Distinct Activation Pathways Confer Cyclin-Binding Specificity on Cdk1 and Cdk2 in Human Cells

Abstract

Summary In metazoans, different cyclin-dependent kinases (CDKs) bind preferred cyclin partners to coordinate cell division. Here we investigate these preferences in human cells, and show that cyclin A assembles with Cdk1 only after complex formation with Cdk2 reaches a plateau, in late S and G2 phases. To understand the basis for Cdk2’s competitive advantage despite Cdk1’s greater abundance, we dissect their activation pathways by chemical genetics. Cdk1 and Cdk2 are activated by kinetically distinct mechanisms, even though they share the same CDK-activating kinase (CAK), Cdk7. We recapitulate cyclin A’s selectivity for Cdk2 in extracts, and override it with a yeast CAK that phosphorylates monomeric Cdk1, redirecting Cdk1 into a pathway normally restricted to Cdk2. Conversely, upon Cdk7 inhibition in vivo, cyclin B, which normally binds Cdk1 nearly exclusively, is diverted to Cdk2. Therefore, differential ordering of common activation steps promotes CDK-cyclin specificity, with Cdk7 acting catalytically to enforce fidelity.

Cyclin A–Cdk1 regulates the origin firing program in mammalian cells

“…S2 A). These results are consistent with the recent report that cyclin A2 starts to form a complex with Cdk1 at mid-S phase (21). Cyclin A2-Cdk1 activity was detected earlier and enhanced in Chk1 del/Ϫ MEFs when compared with Chk1 lox/Ϫ MEFs (Fig.…”

“…S8), the origin activation program appeared to be regulated not only by induction of Cdks and their binding to prereplicative complex components, but also by alternative ways such as complex formation with cyclins or regulation of inhibitory phosphorylation of Cdks. In this regard, it was very recently reported that Cdk1 started to form a complex with cyclin A2 after cyclin A2-Cdk2 complexes reached a plateau in mid S phase (21). Taken together, our results suggest that cyclin A2-Cdk1 may regulate origin firing program through both its specific accessibility to late origins and regulation of Cdk1 activity at late S phase.…”

Chk1–cyclin A/Cdk1 axis regulates origin firing programs in mammals

“…These results are consistent with those of a recent study using centrifugal cell elutriation which showed that cyclin A assembles with Cdk1 only after complex formation with Cdk2 reaches a plateau during late S and G2 phases (Merrick et al 2008). Importantly, cyclin A2-Cdk1 activity was detected earlier and was enhanced in Chk1 del/− MEFs.…”

Chemical-genetic analysis of cyclin dependent kinase 2 function reveals an important role in cellular transformation by multiple oncogenic pathways

“…In primary human tumors, CDK2 abundance is frequently found to be elevated severalfold, and its associated kinase activity may be elevated up to 40-fold compared with nontumorigenic tissues (4)(5)(6)(7)23). Both CDK2 AS and CDK2 WT MEFs expressed human protein ∼10-fold higher than endogenous mouse CDK2 (24) (Fig. S1 E and F).…”