p53 tumor suppressor gene: implications for iatrogenic cancer and cancer therapy.
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Carcinogens↗
Biomedical subjects
C C Harris
Publications and source records attributed to C C Harris.
p53 mutations and occupational exposures in a surgical series of lung cancers.
p53 mutations are frequent in malignant lung tumors. Of 88 surgically treated lung cancers from cigarette smokers previously evaluated for p53 mutations, 45 tumors (51.1%) had mutations in exons 5-8 (D. G. Guinee, Jr. et al., Carcinogenesis (Lond.), 16: 993-1002, 1995). We report here the examination of 13 occupational exposures and 13 high-risk occupations in relation to these p53 mutations. Two molecular abnormalities were associated with occupational exposures: (a) G:C-->T:A transversions on the coding (nontranscribed) strand (n = 13) were associated with chromate exposure and employment in the metal industry (P < 0.05) and marginally associated with nickel exposure (P = 0.056); and (b) G:C-->A:T transitions at non-CpG sites (n = 9) were associated with work in the petrochemical industry (P = 0.05). No association was found between p53 mutations and gender, cigarette pack-years, tumor histology, age at diagnosis, or family history of lung cancer. Because all three chromate-exposed subjects had large cell carcinomas exhibiting G: C-->T:A coding-strand transversions, follow-up of a cohort with this exposure should clarify the association with the p53 gene.
Adult↗
TP53 tumour suppressor gene: clues to molecular carcinogenesis and cancer therapy.
The tumour suppressor gene product TP53 is clearly a component in several biochemical pathways, including transcription, DNA repair, genomic stability, cell cycle control and apoptosis, that are central to human carcinogenesis. TP53 is functionally inactivated by mutational, viral and cellular mechanisms in the majority of human cancers. Analysis of the spectrum of TP53 mutations provides clues to the aetiology and molecular pathogenesis of cancer. Recent insight into the TP53 mediated biochemical pathways of cell cycle arrest and apoptosis has provided further understanding of the mechanisms related to TP53 mediated tumour suppression. This in turn may provide the potential molecular targets for the development of rational multimodality cancer therapy, including chemotherapy, immunotherapy and gene therapy strategies. The convergence of previously parallel lines of basic, clinical and epidemiological investigation may provide an opportunity for the rapid transfer of research findings from the laboratory to the clinic.
Animals↗
p53: at the crossroads of molecular carcinogenesis and molecular epidemiology.
The p53 tumor suppressor gene is frequently mutated in human cancer, including squamous cell carcinoma and basal cell carcinoma of the skin, but is rarely mutated in skin melanoma. The p53 mutation spectrum provides insight into both the etiology of human cancer and the functional regions of the encoded protein that lead to clonal expansion of the p53 mutant cell.
Animals↗
Anti-p53 antibodies in sera from patients with chronic obstructive pulmonary disease can predate a diagnosis of cancer.
Serum anti-p53 antibodies (p53-Abs) may be surrogate markers for both p53 alterations and preclinical cancer. Ancillary to a prospective trial to abate progressive development of clinical stages of chronic obstructive pulmonary disease, we conducted a retrospective, nested case-control study. Twenty-three cases were diagnosed with cancer during the trial. Enzyme immunoassay, immunoblotting, and immunoprecipitation were used to detect p53-Abs in serum, immunohistochemistry (IHC) to detect p53 accumulation, and single-strand conformation polymorphism and DNA sequencing to detect p53 mutations in tumor samples. p53-Abs were detected by three types of assays in five (23%) of the cancer patients, 80% of whom had detectable p53-Abs before diagnosis: 2 lung cancers (7 and 6 months before), 1 prostate cancer (11 months), and 1 breast cancer (5 months). Four Ab-positive patients had IHC-positive tumors. Two of 4 Ab-positive patients and 2 of 14 Ab-negative had p53 missense mutations or base pair deletion and IHC-positive tumors. The 44 noncancer COPD controls, matched with the cancer cases for age, gender, and smoking habits, were negative for p53-Abs. These results indicate that p53-Abs may facilitate the early diagnosis of cancer in a subset of smokers with chronic obstructive pulmonary disease who are at an increased cancer risk.
