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)

Mutagenesis of the p53 tumor-suppressor gene represents the most common genetic alteration in human malignancies but has not yet been investigated in Klatskin tumors. Cancerous and normal liver tissues were obtained from 12 patients after surgical resection of Klatsin tumors. Genomic DNA was extracted and served as a template for PCR amplification and sequencing of a 1,574-bp fragment of the p53 gene comprising the exons 5 through 8. Immunohistochemical expression analysis was performed using five different antibodies. Missense mutations were detected in 2 of 12 patients--one transversion on codon 273 (Arg --> Leu) and a transition on codon 168 (His --> Arg). In all specimens, immunohistochemistry was negative regarding a nuclear overexpression. An apparent clinicopathologic impact of p53 mutations was not observed. This report on mutagenesis of the p53 gene in Klatskin tumors shows that the most commonly mutated tumor suppressor gene in human cancers is also mutated in a subset of patients with Klatskin tumors. Assessment of a clinical or pathological impact of p53 mutagenesis on Klatskin tumors requires evaluation in larger studies.
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PMID:p53 mutagenesis in Klatskin tumors. 974 11

A new cell line, Yumoto, derived from a squamous cell carcinoma of the uterine cervix, was established from serially transplanted tumor tissues in nude mice. Monolayer cultured cells were polygonal and formed pavement-like sheet. They showed a piling-up tendency and were devoid of contact inhibition. Electron micrographs demonstrated the presence of microvilli on the cell surface, abundant tonofilaments in the cytoplasm, and the connection with desmosomes. These electron micrographical characteristics of Yumoto cells were consistent with those of squamous cell origin. Yumoto cells were highly tumorigenic in BALB/c nude mice and produced a well-differentiated squamous cell carcinoma of keratinizing type which closely resembled to the original tumor tissues in nude mice. The presence of HPV DNA was examined using polymerase chain reaction and Southern blot analysis, but no known types of HPV DNA could be detected. Exons 2 through 11 of the p53 gene were analyzed by direct DNA sequencing, revealing a homozygous mutation at codon 281 in exon 8, GAC to CAC (Asp-->His). Furthermore, physical p53-gene deletion was demonstrated by dual-color fluorescence in situ hybridization. This cell line is useful for studying the carcinogenesis of cervical carcinoma and for investigating the biological characteristics of a HPV-negative and mutated p53 squamous cell carcinoma of the uterine cervix.
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PMID:Establishment and characterization of a new HPV-negative squamous cell carcinoma cell line (Yumoto) from the human uterine cervix. 979 Jul 85

Interleukin-1 (IL-1) causes G1-phase growth arrest of A375-C6 human melanoma cells by hypophosphorylation of the retinoblastoma susceptibility gene product Rb. Because p53 and p21/WAF1 proteins are key components of growth arrest pathways involving Rb hypophosphorylation, we tested the functional role of these two proteins in IL-1 action. Exposure to IL-1 caused induction of both p53 and p21/WAF1 proteins. However, inhibition of p53 function by the K1 mutant of SV40-T antigen or by m175 (Arg to His) dominant-negative mutant of p53 did not result in abrogation of IL-1 action, suggesting that p53 function is not required for growth arrest by IL-1. Studies aimed at testing the role of p21/WAF1 in IL-1 action indicated that IL-1 induced p21/WAF1 expression independently of the p53 status of the cells. However, inhibition of p21/WAF1 expression resulted in only a marginal rescue from the growth-arresting action of IL-1. These findings imply that despite their induction, neither wild-type p53 nor p21 can fully account for the growth arrest by IL-1. Thus, a p53- and p21-independent pathway(s) mediates IL-1 action.
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PMID:The G1-phase growth-arresting action of interleukin-1 is independent of p53 and p21/WAF1 function. 980 20

We have previously identified a p53-independent apoptotic response that is delayed until 48-72 h after irradiation of colorectal adenoma and carcinoma cells. Because the delay appears to be in part due to a transient G2 cell cycle arrest, the importance of this checkpoint in the mechanism of ionizing radiation (IR)-induced death of colorectal tumor cells was investigated. An adenoma cell line with (282Arg-->Trp) mutant p53 (S/RG/C2) and a carcinoma cell line (PC/JW/FI) lacking p53 protein treated with 5 Gy IR in the presence of 1.5 mm caffeine (CAF) reduced IR-induced G2 arrest and increased the level of apoptosis (1.5-1.6-fold) 24 h after treatment. Increased IR apoptotic cell death with CAF significantly reduced IR cell survival over a 7-day period in S/RG/C2 and PC/JW/FI. To investigate whether CAF radiosensitization correlated with lack of wild-type (wt) p53, we studied transfected derivatives of an adenoma-derived cell line (PC/AA/C1), in which the endogenous wt p53 activity was disrupted by the expression of a dominant negative (273Arg-->His) p53 mutant protein (designated AA/273p53/B). This p53-defective cell line was also radiosensitized by CAF, whereas the vector control (AA/PCMV/D), which retained wt p53 activity, was not. In addition, as with the S/RG/C2 and PC/JW/FI cell lines, the 7-day IR cell survival was reduced significantly in AA/273p53/B compared with the vector control cell line. This suggests that radiosensitization by CAF and increased cell death is dependent on loss of wt p53 function. Interestingly, radiosensitization of the AA/273p53/B cell line was not associated with accelerated apoptosis but correlated with increased polyploid giant cells, which have been associated with disruption of cell cycle checkpoints and genomic instability. These results demonstrate that G2 checkpoint inhibition with CAF leads to preferential IR cell killing in cell lines in which wt p53 is inactivated and that this increased cell killing is not necessarily dependent on increased IR-induced apoptosis.
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PMID:Inhibition of radiation-induced G2 delay potentiates cell death by apoptosis and/or the induction of giant cells in colorectal tumor cells with disrupted p53 function. 981 21

A substantial portion of patients with estrogen receptor-positive breast cancer fail to respond to estrogen depletion or to the antiestrogen tamoxifen. The molecular changes that lead to tamoxifen resistance and estrogen-independent growth are unknown. To test the hypothesis that a p53 mutation could result in tamoxifen resistance and estrogen-independent growth, the MCF-7 cell line was transfected with p53 cDNA which was mutated at codon 179 (histidine to glutamine). MCF-7 is an estrogen receptor-positive, estrogen-dependent, tamoxifen-sensitive cell line with only wild-type p53. The presence of transfected mutant p53 cDNA was verified by the PCR, and overexpression of p53 protein was assessed by Western blotting. Five separate mutant-transfected clones were selected and tested in subsequent growth experiments. In monolayer culture, there was no consistent evidence of estrogen-independent growth or tamoxifen resistance in the mutant transfectants compared with vector-only controls or the parental cell line. In soft agar growth experiments, four of five mutant transfectants remained sensitive to tamoxifen in a dose-dependent manner. In the presence of wild-type p53, mutant 179 p53 protein does not result in estrogen-independent growth or tamoxifen resistance. These results do not exclude the possibility that other p53 mutational types could result in tamoxifen resistance, or that loss of the remaining wild-type allele may be necessary to result in this phenotype.
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PMID:p53 mutation and tamoxifen resistance in breast cancer. 981 13

