title: MAL decreases the internalization of the aquaporin-2 water channel.
abstract: Body water homeostasis depends critically on the hormonally regulated trafficking of aquaporin-2 (AQP2) water channels in renal collecting duct epithelial cells. Several types of posttranslational modifications are clearly involved in controlling the distribution of AQP2 between intracellular vesicles and the apical plasma membrane. Little is known, however, about the protein interactions that govern the trafficking of AQP2 between these organelles. MAL is a detergent-resistant membrane-associated protein implicated in apical sorting events. We wondered, therefore, whether MAL plays a role in the regulated trafficking of AQP2 between intracellular vesicles and the apical surface. We find that AQP2 and MAL are coexpressed in epithelial cells of the kidney collecting duct. These two proteins interact, both in the native kidney and when expressed by transfection in cultured cells. The S256-phosphorylated form of AQP2 appears to interact more extensively with MAL than does the water channel protein not phosphorylated at this serine. We find that MAL is not involved in detergent-resistant membrane association or apical delivery of AQP2 in LLC-PK(1) renal epithelial cells. Instead, MAL increases the S256 phosphorylation and apical surface expression of AQP2. Furthermore, internalization experiments show that MAL induces surface expression of AQP2 by attenuating its internalization. Thus, the involvement of MAL in the cell surface retention of apical membrane proteins could play an important role in regulated absorption and secretion in transporting epithelia.
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, 333 Cedar Street, New Haven, CT 06520, USA.
authors.forename: Erik-Jan
authors.initials: EJ
authors.lastname: Kamsteeg
authors.forename: Amy S
authors.initials: AS
authors.lastname: Duffield
authors.forename: Irene B M
authors.initials: IB
authors.lastname: Konings
authors.forename: Joanna
authors.initials: J
authors.lastname: Spencer
authors.forename: Philipp
authors.initials: P
authors.lastname: Pagel
authors.forename: Peter M T
authors.initials: PM
authors.lastname: Deen
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Caplan
mesh_terms: D000818:Animals; D051399:Aquaporin 2 / Q000032:analysis / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D003902:Detergents / Q000737:chemistry; D007685:Kidney Tubules, Collecting / Q000737:chemistry / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000032:analysis / Q000378:metabolism*; D009185:Myelin Proteins / Q000032:analysis / Q000378:metabolism*; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D010766:Phosphorylation; D021381:Protein Transport; D011510:Proteolipids / Q000032:analysis / Q000378:metabolism*
chemical_list: D051399:Aquaporin 2; D003902:Detergents; D026901:Membrane Transport Proteins; D009185:Myelin Proteins; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D011510:Proteolipids