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)

The proteasome has been shown to be involved in exit from mitosis by bringing about destruction of mitotic cyclins. Here, we present evidence that the proteasome is also required for proper completion of S phase and for entry into mitosis in the sea urchin embryonic cleavage cycle. A series of structurally related peptide-aldehydes prevent nuclear envelope breakdown in their order of inhibitory efficacies against the proteasome. Their efficacies in blocking exit from S phase and exit from mitosis correlate well, indicating that the proteasome is involved at both these steps. Mitotic histone HI kinase activation and tyrosine dephosphorylation of p34(cdc2) kinase are blocked by inhibition of the proteasome, indicating that the proteasome plays an important role in the pathway that leads to embryonic p34(cdc2 )kinase activation. Arrested embryos continued to incorporate [(3)H]thymidine and characteristically developed large nuclei. Pre-mitotic arrest can be overcome by treatment with caffeine, a manoeuvre that is known to override the DNA replication checkpoint. These data demonstrate that the proteasome is involved in the control of termination of S phase and consequently in the initiation of M phase of the first embryonic cell cycle.
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PMID:Inhibiting proteasome activity causes overreplication of DNA and blocks entry into mitosis in sea urchin embryos. 1089 81

Recently, it was shown that conversion of cdk5 activator protein p35 to a C-terminal fragment p25 promotes a deregulation of cdk5 activity, which may contribute to neurodegeneration in Alzheimer's disease. In this study, we present evidence that calpain is a protease involved in the conversion of p35 to p25. To activate calpain, rat cerebellar granule neurons were treated with maitotoxin (MTX). A C-terminus-directed anti-p35 antibody detected that p35 conversion to p25 paralleled the formation of calpain-generated alpha-spectrin (alpha-fodrin) breakdown products (SBDP's) in a maitotoxin-dose-dependent manner. Two calpain inhibitors (MDl28170 and SJA6017) reduced p35 processing but were unchanged when exposed to the caspase inhibitor carbobenzoxy-Asp-CH(2)OC(=O)-2, 6-dichlorobenzene or the proteasome inhibitors (lactacystin and Z-Ile-Glu(OtBu)Ala-Leu-CHO). p35 protein was also degraded to p25 when rat brain lysate was subjected to in vitro digestion with purified mu- and m-calpains. Additionally, in a rat temporary middle cerebral artery occlusion model, p35 processing to p25 again paralleled SBDP formation in the ischemic core. Lastly, in malonate-injured rat brains, the ipsilateral side showed a striking correlation of SBDP formation with p35 to p25 conversion and tau phosphorylation (at Ser202 and Thr205) increase. These data suggest that calpain is a major neuronal protease capable of converting p35 to p25 and might play a pathological role of activating cdk5 and its phosphorylation of tau in Alzheimer's disease.
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PMID:Processing of cdk5 activator p35 to its truncated form (p25) by calpain in acutely injured neuronal cells. 1090 89

A consistent relationship has been established between the development of Kaposi's sarcoma (KS) and human herpes virus-8 (HHV8) infection. HHV8-encoded v-cyclin, through its complexing with cyclin-dependent kinase 6, contributes to the phosphorylation and proteasome-mediated degradation of p27(Kip1). On the other hand, down-regulation of p27(Kip1) expression seems to facilitate metastatic dissemination in a variety of human neoplasms. Although the neoplastic nature of KS remains controversial, it has been repeatedly demonstrated that in some patients KS may behave as a malignant neoplasm and follow an ominous course, especially in HIV-positive patients and when associated with extracutaneous involvement. To determine whether decreased p27(Kip1) levels are also related to more aggressive behaviour in KS, it was decided to investigate p27(Kip1) immunoreactivity in KS biopsy specimens and its possible changes in relation to cutaneous versus extracutaneous involvement and HIV serological status. Forty-nine cases of KS (29 AIDS-related and 21 classical) corresponding to 30 cutaneous biopsy specimens (ten macules, seven plaques, and 13 tumours) and 19 extracutaneous biopsy specimens were immunostained to determine the expression of p27(Kip1) and the proliferation marker Ki-67 antigen. The mean percentages of p27(Kip1)-positive cells were significantly higher in biopsy specimens from skin lesions (77.8+/-21.1) than in those from extracutaneous locations (42.0+/-26.0). Amongst cutaneous lesions, p27(Kip1) expression was significantly higher in macules (83.8+/-18.5) and plaques (91.4+/-6.4) than in tumours (65.8+/-22.6). Ki-67 immunoreactivity showed no correlation with any of the variables studied. These results lend support to the hypothesis that decreased levels of p27(Kip1), which may have been brought about by HHV8 infection, play a role in KS progression through its various histopathological stages, to its eventual extracutaneous spread.
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PMID:Decreased immunoreactivity for cell-cycle regulator p27(Kip1) in Kaposi's sarcoma correlates with higher stage and extracutaneous involvement. 1091 13

