Line-1 Hypomethylation in Multistage Carcinogenesis of the Uterine Cervix


Objective: To evaluate characteristics of global hypomethylation in evolution of cervical cancer. Materialsand
Methods: Eight cases of squamous cell carcinoma (SCC) and seven cases of carcinoma in situ (CIS) werestudied. Each of the SCC samples contained CIS, and all SCC and CIS samples contained normal ectocervicalepithelium. 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 combinedbisulfite restriction analysis (COBRA) PCR (polymerase chain reaction) protocol. The percentage of L1hypomethylation for SCC, CIS and normal epithelium was compared.
Results: In the SCC cohort, the L1hypomethylation 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 L1hypomethylation 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 twosample groups (unpaired t-Test, P = 0.2).
Conclusions: In our study, there was a significant correlation betweenthe 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.