EFFECTS OF TAMOXIFEN AND RETINOIC ACID ON CELL-GROWTH AND C-MYC GENE-EXPRESSION IN HUMAN BREAST AND CERVICAL-CANCER CELLS

The effects of estradiol, tamoxifen, and retinoic acid on the prolifer ation of breast and cervical cancer cells were investigated. Estrogen stimulated only MCF-7 cell growth, whereas tamoxifen and retinoic acid inhibited the proliferation of all cells studied. Northern blot analy sis indicated that estradiol up-regulates c-myc mRNA level in all cell lines studied regardless of the estrogen receptor status in the cells . On the contrary, tamoxifen inhibits c-myc gene expression in all cel l lines studied except in MCF-7 cells where the c-myc transcript was n ot affected The inhibitory effect of tamoxifen on c-myc gene expressio n and cell proliferation in estrogen receptor-negative cells suggest a n estrogen receptor-independent mechanism. The results also suggest th at different mechanisms are involved in the regulation of cell growth and c-myc gene expression in different cancer cells by estrogen and ta moxifen.