Higher incidence of p53 mutation in cervical carcinomas with intermediate-risk HPV infection

Incomplete inhibition of the Rb tumor suppressor pathway in the context of inactivated p53 is sufficient for pancreatic islet tumorigenesis

Here, we describe the surprising residual capability of the Rb pathway to negatively regulate proliferation and tumorigenesis in a SV40 large T antigen (Tag)-driven mouse model of pancreatic islet carcinogenesis. Heterogeneous Tag expression during all progression stages suggested that a threshold level of the T antigen oncoprotein might be deterministic for beta-cell hyperproliferation and led us to hypothesize that Tag might not be fully inhibiting the tumor suppressor activity of Rb. Moreover, genomic profiling of these tumors by array CGH pointed to regions of loss on chromosomes 6 and 14, where the Rb pathway inhibitor p27 and Rb itself, respectively, reside. Indeed, genetic ablation of the p27(Kip1) or Rb genes accentuated Tag-induced tumorigenesis, with loss of Rb in particular broadly enhancing multiple parameters of tumorigenesis including the frequency and growth rates of premalignant lesions, of nascent solid tumors, and of invasive carcinomas. The data indicate that attenuation rather than complete inactivation of Rb tumor suppressor gene function, in the context of p53 inhibition, is sufficient to initiate tumorigenesis in this model of islet cell cancer, with the demonstrable possibility that subsequent losses of Rb or its regulators can enhance malignant progression. The results may be relevant to human papillomavirus (HPV)-induced cervical neoplasias where E7 oncogene expression levels or activity (in the case of intermediate/low-risk HPV subtypes) incompletely inhibits Rb tumor suppressor functions, as well as to other neoplasias where initiating oncogenic or tumor suppressor events reduce but do not abrogate Rb function.

Characterization of human papillomavirus infection, P53 and Ki-67 expression in cervix cancer of Mozambican women

In this study, we aimed at evaluating the distribution of HPV types and the expression of P53 and Ki-67 in cervix carcinomas of Mozambican women. Fourty-seven invasive carcinomas, 10 CIN III, and 10 normal cervix were studied. P53 and Ki-67 expression was examined immunohistochemically. HPV infection and HPV types were detected by PCR (GP5+/bio-GP6+) and enzyme-immunoassay, respectively. Expression of P53 and Ki-67 and detection of HPV were as follows: normal cervix--0%, 10%, and 0%, respectively; CIN III--10%, 0%, and 100%, respectively; invasive carcinomas--50%, 55.5%, and 70%, respectively. HPV 16 was identified in 54% of invasive carcinomas, HPV 31, 33, 35, and 45 in 23%, "unidentified" HPV in 19%, and HPV 18 in 4% of invasive carcinomas. No significant associations were observed between P53 expression, Ki-67 expression, and HPV infection. In conclusion, we observed a high frequency of HPV infection in CIN III lesions and invasive carcinomas from Mozambican women, with HPV 16 representing the most frequent viral type. HPV status was not related to P53 and Ki-67 expression. Both P53 and Ki-67 are associated with invasive cervix carcinomas, mainly of the squamous keratinizing histotype.

Detection and typing of HPV genotypes in various cervical lesions by HPV oligonucleotide microarray

OBJECTIVES

This study was conducted to evaluate a clinical efficacy of human papillomavirus (HPV) oligonucleotide microarray (Biomedlab Co., Seoul, South Korea) for the detection of HPVs in various cervical lesions.

RESULTS

HPV DNAs from 234 patients were analysed by two methods. Among those, 212 patients were classified into 5 groups according to the histologic diagnosis: chronic cervicitis, cervical intraepithelial neoplasia (CIN) I, CIN II, CIN III, and invasive cervical carcinoma. PCR-RFLP could detect 7 types of high-risk HPVs (HPV 16/18/31/33/35/52/58) and HPV microarray could detect 15 types of high-risk HPVs (HPV 16/18/31/33/35/39/45/51/52/56/58/59/66/68/69) and 7 types of low-risk HPVs (HPV 6/11/34/40/42/43/44).HPV genotyping by HPV oligonucleotide microarray revealed that HPV16 was the most frequent type (30.2%) in all specimens tested and was significantly more frequent in CIN III and invasive carcinomas than other lesions.

METHODS

HPV DNAs were detected in 158 and 174 of the 234 cervical samples by PCR-RFLP and HPV microarray, respectively. The correlation between the two methods was good in detecting HPVs in general (kappa index = 0.69) and HPVs 31 and 52 (kappa index = 0.70 and 0.70, respectively) and excellent in detecting HPVs 16, 18, 33, 35, and 58 (kappa index = 0.90, 0.88, 0.92, 0.77, and 0.84, respectively). Double HPV infection was detected in 10 cases and one triple infection was detected. By combining cytology and HPV testing, the sensitivity was improved to 87.5, 95.5, 96.1, and 97.2% in CIN I, CIN II, CIN III, and carcinoma, respectively.

CONCLUSIONS

This results suggest that HPV oligonucleotide microarray is a highly comparable method to the previously used PCR-RFLP method for the detection of HPVs in cervical specimens. Genetic informations for HPV infection in cervical specimens may offer new strategies in manipulating the patients harboring cervical intraepithelial neoplasia and cervical carcinoma.

PTEN/MMAC1 mutations correlate inversely with an altered p53 tumor suppressor gene in gynecologic tumors

OBJECTIVE

This study was conducted to evaluate the different mutations of p53 and compare p53 expression in gynecologic tumors in African American and Chinese women.

METHOD

Tumor samples were collected from Atlanta, Ga, hospitals and National Taiwan University Hospital, Taiwan. Samples were examined for different mutations using electrophoretic variants after single-stranded conformational analysis (SSCA). Cell lines obtained from the American Type Culture Collection were also used.

RESULTS

Mutations were identified in the gene for the tumor protein p53 at codons 156, 157, 176, 183, 246, and 248 at sites predicted to disrupt DNA binding. Collectively, an altered p53 status was found in about 28% of all tumors with similar frequencies observed between the African American and Chinese women. African American or Chinese women did not have common polymorphism.

CONCLUSION

This study showed that in mutations in the PTEN/MMAC1 gene correlated inversely with an altered p53 status. Similar findings were found in 2 tumor cell lines examined. As p53 changes are associated with late stage cancers, we favor the possibility that in certain tumor subtypes, PTEN/MMAC1 genes alteration may be useful clinically in the evaluation of the tumor.

The role of TP53 in Cervical carcinogenesis

Functional loss of the tumor suppressor p53 by alterations in its TP53 gene is a frequent event in cancers of different anatomical regions. Cervical cancer is strongly linked to infection by high-risk human papillomavirus (HPV) types. The viral oncoprotein E6 has the ability to associate with and neutralize the function of p53. E6 interacts with a 100-kDa cellular protein, termed E6 associated protein (E6AP; also called ubiquitin-protein ligase E3A or UBE3A), which functions as an ubiquitin protein ligase. The dimeric complex then binds p53 and E6AP catalyzes multi-ubiquitination and degradation of p53. The ability to promote p53 degradation is an exclusive property of E6 from the high-risk HPV types. Indeed, the low-risk E6 proteins lack this activity, although they can bind p53. Consistent with the E6 function of the high-risk HPV types, the majority of cervical cancer cells have a wild-type p53 gene, but the protein levels are strongly decreased. Several independent studies have shown that in a small percentage of cervical tumors the p53 gene is mutated. However, this event appears to be unrelated to the presence or absence of HPV infection and the nature of the tumor.