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A conserved N‐terminal serum and glucocorticoid kinase‐1 (Sgk‐1) variant with enhanced stability, preferential membrane localization and greater stimulation of epithelial Na+ transport
Author(s) -
Raikwar Nandita S,
Snyder Peter M,
Thomas Christie P
Publication year - 2008
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.22.1_supplement.934.9
Subject(s) - epithelial sodium channel , sgk1 , microbiology and biotechnology , hek 293 cells , chemistry , ubiquitin , biology , kinase , biochemistry , receptor , gene , sodium , organic chemistry
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 N‐terminus of Sgk1 contains instability motifs that are targets for ubiquitination resulting in a rapidly degraded protein. By bioinformatic analysis we identified three alternate transcripts of human Sgk1 that differed at their 5′ end. These variants are widely expressed, are conserved from rodent to man and are predicted to encode N‐terminal variants. One of these variants, Sgk1B, diverges from Sgk1 by 120 aa. When expressed in HEK293 cells, Sgk1 was less abundant than sgk1B and substantially increased with the proteasomal inhibitor ALLN but not with lysosomal inhibitor chloroquine. Protein turnover analysis demonstrated that the half life of Sgk1B was greater than Sgk1 correlating with decreased ubiquitination of Sgk1B as compared to Sgk1. Immunocytochemical studies showed that in contrast to Sgk1, Sgk1B is preferentially targeted to the plasma membrane. When expressed with ENaC subunits in FRT epithelia, Sgk1B had a significantly greater effect on amiloride‐sensitive short circuit current as compared to Sgk1. Together the data demonstrate that a conserved N‐terminal variant of Sgk1 shows improved stability, enhanced membrane association and greater stimulation of Na+ transport in a heterologous expression system. NHLBI and VA