Purpose of review: The serum and glucocorticoid regulated kinase (SGK) family of protein kinases shares similar biochemical and hormonal signaling properties; however, the SGK kinases also exhibit distinct differences in regulating renal sodium (Na(+)) transport. This review will highlight recent advances in our understanding of the specificity of SGK kinase signaling and regulation of renal Na(+) transport.
Recent findings: Differential expression of SGK kinases at the cellular and subcellular levels contributes to signaling specificity. New evidence indicates that SGK1 associates with the apical cell membrane of cortical collecting duct cells to regulate open probability of the epithelial Na(+) channel (ENaC). Scaffold proteins can also recruit SGK1 to multiprotein complexes for regulation of ENaC expression in the apical membrane. Recent SGK1 knockout models have implicated the NaCl co-transporter (NCC) as another target of SGK1 regulation. Less is known about the function of SGK2 or SGK3, but both kinases can regulate Na(+)/H(+) exchanger 3 (NHE3) activity.
Summary: The SGK kinases assume distinct roles in regulating Na transport in both proximal and distal elements of the kidney tubule. Future examination of the molecular mechanisms by which the SGK kinases regulate specific substrates will inform our understanding of how these kinases contribute to the physiology of renal Na(+) transport.