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.
IntroductionThe renin-angiotensin-aldosterone system plays a major role in the control of blood pressure, extracellular fluid volume, and electrolyte balance, largely through the regulation of urinary Na + excretion. The aldosterone-sensitive distal nephron (ASDN), composed of the late distal convoluted tubule, connecting tubule, and cortical and medullary collecting ducts, is the final arbiter of renal Na + excretion. In the ASDN, transepithelial Na + absorption occurs by apical Na + entry via the epithelial Na + channel (ENaC) and basolateral Na + exit via the Na + ,K + -ATPase. ENaC, composed of 3 subunits (α, β, and γ), constitutes the rate-limiting step in this process, and changes in its activity and/or plasma membrane abundance constitute key regulatory steps. Aldosterone increases transepithelial Na + transport in the ASDN in large part through ENaCα induction in this region (1). Aldosterone increases ENaC function in 2 phases: an early phase involving upregulation of preexisting transport machinery and aldosterone-induced regulatory proteins, notably serum- and glucocorticoid-induced kinase-1 (Sgk1), which regulates the plasma membrane abundance of ENaC in part through phosphorylation of the ubiquitin ligase Nedd4-2 (2); and a delayed phase of aldosterone action involving de novo synthesis of ENaC, either from the liganded mineralocorticoid receptor directly binding hormone response elements in the ENaCα promoter to activate transcription (1) or through indirect