Book of Abstracts: Albany 2003
June 17-21 2003
CDK4 and CDK6 Differ in Their Binding Affinity to p21WAF
G1 phase progression in mammalian cells is provided by a family of cyclin-dependent serine/threonine kinases (CDK). The kinase activity of CDK is mostly regulated by a) cyclin co-factor binding, b) Thr/Tyr phosphorylation and c) binding of INK/WAF family inhibitors. Two early G1 phase kinases, CDK4 and CDK6, consist of two domains with a catalytic cleft "in between" and contain significant homology (~78%) including ATP binding portions, the helix alpha1 part that interacts with cyclin D1-3, catalytic cleft and INK inhibitor binding portion. Both CDK4 and CDK6 are catalytically active in DoHH2 cell line that was derived from malignant follicular lymphoma. Cyclin D-CDK4 complexes contained significant amount of 21WAF and were still active in untreated dividing cells. However, CDK6/cyclin D complexes were p21WAF free. The treatment with transforming growth factor beta1 (TGFbeta1) in vitro led to notable growth arrest that was associated with the inhibition of both CDK4 and CDK6 kinase activity. Moreover, p21WAF was bound to CDK6 due to the treatment. The total level of CDK4, CDK6 and cyclin D type co-factors was unaffected by the treatment, but the assembly of CDK-cyclin D was then disturbed. We hypothesized that CDK4 and CDK6 differ in the affinity to 21WAF. In contrast to the close homology and the similarity in their targets, we speculate that CDK4 and CDK4 are subdued to different regulation circuits in our model cell line.
This work was supported by the Grant 304/01/0564 of Czech Republic Grant Agency and by the Grant MSM111100003 of Czech Ministry of Education, Youth and Sport.
Laboratory of Molecular Pathology