Regulation of mitochondrial transcription factor A expression by high glucose.
Mitochondrial transcription factor A (Tfam, previously mtTFA) is a key regulator of mitochondrial DNA (mtDNA) transcription and replication. We have reported that overexpression of nuclear respiratory factor-1 (NRF-1) and high concentration (50 mM) of glucose increased the promoter activity of the rat Tfam in L6 rat skeletal muscle cells. In this study, we investigated the mechanism of high glucose-induced Tfam transactivation. The addition of 50 mM glucose for 24 h increased Tfam promoter activity up to twofold. The glucose-induced Tfam expression was dose-dependent and cell-type specific. Glucose increased the Tfam promoter-driven transactivity in L6 (skeletal muscle), HIT (pancreatic beta-cell), and CHO (ovary) cells, but not in HepG2 (hepatoma), HeLa, and CV1 (kidney) cells. Among various monosaccharides, only glucose and fructose increased the Tfam promoter activity. Oxidative stress might not be involved in glucose-induced Tfam expression since treatment with antioxidants such as vitamin C, vitamin E, probucol, or alpha-lipoic acid did not suppress the induction. None of the inhibitors of protein kinase C, MAP kinase, and PI3 kinase altered the glucose-induced Tfam promoter activity, suggesting that general phosphorylation is involved in its signaling. However, a dominant negative mutant of NRF-1, in which 200 amino acids of C-terminus were truncated, completely suppressed the glucose-induced Tfam induction. It was concluded that high glucose-induced Tfam transcription in L6 cells might be mediated by NRF-1.
Choi
Yon Sik
YS
Asan Institute for Life Sciences, University of Ulsan, Seoul 138-736, Korea.
Lee
Ki-Up
KU
Pak
Youngmi Kim
YK
D000818:Animals; D000975:Antioxidants / Q000378:metabolism; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D005947:Glucose / Q000378:metabolism*; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D051265:NF-E2-Related Factor 1; D009687:Nuclear Proteins; D051266:Nuclear Respiratory Factor 1; D051264:Nuclear Respiratory Factors; D011401:Promoter Regions, Genetic; D051381:Rats; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
D000975:Antioxidants; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D024101:Mitochondrial Proteins; D051265:NF-E2-Related Factor 1; C495633:NRF1 protein, human; C495632:Nfe2l1 protein, rat; D009687:Nuclear Proteins; D051266:Nuclear Respiratory Factor 1; D051264:Nuclear Respiratory Factors; C499631:TFAM protein, human; C489030:Tfam protein, rat; D015534:Trans-Activators; D014157:Transcription Factors; C422562:mitochondrial transcription factor A; D005947:Glucose