Progesterone Pre-treatment Potentiates EGF Pathway Signaling in The Breast Cancer Cell Line ZR-75*

Abstract

Progesterone in hormone replacement therapy (HRT) preparations increases, while hysterectomy greatly reduces, the incidence of breast cancer. Cross-talk between the progesterone and growth factor signaling pathways occurs at multiple levels and this maybe a key factor in breast cancer survival and progression. To test this hypothesis, we characterized the effect of progesterone pre-treatment on the sensitization of the epidermal growth factor (EGF) signaling pathway to EGF in the breast cancer cell line ZR-75. For the first time in ZR-75 cells and in agreement with previous work using synthetic progestins, we demonstrate that pre-treatment with the natural ligand progesterone increases EGF receptor (EGFR) levels and subsequent ligand-dependent phosphorylation. Downstream we demonstrate that progesterone alone increases erk-1 + 2 phosphorylation, potentiates EGF-phosphorylated erk-1 + 2 and maintains these levels elevated for 24 h; over 20 h longer than in vehicle treated cells. Additionally, progesterone increased the levels of STAT5, another component of the EGF signaling cascade. Progesterone increased EGF mediated transcription of a c-fos promoter reporter and the nuclear localization of the native c-fos protein. Furthermore, progesterone and EGF both alone and in combination, significantly increase cell proliferation. Several results presented herein demonstrate the conformity between the action of the natural ligand progesterone with that of synthetic progestins such as MPA and R5020 and allows the postulation that the progestin/progesterone-dependent increase of EGF signaling provides a survival advantage to burgeoning cancer cells and may contribute to the breast cancer risk associated with endogenous progesterone and with progestin-containing HRT.

Progesterone promotes focal adhesion formation and migration in breast cancer cells through induction of protease-activated receptor-1

“…Given the requirement of breast cells to proliferate, migrate, and invade during the luteal phase and pregnancy, it has been speculated that progestins hijack these signaling pathways in breast cancer cells. Progesterone and progestins have been previously reported to stimulate breast cancer cell migration and invasion (Carvajal et al 2005, Kato et al 2005b, Fu et al 2008. Indeed, in postmenopausal women receiving hormone replacement therapy (HRT), the presence of progestagenic compounds increases breast cancer incidence (Beral 2003).…”

ck2-Dependent Phosphorylation of Progesterone Receptors (PR) on Ser81 Regulates PR-B Isoform-Specific Target Gene Expression in Breast Cancer Cells

“…Recently, progesterone was shown to mediate mammary stem cell self-renewal via paracrine mechanisms in which secreted factors (Wnt, RANKL) derived from PR-positive cells influence the PR-null stem cell niche (37). In PR-positive breast cancer cells, PR action drives proliferation, prosurvival signaling, and early invasion primarily by autocrine mechanisms (10,25,61). In an environment where steroid hormones are no longer required to drive cellular proliferation (i.e., during SR-positive tumor progression), the increased expression and constitutive activation of PR-activating protein kinases may promote increased cell survival and uncontrolled growth (i.e., in the face of endocrine therapies primarily directed against ER).…”

Progesterone Stimulates Proliferation and Promotes Cytoplasmic Localization of the Cell Cycle Inhibitor p27 in Steroid Receptor Positive Breast Cancers

“…Although a stimulatory effect of P/PS on cell proliferation in breast cancer cell lines and in mouse cancer models has been described previously [3,5,12], this study provides the first demonstration that P/PS regulates the intracellular localization of the cell cycle inhibitor p27 in vivo and in vitro that may enhance cell proliferation. The treatment with E + P in ovariectomized rats markedly increased incidence of mammary carcinoma and resulted in tumors with increased proliferation and decreased expression of nuclear p27 compared with E treatment.…”

“…In human breast cancer cell lines in vitro, PS influence cell proliferation, survival, responsiveness to growth factors, and cell morphology [3][4][5][6]. However, how PS and the endogenous P contribute to growth of ER+ PR+ breast cancers in vivo remains poorly understood.…”