Aged↗
Abrogation of p53-induced apoptosis by the hepatitis B virus X gene.
The p53 tumor suppressor gene product is a transcriptional transactivator and a potent apoptotic inducer. The fact that many of the DNA tumor virus oncoproteins bind to p53 and affect these p53 functions indicates that this interaction is an important step in oncogenic transformation. We and others have recently demonstrated that the hepatitis B virus oncoprotein, HBx, can form a complex with p53 and inhibit its DNA consensus sequence binding and transcriptional transactivator activity. Using a microinjection technique, we report here that HBx efficiently blocks p53-mediated apoptosis and describe the results of studies exploring two possible mechanisms of HBx action. First, inhibition of apoptosis may be a consequence of the failure of p53, in the presence of HBx, to upregulate genes, such as p21WAF1, Bax, or Fas, that are involved in the apoptotic pathway. Data consistent with this hypothesis include HBx reduction of p53-mediated p21WAF1 expression. Alternatively, HBx could affect p53 binding to the TFIIH transcription-nucleotide excision repair complex as HBx binds to the COOH terminus of p53 and inhibits its binding to XPB or XPD. Binding of p53 to these constituents of the core TFIIH is a process that may be involved in apoptosis. Because the HBx gene is frequently integrated into the genome of hepatocellular carcinoma cells, inhibition of p53-mediated apoptosis by HBx may provide a clonal selective advantage for hepatocytes expressing this integrated viral gene during the early stages of human liver carcinogenesis.
Apoptosis↗
Anti-p53 antibodies in sera of workers occupationally exposed to vinyl chloride.
BACKGROUND: The p53 tumor suppressor gene (also known as TP53) is often mutated in a wide variety of cancers, including angiosarcoma of the liver (ASL). Anti-p53 antibodies have been detected in the sera of patients with leukemia, childhood lymphoma, or cancers such as those of the breast, lung, colon, esophagus, and liver (hepatocellular carcinoma). PURPOSE: The objective of this study was to determine the prevalence and time of appearance of serum anti-p53 antibodies during the pathogenesis of ASL associated with occupational exposure to vinyl chloride. METHODS: Enzyme-linked immunoassay (EIA) was used to detect anti-p53 antibodies in 148 serum samples from 92 individuals occupationally exposed (in France or in Kentucky) to vinyl chloride; 15 of these individuals (six from France and nine from Kentucky) had ASL. A subset of coded EIA-positive and EIA-negative sera was further analyzed for anti-p53 antibodies by immunoblotting and immunoprecipitation. Nucleotide sequence analysis of exons 5-8 of the p53 gene was conducted on ASL DNA from six patients. We tested sera from 31 men who had no occupational exposure to vinyl chloride; they made up the control group. Statistical analyses were done using the Kruskal-Wallis chi-squared approximation and the Wilcoxon two-sample test for normal approximation. All P values result from two-sided tests. RESULTS: Fourteen serum samples (from nine individuals) were positive in the EIA. Five of the 15 individuals with ASL were positive for anti-p53 antibodies by EIA, immunoblotting, and immunoprecipitation: one individual at 11.3 and 10.8 years before diagnosis, another at 4 months before and shortly after diagnosis, and three when diagnosed or shortly thereafter. Four of the 77 vinyl chloride-exposed workers without diagnosed ASL were positive for anti-p53 antibodies; two of the four had symptoms related to vinyl chloride toxicity. Tumors from three of the six vinyl chloride-exposed workers from which sufficient DNA for analysis was obtained had A:T to T:A missense mutations of the p53 gene. Anti-p53 antibodies were detected in two of these individuals. Among the control group, two of 15 serum samples from 15 lung cancer patients and zero of 15 serum samples from control subjects without cancer had anti-p53 antibodies as substantially lower levels than the nine (10%) of 92 vinyl chloride-exposed workers who were positive for anti-p53 antibodies. CONCLUSIONS AND IMPLICATIONS: Serum anti-p53 antibodies can predate clinical diagnosis of certain tumors, such as ASL, and may be useful in identifying individuals at high cancer risk, such as workers with occupational exposure to vinyl chloride.
