Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Flavopiridol (L86-8275), a N-methylpiperidinyl, chlorophenyl flavone, can inhibit cell cycle progression in either G1 or G2 and is a potent cyclin-dependent kinase (CDK) 1 inhibitor. In this study, we used MCF-7 breast carcinoma cells that are wild type for p53 and pRb positive and contain CDK4-cyclin D1 and MDA-MB-468 breast carcinoma cells that are mutant p53, pRb negative, and lack CDK4-cyclin D1 to investigate the G1 arrest produced by Flavopiridol. Recombinant CDK4-cyclin D1 was inhibited potently by Flavopiridol (Kiapp, 65 nM), competitive with respect to ATP. Surprisingly, CDK4 immunoprecipitates derived from Flavopiridol-treated MCF-7 cells (3 h, 300 nM Flavonolpiridol) had an approximately 3-fold increased kinase activity compared with untreated cells. Cyclin D and CDK4 levels were not different at 3 hr, but cyclin D levels and CDK4 kinase activity decreased thereafter. The phosphorylation state of pRb was shifted from hypercoincident to hypocoincident with the development of G1 arrest. Asynchronous MDA-MB-468 cells were inhibited in cell cycle progression at both G1 and G2 by Flavopiridol. Flavopiridol inhibited the in vitro kinase activity of CDK2 using an immune complex kinase assay (IC50, 100 nM at 400 microM ATP). Immunoprecipitated CDK2 kinase activity from either MCF-7 or MDA-MB-468 cells exposed to Flavopiridol (300 nM) for increasing time showed an initial increased activity (approximately 1.5-fold at 3 h) compared with untreated cells, followed by a loss of kinase activity to immeasurable levels by 24 h. This increased immunoprecipitated kinase activity was dependent on the Flavopiridol concentration added to intact cells and was associated with a reduction of CDK2 tyrosine phosphorylation. Cyclin E and A levels were not altered to the same extent as cyclin D, and neither CDK4 nor CDK2 levels were changed in response to Flavopiridol. Inhibition of the CDK4 and/or CDK2 kinase activity by Flavopiridol can therefore account for the G1 arrest observed after exposure to Flavopiridol.
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PMID:Flavopiridol induces G1 arrest with inhibition of cyclin-dependent kinase (CDK) 2 and CDK4 in human breast carcinoma cells. 867 31

Cell cycle progression is mainly controlled by the hetero-dimeric protein kinase complex named SPF (S-phase promoting factor) and MPF (M-phase promoting factor), consisting of CDKs and the regulator cyclins, which are involved in G1/S and G2/M transitions, respectively. Moreover, SPF is modulated by not only various oncoproteins positively, but also tumor suppresive gene products negatively. These regulator proteins are extremely unstable in cells, oscillating during cell cycle, and cell cycle stage-dependent destruction of specific factors is required for cell cycle progression, but molecular mechanism of their destabilization remains to be clarified. The ubiquitin-proteasome system is responsible for selective- and ATP-dependent degradation of various types of short-lived proteins in the cytoplasm and the nucleus. In this article, we review briefly the proteolytic pathway mediated by ubiquitin and the proteasome, and the degradation mechanism of major cell cycle protein factors, such as Mos, p53, cyclin B, Fos/Jun and NFkappaB/IkappaB.
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PMID:[Degradation mechanism of cell cycle factors by the proteasome]. 890 49

Human papillomavirus (HPV) infection is believed to play a central role in cervical carcinogenesis. Specifically, two viral oncoproteins, E6 and E7, possess transforming ability and have been shown to interact with the cellular tumor suppressors p53 and p105, the retinoblastoma (Rb) gene product. To test the hypothesis that E6 and E7 play an active role in the maintenance of the malignant phenotype and may be ideal targets for antigene therapy, we tested the antiproliferative effects of phosphorothioate oligodeoxynucleotides (oligos) targeting HPV-16 E6 and E7 in cervical cancer cell lines and primary tumor explants. The ATP cell viability assay was used to measure growth effects of 27-mer antisense oligos targeting the ATG translational start region of HPV-16 E6 and E7 sequences in HPV-16-positive cell lines SiHa and CaSki and four advanced, primary cervical tumor explants. A random oligo sequence, an HPV-18-positive and HPV-negative cell line, one histologically confirmed endometrial and two ovarian tumors were used as negative controls. HPV type was confirmed by hybrid capture techniques. Cell lines and sterile (staging laparotomy) tumor cells were plated at 5000 cells/0.1 ml and 100,000 cells/0.5 ml in 96-well plates or soft agar, respectively, and incubated at 37 degrees C with a single treatment of oligos at 0-16 microM. E6/E7 combinations at a fixed ratio of 1:1 were used at 0-8 microM for each oligo. Cellular ATP was measured by luciferin/luciferase fluorescence on Day 6. HPV-16 E6 and E7 oligos showed antiproliferative effects in all HPV-16-positive cell lines and primary tumor explants (IC50s 6.9-9.5 microM for cell lines, 9.1-12.1 microM primary cervical tumors), while the HPV-negative C33-A cell line and HPV-18-positive cell line HeLa were relatively insensitive to the HPV-16 oligos (IC50s > 30 microM extrapolated). The endometrial and two ovarian primary tumors were also insensitive to the HPV E6 and E7 oligos (IC50s > 25 microM extrapolated). Random oligos had little effect on cell growth at concentrations up to 16 microM (< 25% inhibition), except in CaSki (@50% inhibition at 16 microM). Combinations of E6 and E7 demonstrated mixed synergistic and antagonistic effects as determined by combination indices (CI) derived from median effect parameters. In the HPV-16-positive primary cervical tumors and the cell line SiHa, E6/E7 combinations were synergistic at low doses (< 25% growth inhibitory dose range) and antagonistic at doses above this. For the HPV-16-positive cell line CaSki, however, E6/E7 combinations were antagonistic at all dose ranges. Phosphorothioate oligos directed against the viral oncogenes E6 and E7 were shown to have antiproliferative effects specific to HPV-containing cancer cells. These specific antiproliferative effects suggest that HPV-16 E6 and E7 sequences play an active role in the malignant growth properties of cervical cancer cells and may be ideal targets for antigene therapy.
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PMID:In vitro antigene therapy targeting HPV-16 E6 and E7 in cervical carcinoma. 899 42

A crude fraction that contains ubiquitin-protein ligases contains also a proteolytic activity of approximately 100 kDa that cleaves p53 to several fragments. The protease does not require ATP and is inhibited in the crude extract by an endogenous approximately 250 kDa inhibitor. The proteinase can be inhibited by chelating the Ca2+ ions, by specific cysteine proteinase inhibitors and by peptide aldehyde derivatives that inhibit calpains. Purified calpain demonstrates an identical activity that can be inhibited by calpastatin, the specific protein inhibitor of the enzyme. Thus, it appears that the activity we have identified in the extract is catalyzed by calpain. The calpain in the extract degrades also N-myc, c-Fos and c-Jun, but not lysozyme. In crude extract, the calpain activity can be demonstrated only when the molar ratio of the calpain exceeds that of its native inhibitor. Recent experimental evidence implicates both the ubiquitin proteasome pathway and calpain in the degradation of the tumor suppressor, and it was proposed that the two pathways may play a role in targeting the protein under various conditions. The potential role of the two systems in this important metabolic process is discussed.
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PMID:On the involvement of calpains in the degradation of the tumor suppressor protein p53. 910 77

