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{{Infobox_gene}}
{{Infobox_gene}}
'''WNK lysine deficient protein kinase 1''', also known as '''WNK1''', is an enzyme that in humans is encoded by the ''WNK1'' [[gene]].<ref name="entrez">{{cite web | title = Entrez Gene: WNK1 WNK lysine deficient protein kinase 1| url = https://www.ncbi.nlm.nih.gov/sites/entrez?Db=gene&Cmd=ShowDetailView&TermToSearch=65125| accessdate = }}</ref> The human gene is located on short arm of chromosome 12 (12p13.3).


WNK1 is also known as [[Human accelerated regions|Human Accelerated Region]] 5.  WNK1 may have played a key role in differentiating Humans from Apes.
'''WNK (lysine deficient protein kinase 1)''', also known as '''WNK1''', is an enzyme that is encoded by the ''WNK1'' [[gene]].<ref name="Shekarabi_2017">{{cite journal | vauthors = Shekarabi M, Zhang J, Khanna AR, Ellison DH, Delpire E, Kahle KT | title = WNK Kinase Signaling in Ion Homeostasis and Human Disease | journal = Cell Metabolism | volume = 25 | issue = 2 | pages = 285–299 | date = February 2017 | pmid = 28178566 | doi = 10.1016/j.cmet.2017.01.007  }}</ref><ref name="Hadchouel_2016" /><ref name="Bazúa-Valenti_2015" /><ref name="Xu_2005" /><ref name="Huang_2015">{{cite journal | vauthors = Huang CL, Cheng CJ | title = A unifying mechanism for WNK kinase regulation of sodium-chloride cotransporter | journal = Pflügers Archiv | volume = 467 | issue = 11 | pages = 2235–41 | date = November 2015 | pmid = 25904388 | pmc = 4601926 | doi = 10.1007/s00424-015-1708-2  }}</ref> WNK1 is [[serine-threonine kinase]] and part of the "with no lysine/K" kinase WNK family.<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016">{{cite journal | vauthors = Hadchouel J, Ellison DH, Gamba G | title = Regulation of Renal Electrolyte Transport by WNK and SPAK-OSR1 Kinases | journal = Annual Review of Physiology | volume = 78 | pages = 367–89 | date = 2016 | pmid = 26863326 | doi = 10.1146/annurev-physiol-021115-105431 }}</ref><ref name="Bazúa-Valenti_2015">{{cite journal | vauthors = Bazúa-Valenti S, Gamba G | title = Revisiting the NaCl cotransporter regulation by with-no-lysine kinases | journal = American Journal of Physiology. Cell Physiology | volume = 308 | issue = 10 | pages = C779-91 | date = May 2015 | pmid = 25788573 | pmc = 4436992 | doi = 10.1152/ajpcell.00065.2015  }}</ref><ref name="Huang_2015" /> The predominant role of WNK1 is the regulation of cation-Cl<sup>−</sup> cotransporters (CCCs) such as the [[sodium chloride cotransporter]] ([[Sodium chloride cotransporter|NCC]]), basolateral Na-K-Cl symporter ([[NKCC1]]), and potassium chloride cotransporter (KCC1) located within the kidney.<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /><ref name="Huang_2015" /> CCCs mediate ion homeostasis and modulate [[blood pressure]] by transporting [[ion]]s in and out of the [[Cell (biology)|cell]].<ref name="Shekarabi_2017" /> ''WNK1'' mutations as a result have been implicated in blood pressure disorders/diseases; a prime example being familial hyperkalemic hypertension (FHHt).<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /><ref name="Bazúa-Valenti_2015" /><ref name="Xu_2005" /><ref name="Huang_2015" />


==Structure==
== Structure ==
The WNK1 protein is composed of 2382 amino acids (molecular weight 230 kDa). The protein contains a small [[N-terminus|N-terminal]] [[protein domain|domain]] followed by the kinase domain and a long [[C-terminus|C-terminal]] tail. The kinase domain has some similarity to the [[MAP kinase kinase kinase|MEKK protein kinase]] family.
The WNK1 [[protein]] is composed of 2382 amino acids (molecular weight 230 kDa).<ref name="Xu_2005">{{cite journal | vauthors = Xu BE, Lee BH, Min X, Lenertz L, Heise CJ, Stippec S, Goldsmith EJ, Cobb MH | title = WNK1: analysis of protein kinase structure, downstream targets, and potential roles in hypertension | journal = Cell Research | volume = 15 | issue = 1 | pages = 6–10 | date = January 2005 | pmid = 15686619 | doi = 10.1038/sj.cr.7290256  }}</ref> The [[protein]] contains a kinase domain located within its short [[N-terminus|N-terminal]][[Protein domain|domain]] and a long [[C-terminus|C-terminal]] tail.<ref name="Xu_2005" /> The [[kinase]] domain has some similarity to the [[MAP kinase kinase kinase|MEKK protein kinase]] family.<ref name="Xu_2005" /> As a member of the WNK family, the kinase's catalytic lysine residue is uniquely located in beta strand 2 of the [[glycine loop]].<ref name="Xu_2005" />  In order to have kinase activity, WNK1 must [[Autophosphorylation|autophosphorylate]] the serine 382 residue found in its activation loop.<ref name="Xu_2005" /><ref name="Shekarabi_2017" /> Further, phosphorylation at another site (Ser378) increases WNK1 activity.<ref name="Shekarabi_2017" /> An autoinhibitory domain is located within the [[C-terminal domain]] along with a HQ domain that is needed for WNK1 interactions with other WNKs.<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /><ref name="Bazúa-Valenti_2015" /><ref name="Xu_2005" /> The interactions between WNKs play an important role in function; ''WNK1'' mutants that lack an HQ domain also lack kinase activity.


