Journal of Biological Chemistry
Volume 273, Issue 49, 4 December 1998, Pages 32901-32909
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CELL BIOLOGY AND METABOLISM
Co-regulation of Tissue-specific Alternative Human Carnitine Palmitoyltransferase Iβ Gene Promoters by Fatty Acid Enzyme Substrate*

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Carnitine palmitoyltransferase I (CPT-I) catalyzes the rate-determining step in mitochondrial fatty acid β-oxidation. CPT-I has two structural genes (α and β) that are differentially expressed among tissues. Our CPT-Iβ isolates from a human cardiac cDNA library contained two different extreme 5′-sequences derived from short alternative first untranslated exons that utilize a common splice acceptor site in exon 2. Primer extension identified single dominant start sites for each transcript, and ribonuclease protection assays showed the presence of one 5′-exon in liver, muscle, and heart mRNAs, indicating that the cognate promoter U (upstream/ubiquitous) is active in each of these tissues. By contrast, mRNAs containing the alternative 5′-exon were present only in muscle and heart, indicating a muscle-specific promoter M (muscle). CPT-Iβ mRNA levels increased markedly in tissues of fasted rats, when circulating free fatty acid concentrations are elevated. Using CPT-Iβ promoter/reporter transient transfection of murine C2C12 myotubes and HepG2 hepatocytes, fatty acids were found to increase promoter activity in a peroxisome proliferator-activated receptor α (PPARα)-dependent fashion. A promoter fatty acid response element (FARE) was mapped, mutation of which ablated fatty acid-mediated production of both transcripts. PPARα/retinoid X receptor α formed specific complexes with oligonucleotides containing the FARE, and anti-PPARα antibody shifted nuclear protein-DNA complexes, confirming the role of this factor in regulating the expression of this critical metabolic enzyme gene. The constitutive repressor chicken ovalbumin upstream promoter transcription factor competitively binds at the FARE and modulates fatty acid induction of the promoters.

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March of Dimes Basil O'Connor Scholar, Capps Scholar in Diabetes of the Harvard Medical School, and recipient of NIDDK Independent Scientist Award K02-DK02461.

*

This work was supported in part by grants (to T. G.) from the American Diabetes Association and the Interim Support Fund of the Massachusetts General Hospital and by Grant 13-526-956 from the American Heart Association, Massachusetts Affiliate, Inc., Grant 5-FY96-0116 from the March of Dimes Birth Defects Research Foundation, and Grant HD35685 from the National Institutes of Health.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

These two authors contributed equally to this work.

Recipient of Research Fellowship 9820051T from the American Heart Association, Massachusetts Affiliate, Inc.