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Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

New findings (Burton et al., 2005; Kraft et al., 2005) demonstrate the direct recognition of D and KEN boxes, short sequence elements in substrates of the anaphase-promoting complex/cyclosome (APC/C), by APC/C coactivators and indicate a special role for the D box in the assembly of catalytically active APC/C.
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PMID:The D box asserts itself. 1594 34

The anaphase-promoting complex/cyclosome (APC/C) is a multisubunit E3 ligase required for ubiquitin-dependent proteolysis of cell-cycle-regulatory proteins, including mitotic cyclins and securin/Pds1. Regulation of APC/C activity and substrate recognition, mediated by the coactivators Cdc20 and Cdh1, is fundamental to cell-cycle control. However, the precise mechanism by which coactivators stimulate APC/C ubiquitylation activity and the nature of the substrate-binding sites on the activated APC/C are not understood. Here, we show that the optimal interaction of substrate with APC/C is dependent specifically on the simultaneous association of coactivator. This is consistent with a model whereby both core APC/C subunits and coactivators contribute recognition sites for substrates, accounting for the bipartite nature (D and KEN boxes) of most APC/C degradation signals. A direct and stoichiometric function for the coactivators could explain how specific substrates are recognized by APC/C in a cell-cycle-specific manner, and how coactivator stimulates APC/C ubiquitylation activity.
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PMID:Coactivator functions in a stoichiometric complex with anaphase-promoting complex/cyclosome to mediate substrate recognition. 1611 54

TPX2, a microtubule-associated protein, is required downstream of Ran-GTP to induce spindle assembly. TPX2 activity appears to be tightly regulated during the cell cycle, and we report here one molecular mechanism for this regulation. We found that TPX2 protein levels are cell cycle regulated, peaking in mitosis and declining sharply during mitotic exit. TPX2 is degraded in mitotic extracts, as well as in HeLa cells exiting from mitosis. This instability depends, both in vitro and in vivo, on the anaphase-promoting complex/cyclosome (APC/C), a ubiquitin ligase that controls mitotic progression. In a reconstituted system, TPX2 is efficiently ubiquitinated by APC/C that has been activated by Cdh1. Two discrete elements in TPX2 are required for recognition by APC/C(Cdh1): a KEN box and a novel element in amino acids 1 to 86. Interestingly, the latter element, which has no known APC/C recognition motifs, is required for the ubiquitination of TPX2 by APC/C(Cdh1) in vitro and for its degradation in vivo. We conclude that APC/C(Cdh1) controls the stability of TPX2, thereby ensuring accurate regulation of the spindle assembly in the cell cycle.
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PMID:Anaphase-promoting complex/cyclosome controls the stability of TPX2 during mitotic exit. 1628 63

The spindle checkpoint is a cell cycle surveillance mechanism that ensures the fidelity of chromosome segregation during mitosis and meiosis. Bub1 is a protein serine-threonine kinase that plays multiple roles in chromosome segregation and the spindle checkpoint. In response to misaligned chromosomes, Bub1 directly inhibits the ubiquitin ligase activity of the anaphase-promoting complex or cyclosome (APC/C) by phosphorylating its activator Cdc20. The protein level and the kinase activity of Bub1 are regulated during the cell cycle; they peak in mitosis and are low in G1/S phase. Here we show that Bub1 is degraded during mitotic exit and that degradation of Bub1 is mediated by APC/C in complex with its activator Cdh1 (APC/C(Cdh1)). Overexpression of Cdh1 reduces the protein levels of ectopically expressed Bub1, whereas depletion of Cdh1 by RNA interference increases the level of the endogenous Bub1 protein. Bub1 is ubiquitinated by immunopurified APC/C(Cdh1) in vitro. We further identify two KEN-box motifs on Bub1 that are required for its degradation in vivo and ubiquitination in vitro. A Bub1 mutant protein with both KEN-boxes mutated is stable in cells but fails to elicit a cell cycle phenotype, indicating that degradation of Bub1 by APC/C(Cdh1) is not required for mitotic exit. Nevertheless, our study clearly demonstrates that Bub1, an APC/C inhibitor, is also an APC/C substrate. The antagonistic relationship between Bub1 and APC/C may help to prevent the premature accumulation of Bub1 during G1.
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PMID:KEN-box-dependent degradation of the Bub1 spindle checkpoint kinase by the anaphase-promoting complex/cyclosome. 1715 72