One reason for the failure of chemotherapy is the overexpression of the multidrug resistance gene, MDR1. The product of this gene is the multidrug transporter P-glycoprotein, an ATP-dependent pump that extrudes drugs from the cytoplasm. Some tumors inherently express P-glycoprotein, whereas others acquire the ability to do so after exposure to certain chemotherapeutic agents, often by the mechanism of gene amplification. Classical Wilms' tumors (nephroblastoma) typically respond to therapy and have a good prognosis. On the contrary, anaplastic Wilms' tumors are generally refractory to chemotherapy. These anaplastic variants are rare (4.5% of all Wilms' tumors reported in the United States), aggressive, and often fatal forms of tumor, which are commonly thought to result from the progression of classical Wilms' tumors. To investigate the basis for this differential response to therapy, we examined a number of classical and anaplastic Wilms' tumors for the expression of the MDR1 gene by immunohistochemical and mRNA analysis. Classical Wilms' tumors consistently did not express P-glycoprotein except in areas of tubular differentiation, as in normal kidney. Similarly, two of three anaplastic tumors failed to show P-glycoprotein expression. In contrast, cultured cells derived from a third anaplastic tumor, W4, exhibited strong P-glycoprotein expression and were drug resistant in vitro. Southern analysis revealed that W4 cells contained a single copy of the MDR1 gene per haploid genome similar to normal cells, demonstrating that the overexpression of MDR1 was not caused by gene amplification. Transcriptional activation of the MDR1 gene would be in keeping with the concept that p53 might act as a transcriptional repressor of the MDR1 gene.
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PMID:Anaplasia and drug selection-independent overexpression of the multidrug resistance gene, MDR1, in Wilms' tumor. 912 18

Simian virus 40 (SV40) encodes two proteins, large T antigen and small t antigen that contribute to virus-induced tumorigenesis. Both proteins act by targeting key cellular regulatory proteins and altering their function. Known targets of the 708-amino-acid large T antigen include the three members of the retinoblastoma protein family (pRb, p107, and p130), members of the CBP family of transcriptional adapter proteins (cap-binding protein [CBP], p300, and p400), and the tumor suppressor p53. Small t antigen alters the activity of phosphatase pp2A and transactivates the cyclin A promoter. The first 82 amino acids of large T antigen and small t antigen are identical, and genetic experiments suggest that an additional target(s) important for transformation interacts with these sequences. This region contains a motif similar to the J domain, a conserved sequence found in the DnaJ family of molecular chaperones. We show here that mutations within the J domain abrogate the ability of large T antigen to transform mammalian cells. To examine whether a purified 136-amino-acid fragment from the T antigen amino terminus acts as a DnaJ-like chaperone, we investigated whether this fragment stimulates the ATPase activity of two hsc70s and discovered that ATP hydrolysis is stimulated four- to ninefold. In addition, ATPase-defective mutants of full-length T antigen, as well as wild-type small t antigen, stimulated the ATPase activity of hsc70. T antigen derivatives were also able to release an unfolded polypeptide substrate from an hsc70, an activity common to DnaJ chaperones. Because the J domain of T antigen plays essential roles in viral DNA replication, transcriptional control, virion assembly, and tumorigenesis, we conclude that this region may chaperone the rearrangement of multiprotein complexes.
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PMID:The amino-terminal transforming region of simian virus 40 large T and small t antigens functions as a J domain. 923 32

Ataxia-telangiectasia (A-T) is a recessive multi-system disorder caused by mutations in the ATM gene at 11q22-q23 (ref. 3). The risk of cancer, especially lymphoid neoplasias, is substantially elevated in A-T patients and has long been associated with chromosomal instability. By analysing tumour DNA from patients with sporadic T-cell prolymphocytic leukaemia (T-PLL), a rare clonal malignancy with similarities to a mature T-cell leukaemia seen in A-T, we demonstrate a high frequency of ATM mutations in T-PLL. In marked contrast to the ATM mutation pattern in A-T, the most frequent nucleotide changes in this leukaemia were missense mutations. These clustered in the region corresponding to the kinase domain, which is highly conserved in ATM-related proteins in mouse, yeast and Drosophila. The resulting amino-acid substitutions are predicted to interfere with ATP binding or substrate recognition. Two of seventeen mutated T-PLL samples had a previously reported A-T allele. In contrast, no mutations were detected in the p53 gene, suggesting that this tumour suppressor is not frequently altered in this leukaemia. Occasional missense mutations in ATM were also found in tumour DNA from patients with B-cell non-Hodgkin's lymphomas (B-NHL) and a B-NHL cell line. The evidence of a significant proportion of loss-of-function mutations and a complete absence of the normal copy of ATM in the majority of mutated tumours establishes somatic inactivation of this gene in the pathogenesis of sporadic T-PLL and suggests that ATM acts as a tumour suppressor. As constitutional DNA was not available, a putative hereditary predisposition to T-PLL will require further investigation.
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PMID:Clustering of missense mutations in the ataxia-telangiectasia gene in a sporadic T-cell leukaemia. 928 6

