Two glucose-signaling pathways in S14 gene transcription in primary hepatocytes: a common role of protein phosphorylation.

Abstract

Transcription of the rat S14 gene is induced in response to increased carbohydrate metabolism in the liver. Because carbohydrate-induced changes in lipogenesis are mediated in part by changes in phosphorylation of multiple proteins, we investigated the role of protein phosphorylation on transcriptional regulation of the two carbohydrate response elements, a thyroid hormone receptor-independent carbohydrate response element and a thyroid receptor-dependent glucose response element located up-stream of the S14 gene. S14 reporter constructs were transiently transfected into rat primary hepatocytes and incubated with the protein or phosphatase inhibitor okadaic acid calyculin-A, or one of several protein kinase activators. Low dose okadaic acid blocked glucose induction from both elements without inhibiting glucose metabolism. Calyculin-A, a preferential phosphatase-1 inhibitor, only blocked the glucose response when glucose metabolism was inhibited. The protein kinase-C activator, 12-myristate 13-acetate, did not change the glucose responses, whereas the protein kinase-A activator, 8-(4-chlorophenylthio)cAMP, inhibited S14 transcription by inhibiting glucose metabolism. In contrast, the calcium ionophore A23187, a calmodulin kinase activator, mimicked the effect of low dose okadaic acid, but had no effect on glucose metabolism. We conclude that protein phosphatase-2A and calmodulin kinases may be involved in the glucose signaling pathway of the S14 gene. A similar phosphorylation step may be involved in the two distinct glucose response pathways.

"Spot 14" Protein: A Metabolic Integrator in Normal and Neoplastic Cells

“…The precise identity of the accessory factor for the S14 CHORE has yet to be established. The effect of carbohydrate on S14 gene regulation involves both protein phosphorylation (51), and the maintenance of a specific intracellular calcium pool that signals for reduced transcription (52), indicating further complexity of the regulatory system.…”

Glucose-stimulated Somatostatin Gene Expression in the Brockmann Bodies of Rainbow Trout (Oncorhynchus mykiss) Results from Increased mRNA Transcription and not from Altered mRNA Stability

“…Our previous study indicated that glucose metabolites generated after the aldolase step of glycolysis were capable of stimulating expression of PPSS II mRNAs (Ehrman et al , 2000). It is conceivable that one or more of these metabolites could activate specific trans -acting factors that, in turn, modulate gene transcription via carbohydrate-responsive elements (CHORE) in promoter regions of the SS genes, as is the case for other glucose sensitive genes ( e.g ., S14; Sudo and Mariash, 1994).…”

Prevention of endotoxin-induced lethality in mice by calmodulin kinase activator

“…It was reported that calcium ionophore A23187 was used as a CaM kinase activator, because of the ability to enhance intracellular Ca 2+ [43,44]. Lethal toxicity induced by compound 506 in mice was completely prevented by calcium ionophore A23187 administered 15 min after injection of compound 506 (Table 1).…”