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J. Biol. Chem., Vol. 280, Issue 27, 25637-25643, July 8, 2005

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-Kinase 1, a New Component in Apical Protein Transport^*

Martin Heine, Catharina I. Cramm-Behrens, Athar Ansari, Hsueh-Ping Chu, Alexey G. Ryazanov, Hassan Y. Naim¶, and Ralf Jacob||

From the Department of Cell Biology and Cell Pathology, Philipps-University Marburg, D-35033 Marburg, Germany, the Department of Pharmacology, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, Piscataway, New Jersey 08854-5635, and the^¶ Department of Physiological Chemistry, School of Veterinary Medicine D-30559 Hannover, Germany

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 -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.

Received for publication, February 28, 2005 , and in revised form, April 14, 2005.

^* This work was supported by the Deutsche Forschungsgemeinschaft, Bonn, Germany Grants JA 1033/1-2 (to H. Y. N. and R. J.) and Sonderforschungsbereich 593 (to R. J.) and by the National Institute of Health Grants RO1 GM57300 and RO1 CA81102 (to A. G. R.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement"in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^|| To whom correspondence should be addressed: Dept. of Cell Biology and Cell Pathology, University of Marburg, Robert-Koch-Str. 6, D-35033 Marburg, Germany. Tel.: 49-6421-286-6482; Fax: 49-6421-286-6414; E-mail: jacob{at}staff.uni-marburg.de.

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