EXAMINATION OF THE DNA METHYLATION PROPERTIES IN NONTUMORIGENIC AND TUMORIGENIC BREAST EPITHELIAL-CELL LINES

Molecular changes in the progressive state of tumorigenesis often incl ude altered patterns of DNA methylation. Utilizing a series of breast epithelial cell lines, the overall 5-methylcytosine content in genomic DNA demonstrated an overall decrease when comparing two malignant cel l lines (MCF-7 and T47D) with a mortal cell line (MCF I 2M) and severa l derivative cell lines of the immortalized MCF10 cultures (MCF10A,-2A , -5A, A1neoT2, and 139B6). Further investigation on the methylation s tatus of these cells lines indicated no difference in DNA methyltransf erase activity; both at a protein and mRNA levels in the nontumorigeni c cell lines examined while activity was 3-10 fold higher in the tumor igenic lines (MCF7, T47D, SkBr3, MB-MDA-231, -468). Examination of the CPG island in the 5' promoter region of the estrogen receptor gene in dicates that this region is unmethylated in the mortal and immortal no ntumorigenic lines as well as the tumorigenic lines examined, with the exception of the estrogen receptor negative breast cell line MB-MDA-4 68 which appears to be partially methylated at this site. These result s indicate methylation of this CpG island does not account for the ina ctivation of the estrogen receptor gene in immortalized nontumorigenic breast cells, suggesting another mechanism of transcriptional inactiv ation of ER in this environment.