The roles of Fzy/Cdc20 and Fzr/Cdh1 in regulating the destruction of cyclin B in space and time

Abstract

In Drosophila cells cyclin B is normally degraded in two phases: (a) destruction of the spindle-associated cyclin B initiates at centrosomes and spreads to the spindle equator; and (b) any remaining cytoplasmic cyclin B is degraded slightly later in mitosis. We show that the APC/C regulators Fizzy (Fzy)/Cdc20 and Fzy-related (Fzr)/Cdh1 bind to microtubules in vitro and associate with spindles in vivo. Fzy/Cdc20 is concentrated at kinetochores and centrosomes early in mitosis, whereas Fzr/Cdh1 is concentrated at centrosomes throughout the cell cycle. In syncytial embryos, only Fzy/Cdc20 is present, and only the spindle-associated cyclin B is degraded at the end of mitosis. A destruction box–mutated form of cyclin B (cyclin B triple-point mutant [CBTPM]–GFP) that cannot be targeted for destruction by Fzy/Cdc20, is no longer degraded on spindles in syncytial embryos. However, CBTPM–GFP can be targeted for destruction by Fzr/Cdh1. In cellularized embryos, which normally express Fzr/Cdh1, CBTPM–GFP is degraded throughout the cell but with slowed kinetics. These findings suggest that Fzy/Cdc20 is responsible for catalyzing the first phase of cyclin B destruction that occurs on the mitotic spindle, whereas Fzr/Cdh1 is responsible for catalyzing the second phase of cyclin B destruction that occurs throughout the cell. These observations have important implications for the mechanisms of the spindle checkpoint.

Anaphase-promoting complex-dependent proteolysis of cell cycle regulators and genomic instability of cancer cells

“…Recently, it has been shown that interaction between Mad2 and Cdc20 requires Cdk activity (Chung and Chen, 2003;D'Angiolella et al, 2003). When the spindle checkpoint is activated, the proteolytic destruction of securin (Zur and Brandeis, 2001) and cyclin B (Raff et al, 2002) by APC Cdc20 is inhibited, which leads to cell cycle arrest with unseparated chromatids (Cohen-Fix et al, 1996;Zou et al, 1999b), avoiding the risk of chromosome missegregation and mitotic catastrophe. Spindle checkpointdeficient cells develop numerical chromosome instabilities, as reported for a number of different cancers such as colon, lung, breast and bladder cancer, and leukemia and lymphoma cells, where mutations in the Mad and Bub genes are identified especially in the kinetochore localization domain (Cahill et al, 1998;Masuda and Takahashi, 2002;Ru et al, 2002).…”

The benefits of local depletion: The centrosome as a scaffold for ubiquitin-proteasome-mediated degradation

“…A non-degradable allele of cyclin B obtained by mutating its APC/C binding sites persists on centrosomes throughout mitosis, suggesting cyclin B removal from metaphase centrosomes involves its polyubiquitination and subsequent degradation. 60 APC/C-mediated cyclin B degradation requires Vihar, an E2 ubiquitin-conjugating enzyme that also localizes to centrosomes during metaphase before disappearing as mitosis progresses ( Fig. 2A, bottom panel).…”

HEF1-Aurora A Interactions: Points of Dialog between the Cell Cycle and Cell Attachment Signaling Networks

“…1G), centrosomes are centers for ubiquitination activity, governing the action of the anaphase promoting complex/ cyclosome (APC/C) in causing the degradation of substrates such as cyclin B. [45][46][47] Separate studies indicate that the centrosome may also nucleate cellular degradation and proteasome activation at other phases in the cell cycle as well. 48 In 2001, Piel et al made the intriguing observation that the mother centriole must undergo an excursion to the region of the midbody to allow completion of cytokinesis, suggesting delivery of some final signal to promote excision.…”