Global DNA methylation in relation to hMLH1 and hMSH2 protein immunoreactivity in sporadic human endometrial carcinomas

Overall DNA methylation status was studied in a group of 28 sporadic human endometrial carcinomas (ECs) using the [32P]-postlabeling technique. Moreover, expression of the DNA mismatch repair proteins (hMLH1 and hMSH2) was investigated in ECs using immunohistochemistry. Mean 5-methyldeoxycytosine (m5dC) content in the studied group was 3.48±0.37% (range, 2.89-4.12%). The mean m5dC scores were significantly different between early (3.35±0.33%) and advanced (3.66±0.36%) endometrial neoplasms (χ2-test; p=0.03). There was a markedly increased overall DNA methylation with the degree of histological differentiation and with the infiltration of the myometrium (p<0.05). Loss of hMLH1 and hMSH2 expression was reported in 7 (25%) and 5 (18%) tumors, respectively, but the immunoreactivity did not correlate with the known clinicopathological variables of cancer. In addition, no obvious correlation was found between global m5dC content and the lack of hMLH1 and hMSH2 protein expression in human uterine tumors (p=0.97 and p=0.19 for hMLH1 and hMSH2, respectively; Spearman's rank correlation test). Our results clearly show that alterations in global DNA methylation may influence tumor progression, but they are not directly associated with the inactivation of the mismatch-repair machinery in sporadic human ECs.