Degradation of Human RAP80 is Cell Cycle Regulated by Cdc20 and Cdh1 Ubiquitin Ligases

Abstract

Receptor-associated protein 80 (RAP80) is a component of the BRCA1-A complex that recruits BRCA1 to DNA damage sites in the DNA damage-induced ubiquitin signaling pathway. RAP80-depleted cells showed defective G(2)-Mphase checkpoint control. In this study, we show that RAP80 protein levels fluctuate during the cell cycle. Its expression level peaked in the G(2) phase and declined during mitosis and progression into the G(1) phase. Also, RAP80 is polyubiquitinated and degraded by the anaphase-promoting complex (APC/C)(Cdc20) or (APC/C)(Cdh1). Consistent with this, knockdown of Cdc20 or Cdh1 expression by transfecting with small interfering RNAs blocked RAP80 degradation during mitosis or the G1 phase, respectively. A conserved destruction box (D box) in RAP80 affected its stability and ubiquitination, which was dependent on APC/cyclosome(Cdc20) (C-Cdc20) or APC/cyclosome(Cdh1) (C-Cdh1). In addition, overexpression of RAP80 destruction box1 deletion mutant attenuated mitotic progression. Thus, APC/C-Cdc20 or APC/C-Cdh1 complexes regulate RAP80 stability during mitosis to the G(1) phase, and these events are critical for a novel function of RAP80 in mitotic progression.