==Function==
== Function ==
The WNK1 gene encodes a [[cytoplasmic]] [[serine-threonine kinase]] expressed in the [[Anatomical terms of location#Proximal and distal|distal]] [[nephron]].<ref name="entrez"/>
The WNK1 gene encodes a [[cytoplasmic]] [[serine-threonine kinase]] expressed in the [[Anatomical terms of location#Proximal and distal|distal]] [[nephron]].<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /><ref name="Xu_2005" /> Studies have shown that WNK1 can activate multiple CCCs.<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /> WNK1 however, does not directly phosphorylate the CCCs themselves rather it phosphorylates other [[Serine/threonine-specific protein kinase|serine-threonine kinases]]: Sterile20 related proline-alanine-rich kinase (SPAK) and oxidative stress response kinase 1 ([[OXSR1]]).<ref name="Hadchouel_2016" /><ref name="Shekarabi_2017" /><ref name="Bazúa-Valenti_2015" /> Phosphorylation of SPAK's T loop located in its catalytic domain will activate SPAK, which will go on to phosphorylation the CCC's N-terminaldomain.<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /> Hence, WNK1 activates CCCs indirectly as an upstream regulator of SPAK/OSR1.<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /><ref name="Bazúa-Valenti_2015" />


The protein appears to be part of the [[ERK5]] [[MAP kinase]] pathway upstream of [[MAP3K2|MEKK2]] / [[MAP3K3|MEKK3]] and to function as a [[tetramer]]. It selectively binds to and [[phosphorylate]]s synaptotagmin 2 ([[SYT2]]) within its calcium-binding C2 domains. It activates the serum- and glucocorticoid-inducible protein kinase [[SGK1]], leading to activation of the [[epithelial sodium channel]]. It along with WNK4 stimulates clathrin-dependent endocytosis of renal outer medullar potassium 1 ([[ROMK|ROMK1]]). It (and [[WNK4]]) interactes with intersectin ([[ITSN1]], [[ITSN2]]).
=== Sodium Reabsorption ===
[[File:NCC diagram.png|left|thumb|WNK1 homodimer phosphorylates SPAK/OSR1, which then subsequently activates the NCC via phosphorylation. Activated NCC allows the influx of Na<sup>+</sup> ions and Cl<sup>−</sup> ions.]]
[[File:WNK1 activation of ENaC.png|left|thumb|WNK1 homodimer phosphorylates SGK1 which leads to increased ENaC expression.]]
In the [[distal convoluted tubule]] (DCT), WNK1 is a potent activator of the NCC that results in an increase in [[Sodium reabsorption|sodium re absorption]] that drives an increase in blood pressure.<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /><ref name="Bazúa-Valenti_2015" /> The WNK1 mutant found in FHHt harbors a large deletion within [[intron]] 1 that causes an increase in the [[Gene expression|expression]] of full length WNK1.<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /><ref name="Bazúa-Valenti_2015" /><ref name="Xu_2005" /> The boost in WNK1 leads to increases in NCC activation that promotes the high blood pressure/[[hypertension]] associated with FHHt.<ref name="Shekarabi_2017" /><ref name="Hadchouel_2016" /><ref name="Bazúa-Valenti_2015" /><ref name="Xu_2005" /> WNK1 activates the serum-and glucocorticoid-inducible protein kinase [[SGK1]], leading to increased expression of the [[epithelial sodium channel]] (ENaC), which also promotes sodium re absorption.<ref name="Hadchouel_2016" />


==Clinical significance==
=== Potassium Secretion ===
WNK1 has [[mutation]]s associated with [[Gordon hyperkalemia-hypertension syndrome]] ([[pseudohypoaldosteronism]] Type II, featuring [[hypertension]]) and [[congenital sensory neuropathy]] ([[Hereditary sensory and autonomic neuropathy|HSAN]] Type II, featuring loss of [[perception]] to [[pain]], [[touch]], and [[heat]] due to a loss of peripheral [[sensory nerve]]s).<ref name="pmid18521183">{{cite journal |vauthors=Shekarabi M, Girard N, Rivière JB, etal | title=Mutations in the nervous system--specific HSN2 exon of WNK1 cause hereditary sensory neuropathy type II | journal=J Clin Invest |date=July 2008 | volume=118 | issue=7 | pages=2496–2505 | pmid=18521183 | pmc=2398735 | accessdate=2008-11-04| doi=10.1172/JCI34088 }}</ref>  ''See also:'' [[HSN2|HSN2 gene]].