The development of resistance to radiation and chemotherapeutic agents that cause DNA damage is a major problem for the treatment of breast and other cancers. The p53 tumor suppressor gene plays a direct role in the signaling of cell cycle arrest and apoptosis in response to DNA damage, and p53 gene mutations have been correlated with increased resistance to DNA-damaging agents. Herpes simplex virus thymidine kinase (HSV-tk) gene transfer followed by ganciclovir (GCV) treatment is a novel tumor ablation strategy that has shown good success in a variety of experimental tumor models. However, GCV cytotoxicity is believed to be mediated by DNA damage-induced apoptosis, and the relationship between p53 gene status, p53-mediated apoptosis, and the sensitivity of human tumors to HSV-tk/GCV treatment has not been firmly established. To address this issue, we compared the therapeutic efficacy of adenovirus-mediated HSV-tk gene transfer and GCV treatment in two human breast cancer cell lines: MCF-7 cells, which express wild-type p53, and MDA-MB-468 cells, which express high levels of a mutant p53 (273 Arg-His). Treating MCF-7 cells with AdHSV-tk/GCV led to the predicted increase in endogenous p53 and p21WAF1/CIP1 protein levels, and apoptosis was observed in a significant proportion of the target cell population. However, treating MDA-MB-468 cells under the same conditions resulted in a much stronger apoptotic response in the absence of induction in p21WAF1/CIP1 protein levels. This latter result suggested that HSV-tk/GCV treatment can activate a strong p53-independent apoptotic response in tumor cells that lack functional p53. To confirm this observation, four additional human breast cancer cell lines expressing mutant p53 were examined. Although a significant degree of variability in GCV chemosensitivity was observed in these cell lines, all displayed a greater reduction in cell viability than MCF-7 or normal mammary cells treated under the same conditions. These results suggest that endogenous p53 status does not correlate with chemosensitivity to HSV-tk/GCV treatment. Furthermore, evidence for a p53-independent apoptotic response serves to extend the potential of this therapeutic strategy to tumors that express mutant p53 and that may have developed resistance to conventional genotoxic agents.
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PMID:Differential chemosensitivity of breast cancer cells to ganciclovir treatment following adenovirus-mediated herpes simplex virus thymidine kinase gene transfer. 1019 85

Nerve growth factor (NGF)-induced neurite outgrowth from rat PC12 cells was coincident with elevated (>/=2-fold) levels of endogenous ubiquitin (Ub) protein conjugates, elevated rates of formation of 125I-labeled Ub approximately E1 (Ub-activating enzyme) thiol esters and 125I-labeled Ub approximately E2 (Ub carrier protein) thiol esters in vitro, and enhanced capacity to synthesize 125I-labeled Ub-protein conjugates de novo. Activities of at least four E2s were increased in NGF-treated cells, including E2(14K), a component of the N-end rule pathway. Ubiquitylation of 125 I-labeled beta-lactoglobulin was up to 4-fold greater in supernatants from NGF-treated cells versus untreated cells and was selectively inhibited by the dipeptide Leu-Ala, an inhibitor of Ub isopeptide ligase (E3). However, Ub-dependent proteolysis of 125I-labeled beta-lactoglobulin was not increased in supernatants from NGF-treated cells, suggesting that neurite outgrowth is promoted by enhanced rates of synthesis (rather than degradation) of Ub-protein conjugates. Consistent with this observation, neurite outgrowth was induced by proteasome inhibitors (lactacystin and clasto-lactacystin beta-lactone) and was associated with elevated levels of ubiquitylated protein and stabilization of the Ub-dependent substrate, p53. Lactacystin-induced neurite outgrowth was blocked by the dipeptide Leu-Ala (2 mM) but not by His-Ala. These data 1) demonstrate that the enhanced pool of ubiquitylated protein observed during neuritogenesis in PC12 cells reflects coordinated up-regulation of Ub-conjugating activity, 2) suggest that Ub-dependent proteolysis is a negative regulator of neurite outgrowth in vitro, and 3) support a role for E2(14K)/E3-mediated protein ubiquitylation in PC12 cell neurite outgrowth.
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PMID:Neurite outgrowth in PC12 cells. Distinguishing the roles of ubiquitylation and ubiquitin-dependent proteolysis. 1020 96

The cyclin-dependent kinase inhibitor 2a (Cdkn2a) locus encodes two distinct tumor suppressors, p16INK4a and p19ARF, whose functions interrelate in the regulation of cell proliferation as key components of the retinoblastoma and p53 pathways, respectively. In many types of cancer, alterations of Cdkn2a abrogate the functions of both suppressors, implying that both are integral to the genesis of certain cancer types. While this has been observed in mouse lung adenocarcinogenesis, recent observations also suggested that naturally occurring variation at the Cdkn2a locus is probably operative in the development of these tumors. Firstly, two common haplotypes of mouse Cdkn2a have been identified, each of which encodes cosegregating variants of p16INK4a and p19ARF. The p16INK4a variants differ at amino acids 18 (histidine or proline) and 51 (valine or isoleucine), whereas the p19ARF variants differ only at amino acid 72 (histidine or arginine). Secondly, genetic resistance to lung tumor formation appears to segregate with one particular haplotype, which also is deleted preferentially in lung adenocarcinomas of Cdkn2a heterozygous mice. Here we attempt to explain these observations and to characterize further the roles of p16INK4 and p19ARF in mouse lung tumorigenesis by examining the function and expression of each of the variants of Cdkn2a. Functional analysis showed that the proline 18/isoleucine 51 p16INK4a variant was diminished in cdk6 binding, cdk6 inhibition and NIH/3T3 fibroblast growth suppression compared with the histidine 18/valine 51 variant, whereas both of the p19ARF variants suppressed growth with similar potencies. Also, the different alleles for p16INK4a and p19ARF were transcribed equally in the normal lungs of Cdkn2a heterozygotes, as determined by comparative reverse transcription-polymerase chain reaction-single-stranded conformation polymorphism analysis. These results indicate that strain-specific variation in p16INK4a function is exploited in mouse lung tumorigenesis and strongly implicate a role for p16INK4a in lung cancer predisposition and development.
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PMID:Cdkn2a encodes functional variation of p16INK4a but not p19ARF, which confers selection in mouse lung tumorigenesis. 1036 10

p73 is a recently cloned tumor suppressor gene that is highly homologous to p53, and the products of both possess similar functions in inhibiting cell growth and inducing apoptosis. Interestingly, the COOH-terminal region of p53 displays no significant homology with that of p73. Moreover, p73 has an additional segment at its COOH terminus. Recently, we have found two mutations of p73 with amino acid substitution (P405R and P425L) in primary neuroblastomas. Because the region (amino acid residues 382-491) contains a glutamine- and proline-rich domain, we hypothesized that it has a transactivation function, and the mutations found in tumors result in loss of function. To test it, we used the yeast GAL4 DNA-binding fusion system. Yeast transformants expressing a GAL4-p73(1-112) or a GAL4-p73alpha(380-513) fusion protein were grown in SD medium lacking histidine and tryptophan and exhibited a significant induction of beta-galactosidase activity. Transient transfection experiments revealed that both of fusion proteins could induce the chloramphenicol acetyltransferase activity in mammalian cells, indicating that the COOH-terminal as well as NH2-terminal regions of p73 had significantly high levels of transactivation activity. Furthermore, the former activity was severely impaired in two naturally occurring mutant forms found in neuroblastomas. These suggest that, unlike p53, p73 has two domains with transactivation function, one in the NH2-terminal region and the other in the COOH-terminal region. Loss of function mutation in the latter might be involved in tumorigenesis and/or tumor progression.
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PMID:Identification of a transactivation activity in the COOH-terminal region of p73 which is impaired in the naturally occurring mutants found in human neuroblastomas. 1038 37

