title: Alpha-kinase 1, a new component in apical protein transport.
abstract: A key aspect in the structure of epithelial cells is the maintenance of a polarized organization based on a highly specific sorting machinery for cargo destined for the apical or the basolateral membrane domain at the exit site of the trans-Golgi network. We could recently identify two distinct post-trans-Golgi network vesicle populations that travel along separate routes to the plasma membrane, a lipid raft-dependent and a lipid raft-independent pathway. A new component of raft-carrying apical vesicles is alpha-kinase 1 (ALPK1), which was identified in immunoisolated vesicles carrying raft-associated sucrase-isomaltase (SI). This kinase was absent from vesicles carrying raft-non-associated lactase-phlorizin hydrolase. The expression of ALPK1 increases by the time of epithelial cell differentiation, whereas the intracellular localization of ALPK1 on apical transport vesicles was confirmed by confocal analysis. A phosphorylation assay on isolated SI-carrying vesicles revealed the phosphorylation of a protein band of about 105 kDa, which could be identified as the motor protein myosin I. Finally, a specific reduction of ALPK1-expression by RNA interference results in a significant decrease in the apical delivery of SI. Taken together, our data suggest that the phosphorylation of myosin I by ALPK1 is an essential process in the apical trafficking of raft-associated SI.
authors.affiliation: Department of Cell Biology and Cell Pathology, Philipps-University Marburg, D-35033 Marburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Heine
authors.forename: Catharina I
authors.initials: CI
authors.lastname: Cramm-Behrens
authors.forename: Athar
authors.initials: A
authors.lastname: Ansari
authors.forename: Hsueh-Ping
authors.initials: HP
authors.lastname: Chu
authors.forename: Alexey G
authors.initials: AG
authors.lastname: Ryazanov
authors.forename: Hassan Y
authors.initials: HY
authors.lastname: Naim
authors.forename: Ralf
authors.initials: R
authors.lastname: Jacob
mesh_terms: D000818:Animals; D019556:COS Cells; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000201:enzymology; D016764:Cell Polarity / Q000502:physiology*; D002522:Chlorocebus aethiops; D004285:Dogs; D004847:Epithelial Cells / Q000201:enzymology*; D005089:Exocytosis / Q000502:physiology; D006801:Humans; D007534:Isomaltose / Q000378:metabolism; D007668:Kidney / Q000166:cytology; D021962:Membrane Microdomains / Q000201:enzymology*; D024461:Myosin Type I / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D021381:Protein Transport / Q000502:physiology; D019311:Staurosporine / Q000494:pharmacology; D021601:trans-Golgi Network / Q000201:enzymology
chemical_list: D047428:Protein Kinase Inhibitors; D007534:Isomaltose; D011494:Protein Kinases; D024461:Myosin Type I; D019311:Staurosporine