Classical membrane progesterone receptors in murine mammary carcinomas: agonistic effects of progestins and RU-486 mediating rapid non-genomic effects

Abstract

In this article, we demonstrate the expression of functional progesterone binding sites at the cell membrane in murine mammary carcinomas that are stimulated by progestins and inhibited by antiprogestins. Using confocal immunofluorescence, ligand binding and cell compartment-specific western blots, we were able to identify the presence of the classical progesterone receptors. Medroxyprogesterone acetate (MPA) and RU-486 (1 × 10(-11) and 1 × 10(-8) M) behaved as agonists activating extracellular signal-regulated kinases (ERKs) and progestin-regulated proteins, except for Cyclin D1 and Tissue factor which failed to increase with 1 × 10(-8) M RU-486, an experimental condition that allows PR to bind DNA. These results predicted a full agonist effect at low concentrations of RU-486. Accordingly, at concentrations lower than 1 × 10(-11) M, RU-486 increased cell proliferation in vitro. This effect was abolished by incubation with the ERK kinase inhibitor PD 98059 or by OH-tamoxifen. In vivo, at a daily dose of 1.2 μg/kg body weight RU-486 increased tumor growth, whereas at 12 mg/kg induces tumor regression. Our results indicate that low concentrations of MPA and RU-486 induce similar agonistic non-genomic effects, whereas RU-486 at higher concentrations may inhibit cell proliferation by genomic-induced effects. This suggests that RU-486 should be therapeutically administered at doses high enough to guarantee its genomic inhibitory effect.

Apigenin Induces Apoptosis and Blocks Growth of Medroxyprogesterone Acetate-Dependent BT-474 Xenograft Tumors

“…*p<0.05, significantly different from control determined. A previous study indicated that membraneassociated PR is insensitive to the negative regulatory effect of antiprogestins [47], thus it is possible that membraneassociated PR mediates MPA-dependent down-regulation of RANKL. Moreover, the effect of progestin-dependent RANKL on human breast cancer progression is controversial [48], and it is possible that progestin regulates expression of RANKL via different mechanisms in murine and human mammary cells [49].…”

Progesterone increases nitric oxide synthesis in human vascular endothelial cells through activation of membrane progesterone receptor-α

“…Conversely, the lack of MPA activity is difficult to reconcile with a nPR-dependent mechanism because MPA has high binding affinity for the nPR and activates it (58). Finally, the finding that progesterone acts at the cell surface to increase NO production is not consistent with an involvement of the nPR because to date clear evidence that the nPR is expressed on the cell surface has been obtained for only a few types of vertebrate cells (5). Although Boonyaratanakornkit et al (4) unambiguously demonstrated that progesterone rapidly activates intracellular signaling through the nPR in an extranuclear location in breast cancer cells, they could not detect nPR by ICC on the plasma membranes of any of the cell types they examined (3).…”

The bromodomain inhibitor OTX015 (MK-8628) exerts anti-tumor activity in triple-negative breast cancer models as single agent and in combination with everolimus

“…The human epidermal growth factor receptor 2 (HER2) is also overexpressed in 20% of breast tumors, most of which are hormone receptor-negative [1]. These three receptors offer defined therapeutic targets, such as is the case with tamoxifen and trastuzumab [1, 2]. However, about 15% of breast cancers lack estrogen and progesterone receptors as well as HER2, representing an aggressive and heterogeneous subtype group known as triple-negative breast cancer (TNBC) [1].…”