title: Regulation of the epithelial Na+ channel by the RH domain of G protein-coupled receptor kinase, GRK2, and Galphaq/11.
abstract: The G protein-coupled receptor kinase (GRK2) belongs to a family of protein kinases that phosphorylates agonist-activated G protein-coupled receptors, leading to G protein-receptor uncoupling and termination of G protein signaling. GRK2 also contains a regulator of G protein signaling homology (RH) domain, which selectively interacts with α-subunits of the Gq/11 family that are released during G protein-coupled receptor activation. We have previously reported that kinase activity of GRK2 up-regulates activity of the epithelial sodium channel (ENaC) in a Na(+) absorptive epithelium by blocking Nedd4-2-dependent inhibition of ENaC. In the present study, we report that GRK2 also regulates ENaC by a mechanism that does not depend on its kinase activity. We show that a wild-type GRK2 (wtGRK2) and a kinase-dead GRK2 mutant ((K220R)GRK2), but not a GRK2 mutant that lacks the C-terminal RH domain (ΔRH-GRK2) or a GRK2 mutant that cannot interact with Gαq/11/14 ((D110A)GRK2), increase activity of ENaC. GRK2 up-regulates the basal activity of the channel as a consequence of its RH domain binding the α-subunits of Gq/11. We further found that expression of constitutively active Gαq/11 mutants significantly inhibits activity of ENaC. Conversely, co-expression of siRNA against Gαq/11 increases ENaC activity. The effect of Gαq on ENaC activity is not due to change in ENaC membrane expression and is independent of Nedd4-2. These findings reveal a novel mechanism by which GRK2 and Gq/11 α-subunits regulate the activity ENaC.
authors.affiliation: Discipline of Physiology, The Bosch Institute, Faculty of Medicine, The University of Sydney, Sydney, NSW 2006, Australia.
authors.forename: Il-Ha
authors.initials: IH
authors.lastname: Lee
authors.forename: Sung-Hee
authors.initials: SH
authors.lastname: Song
authors.forename: Craig R
authors.initials: CR
authors.lastname: Campbell
authors.forename: Sharad
authors.initials: S
authors.lastname: Kumar
authors.forename: David I
authors.initials: DI
authors.lastname: Cook
authors.forename: Anuwat
authors.initials: A
authors.lastname: Dinudom
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D056827:Endosomal Sorting Complexes Required for Transport / Q000235:genetics / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D053503:Epithelial Sodium Channels / Q000096:biosynthesis* / Q000235:genetics; D054769:G-Protein-Coupled Receptor Kinase 2 / Q000235:genetics / Q000378:metabolism*; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology; D057809:HEK293 Cells; D006801:Humans; D020125:Mutation, Missense; D000075702:Nedd4 Ubiquitin Protein Ligases; D017434:Protein Structure, Tertiary; D051381:Rats; D011916:Rats, Inbred F344; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; C000618479:NEDD4L protein, rat; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618483:Nedd4 protein, human; C000618484:Nedd4 protein, rat; C000618485:Nedd4L protein, human; D044767:Ubiquitin-Protein Ligases; C496567:GRK2 protein, human; C496569:Grk2 protein, rat; D054769:G-Protein-Coupled Receptor Kinase 2; D043802:GTP-Binding Protein alpha Subunits, Gq-G11