title: Identification and Molecular Mechanisms of the Rapid Tonicity-induced Relocalization of the Aquaporin 4 Channel.
abstract: The aquaporin family of integral membrane proteins is composed of channels that mediate cellular water flow. Aquaporin 4 (AQP4) is highly expressed in the glial cells of the central nervous system and facilitates the osmotically driven pathological brain swelling associated with stroke and traumatic brain injury. Here we show that AQP4 cell surface expression can be rapidly and reversibly regulated in response to changes of tonicity in primary cortical rat astrocytes and in transfected HEK293 cells. The translocation mechanism involves PKA activation, influx of extracellular calcium, and activation of calmodulin. We identify five putative PKA phosphorylation sites and use site-directed mutagenesis to show that only phosphorylation at one of these sites, serine 276, is necessary for the translocation response. We discuss our findings in the context of the identification of new therapeutic approaches to treating brain edema.
authors.affiliation: From the Molecular Organisation and Assembly in Cells Doctoral Training Centre, University of Warwick, Coventry CV4 7AL.
authors.forename: Philip
authors.initials: P
authors.lastname: Kitchen
authors.affiliation: the Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB.
authors.forename: Rebecca E
authors.initials: RE
authors.lastname: Day
authors.affiliation: From the Molecular Organisation and Assembly in Cells Doctoral Training Centre, University of Warwick, Coventry CV4 7AL.
authors.forename: Luke H J
authors.initials: LH
authors.lastname: Taylor
authors.affiliation: the Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB.
authors.forename: Mootaz M
authors.initials: MM
authors.lastname: Salman
authors.affiliation: the School of Life & Health Sciences and Aston Research Centre for Healthy Ageing, Aston University, Aston Triangle, Birmingham B4 7ET, and r.m.bill@aston.ac.uk.
authors.forename: Roslyn M
authors.initials: RM
authors.lastname: Bill
authors.affiliation: the Biomedical Research Centre, Sheffield Hallam University, Howard Street, Sheffield S1 1WB, m.conner@shu.ac.uk.
authors.forename: Matthew T
authors.initials: MT
authors.lastname: Conner
authors.affiliation: the School of Clinical and Experimental Medicine, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom a.c.conner@bham.ac.uk.
authors.forename: Alex C
authors.initials: AC
authors.lastname: Conner
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D051401:Aquaporin 4 / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001253:Astrocytes / Q000378:metabolism; D001929:Brain Edema / Q000235:genetics / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D009997:Osmotic Pressure; D010766:Phosphorylation; D021381:Protein Transport; D051381:Rats
chemical_list: D051401:Aquaporin 4; D002147:Calmodulin; D017868:Cyclic AMP-Dependent Protein Kinases; D002118:Calcium
keywords: aquaporin; astrocyte; homeostasis; hypotonicity; protein translocation; rapid trafficking; regulation; water channel