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

The retinoblastoma-related protein p130 is a putative negative regulator of cell proliferation in mammalian cells. In this study, p130 is shown to exist in multiple phosphorylated forms in human cells. In glioblastoma T98G cells synchronized by serum deprivation, specific phosphorylated forms of p130 are found at different times after serum re-stimulation. Two phosphorylated forms of p130 only found in serum-arrested T98G cells and in early G1 phase associate with the adenovirus oncoprotein E1A in vitro. One of these two forms corresponds to the in vivo E1A-associated p130 in 293 cells, which express endogenous E1A protein. Moreover, p130 undergoes an abrupt shift to a unique phosphorylated form in mid G1 which is the only p130 form found during the remaining phases of the cell cycle. This phosphorylated form possesses an associated histone H1 kinase activity that is most active in late S phase and G2/M. The cell cycle-dependent expression pattern of cyclins in T98G cells is compatible with cyclin D1/CDK complexes driving the shift to this phosphorylated p130 form in mid G1. These results suggest that the putative growth inhibitory function of p130 is regulated by phosphorylation of this protein. They also suggest that differential phosphorylation of p130 during the cell cycle plays distinct roles in the regulation of p130 function.
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PMID:Cell cycle-dependent phosphorylation of the retinoblastoma-related protein p130. 765 44

The mammalian nuclear protein E2F-1 has recently been cloned based on its ability to bind the retinoblastoma protein. To determine whether E2F-1 plays a role in the control of the cell proliferation, we introduced an inducible construct expressing an E2F-1 antisense RNA into the human glioblastoma T98G cell line and assessed DNA synthesis during the cell cycle. Expression of the antisense transcripts during the G1-S transition resulted in a marked delay in the completion of DNA synthesis. Band-shift analysis of bacterially produced E2F-1 showed that this protein bound to the promoters of human DNA polymerase-alpha, cyclin D1, and c-myb but not to the cdc2 gene promoter. E2F-1 also transactivated the bound promoters in transient transfection assays. These results suggest a major role for E2F-1 in the control of cell cycle progression via transcriptional regulation of proliferation-associated genes.
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PMID:Correlation between E2F-1 requirement in the S phase and E2F-1 transactivation of cell cycle-related genes in human cells. 813 37

The aim of this study was to demonstrate that the induction of growth arrest in human glioblastoma multiforme (GBM) cell lines by retrovirus-mediated transduction of growth control genes was dependent upon the integrity of specific endogenous control pathways. We assessed the status of the endogenous p16INK4A, p21CIP1, pRb, or p53 genes in eight GBM lines. As expected, we found varied combinations of gene defects. The outcome of transducing five of these cell lines with p16INK4A, p21CIP1, pRb, or p53 genes was not entirely predictable. The growth-inhibitory effects mediated by the transfer of the gene encoding p16 was dependent on the presence of the pRb protein, but was independent of p53 status. p21, a broadly active CDK inhibitor and a strong inducer of growth arrest, was not a universal growth suppressor in the group of glioblastoma cell lines analyzed. The suppression of GBM cell proliferation by viruses encoding pRb or p53 was generally predictable and appeared to be independent of the status of either p16 or p21. Suppression of cell growth was assessed by a colony formation assay, by observance of alterations in morphology, and by cell viability staining for trypan blue exclusion. Our findings suggest that to accomplish the suppression of GBM cell proliferation by the transduction of these cell-cycle control genes, the status of endogenous cell-cycle control genes must be taken into account.
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PMID:Restoration of growth arrest by p16INK4, p21WAF1, pRB, and p53 is dependent on the integrity of the endogenous cell-cycle control pathways in human glioblastoma cell lines. 945 56

DNA damaging agents such as ultraviolet (UV) induce cell cycle arrest followed by apoptosis in cells where irreparable damage has occurred. Here we show that during early phase G1 arrest which occurs in UV-irradiated human U343 glioblastoma cells, there are (1) decreases in cyclin D1 and cdk4 levels which parallel a loss of S-phase promoting cyclin D1/cdk4 complexes, and (2) increases in p53 and p21 protein levels. We also show that the late phase UV-induced apoptosis of U343 cells occurs after cell cycle re-entry and parallels the reappearance of cyclin D1 and cdk4 and cyclin D1/cdk4 complexes. These findings suggest that cyclin D1 can abrogate UV-induced G1 arrest and that the p53-mediated apoptosis that occurs in these cells is dependent on cyclin D1 levels. We examined these possibilities using U343 cells that ectopically express cyclin D1 and found that indeed cyclin D1 can overcome the cell cycle arrest caused by UV. Moreover, the appearance of p53 protein and the induction of apoptosis in UV-irradiated cells was found to be dependent on the level of ectopically expressed cyclin D1. These findings, therefore, indicate that expression of cyclin D1 following DNA damage is essential for cell cycle re-entry and p53-mediated apoptosis.
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PMID:Role for cyclin D1 in UVC-induced and p53-mediated apoptosis. 1038 51