Proliferating myoblasts already express MyoD before the induction of differentiation. Overexpression of MyoD in normal and transformed cell lines was shown to block cells from entering S phase, suggesting that the MyoD growth suppressive effect must be tightly controlled in growing myoblasts. Here we show that during G1 phase, but not in G2, MyoD abundance is down-regulated by the ubiquitin-proteasome pathway through phosphorylation of serine 200. Roscovitine, a specific inhibitor of cyclin-Cdk2 complexes, prevents both phosphorylation and degradation of MyoD in G1. Inhibition of the ubiquitin-dependent proteasome pathway by MG132 results in stabilization of MyoD-wt, with little effect on a MyoD mutant where serine 200 is replaced by an alanine. Our results show that MyoD Ser200 is the substrate for phosphorylation by cyclin E-Cdk2 stimulating its degradation by the ubiquitin-proteasome system which controls MyoD levels in G1. Phosphorylation/degradation of MyoD at the end of G1 thus represents the regulatory checkpoint in growing myoblasts allowing progression into S phase in a manner similar to the recently examplified cdk2-phosphorylation/degradation of p27(Kip1).
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PMID:Cyclin E-cdk2 phosphorylation promotes late G1-phase degradation of MyoD in muscle cells. 1094 2

We studied the ability of F9 teratocarcinoma cells to arrest in G1/S and G2/M checkpoints after gamma-irradiation. Wild-type p53 protein was rapidly accumulated in F9 cells after gamma-irradiation, however, this was followed not by a G1/S arrest but by a short and reversible delay of the cell cycle in G2/M. In order to elucidate the reasons of the lack of G1/S arrest in F9 cells, we investigated the expression of p53 downstream target Cdk inhibitor p21WAF1/CIP1. In spite of p53-dependent activation of p21WAF1/CIP1 gene promoter and p21WAF1/CIP1 mRNA accumulation upon irradiation, the p21WAF1/CIP1 protein was not detected by either immunoblot or immunofluorescence techniques. However, the cells treated with a specific proteasome inhibitor lactacystin revealed the p21WAF1/CIP1 protein both in non-irradiated and irradiated cells. Therefore we suggest that p21WAF1/CIP1 protein is degraded by a proteasome-dependent mechanism in F9 cells and the lack of G1/S arrest after gamma-irradiation is due to this degradation. We also examined the expression and activity of cell cycle regulatory proteins: G1- and G2-cyclins and cyclin-dependent kinases. In the absence of functional p21WAF1/CIP1 inhibitor, the activity of G1 cyclin/Cdk complexes was insufficiently inhibited to cause a G1 arrest, whereas a decrease of cdc2 and cyclin B1-associated kinase activities was enough to contribute to a reversible G2 arrest following gamma-irradiation. After gamma-irradiation, the majority of F9 cells undergo apoptosis implying that wt-p53 likely triggers pro-apoptotic gene expression in DNA damaged cells. Elimination of defected cells might ensure maintenance of genome integrity in the remaining cell population.
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PMID:F9 embryonal carcinoma cells fail to stop at G1/S boundary of the cell cycle after gamma-irradiation due to p21WAF1/CIP1 degradation. 1095 79

Microtubule damages induced by paclitaxel inhibit proteasome-dependent degradation of cyclin B, resulting in a sustained activation of cyclin B/cdc2 kinase and a cell cycle arrest in mitosis. It has been previously shown that this kinase activity is also required for paclitaxel-induced apoptosis. We found here that paclitaxel increased cdc2 mRNA and protein levels and led to an accumulation of cdc2 in the active dephosphorylated form in NIH-OVCAR-3 cells. The addition of cycloheximide inhibited the paclitaxel-induced increase in cdc2 protein level, further indicating that paclitaxel stimulates cdc2 synthesis. This increase in cdc2 synthesis is a consequence of paclitaxel-induced arrest in mitosis. Indeed, dual analysis of DNA and cdc2 protein contents indicated that cdc2 up-regulation occurred in cells arrested with a G2/M DNA content. Furthermore, no up-regulation of cdc2 protein was observed when paclitaxel-treated cells were prevented from entering mitosis by treatment with purvalanol A, a cyclin-dependent kinase (CDK) inhibitor, or stimulated to exit mitosis with 2-AP, a non-specific kinase inhibitor. In addition, when paclitaxel-induced apoptosis was inhibited by Bcl-2 over-expression, cdc2 up-regulation did not occur, leading to a lower level of activation of the cyclin B/cdc2 complex. Taken together, these results indicated that paclitaxel-induced cdc2 protein synthesis participates in a positive feedback loop designed to increase the activity of cyclin B/cdc2 kinase and thus may play a role in paclitaxel-induced apoptosis.
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PMID:Up-regulation of cdc2 protein during paclitaxel-induced apoptosis. 1095 85

Deregulation of cell cycle checkpoints is an almost universal abnormality in human cancers and is most often due to loss-of-function mutations of tumor suppressor genes such as Rb, p53, or p16(INK4a). In this study, we demonstrate that BCR/ABL inhibits the expression of a key cell cycle inhibitor, p27(Kip1), by signaling through a pathway involving phosphatidylinositol 3-kinase (PI3K). p27(Kip1) is a widely expressed inhibitor of cdk2, an essential cell cycle kinase regulating entry into S phase. We demonstrate that the decrease of p27(Kip1) is directly due to BCR/ABL in hematopoietic cells by two different approaches. First, induction of BCR/ABL by a tetracycline-regulated promoter is associated with a reversible down-regulation of p27(Kip1). Second, inhibition of BCR/ABL kinase activity with the Abl tyrosine kinase inhibitor STI571 rapidly increases p27(Kip1) levels. The PI3K inhibitor LY-294002 blocks the ability of BCR/ABL to induce p27(Kip1) down-regulation and inhibits BCR/ABL-induced entry into S phase. The serine/threonine kinase AKT/protein kinase B is a known downstream target of PI3K. Transient expression of an activated mutant of AKT was found to decrease expression of p27(Kip1), even when PI3K was inhibited by LY-294002. The mechanism of p27(Kip1) regulation is primarily related to protein stability, since inhibition of proteasome activity increased p27(Kip1) levels in BCR/ABL-transformed cells, whereas very little change in p27 transcription was found. Overall, these data are consistent with a model in which BCR/ABL suppresses p27(Kip1) protein levels through PI3K/AKT, leading to accelerated entry into S phase. This activity is likely to explain in part previous studies showing that activation of PI3K was required for optimum transformation of hematopoietic cells by BCR/ABL in vitro and in vivo.
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PMID:BCR/ABL regulates expression of the cyclin-dependent kinase inhibitor p27Kip1 through the phosphatidylinositol 3-Kinase/AKT pathway. 1101 Sep 72

RNA polymerase II CTD kinases are key elements in the control of mRNA synthesis. They constitute a family of cyclin-dependent kinases activated by C-type cyclins. Unlike most cyclin-dependent kinase complexes, which are composed of a catalytic and a regulatory subunit, the yeast CTD kinase I complex contains three specific subunits: a kinase subunit (Ctk1), a cyclin subunit (Ctk2), and a third subunit (Ctk3) of unknown function that does not exhibit any similarity to known proteins. Like the Ctk2 cyclin that is regulated at the level of protein turnover, Ctk3 is an unstable protein processed through a ubiquitin-proteasome pathway. Interestingly, Ctk2 and Ctk3 physical interaction is required to protect both subunits from degradation, pointing to a new mechanism for cyclin turnover regulation. We also show that Ctk2 and Ctk3 can each interact independently with the kinase. However, despite the formation of CDK/cyclin complexes in vitro, the Ctk2 cyclin is unable to activate its CDK: both Ctk2 and Ctk3 are required for Ctk1 CTD kinase activation. The different specific features governing CTDK-I regulation probably reflect requirement for the transcriptional response to multiple growth conditions.
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PMID:Activation of the cyclin-dependent kinase CTDK-I requires the heterodimerization of two unstable subunits. 1111 53

Recently, we identified two Trpanosoma brucei cyclin genes, CYC2 and CYC3, by rescue of the Saccharomyces cerevisiae mutant DL1, which is deficient in CLN G1 cyclin function. CYC3 has a low level of sequence identity to mitotic B-type cyclins from a variety of organisms. In order to examine whether CYC3 associates in vivo with a trypanosome cdc2-related kinase (CRK), the CYC3 gene was fused with the TY-epitope tag, integrated into the trypanosome genome and expressed under inducible control. CYC3ty was demonstrated to associate with the CRK-binding factor p12cks1 and histone H1 kinase activity could be detected in CYC3ty immune precipitated fractions, which demonstrates that CYC3ty associates in vivo with an active trypanosome CRK. Both CYC3ty and CYC2ty were shown to have a half-life of less than one cell cycle, which was significantly elongated by specific proteasome inhibitors, strongly suggesting that CYC3ty and CYC2ty are substrates for proteasome degradation. This is consistent with the presence in CYC3 of a putative destruction box motif that defines proteins for degradation via the ubiquitin degradation pathway. These results are consistant with proteolysis by the proteasome being involved in regulation of the cellular cyclin concentration in trypanosomes.
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PMID:The CYC3 gene of trypanosoma brucei encodes a cyclin with a short half-life. 1116 36

The Cdc25 A phosphatase is required for the G1-S transition of the cell cycle and is overexpressed in human cancers. We found that it is ubiquitylated and rapidly degraded by the proteasome and that its levels increase from G1 until mitosis. By treating cells with the DNA synthesis inhibitor hydroxyurea, Cdc25 A rapidly decreased in abundance, and this was accompanied by an increase in Cdk2 phosphotyrosine content and a decrease in Cdk2 kinase activity. Cdc25 A overexpression altered the ability of cells to arrest in the presence of hydroxyurea, and caused them to undergo premature chromosome condensation. Cdc25 A overexpression could render tumor cells less sensitive to DNA replication checkpoints, thereby contributing to their genomic instability.
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PMID:Human Cdc25 A inactivation in response to S phase inhibition and its role in preventing premature mitosis. 1125 29


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