Cyclin A is targeted for mitotic destruction by the anaphase promoting complex/cyclosome (APC/C) and degradation proceeds even when proteolysis of other APC/C substrates are blocked by the spindle assembly checkpoint. Instead of a simple destruction box, a complex N-terminal destruction signal has been implicated in Cyclin A. We show here that Drosophila Cyclin A destruction employs both N- and C-terminal residues, which emphasize that a synergistic action by different parts of the protein facilitates recognition and degradation. The first KEN box, first D-box and an aspartic acid at position 70 are required at the N-terminus and they make additive contributions when the spindle checkpoint is active. From the C-terminal region, the cyclin box contributes. Single point mutations in these four elements abolish mitotic destruction. Additionally, eight lysines in the neighborhood of the N-terminal signals, which could serve as potential ubiquitin acceptor sites, are preferentially used for proteolysis. Mutations in these lysines and the N-terminal signals cause mitotic stability. However, mutating the lysines alone, only delays mitotic progression. Thus, presumably, lysines elsewhere in the protein are used when the preferred ones are absent and this requires the N-terminal signals. Furthermore, our results suggest that some function of the cyclin box other than Cdk1 binding promotes spindle checkpoint-independent recognition of Cyclin A by the APC/C.
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PMID:Cyclin A degradation employs preferentially used lysines and a cyclin box function other than Cdk1 binding. 1731 14

We reported here an efficient and generally applicable genomic analysis that uses transcriptional profiling to identify candidate substrates of regulatory enzymes, such as kinases and ubiquitin ligases. We applied this strategy to the anaphase-promoting complex/cyclosome (APC/C), a ubiquitin ligase that controls sister chromatid separation and exit from mitosis. We found that a microtubule-associated protein, CKAP2, is a substrate of APC/C and demonstrated that ubiquitination and degradation of CKAP2 in vitro require a KEN-box and is mediated by Cdh1, an activator of APC/C. We showed that the levels of CKAP2 fluctuated across the cell cycle in culture cells, high in mitosis and low during mitotic exit. Overexpression of Cdh1 reduced the levels of CKAP2 in a KEN-box-dependent manner, while knockdown of Cdh1 increased the half-life of CKAP2. CKAP2 associated with centrosomal microtubules in late G(2), but only after the separation of the duplicated centrosomes. During mitosis, CKAP2 associated with spindle poles and with spindle microtubules from prophase through anaphase and dis-appeared from microtubules during cytokinesis. The function of CKAP2 during mitosis does not seem essential, as efficient knockdown of CKAP2 neither altered the cell cycle distribution of the cells, nor generated observable mitotic defects. On the other hand, ectopic expression of either the wild-type or a non-degradable CKAP2 led to a mitotic arrest with monopolar spindles containing highly bundled microtubules. We concluded that CKAP2 is a physiological substrate of APC/C during mitotic exit and that a tight regulation of the CKAP2 protein level is critical for the normal mitotic progression.
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PMID:CKAP2 is a spindle-associated protein degraded by APC/C-Cdh1 during mitotic exit. 1737 72

The recently identified centrosome protein Nlp (ninein-like protein) is a key regulator in centrosome maturation, which contributes to chromosome segregation and cytokinesis. However, the mechanism(s) controlling Nlp expression remains largely unknown. Here we have shown that Nlp expression is cell cycle-dependent with a peak at G(2)/M transition in human cells. Nlp is a short-lived protein and degraded by the proteasome via the anaphase-promoting cyclosome complex (APC/c) pathway. It interacts with the APC/c through the APC2 or Cdc27 subunits and is ubiquitinated. Following treatment with proteasome inhibitors, its protein level is elevated. Nlp binds in vivo to the degradation-targeting proteins Cdh1 and Cdc20, and overexpression of Cdh1 and Cdc20 enhances Nlp degradation. Using point mutations of the two putative degradation signals in Nlp, we have found that its degradation requires intact KEN-box and D-box. Interestingly, the Lys-Glu-Asn-D-box-mutated Nlp exhibits a much stronger capability of inducing anchorage-independent growth and multinuclearity compared with the wild type Nlp. Taken together, these findings indicate that Nlp expression is cell cycle-dependent and regulated by APC-mediated protein degradation.
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PMID:Cell cycle-dependent expression of centrosomal ninein-like protein in human cells is regulated by the anaphase-promoting complex. 1740 70

