Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0033036 (APC)
 10,214 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The ubiquitin-dependent proteolysis of mitotic cyclin B, which is catalyzed by the anaphase-promoting complex/cyclosome (APC/C) and ubiquitin-conjugating enzyme H10 (UbcH10), begins around the time of the metaphase-anaphase transition and continues through G1 phase of the next cell cycle. We have used cell-free systems from mammalian somatic cells collected at different cell cycle stages (G0, G1, S, G2, and M) to investigate the regulated degradation of four targets of the mitotic destruction machinery: cyclins A and B, geminin H (an inhibitor of S phase identified in Xenopus), and Cut2p (an inhibitor of anaphase onset identified in fission yeast). All four are degraded by G1 extracts but not by extracts of S phase cells. Maintenance of destruction during G1 requires the activity of a PP2A-like phosphatase. Destruction of each target is dependent on the presence of an N-terminal destruction box motif, is accelerated by additional wild-type UbcH10 and is blocked by dominant negative UbcH10. Destruction of each is terminated by a dominant activity that appears in nuclei near the start of S phase. Previous work indicates that the APC/C-dependent destruction of anaphase inhibitors is activated after chromosome alignment at the metaphase plate. In support of this, we show that addition of dominant negative UbcH10 to G1 extracts blocks destruction of the yeast anaphase inhibitor Cut2p in vitro, and injection of dominant negative UbcH10 blocks anaphase onset in vivo. Finally, we report that injection of dominant negative Ubc3/Cdc34, whose role in G1-S control is well established and has been implicated in kinetochore function during mitosis in yeast, dramatically interferes with congression of chromosomes to the metaphase plate. These results demonstrate that the regulated ubiquitination and destruction of critical mitotic proteins is highly conserved from yeast to humans.
 ...
PMID:Cell cycle-regulated proteolysis of mitotic target proteins. 1056 81

In late mitosis and G1, a complex of the essential initiation proteins Mcm2-7 are assembled onto replication origins to 'license' them for initiation. At other times licensing is inhibited by cyclin-dependent kinases (CDKs) and geminin, thus ensuring that origins fire only once per cell cycle. Here we show that, paradoxically, CDKs are also required to inactivate geminin and activate the licensing system. On exit from metaphase in Xenopus laevis egg extracts, CDK-dependent activation of the anaphase-promoting complex (APC/C) results in the transient polyubiquitination of geminin. This ubiquitination triggers geminin inactivation without requiring ubiquitin-dependent proteolysis, and is essential for replication origins to become licensed. This reveals an unexpected role for CDKs and ubiquitination in activating chromosomal DNA replication.
 ...
PMID:Non-proteolytic inactivation of geminin requires CDK-dependent ubiquitination. 1476 79

In late mitosis and G1, Mcm2-7 are assembled onto replication origins to 'license' them for initiation. At other cell cycle stages, licensing is inhibited, thus ensuring that origins fire only once per cell cycle. Three additional factors--the origin recognition complex, Cdc6 and Cdt1--are required for origin licensing. We examine here how licensing is regulated in Xenopus egg extracts. We show that Cdt1 is downregulated late in the cell cycle by two different mechanisms: proteolysis, which occurs in part due to the activity of the anaphase-promoting complex (APC/C), and inhibition by a protein called geminin. If both these regulatory mechanisms are abrogated, extracts undergo uncontrolled re-licensing and re-replication. The extent of re-replication is limited by checkpoint kinases that are activated as a consequence of re-replication itself. These results allow us to build a comprehensive model of how re-replication of DNA is prevented in Xenopus, with Cdt1 regulation being the key feature. The results also explain the original experiments that led to the proposal of a replication licensing factor.
 ...
PMID:Cdt1 downregulation by proteolysis and geminin inhibition prevents DNA re-replication in Xenopus. 1561 77