There is often a considerable lapse of time between the definition of what causes a disease in the laboratory and the development of successful therapy. However, the history of medicine teaches us that the need to understand the scientific basis of disease before the discovery of new treatments is both essential and inevitable. During the middle of the 19th century, the work of the great German pathologist, Rudolf Virchow, defined disease as having an anatomic or histologic basis. In the clinic, this scientific perspective would lead to increasingly effective and, often, increasingly aggressive surgical approaches to disease. Later in the 19th century, Koch's discovery of the tubercle bacillus (a discovery Virchow disbelieved and publication of which he thwarted, since he hypothesized that cancer, not microbes, caused consumption!), would define a microbiological basis for disease. With bacteria defined as a major cause of human suffering, the stage was set for the development of the discovery of effective antibiotics. In the early 20th century, the pioneering work of Banting, Best and others would show that disease can also have an endocrine or metabolic basis. This new body of scientific knowledge would lead not only to the specific discovery of insulin as an effective treatment for diabetes but also to a more general understanding of the role of hormones, vitamins and co-factors in human health and disease. Basic medical research and its successful translation into effective treatments has fundamentally altered the cause of human death. In the developed world, where access to the benefit of this work is available, infectious disease is not the problem it was in the days of Pasteur, Metchnikoff and Ehrlich. As we approach the millennium, science is now teaching us that diseases, particularly cancer, can have a molecular or genetic basis. Can successful application of this new knowledge be far behind? We are already seeing the application of this new knowledge in cancer drug screening and cancer drug development. At the NCI, for example, the old in vivo mouse screen using mouse lymphomas has been shelved; it discovered compounds with some activity in lymphomas, but not the common solid tumors of adulthood. It has been replaced with an initial in vitro screen of some sixty cell lines, representing the common solid tumors-ovary, G.I., lung, breast, CNS, melanoma and others. The idea was to not only discover new drugs with specific anti-tumor activity but also to use the small volumes required for in vitro screening as a medium to screen for new natural product compounds, one of the richest sources of effective chemotherapy. The cell line project had an unexpected dividend. The pattern of sensitivity in the panel predicted the mechanism of action of unknown compounds. An antifolate suppressed cell growth of the different lines like other antifolates, anti-tubulin compounds suppressed like other anti-tubulins, and so on. It now became possible, at a very early stage of cancer drug screening, to select for drugs with unknown-and potentially novel-mechanisms of action. The idea was taken to the next logical step, and that was to characterize the entire panel for important molecular properties of human malignancy: mutations in the tumor suppressor gene p53, expression of important oncogenes like ras or myc, the gp170 gene which confers multiple drug resistance, protein-specific kinases, and others. It now became possible to use the cell line panel as a tool to detect new drugs which targeted a specific genetic property of the tumor cell. Researchers can now ask whether a given drug is likely to inhibit multiple drug resistance or kill cells which over-express specific oncogenes at the earliest phase of drug discovery. In this issue of The Oncologist, Tom Connors celebrates the fiftieth anniversary of cancer chemotherapy. His focus is on the importance of international collaboration in clinical trials and the negative impact of unnecessary bureaucracy and regulation. As a student of Tom's in the 1970s in London, working on hepatoma-specific alkylating agents at Charing Cross Hospital in collaboration with his lab on the other side of town, I can attest to the fact that the regulatory hurdles to cancer drug development just twenty years later have added immeasurably to the effort and cost of cancer drug development. However, I look with optimism to the future of cancer diagnosis, prevention and treatment. It is a future where what we are learning now about the molecular and genetic basis of cancer will find their clinical outlet just as surely as the anatomic, microbial, metabolic and endocrine basis for disease has in the past. This new knowledge will provide new techniques in molecular diagnosis, which will allow us to predict which in situ cancers are destined for malignant behavior, and which can be safely watched without the need for intervention. Individual patient risk for particular cancers will be accurately predictable, so that patients can alter lifestyle habits or begin other prevention strategies. Oncogenes and growth suppressor genes give us new targets to inhibit or replace. Tumor-specific kinases will meet their inhibitors. The oncologist will play a leading role in understanding, applying and interpreting this new information in the clinic-an exciting and challenging future!
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PMID:Cancer Drug Development: New Targets for Cancer Treatment. 1038 87


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