title: Influence of phosphorylation of p35, an activator of cyclin-dependent kinase 5 (cdk5), on the proteolysis of p35.
abstract: Cyclin-dependent kinase 5 (cdk5) is involved in the development of the nervous system and neuronal process outgrowth, and it regulates several intracellular processes including cytoskeletal dynamics. Dysregulation of cdk5 has been implicated in many disorders of the nervous system. The activity of the kinase is regulated by binding of cdk5 activators (p35, p39, p67). We examined the phosphorylation of p35, and the role of phosphorylation in regulating the proteolysis of the p35 protein. By detecting changes in electrophoretic mobility, we observed that a significant proportion of p35 is phosphorylated in rat brain tissue. In cultured neurons, the phosphorylation was prevented by roscovitine, an inhibitor of cdk5 and some other cdks. The phosphatase inhibitor okadaic acid induced p35 degradation in neuronal cultures which was sensitive to the proteasome inhibitor lactacystin. These latter results agree with some previous studies showing that phosphorylation regulates proteasomal degradation of p35. Treatment of brain homogenate with okadaic acid in the presence of ATP led to accumulation of p35 phosphorylated also by a kinase that was not inhibited by roscovitine. This implies that the effect of okadaic acid on p35 degradation could also be contributed by a non-cdk kinase. The calpain protease has been shown to cleave p35. Our results suggest that this process may also be modulated by p35 phosphorylation under some conditions. We conclude that p35 phosphorylation influences the proteasome-mediated degradation of p35 and calpain-mediated cleavage of p35 to p25.
authors.affiliation: Department of Neuroscience and Neurology, University of Kuopio, P.O. Box 1627, Finland. petri.kerokoski@uku.fi
authors.forename: Petri
authors.initials: P
authors.lastname: Kerokoski
authors.forename: Tiina
authors.initials: T
authors.lastname: Suuronen
authors.forename: Antero
authors.initials: A
authors.lastname: Salminen
authors.forename: Hilkka
authors.initials: H
authors.lastname: Soininen
authors.forename: Tuula
authors.initials: T
authors.lastname: Pirttilä
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D001923:Brain Chemistry; D002154:Calpain / Q000378:metabolism; D002478:Cells, Cultured; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology; D009097:Multienzyme Complexes / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D019319:Okadaic Acid / Q000494:pharmacology; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D011687:Purines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D000077546:Roscovitine
chemical_list: D004791:Enzyme Inhibitors; D009097:Multienzyme Complexes; D009419:Nerve Tissue Proteins; D011687:Purines; C089495:neuronal Cdk5 activator (p25-p35); D000077546:Roscovitine; C067713:lactacystin; D019319:Okadaic Acid; D000255:Adenosine Triphosphate; D051360:Cyclin-Dependent Kinase 5; C495907:Cdk5 protein, rat; D018844:Cyclin-Dependent Kinases; D002154:Calpain; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine