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

Mutations of p53 and human papillomavirus infection in cervical carcinoma

BACKGROUND

Oncogenic human papillomavirus (HPV) infection has been implicated in the pathogenesis of cervical carcinoma. The HPV oncoproteins E6 and E7 are though to play a crucial role in this process by their interactions with the p53 protein and the retinoblastoma susceptibility gene product, respectively. The E6 protein binds to and stimulates the degradation of the p53 protein. Mutations involving evolutionary conserved regions of the p53 gene also can alter p53 function. Point mutations of p53 frequently have been identified in a wide variety of human tumors.

METHODS

Forty-five cervical carcinoma samples were evaluated for the presence of mutations involving exons 5-8 of the p53 gene with polymerase chain reaction (PCR) amplification of genomic DNA, followed by single-stranded conformation polymorphism analysis and/or direct sequencing. The status of oncogenic HPV infection in the tumor tissues was analyzed by Southern blot and PCR.

RESULTS

Forty-two of 45 cervical carcinomas showed oncogenic HPV DNA: Of three HPV-negative samples, one harbored a missense point mutation of the p53 gene. An additional p53 point mutations was identified in a tumor with HPV 18 infection.

CONCLUSIONS

Oncogenic HPV DNA can be identified in most cervical carcinomas. Mutations involving conserved regions of p53, although infrequent in cervical cancer, occur preferentially in tumors without HPV infection. Inactivation of p53 function is important in the pathogenesis of cervical carcinoma.

Absence of human papillomavirus type 16 E6 transcripts in HPV 16-infected, cytologically normal cervical scrapings

By a combination of reversed transcription and subsequent polymerase chain reaction (RNA-PCR), 23 cytologically normal cervical scrapings, positive for the presence of human papillomavirus type 16 (HPV 16) DNA, were analyzed for the presence of transcripts originating from the E6 region of the viral genome. This region is thought to be involved in transformational, tumorigenic events. No mRNAs of the E6 region were detectable using the most sensitive PCR-mediated procedure currently available. Since it was previously shown that in cytological abnormal cervical scrapings about one-half of the samples positive for HPV 16 DNA express mRNAs of the E6 region, a difference between normal and abnormal cervical scrapings, when the HPV 16 is present, exists. The observed difference between cytologically normal and abnormal, HPV-DNA-positive cervical scrapes may eventually be used as a prognostic marker for screening of women at risk for the development of cervical carcinoma. However, firm establishment of the putative correlation between tumor progression and the presence of E6 transcripts requires extensive follow-up analysis of HPV-positive patients.

Inhibition of cervical carcinoma cell line proliferation by the introduction of a bovine papillomavirus regulatory gene

Human papillomavirus (HPV) E6 and E7 oncogenes are expressed in the great majority of human cervical carcinomas, whereas the viral E2 regulatory gene is usually disrupted in these cancers. To investigate the roles of the papillomavirus E2 genes in the development and maintenance of cervical carcinoma, the bovine papillomavirus (BPV) E2 gene was acutely introduced into cervical carcinoma cell lines by infection with high-titer stocks of simian virus 40-based recombinant viruses. Expression of the BPV E2 protein in HeLa, C-4I, and MS751 cells results in specific inhibition of the expression of the resident HPV type 18 (HPV18) E6 and E7 genes and in inhibition of cell growth. HeLa cells, in which HPV gene expression is nearly completely abolished, undergo a dramatic and rapid inhibition of proliferation, which appears to be largely a consequence of a block in progression from the G1 to the S phase of the cell cycle. Loss of HPV18 gene expression in HeLa cells is also accompanied by a marked increase in the level of the cellular p53 tumor suppressor protein, apparently as a consequence of abrogation of HPV18 E6-mediated destabilization of p53. The proliferation of HT-3 cells, a human cervical carcinoma cell line devoid of detectable HPV DNA, is also inhibited by E2 expression, whereas two other epithelial cell lines that do not contain HPV DNA are not inhibited. Thus, a number of cervical carcinoma cell lines are remarkably sensitive to growth inhibition by the E2 protein. Although BPV E2-mediated inhibition of HPV18 E6 and E7 expression may contribute to growth inhibition in some of the cervical carcinoma cell lines, the BPV E2 protein also appears to exert a growth-inhibitory effect that is independent of its effects on HPV gene expression.

