Evidence against the peroxisome proliferator-activated receptor alpha (PPARalpha) as the mediator for polyunsaturated fatty acid suppression of hepatic L-pyruvate kinase gene transcription.
The glycolytic enzyme, L-pyruvate kinase (L-PK), plays an important role in hepatic glucose metabolism. Insulin and glucose induce L-PK gene expression, while glucagon and polyunsaturated fatty acids (PUFA) inhibit L-PK gene expression. We have been interested in defining the PUFA regulation of L-PK. The cis-regulatory target for PUFA action includes an imperfect direct repeat (DR1) that binds HNF-4. HNF4 plays an ancillary role in the insulin/glucose-mediated transactivation of the L-PK gene. Because the fatty acid-activated nuclear receptor, peroxisome proliferator-activated receptor (PPARalpha), binds DR1-like elements and has been reported to interfere with HNF4 action, we examined the role PPARalpha plays in the regulation of L-PK gene transcription. Feeding rats either fish oil or the potent PPARalpha activator, WY14,643, suppressed rat hepatic L-PK mRNA and gene transcription. The PPARalpha-null mouse was used to evaluate the role of the PPARalpha in hepatic transcriptional control of L-PK. While WY14,643 control of L-PK gene expression required the PPARalpha, PUFA regulation of L-PK gene expression was independent of the PPARalpha. Transfection studies in cultured primary hepatocytes localized the cis-regulatory target for WY14,643/PPARalpha action to the L-PK HNF4 binding site. However, PPARalpha/RXRalpha heterodimers did not bind this region. Although both WY14,643 and PUFA suppress L-PK gene transcription through the same element, PUFA regulation of L-PK does not require the PPARalpha and PPARalpha/RXRalpha does not bind the L-PK promoter. These studies suggest that other intermediary factors are involved in both the PUFA and PPARalpha regulation of L-PK gene transcription.
Pan
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DA
Departments of Physiology, Biochemistry, Botany, and Plant Pathology, Michigan State University, East Lansing, MI 48824, USA.
Mater
M K
MK
Thelen
A P
AP
Peters
J M
JM
Gonzalez
F J
FJ
Jump
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D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002994:Clofibrate / Q000494:pharmacology; D042926:Cytochrome P-450 CYP4A; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics; D017931:DNA Primers / Q000235:genetics; D004042:Dietary Fats, Unsaturated / Q000008:administration & dosage; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D005395:Fish Oils / Q000008:administration & dosage; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D006899:Mixed Function Oxygenases / Q000235:genetics; D020025:Peroxisome Proliferators / Q000494:pharmacology; D011401:Promoter Regions, Genetic; D011743:Pyrimidines / Q000494:pharmacology; D011770:Pyruvate Kinase / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects
D017931:DNA Primers; D004042:Dietary Fats, Unsaturated; D005231:Fatty Acids, Unsaturated; D005395:Fish Oils; D020025:Peroxisome Proliferators; D011743:Pyrimidines; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; C006253:pirinixic acid; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D042926:Cytochrome P-450 CYP4A; D011770:Pyruvate Kinase; D002994:Clofibrate