For more than two-thirds of this century we have known that one of the most common and profound phenotypes of cancer cells is their propensity to utilize and catabolize glucose at high rates. This common biochemical signature of many cancers, particularly those that are poorly differentiated and proliferate rapidly, has remained until recently a "metabolic enigma." However, with many advances in the biological sciences having been applied to this problem, cancer cells have begun to reveal their molecular strategies in maintaining an aberrant metabolic behavior. Specifically, studies performed over the past two decades in our laboratory demonstrate that hexokinase, particularly the Type II isoform, plays a critical role in initiating and maintaining the high glucose catabolic rates of rapidly growing tumors. This enzyme converts the incoming glucose to glucose-6-phosphate, the initial phosphorylated intermediate of the glycolytic pathway and an important precursor of many cellular "building blocks." At the genetic level the tumor cell adapts metabolically by first increasing the gene copy number of Type II hexokinase. The enzyme's gene promoter, in turn, shows a wide promiscuity toward the signal transduction cascades active within tumor cells. It is activated by glucose, insulin, low oxygen "hypoxic" conditions, and phorbol esters, all of which enhance the rate of transcription. Also, the tumor cell uses the tumor suppressor p53, which is usually modified by mutations to debilitate cell cycle controls, to further activate hexokinase gene transcription. This results in both enhanced levels of the enzyme, which binds to mitochondrial porins thus gaining preferential access to mitochondrially generated ATP, and in a decreased susceptibility to product inhibition and proteolytic degradation. Significantly, these multiple strategies all work together to enable tumor cells to develop a metabolic strategy compatible with rapid proliferation and prolonged survival.
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PMID:Aberrant glycolytic metabolism of cancer cells: a remarkable coordination of genetic, transcriptional, post-translational, and mutational events that lead to a critical role for type II hexokinase. 938 94

We have proposed that reduced activity of inosine-5'-monophosphate dehydrogenase (IMPD; IMP:NAD oxidoreductase, EC 1.2.1.14), the rate-limiting enzyme for guanine nucleotide biosynthesis, in response to wild-type p53 expression, is essential for p53-dependent growth suppression. A gene transfer strategy was used to demonstrate that under physiological conditions constitutive IMPD expression prevents p53-dependent growth suppression. In these studies, expression of bax and waf1, genes implicated in p53-dependent growth suppression in response to DNA damage, remains elevated in response to p53. These findings indicate that under physiological conditions IMPD is a rate-determining factor for p53-dependent growth regulation. In addition, they suggest that the impd gene may be epistatic to bax and waf1 in growth suppression. Because of the role of IMPD in the production and balance of GTP and ATP, essential nucleotides for signal transduction, these results suggest that p53 controls cell division signals by regulating purine ribonucleotide metabolism.
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PMID:Inosine-5'-monophosphate dehydrogenase is a rate-determining factor for p53-dependent growth regulation. 943 88

Human papillomavirus (HPV) 16 E6 induces the degradation of the tumour suppressor protein p53 by the ubiquitin-dependent proteolysis pathway. In vitro, this process involves the formation of a trimolecular complex between E6, p53 and a cellular protein E6-associated protein (E6-AP). However, an analysis of their potential interactions in vivo has not been carried out. We have established a model for the expression and analysis of the interactions of these three proteins in insect cells, a eukaryotic system where potentially crucial modifications of the proteins will occur. In baculovirus-infected cells the degradation of p53 can occur. However, p53 is only degraded early in the infectious cycle due to a lack of ATP at later times. Consequently, substantial quantities of material can be produced in this system for further analysis. Evidence is also provided that, in vivo, E6 can interact with p53 in the absence of E6-AP and that E6-AP can interact with p53 in the absence of E6. Furthermore, analysis of the subcellular localization of the proteins using both biochemical fractionation and indirect immunofluorescence suggests that the degradation of p53 occurs in the perinuclear region of the cell.
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PMID:Characterization of the interactions of human papillomavirus type 16 E6 with p53 and E6-associated protein in insect and human cells. 951 27


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