Repression of endogenous p53 transactivation function in HeLa cervical carcinoma cells by human papillomavirus type 16 E6, human mdm-2, and mutant p53

Somatic mutations in the p53 tumor suppressor gene represent the single most common genetic alteration observed in human cancers. Interestingly, the great majority of malignant tumors of the cervix uteri contain wild-type p53 alleles together with the DNA of specific types of human papillomaviruses (HPVs), while the small portion of HPV-negative cervical carcinomas often carry alterations in the p53 tumor suppressor gene. Transcriptional activation of yet-undefined cellular regulatory genes has been implicated to play a key role for the tumor-suppressive activity of wild-type p53, as mutant p53 in general has lost the activity to stimulate p53-responsive reporter plasmids. The detection of DNA-binding-competent and transcriptionally active p53 protein in HeLa cervical carcinoma cells enabled us to investigate the in vivo effects of putative modulators on endogenous p53 function in cervical cancer cells. We show that the transcriptional stimulatory activity of HeLa cell p53 is strongly repressed by overexpression of E6 protein from oncogenic HPV type 16 (HPV16) but is not influenced by low-risk HPV6 E6. Similar to HPV16 E6, cellular oncoproteins such as mutant p53 or the product of the human mdm-2 gene also negatively interfere with p53-mediated transactivation in HeLa cells. Our findings indicate that, within a cervical cancer cell, the expression of E6 protein from high-risk HPV16, but not from low-risk HPV6, can lead to the same functional consequences as a mutation of the p53 gene. These results could provide a biochemical basis for the inverse correlation between the presence of HPV sequences and somatic mutations of the p53 gene in cervical carcinomas.

TP53 tumor-suppressor gene and human carcinogenesis

The wild-type tumor-suppressor TP53 gene encodes for a nuclear protein which has been shown to act as a transcriptional modulator. The cellular role of the p53 protein is the control of cell proliferation, particularly important in stressed cells. The TP53 gene is frequently mutated in sporadic and familial human cancers. Most transforming mutations localize in highly conserved domains of the gene and define hot-spot regions that have a certain degree of tissue specificity. Moreover, most mutations are point mutations and the type and localization of the nucleotide substitution may sometimes help in recognizing the carcinogenic agent. This is the case for C to T transitions at dipyrimidine sites induced by UV radiation in cutaneous epitheliomas. Inactivation of p53 protein can also occur through mechanisms other than genetic alteration, such as binding to viral or cellular proteins. Loss of wild-type TP53 function seems therefore to play a crucial role in cell transformation in human cancers, either during carcinogenesis or later in tumor progression.

Immunohistochemical analysis of p53 expression in anal squamous neoplasia

AIMS

To determine the pattern of expression of the p53 tumour suppressor gene product in anal squamous neoplasia, and to determine if this could be used as a marker of disease progression. The association between p53 expression and human papillomavirus (HPV) 16 DNA status of the anal lesions was also investigated.

METHODS

The presence and localisation of the p53 protein in formalin fixed, paraffin wax embedded specimens of anal squamous epithelium (normal and neoplastic) was examined using immunohistochemical staining with a panel of two monoclonal antibodies (DO-1, DO-7) and one polyclonal antibody (CM-1). Thirty nine normal anal epithelia, 14 anal intraepithelial neoplasia (AIN) grade 1, seven AIN 2, and 20 AIN 3 specimens were obtained from patients without demonstrable invasive disease; twelve AIN 3 specimens adjacent to invasive disease and 34 anal squamous cancers were also examined. Genomic DNA from all 126 specimens was extracted and analysed for HPV 16 DNA using the polymerase chain reaction (PCR).

RESULTS

Nuclear p53 was strongly expressed in 67% (23/34) of invasive anal squamous tumours, 75% (9/12) of AIN 3 specimens adjacent to invasive disease, and in 60% (12/20) of AIN 3 specimens obtained from patients without demonstrable invasive disease. Two of the patients in the latter group with positively staining specimens subsequently developed invasive tumours which had staining characteristics similar to those of the AIN 3 specimens. p53 protein was expressed in very low concentrations in low grade AIN and not at all in normal anal squamous epithelium. In those specimens which stained positively for p53, HPV 16 DNA sequences were detected in 69.5% (16/23) of invasive disease, 77.7% (7/9) of AIN 3 adjacent to invasive disease, 75% (9/12) of AIN 3 obtained from patients without demonstrable invasive disease, 33.3% (2/6) of AIN 2, and in 40% (2/5) of AIN 1. There was no significant correlation between p53 immunostaining and HPV 16 DNA status (p < 0.05).