The TRAIL death receptor KILLER/DR5 is induced by DNA damaging agents in wild-type p53-expressing cells. Here we show that, unlike the p53-target CDK-inhibitor p21WAF1/CIP1, the TRAIL death receptor KILLER/DR5 is only induced in cells undergoing p53-dependent apoptosis and not cell cycle arrest. Thus GM glioblastoma cells carrying an inducible MMTV-driven p53 gene undergo cell cycle arrest and upregulate p21 but not KILLER/DR5 expression upon dexamethasone exposure. WI38 normal lung fibroblasts undergoing cell cycle arrest in response to ionizing irradiation also induce p21 but not KILLER/DR5 gene expression. KILLER/DR5 upregulation is also deficient in irradiated lymphoblastoid cells derived from patients with Ataxia Teleangiectasia suggesting a role for the ATM-p53 pathway in regulating KILLER/DR5 expression after DNA damage. Inhibition of transcription by Actinomycin D blocks both KILLER/DR5 and p21 induction in cells undergoing p53-dependent apoptosis. Our results suggest that the p53-dependent transcriptional induction of KILLER/DR5 death receptor is restricted to cells undergoing apoptosis and not cells undergoing exclusively p53-dependent G1 arrest.
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PMID:Induction of the TRAIL receptor KILLER/DR5 in p53-dependent apoptosis but not growth arrest. 1059 42

The c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) pathway is activated by numerous cellular stresses. Although it has been implicated in mediating apoptosis and growth factor signaling, its role in regulating cell growth is not yet clear. Here, the influence of JNK on basal (unstimulated) growth of human tumor glioblastoma T98G cells was investigated using highly specific JNK antisense oligonucleotides to inhibit JNK expression. Transient depletion of either JNK1 or JNK2 suppressed cell growth associated with an inhibition of DNA synthesis and cell cycle arrest in S phase. The growth-inhibitory potency of JNK2 antisense ((JNK)2 IC(50) = 0.14 micrometer) was greater than that of JNK1 antisense ((JNK)1 IC(50) = 0.37 micrometer), suggesting that JNK2 plays a dominant role in regulating growth of T98G cells. Indeed, JNK2 antisense-treated populations exhibited greater inhibition of DNA synthesis and accumulation of S-phase cells than did the JNK1 antisense-treated cultures, with a significant proportion of these cells detaching from the tissue culture plate. JNK2 (but not JNK1) antisense-treated cultures exhibited marked elevation in the expression of the cyclin-dependent kinase inhibitor p21(cip1/waf1) accompanied by inhibition of Cdk2/Cdc2 kinase activities. Taken together, these results indicate that JNK is required for growth of T98G cells in nonstress conditions and that p21(cip1/waf1) may contribute to the sustained growth arrest of JNK2-depleted T98G cultures.
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PMID:c-Jun N-terminal kinase is essential for growth of human T98G glioblastoma cells. 1082 81

The PTEN tumor suppressor acts as a phosphatase for phosphatidylinositol-3,4,5-trisphosphate (PIP3) [1, 2]. We have shown previously that PTEN negatively controls the G1/S cell cycle transition and regulates the levels of p27(KIP1), a CDK inhibitor [3, 4]. Recently, we and others have identified an ubiquitin E3 ligase, the SCF(SKP2) complex, that mediates p27 ubiquitin-dependent proteolysis [5-7]. Here we report that PTEN and the PI 3-kinase pathway regulate p27 protein stability. PTEN-deficiency in mouse embryonic stem (ES) cells causes a decrease of p27 levels with concomitant increase of SKP2, a key component of the SCF(SKP2) complex. Conversely, in human glioblastoma cells, ectopic PTEN expression leads to p27 accumulation, which is accompanied by a reduction of SKP2. We found that ectopic expression of SKP2 alone is sufficient to reverse PTEN-induced p27 accumulation, restore the kinase activity of cyclin E/CDK2, and partially overcome the PTEN-induced G1 cell cycle arrest. Consistently, recombinant SCF(SKP2) complex or SKP2 protein alone can rescue the defect in p27 ubiquitination in extracts prepared from cells treated with a PI 3-kinase inhibitor. Our findings suggest that SKP2 functions as a critical component in the PTEN/PI 3-kinase pathway for the regulation of p27(KIP1) and cell proliferation.
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PMID:PTEN regulates the ubiquitin-dependent degradation of the CDK inhibitor p27(KIP1) through the ubiquitin E3 ligase SCF(SKP2). 1125 Jan 55

