... reduplication. Conversely, Chk1 depletion promotes senescence by inducing p21 binding to cyclin D1– and cyclin E1–CDK complexes and downregulating CDK6, whereas knockdown of the checkpoint kinase Chk2 enables RB phosphorylation and delays G2 exit. In conclusion, p21 and Chk2 oppose Chk1 to maintain RB activity...

...El Kahina Meziane; Suzanne J. Randle; David E. Nelson; Mikhail Lomonosov; Heike Laman Fbxo7 is an unusual F-box protein because most of its interacting proteins are not substrates for ubiquitin-mediated degradation. Fbxo7 directly binds p27 and Cdk6, enhances the level of cyclin D–Cdk6 complexes...