CONCLUSIONS

Aberrant expression of the p53 gene product is probably involved in the pathogenesis of anal squamous neoplasia. Long term follow up studies of all patients with AIN are required to determine if this could be used as a marker of likely disease progression from high grade AIN to invasive disease. There does not seem to be an association between the presence or absence of HPV 16 DNA sequences and mutant p53 proteins in anal squamous neoplasia.

Prognostic significance of human papillomavirus genomes (type-16, -18) and aberrant expression of p53 protein in human esophageal cancer

The presence and distribution of human papillomavirus (HPV) DNA or of increased expression of the p53 protein were determined in 71 patients with esophageal squamous-cell carcinoma (SCC) by in situ hybridization with biotinylated DNA probes for HPV-16, -18, -31 and -33, and immunohistochemical techniques using antibody to p53 protein. Of 71 patients from Kochi prefecture, 24 (Group I) were positive for HPV DNA, including 10 for HPV type-16 and 14 for HPV type-18; in contrast, none were positive for HPV-31 or -33. Of the remaining 47 patients, 24 (Group II) showed positive nuclear staining in cancer cells with p53 antibody. The group of 23 patients with neither HPV nor p53 expression (Group III) had a significantly better survival rate than Group I or II. These results suggest that HPV-16 and -18 may play a role in the pathogenesis of esophageal SCC, particularly with regard to its striking geographical distribution; that esophageal cancers do occur in the absence of HPV infection when over-expression of p53 is present; and that the presence of HPV infection and over-expression of p53 may each be a factor indicating a relatively poor prognosis.

Human papillomaviruses, tumour suppressor genes and cervical cancer

There is now a considerable body of evidence that links HPV infection with anogenital squamous carcinoma, particularly for specific 'high risk' HPV types (HPV16 and 18) and invasive carcinoma of the cervix. Recent advances in the molecular study of these viruses have elucidated some potential mechanisms by which they may contribute to the development of these diseases. In this review we concentrate on the interactions of 2 of the HPV encoded proteins, E6 and E7, with cellular tumour suppressor gene products. We provide a model of how these interactions may be important in tumourigenesis and draw together current knowledge of this exciting and rapidly evolving field.

The multistep nature of cancer

Cancer is a distinct type of genetic disease in which not one, but several, mutations are required. Each mutation drives a wave of cellular multiplication associated with gradual increases in tumor size, disorganization and malignancy. Three to six such mutations appear to be required to complete this process.

Over-expression of p53 protein in human laryngeal carcinoma

We examined the expression of tumor-suppressor protein p53 in a variety of laryngeal carcinomas from 43 patients (25 primary, 13 metastatic and 5 recurrent cases), 13 normal laryngeal tissues and 7 benign laryngeal nodule biopsy specimens, using the polyclonal antibody CM-1. Previously we have reported a high incidence of ras mutations (51%) and human papillomavirus (HPV) infection (37%) in these laryngeal carcinomas. p53 protein was detected by immunohistochemistry in 65% of laryngeal carcinomas (60% of primary, 69% of metastatic and 80% of recurrent cases). No correlation was found between p53 over-expression and histological grading of the tumors. None of the specimens from normal larynx and laryngeal nodules revealed any detectable level of this protein. Furthermore, 11 (69%) of 16 HPV-positive cases and 17 (77%) of 22 cases with ras mutation showed variable grades of p53 expression. Twelve (71%) of 17 laryngeal carcinomas in current study having both p53 over-expression and ras mutation were moderately or poorly differentiated. Likewise, positivity for these 2 parameters was significantly increased in metastatic tumors (9 of 13 cases, 69%) as compared with primary and recurrent tumors (8 of 30 cases, 27%) (p < 0.01). Our results suggest that multiple factors are involved in this malignancy, and that the simultaneous over-expression of p53 and the presence of ras mutation may be related to the progression stage of laryngeal carcinoma.

p53 immunoreactivity in inflammatory and neoplastic diseases of the uterine cervix

Immunoreactivity for the tumour suppressor gene product p53 is commonly found in many different human malignancies and few premalignant lesions. Data on cervical neoplasms, however, are still lacking. We retrospectively investigated p53 immunoreactivity in 92 lesions of the uterine cervix, including 44 cases of chronic cervicitis, 29 squamous intraepithelial lesions (SILs), and 19 invasive carcinomas. p53 immunoreactivity, confined to the basal cell layer, was detected in 74 per cent of cases showing chronic cervicitis and in all cases with low-grade SILs. Conversely, suprabasal and/or diffuse p53 immunoreactivity was exclusively demonstrated in 25 per cent of high-grade SILs and in 74 per cent of invasive carcinomas. The results of this investigation document a high prevalence of p53-immunoreactive malignant tumours of the uterine cervix. In high-grade SILs, p53-immunoreactive cells paralleled the height of involvement by dysplastic changes within the squamous epithelium. A prolonged half-life of the protein is the most likely explanation for the occurrence of p53 immunoreactivity in neoplastic cells. The unexpected finding of p53-immunoreactive cells in inflammatory lesions, though possibly related to an increased proliferation rate of the basal cell compartment, requires further study and underlines the need for a careful approach to p53 immunocytochemistry.

