TRANSCRIPTIONAL ACTIVATION OF FUNCTIONAL ENDOGENOUS ESTROGEN-RECEPTORGENE-EXPRESSION IN MCF10AT CELLS - A MODEL FOR EARLY BREAST-CANCER

Utilizing the MCF10AT xenograft model for progression of human prolife rative breast disease, we detected expression of the endogenous estrog en receptor (ER) gene only in MCF10AneoT and cells of the MCF10AT syst em, all of which stably express a transfected mutated T24 Ha-ras gene. ER transcripts were undetectable in the parental MCF10A cells and in MCF10A cells transfected with normal c-Ha-ras or vector. ER transcript s expressed in MCF10AT cells contain a normal full-length ER coding re gion and direct synthesis of a normally sized ER protein. The protein is functional based on its ability to mediate estradiol (E-2)-induced increases of transcription from both endogenous and exogenous E-2-regu lated genes. Transcriptional activation of the endogenous ER gene does not appear to be related to a change in methylation status of the gen e since a diagnostic CpG site in exon 1 that is methylated in ER-negat ive breast tumors and completely unmethylated in ER-positive breast tu mors is hypomethylated to the same extent in ER-negative MCF10A cells and ER-positive MCF10AT cells. E-2 increased both the number and size of soft-agar colonies formed by MCF10AT3c cells, a line from a third g eneration MCF10AT xenograft lesion. This suggests that xenograft passa ge has selected for growth regulatory pathways that are E-2-responsive and that identification of these pathways and their role in progressi on will aid in determining how E-2 acts to increase risk of breast can cer.