Adult↗
Mutagens from heated Chinese and U.S. cooking oils.
BACKGROUND: The lung cancer incidence in Chinese women is among the highest in the world, but tobacco smoking accounts for only a minority of the cancers. Epidemiologic investigations of lung cancer among Chinese women have implicated exposure to indoor air pollution from wok cooking, where the volatile emissions from unrefined cooking oils are mutagenic. PURPOSE: This study was conducted to identify and quantify the potentially mutagenic substances emitted from a variety of cooking oils heated to the temperatures typically used in wok cooking. METHODS: Several cooking oils and fatty acids were heated in a wok to boiling, at temperatures (for the cooking oils) that ranged from 240 degrees C to 280 degrees C (typical cooking temperatures in Shanghai, China). The oils tested were unrefined Chinese rapeseed, refined U.S. rapeseed (known as canola), Chinese soybean, and Chinese peanut in addition to linolenic, linoleic, and erucic fatty acids. Condensates of the emissions were collected and tested in the Salmonella mutation assay (using Salmonella typhimurium tester strains TA98 and TA104). Volatile decomposition products also were subjected to gas chromatography and mass spectroscopy. Aldehydes were detected using high-performance liquid chromatography and UV spectroscopy. RESULTS: 1,3-Butadiene, benzene, acrolein, formaldehyde, and other related compounds were qualitatively and quantitatively detected, with emissions tending to be highest for unrefined Chinese rapeseed oil and lowest for peanut oil. The emission of 1,3-butadiene and benzene was approximately 22-fold and 12-fold higher, respectively, from heated unrefined Chinese rapeseed oil than from heated peanut oil. Lowering the cooking temperatures or adding an antioxidant, such as butylated hydroxyanisole, before cooking decreased the amount of these volatile emissions. Among the individual fatty acids tested, heated linolenic acid produced the greatest quantities of 1,3-butadiene, benzene, and acrolein. Separately, the mutagenicity of individual volatile emission condensates was correlated with linolenic acid content (r = .83; P = .0004). Condensates from heated linolenic acid, but not linoleic or erucic acid, were highly mutagenic. CONCLUSIONS: These studies, combined with experimental and epidemiologic findings, suggest that high-temperature wok cooking with unrefined Chinese rapeseed oil may increase lung cancer risk. This study indicates methods that may reduce that risk. IMPLICATIONS: The common use of wok cooking in China might be an important but controllable risk factor in the etiology of lung cancer. In the United States, where cooking oils are usually refined for purity, additional studies should be conducted to further quantify the potential risks of such methods of cooking.
China↗
Effects of p53 mutants on wild-type p53-mediated transactivation are cell type dependent.
