The N-terminal peptide of the Kaposi's sarcoma-associated herpesvirus (KSHV)-cyclin determines substrate specificity.
Cyclin-dependent kinases (Cdks) are activated by cyclin binding and phosphorylation by the Cdk-activating kinase (CAK). Activation of Cdk6 by the D-type cyclins requires phosphorylation of Cdk6 by CAK on threonine 177. In contrast, Cdk6 is activated by the Kaposi's sarcoma-associated herpesvirus (KSHV)-cyclin in the absence and presence of CAK phosphorylation. The activity of Cdk6.KSHV-cyclin complexes was investigated here by analyzing mutants of the KSHV-cyclin and Cdk6 in vitro as well as in U2OS cells. Deletion of the N terminus of the KSHV-cyclin affects the substrate specificity indicating that the N terminus is required for phosphorylation of histone H1 but not for other substrates. Mutation of residues in the region 180-200 of the KSHV-cyclin decreases the binding affinity to Cdk6 in U2OS cells but increases the activity of Cdk6.KSHV-cyclin complexes in vitro indicating that low affinity binding of cyclins to the Cdk subunit might favor increased on- or off-rates of Cdk substrates. Expression of high levels of p16(INK4a) in cells leads to the formation of a heterotrimeric complex composed of Cdk6, KSHV-cyclin, and p16(INK4a). Some of the Cdk6 .KSHV-cyclin.p16 complexes were found to be active indicating that there might be different modes of p16 binding to Cdk6.cyclin complexes.
Kaldis
Philipp
P
Mouse Cancer Genetics Program, National Cancer Institute, NCI-Frederick, Frederick, Maryland 21702-1201, USA. kaldis@ncifcrf.gov
D000255:Adenosine Triphosphate / Q000494:pharmacology; D001483:Base Sequence; D045744:Cell Line, Tumor; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D016213:Cyclins / Q000737:chemistry* / Q000502:physiology*; D004789:Enzyme Activation; D019288:Herpesvirus 8, Human; D006801:Humans; D008969:Molecular Sequence Data; D013379:Substrate Specificity; D014764:Viral Proteins / Q000737:chemistry* / Q000502:physiology*
D016213:Cyclins; D014764:Viral Proteins; D000255:Adenosine Triphosphate; C495911:CDK6 protein, human; D051361:Cyclin-Dependent Kinase 6; D018844:Cyclin-Dependent Kinases