Line-1 hypomethylation in multistage carcinogenesis of the uterine cervix.

OBJECTIVE To evaluate characteristics of global hypomethylation in evolution of cervical cancer. MATERIALS AND METHODS Eight cases of squamous cell carcinoma (SCC) and seven cases of carcinoma in situ (CIS) were studied. Each of the SCC samples contained CIS, and all SCC and CIS samples contained normal ectocervical epithelium. Microdissection was performed to separate normal epithelium, CIS and SCC prior to DNA extraction. Hypomethylation levels of long interspersed nuclear elements (LINE-1 or L1) were measured with a combined bisulfite restriction analysis (COBRA) PCR (polymerase chain reaction) protocol. The percentage of L1 hypomethylation for SCC, CIS and normal epithelium was compared. RESULTS In the SCC cohort, the L1 hypomethylation level showed progressive increase comparing normal epithelium (59.4 +/- 8.86%) to CIS (64.37 +/- 7.32%) and SCC (66.3 +/- 7.26%) (repeated measurement ANOVA, P = 0.005). A significantly greater L1 hypomethylation level was found in CIS (62.06 +/- 3.44 %) compared to normal epithelium (60.03 +/- 3.69 %) (paired t-Test, P = 0.03). No significant difference in L1 hypomethylation level was noted between CIS of the two sample groups (unpaired t-Test, P = 0.2). CONCLUSIONS In our study, there was a significant correlation between the degree of hypomethylation and progression from normal ectocervical mucosa to CIS and invasive cancer. Laboratory assessment of biopsies for this molecular event may have clinical significance.