Regulation of rat hepatic L-pyruvate kinase promoter composition and activity by glucose, n-3 polyunsaturated fatty acids, and peroxisome proliferator-activated receptor-alpha agonist.
Carbohydrate regulatory element-binding protein (ChREBP), MAX-like factor X (MLX), and hepatic nuclear factor-4alpha (HNF-4alpha) are key transcription factors involved in the glucose-mediated induction of hepatic L-type pyruvate kinase (L-PK) gene transcription. n-3 polyunsaturated fatty acids (PUFA) and WY14643 (peroxisome proliferator-activated receptor alpha (PPARalpha) agonist) interfere with glucose-stimulated L-PK gene transcription in vivo and in rat primary hepatocytes. Feeding rats a diet containing n-3 PUFA or WY14643 suppressed hepatic mRNA(L-PK) but did not suppress hepatic ChREBP or HNF-4alpha nuclear abundance. Hepatic MLX nuclear abundance, however, was suppressed by n-3 PUFA but not WY14643. In rat primary hepatocytes, glucose-stimulated accumulation of mRNA(LPK) and L-PK promoter activity correlated with increased ChREBP nuclear abundance. This treatment also increased L-PK promoter occupancy by RNA polymerase II (RNA pol II), acetylated histone H3 (Ac-H3), and acetylated histone H4 (Ac-H4) but did not significantly impact L-PK promoter occupancy by ChREBP or HNF-4alpha. Inhibition of L-PK promoter activity by n-3 PUFA correlated with suppressed RNA pol II, Ac-H3, and Ac-H4 occupancy on the L-PK promoter. Although n-3 PUFA transiently suppressed ChREBP and MLX nuclear abundance, this treatment did not impact ChREBP-LPK promoter interaction. HNF4alpha-LPK promoter interaction was transiently suppressed by n-3 PUFA. Inhibition of L-PK promoter activity by WY14643 correlated with a transient decline in ChREBP nuclear abundance and decreased Ac-H4 interaction with the L-PK promoter. WY14643, however, had no impact on MLX nuclear abundance or HNF4alpha-LPK promoter interaction. Although overexpressed ChREBP or HNF-4alpha did not relieve n-3 PUFA suppression of L-PK gene expression, overexpressed MLX fully abrogated n-3 PUFA suppression of L-PK promoter activity and mRNA(L-PK) abundance. Overexpressed ChREBP, but not MLX, relieved the WY14643 inhibition of L-PK. In conclusion, n-3 PUFA and WY14643/PPARalpha target different transcription factors to control L-PK gene transcription. MLX, the heterodimer partner for ChREBP, has emerged as a novel target for n-3 PUFA regulation.
Xu
Jinghua
J
Department of Physiology, Michigan State University, East Lansing, Michigan 48824, USA.
Christian
Barbara
B
Jump
Donald B
DB
D000818:Animals; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / Q000378:metabolism; D002478:Cells, Cultured; D004790:Enzyme Induction / Q000187:drug effects / Q000235:genetics; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D051557:Hepatocyte Nuclear Factor 4 / Q000378:metabolism; D022781:Hepatocytes / Q000201:enzymology; D008099:Liver / Q000201:enzymology*; D008297:Male; D047493:PPAR alpha / Q000819:agonists; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics*; D011743:Pyrimidines / Q000494:pharmacology; D011770:Pyruvate Kinase / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D005231:Fatty Acids, Unsaturated; D051557:Hepatocyte Nuclear Factor 4; C496594:Hnf4a protein, rat; C513412:MLX protein, rat; C442825:Mlxipl protein, rat; D047493:PPAR alpha; D011743:Pyrimidines; D015534:Trans-Activators; C006253:pirinixic acid; D011770:Pyruvate Kinase; D005947:Glucose