title: Regulation of APC/CCdc20 activity by RASSF1A-APC/CCdc20 circuitry.
abstract: RASSF1A is a key tumor-suppressor gene that is often inactivated in a wide variety of solid tumors. Studies have illustrated that RASSF1A plays vital roles in the regulation of cell-cycle progression and functions as a guardian of mitosis. Nevertheless, the precise mechanism of RASSF1A-dependent regulation of mitosis remains largely unclear. APC/C(Cdc20) is the master switch and regulator of mitosis. The activity of APC/C(Cdc20) is tightly controlled by phosphorylation and specific inhibitors to ensure the sequential ubiquitination of downstream targets. Here, we report on the novel finding of a regulated circuitry that controls the timely expression and hence activity of APC/C(Cdc20) during mitosis. Our study showed that RASSF1A and APC/C(Cdc20) form a molecular relay that regulates the APC/C(Cdc20) activity at early mitosis. We found that RASSF1A inhibits APC/C(Cdc20) function through its D-box motifs. Paradoxically, RASSF1A was also demonstrated to be ubiquitinated by APC/C(Cdc20) in vitro and degraded at prometaphase despite of active spindle checkpoint presence. The first two unique D-boxes at the N-terminal of RASSF1A served as specific degron recognized by APC/C(Cdc20). Importantly, we found that Aurora A and Aurora B directly phosphorylate RASSF1A, a critical step by which RASSF1A switches from being an inhibitor to a substrate of APC/C(Cdc20) during the course of mitotic progression. As a result of RASSF1A degradation, APC/C(Cdc20) can then partially activate the ubiquitination of Cyclin A in the presence of spindle checkpoint. This circuitry is essential for the timely degradation of Cyclin A. To conclude, our results propose a new model for RASSF1A-APC/C(Cdc20) interaction in ensuring the sequential progression of mitosis.
authors.affiliation: Department of Anatomical and Cellular Pathology, State Key Laboratory in Oncology in South China, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China.
authors.forename: C
authors.initials: C
authors.lastname: Chow
authors.forename: N
authors.initials: N
authors.lastname: Wong
authors.forename: M
authors.initials: M
authors.lastname: Pagano
authors.forename: S W-M
authors.initials: SW
authors.lastname: Lun
authors.forename: K-I
authors.initials: KI
authors.lastname: Nakayama
authors.forename: K
authors.initials: K
authors.lastname: Nakayama
authors.forename: K-W
authors.initials: KW
authors.lastname: Lo
mesh_terms: D025601:Adenomatous Polyposis Coli Protein / Q000378:metabolism*; D064107:Aurora Kinase B; D064127:Aurora Kinases; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism*; D019925:Cyclin A / Q000378:metabolism; D057809:HEK293 Cells; D006367:HeLa Cells; D006801:Humans; D008938:Mitosis; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034622:RNA Interference; D014162:Transfection; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C555337:APC protein, human; D025601:Adenomatous Polyposis Coli Protein; D064199:Cdc20 Proteins; D018797:Cell Cycle Proteins; D019925:Cyclin A; C411762:RASSF1 protein, human; D025521:Tumor Suppressor Proteins; C577488:CDC20 protein, human; C576921:AURKB protein, human; D064107:Aurora Kinase B; D064127:Aurora Kinases; D017346:Protein Serine-Threonine Kinases