Examining the mechanistic relationship of APC/C^CDH1 and its interphase inhibitor EMI1

Abstract

Proper protein destruction by the ubiquitin (Ub)-proteasome system is vital for a faithful cell cycle. Hence, the activity of Ub ligases is tightly controlled. The Anaphase-Promoting Complex/Cyclosome (APC/C) is a 1.2 MDa Ub ligase responsible for mitotic progression and G1 maintenance. At the G1/S transition, the APC/C is inhibited by EMI1 to prevent APC/C-dependent polyubiquitination of cell cycle effectors. EMI1 uses several interaction motifs to block the recruitment of APC/C substrates as well as the APC/C-associated E2s, UBE2C, and UBE2S. Paradoxically, EMI1 is also an APC/C substrate during G1. Using a comprehensive set of enzyme assays, we determined the context-dependent involvement of the EMI1 motifs in APC/C-dependent ubiquitination of EMI1 and other substrates. Furthermore, we demonstrated that an isolated C-terminal peptide fragment of EMI1 activates APC/Cdependent substrate priming by UBE2C. Together, these findings reveal the multiple roles of the EMI1 C-terminus for G1 maintenance and the G1/S transition.

Activities and binding partners of E3 ubiquitin ligase DTX3L and its roles in cancer

“…Based on their Ub transfer mechanisms, E3 ligases are classified as homologous to E6AP carboxyl terminus (HECT), RING-between-RING (RBR) and really interesting new gene (RING) proteins. There are over 600 RING-type E3 ligases and only some of them, such as the homodimeric IDOL [8,9] , the BRCA1/BARD1 heterodimer [10][11][12] , and the anaphase promoting complex/cyclosome (APC/C) [13][14][15] have been well characterised and validated as potential drug targets [16,17] . These findings stress the importance that the functional consequences of ubiquitination mediated by RING-type E3 ligases have and that there is a need to systematically characterise E3 ligases in order to understand their roles in signalling pathways.…”