==Comparative genomics==
WNK1 regulates [[potassium channel]]s found in the [[Collecting duct system|cortical collecting duct]] (CCD) and [[connecting tubule]] (CNT).<ref name="Hadchouel_2016" /> Renal outer medullar potassium 1 ([[ROMK|ROMK1]]) and l[[BK channel|arge conductance calcium-activated potassium channe]]<nowiki/>l (BKCa) are the two primary channels for potassium secretion.<ref name="Hadchouel_2016" /> WNK1 indirectly stimulates [[Receptor-mediated endocytosis|clathrin-dependent endocytosis]] of ROMK1 by a potential interaction with [[Intersectin 1|intersectin]] (ITSN1); thus, kinase activity is not needed.<ref name="Hadchouel_2016" /> Another possible mechanism of ROMK1 regulation is via autosomal recessive hypercholeserolemia (ACH), which is a clathrin adaptor molecule.<ref name="Hadchouel_2016" /> ACH phosphorylation by WNK1 promotes the translocation of ROMK1 to [[Clathrin-coated pit|clathrin coated pits]] triggering [[endocytosis]].<ref name="Hadchouel_2016" /> WNK1 may indirectly activate BKCa by inhibiting the actions of extracellular signal–regulated kinases (ERK1 and ERK2) that lead to lysomal degradation.<ref name="Hadchouel_2016" />
The gene belongs to a group of four related protein kinases (WNK1, [[WNK2]], [[WNK3]], [[WNK4]]).


Homologs of this protein have been found in ''[[Arabidopsis thaliana]]'', ''[[Caenorhabditis elegans|C. elegans]]'', ''[[Chlamydomonas reinhardtii]]'' and ''[[Vitis vinifera]]'' as well as in vertebrates including ''[[Danio rerio]]'' and ''[[Taeniopygia guttata]]''.
=== Cell Volume Regulation ===


==References==
The NKCC1/2 cotransporters are regulated by intracellular Cl<sup>−</sup> concentration.<ref name="Huang_2015" /> Studies point to WNK1 as key effector that couples Cl<sup>−</sup> concentration to NKCC1/2 function.<ref name="Shekarabi_2017" /><ref name="Huang_2015" /> In [[Tonicity|hypertonic]] (high extracellular Cl<sup>−</sup> ) conditions that trigger cell shrinkage, an unknown mechanism upregulates WNK1 expression to counteract the volume loss.<ref name="Shekarabi_2017" /> The increased WNK1 leads to activation of SPAK/OSR1 that activate NKCC1/2 via subsequent phosphorylation.<ref name="Shekarabi_2017" /><ref name="Huang_2015" /> NKCC1/2 will promote the influx of Na<sup>+</sup>, K<sup>+</sup>, and Cl<sup>−</sup> ions into the cell thereby causing the flow of water into the cell.<ref name="Shekarabi_2017" /> In the reverse circumstances, where [[Tonicity|hypotonic]] (low extracellular Cl<sup>−</sup> ) conditions induce cell swelling, WNK1 is inhibited.<ref name="Shekarabi_2017" /> Another cotransporter, KCC is inactive when phosphorylated; without activated WNK1, KCC does not undergo phosphorylation and can activate.<ref name="Shekarabi_2017" /> The cotransporter will promote the efflux of K<sup>+</sup> and Cl<sup>−</sup> ions and cause the flow of water out of the cell to combat swelling.<ref name="Shekarabi_2017" />
{{reflist}}


==Further reading==
=== WNK1 in the Brain ===
{{refbegin | 2}}
*{{cite journal  | vauthors=Hart GW, Haltiwanger RS, Holt GD, Kelly WG |title=Nucleoplasmic and cytoplasmic glycoproteins. |journal=Ciba Found. Symp. |volume=145 |issue=  |pages= 102–12, discussion 112–8 |year= 1989 |pmid= 2507249 |doi=  }}
*{{cite journal  |vauthors=Nakajima D, Okazaki N, Yamakawa H, etal |title=Construction of expression-ready cDNA clones for KIAA genes: manual curation of 330 KIAA cDNA clones. |journal=DNA Res. |volume=9 |issue= 3 |pages= 99–106 |year= 2003 |pmid= 12168954 |doi=10.1093/dnares/9.3.99  }}
*{{cite journal  |vauthors=Xu BE, Lee BH, Min X, etal |title=WNK1: analysis of protein kinase structure, downstream targets, and potential roles in hypertension. |journal=Cell Res. |volume=15 |issue= 1 |pages= 6–10 |year= 2005 |pmid= 15686619 |doi= 10.1038/sj.cr.7290256 }}
*{{cite journal  | vauthors=Subramanya AR, Yang CL, McCormick JA, Ellison DH |title=WNK kinases regulate sodium chloride and potassium transport by the aldosterone-sensitive distal nephron. |journal=Kidney Int. |volume=70 |issue= 4 |pages= 630–4 |year= 2006 |pmid= 16820787 |doi= 10.1038/sj.ki.5001634 }}
*{{cite journal  | vauthors=Huang CL, Kuo E |title=Mechanisms of disease: WNK-ing at the mechanism of salt-sensitive hypertension. |journal=Nature Clinical Practice Nephrology |volume=3 |issue= 11 |pages= 623–30 |year= 2007 |pmid= 17957199 |doi= 10.1038/ncpneph0638 }}
*{{cite journal  | vauthors=Bonaldo MF, Lennon G, Soares MB |title=Normalization and subtraction: two approaches to facilitate gene discovery. |journal=Genome Res. |volume=6 |issue= 9 |pages= 791–806 |year= 1997 |pmid= 8889548 |doi=10.1101/gr.6.9.791  }}
*{{cite journal  |vauthors=Nagase T, Ishikawa K, Nakajima D, etal |title=Prediction of the coding sequences of unidentified human genes. VII. The complete sequences of 100 new cDNA clones from brain which can code for large proteins in vitro. |journal=DNA Res. |volume=4 |issue= 2 |pages= 141–50 |year= 1997 |pmid= 9205841 |doi=10.1093/dnares/4.2.141  }}
*{{cite journal  |vauthors=Moore TM, Garg R, Johnson C, etal |title=PSK, a novel STE20-like kinase derived from prostatic carcinoma that activates the c-Jun N-terminal kinase mitogen-activated protein kinase pathway and regulates actin cytoskeletal organization. |journal=J. Biol. Chem. |volume=275 |issue= 6 |pages= 4311–22 |year= 2000 |pmid= 10660600 |doi=10.1074/jbc.275.6.4311  }}
*{{cite journal  |vauthors=Disse-Nicodème S, Achard JM, Desitter I, etal |title=A new locus on chromosome 12p13.3 for pseudohypoaldosteronism type II, an autosomal dominant form of hypertension. |journal=Am. J. Hum. Genet. |volume=67 |issue= 2 |pages= 302–10 |year= 2000 |pmid= 10869238 |doi=10.1086/303020  | pmc=1287179  }}
*{{cite journal  |vauthors=Wilson FH, Disse-Nicodème S, Choate KA, etal |title=Human hypertension caused by mutations in WNK kinases. |journal=Science |volume=293 |issue= 5532 |pages= 1107–12 |year= 2001 |pmid= 11498583 |doi= 10.1126/science.1062844 }}
*{{cite journal  | vauthors=Veríssimo F, Jordan P |title=WNK kinases, a novel protein kinase subfamily in multi-cellular organisms. |journal=Oncogene |volume=20 |issue= 39 |pages= 5562–9 |year= 2001 |pmid= 11571656 |doi= 10.1038/sj.onc.1204726 }}
*{{cite journal  |vauthors=Xu BE, Min X, Stippec S, etal |title=Regulation of WNK1 by an autoinhibitory domain and autophosphorylation. |journal=J. Biol. Chem. |volume=277 |issue= 50 |pages= 48456–62 |year= 2003 |pmid= 12374799 |doi= 10.1074/jbc.M207917200 }}
*{{cite journal  |vauthors=Strausberg RL, Feingold EA, Grouse LH, etal |title=Generation and initial analysis of more than 15,000 full-length human and mouse cDNA sequences. |journal=Proc. Natl. Acad. Sci. U.S.A. |volume=99 |issue= 26 |pages= 16899–903 |year= 2003 |pmid= 12477932 |doi= 10.1073/pnas.242603899  | pmc=139241 }}
*{{cite journal  |vauthors=Vitari AC, Deak M, Collins BJ, etal |title=WNK1, the kinase mutated in an inherited high-blood-pressure syndrome, is a novel PKB (protein kinase B)/Akt substrate. |journal=Biochem. J. |volume=378 |issue= Pt 1 |pages= 257–68 |year= 2004 |pmid= 14611643 |doi= 10.1042/BJ20031692  | pmc=1223938 }}
*{{cite journal  |vauthors=Delaloy C, Lu J, Houot AM, etal |title=Multiple promoters in the WNK1 gene: one controls expression of a kidney-specific kinase-defective isoform. |journal=Mol. Cell. Biol. |volume=23 |issue= 24 |pages= 9208–21 |year= 2004 |pmid= 14645531 |doi=10.1128/MCB.23.24.9208-9221.2003  | pmc=309643  }}
*{{cite journal  |vauthors=Xu BE, Stippec S, Lenertz L, etal |title=WNK1 activates ERK5 by an MEKK2/3-dependent mechanism. |journal=J. Biol. Chem. |volume=279 |issue= 9 |pages= 7826–31 |year= 2004 |pmid= 14681216 |doi= 10.1074/jbc.M313465200 }}
*{{cite journal  |vauthors=Fu GK, Wang JT, Yang J, etal |title=Circular rapid amplification of cDNA ends for high-throughput extension cloning of partial genes. |journal=Genomics |volume=84 |issue= 1 |pages= 205–10 |year= 2005 |pmid= 15203218 |doi= 10.1016/j.ygeno.2004.01.011 }}
*{{cite journal  |vauthors=Jin J, Smith FD, Stark C, etal |title=Proteomic, functional, and domain-based analysis of in vivo 14-3-3 binding proteins involved in cytoskeletal regulation and cellular organization. |journal=Curr. Biol. |volume=14 |issue= 16 |pages= 1436–50 |year= 2004 |pmid= 15324660 |doi= 10.1016/j.cub.2004.07.051 }}
{{refend}}


