Abstract
BackgroundHigh risk type human papilloma viruses (HR-HPV) induce carcinomas of the uterine cervix by expressing viral oncogenes E6 and E7. Oncogene E7 of HR-HPV disrupts the pRb/E2F interaction, which negatively regulates the S phase entry. Expression of tumor suppressor p16ink4a drastically increases in majority of HR-HPV associated carcinomas due to removal of pRb repression. The p16ink4a overexpression is an indicator of an aberrant expression of viral oncogenes and may serve as a marker for early diagnostic of cervical cancer. On the other hand, in 25–57% of cervical carcinomas hypermethylation of the p16 INK4a promoter has been demonstrated using a methylation-specific PCR, MSP. To evaluate a potential usage of the p16 INK4a 5' CpG island hypermethylation as an indicator of tumor cell along with p16ink4a overexpression, we analyzed the methylation status of p16 INK4a in cervical carcinomasMethodsMethylation status of p16 INK4a was analyzed by MSP and by bisulfite-modified DNA sequencing. The expression of p16ink4a was analyzed by RT-PCR and by immunohistochemical technique.ResultsThe extensive methylation within p16 INK4a 5' CpG island was not detected either in 13 primary cervical carcinomas or in 5 cancer cell lines by bisulfite-modified DNA sequencing (including those that were positive by MSP in our hands). The number and distribution of rare partially methylated CpG sites did not differ considerably in tumors and adjacent normal tissues. The levels of the p16 INK4a mRNA were increased in carcinomas compared to the normal tissues independently of the number of partially methylated CpGs within 5'CpG island. The transcriptional activation of p16 INK4a was accompanied by p16ink4a cytoplasmic immunoreactivity in the majority of tumor cells and presence of a varied number of the p16 positive nuclei in different tumors.ConclusionHypermethylaion of the p16INK4a 5' CpG island is not a frequent event in HR-HPV-positive cervical carcinomas and cannot be an effective marker of cancer cells with up-regulated expression of p16ink4a. Our data confirm other previous studies claiming specific p16INK4a up-regulation in the majority of cervical carcinomas at both the protein and mRNA levels. Cytoplasmic accumulation of p16ink4a is a feature of cervical carcinomas.
Highlights
High risk type human papilloma viruses (HR-HPV) induce carcinomas of the uterine cervix by expressing viral oncogenes E6 and E7
Analysis of the 5' CpG island methylation by MSP and bisulfite-modified DNA sequencing First the methylation status of the region around the p16 INK4a translation start site was analyzed by methylationspecific PCR (MSP) with commonly used primers [30]
This region of the p16 INK4a CpG island was reported to be methylated in many types of tumors including cervical squamous cell carcinomas [3,22,23,24,25,26,27,30]
Summary
High risk type human papilloma viruses (HR-HPV) induce carcinomas of the uterine cervix by expressing viral oncogenes E6 and E7. Oncogene E7 of HR-HPV disrupts the pRb/E2F interaction, which negatively regulates the S phase entry. Expression of tumor suppressor p16ink4a drastically increases in majority of HR-HPV associated carcinomas due to removal of pRb repression. To evaluate a potential usage of the p16 INK4a 5' CpG island hypermethylation as an indicator of tumor cell along with p16ink4a overexpression, we analyzed the methylation status of p16 INK4a in cervical carcinomas. In normal cells p16ink4a functions as a negative regulator of cell cycle progression by controlling the activity of tumor suppressor pRb. P16ink4a inhibits phosphorylation of pRb by cyclinD-Cdk4/Cdk complexes. In tumor cells the pRBE2F interaction may be distured by different ways, including mutations or inappropriate phosphorylation of pRb due to Cdk orCdk kinases overexpression or loss of the p16ink4a inhibitor [1]. The p16ink4a overexpression cannot inhibit cell cycle progression in these tumor cells in the absence of pRb
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