The spectrum of p53 mutations differs among human cancer types. We have hypothesized that the p53 mutational spectrum observed in particular tumor types reflects the functional ability of different p53 mutants to modulate wild-type (WT) p53-dependent gene transcription. Missense p53 mutants representing several mutational hotspot codons were cotransfected with WT p53 and analysed for their effects on p53-dependent transactivation of a reporter construct containing a specific p53 binding sequence (PG13-CAT) in human tumor cell lines lacking endogenous p53. Our results show that the ability of p53 mutants to inhibit WT p53-mediated transactivation is cell type dependent. In cell lines derived from a lung adenocarcinoma and a mesothelioma, the transactivation function of WT p53 was strongly inhibited by all p53 mutants examined. However, in cell lines derived from a prostate carcinoma and an osteosarcoma, the mutants examined generally had only minimal dominant negative effects. In cell lines derived from a hepatocellular carcinoma and an ovarian carcinoma, two mutants (248trp and 273his) enhanced WT p53-mediated transactivation of the reporter construct. Additional mutants retained the ability to inhibit WT p53-mediated transactivation in these cell lines. In addition, in a series of four breast tumor cell lines, the p53 mutants examined had similar effects on WT p53 transactivation ability including enhanced transactivation activity in the 273his cotransfectants. The p53 mutants were incapable of transactivating the PG13-CAT reporter in the absence of WT p53 expression. Therefore, the dominant negative effects of p53 mutants on WT p53 function may vary depending on the particular cell type. In addition, mutants with stronger inhibitory capabilities may confer a selective advantage during the tumorigenic process.
Base Sequence↗
SV40-induced immortalization and ras-transformation of human bronchial epithelial cells.
Non-tumorigenic SV40-immortalized human cells may be transformed to tumorigenicity by activated oncogenes, but the molecular genetics of this process are still poorly understood. We describe here 4SV40-transformed bronchial epithelial (BE) cell lines that became immortalized after a period of crisis, and then transfection of 6 BE lines or sub-lines with an activated c-Ha-ras (EJ-ras) oncogene. pSV2neo-transfected cells did not form any tumors in athymic nude mice. Even though each of the EJ-ras-transfected lines was shown to be expressing the mutant ras gene, only one cell line, BEAS-2B, and 2 of its sub-lines were tumorigenic after transfection. We conclude that immortalization is not sufficient for BE cells to be transformed by the EJ-ras oncogene. Thus there are at least 2 unknown genetic events in this in vitro model of carcinogenesis: escape from crisis (immortalization), and development of ability to cooperate with activated ras in tumorigenic transformation. We found no evidence that either immortalization or ability to complement ras is related to abnormalities of the SV40 T antigens, of p110RB or of p53.
Animals↗
1995 Deichmann Lecture--p53 tumor suppressor gene: at the crossroads of molecular carcinogenesis, molecular epidemiology and cancer risk assessment.
Carcinogenesis is a multistage process involving activation of protooncogenes, e.g., ras, and inactivation of tumor suppressor genes, e.g., p53 and p16INK4.p53 is a prototype tumor suppressor gene that is well suited for analysis of mutational spectrum in human cancers; it is the most common genetic lesion in human cancers, it is a reasonable size for a molecular target, and it may indicate selection of mutations with pathobiological significance. The p53 mutational spectrum differs among cancers of the colon, lung, esophagus, breast, liver, brain, reticuloendothelial tissues and hemopoietic tissues. Analysis of these mutations can provide clues to the etiology of these diverse tumors and to the function of specific regions of p53. Transitions predominate in colon, brain and lymphoid malignancies. Mutational hotspots at CpG dinucleotides in codons 175, 245, 248, 273 and 282 may reflect endogenous mutagenic mechanisms, e.g., deamination of 5-methylcytosine to thymidine. Oxy-radicals including nitric oxide may enhance the rate of deamination. G:C to T:A transversions are the most frequent substitutions observed in cancers of the lung, breast, esophagus and liver, and are more likely to be due to bulky carcinogen-DNA adducts. G to T transversion is more common in lung cancers from smokers when compared to never smokers. The high frequency of p53 mutations in the nontranscribed DNA strand is a reflection of strand specific repair, p53 mutation and/or accumulation of p53 protein can be preinvasive events in bronchial or esophageal carcinogenesis, p53 mutations also generally indicate a poor prognosis. In geographic areas where hepatitis B virus (HBV) and aflatoxin B1 are cancer risk factors, most mutations are at the third nucleotide pair of codon 249. In geographic areas where hepatitis B and C virus--but not aflatoxin B1--are risk factors, the p53 mutations are distributed in numerous codons. HBV X protein complexes with the p53 protein and inhibits its sequence specific DNA binding, transactivating and apoptotic capacity. The mutation load of 249ser mutant cells in nontumorous liver is positively correlated with dietary aflatoxin B1 exposure. The induction of skin carcinoma by ultraviolet light is indicated by the occurrence of p53 mutations at dipyrimidine sites including CC to TT double base changes. In summary, these differences in mutational frequency and spectrum among human cancer types suggest the etiological contributions in both exogenous and endogenous factors to human carcinogenesis and have implications for human cancer risk assessment.
