WNK1, the kinase mutated in an inherited high-blood-pressure syndrome, is a novel PKB (protein kinase B)/Akt substrate.
Recent evidence indicates that mutations in the gene encoding the WNK1 [with no K (lysine) protein kinase-1] results in an inherited hypertension syndrome called pseudohypoaldosteronism type II. The mechanisms by which WNK1 is regulated or the substrates it phosphorylates are currently unknown. We noticed that Thr-60 of WNK1, which lies N-terminal to the catalytic domain, is located within a PKB (protein kinase B) phosphorylation consensus sequence. We found that PKB phosphorylated WNK1 efficiently compared with known substrates, and both peptide map and mutational analysis revealed that the major PKB site of phosphorylation was Thr-60. Employing a phosphospecific Thr-60 WNK1 antibody, we demonstrated that IGF1 (insulin-like growth factor) stimulation of HEK-293 cells induced phosphorylation of endogenously expressed WNK1 at Thr-60. Consistent with PKB mediating this phosphorylation, inhibitors of PI 3-kinase (phosphoinositide 3-kinase; wortmannin and LY294002) but not inhibitors of mammalian target of rapamycin (rapamycin) or MEK1 (mitogen-activated protein kinase kinase-1) activation (PD184352), inhibited IGF1-induced phosphorylation of endogenous WNK1 at Thr-60. Moreover, IGF1-induced phosphorylation of endogenous WNK1 did not occur in PDK1-/- ES (embryonic stem) cells, in which PKB is not activated. In contrast, IGF1 still induced normal phosphorylation of WNK1 in PDK1(L155E/L155E) knock-in ES cells in which PKB, but not S6K (p70 ribosomal S6 kinase) or SGK1 (serum- and glucocorticoid-induced protein kinase 1), is activated. Our study provides strong pharmacological and genetic evidence that PKB mediates the phosphorylation of WNK1 at Thr-60 in vivo. We also performed experiments which suggest that the phosphorylation of WNK1 by PKB is not regulating its kinase activity or cellular localization directly. These results provide the first connection between the PI 3-kinase/PKB pathway and WNK1, suggesting a mechanism by which this pathway may influence blood pressure.
Vitari
Alberto C
AC
MRC Protein Phosphorylation Unit, School of Life Sciences, MSI/WTB complex, University of Dundee, Dow Street, Dundee DD1 5EH, Scotland, UK. a.c.vitari@dundee.ac.uk
Deak
Maria
M
Collins
Barry J
BJ
Morrice
Nick
N
Prescott
Alan R
AR
Phelan
Anne
A
Humphreys
Sian
S
Alessi
Dario R
DR
D000918:Antibody Specificity; D002384:Catalysis; D002460:Cell Line; D006801:Humans; D006973:Hypertension / Q000235:genetics; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D015778:Minor Histocompatibility Antigens; D009154:Mutation; D010766:Phosphorylation; D010769:Phosphothreonine / Q000032:analysis / Q000276:immunology; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D011546:Pseudohypoaldosteronism / Q000235:genetics; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D013577:Syndrome; D000076204:WNK Lysine-Deficient Protein Kinase 1
D047908:Intracellular Signaling Peptides and Proteins; D015778:Minor Histocompatibility Antigens; D011518:Proto-Oncogene Proteins; D010769:Phosphothreonine; D007334:Insulin-Like Growth Factor I; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D000076204:WNK Lysine-Deficient Protein Kinase 1; C498743:WNK1 protein, human; C116919:mitogen and stress-activated protein kinase 1