Regulation of WNK1 kinase by extracellular potassium.
BACKGROUND
Mutations of WNK kinase genes were identified as the cause of a hereditary hypertensive disease, pseudohypoaldosteronism type II; however, little is known about the regulation of WNK kinases. In the present study, we focused on anisosmotic conditions as the initial clues for clarifying a stimulating factor for WNK kinase activity.


METHODS
Endogenous WNK kinase activity in COS7 cells was monitored by the phosphorylation of its substrate, OSR1.


RESULTS
Knockdown experiments revealed that WNK1 was a major WNK kinase in COS7 cells. In contrast to the transient increase in WNK1 activity caused by hypertonic medium, hypotonic medium increased the phosphorylation of OSR1 for 24 h, suggesting that the hypotonic medium included a signal for continuously stimulating WNK1 kinase activity. To identify the signal, ion substitution experiments were performed. Surprisingly, even isotonic media with low Cl(-) or low K(+) was found to increase OSR1 phosphorylation as well as the hypotonic medium. Furthermore, WNK1 activation by the hypotonic medium was completely blocked by quinine (500 μM) but not by 5-nitro-2-(3-phenylpropylamino) benzoic acid (100 μM), and this inhibition was closely correlated with the inhibition of (86)Rb(+) (=K(+)) efflux but not with the inhibition of (125)I(-) (=Cl(-)) efflux. These results suggest that K(+), rather than hypotonicity or low Cl(-), may be an important regulator for WNK1 activation. Finally, we confirmed that high K(+) and low K(+) media under the physiological range decreased and increased WNK1 activity, respectively.


CONCLUSIONS
Extracellular K(+) is an important regulator of WNK1 kinase activity.
Department of Nephrology, Graduate School of Medical and Dental Sciences, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo, Tokyo 113-8519, Japan.
Shotaro
S
Naito
Akihito
A
Ohta
Eisei
E
Sohara
Eriko
E
Ohta
Tatemitsu
T
Rai
Sei
S
Sasaki
Shinichi
S
Uchida
D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D007038:Hypotonic Solutions / Q000494:pharmacology; D047908:Intracellular Signaling Peptides and Proteins; D015778:Minor Histocompatibility Antigens; D009994:Osmolar Concentration; D011188:Potassium / Q000502:physiology*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D011546:Pseudohypoaldosteronism / Q000235:genetics; D000076204:WNK Lysine-Deficient Protein Kinase 1
D007038:Hypotonic Solutions; D047908:Intracellular Signaling Peptides and Proteins; D015778:Minor Histocompatibility Antigens; C118135:OXSR1 protein, human; D017346:Protein Serine-Threonine Kinases; D000076204:WNK Lysine-Deficient Protein Kinase 1; C498743:WNK1 protein, human; D011188:Potassium