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Results for “p53 absence”

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At least 19 recordsLinked to original sources

PubMed2025

A tumorigenesis threshold for endogenous Myc revealed by dosage-compensation for Myc-haploinsufficiency in the absence of p53.

The MYC proto-oncogene is crucial for neoplasia in most tumors. Overexpressed, oncogenic MYC amplifies the flux through most major processes but does not specify a unique carcinogenic pathway. This "amplifier" model suggests that MYC must exceed an expression threshold to become oncogenic. We designed a genetic test of this model, using the mouse Trp53 null mutant (p53KO) as a highly robust tumor generator to examine the effect of a modest change in the endogenous Myc level (Myc +/-). Strikingly, tumor-free survival is greatly extended in p53KO mice with haploid Myc gene-dosage, yet in the tumors that do develop (mainly hemangiosarcomas and thymic lymphomas), their Myc deficit has been invariably compensated either by increasing Myc genomic dosage (hemangiosarcomas) or expression (lymphomas). Furthermore, acutely halving the endogenous Myc gene-dosage in established tumor allografts curtails growth rates. These results indicate that even an incremental reduction of MYC activity can be salutary in cancer and that one of the major tumor suppressor functions of p53 derives from its ability to prevent MYC overexpression. Myc generates acute DNA damage by several mechanisms and accordingly, p53's anti-Myc function may be inextricably linked to its role in genome integrity surveillance.

Myc haplo-insufficiency↗

PubMed1992

Absence of p53 gene mutations in primary nasopharyngeal carcinomas.

Alterations in the p53 tumor suppressor gene and Epstein-Barr virus status were investigated in 15 nasopharyngeal carcinoma (NPC) biopsies, 4 xenografts, and 2 cell lines from the Cantonese region of southern China. One other established NPC cell line obtained from a northern Chinese patient was also studied. Restriction fragment length polymorphism analysis revealed a loss of heterozygosity for chromosome 17p, where the p53 gene resides, in only one of 15 NPC biopsies. Polymerase chain reaction-single-stranded conformational polymorphism analysis and direct sequencing failed to detect sequence alterations in exons 5 through 8 of the p53 gene in the 15 tumors and in the 4 NPC xenografts, all of which tested positive for Epstein-Barr virus. In contrast, the 3 NPC cell lines were all negative for Epstein-Barr virus and contained G----C transversions in the p53 gene, with cell lines CNE-1 and CNE-2 harboring identical AGA (arginine) to ACA (threonine) changes at codon 280. These results suggest that p53 inactivation is not a necessary component of nasopharyngeal carcinogenesis in Cantonese but may be important in the establishment of cell lines derived from these tumors.

Base Sequence↗

PubMed1992

p53 mutations in human malignant gliomas: comparison of loss of heterozygosity with mutation frequency.

Mutations in the p53 gene were analyzed in 40 gliomas using the single strand conformation polymorphism assay together with restriction fragment length polymorphism analysis to assess loss of heterozygosity for 17p alleles in the same tumors. Mutations occurred in 40% of the gliomas and were found in exons 4-8 of the p53 gene. G:C to T:A transversions, which occur in high frequency in some lung (greater than 50%), liver (greater than 80%), breast (30%), and esophageal cancers (25%), were noted in greater than 25% of the gliomas studied here. These transversions were clustered in exon 5 from codons 156 to 168, a region of the p53 gene not previously associated with a high frequency of mutation, and may represent a new hot spot for mutations in certain cancers. The majority of gliomas (27 of 38) analyzed here retained both 17p alleles. The frequency of p53 mutations was 37% in this group of tumors and increased to 64% in tumors with one 17p allele. Allelic loss for chromosome 17p occurred in 4 of 11 gliomas independently of mutations in the p53 gene. Absence of p53 mutations in 36% of the tumors with one 17p allele suggests that a tumor suppressor gene other than p53 may be located on chromosome 17p and involved in progression to malignancy of some gliomas.

Adolescent↗

PubMed2025

Aberrant TERT expression: linking chronic inflammation to hepatocellular carcinoma†.