==External links==
In the mature brain, the [[Gamma-Aminobutyric acid|GABA]] neurotransmitter represents the major inhibitory signal used in neuronal signaling.<ref name="Shekarabi_2017" /> GABA activates the [[GABAA receptor|GABA<sub>A</sub> receptor]] which is a Cl<sup>−</sup> ion channel.<ref name="Shekarabi_2017" /> Cl<sup>−</sup> ions will enter the neuron causing [[Hyperpolarization (biology)|hyperpolarization]] and inhibition of signaling.<ref name="Shekarabi_2017" /> During brain development however, GABA<sub>A</sub> activation will allow Cl<sup>−</sup> ions to leave the neuron causing the neuron to depolarize.<ref name="Shekarabi_2017" /> Thus, GABA is an [[Neurotransmitter|excitatory neurotransmitter]] during development.<ref name="Shekarabi_2017" /> WNK1 has been implicated in the developmental switch from excitatory to inhibitory GABA signaling via interaction with NKCC1 and KCCs.<ref name="Shekarabi_2017" /> WNK1 phosphorylates SPAK/OSR1 which then phosphorylates KCC2 inhibiting the flow of Cl<sup>−</sup> ions out of the cell during development.<ref name="Shekarabi_2017" />
* [https://www.ncbi.nlm.nih.gov/books/NBK65707/ GeneReviews/NCBI/NIH/UW entry on Pseudohypoaldosteronism Type II]
[[File:WNK1 inhibition.png|thumb|
* [https://www.ncbi.nlm.nih.gov/books/NBK49247/ GeneReviews/NIH/NCBI/UW entry on Hereditary Sensory and Autonomic Neuropathy Type II]
WNK4 binds WNK1 inhibiting WNK1 activation. Cl<sup>−</sup> ions bind the WNK1 homodimer inhibiting kinase activity. Both of these mechanisms prevent the activation of the NCC.   
]]


{{PDB Gallery|geneid=65125}}
== Regulation of WNK1 ==
{{Serine/threonine-specific protein kinases}}
The concentrations of Cl<sup>−</sup> ions and K<sup>+</sup> ion play a major role in regulating WNK1 activity.<ref name="Shekarabi_2017" /><ref name="Huang_2015" /> In the DCT, the plasma concentration of K<sup>+</sup> ion is thought to impact the concentration Cl<sup>−</sup> ions within the nephron.<ref name="Shekarabi_2017" /><ref name="Huang_2015" /> High plasma K<sup>+</sup> concentration down regulates WNK1 activity and prevents Cl<sup>−</sup> ion from entering the [[nephron]] via the NCC.<ref name="Shekarabi_2017" /><ref name="Huang_2015" />  The opposite occurs when plasma K<sup>+</sup> concentration is low; increased WNK1 activity boosts NCC activity promoting reabsorption of Cl<sup>−</sup> ions.<ref name="Shekarabi_2017" /><ref name="Huang_2015" />  When there is an abundance of Cl<sup>−</sup> ions within the [[nephron]], WNK1 activity is inhibited by the binding of a Cl<sup>−</sup> ion to WNK1's catalytic domain.<ref name="Shekarabi_2017" /><ref name="Huang_2015" />


