p42, a novel cyclin-dependent kinase-activating kinase in mammalian cells.
The cyclin-dependent kinase (CDK)-activating kinase (CAK) phosphorylates a conserved threonine residue on CDKs and activates them. Two known classes of CAKs are represented by monomeric Cak1p in budding yeast Saccharomyces cerevisiae and by heterotrimeric CDK7-cyclin H-Mat1 in human and other metazoa. We report here the identification of p42, a novel CAK activity in human cells. p42 has sequence homology to both Cak1p and CDK7 groups of CAKs. p42 is essential for the phosphorylation of Thr-160 and activation of CDK2. A dominant-negative p42 mutant, T161A, and posttranscriptional gene silencing of p42 with RNA(i)-impaired Thr-160 phosphorylation and activity of CDK2. Purified p42 phosphorylated glutathione S-transferase-CDK2 at Thr-160 within the T-loop and activated its histone H1 kinase activity. Finally, p42 is indispensable for cell growth. Cells lacking p42 were incapable of growing and forming colonies whereas cells with a reduced level of p42 grew at significantly slower rates than control cells. Our findings suggest that p42 represents a novel CAK activity in mammalian cells.
Liu
Yu
Y
Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030, USA.
Wu
Chaowei
C
Galaktionov
Konstantin
K
D000595:Amino Acid Sequence; D000818:Animals; D042846:CDC2-CDC28 Kinases / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000235:genetics / Q000378:metabolism*; D029721:Drosophila Proteins / Q000235:genetics; D004789:Enzyme Activation; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D000095043:Cyclin-Dependent Kinase-Activating Kinase
D029721:Drosophila Proteins; D011994:Recombinant Proteins; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D000095043:Cyclin-Dependent Kinase-Activating Kinase