Telomerase reverse transcriptase (TERT), the catalytic enzyme component of telomerase, plays multiple roles in cellular biology. Its canonical function is primarily associated with telomere maintenance and genomic stability. In addition, several studies revealed critical non-canonical extra-telomeric functions of TERT in various cellular processes, including cell proliferation and survival, DNA damage response, transcription, signal transduction, and metabolic regulation, both in normal and in cancer cells. Notably, TERT is aberrantly upregulated in more than 80% of hepatocellular carcinoma (HCC) cases, making it an important target in liver cancer research. However, due to the diversity and complexity of TERT's functions in vivo, the precise mechanisms by which TERT contributes to the initiation and progression of HCC remain unclear. A recent study published in The Journal of Pathology using the Alb-Cre;TertTg mouse model and clinical HCC samples addresses the role of TERT in hepatocarcinogenesis. The study demonstrates that TERT promotes cell cycle progression and hepatocarcinogenesis by enhancing NF-κB promoter activity and facilitating the ubiquitination of p21. Notably, absence of functional p53 accelerates liver tumor development in TERT transgenic mice. These findings further underscore the critical role of TERT in inflammation-driven hepatocarcinogenesis and provide new insights into its underlying mechanisms. © 2025 The Author(s). The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Telomerase↗

PubMed1992

Missense mutations and a deletion of the p53 gene in human gastric cancer.

To investigate the molecular pathogenesis of human gastric cancers the p53 gene, a suppressor oncogene, was analyzed in 12 human gastric cell lines. Southern blot and Northern blot analysis revealed a total deletion of p53 gene in KATO-III cells but no major abnormality of p53 gene in other cell lines. By the use of the reverse-transcriptase polymerase chain reaction and direct sequencing 7 cell lines showed point mutations of p53 gene resulting in amino-acid substitutions. Most of them were rare mutations which had not been observed in other types of cancers. One of these mutations was also detected through the use of PCR and oligomer-specific hybridization. Six out of 7 cell lines with mutations of p53 gene also lost one allele of chromosome 17p. Immunoblotting of cell lysates with an antibody specific to p53 demonstrated the absence of p53 protein in KATO-III cell. By contrast, the high levels of the p53 protein were observed in 5 cell lines all of which contained mutations of p53 gene. These results further suggest that the inactivation of p53 gene may play an important role in the transformation of gastric cells to the malignant phenotype. KATO-III cells might be a good model for studying the significance of the loss of p53 gene in cellular transformation.

Alleles↗

PubMed1992

Increased expression and mutation of p53 in choroidal melanoma.

Using CM-1 antibody directed against the human p53 protein, high levels of mutant p53 protein expression were found in 12 out of 18 malignant choroidal melanomas. In contrast, we failed to observe elevated p53 expression, indicating the absence of p53 mutation in seven choroidal naevi, a potentially premalignant condition that can progress to form malignant melanoma. For two choroidal melanomas, we demonstrated that high levels of p53 protein were accompanied by exon 7 mutations. The mutations were found at codon 238, TGT-->TTT and codon 253, ACC-->AGC. These observations suggest that acquisition of abnormalities of the p53 gene may be an important step in the development of malignant melanoma.

Animals↗

PubMed1992

Expression of p53 mutant nuclear phosphoprotein in oral carcinoma and potentially malignant oral lesions.

An immunohistochemical study of primary oral squamous cell carcinomas (n = 37) with a monoclonal antibody (PAb 1801) specific to p53 antioncogene product demonstrated nuclear overexpression of the mutant protein in 35% of cases. Those positive included carcinomas without deep invasion suggesting that p53 mutation may occur in the early stages of progression of a malignancy. This is supported by the observation that mutant protein was detectable in limited amounts in 2 cases of oral mucosal dysplasia (n = 12). None of the normal or reactive oral mucosal tissues (n = 17) were positive for p53. The presence or absence of p53 was not correlated with the site of the lesion or its degree of differentiation. Our data suggest that p53 gene mutations are commonly involved in oral cancer but are neither sufficient nor necessary for the development of malignancy. Nevertheless, as this mutation is the commonest genetic change described so far in cancers in white caucasoids, it is possible that its presence can be used as a marker of risk in a high proportion of malignant and potentially malignant oral lesions.

