Accumulation of cyclin B1 requires E2F and cyclin-A-dependent rearrangement of the anaphase-promoting complex

Abstract

In mammalian somatic-cell cycles, progression through the G1-phase restriction point and initiation of DNA replication are controlled by the ability of the retinoblastoma tumour-suppressor protein (pRb) family to regulate the E2F/DP transcription factors. Continuing transcription of E2F target genes beyond the G1/S transition is required for coordinating S-phase progression with cell division, a process driven by cyclin-B-dependent kinase and anaphase-promoting complex (APC)-mediated proteolysis. How E2F-dependent events at G1/S transition are orchestrated with cyclin B and APC activity remains unknown. Here, using an in vivo assay to measure protein stability in real time during the cell cycle, we show that repression of E2F activity or inhibition of cyclin-A-dependent kinase in S phase triggers the destruction of cyclin B1 through the re-assembly of APC, the ubiquitin ligase that is essential for mitotic cyclin proteolysis, with its activatory subunit Cdh1. Phosphorylation-deficient mutant Cdh1 or immunodepletion of cyclin A resulted in assembly of active Cdh1-APC even in S-phase cells. These results implicate an E2F-dependent, cyclin A/Cdk2-mediated phosphorylation of Cdh1 in the timely accumulation of cyclin B1 and the coordination of cell-cycle progression during the post-restriction point period.

Regulation of APCCdh1 E3 ligase activity by the Fbw7/cyclin E signaling axis contributes to the tumor suppressor function of Fbw7

“…More importantly, we further demonstrated that ectopic expression of cyclin E led to an increase in the phosphorylation of endogenous Cdh1 ( Figure 4H), whereas depletion of cyclin E resulted in a sharp decrease in endogenous Cdh1 phosphorylation ( Figure 4I). Therefore, consistent with previous reports [25,44,45], these results support a model that the Fbw7/cyclin E signaling pathway potentially regulates the E3 ligase activity of APC Cdh1 by affecting the interaction of Cdh1 with the APC core subunit primarily through regulating Cdh1 phosphorylation status ( Figure 6). …”

“…It was previously reported that phosphorylation of Cdh1 by Cdk2/cyclin A at multiple sites (S40, T121, S151 and S163) located at the N terminus of Cdh1 could lead to the dissociation of Cdh1 from the APC/C core subunit, thus terminating the E3 ligase activity of APC Cdh1 before S phase entry [44]. Later work by Keck et al [25] expanded this finding by demonstrating that Cdk2/cyclin E could also phosphorylate Cdh1 to inactivate Cdh1.…”

A model for restriction point control of the mammalian cell cycle

“…ak, J.J. Tyson / Journal of Theoretical Biology 230 (2004) 563-579At Start, Cdh1 must be inactivated so that mitotic cyclins may reappear. In budding yeast, this is the job of Clb5/Cdc28 (Shirayama et al, 1999), and in mammalian cells, of CycA/Cdk2 (Lukas et al, 1999). More on this shortly.…”

Cyclin A/cdk2 coordinates centrosomal and nuclear mitotic events

“…Cyclin A/cdk2 appears to be involved in the activation (Furuno et al, 1999;Mitra and Enders, 2004), and possibly the stabilization of cyclin B, the latter by indirectly inhibiting the anaphase-promoting complex/cyclosome (APC/C) (Lukas et al, 1999). Cyclin A is itself destroyed by the APC/C at prometaphase (den Elzen and Pines, 2001) inferring that its activity is required until that time.…”