Amplification of the epidermal growth factor receptor (EGFR) gene is found in about 40% of glioblastomas (GBMs) but is rarely detected in GBM cell lines. We confirmed that the exceptional SKMG-3 GBM cell line retained amplified EGFR genes in vitro, and found that these sequences were concentrated on extra-chromosomal DNA particles similar to double-minute chromosomes. The cells contained two other gene mutations that are associated with high-grade astrocytic tumors: extra-chromosomal amplification of the cyclin-dependent kinase-4 (CDK4) gene and a homozygous mutation within the PTEN tumor suppressor gene. Immunoblots revealed very high levels of EGFR, moderately increased expression of CDK4, and no detectable PTEN protein. The overexpressed SKMG-3 EGFRs responded to exogenous ligand and resembled normal rather than mutant receptors. A heterozygous mutation of the p53 gene (p53R282W) correlated with failure of radiation to induce the expression of cyclin-dependent kinase inhibitor p21waf1 or an early G1 cell cycle arrest. Although each of these gene mutations occurs in GBMs, SKMG-3 cells had an unusual genotype in that a p53 gene mutation co-existed with amplified EGFR genes. Nonetheless, the SKMG-3 cell line can be exploited as a model to study how oncogenic EGFR signals in GBM cells interact with over-expressed CDK4 and loss of PTEN to confer the malignant phenotype.
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PMID:Glioblastoma-related gene mutations and over-expression of functional epidermal growth factor receptors in SKMG-3 glioma cells. 1151 90

Cyclin K, a newly recognized member of the "transcription" cyclin family, may play a dual role by regulating CDK and transcription. Using cDNA microarray technology, we found that cyclin K mRNA was dramatically increased in U373MG, a glioblastoma cell line deficient in wild-type p53, in the presence of exogenous p53. An electrophoretic mobility-shift assay showed that a potential p53-binding site (p53BS) in intron 1 of the cyclin K gene could indeed bind to p53 protein. Moreover, a heterologous reporter assay revealed that the p53BS possessed p53-dependent transcriptional activity. Colony-formation assays indicated that overexpression of cyclin K suppressed growth of T98G, U373MG and SW480 cells. The results suggested that cyclin K may play a role in regulating the cell cycle or apoptosis after being targeted for transcription by p53.
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PMID:Cyclin K as a direct transcriptional target of the p53 tumor suppressor. 1198 47

Glioblastoma (GBM) remains one of the most challenging solid cancers to treat due to its highly proliferative, angiogenic and invasive nature. The small molecule CDK inhibitor, flavopiridol, has demonstrated antitumor activity in human xenograft models and is currently in clinical trials showing efficacy in patients with advanced disease. We have developed an experimental animal model using the murine glioma GL261 cells as a novel in vivo system to screen potential therapeutic agents for GBM. Results of in vitro testing demonstrate that flavopiridol has several relevant clinical characteristics such as its ability to: 1. inhibit cell growth; 2. inhibit cell migration; 3. decrease expression of cyclin D1, CDK4 and p21; 4. induce apoptosis in cells with high levels of p27 expression; and 5. decrease the expression of the anti-apoptotic protein Bcl-2. The mechanism by which flavopiridol induces apoptosis is mitochondrial-mediated. We demonstrate by electron microscopy and immunohistochemistry that drug treatment induces mitochondrial damage that was accompanied by the release of cytochrome c into the cytosol together with the translocation of apoptosis inducing factor (AIF) into the nucleus. This finding in murine glioma cells differs from the mechanism of flavopiridolinduced cell death reported by us for human glioma cells (Alonso et al., Mol Cancer Ther 2003; 2:139) where drug treatment induced a caspase- and cytochrome c-independent pathway in the absence of detectable damage to mitochondria. In apoptotic human glioma cells only translocation of AIF into the nucleus occurred. Thus, the same drug kills different types of glioma cells by different mitochondrial-dependent pathways.
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PMID:Flavopiridol induces mitochondrial-mediated apoptosis in murine glioma GL261 cells via release of cytochrome c and apoptosis inducing factor. 1273 34


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