Carcinoma↗

PubMed1992

p53 protein expression in transitional mucosa and adenocarcinomas of the colorectum.

Transitional mucosa, the nonneoplastic mucosa adjacent to colorectal adenocarcinomas, exhibits some morphologic and histochemical abnormalities. It is unclear, however, whether transitional mucosa is a preneoplastic or reactive phenomenon. Though normal p53 functions as a tumor suppressor, p53 gene alterations have been proposed as a step in malignant transformation, and aberrant p53 protein expression has been described in a high percentage of colonic adenocarcinomas. Since p53 protein normally has a short half-life, immunohistochemical detection of the protein is considered to be evidence of abnormal p53 expression. We analyzed p53 protein expression immunohistochemically on frozen tissue samples of transitional mucosa, normal mucosa, and tumor from 20 cases. In all 20 cases the transitional mucosa and normal mucosa failed to express p53, while 13 of 20 adenocarcinomas showed positive immunoreactivity characterized by intense nuclear staining. There was no correlation between tumor stage and p53 expression. The absence of staining for p53 protein in TM does not support the theory that transitional mucosa is a preneoplastic phenomenon.

Adenocarcinoma↗

PubMed2026

Association of HPV16 infection with p53 and survivin expression in oral squamous cell carcinoma.

Oral squamous cell carcinoma (OSCC) is the most common malignancy of the oral cavity and a major public health concern worldwide. This study aimed to investigate the relationship between p53 and survivin expression, clinicopathologic parameters and HPV16 infection in OSCC in order to elucidate the potential role of HPV16 in its pathogenesis.The study enrolled 45 patients who underwent surgical treatment for histologically confirmed OSCC. Tumor specimens were formalin-fixed and paraffin-embedded (FFPE) and histologically analyzed using hematoxylin/eosin staining. Immunohistochemistry for p53 and survivin was performed using the DAKO system. DNA extracted from FFPE tumor tissues was analyzed for HPV16 genome presence using polymerase chain reaction (PCR). All patients were followed for three years after primary treatment.No statistically significant associations were observed between p53 or survivin expression and clinicopathologic parameters including age, gender, tumor site, grade, stage, recurrence, metastasis or HPV16 status (P > 0.05). Among HPV16-positive patients (11/45, 24.4%), low survivin expression (<5%) was found in 8/11 (73%) patients, while high p53 expression (>10%) was observed in 7/11 (64%) patients. Disease-free interval did not differ significantly between patients with low vs. high p53 (P = 0.220) or survivin expression (P = 0.580). A significant correlation was detected between p53 and survivin expression (P = 0.04). HPV16 positivity was significantly associated with the absence of p53 immunoreactivity.These findings suggest that HPV16-independent oncogenic pathways are likely predominant in OSCC, while HPV16 infection may be associated with a distinct molecular subset characterized by absent p53 expression (p53-; survivin+/-; HPV16+). These results underscore the biological heterogeneity of OSCC and may have implications for future biomarker-based stratification of patients.

HPV16↗

PubMed1992

p53: the ultimate tumor suppressor gene?

Alterations in the gene encoding the cellular p53 protein are perhaps the most frequent type of genetic lesions in human cancer. At the heart of these alterations is the abrogation of the tumor suppressor activity of the normal p53. In many cases this is achieved through point mutations in p53, which often result in pronounced conformational changes. Such mutant polypeptides, which tend to accumulate to high levels in cancer cells, are believed to exert a dominant negative effect over coexpressed normal p53. Extensive research on p53, especially in the course of the last 3 years, has already provided much insight into the biological and biochemical mechanisms that underlie its capacity to act as a potent tumor suppressor. There are now many indications that p53 may play a central role in the control of cell proliferation, cell survival, and differentiation. Nevertheless, despite the purported importance of p53 for such crucial processes, mice can develop apparently without any defect in the total absence of p53. This raises the possibility that p53 may become critically limiting only when normal growth control is lost.

