A conserved cyclin-binding domain determines functional interplay between anaphase-promoting complex-Cdh1 and Cyclin A-Cdk2 during cell cycle progression

Periodic activity of the anaphase-promoting complex (APC) ubiquitin ligase determines progression through multiple cell cycle transitions by targeting cell cycle regulators for destruction. At the G,IS transition, phosphoryla tion-dependent dissociation of the Cdh1-activating subunit inhibits the APC , allowing stabilization of proteins required for subsequent cell cycle pro gression. Cyclin-dependent kinases (CDKs) that initiate and maintain Cdh1 p hosphorylation have been identified. However, the issue of which cyclin-CDK complexes are involved has been a matter of debate, and the mechanism of h ow cyclin-CDKs interact with APC subunits remains unresolved. Here we subst antiate the evidence that mammalian cyclin A-Cdk2 prevents unscheduled APC reactivation during S phase by demonstrating its periodic interaction with Cdh1 at the level of endogenous proteins. Moreover, we identified a conserv ed cyclin-binding motif within the Cdhl WD-40 domain and show that its disr uption abolished the Cdh1-cyclin A-Cdk2 interaction, eliminated Cdh1-associ ated histone H1 kinase activity, and impaired Cdhl phosphorylation by cycli n A-Cdk2 in vitro and in vivo, Overexpression of cyclin binding-deficient C dhl stabilized the APC-Cdh1 interaction and induced prolonged cell cycle ar rest at the G(1)/S transition. Conversely, cyclin binding-deficient Cdhl lo st its capability to support APC-dependent proteolysis of cyclin A but not that of other APC substrates such as cyclin B and securin Pds1. Collectivel y, these data provide a mechanistic explanation for the mutual functional i nterplay between cyclin A-Cdk2 and APC-Cdh1 and the first evidence that Cdh l may activate the APC by binding specific substrates.