Submitted on July 21, 2006
Accepted on December 28, 2006
Subcellular Location of Serum- and Glucocorticoid-Induced Kinase-1 (SGK1) in Renal and Mammary Epithelial Cells
Emily Ann Cordas1, Anikó Náray-Fejes-Tóth1, and Géza Fejes-Tóth1*
1 Department of Physiology, Dartmouth Medical School, Lebanon, New Hampshire, United States
* To whom correspondence should be addressed. E-mail: aniko.fejes-toth{at}Dartmouth.EDU.
Serum- and glucocorticoid-induced kinase-1 (SGK1) is involved in aldosterone-induced Na+ reabsorption by increasing epithelial Na+ channel (ENaC) activity in cortical collecting duct (CCD) cells, but its exact mechanisms of action is unknown. Although several potential targets like Nedd4-2 have been described in expression systems, endogenous substrates mediating the physiological effects of SGK1 remain to be identified. In addition, subcellular localization studies of SGK1 have provided controversial results. We determined the subcellular location of SGK1 using SGK1-autofluorescent protein (AFP) fusion proteins. Rabbit CCD (RCCT-28A) cells were transiently transfected with a construct encoding for SGK1-AFP and stained or co-transfected with markers for various subcellular compartments. In live cells, transiently expressed SGK1-AFP clearly co-localized with the mitochondrial marker, Rhodamine 123. Similarly, SGK1-AFP co-localized with the mitochondrial marker, MitoTracker, when stably expressed using a retroviral system in either RCCT-28A cells or the mammary epithelial cell line, MCF10A. To determine which region of SGK1 is responsible for this subcellular localization, we generated RCCT-28A cell lines stably expressing SGK1 mutants. The results indicate that the N-terminal 60 amino acid region of SGK1 is necessary and sufficient for its subcellular localization. Localization of SGK1 to the mitochondria raises the possibility that SGK1 may play a role in regulating energy metabolism.
