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 ha s been proposed as a predictor of the response of the tumour to endocr ine (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 no t pS2 mRNA, is also induced, to a lesser extent, by progesterone, 5 al pha-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 ste roid hormones is clearly separable from its response to oestrogen. Suc h behaviour in breast rumours in vivo could explain the lack of absolu te correlation between marker gene expression and anti-oestrogen sensi tivity and between the expression of individual marker genes.