Animals↗

PubMed1992

Multiple oncogenes and tumor suppressor genes are structurally and functionally intact during hepatocarcinogenesis in hepatitis B virus transgenic mice.

In the current study we sought to elucidate the molecular mechanisms which might contribute to hepatocarcinogenesis in a hepatitis B virus (HBV) envelope transgenic mouse model in which chronic hepatocellular injury and inflammation lead to regenerative hyperplasia and eventually to the development of chromosomal abnormalities and hepatocellular carcinoma (HCC), thereby reiterating many of the pathophysiological events that occur prior to the development of HCC in chronic HBV infection in humans. We have previously demonstrated that HBV envelope gene expression is decreased in regenerating hepatocytes and preneoplastic nodules early in the disease process and that expression of alpha-fetoprotein and the multidrug transporter gene mdr-III is activated in the tumors that develop in this model, but not prior to tumor development. In the current study, we examined the structure and expression of a large panel of dominant acting oncogenes and tumor suppressor genes in the liver at all stages of the disease process in order to determine the extent to which they contribute to hepatocarcinogenesis in these transgenic mice. To our surprise, no changes were observed in the structure or function of any of these genes, many of which are commonly activated in other rodent models of hepatocarcinogenesis but rarely activated in human HCC. These findings suggest that the HBV transgenic mouse model is different from most other rodent models of hepatocarcinogenesis and that it may relate more closely to the events involved in HBV-induced human hepatocarcinogenesis, where generalized chromosomal abnormalities are common, while structural and functional changes in most of the commonly studied positive-acting oncogenes examined herein are not. Since p53 and RB mutations have recently been reported to be late events in human hepatocarcinogenesis, the structural integrity of the RB locus and the absence of p53 mutations in the HBV transgenic mouse model suggest that they may represent a relatively early stage of hepatocellular tumorigenesis and that further manipulation of this model is warranted in order to more fully reproduce the molecular-genetic events that characterize HBV-induced HCC in humans.

Animals↗

PubMed2025

p53 Regulates Nuclear Architecture to Reduce Carcinogen Sensitivity and Mutagenic Potential.

The p53 tumor suppressor is an indispensable regulator of DNA damage responses that accelerates carcinogenesis when mutated. In this report, we uncover a new mechanism by which p53 maintains genomic integrity in the absence of canonical DNA damage response activation. Specifically, loss of p53 dramatically alters chromatin structure at the nuclear periphery, allowing increased transmission of an environmental carcinogen, ultraviolet (UV) radiation, into the nucleus. Genome-wide mapping of UV-induced DNA lesions in p53-deficient primary cells reveals elevated lesion abundance in regions corresponding to locations of high mutation burden in malignant melanomas. These findings uncover a novel role of p53 in the suppression of mutations that contribute to cancer and highlight the critical influence of nuclear architecture in regulating sensitivity to carcinogens.

Journal Article↗

PubMed1992

Comparative evaluation of HIV infected foreign students and Indian with AIDS in Chandigarh, India.

Out of a total of 1,600 foreign students who came to India between June 1989 and October 1990, 22 were seropositive for HIV-1. Ten showed antibodies to all the gene products. Antibodies to gp160 and p24 were present in all the seropositives while antibodies to p53, p15/17 were significantly higher in healthy seropositives than in patients with full blown AIDS. Absence of antibodies to p15/17 and p53 thus appeared to be a more sensitive criterion of end stage disease than absence of anti- p24 antibodies. When seropositive samples from African students were checked for HIV-2 antibodies by ELISA, 13/22 were found to be positive. Further, 2/10 Indians with full blown AIDS were also strongly positive for HIV-2. These data could be of relevance for formulating future strategies for population-based screening for HIV-2.

