G2 checkpoint in uterine cervical cancer with HPV 16 E6 according to p53 polymorphism and its screening value

We aimed to verify not only whether homozygous Arg at codon 72 of the p53 apoptotic domain is a possible risk factor for cervical human papillomavirus (HPV)-related cancer, but whether degraded p53 may have an effect on a G2 checkpoint of the cell cycle. The implication of the codon 72 polymorphism of p53 in cervical tumor remains controversial. Furthermore, G2 checkpoint alteration and its relationship with p53, the codon 72 allotype, according to HPV infection in cervical tumors, has not been studied.

The purified genomic DNA from 252 archival cervical tissues [102 cervical intraepithelial neoplasias (CINs) and 46 squamous cell carcinomas of the uterine cervix (SCCs), and 104 normal] were amplified by nested polymerase chain reaction (PCR) for HPV-16/HPV-18. In addition, all of them were amplified by PCR for exon 4 of p53, where the codon 72 resides. The amplified PCR products were then sequenced using the forward primer. A polymorphism analysis was done by SnaPshot ddNTP primer extension and following direct sequencing. The reaction mixture was treated with 0.25 unit of shrimp alkaline phosphatase (Amersham) at 37 degrees C for 1 h, subsequently performed in an ABI Prism 310 Genetic Analyzer (Perkin-Elmer). The archival slides were incubated overnight at 4 degrees C using mouse anti-human recombinant cyclin B1 polyclonal antibody or mouse anti-Xenopus p34(cdc2) monoclonal antibody for immunohistochemistry (Santa Cruz Biotech, Santa Cruz, CA).

The frequency of Arg allelic homozygosity was high in both cases (89.1%) and the control (80.8%) group (P = 0.4703). All groups except CIN were in Hardy-Weinberg equilibrium. There was no significant difference in the frequency of p53 polymorphism between the HPV-positive (Arg, 88.0%) and the negative (Arg, 88.8%) groups, or between CIN (Arg, 88.2%) and SCC (Arg, 89.1%). Both immunoreactivities to cyclin B and p34(cdc2) were strongly correlated with the HPV infection (P = 0.0001) and the histological types (P = 0.0001) between CIN and SCC, being strongly correlated with each other (alpha:0.62954, P = 0.0001).

The particular type of the p53 polymorphism does not bear relation to the progression of cervical cancer, HPV infection, or to the p53 codon 72 polymorphism. However, the G2 checkpoint appears to be altered in the case of a HPV-positive SCC.