Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.22 (cdc2)
 8,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

To maintain genome integrity in eukaryotes, DNA must be duplicated precisely once before cell division occurs. A process called replication licensing ensures that chromosomes are replicated only once per cell cycle. Its control has been uncovered by the discovery of the CDKs (cyclin dependent kinases) as master regulators of the cell cycle and the initiator proteins of DNA replication, such as the Origin Recognition Complex (ORC), Cdc6/18, Cdt1 and the MCM complex. At the end of mitosis, the MCM complex is loaded on to chromatin with the aid of ORC, Cdc6/18 and Cdt1, and chromatin becomes licensed for replication. CDKs, together with the Cdc7 kinase, trigger the initiation of replication, recruiting the DNA replicating enzymes on sites of replication. The activated MCM complex appears to play a key role in the DNA unwinding step, acting as a replicating helicase and moves along with the replication fork, at the same time bringing the origins to the unlicensed state. The cycling of CDK activity in the cell cycle separates the two states of replication origins, the licensed state in G1-phase and the unlicensed state for the rest of the cell cycle. Only when CDK drops at the completion of mitosis, is the restriction on licensing relieved and a new round of replication is allowed. Such a CDK-regulated licensing control is conserved from yeast to higher eukaryotes, and ensures that DNA replication takes place only once in a cycle. Xenopus laevis and mammalian cells have an additional system to control licensing. Geminin, whose degradation at the end of mitosis is essential for a new round of licensing, has been shown to bind Cdt1 and negatively regulate it, providing a new insight into the regulation of DNA replication in higher eukaryotes.
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PMID:Control of DNA replication licensing in a cell cycle. 1205 57

Geminin is an unstable inhibitor of DNA replication that negatively regulates the licensing factor CDT1 and inhibits pre-replicative complex (pre-RC) formation in Xenopus egg extracts. Here we describe a novel function of Geminin. We demonstrate that human Geminin protects CDT1 from proteasome-mediated degradation by inhibiting its ubiquitination. In particular, Geminin ensures basal levels of CDT1 during S phase and its accumulation during mitosis. Consistently, inhibition of Geminin synthesis during M phase leads to impairment of pre-RC formation and DNA replication during the following cell cycle. Moreover, we show that inhibition of CDK1 during mitosis, and not Geminin depletion, is sufficient for premature formation of pre-RCs, indicating that CDK activity is the major mitotic inhibitor of licensing in human cells. Taken together with recent data from our laboratory, our results demonstrate that Geminin is both a negative and positive regulator of pre-RC formation in human cells, playing a positive role in allowing CDT1 accumulation in G2-M, and preventing relicensing of origins in S-G2.
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PMID:Human geminin promotes pre-RC formation and DNA replication by stabilizing CDT1 in mitosis. 1525 90

The regulation of a pre-replicative complex (pre-RC) at origins ensures that the genome is replicated only once per cell cycle. Cdt1 is an essential component of the pre-RC that is rapidly degraded at G1-S and also inhibited by Geminin (Gem) protein to prevent re-replication. We have previously shown that destruction of the Drosophila homolog of Cdt1, Double-parked (Dup), at G1-S is dependent upon cyclin-E/CDK2 and important to prevent re-replication and cell death. Dup is phosphorylated by cyclin-E/Cdk2, but this direct phosphorylation was not sufficient to explain the rapid destruction of Dup at G1-S. Here, we present evidence that it is DNA replication itself that triggers rapid Dup destruction. We find that a range of defects in DNA replication stabilize Dup protein and that this stabilization is not dependent on ATM/ATR checkpoint kinases. This response to replication stress was cell-type specific, with neuroblast stem cells of the larval brain having the largest increase in Dup protein. Defects at different steps in replication also increased Dup protein during an S-phase-like amplification cell cycle in the ovary, suggesting that Dup stabilization is sensitive to DNA replication and not an indirect consequence of a cell-cycle arrest. Finally, we find that cells with high levels of Dup also have elevated levels of Gem protein. We propose that, in cycling cells, Dup destruction is coupled to DNA replication and that increased levels of Gem balance elevated Dup levels to prevent pre-RC reformation when Dup degradation fails.
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PMID:Levels of the origin-binding protein Double parked and its inhibitor Geminin increase in response to replication stress. 1614 Dec 38

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.
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PMID:The APC/C inhibitor, Emi1, is essential for prevention of rereplication. 1723 84

In vertebrates Cdk1 is required to initiate mitosis; however, any functionality of this kinase during S phase remains unclear. To investigate this, we generated chicken DT40 mutants, in which an analog-sensitive mutant cdk1 as replaces the endogenous Cdk1, allowing us to specifically inactivate Cdk1 using bulky ATP analogs. In cells that also lack Cdk2, we find that Cdk1 activity is essential for DNA replication initiation and centrosome duplication. The presence of a single Cdk2 allele renders S phase progression independent of Cdk1, which suggests a complete overlap of these kinases in S phase control. Moreover, we find that Cdk1 inhibition did not induce re-licensing of replication origins in G2 phase. Conversely, inhibition during mitosis of Cdk1 causes rapid activation of endoreplication, depending on proteolysis of the licensing inhibitor Geminin. This study demonstrates essential functions of Cdk1 in the control of S phase, and exemplifies a chemical genetics approach to target cyclin-dependent kinases in vertebrate cells.
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PMID:An essential role for Cdk1 in S phase control is revealed via chemical genetics in vertebrate cells. 1763 36

