title: Effects of cyclin-dependent kinase-5 activity on apoptosis and tau phosphorylation in immortalized mouse brain cortical cells.
abstract: Cyclin-dependent kinase-5 (CDK5), a unique CDK family member, is active primarily in the central nervous system (CNS). Previous studies suggest that CDK5 is proapoptotic and contributes to tau hyperphosphorylation and neurodegeneration in Alzheimer's disease. The objective of this study was to examine CDK5 effects on apoptotic progression and tau phosphorylation. Immortalized embryonic mouse brain cortical cells were used to establish a stable cell line that overexpressed wild-type human tau. In these studies, thapsigargin, which induces endoplasmic reticulum stress and can cause accumulation of misfolded proteins, was used to induce apoptosis. Caspase-3 activity and poly-(ADP-ribose)-polymerase (PARP) cleavage, as measures of apoptosis, were significantly increased 24 and 48 hr after thapsigargin treatment, and these events were unaffected by tau expression. Although transient coexpression of CDK5 and its activator, p25, increased CDK5 activity greater than tenfold, increases in caspase-3 activity in response to thapsigargin treatment were unaffected by the presence of CDK5/p25. Tau phosphorylation at the PHF-1 epitope, but not the Tau-1 epitope, was increased significantly in CDK5/p25-transfected cells compared to cells transfected with dominant negative CDK5 (DNCDK5). The PHF-1 epitope remained phosphorylated until 48 hr after thapsigargin treatment in the CDK5/p25-transfected cells. Over the course of apoptosis in this model, phosphorylation of the Tau-1 epitope was unaffected in cells transfected with DNCDK5, vector, or CDK5/p25. In summary, these results demonstrate that CDK5 does not have a significant impact on tau phosphorylation and thapsigargin-induced apoptosis in this neuronal cell model.
authors.affiliation: Department of Psychiatry, University of Alabama at Birmingham, Birmingham, Alabama 35294-0001, USA.
authors.forename: Shirley B
authors.initials: SB
authors.lastname: Shelton
authors.forename: Pavan
authors.initials: P
authors.lastname: Krishnamurthy
authors.forename: Gail V W
authors.initials: GV
authors.lastname: Johnson
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D000911:Antibodies, Monoclonal / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002540:Cerebral Cortex / Q000166:cytology / Q000378:metabolism / Q000502:physiology*; D000090266:Chromobox Protein Homolog 5; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases / Q000502:physiology*; D004318:Doxycycline / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D020536:Enzyme Activators / Q000494:pharmacology; D000939:Epitopes / Q000187:drug effects / Q000502:physiology; D006801:Humans; D051379:Mice; D009419:Nerve Tissue Proteins / Q000378:metabolism; D009474:Neurons / Q000378:metabolism / Q000502:physiology*; D010766:Phosphorylation; D010957:Plasmids / Q000235:genetics; D019284:Thapsigargin / Q000494:pharmacology; D014162:Transfection; D016875:tau Proteins / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D000911:Antibodies, Monoclonal; C000715594:CBX5 protein, human; D020536:Enzyme Activators; D000939:Epitopes; D009419:Nerve Tissue Proteins; C085349:PHF-1 monoclonal antibody; C089495:neuronal Cdk5 activator (p25-p35); D016875:tau Proteins; D000090266:Chromobox Protein Homolog 5; D019284:Thapsigargin; D051360:Cyclin-Dependent Kinase 5; C495905:CDK5 protein, human; C495906:Cdk5 protein, mouse; D018844:Cyclin-Dependent Kinases; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D004318:Doxycycline