Abstract 1569: Mitochondrial Transcription Factors Regulate SERCA2 Gene Transcription
Background: ATP produced by mitochondrial (Mt) respiratory enzymes is critical for the excitation-contraction coupling. Expression of mRNAs for Mt enzyme is controlled by Mt transcriptional machinery composed of Tfam, a Mt-DNA transcription factor, and Tfb2m, a co-factor of Tfam. Previously, we have demonstrated that mRNA expression levels of these Mt transcription factors were closely correlated with SERCA2 mRNA level and cardiac function (fractional shortening, +dP/dt and tau) in rat myocardial infarction model. Therefore in this study, we tested the hypothesis that Mt transcription factors directly regulate the transcription of the SERCA2 gene as well as Mt genes and contribute to control cardiac function.
Results: Analyses were done by using rat SERCA2 gene promoter and expression vectors for Mt transcription factors in the neonatal rat cultured cardiac myocytes. Overexpression of Tfam and Tfb2m activated SERCA2 gene transcription by 2.23 fold followed by the 1.38 times increase of SERCA2 protein. On the contrary, ablation of Tfam and/or Tfb2m using their siRNAs significantly decreased SERCA2 gene transcription and mRNA expression level by 48%. Serial deletion analysis of the SERCA2 gene promoter revealed that the responsive elements for Tfam and Tfb2m were located from −1,829 to −1,351 nt promoter region. Since the Mt DNA copy number did not change after Tfam and/or Tfb2m transfection in this experimental condition, changes in SERCA2 gene transcription level are suggested to be a direct effect of Mt transcription factors. Indeed, chromatin immunoprecipitation assay disclosed that Tfam and Tfb2m make a complex and bind to the −1,829 to −1,351 nt promoter region of the SERCA2 gene. Furthermore, Tfam and Tfb2m proteins were detected in the nucleus as well as in mitochondria by specific antibody staining.
Conclusion: These studies suggest that Mt transcription factors can be used for the transcription of the gene encoded by nucleus. More importantly, our data provide a new paradigm of the energy supply and expenditure in the myocardium that the transcription of genes for Mt respiratory chain enzymes, which produces ATP and the gene of SERCA2, which consumes ATP are, at least in part, coordinately regulated by the same transcription factors, Tfam and Tfb2m.