Cloning of human acetyl-CoA carboxylase beta promoter and its regulation by muscle regulatory factors.
ABSTRACT The 280-kDa beta-isoform of acetyl-CoA carboxylase (ACCbeta) is predominantly expressed in heart and skeletal muscle, whereas the 265-kDa alpha-isoform (ACCalpha) is the major ACC in lipogenic tissues. The ACCbeta promoter showed myoblast-specific promoter activity and was strongly induced by MyoD in NIH3T3 cells. Serial deletions of the promoter revealed that MyoD acts on the E-boxes located at positions -498 to -403 and on the proximal region including the 5'-untranslated region. Destruction of the E-boxes at positions -498 to -403 by site-directed mutagenesis resulted in a significant decrease of MyoD responsiveness. The "TGAAA" at -32 to -28 and the region around the transcription start site play important roles in basal transcription, probably as a TATA box and an Inr element, respectively. Mutations of another E-box at -14 to -9 and a "GCCTGTCA" sequence at +17 to +24 drastically decreased the MyoD responsiveness. The novel cis-element GCCTGTCA was preferentially bound by MyoD homodimer in EMSA and conferred MyoD responsiveness to a luciferase reporter, which was repressed by the overexpression of E12. This finding is unique since activation via E-boxes is mediated by heterodimers of MyoD and E-proteins. We screened a human skeletal muscle cDNA library to isolate clones expressing proteins that bind to the region around the GCCTGTCA (+8 to +27) sequence, and isolated Myf4 and Myf6 cDNAs. Electrophoretic mobility shift assay showed that recombinant Myf4 and Myf6 bind to this novel cis-element. Moreover, transient expression of Myf6 induced significant activation on the ACCbeta promoter or an artificial promoter harboring this novel cis-element. These findings suggest that muscle regulatory factors, such as MyoD, Myf4, and Myf6, contribute to the muscle-specific expression of ACCbeta via E-boxes and the novel cis-element GCCTGTCA.
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ABSTRACT: Uncoupling protein-3 (UCP3) gene is a member of the mitochondrial carrier superfamily preferentially expressed in skeletal muscle and up-regulated by fatty acids. Peroxisome proliferator-activated receptor (PPAR)alpha and PPARdelta (also known as PPARbeta) mediate human UCP3 gene regulation by fatty acids through a direct-repeat (DR-1) element in the promoter. DR-1 mutation renders UCP3 promoter unresponsive to PPAR ligand in vitro and consistently blocks gene induction by fatty acids in vivo. Although they act through separate sites in the promoter, MyoD and PPAR-dependent regulatory pathways are functionally connected: only in the presence of MyoD, does UCP3 become sensitive to PPAR ligand-dependent regulation. MyoD controls UCP3 promoter activity through a noncanonical Ebox site located in the proximal region, close to transcription initiation site. Moreover, acetylation processes play a crucial role in the control of UCP3 gene regulation. The coactivator p300 protein enhances PPAR ligand-mediated regulation whereas a mutant form devoid of histone acetylase activity blocks the response of the promoter to fatty acids. Conversely, histone deacetylase-1 blunts MyoD-dependent expression of the UCP3 promoter and reduces PPAR-dependent responsiveness. A mutated form of MyoD unable to be acetylated has a lower transactivation capacity on the human UCP3 promoter with respect to wild-type MyoD. It is concluded that MyoD and PPAR-dependent pathways mediate human UCP3 gene regulation and that acetylase activity elicited by coregulators is implicated in the functional interaction between these regulatory pathways. Therefore the convergence of MyoD and PPAR-dependent pathways provides a molecular mechanism for skeletal muscle specificity and fatty acid regulation of human UCP3 gene.Molecular Endocrinology 11/2003; 17(10):1944-58. · 4.75 Impact Factor
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ABSTRACT: Acetyl-CoA carboxylase 2 (ACC)2 is a key regulator of mitochondrial fat oxidation. To examine the impact of ACC2 deletion on whole-body energy metabolism, we measured changes in substrate oxidation and total energy expenditure in Acc2(-/-) and WT control mice fed either regular or high-fat diets. To determine insulin action in vivo, we also measured whole-body insulin-stimulated liver and muscle glucose metabolism during a hyperinsulinemic-euglycemic clamp in Acc2(-/-) and WT control mice fed a high-fat diet. Contrary to previous studies that have suggested that increased fat oxidation might result in lower glucose oxidation, both fat and carbohydrate oxidation were simultaneously increased in Acc2(-/-) mice. This increase in both fat and carbohydrate oxidation resulted in an increase in total energy expenditure, reductions in fat and lean body mass and prevention from diet-induced obesity. Furthermore, Acc2(-/-) mice were protected from fat-induced peripheral and hepatic insulin resistance. These improvements in insulin-stimulated glucose metabolism were associated with reduced diacylglycerol content in muscle and liver, decreased PKC activity in muscle and PKCepsilon activity in liver, and increased insulin-stimulated Akt2 activity in these tissues. Taken together with previous work demonstrating that Acc2(-/-) mice have a normal lifespan, these data suggest that Acc2 inhibition is a viable therapeutic option for the treatment of obesity and type 2 diabetes.Proceedings of the National Academy of Sciences 11/2007; 104(42):16480-5. · 9.74 Impact Factor
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ABSTRACT: mRNA encoding a variant acetyl-CoA carboxylase (ACC)-alpha isozyme, transcribed from a downstream promoter, PIII, was detected in human tissues. Such exon 5A-containing transcripts (E5A-mRNA) encode ACC-alpha with a distinct N-terminus, with 15/17 residues identical to those encoded by the ovine mRNA. In the current study we used antisera directed against the E5A N-terminus to verify that ovine E5A translates are present in tissues consistent with the distribution of E5A-mRNA. The presence of E5A alters the context of adjacent regulatory phosphorylation sites in E6, which may indicate altered regulation of activity for this isozyme. Sequences with high identity to the proximal promoter of PIII and E5A are present in the mouse and rat ACC-alpha genes, however, the coding region of E5A is not conserved, and E5A transcripts are not detected in tissues. Thus E5A must have been present in a common ancestor of rodents, primates, and ruminants, and has become nonfunctional in the former. A minor human PIII-derived mRNA containing an additional 111-bp sequence encoded by a downstream exon, E5B, was also detected. E5B encodes an in-frame stop-codon such that the E5A open-reading frame is terminated, however, ACC-alpha translation may be re-initiated from a downstream AUG in E6, potentially generating an isozyme lacking the N-terminal phosphorylation sites. Transcription of human ACC-alpha from at least three promoters and the potential to generate ACC-alpha isozymes with differential susceptibilities to phosphorylation indicate that the regulation of fatty acid synthesis in human tissues is likely to be complex.Biochimica et Biophysica Acta 12/2003; 1634(3):97-106. · 4.66 Impact Factor