The endocycle is a commonly observed variant cell cycle in which cells undergo repeated rounds of DNA replication with no intervening mitosis. How the cell cycle machinery is modified to transform a mitotic cycle into endocycle has long been a matter of interest. In both plants and animals, the transition from the mitotic cycle to the endocycle requires Fzr/Cdh1, a positive regulator of the Anaphase-Promoting Complex/Cyclosome (APC/C). However, because many of its targets are transcriptionally downregulated upon entry into the endocycle, it remains unclear whether the APC/C functions beyond the mitotic/endocycle boundary. Here, we report that APC/C Fzr/Cdh1 activity is required to promote the G/S oscillation of the Drosophila endocycle. We demonstrate that compromising APC/C activity, after cells have entered the endocycle, inhibits DNA replication and results in the accumulation of multiple APC/C targets, including the mitotic cyclins and Geminin. Notably, our data suggest that the activity of APC/C Fzr/Cdh1 during the endocycle is not continuous but is cyclic, as demonstrated by the APC/C-dependent oscillation of the pre-replication complex component Orc1. Taken together, our data suggest a model in which the cyclic activity of APC/C Fzr/Cdh1 during the Drosophila endocycle is driven by the periodic inhibition of Fzr/Cdh1 by Cyclin E/Cdk2. We propose that, as is observed in mitotic cycles, during endocycles, APC/C Fzr/Cdh1 functions to reduce the levels of the mitotic cyclins and Geminin in order to facilitate the relicensing of DNA replication origins and cell cycle progression.
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PMID:APC/CFzr/Cdh1 promotes cell cycle progression during the Drosophila endocycle. 1832 83

Endoreplicating cells undergo multiple rounds of DNA replication leading to polyploidy or polyteny. Oscillation of Cyclin E (CycE)-dependent kinase activity is the main driving force in Drosophila endocycles. High levels of CycE-Cdk2 activity trigger S phase, while down-regulation of CycE-Cdk2 activity is crucial to allow licensing of replication origins. In mitotic cells relicensing in S phase is prevented by Geminin. Here we show that Geminin protein oscillates in endoreplicating salivary glands of Drosophila. Geminin levels are high in S phase, but drop once DNA replication has been completed. DNA licensing is coupled to mitosis through the action of the anaphase-promoting complex/cyclosome (APC/C). We demonstrate that, even though endoreplicating cells never enter mitosis, APC/C activity is required in endoreplicating cells to mediate Geminin oscillation. Down-regulation of APC/C activity results in stabilization of Geminin protein and blocks endocycle progression. Geminin is only abundant in cells with high CycE-Cdk2 activity, suggesting that APC/C-Fzr activity is periodically inhibited by CycE-Cdk2, to prevent relicensing in S-phase cells.
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PMID:The anaphase-promoting complex/cyclosome (APC/C) is required for rereplication control in endoreplication cycles. 1855 83

DNA rereplication leads to genomic instability and has been implicated in the pathology of a variety of human cancers. Eukaryotic DNA replication is tightly controlled to ensure it occurs only once during each cell cycle. Geminin is a critical component of this control, it prevents DNA rereplication from occurring during S, G2, and early M phases by preventing MCM helicases from forming prereplication complexes. Geminin is targeted for degradation by the anaphase-promoting complex (APC/C) from anaphase through G1-phase, however, accumulating evidence indicates that Geminin is downregulated in late S-phase due to an unknown mechanism. Here, we used a high-throughput screen to identify miRNAs that can induce excess DNA replication and found that miR-571 could reduce the protein level of Geminin in late S-phase independent of the APC/C. Furthermore, miR-571 regulated efficient DNA replication and S-phase cell-cycle progression. Strikingly, c-Myc suppressed miR-571 expression by binding directly to the miR-571 promoter. At the beginning of S-phase, Cdk2 phosphorylated c-Myc at Serine 62, promoting its association with the miR-571 promoter region. Collectively, we identify miR-571 as the first miRNA that prevents aberrant DNA replication and the Cdk2-c-Myc-miR-571 axis as a new pathway for regulating DNA replication, cell cycle, and genomic stability in cancer cells. SIGNIFICANCE: These findings identify a novel regulatory mechanism that is critical for maintaining genome integrity by regulating DNA replication and cell-cycle progression.
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PMID:The Cdk2-c-Myc-miR-571 Axis Regulates DNA Replication and Genomic Stability by Targeting Geminin. 3143 61