An evolutionarily conserved N-terminal Sgk1 variant with enhanced stability and improved function.

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Raikwar NS, Snyder PM, Thomas CP

An evolutionarily conserved N-terminal Sgk1 variant with enhanced stability and improved function.

Am J Physiol Renal Physiol. 2008 Nov;295(5):F1440-8. doi: 10.1152/ajprenal.90239.2008. Epub 2008 Aug 27.

PubMed ID
18753299 [ View in PubMed
]
Abstract

Sgk1 is an aldosterone-induced kinase that regulates epithelial sodium channel (ENaC)-mediated Na+ transport in the collecting duct and connecting tubule of the kidney. The NH2 terminus of Sgk1 contains instability motifs that direct the ubiquitination of Sgk1 resulting in a rapidly degraded protein. By bioinformatic analysis, we identified a 5' variant alternate transcript of human Sgk1 (Sgk1_v2) that is widely expressed, is conserved from rodent to humans, and is predicted to encode an Sgk1 isoform, Sgk1_i2, with a different NH2 terminus. When expressed in HEK293 cells, Sgk1_i2 was more abundant than Sgk1 because of an increased protein half-life and this correlated with reduced ubiquitination of Sgk1_i2 and enhanced surface expression of ENaC. Immunocytochemical studies demonstrated that in contrast to Sgk1, Sgk1_i2 is preferentially targeted to the plasma membrane. When coexpressed with ENaC subunits in FRT epithelia, Sgk1_i2 had a significantly greater effect on amiloride-sensitive Na+ transport compared with Sgk1. Together, the data demonstrate that a conserved NH2-terminal variant of Sgk1 shows improved stability, enhanced membrane association, and greater stimulation of epithelial Na+ transport in a heterologous expression system.

DrugBank Data that Cites this Article

Polypeptides
NameUniProt ID
Serine/threonine-protein kinase Sgk1O00141Details