title: RACK1 associates with NHE5 in focal adhesions and positively regulates the transporter activity.
abstract: Na+/H+ exchanger isoform 5 (NHE5) is a brain-enriched NHE that may play important roles in ion homeostasis and cell-volume regulation. However, the regulation mechanism of NHE5 has not been fully elucidated. Here, we show that Receptor for Activated C-kinase 1 (RACK1) directly binds to NHE5 and positively regulates the transporter function. NHE5 co-localized with RACK1 as well as beta1 integrin, paxillin and vinculin, suggesting that NHE5 associates with focal adhesions. By using RACK1 dominant-negative mutants and siRNA, we further show that RACK1 regulates NHE5 both directly and through an integrin-dependent pathway. The NHE5-RACK1 interaction, but not the RACK1-beta1 integrin interaction, was reinforced when cells were spread on an integrin-substrate fibronectin. We propose that RACK1 activates NHE5 both by integrin-dependent and independent pathways, which may coordinate cellular ion homeostasis during cell-matrix adhesion.
authors.affiliation: Department of Biochemistry and Molecular Biology, The University of British Columbia, Canada.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Onishi
authors.forename: Paulo J C
authors.initials: PJ
authors.lastname: Lin
authors.forename: Graham H
authors.initials: GH
authors.lastname: Diering
authors.forename: Warren P
authors.initials: WP
authors.lastname: Williams
authors.forename: Masayuki
authors.initials: M
authors.lastname: Numata
mesh_terms: D000818:Animals; D016466:CHO Cells; D002448:Cell Adhesion; D006224:Cricetinae; D003412:Cricetulus; D005353:Fibronectins / Q000378:metabolism; D022001:Focal Adhesions; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D019012:Integrin beta1 / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D051419:Paxillin / Q000378:metabolism; D011485:Protein Binding; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*; D020798:Two-Hybrid System Techniques; D016596:Vinculin / Q000378:metabolism
chemical_list: D005353:Fibronectins; D019012:Integrin beta1; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D051419:Paxillin; C419368:RACK1 protein, human; D000075370:Receptors for Activated C Kinase; D011956:Receptors, Cell Surface; D017923:Sodium-Hydrogen Exchangers; C117561:sodium-hydrogen exchanger 5; D016596:Vinculin; D019204:GTP-Binding Proteins