Progesterone effect on cell growth, ultrastructural aspect and estradiol receptors of normal human breast epithelial (HBE) cells in culture

The stimulating effect of estradiol (E2) on breast cell growth is well docu mented. However, the actions of progesterone (P) and its derivatives remain controversial. Additional information is therefore necessary. On a culture system of normal human breast epithelial (HBE) cells, we observed an inhib itory effect on cell growth of a long-term P treatment (7 days) in the pres ence or absence of E2, using two methods: a daily cell count providing a hi stometric growth index, and [H-3]-thymidine incorporation during the expone ntial phase of cell growth. A scanning electron microscopy study confirmed these results. Cells exhibited a proliferative appearance after E2 treatmen t, and returned to a quiescent appearance when P was added to E2. In both s tudies, P proved to be as efficient as the synthetic progestin R5020. Moreo ver, the immunocytochemical study of E2 receptors indicated that E2 increas es its own receptor level whereas P and R5020 have the opposite effect, thu s limiting the stimulatory effect of E2 on cell growth. In the HBE cell cul ture system and in long-term treatment, P and R5020 appear predominantly to inhibit cell growth, both in the presence and absence of E2. (C) 2000 Else vier Science Ltd. All rights reserved.