Epigenetic mechanisms and Sp1 regulate mitochondrial citrate carrier gene expression.

This study investigates the transcriptional role of the mitochondrial CIC proximal promoter. The wild-type (but not methylated) -335/-20 bp region of the CIC gene confers gene reporter activity, and the five wild-type (but not methylated) Sp1 binding elements in this region bind human recombinant Sp1. The DNA demethylating agent AzaC or the histone acetylating agent TSA increases CIC transcript and protein levels as well as the binding of Sp1 and of acetylated histones to the -335/-20 bp region of the CIC promoter in SK-N-SH cells but not in HepG2 cells; when untreated these cells exhibit low and high levels of gene expression, respectively. Finally, Sp1 silencing decreases proximal promoter-driven gene reporter activity as well as CIC mRNA and CIC protein in both untreated HepG2 cells and AzaC- and TSA-treated SK-N-SH cells. These results show that methylation, histone acetylation and Sp1 are important in the transcriptional regulation of the CIC proximal promoter.