Furthermore, WNK1 and WNK4 may interact to form heterodimers that inhibit WNK1 function.<ref name="Bazúa-Valenti_2015" /><ref name="Hadchouel_2016" /> WNK4 release from the heterodimer allows WNK1 monomer to bind another WNK1 monomer to promote activation.<ref name="Hadchouel_2016" /><ref name="Bazúa-Valenti_2015" /> WNK1 function can also be inhibited if WNK1 is degraded. There are two enzymes responsible for WNK1 ubiquitination, kelch like 3 (KLHL3) and cullin 3 (CUL3).<ref name="Bazúa-Valenti_2015" /><ref name="Hadchouel_2016" /><ref name="Alessi_2015">{{cite journal | vauthors = Alessi DR, Zhang J, Khanna A, Hochdörfer T, Shang Y, Kahle KT | title = The WNK-SPAK/OSR1 pathway: master regulator of cation-chloride cotransporters | journal = Science Signaling | volume = 7 | issue = 334 | pages = re3 | date = July 2014 | pmid = 25028718 | doi = 10.1126/scisignal.2005365  }}</ref> KLHL3 serves as an adaptor protein that promotes the interaction between WNK1 and Cullin3, which is in a complex containing an E3 ubquitin ligase that attaches the ubiquitin molecules to WNK1.<ref name="Bazúa-Valenti_2015" /> The ubiquitinated WNK1 will subsequently undergo proteasomal degradation.<ref name="Bazúa-Valenti_2015" /><ref name="Hadchouel_2016" /><ref name="Alessi_2015" />


{{gene-12-stub}}
== Clinical significance ==
WNK1 has [[mutation]]s associated with Gordon hyperkalemia-hypertension syndrome ([[pseudohypoaldosteronism]] Type II, featuring [[hypertension]] also called familial hyperkalemic hypertension (FHHt) )<ref name="Shekarabi_2017" /><ref name="Bazúa-Valenti_2015" /><ref name="Xu_2005" /> and [[congenital sensory neuropathy]] ([[Hereditary sensory and autonomic neuropathy|HSAN]] Type II, featuring loss of [[perception]] to [[pain]], [[touch]], and [[heat]] due to a loss of peripheral [[sensory nerve]]s).<ref name="Shekarabi_2017" /><ref>{{cite journal | vauthors = Tang BL | title = (WNK)ing at death: With-no-lysine (Wnk) kinases in neuropathies and neuronal survival | language = en | journal = Brain Research Bulletin | volume = 125 | pages = 92–8 | date = July 2016 | pmid = 27131446 | doi = 10.1016/j.brainresbull.2016.04.017 }}</ref> ''See also:'' [[HSN2|HSN2 gene]].
 
== Comparative genomics ==
The gene belongs to a group of four related protein kinases (WNK1, [[WNK2]], [[WNK3]], [[WNK4]]).<ref name="Shekarabi_2017" /><ref name="Bazúa-Valenti_2015" /><ref name="Xu_2005" />
 
Homologs of this protein have been found in ''[[Arabidopsis thaliana]]'', ''[[Caenorhabditis elegans|C. elegans]]'', ''[[Chlamydomonas reinhardtii]]'' and ''[[Vitis vinifera]]''as well as in vertebrates including ''[[Danio rerio]]'' and ''[[Taeniopygia guttata]]''.<ref name="Bazúa-Valenti_2015" />
 
== References ==
{{Reflist}}
 
[[Category:Enzymes]]

Latest revision as of 09:01, 27 March 2018

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WNK (lysine deficient protein kinase 1), also known as WNK1, is an enzyme that is encoded by the WNK1 gene.[1][2][3][4][5] WNK1 is serine-threonine kinase and part of the "with no lysine/K" kinase WNK family.[1][2][3][5] The predominant role of WNK1 is the regulation of cation-Cl cotransporters (CCCs) such as the sodium chloride cotransporter (NCC), basolateral Na-K-Cl symporter (NKCC1), and potassium chloride cotransporter (KCC1) located within the kidney.[1][2][5] CCCs mediate ion homeostasis and modulate blood pressure by transporting ions in and out of the cell.[1] WNK1 mutations as a result have been implicated in blood pressure disorders/diseases; a prime example being familial hyperkalemic hypertension (FHHt).[1][2][3][4][5]

Structure

The WNK1 protein is composed of 2382 amino acids (molecular weight 230 kDa).[4] The protein contains a kinase domain located within its short N-terminaldomain and a long C-terminal tail.[4] The kinase domain has some similarity to the MEKK protein kinase family.[4] As a member of the WNK family, the kinase's catalytic lysine residue is uniquely located in beta strand 2 of the glycine loop.[4] In order to have kinase activity, WNK1 must autophosphorylate the serine 382 residue found in its activation loop.[4][1] Further, phosphorylation at another site (Ser378) increases WNK1 activity.[1] An autoinhibitory domain is located within the C-terminal domain along with a HQ domain that is needed for WNK1 interactions with other WNKs.[1][2][3][4] The interactions between WNKs play an important role in function; WNK1 mutants that lack an HQ domain also lack kinase activity.

