title: Cyclin-dependent kinase 5 promotes insulin exocytosis.
abstract: Cyclin-dependent kinase 5 (Cdk5) is widely expressed although kinase activity has been described preferentially in neuronal systems. Cdk5 has an impact on actin polymerization during neuronal migration and neurite outgrowth and deregulation of the kinase has been implicated in the promotion of neurodegeneration. Recently it was shown that Cdk5 modulates dopamine signaling in neurons by regulating DARPP-32 function. In addition, Cdk5 phosphorylates munc-18 and synapsin I, two essential components of the exocytotic machinery. We have shown by reverse transcriptase-polymerase chain reaction, immunocytochemistry, and Western blotting that Cdk5 is present in the insulin-secreting pancreatic beta-cell. Subcellular fractionation of isolated beta-cells revealed a glucose-induced translocation of membrane-bound Cdk5 protein to lower density fractions. Inhibition of Cdk5 with roscovitine reduced insulin secretion with approximately 35% compared with control after glucose stimulation and with approximately 65% after depolarization with glucose and KCl. Capacitance measurements performed on single beta-cells that expressed a dominant-negative Cdk5 mutant showed impaired exocytosis. The effect on exocytosis by Cdk5 appeared to be independent of changes in free cytoplasmic Ca(2+) concentration. Taken together these results show that Cdk5 is present in beta-cells and acts as a positive regulator of insulin exocytosis.
authors.affiliation: Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Institutet, Karolinska Hospital, S-171 76 Stockholm, Sweden.
authors.forename: L
authors.initials: L
authors.lastname: Lilja
authors.forename: S N
authors.initials: SN
authors.lastname: Yang
authors.forename: D L
authors.initials: DL
authors.lastname: Webb
authors.forename: L
authors.initials: L
authors.lastname: Juntti-Berggren
authors.forename: P O
authors.initials: PO
authors.lastname: Berggren
authors.forename: C
authors.initials: C
authors.lastname: Bark
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D002118:Calcium / Q000378:metabolism / Q000494:pharmacology; D002465:Cell Movement; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases / Q000502:physiology*; D003593:Cytoplasm / Q000378:metabolism; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis; D005799:Genes, Dominant; D005947:Glucose / Q000378:metabolism; D006131:Growth Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D007328:Insulin / Q000378:metabolism*; D007515:Islets of Langerhans / Q000378:metabolism; D051379:Mice; D008820:Mice, Obese; D009474:Neurons / Q000378:metabolism*; D010766:Phosphorylation; D011189:Potassium Chloride / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077546:Roscovitine; D013347:Subcellular Fractions; D013395:Sucrose / Q000494:pharmacology; D013997:Time Factors; D014162:Transfection
chemical_list: D000199:Actins; D004791:Enzyme Inhibitors; D006131:Growth Inhibitors; D007328:Insulin; D011687:Purines; D012333:RNA, Messenger; D000077546:Roscovitine; D013395:Sucrose; D011189:Potassium Chloride; D051360:Cyclin-Dependent Kinase 5; C495906:Cdk5 protein, mouse; D018844:Cyclin-Dependent Kinases; D005947:Glucose; D002118:Calcium