Cyclin-dependent kinase 5 associated with p39 promotes Munc18-1 phosphorylation and Ca(2+)-dependent exocytosis |
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Authors: | Lilja Lena Johansson Jenny Ulrika Gromada Jesper Mandic Slavena Andrea Fried Gabriel Berggren Per-Olof Bark Christina |
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Institution: | Department of Molecular Medicine, Karolinska Institutet, Karolinska University Hospital, SE-171 76 Stockholm, Sweden. |
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Abstract: | Cyclin-dependent kinase 5 (Cdk5) is a proline-directed serine/threonine protein kinase that requires association with a regulatory protein, p35 or p39, to form an active enzyme. Munc18-1 plays an essential role in membrane fusion, and its function is regulated by phosphorylation. We report here that both p35 and p39 were expressed in insulin-secreting beta-cells, where they exhibited individual subcellular distributions and associated with membranous organelles of different densities. Overexpression of Cdk5, p35, or p39 showed that Cdk5 and p39 augmented Ca(2+)-induced insulin exocytosis. Suppression of p39 and Cdk5, but not of p35, by antisense oligonucleotides selectively inhibited insulin exocytosis. Transient transfection of primary beta-cells with Munc18-1 templates mutated in potential Cdk5 or PKC phosphorylation sites, in combination with Cdk5 and the different Cdk5 activators, suggested that Cdk5/p39-promoted Ca(2+)-dependent insulin secretion from primary beta-cells by phosphorylating Munc18-1 at a biochemical step immediately prior to vesicle fusion. |
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