Mitotic progression is controlled by proteolytic destruction of securin and cyclin. The mitotic E3 ubiquitin ligase, known as the anaphase promoting complex or cyclosome (APC/C), in partnership with its activators Cdc20p and Cdh1p, targets these proteins for degradation. In the presence of defective kinetochore-microtubule interactions, APC/C(Cdc20) is inhibited by the spindle checkpoint, thereby delaying anaphase onset and providing more time for spindle assembly. Cdc20p interacts directly with Mad2p, and its levels are subject to careful regulation, but the precise mode(s) of APC/C( Cdc20) inhibition remain unclear. The mitotic checkpoint complex (MCC, consisting of Mad3p, Mad2p, Bub3p and Cdc20p in budding yeast) is a potent APC/C inhibitor. Here we focus on Mad3p and how it acts, in concert with Mad2p, to efficiently inhibit Cdc20p. We identify and analyse the function of two motifs in Mad3p, KEN30 and KEN296, which are conserved from yeast Mad3p to human BubR1. These KEN amino acid sequences resemble 'degron' signals that confer interaction with APC/C activators and target proteins for degradation. We show that both Mad3p KEN boxes are necessary for spindle checkpoint function. Mutation of KEN30 abolished MCC formation and stabilised Cdc20p in mitosis. In addition, mutation of Mad3-KEN30, APC/C subunits, or Cdh1p, stabilised Mad3p in G1, indicating that the N-terminal KEN box could be a Mad3p degron. To determine the significance of Mad3p turnover, we analysed the consequences of MAD3 overexpression and found that four-fold overproduction of Mad3p led to chromosome bi-orientation defects and significant chromosome loss during recovery from anti-microtubule drug induced checkpoint arrest. In conclusion, Mad3p KEN30 mediates interactions that regulate the proteolytic turnover of Cdc20p and Mad3p, and the levels of both of these proteins are critical for spindle checkpoint signaling and high fidelity chromosome segregation.
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PMID:Mad3 KEN boxes mediate both Cdc20 and Mad3 turnover, and are critical for the spindle checkpoint. 1740 66

Microtubule associated proteins are involved in regulation of microtubule dynamics. Its mutation and dysregulation result in severe consequences such as mitotic block and apoptosis. NuSAP has been reported as a microtubule associated protein, depletion of which by RNAi results in spindle deficiency and cytokinesis failure. However, its role in regulation of cell cycle and how NuSAP protein is controlled during cell cycle progression still remains unclear. Here we show that NuSAP can be ubiquitinated and degraded by APC/C-hCdh1 E3 ligase. Evolutionally conserved KEN box functions as the degron of NuSAP. Overexpression of NuSAP induces mitotic arrest and the microtubule associated domain and nuclear localization are both required for NuSAP to induce mitotic arrest. Furthermore, overexpression of NuSAP results in cells accumulation with microtubule bundling and spindle deficiency. Thus, our results give evidence for the first time that NuSAP protein level is tightly regulated by the APC/C ubiquitin ligase complex and NuSAP induces mitotic arrest dependent of its microtubule affinity.
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PMID:NuSAP is degraded by APC/C-Cdh1 and its overexpression results in mitotic arrest dependent of its microtubules' affinity. 1761 83

The APC/C(Cdh1) (anaphase promoting complex/cyclosome) targets numerous cell cycle proteins for ubiquitin mediated degradation in late mitosis and G1. The KEN box is one of two major recognition motifs of APC/C(Cdh1) substrates. This motif is however very common and shared by a tenth of the human proteome, the vast majority of which are obviously not APC/C substrates. We have observed that most known functional KEN boxes are followed by a proline residue and show that this proline plays a role in APC/C(Cdh1) specific degradation. This insight can be instrumental for identifying novel APC/C(Cdh1) substrates. We used this KENxP motif to identify human Aurora B and Kid as APC/C(Cdh1) substrates. The degradation of Xenopus XKid at metaphase by APC/C(Cdc20) is essential for chromatid segregation. Human Kid in contrast is degraded later and its APC/C(Cdh1) specific degradation is not required for mitotic progress. It is thus likely that Kid inactivation in G1 takes place both by nuclear sequestration and degradation by the APC/C(Cdh1).
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PMID:Human Kid is degraded by the APC/C(Cdh1) but not by the APC/C(Cdc20). 1772 74


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