Methylation of the Selected Introns in Advanced-Stage Ovarian Carcinomas.

Advanced-stage ovarian cancer (OC) is among the most fatal female genital tract neoplasms worldwide. Although different genetic mechanisms have been shown to be involved in ovarian carcinogenesis, the role of introns methylation is still unresolved. We performed methylation analysis of introns 1, 3, and 4 of the to identify patterns in primary stage III OCs, corresponding metastases, and healthy tissues. The study involved samples of paraffin-embedded tissues obtained from 80 patients with stage III OCs, who underwent surgery at the Department of Gynecology and Gynecologic Oncology of the Military Institute of Medicine in Warsaw, Poland. Altogether, 40 serous-type G2/3 OCs and 40 endometrioid-type G2/3 OCs were included. From the same patient, metastatic and normal tissues were simultaneously analyzed. As a control group, 80 tissue samples were collected from patients after bariatric operations. Human ovarian cancer A2780 cell line was also investigated. Total genomic DNA was isolated from paraffin-embedded tissue blocks and the methylation analysis was performed by bisulfite DNA conversion, DNA amplification with specific primers, cloning, and DNA sequencing. All of the samples of intron 1 of were un-methylated in OCs, metastatic tissues, and in healthy tissues from the same patient. Also, no methylation of intron 1 was detected in cells from the human A2780 ovarian cancer cell line and in all samples from control group. In all samples, introns 3 and 4 of the were methylated in primary tumors, metastatic tissue, and in healthy tissue from the same patient, in human A2780 ovarian cell line, and in DNA samples from healthy patients. None of the clinicopatholocal features was related to the introns methylation status. Our data on introns methylation sheds new light on the mechanism of p53 activity for a better understanding of cancer biology. The study suggests the existence of an additional regulation rule of activity that involves demethylation-methylation mechanisms. Methylation at introns 3 and 4 may also overall help in protecting against damage by viral restrictases or viral DNA integration.