Use of semi-quantitative PCR for human papillomavirus DNA type 16 to identify women with high grade cervical disease in a population presenting with a mildly dyskaryotic smear report

The aim of this study was to assess whether qualitative or semi-quantitative detection of human papillomavirus type 16 (HPV 16) can help to identify women with major grade cervical intraepithelial neoplasia (CIN 2 and CIN 3) among those referred with a smear suggesting mild dyskaryosis. The study population consisted of 200 women sequentially attending the Royal Free Hospital colposcopy clinic. All women were investigated by cytology, colposcopy and, where appropriate, histopathology, and HPV 16 DNA was detected in cervical scrape samples using the polymerase chain reaction (PCR). A final clinical diagnosis of normal, wart virus infected (WVI), CIN 1, CIN 2 or CIN 3 was made in 179 women. On the basis of the qualitative PCR data, the presence of HPV 16 DNA was of borderline use in identifying women with high grade cervical disease [63/113 (normal/WVI/CIN 1) vs 46/66 (CIN 2/CIN 3); P = 0.065]. However, semi-quantitative PCR analysis showed that a high/medium HPV 16 result was significantly associated with high-grade disease [29/113 (normal/WVI/CIN 1) vs 38/66 (CIN 2/CIN 3); P = 0.0001]. Furthermore, semi-quantitative PCR and cytology were performed on the repeat smear taken immediately prior to colposcopy. The combined laboratory results show that 53/60 women with biopsy proven high-grade disease were identified, as were 26/95 women who were either normal or who had low grade cervical disease. The possibility of using such an approach for selecting women for more rapid or for routine colposcopy appointments in the two groups respectively is discussed.

Overexpression of p53 in Hodgkin's disease: lack of correlation with Epstein-Barr virus infection

Recent work has shown that p53 gene mutations are frequently found in Epstein-Barr virus (EBV)-positive and EBV-negative cases of Burkitt's lymphoma but not in EBV-associated undifferentiated nasopharyngeal carcinomas (NPCs). Similar viral gene expression patterns are observed in undifferentiated NPCs and in EBV-positive cases of Hodgkin's disease (HD), suggesting that the contribution of the virus to the pathogenesis of these malignancies may also be similar. We have analysed 116 cases of HD for EBV association and for immunohistologically detectable overexpression of p53. p53 overexpression was detected in the tumour cell population of 37 (32 per cent) of the cases. Fifteen cases showed p53-specific labelling of more than 40 per cent of tumour cells; in six of these, virtually all tumour cells were stained. In eight cases, between 5 and 40 per cent of tumour cells were labelled, and in another 14 cases, less than 5 per cent of tumour cells expressed detectable amounts of p53. EBV-positive HD cases were found in all groups with different levels of p53 overexpression as well as amongst p53-negative cases. While a more detailed analysis of the p53 gene in HD is required, these data show that overexpression of p53 in HD is heterogeneous and that there is no simple correlation between EBV infection and p53 overexpression.

Human papillomavirus type 16 in tumor tissue of low-stage squamous carcinoma of the uterine cervix in relation to ploidy grade and prognosis

BACKGROUND

The relationship among the presence of human papillomavirus (HPV) in tumor cells, DNA ploidy, and the prognosis of squamous cell carcinoma of the uterine cervix was studied.

METHODS

HPV 16 was detected using the polymerase chain reaction on paraffin-embedded material from 69 patients with Stage IB and IIA carcinoma of the uterine cervix. The presence or absence of HPV was related to age, survival, and ploidy status as measured by DNA flow cytometry. All patients were treated by radical surgery.

RESULTS

Thirty-four patients had HPV 16, and 35 did not. The mean age of the patients differed statistically significantly between the HPV-positive group (51.1 years) and the HPV-negative group (45.1 years, P = 0.015). No difference was found in the mean DNA index (1.21 versus 1.22, P = 0.85) or 5-year survival rate (85% versus 86%, P = 0.87) between the two groups.

