title: Polarized trafficking and surface expression of the AQP4 water channel are coordinated by serial and regulated interactions with different clathrin-adaptor complexes.
abstract: Aquaporin 4 (AQP4) is the predominant water channel in the brain. It is targeted to specific membrane domains of astrocytes and plays a crucial role in cerebral water balance in response to brain edema formation. AQP4 is also specifically expressed in the basolateral membranes of epithelial cells. However, the molecular mechanisms involved in its polarized targeting and membrane trafficking remain largely unknown. Here, we show that two independent C-terminal signals determine AQP4 basolateral membrane targeting in epithelial MDCK cells. One signal involves a tyrosine-based motif; the other is encoded by a di-leucine-like motif. We found that the tyrosine-based basolateral sorting signal also determines AQP4 clathrin-dependent endocytosis through direct interaction with the mu subunit of AP2 adaptor complex. Once endocytosed, a regulated switch in mu subunit interaction changes AP2 adaptor association to AP3. We found that the stress-induced kinase casein kinase (CK)II phosphorylates the Ser276 immediately preceding the tyrosine motif, increasing AQP4-mu 3A interaction and enhancing AQP4-lysosomal targeting and degradation. AQP4 phosphorylation by CKII may thus provide a mechanism that regulates AQP4 cell surface expression.
authors.affiliation: Service de Biologie Cellulaire, Département de Biologie Cellulaire et Moléculaire, CEA/Saclay, F-91191 Gif-sur-Yvette, Cedex, France.
authors.forename: R
authors.initials: R
authors.lastname: Madrid
authors.forename: S
authors.initials: S
authors.lastname: Le Maout
authors.forename: M B
authors.initials: MB
authors.lastname: Barrault
authors.forename: K
authors.initials: K
authors.lastname: Janvier
authors.forename: S
authors.initials: S
authors.lastname: Benichou
authors.forename: J
authors.initials: J
authors.lastname: Mérot
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D051401:Aquaporin 4; D020346:Aquaporins / Q000378:metabolism*; D047390:Casein Kinase II; D002460:Cell Line; D002966:Clathrin / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004285:Dogs; D004705:Endocytosis; D007930:Leucine / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D008969:Molecular Sequence Data; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D021382:Protein Sorting Signals; D021381:Protein Transport; D051381:Rats; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000378:metabolism; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
chemical_list: C496032:Aqp4 protein, rat; D051401:Aquaporin 4; D020346:Aquaporins; D002966:Clathrin; D004268:DNA-Binding Proteins; D021382:Protein Sorting Signals; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D014443:Tyrosine; D012694:Serine; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D007930:Leucine