Cyclin-dependent kinases (CDKs) restrict DNA replication origin firing to once per cell cycle by preventing the assembly of prereplicative complexes (pre-RCs; licensing) outside of G1 phase. Paradoxically, under certain circumstances, CDKs such as cyclin E-cdk2 are also required to promote licensing. Here, we show that CDK phosphorylation of the essential licensing factor Cdc6 stabilizes it by preventing its association with the anaphase promoting complex/cyclosome (APC/C). APC/C-dependent Cdc6 proteolysis prevents pre-RC assembly in quiescent cells and, when cells reenter the cell cycle from quiescence, CDK-dependent Cdc6 stabilization allows Cdc6 to accumulate before the licensing inhibitors geminin and cyclin A which are also APC/C substrates. This novel mechanism for regulating protein stability establishes a window of time prior to S phase when pre-RCs can assemble which we propose represents a critical function of cyclin E.
 ...
PMID:CDKs promote DNA replication origin licensing in human cells by protecting Cdc6 from APC/C-dependent proteolysis. 1617 49

Emi1 (early mitotic inhibitor) inhibits APC/C (anaphase-promoting complex/cyclosome) activity during S and G2 phases, and is believed to be required for proper mitotic entry. We report that Emi1 plays an essential function in cell proliferation by preventing rereplication. Rereplication seen after Emi1 depletion is due to premature activation of APC/C that results in destabilization of geminin and cyclin A, two proteins shown here to play redundant roles in preventing rereplication in mammalian cells. Geminin is known to inhibit the replication initiation factor Cdt1. The rereplication block by cyclin A is mediated through its association with S and G2/M cyclin-dependent kinases (Cdks), Cdk2 and Cdk1, suggesting that phosphorylation of proteins by cyclin A-Cdk is responsible for the block. Rereplication upon Emi1 depletion activates the DNA damage checkpoint pathways. These data suggest that Emi1 plays a critical role in preserving genome integrity by blocking rereplication, revealing a previously unrecognized function of this inhibitor of APC/C.
 ...
PMID:The APC/C inhibitor, Emi1, is essential for prevention of rereplication. 1723 84

DNA replication must be tightly controlled to prevent initiation of a second round of replication until mitosis is complete. So far, components of the pre-replicative complex (Cdt1, Cdc6 and geminin) were considered key players in this regulation. In a new study, Machida and Dutta have shown that depletion of Emi1 caused cells to replicate their DNA more than once per cell cycle 1. This effect was dependent on the ability of Emi1 to inhibit the APC/C. In addition to its role in regulating entry into mitosis, oscillation of APC/C activity regulates pre-RC formation: high APC/C activity in late M/G1 allows pre-RC formation and low APC/C activity in S/G2 prevents pre-RC formation for a second time thereby preventing rereplication. Each redundant pathway to prevent rereplication is dependent on regulating one of the pre-RC components, and all of the pathways are co-regulated by Emi1 through the APC/C. In this commentary we discuss how this new role of Emi1 adds to our understanding of the regulation of replication initiation. We also review the literature to analyze whether APC/C has a role in regulating endoreduplication (a normal state of polyploidy in some differentiated cells). Similarly a role of premature APC/C activation in genomic instability of tumors is discussed.
 ...
PMID:APC/C--the master controller of origin licensing? 1731 58

Ubiquitin-mediated proteolysis is critical for the alternation between DNA replication and mitosis and for the key regulatory events in mitosis. The anaphase-promoting complex/cyclosome (APC/C) is a conserved ubiquitin ligase that has a fundamental role in regulating mitosis and the cell cycle in all eukaryotes. In vertebrate cells, early mitotic inhibitor 1 (Emi1) has been proposed as an important APC/C inhibitor whose destruction may trigger activation of the APC/C at mitosis. However, in this study, we show that the degradation of Emi1 is not required to activate the APC/C in mitosis. Instead, we uncover a key role for Emi1 in inhibiting the APC/C in interphase to stabilize the mitotic cyclins and geminin to promote mitosis and prevent rereplication. Thus, Emi1 plays a crucial role in the cell cycle to couple DNA replication with mitosis, and our results also question the current view that the APC/C has to be inactivated to allow DNA replication.
 ...
PMID:Emi1 is needed to couple DNA replication with mitosis but does not regulate activation of the mitotic APC/C. 1748 88