CONCLUSIONS

The high prevalence of HPV 16 in cervical cancer, which appeared to be correlated with age (in combination with its presence in diploid and aneuploid tumors), indicated the important role of HPV 16 in the evolution of cervical cancer. However, using stepwise Cox regression analysis, the presence of HPV 16 had no additional prognostic value over lymph node metastases findings.

Immunohistochemical analysis of p53 protein overexpression in normal, premalignant, and malignant tissues of the cervix uteri

Two hundred and thirty-eight cervical lesions ranging from normal to malignant were examined for overexpression of p53 protein. Whereas p53 protein was identified in 62 per cent of invasive squamous cell carcinomas, 11 per cent of invasive adenocarcinomas, and 7 per cent of squamous cell carcinomas in situ, no staining was found in adenocarcinoma in situ, dysplastic tissue, condyloma, and normal tissue. In 9 per cent of the positive cases of invasive squamous cell carcinomas, 5-50 per cent of the tumour cells were immunoreactive for p53 protein, whereas the other positive specimens were characterized by only rare p53-positive cells. We conclude that in invasive cervical carcinomas widespread overexpression of p53 protein is unusual, but occasional positive nuclei can be found frequently. Furthermore, our results indicate that altered expression of p53 protein may be involved in the progression of cervical carcinomas.

Cervical carcinoma: low frequency of allele loss at loci implicated in other common malignancies

Twenty cervical carcinomas were examined for loss of heterozygosity (LOH) using 22 RFLP markers, which mapped to regions of putative oncosuppressor gene loci, identified as candidates in other common solid tumours. Allele losses were identified in six of the eight chromosomal arms examined, but at a significantly lower frequency than that reported in other common solid tumours. No association was observed between allele losses at any chromosomal location and the presence or integration of 'high risk' types of HPV determined by a sensitive, specific PCR method. HPV 16, 18 or 33 were found in the majority (75%) of these tumours. We have looked at only a limited subset of chromosomal regions, but the results, so far, imply that carcinoma of the cervix may arise by different molecular events than other common solid tumours, and support the view that one of the distinctive events may be infection with HPV. Alternatively, similar molecular events may be occurring, but in regions of the genome not yet identified as targets in other solid tumours.

Frequent occurrence of p53 gene mutations in uterine cancers at advanced clinical stage and with aggressive histological phenotypes

The clinical and pathological significance of mutation of the p53 tumor-suppressor gene was examined in 108 cases of primary uterine cancers using single-strand conformation polymorphism and direct DNA sequencing analyses. Mutation of the p53 gene was detected in 19 (31%) of 62 cases of cancer of the uterine corpus and was more frequent in groups at an advanced clinical stage and/or with aggressive histology. Among four adenocarcinomas arising in the lowest portion of the uterine corpus, three showed integration of human papillomavirus (HPV) types 16 and/or 18 DNA, and two of them also showed p53 mutation. In cancer of the uterine cervix, p53 mutations were rare; 7% (3/46) in total, 3% (1/30) of cases with integration of HPV types 16 and/or 18 DNA and 13% (2/16) of cases without HPV DNA integration. Three mutations were detected among two cases at clinical stage IV and two cases of undifferentiated cervical carcinoma. Immunohistochemically, all five cases of uterine cancer which showed diffuse (> 50% of cancer cells) nuclear staining of p53 protein also carried the p53 mutation. Therefore, p53 alterations were suggested to be involved in the development of uterine cancers showing aggressive biological behavior. Although a high incidence of HPV DNA integration and a low incidence of p53 mutation were confirmed in cancer of the uterine cervix, there was no inverse association between integration of HPV types 16 and/or 18 DNA and p53 mutation.

Detection of single-base mutations in a mixed population of cells: a comparison of SSCP and direct sequencing

Single-base-pair changes in several genes have been shown to be important in carcinogenesis. We have compared the sensitivity of two commonly used techniques for detection of single-base-pair changes. Defined populations of cells were prepared by mixing wild-type Chinese hamster ovary cells with cells carrying a known mutation in the CTP synthetase gene. RNA was extracted and analyzed for the mutation by single-strand conformational polymorphism and direct sequence analysis of polymerase chain reaction products. We found that both techniques were able to detect the mutation when it was present in 25% of the cells, but that direct sequencing was slightly more sensitive and able to detect the mutation when it was present in only 20% of the population.