EXPRESSION OF INSULIN-LIKE GROWTH-FACTOR BINDING-PROTEINS BY T-47D HUMAN BREAST-CANCER CELLS - REGULATION BY PROGESTINS AND ANTIESTROGENS

We have used ligand blotting and Northern blotting techniques to examine the effects of progestins and antiestrogens on expression of insulin-like growth factor binding proteins (IGFBPs) by T-47D human breast cancer cells under conditions where these agents are growth inhibitory. Under basal conditions, conditioned medium from T-47D cells was found to contain IGFBPs of 39, 33, and 27 kDa. Northern blot and/or Western blot analysis have identified these as IGFBP 2, 5, and 4, respectively. Medroxyprogesterone acetate (MPA) treatment resulted in a time- and dose-dependent decrease in IGFBP 4 and 5 mRNA abundance and secretion of these proteins, while little if any effect was observed on IGFBP 2 expression. A decrease in the steady state mRNA levels for IGFBP 4 and 5 was observed with as little as 0.1 nM MPA. Using 10 nM MPA a maximum decrease in IGFBP 4 and 5 mRNA levels was observed between 12 and 24 hours. While RU 486 alone had little or no effect on IGFBP 4 expression, it inhibited the effect of MPA. However, in the same samples, IGFBP 5 expression was inhibited by RU 486, and RU 486 was unable to reverse the effects of progestins on the expression of IGFBP 5. Furthermore, another synthetic progestin, Org 2058, but not dexamethasone, inhibited IGFBP 4 and IGFBP 5 expression. The antiestrogen ICI 164384 also transiently decreased the steady state mRNA levels of both IGFBP 4 and IGFBP 5. Regulation of expression of the IGFBPs by these agents suggests a potential role for the IGFBPs in the growth response of T-47D cells to these agents.