[Regulation of pyruvate kinase gene expression and its clinical application]

Abstract

Pyruvate kinase (PK), an important glycolytic enzyme, has two genes per haploid genome in mammals and each gene encodes two isozymes. The L gene produces the L- and R-types using alternative promoters. The M gene generates the M1- and M2-types by alternative RNA splicing. Expression of the PK isozymes is tissue-specific and regulated developmentally. Carcinogenesis apparently reverses the developmental process. Expression of the L-type is regulated by dietary and hormonal factors. These regulations occurred at post-transcriptional as well as transcriptional levels. The transcription of hepatic L-type PK is stimulated by insulin and inhibited by glucagon. The insulin action requires ongoing protein synthesis and metabolism of glucose, and is enhanced by glucocorticoid. Dietary fructose also stimulates expression of the L-type in liver, kidney, and small intestine, but its mechanism is dependent on tissues, and on plasma insulin levels in the case of the liver. In normal liver, the fructose induction is explained by stimulation of gene transcription. On the other hand, fructose acts mainly at the post-transcriptional level in diabetic liver and other tissues. These fructose effects are attributable to common metabolite(s) of fructose and glycerol. Studies on transgenic mice indicate that the 5'-flanking region up to -3 kb of the L-type PK gene contains cis-acting elements responsible for insulin regulation and tissue-specific expression of the L-type. Further analysis using a transient expression assay revealed the presence of multiple elements necessary for expression of the L-type in hepatocytes in the region up to -170b.(ABSTRACT TRUNCATED AT 250 WORDS)