-
[show abstract]
[hide abstract]
ABSTRACT: We previously reported that (-)-epigallocatechin-3-gallate (EGCG) increased the level of SHARP-1 mRNA via a phosphoinositide 3-kinase/atypical protein kinase C lambda signaling pathway in rat H4IIE hepatoma cells. In the present study, we investigated other signaling pathway(s). Treating with either compound-C, BAY11-7082, or both, partially blocked the up-regulation of the SHARP-1 gene by EGCG. This suggests that AMP-activated protein kinase (AMPK)- and nuclear factor-kappa B (NF-κB)-signaling pathways were additively involved in the induction mediated by EGCG. Indeed, an AMPK activator induced a level of SHARP-1 mRNA. Although actinomycin D partially blocked the EGCG-induction of that SHARP-1 mRNA level, the nucleotide sequence between -1501 and -1 in the rat SHARP-1 gene did not positively respond to EGCG and NF-κB, respectively. Thus, we conclude that EGCG stimulates multiple signaling pathways in the SHARP-1 gene expression at the transcriptional and post-transcriptional levels and that there is no regulatory region susceptible to EGCG and NF-κB in the examined region.
Food Chemistry 09/2012; 134(2):783-8. · 3.65 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: 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-κB interfering with the insulin action. The protein levels of the NF-κB were rapidly decreased by an EGCG treatment. Finally, the mechanism(s) of transcriptional activation of the rat SHARP-2 gene by both NF-κB and EGCG was analyzed. While overexpression of the NF-κB 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-κB p65 protein.
Journal of Agricultural and Food Chemistry 09/2012; 60(39):9850-5. · 2.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Small compounds that activate the insulin-dependent signaling pathway have potential therapeutic applications in controlling type 2 diabetes mellitus. The rat enhancer of split- and hairy-related protein-2 (SHARP-2) is an insulin-inducible transcription factor that decreases expression of the phosphoenolpyruvate carboxykinase gene, a gluconeogenic enzyme gene. In this study, we screened for soybean isoflavones that can induce the rat SHARP-2 gene expression and analyzed their mechanism(s). Genistein and (S)-Equol, a metabolite of daidzein, induced rat SHARP-2 gene expression in H4IIE rat hepatoma cells. The (S)-Equol induction was mediated by both the phosphoinositide 3-kinase- and protein kinase C (PKC)-pathways. When a dominant negative form of atypical PKC lambda (aPKCλ) was expressed, the induction of SHARP-2 mRNA level by (S)-Equol was inhibited. In addition, Western blot analyses showed that (S)-Equol rapidly activated both aPKCλ and classical PKC alpha. Furthermore, the (S)-Equol induction was inhibited by treatment with a RNA polymerase inhibitor or a protein synthesis inhibitor. Finally, a reporter gene assay revealed that the transcriptional stimulation by (S)-Equol was mediated by nucleotide sequences located between -4687 and -4133 of the rat SHARP-2 gene. Thus, we conclude that (S)-Equol is an useful dietary supplement to control type 2 diabetes mellitus.
Archives of Biochemistry and Biophysics 06/2012; 525(1):32-9. · 2.93 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The rat enhancer of split- and hairy-related protein-1 (SHARP-1) is an insulin-inducible transcriptional repressor. In this study, we examined issues of whether (-)-epigallocatechin-3-gallate (EGCG), a green tea polyphenol, regulates the expression of the rat SHARP-1 gene and which signaling pathway mediates the regulation. When H4IIE cells were treated with EGCG, SHARP-1 mRNA levels rapidly increased. Pretreatments with inhibitors for either phosphoinositide 3-kinase (PI 3-K) or protein kinase C partially blocked EGCG induction. Atypical protein kinase C lambda (aPKCλ) is known as a downstream target of PI 3-K in the liver. When a dominant-negative form of aPKCλ was expressed, the EGCG-induced SHARP-1 mRNAs was inhibited. Finally, Western blot analysis revealed that EGCG rapidly and temporarily stimulates aPKCλ phosphorylation. Thus, we conclude that EGCG induces SHARP-1 gene expression via a PI 3-K/aPKCλ signaling pathway.
Journal of Agricultural and Food Chemistry 11/2011; 59(24):13360-4. · 2.82 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Small compounds that activate the insulin-dependent signaling pathway have potential therapeutic applications in controlling insulin-independent diabetes mellitus. In this study, we investigated whether soybean isoflavones could induce the expression of SHARP-2, a downstream component of insulin-dependent signaling pathway, associated with the regulation of blood glucose. One such compound called genistein, rapidly and temporarily induced SHARP-2 mRNA levels in a dose-dependent manner in rat H4IIE hepatoma cells. This induction process was rapidly stimulated by a protein kinase C (PKC) activator and blocked by a PKC inhibitor, suggesting that SHARP-2 may be induced via PKC activation. Upon Western blot analysis, genistein showed a stimulation of PKC phosphorylation. Therefore, we concluded that genistein might transcriptionally induce SHARP-2 through the activation of PKC in H4IIE cells. Our results suggest that genistein might be a useful dietary supplement to control insulin-independent diabetes mellitus by inducing the SHARP-2 expression via a bypass of the insulin-dependent signaling pathway.
Frontiers in bioscience (Elite edition) 01/2011; 3:1534-40.
