ESTROGEN-INDUCED GENES, PLIV-1 AND PS2, RESPOND DIVERGENTLY TO OTHER STEROID-HORMONES IN MCF-7 CELLS

The level of oestrogen-responsive gene expression in breast tumours has been proposed as a predictor of the response of the tumour to endocrine (anti-oestrogen) therapy. We demonstrate that different oestrogen-responsive genes may differ in their responses to other hormones. pLIV-1 and pS2 are two oestrogen-regulated genes that are expressed in the MCF-7 human breast cancer cell line. We show that pLIV-1 mRNA, but not pS2 mRNA, is also induced, to a lesser extent, by progesterone, 5 alpha-dihydrotestosterone and dexamethasone. For pLIV-1, combinations of these hormones with oestradiol and with the pure anti-oestrogen, ICI 164384, indicate that the mechanism of its response to these other steroid hormones is clearly separable from its response to oestrogen. Such behaviour in breast rumours in vivo could explain the lack of absolute correlation between marker gene expression and anti-oestrogen sensitivity and between the expression of individual marker genes.