Acquired Immunodeficiency Syndrome↗

PubMed1992

Immunoreactivity for p53 protein in malignant mesothelioma and non-neoplastic mesothelium.

The presence of p53 protein in non-neoplastic pleural mesothelium (40 cases) and in human malignant mesothelioma (36 cases) was assessed immunohistochemically using the antibodies DO7, CM-1, and PAb240. In a quarter of the malignant mesotheliomas, there was nuclear immunoreactivity for p53 protein with both the DO7 and CM-1 antibodies. There were no statistically significant differences between the various mesothelioma subtypes (P > 0.05). No immunoreactivity was found with the PAb240 antibody, suggesting absence of mutant-type p53 protein. Nonneoplastic mesothelium was not immunoreactive with any of the antibodies. We conclude that there is immunoreactivity for p53 protein in some mesotheliomas. p53 protein immunoreactivity could be used to discriminate between neoplastic and reactive mesothelium.

Epithelium↗

PubMedDate not supplied

Low, intermediate and high grade breast carcinomas as determined by histotyping, immunohistochemical prognosticators and histological grading.

Low grade breast cancers i.e. mucinous (17 cases--3.2%), tubular (7 cases--1.3%) and invasive cribriform carcinomas (3 cases--0.5%) have been identified within a series of 524 breast cancers only by histotyping in hematoxylin-eosin stained sections: the reactivities of immunohistochemical prognosticators as estrogen/progesterone receptors (ER, PgR), growth fraction (GF: Ki67), p53 and c-erbB-2 oncoproteins are in agreement with clinical behaviours. Invasive papillary carcinomas (9 cases--1.6%) are not to be considered low grade carcinomas. Intermediate grade cancers are also determined by histotyping. Medullary carcinoma (13 cases--3.4%) has a paradoxical behaviour displaying a favourable clinical prognosis together with high grading and GF, absence of ER, PgR, high p53 and c-erbB-2 values, as compared with invasive ductal carcinomas: an extensive tissue immune response as suggested by a heavy lymphocyte infiltration may explain this behaviour. Invasive lobular carcinoma (62--11.6%) shows an intermediate immunohistochemical pattern, paralleling an intermediate prognosis, when compared with low and high grade carcinomas: ER, PgR and GF positivities are nearly the same as in ductal carcinomas whereas grading, p53 and c-erbB-2 are less expressed. These data are confirmed both for lobular carcinomas as a whole and for all variants of this kind of tumors. Invasive ductal carcinomas (413 cases--79%) may be stratified on three prognostic classes corresponding to histological grading (G1, G2, G3). Significant relationships of grading with all the immunohistochemical prognosticators studied has been observed. It may be concluded that grading is a parameter of paramount importance in this group of tumors.

Antigens, Neoplasm↗

PubMed1992

Markers for dysplasia of the upper aerodigestive tract. Suprabasal expression of PCNA, p53, and CK19 in alcohol-fixed, embedded tissue.

