title: An APC/C inhibitor stabilizes cyclin B1 by prematurely terminating ubiquitination.
abstract: The anaphase-promoting complex/cyclosome (APC) is a ubiquitin ligase that is required for exit from mitosis. We previously showed that tosyl arginine methyl ester (TAME) inhibits APC-dependent proteolysis by competing with the C-terminal isoleucine-arginine tail of the APC activator cell division cycle 20 (Cdc20) for APC binding. Here we show that in the absence of APC substrates, TAME ejects Cdc20 from the APC by promoting Cdc20 autoubiquitination in its N-terminal region. Cyclin B1 antagonizes TAME's effect by promoting binding of free Cdc20 to the APC and by suppressing Cdc20 autoubiquitination. Nevertheless, TAME stabilizes cyclin B1 in Xenopus extracts by two mechanisms. First, it reduces the k(cat) of the APC-Cdc20-cyclin B1 complex without affecting the K(m), slowing the initial ubiquitination of unmodified cyclin B1. Second, as cyclin B1 becomes ubiquitinated, it loses its ability to promote Cdc20 binding to the APC in the presence of TAME. As a result, cyclin B1 ubiquitination terminates before reaching the threshold necessary for proteolysis.
authors.affiliation: Department of Cell Biology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Xing
authors.initials: X
authors.lastname: Zeng
authors.forename: Randall W
authors.initials: RW
authors.lastname: King
mesh_terms: D000595:Amino Acid Sequence; D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D001120:Arginine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001483:Base Sequence; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D002457:Cell Extracts; D056744:Cyclin B1 / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology; D019938:Cyclin D1 / Q000235:genetics / Q000378:metabolism*; D005260:Female; D008938:Mitosis / Q000187:drug effects; D008969:Molecular Sequence Data; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism; D043743:Ubiquitin-Protein Ligase Complexes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects; D014981:Xenopus; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D064199:Cdc20 Proteins; C577501:Cdc20 protein, Xenopus; D018797:Cell Cycle Proteins; D002457:Cell Extracts; D056744:Cyclin B1; D029867:Xenopus Proteins; D019938:Cyclin D1; C026512:arginine methyl ester; D001120:Arginine; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome