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)

Although all three D cyclins bind and activate cdks 2, 4 and 6, Fbxo7 has been characterised as a selective enhancer of cdk6 activity. It increases activation by directly facilitating cdk6 interaction with viral and cellular D cyclins. Fbxo7 overexpression has transforming activity in murine fibroblasts, and it is also highly expressed in human cancers, suggesting it is a potential oncogene. Fbxo7 has the ability to activate cell cycle regulators, and is part of an E3 ubiquitin ligase. We postulate Fbxo7 coordinates the ubiquitination of its substrates with cell cycle entry. It may therefore represent a means to integrate cell signals and control disparate biological processes during the early part of the cell cycle.
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PMID:Fbxo7 gets proactive with cyclin D/cdk6. 1641 Jul 30

MEF is an ETS-related transcription factor with strong transcriptional activating activity that affects hematopoietic stem cell behavior and is required for normal NK cell and NK T-cell development. The MEF (also known as ELF4) gene is repressed by several leukemia-associated fusion transcription factor proteins (PML-retinoic acid receptor alpha and AML1-ETO), but it is also activated by retroviral insertion in several cancer models. We have previously shown that cyclin A-dependent phosphorylation of MEF largely restricts its activity to the G(1) phase of the cell cycle; we now show that MEF is a short-lived protein whose expression level also peaks during late G(1) phase. Mutagenesis studies show that the rapid turnover of MEF in S phase is dependent on the specific phosphorylation of threonine 643 and serine 648 at the C terminus of MEF by cdk2 and on the Skp1/Cul1/F-box (SCF) E3 ubiquitin ligase complex SCF(Skp2), which targets MEF for ubiquitination and proteolysis. Overexpression of MEF drives cells through the G(1)/S transition, thereby promoting cell proliferation. The tight regulation of MEF levels during the cell cycle contributes to its effects on regulating cell cycle entry and cell proliferation.
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PMID:The ETS protein MEF is regulated by phosphorylation-dependent proteolysis via the protein-ubiquitin ligase SCFSkp2. 1658 86

Skp2 fulfills the definition of an oncoprotein with its frequent overexpression in cancer cells and oncogenic activity in various laboratory assays and therefore is a potential cancer therapy target. The best-known function of Skp2 is that of an F-box protein of the SCF(Skp2)-Roc1 E3 ubiquitin ligase targeting the cyclin-dependent kinase inhibitor p27(Kip1). Knockdown of Skp2 generally leads to accumulation of p27 but its effects on cancer cells are less certain. Another function of Skp2 is its stable interaction with cyclin A, which directly protects cyclin A from inhibition by p27 in in vitro kinase assays. Here, we report that an 18-residue blocking peptide of Skp2-cyclin A interaction can indirectly inhibit cyclin A/Cdk2 kinase activity dependent on the presence of p27 in in vitro kinase assays. Transmembrane delivery of this blocking peptide can induce cell death in a panel of four cancer cell lines in which Skp2 knockdown only have mild inhibitory effects. This Skp2-cyclin A interaction blocking peptide can synergize with a previously identified E2F1-derived LDL peptide, which blocks its access to cyclin A, in killing cancer cells. IC(50) of the Skp2-cyclin A blocking peptide correlated with abundance of Skp2, its intended target, in cancer cells. These results suggest that Skp2-cyclin A interaction plays an important role in cancer cell survival and is an attractive target for cancer drug discovery.
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PMID:Disrupting Skp2-cyclin A interaction with a blocking peptide induces selective cancer cell killing. 1730 64

The DNA polymerase delta processivity factor Proliferating Cell Nuclear Antigen (PCNA) promotes the DNA damage-induced degradation of the replication initiation factor Cdt1 via the CRL4(Cdt2) E3 ubiquitin ligase complex. Here we demonstrate that PCNA promotes the ubiquitylation and degradation of the CDK inhibitor p21 in cells irradiated with low dose of ultraviolet (UV) by a similar mechanism. Human cells that are depleted of Cul4, DDB1 (damage-specific DNA-binding protein-1), or the DCAF Cdt2, are deficient in the UV-induced ubiquitylation and degradation of p21. Depletion of mammalian cells of PCNA by siRNA, or mutations in p21 that abrogate PCNA binding, prevent UV-induced p21 ubiquitylation and degradation, indicating that physical binding with PCNA is necessary for the efficient ubiquitylation of p21 via the CRL4(Cdt2) ubiquitin ligase. Cdt2 functions as the substrate recruiting factor for p21 to the rest of the CRL4 ubiquitin ligase complex. The CRL4(Cdt2) E3 ubiquitin ligase ubiquitylates p21 both in vivo and in vitro, and its activity is dependent on the interaction of p21 with PCNA. Finally, we show that the CRL4(Cdt2) and the SCF(Skp2) ubiquitin ligases are redundant with each other in promoting the degradation of p21 during an unperturbed S phase of the cell cycle.
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PMID:PCNA-dependent regulation of p21 ubiquitylation and degradation via the CRL4Cdt2 ubiquitin ligase complex. 1879 47

Meiosis is coupled to gamete development and must be well regulated to prevent aneuploidy. During meiotic maturation, Drosophila oocytes progress from prophase I to metaphase I. The molecular factors controlling meiotic maturation timing, however, are poorly understood. We show that Drosophila alpha-endosulfine (endos) plays a key role in this process. endos mutant oocytes have a prolonged prophase I and fail to progress to metaphase I. This phenotype is similar to that of mutants of cdc2 (synonymous with cdk1) and of twine, the meiotic homolog of cdc25, which is required for Cdk1 activation. We found that Twine and Polo kinase levels are reduced in endos mutants, and identified Early girl (Elgi), a predicted E3 ubiquitin ligase, as a strong Endos-binding protein. In elgi mutant oocytes, the transition into metaphase I occurs prematurely, but Polo and Twine levels are unaffected. These results suggest that Endos controls meiotic maturation by regulating Twine and Polo levels, and, independently, by antagonizing Elgi. Finally, germline-specific expression of the human alpha-endosulfine ENSA rescues the endos mutant meiotic defects and infertility, and alpha-endosulfine is expressed in mouse oocytes, suggesting potential conservation of its meiotic function.
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PMID:alpha-Endosulfine is a conserved protein required for oocyte meiotic maturation in Drosophila. 1892 52

Loss of the CDK inhibitor p27(KIP1) is widely linked with poor prognosis in human cancer. In Wnt10b-expressing mammary tumors, levels of p27(KIP1) were extremely low; conversely, Wnt10b-null mammary cells expressed high levels of this protein, suggesting Wnt-dependent regulation of p27(KIP1). Interestingly we found that Wnt-induced turnover of p27(KIP1) was independent from classical SCF(SKP2)-mediated degradation in both mouse and human cells. Instead, turnover required Cullin 4A and Cullin 4B, components of an alternative E3 ubiquitin ligase induced in response to active Wnt signaling. We found that CUL4A was a novel Wnt target gene in both mouse and human cells and that CUL4A physically interacted with p27(KIP1) in Wnt-responding cells. We further demonstrated that both Cul4A and Cul4B were required for Wnt-induced p27(KIP1) degradation and S-phase progression. CUL4A and CUL4B are therefore components of a conserved Wnt-induced proteasome targeting (WIPT) complex that regulates p27(KIP1) levels and cell cycle progression in mammalian cells.
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PMID:A functional link between Wnt signaling and SKP2-independent p27 turnover in mammary tumors. 1905 88

Artemis, a member of the SNM1 gene family, is a known phosphorylation target of ATM, ATR, and DNA-PKcs. We have previously identified two serine residues in Artemis (Ser(516) and Ser(645)) that are subject to phosphorylation by ATM and are involved in mediating recovery from the G(2)/M checkpoint in response to ionizing radiation. Here we show that these same sites are also phosphorylated by ATR in response to various types of replication stress including UVC, aphidicolin, and hydroxyurea. We also show that mutation of the Ser(516) and Ser(645) residues causes a prolonged S phase checkpoint recovery after treatment with UV or aphidicolin, and that this delayed recovery process coincides with a prolonged stabilization of cyclin E and down-regulation of Cdk2 kinase activity. Furthermore, we show that Artemis interacts with the F-box protein Fbw7, and that this interaction regulates cyclin E degradation through the SCF(Fbw7) E3 ubiquitin ligase complex. The interaction between Artemis and Fbw7 is regulated by phosphorylation of Ser(516) and Ser(645) sites that occur in response to replication stress. Thus, our findings suggest a novel pathway of recovery from the S phase checkpoint in that in response to replication stress phosphorylation of Artemis by ATR enhances its interaction with Fbw7, which in turn promotes ubiquitylation and the ultimate degradation of cyclin E.
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PMID:Artemis regulates cell cycle recovery from the S phase checkpoint by promoting degradation of cyclin E. 1942 8

Phyllodes tumors of the breast are diagnostically and managerially enigmatic, as their malignant potential is difficult to predict based on the standard morphologic criteria. Thus, there is a need for additional markers of biologic potential. Although a number of ancillary tests have been reported, consensus in the literature is lacking. We studied 38 cellular fibroadenomas and phyllodes tumors of various grade (World Health Organization benign, borderline, and malignant) with a panel of immunohistochemical stains (p53, CD117, phospho-Histone3, mdm2, cdk4) and screened 26 of the tumors for mutations across 30 cancer-related genes using PCR and mass-spectrometry based methods. p53 and phospho-Histone3 (mitotic marker) showed increased staining in higher grade phyllodes tumors. CD117, mdm2, and cdk4 showed no difference in expression across different grades of phyllodes tumors. Mutational analysis revealed an S8R substitution in FBX4 (an E3 ubiquitin ligase) in 3 cases: 1 benign and 2 borderline. The S8R substitution seems to be more common in phyllodes tumors (11.5%) as compared with other cancers. FBX4 S8R cases had high cyclin D1 expression, but this finding was not specific. Our data support earlier studies showing that p53 has potential use in pathologic assessment of phyllodes tumors, and we newly characterized phospho-Histone3 for this application. Further studies are needed to characterize the molecular pathogenesis of the phyllodes tumors, as we were unable to identify activating mutations despite screening for a large panel of activating hotspot mutations. The significance of the FBX4 substitution deserves further investigation.
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PMID:Immunohistochemical and molecular markers in breast phyllodes tumors. 2103 Aug 60

Artemis, a member of the SNM1 gene family, is a multifunctional phospho-protein that has been shown to have important roles in V(D)J recombination, DNA double strand break repair, and stress-induced cell-cycle checkpoint regulation. We show here that Artemis interacts with the Cul4A-DDB1 E3 ubiquitin ligase via a direct interaction with the substrate-specificity receptor DDB2. Furthermore, Artemis also interacts with the CDK inhibitor and tumor suppressor p27, a substrate of the Cul4A-DDB1 ligase, and both DDB2 and Artemis are required for the degradation of p27 mediated by this complex. We also show that the regulation of p27 by Artemis and DDB2 is important for cell cycle progression in normally proliferating cells and in response to serum deprivation. These findings thus define a function for Artemis as an effector of Cullin-based E3 ligase-mediated ubiquitylation, demonstrate a novel pathway for the regulation of p27, and show that Cul4A-DDB1(DDB2-Artemis) regulates G1 phase cell cycle progression in mammalian cells.
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PMID:Artemis interacts with the Cul4A-DDB1DDB2 ubiquitin E3 ligase and regulates degradation of the CDK inhibitor p27. 2213 38

Glucocorticoid therapy is an important treatment modality of hematological malignancies, especially T-cell acute lymphoblastic leukemia (T-ALL). Glucocorticoids are known to induce a cell cycle arrest and apoptosis in T-lymphoma cells. We could demonstrate that the cell cycle arrest induced by the synthetic glucocorticoid dexamethasone (Dex) clearly precedes apoptosis in human CEM T-ALL and murine S49.1 T-lymphoma cells. Cyclin D3 is strongly downregulated, whereas the CDK inhibitor p27 (Kip1) (p27) is strongly upregulated in response to dexamethasone in these cells. RNAi-mediated knockdown of p27 as well as overexpression of its negative regulator Skp2 revealed the critical function of p27 in the Dex-induced G 1 arrest of CEM cells. Our studies indicate that several mechanisms contribute to the increase of p27 protein in our T-lymphoma cell lines. We found a significant upregulation of p27 mRNA in S49.1 and CEM cells. In addition, Dex treatment activated the mouse p27 promotor in reporter gene experiments, indicating a transcriptional regulation. However, the relatively moderate induction of p27 mRNA levels by Dex did not explain the strong increase of p27 protein in CEM and S49.1 cells. We found clear evidence for a posttranslational mechanism responsible for the robust increase in p27 protein. Dex treatment of S49.1 and CEM cells increases the half-life of p27 protein, which indicates that decreased protein degradation is the primary mechanism of p27 induction by glucocorticoids. Interestingly, we found that Dex treatment decreased the protein and mRNA levels of the negative regulator of p27 protein and E3 ubiquitin ligase subunit Skp2. We conclude that the cell cycle inhibitor p27 and its negative regulator Skp2 are key players in the glucocorticoid-induced growth suppression of T-lymphoma cells and should be considered as potential drug targets to improve therapies of T-cell malignancies.
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PMID:The p27-Skp2 axis mediates glucocorticoid-induced cell cycle arrest in T-lymphoma cells. 2390 23


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