Regulation of ROMK channel and K+ homeostasis by kidney-specific WNK1 kinase.
WNK kinases are serine-threonine kinases with an atypical placement of the catalytic lysine. WNK1, the first member discovered, has multiple alternatively spliced isoforms, including a ubiquitously expressed full-length long form (L-WNK1) and a kidney-specific form (KS-WNK1) predominantly expressed in the kidney. Intronic deletions of WNK1 that increase WNK1 transcript cause pseudohypoaldosteronism type 2, an autosomal-dominant disease characterized by hypertension and hyperkalemia. L-WNK1 inhibits renal K(+) channel ROMK, likely contributing to hyperkalemia in PHAII. Previously, we reported that KS-WNK1 by itself has no effect on ROMK1 but antagonizes L-WNK1-mediated inhibition of ROMK1. Amino acids 1-253 of KS-WNK1 (KS-WNK1(1-253)) are sufficient for reversing the inhibition of ROMK1 caused by L-WNK1(1-491). Here, we further investigated the mechanisms by which KS-WNK1 counteracts L-WNK1 regulation of ROMK1. We reported that two regions of KS-WNK1(1-253) are involved in the antagonism of L-WNK1; one includes the first 30 amino acids unique for KS-WNK1 encoded by the alternatively spliced initiating exon 4A, and the other is equivalent to the autoinhibitory domain (AID) of L-WNK1. Mutations of two phenylalanine residues known to be critical for autoinhibitory function of AID abolish the ability of the AID region of KS-WNK1 to antagonize L-WNK1. To examine the physiological role of KS-WNK1 in the regulation of renal K(+) secretion, we generated transgenic mice that overexpress amino acids 1-253 of KS-WNK1 under the control of a kidney-specific promoter. Transgenic mice have lower serum K(+) levels and higher urinary fractional excretion of K(+) compared with wild type littermates despite the same amount of daily urinary K(+) excretion. Moreover, transgenic mice (compared with wild type littermates) displayed a higher abundance of ROMK on the apical membrane of distal nephron. Thus, KS-WNK1 is an important physiological regulator of renal K(+) excretion, likely through its effects on the ROMK1 channel.
Liu
Zhen
Z
Department of Medicine (Division of Nephrology), University of Texas Southwestern Medical Center, Dallas, Texas 75390-8856, USA.
Wang
Hao-Ran
HR
Huang
Chou-Long
CL
D017398:Alternative Splicing / Q000502:physiology; D019943:Amino Acid Substitution; D000818:Animals; D004789:Enzyme Activation / Q000502:physiology; D005091:Exons / Q000502:physiology; D006706:Homeostasis / Q000502:physiology*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D015778:Minor Histocompatibility Antigens; D009399:Nephrons / Q000201:enzymology / Q000378:metabolism*; D009928:Organ Specificity / Q000502:physiology; D011188:Potassium / Q000652:urine*; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D000076204:WNK Lysine-Deficient Protein Kinase 1
D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; C510693:Kcnj1 protein, mouse; D015778:Minor Histocompatibility Antigens; D024661:Potassium Channels, Inwardly Rectifying; D017346:Protein Serine-Threonine Kinases; D000076204:WNK Lysine-Deficient Protein Kinase 1; C498743:WNK1 protein, human; C498744:Wnk1 protein, mouse; D011188:Potassium