Function

The WNK1 gene encodes a cytoplasmic serine-threonine kinase expressed in the distal nephron.[1][2][4] Studies have shown that WNK1 can activate multiple CCCs.[1][2] WNK1 however, does not directly phosphorylate the CCCs themselves rather it phosphorylates other serine-threonine kinases: Sterile20 related proline-alanine-rich kinase (SPAK) and oxidative stress response kinase 1 (OXSR1).[2][1][3] Phosphorylation of SPAK's T loop located in its catalytic domain will activate SPAK, which will go on to phosphorylation the CCC's N-terminaldomain.[1][2] Hence, WNK1 activates CCCs indirectly as an upstream regulator of SPAK/OSR1.[1][2][3]

Sodium Reabsorption

File:NCC diagram.png
WNK1 homodimer phosphorylates SPAK/OSR1, which then subsequently activates the NCC via phosphorylation. Activated NCC allows the influx of Na+ ions and Cl ions.
File:WNK1 activation of ENaC.png
WNK1 homodimer phosphorylates SGK1 which leads to increased ENaC expression.

In the distal convoluted tubule (DCT), WNK1 is a potent activator of the NCC that results in an increase in sodium re absorption that drives an increase in blood pressure.[1][2][3] The WNK1 mutant found in FHHt harbors a large deletion within intron 1 that causes an increase in the expression of full length WNK1.[1][2][3][4] The boost in WNK1 leads to increases in NCC activation that promotes the high blood pressure/hypertension associated with FHHt.[1][2][3][4] WNK1 activates the serum-and glucocorticoid-inducible protein kinase SGK1, leading to increased expression of the epithelial sodium channel (ENaC), which also promotes sodium re absorption.[2]

Potassium Secretion

WNK1 regulates potassium channels found in the cortical collecting duct (CCD) and connecting tubule (CNT).[2] Renal outer medullar potassium 1 (ROMK1) and large conductance calcium-activated potassium channel (BKCa) are the two primary channels for potassium secretion.[2] WNK1 indirectly stimulates clathrin-dependent endocytosis of ROMK1 by a potential interaction with intersectin (ITSN1); thus, kinase activity is not needed.[2] Another possible mechanism of ROMK1 regulation is via autosomal recessive hypercholeserolemia (ACH), which is a clathrin adaptor molecule.[2] ACH phosphorylation by WNK1 promotes the translocation of ROMK1 to clathrin coated pits triggering endocytosis.[2] WNK1 may indirectly activate BKCa by inhibiting the actions of extracellular signal–regulated kinases (ERK1 and ERK2) that lead to lysomal degradation.[2]

Cell Volume Regulation

The NKCC1/2 cotransporters are regulated by intracellular Cl concentration.[5] Studies point to WNK1 as key effector that couples Cl concentration to NKCC1/2 function.[1][5] In hypertonic (high extracellular Cl ) conditions that trigger cell shrinkage, an unknown mechanism upregulates WNK1 expression to counteract the volume loss.[1] The increased WNK1 leads to activation of SPAK/OSR1 that activate NKCC1/2 via subsequent phosphorylation.[1][5] NKCC1/2 will promote the influx of Na+, K+, and Cl ions into the cell thereby causing the flow of water into the cell.[1] In the reverse circumstances, where hypotonic (low extracellular Cl ) conditions induce cell swelling, WNK1 is inhibited.[1] Another cotransporter, KCC is inactive when phosphorylated; without activated WNK1, KCC does not undergo phosphorylation and can activate.[1] The cotransporter will promote the efflux of K+ and Cl ions and cause the flow of water out of the cell to combat swelling.[1]

WNK1 in the Brain

In the mature brain, the GABA neurotransmitter represents the major inhibitory signal used in neuronal signaling.[1] GABA activates the GABAA receptor which is a Cl ion channel.[1] Cl ions will enter the neuron causing hyperpolarization and inhibition of signaling.[1] During brain development however, GABAA activation will allow Cl ions to leave the neuron causing the neuron to depolarize.[1] Thus, GABA is an excitatory neurotransmitter during development.[1] WNK1 has been implicated in the developmental switch from excitatory to inhibitory GABA signaling via interaction with NKCC1 and KCCs.[1] WNK1 phosphorylates SPAK/OSR1 which then phosphorylates KCC2 inhibiting the flow of Cl ions out of the cell during development.[1]

File:WNK1 inhibition.png
WNK4 binds WNK1 inhibiting WNK1 activation. Cl ions bind the WNK1 homodimer inhibiting kinase activity. Both of these mechanisms prevent the activation of the NCC.

