Serum and glucocorticoid-induced kinase (SGK) 1 and the epithelial sodium channel are regulated by multiple with no lysine (WNK) family members.
The four WNK (with no lysine (K)) protein kinases affect ion balance and contain an unusual protein kinase domain due to the unique placement of the active site lysine. Mutations in two WNKs cause a heritable form of ion imbalance culminating in hypertension. WNK1 activates the serum- and glucocorticoid-induced protein kinase SGK1; the mechanism is noncatalytic. SGK1 increases membrane expression of the epithelial sodium channel (ENaC) and sodium reabsorption via phosphorylation and sequestering of the E3 ubiquitin ligase neural precursor cell expressed, developmentally down-regulated 4-2 (Nedd4-2), which otherwise promotes ENaC endocytosis. Questions remain about the intrinsic abilities of WNK family members to regulate this pathway. We find that expression of the N termini of all four WNKs results in modest to strong activation of SGK1. In reconstitution experiments in the same cell line all four WNKs also increase sodium current blocked by the ENaC inhibitor amiloride. The N termini of the WNKs also have the capacity to interact with SGK1. More detailed analysis of activation by WNK4 suggests mechanisms in common with WNK1. Further evidence for the importance of WNK1 in this process comes from the ability of Nedd4-2 to bind to WNK1 and the finding that endogenous SGK1 has reduced activity if WNK1 is knocked down by small interfering RNA.
Heise
Charles J
CJ
Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9041, USA.
Xu
Bing-e
BE
Deaton
Staci L
SL
Cha
Seung-Kuy
SK
Cheng
Chih-Jen
CJ
Earnest
Svetlana
S
Sengupta
Samarpita
S
Juang
Yu-Chi
YC
Stippec
Steve
S
Xu
Yingda
Y
Zhao
Yingming
Y
Huang
Chou-Long
CL
Cobb
Melanie H
MH
D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D045744:Cell Line, Tumor; D006224:Cricetinae; D003412:Cricetulus; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D017874:Immediate-Early Proteins / Q000235:genetics / Q000378:metabolism*; D015151:Immunoblotting; D047468:Immunoprecipitation; D051379:Mice; D015778:Minor Histocompatibility Antigens; D000075702:Nedd4 Ubiquitin Protein Ligases; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D000076204:WNK Lysine-Deficient Protein Kinase 1; D000099184:Serum-Glucocorticoid Regulated Kinases
D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D017874:Immediate-Early Proteins; D015778:Minor Histocompatibility Antigens; D000075702:Nedd4 Ubiquitin Protein Ligases; D017346:Protein Serine-Threonine Kinases; D044767:Ubiquitin-Protein Ligases; D000076204:WNK Lysine-Deficient Protein Kinase 1; D000099184:Serum-Glucocorticoid Regulated Kinases; C000618479:NEDD4L protein, rat; C000618483:Nedd4 protein, human; C000618484:Nedd4 protein, rat; C000618485:Nedd4L protein, human; C000618461:Nedd4l protein, mouse; C488586:WNK3 protein, human; C433806:WNK4 protein, human; C410410:Wnk1 protein, rat