Regulation of enzyme activity and gene expression of pyruvate kinase by dietary factors

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1. Transcription of hepatic L-type pyruvate kinase (PK) gene is stimulated by insulin/glucose through an enhancer unit. HNF1 and NF1 family proteins bind to L-I and L-II of this unit, respectively. We showed that four members of NF1 family alone did not stimulate the promoter activity of the LPK gene, but that they enhanced the activity of HNF1. In addition,we identified SHARP2 as a L-III binding protein and found that SHARP2 was induced by dietary glucose in rat liver.2. Sp1/Sp3 bound to box B and NFY bound to box C were important for transcriptional stimulation of the PKM gene. Sp1/Sp3 synergistically transactivated the PKM gene by interacting with A subnit of NF-Y.3. Insulin stimulated the PKM gene expression in 3T3-L1 adipocytes even in the absence of glucose. A part of insulin response element was suggested to be present in 2.2k upstream region of the PKM gene. It was suggested that both PI-3 kinase and MAPKK pathways were involved in the insulin regulation of the PKM gene.4. PKM_1 , a nonallosteric isozyme, lacks heterotropic allosteric effect involving fructose-1,6-bisphosphate. We found that Glu-432 hinders the heterotropic allosteric effect by preventing the binding of fructose-1,6-bisphosphate through a repulsive electrostatic interaction. The M_2PK activity was not altered under oxidative stress in hepatoma cells.