Regulation of WNK1

The concentrations of Cl ions and K+ ion play a major role in regulating WNK1 activity.[1][5] In the DCT, the plasma concentration of K+ ion is thought to impact the concentration Cl ions within the nephron.[1][5] High plasma K+ concentration down regulates WNK1 activity and prevents Cl ion from entering the nephron via the NCC.[1][5] The opposite occurs when plasma K+ concentration is low; increased WNK1 activity boosts NCC activity promoting reabsorption of Cl ions.[1][5] When there is an abundance of Cl ions within the nephron, WNK1 activity is inhibited by the binding of a Cl ion to WNK1's catalytic domain.[1][5]

Furthermore, WNK1 and WNK4 may interact to form heterodimers that inhibit WNK1 function.[3][2] WNK4 release from the heterodimer allows WNK1 monomer to bind another WNK1 monomer to promote activation.[2][3] WNK1 function can also be inhibited if WNK1 is degraded. There are two enzymes responsible for WNK1 ubiquitination, kelch like 3 (KLHL3) and cullin 3 (CUL3).[3][2][6] KLHL3 serves as an adaptor protein that promotes the interaction between WNK1 and Cullin3, which is in a complex containing an E3 ubquitin ligase that attaches the ubiquitin molecules to WNK1.[3] The ubiquitinated WNK1 will subsequently undergo proteasomal degradation.[3][2][6]

Clinical significance

WNK1 has mutations associated with Gordon hyperkalemia-hypertension syndrome (pseudohypoaldosteronism Type II, featuring hypertension also called familial hyperkalemic hypertension (FHHt) )[1][3][4] and congenital sensory neuropathy (HSAN Type II, featuring loss of perception to pain, touch, and heat due to a loss of peripheral sensory nerves).[1][7] See also: HSN2 gene.

Comparative genomics

The gene belongs to a group of four related protein kinases (WNK1, WNK2, WNK3, WNK4).[1][3][4]

Homologs of this protein have been found in Arabidopsis thaliana, C. elegans, Chlamydomonas reinhardtii and Vitis viniferaas well as in vertebrates including Danio rerio and Taeniopygia guttata.[3]

References

  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 1.13 1.14 1.15 1.16 1.17 1.18 1.19 1.20 1.21 1.22 1.23 1.24 1.25 1.26 1.27 1.28 1.29 1.30 1.31 1.32 1.33 1.34 1.35 1.36 1.37 Shekarabi M, Zhang J, Khanna AR, Ellison DH, Delpire E, Kahle KT (February 2017). "WNK Kinase Signaling in Ion Homeostasis and Human Disease". Cell Metabolism. 25 (2): 285–299. doi:10.1016/j.cmet.2017.01.007. PMID 28178566.
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 2.14 2.15 2.16 2.17 2.18 2.19 2.20 2.21 2.22 2.23 Hadchouel J, Ellison DH, Gamba G (2016). "Regulation of Renal Electrolyte Transport by WNK and SPAK-OSR1 Kinases". Annual Review of Physiology. 78: 367–89. doi:10.1146/annurev-physiol-021115-105431. PMID 26863326.
  3. 3.00 3.01 3.02 3.03 3.04 3.05 3.06 3.07 3.08 3.09 3.10 3.11 3.12 3.13 3.14 3.15 3.16 Bazúa-Valenti S, Gamba G (May 2015). "Revisiting the NaCl cotransporter regulation by with-no-lysine kinases". American Journal of Physiology. Cell Physiology. 308 (10): C779–91. doi:10.1152/ajpcell.00065.2015. PMC 4436992. PMID 25788573.
  4. 4.00 4.01 4.02 4.03 4.04 4.05 4.06 4.07 4.08 4.09 4.10 4.11 4.12 Xu BE, Lee BH, Min X, Lenertz L, Heise CJ, Stippec S, Goldsmith EJ, Cobb MH (January 2005). "WNK1: analysis of protein kinase structure, downstream targets, and potential roles in hypertension". Cell Research. 15 (1): 6–10. doi:10.1038/sj.cr.7290256. PMID 15686619.
  5. 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 Huang CL, Cheng CJ (November 2015). "A unifying mechanism for WNK kinase regulation of sodium-chloride cotransporter". Pflügers Archiv. 467 (11): 2235–41. doi:10.1007/s00424-015-1708-2. PMC 4601926. PMID 25904388.
  6. 6.0 6.1 Alessi DR, Zhang J, Khanna A, Hochdörfer T, Shang Y, Kahle KT (July 2014). "The WNK-SPAK/OSR1 pathway: master regulator of cation-chloride cotransporters". Science Signaling. 7 (334): re3. doi:10.1126/scisignal.2005365. PMID 25028718.
  7. Tang BL (July 2016). "(WNK)ing at death: With-no-lysine (Wnk) kinases in neuropathies and neuronal survival". Brain Research Bulletin. 125: 92–8. doi:10.1016/j.brainresbull.2016.04.017. PMID 27131446.