Synergistic blockade of mitotic exit by two chemical inhibitors of the APC/C

Authors: 
Katharine L. Sackton1*, Nevena Dimova1*, Xing Zeng1*, Wei Tian2{*, Mengmeng Zhang1, Timothy B. Sackton3, Johnathan Meaders1, Kathleen L. Pfaff1{, Frederic Sigoillot1{, Hongtao Yu2,4, Xuelian Luo2 & Randall W. King1
Journal Citation: 
Nature 2014
Date Published: 
August 24, 2014
PMID: 
doi:10.1038/nature13660

Protein machines are multi-subunit protein complexes that orchestrate highly regulated biochemical tasks. An example is the anaphase-promoting complex/cyclosome (APC/C), a 13-subunit ubiquitin ligase that initiates the metaphase–anaphase transition and mitotic exit by targeting proteins such as securin and cyclin B1 for ubiquitin-dependent destruction by the proteasome12. Because blocking mitotic exit is an effective approach for inducing tumour cell death34, the APC/C represents a potential novel target for cancer therapy. APC/C activation in mitosis requires binding of Cdc20 (ref. 5), which forms a co-receptor with the APC/C to recognize substrates containing a destruction box (D-box)67891011121314. Here we demonstrate that we can synergistically inhibit APC/C-dependent proteolysis and mitotic exit by simultaneously disrupting two protein–protein interactions within the APC/C–Cdc20–substrate ternary complex. We identify a small molecule, called apcin (APC inhibitor), which binds to Cdc20 and competitively inhibits the ubiquitylation of D-box-containing substrates. Analysis of the crystal structure of the apcin–Cdc20 complex suggests that apcin occupies the D-box-binding pocket on the side face of the WD40-domain. The ability of apcin to block mitotic exit is synergistically amplified by co-addition of tosyl-L-arginine methyl ester, a small molecule that blocks the APC/C–Cdc20 interaction1516. This work suggests that simultaneous disruption of multiple, weak protein–protein interactions is an effective approach for inactivating a protein machine.