Analysis of regulatory mechanisms of an insulin-inducible SHARP-2 gene by (S)-Equol

Retinoic acid stimulates transcription of the rat SHARP-2 gene via multiple pathways

Members of the enhancer of split- and hairy-related protein (SHARP) family, SHARP-1 and SHARP-2, are basic helix-loop-helix transcriptional repressors and belong to the clock genes. In this study, an effect of retinoic acid (RA) on the SHARP family gene expression in the differentiated cells was examined. RA rapidly and temporarily induced the SHARP-2 mRNA expression in hepatic H4IIE cells. Then, whether the SHARP-2 mRNA expression is altered by dexamethasone (Dex), insulin, and the combination of RA and Dex or RA and insulin was examined. Dex had different effects on the expression of SHARP-2 mRNA in the presence or absence of RA. Then, the molecular mechanisms were investigated using inhibitors of various signaling molecules. The RA-induction of SHARP-2 mRNA level was mainly inhibited by LY294002, staurosporine, and actinomycin D, respectively. Finally, whether RA acts on the transcriptional regulatory region of the SHARP-2 gene was analyzed using luciferase reporter gene assay. At least two RA-responsive regions were mapped at the nucleotide sequences between -3,700 and -1,600 of the SHARP-2 gene. In addition, this effect was dependent on the retinoic acid receptor and retinoid X receptor. Thus, we conclude that RA stimulated transcription of the SHARP-2 gene via multiple pathways.

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 (aPKCλ) blocked the insulin-induction of the SHARP-2 mRNA level, insulin rapidly activated the mTOR. Insulin did not enhance transcriptional activity from a 3.7 kb 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/aPKCλ- and a PI 3-K/mTOR- pathways and that protein synthesis is required for this induction.

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

The 5'-AMP-activated protein kinase (AMPK) functions as a cellular energy sensor. 5-Aminoimidazole-4-carboxyamide-1-β-D-ribofranoside (AICAR) is a chemical activator of AMPK. In the liver, AICAR suppresses expression of thephosphoenolpyruvate carboxykinase(PEPCK) gene. The rat enhancer of split- and hairy-related protein-2 (SHARP-2) is an insulin-inducible transcriptional repressor and its target is thePEPCKgene. In this study, we examined an issue of whether theSHARP-2gene expression is regulated by AICAR via the AMPK. AICAR increased the level of SHARP-2 mRNA in H4IIE cells. Whereas an AMPK inhibitor, compound-C, had no effects on the AICAR-induction, inhibitors for both phosphoinositide 3-kinase (PI 3-K) and protein kinase C (PKC) completely diminished the effects of AICAR. Western blot analyses showed that AICAR rapidly activated atypical PKC lambda (aPKCλ). In addition, when a dominant negative form of aPKCλ was expressed, the induction of SHARP-2 mRNA level by AICAR was inhibited. Calcium ion is not required for the activation of aPKCλ. A calcium ion-chelating reagent had no effects on the AICAR-induction. Furthermore, the AICAR-induction was inhibited by treatment with an RNA polymerase inhibitor or a protein synthesis inhibitor. Thus, we conclude that the AICAR-induction of theSHARP-2gene is mediated at transcription level by a PI 3-K/aPKCλ pathway.

The active role of leguminous plant components in type 2 diabetes

Diabetes appears to be one of the most frequent noncommunicable diseases in the world. A permanent growth in the incidence of diabetes can be observed and according to the International Diabetes Federation (IDF) the year 2030 will mark the increase in the number of diabetics to 439 mln worldwide. Type 2 diabetes accounts for about 90% of all diabetes incidence. Nutrition model modification not only features the basic element in type 2 diabetes treatment but also constitutes the fundamental factor influencing a morbidity rate decrease. Leguminous plants are a key factor in the diabetic diet; plants such as pulses or soybeans are nutritious products valued highly in nutrition. These legumes are high in the content of wholesome protein and contain large amounts of soluble alimentary fiber fractions, polyunsaturated fatty acids, vitamins and minerals, and bioactive substances with antioxidant, anti-inflammatory, and anticancer activity. They are distinguished by the high amount of bioactive compounds that may interfere with the metabolism of glucose. The most significant bioactive compounds displaying antidiabetic activity in leguminous plants are as follows: genistein and daidzein, alpha-amylase inhibitors, and alpha-glucosidase inhibitors. In vitro research using leguminous plant extracts has confirmed their antidiabetic properties. Leguminous plants should be employed in the promotion of healthy lifestyles in terms of functional food.