Recognition of premalignant lesions in the oral epithelium has the potential to increase survival rates for squamous cell carcinoma of the oral cavity. It has previously been reported that cytokeratin 19 (CK19), a 40-kd epithelial cytoskeletal protein within the suprabasal squamous epithelium, is a specific marker of moderate-to-severe dysplasia and carcinoma in situ in oral cavity squamous epithelium. In contrast, normal epithelium and hyperplastic lesions reportedly express CK19 only in the basal layer if at all. The authors chose to test and extend this hypothesis by studying suprabasal CK19 expression and dysplasia of the oral cavity and upper aerodigestive tract in paraffin-embedded specimens that had been fixed in alcohol, a superior fixative for the preservation of cytokeratins. The authors examined 56 alcohol-fixed, paraffin-embedded specimens including 37 from the oral cavity, using two antibodies specific for CK19 (Ks19.1 and 4.62), an antibody to the nuclear proliferation marker, proliferating cell nuclear antigen (PCNA) (19A2), and an antibody to the putative tumor suppressor gene, p53 (pAb1801). The lesions were classified as normal, hyperplasia, mild dysplasia, moderate dysplasia, severe dysplasia/carcinoma in situ, or invasive squamous cell carcinoma, following standard histologic criteria. Immunocytochemically stained sections were scored for the presence or absence of suprabasal CK19, suprabasal PCNA, and p53 positivity, regardless of location. The immunostaining patterns of the two anti-CK19 antibodies were essentially equivalent. Except for one laryngeal specimen, normal epithelium, when positive, showed CK19 expression only in scattered cells throughout the basal layer. Proliferating cell nuclear antigen-positive nuclei were found exclusively in the basal layer. In areas of hyperplasia, CK19 immunostaining was absent or confined to the basal layer in 20 of 38 specimens and was expressed in suprabasal cells in 18 of 38 hyperplastic specimens. Proliferating cell nuclear antigen immunostaining in all cases of hyperplasia was limited to the basal layer. Severe dysplasia and carcinoma in situ showed suprabasal CK19 staining in six of nine specimens and no CK19 staining in three of nine specimens. In contrast, suprabasal PCNA immunostaining was found in all dysplasia and carcinoma in situ cases. p53 expression was detected in three of nine severe dysplasia/CIS specimens and was immunocytochemically undetectable in all normal, hyperplasia, and mild to moderate dysplasia specimens. The authors conclude that suprabasal CK19 expression is neither a sensitive nor a specific marker of premalignancy in oral epithelium and cannot be used to distinguish hyperplasia from dysplasia. In contrast, a strong correlation between suprabasal expression of PCNA, a marker for proliferating cells, and dysplasia/carcinoma in situ was evident.(ABSTRACT TRUNCATED AT 400 WORDS)

Antigens, Neoplasm↗

PubMed1992

Clonal p53 mutation in primary cervical cancer: association with human-papillomavirus-negative tumours.

Analyses of cancer cell lines and of anal cancers suggest an inverse correlation between infection with human papillomavirus (HPV) and somatic mutation of the p53 tumour-suppressor gene. We have investigated this association in primary cervical tumours. Tumour-tissue samples from 28 women with primary cancer of the cervix were analysed for presence of HPV sequences and for somatic mutations of the p53 gene. Southern blot analysis and the polymerase chain reaction (PCR) showed that 25 of the tumours contained HPV sequences; 20 were HPV16 positive and 5 HPV18 positive. 17 tumours subjected to restriction fragment length polymorphism analysis for the short arm of chromosome 17 showed no evidence of allelic deletion. Sequencing of the entire coding region of the p53 gene by asymmetric PCR detected heterozygous point mutations in only 3 HPV-negative tumours. By contrast, in 21 HPV-positive cancers the p53 sequence was wild-type throughout. Our data indicate that loss of wild-type p53 function is important in the pathology of cervical cancer and that in the absence of an HPV-encoded gene product that mediates loss of p53 function, somatic mutation of the gene is required. This pattern of p53 mutation may partly explain the apparently worse prognosis of HPV-negative cervical cancers.

Adenocarcinoma↗

PubMedDate not supplied

Accumulation of p53 protein correlates with tumour proliferative activity in EBV positive Burkitt's lymphoma.

p53 tumour suppressor gene is often found mutated in Burkitt's lymphoma (BL) cell lines and tumours. We analysed 35 BL tumours for the accumulation of p53 protein, and correlated the results with DNA flow cytometric data on the proliferative activity (SPF), and data on the presence or absence of Epstein-Barr virus (EBV) DNA. More than one-third (37 per cent) of the tumours showed accumulation of p53, which was considered to be consistent with mutation of the p53 gene. Tumours that were positive both for EBV DNA and p53 had significantly higher mean SPF than corresponding EBV DNA negative and/or p53 negative tumours. The proportions of tumour cells with accumulation of p53 appeared to correlate with tumour SPF only in EBV DNA positive BLs. However, there was no apparent association between accumulation of p53 and the presence or absence of EBV DNA. These findings are suggestive of multiple pathways in BL tumour progression.

Adolescent↗