title: The interaction of Munc 18 (p67) with the p10 domain of p35 protects in vivo Cdk5/p35 activity from inhibition by TFP5, a peptide derived from p35.
abstract: In a series of studies, we have identified TFP5, a truncated fragment of p35, the Cdk5 kinase regulatory protein, which inhibits Cdk5/p35 and the hyperactive Cdk5/p25 activities in test tube experiments. In cortical neurons, however, and in vivo in Alzheimer's disease (AD) model mice, the peptide specifically inhibits the Cdk5/p25 complex and not the endogenous Cdk5/p35. To account for the selective inhibition of Cdk5/p25 activity, we propose that the "p10" N-terminal domain of p35, absent in p25, spares Cdk5/p35 because p10 binds to macromolecules (e.g., tubulin and actin) as a membrane-bound multimeric complex that favors p35 binding to Cdk5 and catalysis. To test this hypothesis, we focused on Munc 18, a key synapse-associated neuronal protein, one of many proteins copurifying with Cdk5/p35 in membrane-bound multimeric complexes. Here we show that, in vitro, the addition of p67 protects Cdk5/p35 and has no effect on Cdk5/p25 activity in the presence of TFP5. In cortical neurons transfected with p67siRNA, we also show that TFP5 inhibits Cdk5/p35 activity, whereas in the presence of p67 the activity is protected. It does so without affecting any other kinases of the Cdk family of cyclin kinases. This difference may be of significant therapeutic value because the accumulation of the deregulated, hyperactive Cdk5/p25 complex in human brains has been implicated in pathology of AD and other neurodegenerative disorders.
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Niranjana D
authors.initials: ND
authors.lastname: Amin
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Yali
authors.initials: Y
authors.lastname: Zheng
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Binukumar
authors.initials: B
authors.lastname: Bk
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Varsha
authors.initials: V
authors.lastname: Shukla
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Susan
authors.initials: S
authors.lastname: Skuntz
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Philip
authors.initials: P
authors.lastname: Grant
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Joseph
authors.initials: J
authors.lastname: Steiner
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
authors.forename: Manju
authors.initials: M
authors.lastname: Bhaskar
authors.affiliation: National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892 panth@ninds.nih.gov.
authors.forename: Harish C
authors.initials: HC
authors.lastname: Pant
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism; D051360:Cyclin-Dependent Kinase 5 / Q000378:metabolism; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D006801:Humans; D051379:Mice; D051938:Munc18 Proteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism* / Q000502:physiology*; D019636:Neurodegenerative Diseases; D009474:Neurons / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D000072417:Protein Domains; D014404:Tubulin / Q000378:metabolism
chemical_list: D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D010455:Peptides; C497937:STXBP1 protein, human; C118136:TPPP protein, human; D014404:Tubulin; C089495:neuronal Cdk5 activator (p25-p35); D051360:Cyclin-Dependent Kinase 5; C495905:CDK5 protein, human; D018844:Cyclin-Dependent Kinases