Animals↗
Nitric oxide and ethylnitrosourea: relative mutagenicity in the p53 tumor suppressor and hypoxanthine-phosphoribosyltransferase genes.
Nitric oxide (NO) is a cellular messenger which is mutagenic in bacteria and human TK6 cells and induces deamination of 5-methylcytosine (5meC) residues in vitro. The aims of this study were: (i) to investigate whether NO induces 5meC deamination in codon 248 of the p53 gene in cultured human bronchial epithelial cells (BEAS-2B); and (ii) to compare NO mutagenicity to that of ethylnitrosourea (ENU), a strong mutagen. Two approaches were used: (i) a novel genotypic assay, using RFLP/PCR technology on purified exon VII sequence of the p53 gene; and (ii) a phenotypic (HPRT) mutation assay using 6-thioguanine selection. BEAS-2B cells were either exposed to 4 mM DEA/NO (Et2N[N2O2]Na, an agent that spontaneously releases NO into the medium) or transfected with the inducible nitric oxide synthase (iNOS) gene. The genotypic mutation assay, which has a sensitivity of 1 x 10(-6), showed that 4 mM ENU induces detectable numbers of G --> A transitions in codon 248 of p53 while 5-methylcytosine deamination was not detected in either iNOS-transfected cells or cells exposed to 4 mM DEA/NO. Moreover, ENU was dose-responsively mutagenic in the phenotypic HPRT assay, reaching mutation frequencies of 24 and 96 times that of untreated control cells at ENU concentrations of 4 and 8 mM respectively; by contrast, 4 mM DEA/NO induced no detectable mutations in this assay, nor were any observed in cells transfected with murine iNOS. We conclude that if NO is at all promutagenic in these cells, it is significantly less so than the ethylating mutagen, ENU.
Base Sequence↗
Quantitative image analysis of p53 protein accumulation in keratoacanthomas.
Keratoacanthomas are benign skin tumors that grow rapidly but eventually regress. They occur most commonly in sun-exposed skin and are histologically remarkably similar to squamous cancers. Since mutations of the p53 tumor suppressor gene are found frequently in cutaneous squamous cell carcinomas, we hypothesized that p53 mutations might contribute to the development of keratoacanthomas. To address this question, we did p53 immunohistochemistry with a polyclonal rabbit antiserum, CM-1, that binds both mutant and wild-type p53 proteins. Although wild-type p53 protein degrades rapidly and is generally undetected by immunohistochemistry, mutant p53 protein has a longer half-life and accumulates to detectable levels. We tested 26 formalin-fixed keratoacanthomas and 4 normal skin biopsies. Positive nuclear staining was detected in 20 of 26 (77%) of the keratoacanthomas and in none of the normal skin samples. Nuclear staining occurred in the outermost layer of the neoplasms and not in the keratin-filled central cores. Since nuclear p53 protein within a cutaneous squamous cell carcinoma usually correlates with missense mutation, these data suggest that p53 mutations contribute to the development of this benign neoplasm. The histologic similarity to squamous cell carcinoma and the accumulation of p53 protein suggest progression toward malignancy, but the invariable regression of these tumors suggests an arrest at some point in multistage carcinogenesis. If this model is correct, then genetic analysis of keratoacanthomas may provide clues to the later stages of squamous carcinogenesis including local invasion and metastasis.
