NOVEL PROGESTERONE TARGET GENES IDENTIFIED BY AN IMPROVED DIFFERENTIAL DISPLAY TECHNIQUE SUGGEST THAT PROGESTIN-INDUCED GROWTH-INHIBITION OF BREAST-CANCER CELLS COINCIDES WITH ENHANCEMENT OF DIFFERENTIATION

Progesterone is an important regulator of normal and malignant breast epithelial cells. In addition to stimulating development of normal mam mary epithelium, it can be used to treat hormone-dependent breast tumo rs. However, the mechanism of growth inhibition by progestins is poorl y understood, and only a limited number of progesterone target genes a re known so far. We therefore decided to clone such target genes by me ans of differential display polymerase chain reaction. In this paper, we describe an improved differential display strategy that eliminates false positives, along with the identification of nine positive (TSC-2 2, CD-9, Na+/K+ ATPase alpha 1, desmoplakin, CD-59, FKBP51, and three unknown genes) and one negative progesterone target genes (annexin-VI) from the mammary carcinoma cell line T47D, which is growth-inhibited by progestins. None of these genes have been reported before to be pro gesterone targets. Regulation of desmoplakin, CD-9, CD-59, Na+/K+-ATPa se alpha 1, and annexin-VI by the progestin suggests that progesterone induces T47D cells to differentiate. Three of these genes were repres sed by estradiol and up-regulated by the progestin. Estradiol treatmen t of T47D cells also leads to formation of lamellipodia and delocaliza tion of two cell adhesion proteins, E-cadherin and alpha-catenin. All these effects were reversed by the progestin. These data suggest that estradiol dedifferentiates T47D cells, while progestins have the oppos ite effect. This may be linked to the capacity of progestins to inhibi t tumor growth.