Aldosterone-induced Sgk1 relieves Dot1a-Af9-mediated transcriptional repression of epithelial Na⁺ channel α

Aldosterone plays a major role in the regulation of salt balance and the pathophysiology of cardiovascular and renal diseases. Many aldosterone-regulated genes - including that encoding the epithelial Na⁺ channel (ENaC), a key arbiter of Na⁺ transport in the kidney and other epithelia - have been identified, but the mechanisms by which the hormone modifies chromatin structure and thus transcription remain unknown. We previously described the basal repression of ENaCα by a complex containing the histone H3 Lys79 methyltransferase disruptor of telomeric silencing alternative splice variant a (Dot1a) and the putative transcription factor ALL1-fused gene from chromosome 9 (Af9) as well as the release of this repression by aldosterone treatment. Here we provide evidence from renal collecting duct cells and serum- and glucocorticoid-induced kinase-1 (Sgk1) WT and knockout mice that Sgk1 phosphorylated Af9, thereby impairing the Dot1a-Af9 interaction and leading to targeted histone H3 Lys79 hypomethylation at the ENaCα promoter and derepression of ENaCα transcription. Thus, Af9 is a physiologic target of Sgk1, and Sgk1 negatively regulates the Dot1a-Af9 repressor complex that controls transcription of ENaCα and likely other aldosterone-induced genes.