Limiting genome replication to once per cell cycle is vital for maintaining genome stability. Inhibition of cyclin-dependent kinase 1 (CDK1) with the specific inhibitor RO3306 is sufficient to trigger multiple rounds of genome reduplication. We demonstrated that although anaphase-promoting complex/cyclosome (APC/C) remained inactive during the initial G(2) arrest, it was activated upon prolonged inhibition of CDK1. Using cellular biosensors and live-cell imaging, we provide direct evidence that genome reduplication was associated with oscillation of APC/C activity and nuclear-cytoplasmic shuttling of CDC6 even in the absence of mitosis at the single-cell level. Genome reduplication was abolished by ectopic expression of EMI1 or depletion of CDC20 or CDH1, suggesting the critical role of the EMI1-APC/C axis. In support of this, degradation of EMI1 itself and genome reduplication were delayed after downregulation of PLK1 and beta-TrCP1. In the absence of CDK1 activity, activation of APC/C and genome reduplication was dependent on cyclin A2 and CDK2. Genome reduplication was then promoted by a combination of APC/C-dependent destruction of geminin (thus releasing CDT1), accumulation of cyclin E2-CDK2, and CDC6. Collectively, these results underscore the crucial role of cyclin A2-CDK2 in regulating the PLK1-SCF(beta-TrCP1)-EMI1-APC/C axis and CDC6 to trigger genome reduplication after the activity of CDK1 is suppressed.
 ...
PMID:Cyclin A2-cyclin-dependent kinase 2 cooperates with the PLK1-SCFbeta-TrCP1-EMI1-anaphase-promoting complex/cyclosome axis to promote genome reduplication in the absence of mitosis. 1982 58

By exploiting the cell-cycle-dependent proteolysis of two ubiquitination oscillators, human Cdt1 and geminin, which are the direct substrates of SCF(Skp2) and APC(Cdh1) complexes, respectively, Fucci technique labels mammalian cell nuclei in G(1) and S/G(2)/M phases with different colors. Transgenic mice expressing these G(1) and S/G(2)/M markers offer a powerful means to investigate the coordination of the cell cycle with morphogenetic processes. We attempted to introduce these markers into zebrafish embryos to take advantage of their favorable optical properties. However, although the fundamental mechanisms for cell-cycle control appear to be well conserved among species, the G(1) marker based on the SCF(Skp2)-mediated degradation of human Cdt1 did not work in fish cells, probably because the marker was not ubiquitinated properly by a fish E3 ligase complex. We describe here the generation of a Fucci derivative using zebrafish homologs of Cdt1 and geminin, which provides sweeping views of cell proliferation in whole fish embryos. Remarkably, we discovered two anterior-to-posterior waves of cell-cycle transitions, G(1)/S and M/G(1), in the differentiating notochord. Our study demonstrates the effectiveness of using the Cul4(Ddb1)-mediated Cdt1 degradation pathway common to all metazoans for the development of a G(1) marker that works in the nonmammalian animal model.
 ...
PMID:Illuminating cell-cycle progression in the developing zebrafish embryo. 1992 30

Tetraploidization has been proposed as an intermediate step toward aneuploidy in human cancer but a general mechanism for the induction of tetraploidy during tumorigenesis is lacking. We report that tetraploidization occurs in p53-deficient cells experiencing a prolonged DNA damage signal due to persistent telomere dysfunction. Live-cell imaging revealed that these cells have an extended G2 due to ATM/ATR- and Chk1/Chk2-mediated inhibition of Cdk1/CyclinB and eventually bypass mitosis. Despite their lack of mitosis, the cells showed APC/Cdh1-dependent degradation of the replication inhibitor geminin, followed by accumulation of Cdt1, which is required for origin licensing. Cells then entered a second S phase resulting in whole-genome reduplication and tetraploidy. Upon restoration of telomere protection, these tetraploid cells resumed cell division cycles and proliferated. These observations suggest a general mechanism for the induction of tetraploidization in the early stages of tumorigenesis when telomere dysfunction can result from excessive telomere shortening.
 ...
PMID:Persistent telomere damage induces bypass of mitosis and tetraploidy. 2037 47


1 2 Next >>