Dietary polyunsaturated fatty acids interfere with the insulin/glucose activation of L-type pyruvate kinase gene transcription.
L-type pyruvate kinase (L-PK) is a key glycolytic enzyme regulating the flux of metabolites through the pyruvate-phosphoenolpyruvate cycle (1). The regulation of L-PK is complex involving both hormones and nutrients. We have found that feeding rats diets containing polyunsaturated fatty acids (PUFA) significantly inhibits hepatic pyruvate kinase enzyme activity (> 60%) and suppresses mRNAPK abundance (> 70%). Studies with primary hepatocytes indicate that PUFA act directly on hepatocytes. Specifically, arachidonic (20:4, omega 6) and eicosapentaenoic (20:5, omega 3) acid suppressed both mRNAPK llevels and the activity of a transfected PKCAT (-4300/+12) fusion gene by > 70%. This is due to an inhibition of the insulin/glucose-mediated transactivation of L-PKCAT. Deletion analysis localized PUFA-regulated cis-acting elements to a region within the L-PK proximal promoter, i.e. between -197 and -96 base pairs. This region binds two transcription factors involved in the hormone/nutrient regulation of L-PK gene transcription, i.e. a major late transcription factor-like factor and HNF-4. Linker scanning mutation analysis localized the PUFA-regulated cis-acting elements to the vicinity of the HNF-4 binding site. Thus, PUFA-regulated factors abrogate the insulin/glucose activation of L-PK gene transcription by targeting the HNF-4 elements. These studies suggest that PUFA may have significant effects on hepatic carbohydrate metabolism by inhibiting the L-PK side of the pyruvate-phosphoenolpyruvate cycle.
Liimatta
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Department of Physiology, Michigan State University, East Lansing 48824.
Towle
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Clarke
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D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology; D001483:Base Sequence; D002478:Cells, Cultured; D004268:DNA-Binding Proteins; D003864:Depression, Chemical; D004041:Dietary Fats / Q000494:pharmacology*; D015118:Eicosapentaenoic Acid / Q000494:pharmacology; D004790:Enzyme Induction / Q000187:drug effects; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D005395:Fish Oils / Q000494:pharmacology*; D005947:Glucose / Q000494:pharmacology*; D006019:Glycolysis / Q000187:drug effects; D051557:Hepatocyte Nuclear Factor 4; D007328:Insulin / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008297:Male; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D019301:Oleic Acid; D009829:Oleic Acids / Q000494:pharmacology; D010750:Phosphoproteins; D011770:Pyruvate Kinase / Q000096:biosynthesis* / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D017207:Rats, Sprague-Dawley; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*
D004268:DNA-Binding Proteins; D004041:Dietary Fats; D005231:Fatty Acids, Unsaturated; D005395:Fish Oils; D051557:Hepatocyte Nuclear Factor 4; D007328:Insulin; D009829:Oleic Acids; D010750:Phosphoproteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; C033266:Menhaden oil; D016718:Arachidonic Acid; D019301:Oleic Acid; D015118:Eicosapentaenoic Acid; D011770:Pyruvate Kinase; D005947:Glucose