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)

Two hundred eight primary squamous cell carcinomas of the head and neck have been analyzed with respect to the presence of the retinoblastoma tumor suppressor protein, pRb. Of these, 23 tumors (11%) that preferentially localized to the tonsils revealed complete absence or dramatic reduction in the amount of pRb. Other cell cycle components, cyclin D1 and p16INK4A, which are intimately related to pRb through an autoregulatory loop, were also dramatically decreased or overexpressed, respectively, in these pRb-defective tumors. On the other hand, the majority of the pRb-defective tumors contained the wild-type p53 gene. No evidence was found for genetic defects at the Rb locus in these tumors. Very significantly, in 11 of 12 pRb-defective tonsillar tumors, but in none of 9 pRb-positive tonsillar tumors (P < 10[-7]), DNA of oncogenic human papillomavirus types was identified, providing a strong indication for a human papillomavirus-associated etiology of these tumors and suggesting the functional inactivation of the pRb protein by the viral E7 gene product. In comparison to all head and neck squamous cell carcinomas studied, the pRb-defective tonsillar tumors were in general more poorly differentiated (P = 0.0059), and they were all metastatic at the time of resection. Of particular clinical interest, despite these adverse histopathological factors, the clinical outcome for these patients was relatively favorable, strongly implying that the pRb-defective tumors responded uniformly well toward postoperative radiation therapy.
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PMID:Etiological involvement of oncogenic human papillomavirus in tonsillar squamous cell carcinomas lacking retinoblastoma cell cycle control. 942 48

The effect of a potent mammary carcinogen, anti benzo[g]chrysene 11,12-dihydrodiol 13,14-epoxide, on the progress of human mammary carcinoma MCF-7 cells through the cell cycle was investigated. While these cells, which express wild-type p53, were arrested in G1 after treatment with actinomycin D (a positive control), treatment with the mammary carcinogen did not cause G1 arrest but instead delayed the cells in the DNA synthesis phase. In concert with the absence of a G1 arrest, it was found that though both chemical treatments led to increased levels of p53, only the p53 induced by actinomycin D was transcriptionally active and increased the levels of the cyclin dependent kinase inhibitor, p21(waf1/cip1). Since treatment of the cells with the mammary carcinogen did not abrogate the G1 arrest induced by actinomycin D, the lack of p21(waf1/cip1) and of G1 arrest, resulting from treatment with the mammary carcinogen alone, was not due to some general inhibition of transcription or translation. An analogous difference between these two chemicals was demonstrated also in other human cell systems. The stealth-like property of the mammary carcinogen that allows it to damage DNA without turning on the cells' 'guardian of the genome' defense mechanism presumably increases the likelihood of malignant change because DNA replication continues on a damaged template. It is suggested that this stealth characteristic may be a major contributor to the high carcinogenic potency of this mammary carcinogen and possibly to that of other highly potent carcinogens.
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PMID:Cellular response to DNA damage from a potent carcinogen involves stabilization of p53 without induction of p21(waf1/cip1). 945 Apr 75

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

A decrease in the intracellular concentrations of the transcripts for some tumor suppressor genes has been found during murine lung tumorigenesis; for p15INK4b and p16INK4a, this was due to homozygous deletions. We report here a decrease in the mRNA levels of the mutated in colorectal cancer (Mcc) and adenomatous polyposis coli (Apc) genes in mouse lung tumors and some neoplastic cell lines. This was assessed both by northern blotting and reverse transcriptase-polymerase chain reaction of RNA isolated from lung tumors that had been induced by urethane, N-nitrosodiethylamine, or 3-methylcholanthrene in (A/J x C57BL/6) F1 or A/J mice. A reduced amount of both Mcc and Apc messages was also seen when two neoplastic cell lines, a spontaneous transformant (E9) and a line derived from a chemically induced solid tumor (82-132), were compared with two independently derived nontumorigenic cell lines (E10 and C10); E9 was derived from E10, and all of these lines are probably of alveolar type 2 cell origin. A cell line derived from a chemically induced papillary lung tumor probably of bronchiolar Clara cell origin (LM2) had Mcc mRNA levels similar to those of C10 and E10 but reduced Apc mRNA levels. A line (p53-823) derived from a papillary tumor that arose in a mouse with a mutated p53 transgene had a reduced amount of the Mcc gene product only. These differential changes in the relative amounts of Apc and Mcc messages in LM2 and p53-823) cells may serve as useful models for studying the regulation of their expression. Both messages had half-lives of 6-9 h in normal E10 and neoplastic E9 cells, so decreased message stability does not account for these reductions. This is the first report of estimated degradation rates of these mRNAs. Apc and Mcc message content did not vary as a function of growth status of the cell lines. Single-strand conformation polymorphism analysis did not reveal mutations in Apc coding regions known to have a high mutation frequency in human colon tumors. Loss of heterozygosity of Apc and Mcc was not found in tumors that developed in the F1 mice, implying a lack of allelic deletions. These changes in tumor suppressor gene expression may contribute to the development and maintenance of neoplasia in lung epithelium.
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PMID:Decreased expression of the adenomatous polyposis coli (Apc) and mutated in colorectal cancer (Mcc) genes in mouse lung neoplasia. 947 70

The p16INK4a (alpha and beta form) and p15INK4b genes were analysed for homozygous deletion, hypermethylation and point mutation in B6C3F1 mouse lymphomas induced by 2',3'-dideoxycytidine or 1,3-butadiene. Although the p16INK4a-alpha gene appeared normal in DNA from 2',3'-dideoxycytidine-induced lymphomas, Southern analyses revealed homozygous deletions or rearrangements of the p16INK4a-beta and/or p15INK4b genes in four of 16 tumours. Surprisingly, two of these lymphomas showed exclusive deletions of the p16INK4a EIbeta exon. The p15INK4b promoter region was hypermethylated in two additional 2',3'-dideoxycytidine-induced lymphomas. In contrast, homozygous deletions spanning the p16INK4a and p15INK4b loci were observed in only two of 31 1,3-butadiene-induced tumours. Thus, these cyclin dependent kinase inhibitor genes may play a significant role in chemically induced mouse lymphomas and support the contention of tumour suppressor activity for the p19ARF protein encoded by the p16INK4a-beta gene. Different genetic pathways may be involved in the development of these chemically induced tumours since we have previously shown that mutations in p53 and ras genes are common in 1,3-butadiene- but not 2',3'-dideoxycytidine-induced lymphomas.
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PMID:Inactivations of p16INK4a-alpha, p16INK4a-beta and p15INK4b genes in 2',3'-dideoxycytidine- and 1,3-butadiene-induced murine lymphomas. 948 45

Both tumor suppressor genes p53 and p16(INK4A) play a crucial role in the control of cell cycle and tumor development. In this study 19 malignant fibrous histiocytomas of the bone (MFH-b), a very rare sarcoma entity, were investigated for mutations in p53 and p16 genes by a PCR-SSCP-sequencing analysis. In the tumor samples two p53 mutations and two polymorphisms (one in the p53 gene and one in the p16 gene) were found. The occurrence rate for p53 mutations and the absence of p16 mutations in MFH-b are comparable to the findings for MFH of soft tissues (MFH-st) and osteosarcomas, suggesting that p53 rather than p16 may play a role in tumorigenesis of MFH-b.
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PMID:How is the mutational status for tumor suppressors p53 and p16(INK4A) in MFH of the bone? 948 81

The atomic bombing of Hiroshima and Nagasaki and the nuclear accident at Chernobyl raised the question of prenatal sensitivity to ionizing radiation-induced cancer. In this study, mice were exposed to single doses of gamma-radiation (0.2-2.0 Gy) at different embryonic stages. The tumor incidence increased with dose from 15% in control mice to 35% in mice irradiated with 2.0 Gy on 18 d of prenatal life. Various oncogenic events were investigated in lymphoid, liver, lung, and uterine tumors. We observed threefold to fivefold increases in myc expression in 25% of the lymphomas, and the expression of Ha-ras and p53 genes decreased in 40% and 60% of the lung tumors by twofold to fivefold. Point mutations were tissue specific: Ha-ras codon 61 mutations were found in about 40% of the liver adenocarcinomas, Ki-ras codon 12 mutations in about 17% of lung tumors, and p53 mutations in about 15% of the lymphomas. Amplification and rearrangement of the p53, myc, and Ha-, Ki- and N-ras genes were not detected. Loss of heterozygosity on chromosome 4 at the multiple tumor suppressor 1 and 2 genes was observed in all types of malignancies. Allelic losses on chromosome 11 at the p53 locus were found in lymphoid, liver, and lung tumors, but they were absent from uterine tumors. Multiple oncogenic changes were often detected. The frequency of carcinogenic alterations was similar in spontaneous and radiation-induced lymphoid, liver, and uterine tumors. In radiation-induced lung adenocarcinomas, however, the incidences of many oncogenic changes were different from those found in their spontaneous counterparts. This suggests that different oncogenic pathways are activated during spontaneous and in utero gamma-radiation-induced murine lung carcinogenesis.
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PMID:Carcinogenic alterations in murine liver, lung, and uterine tumors induced by in utero exposure to ionizing radiation. 949 10

Since its discovery as a CDKI (cyclin-dependent kinase inhibitor) in 1993, the tumor suppressor p16 (INK4A/MTS-1/CDKN2A) has gained widespread importance in cancer. The frequent mutations and deletions of p16 in human cancer cell lines first suggested an important role for p16 in carcinogenesis. This genetic evidence for a causal role was significantly strengthened by the observation that p16 was frequently inactivated in familial melanoma kindreds. Since then, a high frequency of p16 gene alterations were observed in many primary tumors. In human neoplasms, p16 is silenced in at least three ways: homozygous deletion, methylation of the promoter, and point mutation. The first two mechanisms comprise the majority of inactivation events in most primary tumors. Additionally, the loss of p16 may be an early event in cancer progression, because deletion of at least one copy is quite high in some premalignant lesions. p16 is a major target in carcinogenesis, rivaled in frequency only by the p53 tumor-suppressor gene. Its mechanism of action as a CDKI has been elegantly elucidated and involves binding to and inactivating the cyclin D-cyclin-dependent kinase 4 (or 6) complex, and thus renders the retinoblastoma protein inactive. This effect blocks the transcription of important cell-cycle regulatory proteins and results in cell-cycle arrest. Although p16 may be involved in cell senescence, the physiologic role of p16 is still unclear. Future work will focus on studies of the upstream events that lead to p16 expression and its mechanism of regulation, and perhaps lead to better therapeutic strategies that can improve the clinical course of many lethal cancers.
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PMID:Role of the p16 tumor suppressor gene in cancer. 950 8

We have studied the role of the oxygen-dependent pyrimidine metabolism in the regulation of cell cycle progression under moderate hypoxia in human cell lines containing functional (T-47D) or non-functional (NHIK 3025, SAOS-2) retinoblastoma gene product (pRB). Under aerobic conditions, pRB exerts its growth-regulatory effects during early G1 phase of the cell cycle, when all pRB present has been assumed to be in the underphosphorylated form and bound in the nucleus. We demonstrate that pRB is dephosphorylated and re-bound in the nucleus in approximately 90% of T-47D cells located in S and G2 phases under moderately hypoxic conditions. Under these conditions, no T-47D cells entered S-phase, and no progression through S-phase was observed. Progression of cells through G2 and mitosis seems independent of their functional pRB status. The p21WAF1/CIP1 protein level was significantly reduced by moderate hypoxia in p53-deficient T-47D cells, whereas p16(INK4a) was not expressed in these cells, suggesting that the hypoxia-induced cell cycle arrest is independent of these cyclin-dependent kinase inhibitors. The addition of pyrimidine deoxynucleosides did not release T-47D cells, containing mainly underphosphorylated pRB, from the cell cycle arrest induced by moderate hypoxia. However, NHIK 3025 cells, in which pRB is abrogated by expression of the HPV18 E7 oncoprotein, and SAOS-2 cells, which lack pRB expression, continued cell cycle progression under moderate hypoxia provided that excess pyrimidine deoxynucleosides were present. NHIK 3025 cells express high levels of p16INK4a under both aerobic and moderately hypoxic conditions, suggesting that the inhibitory function of p16(INK4a) would not be manifested in such pRB-deficient cells. Thus, pRB, a key member of the cell cycle checkpoint network, seems to play a major role by inducing growth arrest under moderate hypoxia, and it gradually overrides hypoxia-induced suppression of pyrimidine metabolism in the regulation of progression through S-phase under such conditions.
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PMID:The retinoblastoma protein-associated cell cycle arrest in S-phase under moderate hypoxia is disrupted in cells expressing HPV18 E7 oncoprotein. 952 26

The occurrence of DNA double strand breaks induces cell cycle arrest in mortal and immortal human cells. In normal, mortal fibroblasts this block to proliferation is permanent. It depends on the growth regulator p53 and a protein p53 induces, the cyclin dependent kinase inhibitor, p21. We show here that following DNA damage in mortal fibroblasts, the induction of p21 and p53 is to a large degree shortlived. By 8 days after a brief exposure to DNA strand breaking agents, bleomycin or actinomycin D, p53 protein is at baseline levels, while the p53 transactivation level is only slightly above its baseline. By this time the concentration of p21 protein, which goes up as high as 100-fold shortly after treatment, is down to just 2-4-fold over baseline levels. Following the drop in p21 concentration a large increase in the expression level of the tumor suppressor gene p16INK4a is observed. This scenario, where a transient increase in p21 is followed by a delayed induction of p16INK4a, also happens with the permanent arrest that occurs with cellular senescence. In fact, these cells treated with agents that cause DNA double strand breaks share a number of additional markers with senescent cells. Our findings indicate that these cells are very similar to senescent cells and that they have additional factor(s) beside p21 and p53 that maintain cell cycle arrest.
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PMID:Agents that cause DNA double strand breaks lead to p16INK4a enrichment and the premature senescence of normal fibroblasts. 952 53


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