Animals↗
Molecular genetics of lung cancer.
The identification of genetic abnormalities in lung cancer and their consequences for cell growth, differentiation and function offer insights into normal cellular function and carcinogenesis. The integration of this knowledge with data from other fields, including epidemiology, toxicology, carcinogen metabolism, clinical genetics and clinical cancer therapy, promises advancements in lung cancer risk assessment, screening, prevention, prognostic assessment and therapy.
Animals↗
Overexpression of human cyclin D1 reduces the transforming growth factor beta (TGF-beta) type II receptor and growth inhibition by TGF-beta 1 in an immortalized human esophageal epithelial cell line.
Cyclin D1 has been implicated in G1 cell cycle progression and is frequently amplified, overtranscribed, and oversynthesized in human tumors, including esophageal carcinomas. To further address the role of cyclin D1 in cell cycle control and tumorigenesis, we have stably transfected the human cyclin D1 in the nontumorigenic esophageal epithelial cell line HET-1A. These transfected cells, which express increased amounts of cyclin D1, have enhanced colony-forming efficiency and saturation density and are resistant to growth inhibition by TGF-beta 1 compared with the parental cell line or a control vector cell clone. The clones which express increased amounts of cyclin D1 exhibited a decrease in the amount of TGF-beta type II receptor, indicating a plausible mechanism for their diminished response to TGF-beta 1. Therefore, deregulated expression of the cyclin D1 gene can modulate the negative growth factor pathway of TGF-beta 1 and may disturb the control of epithelial cell proliferation in esophageal carcinogenesis.
Cell Cycle↗
Expression of the extracellular matrix molecule thrombospondin inversely correlates with malignant progression in melanoma, lung and breast carcinoma cell lines.
Thrombospondin (TSP) is a member of a family of extracellular matrix glycoproteins that may participate in multiple aspects of the metastatic cascade. We report an inverse correlation of steady-state Thbs-1 mRNA and protein expression with malignant progression among murine melanoma and human lung and breast carcinoma cell lines. Murine K-1735 melanoma cell lines of low metastatic potential, including K-1735 lines transfected with the murine nm23-1 cDNA, expressed higher TSP levels than related highly metastatic lines. In a model system of lung carcinoma malignant progression, immortalized human bronchial epithelial cells expressed higher TSP levels than v-Ki-ras, v-Ha-ras or n-ras transfectants, which in turn expressed higher TSP levels than tumor-derived, more aggressive variants. Among 3 unrelated breast carcinoma cell lines, Thbs-1 steady-state mRNA levels were greater in the 2 non-metastatic lines than the metastatic line. Our data show that malignant progression in some cell lines is associated with reduced TSP expression. The suppressive effects of nm23-1 transfection on metastatic potential are also associated with increased TSP expression; ras transfection, which results in increased tumorigenesis, is associated with decreased TSP expression.
Animals↗
Mutations in the p53 tumor suppressor gene: clues to cancer etiology and molecular pathogenesis.
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Aflatoxins↗
Geographic variation of p53 mutational profile in nonmalignant human liver.
Fifty-eight percent of hepatocellular carcinomas (HCCs) from Qidong, China, contain an AGG to AGT mutation at codon 249 of the p53 tumor suppressor gene, a mutation that is rarely seen in HCCs from Western countries. The population of Qidong is exposed to high levels of aflatoxin B1 (AFB1), a fungal toxin that has been shown to induce the same mutation in cultured human HCC cells. To investigate the role of AFB1 and of these p53 mutations in hepatocarcinogenesis, normal liver samples from the United States, Thailand, and Qidong (where AFB1 exposures are negligible, low and high, respectively) were examined for p53 mutations. The frequency of the AGG to AGT mutation at codon 249 paralleled the level of AFB1 exposure, which supports the hypothesis that this toxin has a causative--and probably early--role in hepatocarcinogenesis.
Aflatoxin B1↗