Epigenetics and the control of epithelial sodium channel expression in collecting duct

In eukaryotic nuclei, genomic DNA is compacted with histone and nonhistone proteins into a dynamic polymer termed chromatin. Reorganization of chromatin structure through histone modifications, the action of chromatin factors, or DNA methylation, can profoundly change gene expression. These epigenetic modifications allow heritable and potentially reversible changes in gene functioning to occur without altering the DNA sequence, thus extending the information potential of the genetic code. This review provides an introduction to epigenetic concepts for renal investigators and an overview of our work detailing an epigenetic pathway for aldosterone signaling and the control of epithelial Na(+) channel-alpha (ENaCalpha) subunit gene expression in the collecting duct. This new pathway involves a nuclear repressor complex, consisting of histone H3 Lys-79 methyltransferase disruptor of telomeric silencing-1a (Dot1a), ALL1 fused gene from chromosome 9 (Af9), a sequence-specific DNA-binding protein that binds the ENaCalpha promoter, and potentially other nuclear proteins. This complex regulates targeted histone H3 Lys-79 methylation of chromatin associated with the ENaCalpha promoter, thereby suppressing its transcriptional activity. Aldosterone disrupts the Dot1a-Af9 interaction by serum- and glucocorticoid-induced kinase-1 phosphorylation of Af9, and inhibits Dot1a and Af9 expression, resulting in histone H3 Lys-79 hypomethylation at specific subregions, and derepression of the ENaCalpha promoter. The Dot1a-Af9 pathway may also be involved in the control of genes implicated in renal fibrosis and hypertension.