effect, suggesting the involvement of both phosphoinositide 3-kinase (PI 3-K) and protein kinase C (PKC) pathways. In fact, overexpression of a dominant negative form of atypical protein kinase C lambda (aPKCλ) significantly decreased the induction of the SHARP-1 mRNA. In addition, inhibitors for the small GTPase Rac or Jun N-terminal kinase (JNK) also blocked the induction of SHARP-1 mRNA by insulin. Overexpression of a dominant negative form of Rac1 prevented the activation by insulin. Furthermore, actinomycin D and cycloheximide completely blocked the induction of SHARP-1 mRNA by insulin. Finally, when a SHARP-1 expression plasmid was transiently transfected with various reporter plasmids into H4IIE cells, the promoter activity of PEPCK reporter plasmid was specifically decreased. Thus, we conclude that insulin induces the SHARP-1 gene expression at the transcription level via a both PI 3-K/aPKCλ/JNK- and a PI 3-K/Rac/JNK-signaling pathway; protein synthesis is required for this induction; and that SHARP-1 is a potential repressor of the PEPCK gene expression.

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

“…12,13) Cell culture and treatments with insulin, various inhibitors, or adenoviruses were previously described. 6,7,10) Briefly, for analysis of a signaling pathway(s), 50 μM LY294002, 0.2 μM wortmannin, 0.1 μM staurosporine, 0.1 μM rapamycin, 25 μM PD98059, 10 nM okadaic acid, 10 μM JNK inhibitor II, 50 μM Rac1 inhibitor, 0.8 μM actinomycin D, or 10 μM cycloheximide were added to the medium at 15 min before the addition of 10 nM insulin. The adenovirus was infected with the 500 multiplicity of infection and cultured for an additional 24 h.…”

“…Both a phosphoinositide 3-kinase (PI 3-K)/atypical protein kinase C lambda (aPKCλ)/Jun N-terminal kinase (JNK)-and a PI 3-K/ Rac/JNK-signaling pathway mediate an induction of the level of SHARP-1 mRNA by insulin. 6) However, that of SHARP-2 mRNA remains to be determined except for an involvement of PI 3-K. 4) Compounds that can induce both the SHARP-1 and SHARP-2 gene expression are useful for prevention and treatment of diabetes mellitus. We have reported that food constituents such as genistein, (-)-epigallocatechin-3-gallate (EGCG), and (S)-Equol, which lower blood glucose level in vivo, can stimulate these gene expression in H4IIE cells.…”

5-Aminoimidazole-4-carboxyamide-1-β-D-ribofranoside stimulates the ratenhancer of split- and hairy-related protein-2gene via atypical protein kinase C lambda

“…Therefore, we hypothesize that SHARP-2 is an important transcription factor involving in the regulation of blood glucose levels (9,10). Recently, we have reported that SHARP-1, an isoform of SHARP-2, also involved in the regulation of gene expression by insulin (11).…”

Potential Roles of Dec and Bmal1 Genes in Interconnecting Circadian Clock and Energy Metabolism

“…Recent studies have shown that insulin promotes the phosphorylation of the BMAL1 protein by Akt, thereby suppressing its transcriptional activity [ 103 ]. Furthermore, several studies demonstrated that insulin increases the expression levels of Per1 , Per2 , Dec1 , and Dec2 in cultured cells [ 104 , 105 , 106 , 107 ]. While the molecular mechanisms underlying insulin-induced expression of these clock genes remain to be elucidated, insulin signalling pathways may play an important role in the regulation of the molecular clock because insulin-induced expression of Dec1 and Dec2 was found to be inhibited by the blockade of phosphoinositide 3-kinase, protein kinase C, or mammalian target of rapamycin [ 104 , 105 , 106 ].…”