Regulatory Role Of DNA Methylation In The Expression Of Estrogen Receptor And P16 In Primary Breast Cancer

OBJECTIVE:The present study was undertaken to examine the involvement of methylation of the ER gene,p16 gene on the ER ,p16 status and tumor progression in the primary breast cancer and the role of p16 protein in the primary breast cancer. METHODS:DNA was extracted from 45 cases of the primary breast carcinomas and 15 cases of benign breast lesions. Polymerase chain reaction(PCR),using the extracted DNA and methylation –sensitive restriction enzymes,was performed to detect the methylation of a CpG island in the ER(α)gene(HpaⅡ,HhaⅠ) and p16 gene(HpaⅡ,SacⅡ). The results were compared with the ER,p16 expression by immunostaining. RESULTS:(1)20 of the 45 primary breast cancers were found methylation-positive in the exon 1 of ER(α)gene. No methylation was found in 15 cases benign lesions.Immunohistochemically,17 of the 20methylation–positive cases were negative for ER, whereas 14 of the 25 methylation-negative cases were ER-positive ( p ﹤ 0.05 ) .(2)The methylation-positive rates of grade Ⅰ,Ⅱand Ⅲ breast cancer were respectively 0%,43%,82%(p﹤0.05)for ER. The methylation-positive rates of lymph node group and non-lymph node group were respectively 44% and 45%(p>0.05)for ER. The methylation-positive rates of <3cm group and ≥3cm group were respectively 39% and 48%(p>0.05)for ER.(3)The overexpression rates of p16 protein in the benign lesion and breast cancer were respectively 35.3% and 61.7%(p﹤0.05). The overexpression rates of grade Ⅰ , Ⅱ and Ⅲ breast cancer were respectively 85.7%,64.2%,41.2%(p﹤0.05) for p16. The overexpression rates of lymph node group and non-lymph node group were respectively48% and 80%(p﹤0.05)for p16. The overexpression rates of<3cm group and ≥3cm group were respectively83.3% and48.1%(p﹤0.05). The overexpression rates of ER-positive group and ER-negative group were respectively 64.7% and 60.7%(p>0.05)for p16. (4) The methylation-positive rates of the benign lesion and breast cancer were respectively 13% and 22.2% ( p>0.05 ) for p16 gene.(5) The methylation-positive rates of grade ⅠandⅡ,Ⅲ breast cancer were respectively 0% , 21.4% , 41.2% ( p ﹤ 0.05 ) for p16 gene. The methylation-positive rates of lymph node group and non-lymph node group were respectively 32% and 10% ( p>0.05 ) for p16 gene. The methylation-positive rates of < 3cm group and ≥ 3cm group were respectively 16.7% and 25.9%(p>0.05)for p16 gene. CONCLUSIONS:(1) Methylation of the CpG island of the ER gene is inversely correlated with ER expression in a subset of the primary breast carcinomas. With the increase of histological grade of breast carcinomas, DNA methylation will add.(2)p16 is overexpressed in breast cancer, With the increase of histological grade of breast carcinomas,p16 expression will decrease.In addition, the low expression of p16 in primary breast cancer is associated with tumor size and lymph node involvement.(3) Methylation of the CpG island of the p16 gene is inversely correlated with p16 expression in a subset of the primary breast carcinomas. With the increase ofhistological grade of breast carcinomas, DNA methylation will add.