AROMATASE GENE IS AMPLIFIED IN MCF-7 HUMAN BREAST-CANCER CELLS

The levels of the aromatase gene and its expression in MCF-7 human bre ast cancer cells and seven additional cultured cells were investigated . Using normal human foreskin fibroblasts as the control, the aromatas e gene appeared to be amplified in MCF-7 cells as shown by Southern an d DNA slot blot analyses utilizing human placental aromatase cDNA as t he probe. However, the promoter I.1 and the first exon of the aromatas e gene were not amplified in MCF-7 cells based on results obtained fro m DNA slot blot analysis using oligonucleotide probes having sequences derived from those regions of human aromatase gene. Aromatase was exp ressed at a very low level in this cell line as indicated by Northern blot analysis to measure the level of aromatase mRNA, immunoprecipitat ion analysis to measure the level of aromatase protein, and aromatase activity measurement. Furthermore, nucleotide sequence analysis of the aromatase cDNA obtained from MCF-7 cells by PCR techniques, revealed no sequence difference from that of the enzyme expressed in placenta. These results lead us to conclude that the expression of aromatase in MCF-7 cells is under the control of an unusual promoter and aromatase gene expression is repressed at the transcriptional level; in these ce lls.