Modulation of ATP-induced calcium signaling by progesterone in T47D-Y breast cancer cells.

Extracellular ATP activates purinergic (P(2)) receptors with an increase in intracellular calcium and phosphorylation of MAPK. In this study we have investigated the effect of progesterone/progestin on ATP-induced calcium mobilization and phosphorylation of the kinase ERK in the T47D-Y breast cancer cell line that exhibits no detectable nuclear progesterone receptor expression. Brief pretreatment with progesterone/progestin results in a dose dependent inhibition of ATP-induced intracellular calcium mobilization, and inhibition of ERK phosphorylation. Response to a cell impermeable ligand and inhibition of the response by an inactivating antibody suggests a mechanism of action at the plasma membrane. These results in T47D-Y cells strongly suggest that progesterone can act in a rapid non-nuclear manner to inhibit extracellular ATP effects on intracellular calcium mobilization and ERK activation. This research provides an example of progesterone action in a breast cancer cell line lacking expression of the classical nuclear progesterone receptors.

Progesterone stimulates mitochondrial activity with subsequent inhibition of apoptosis in MCF-10A benign breast epithelial cells.

The effects of progesterone on breast epithelial cells remain poorly defined with observations showing both proliferative and antiproliferative effects. As an example, progesterone levels correlate with increased epithelial cell proliferation, but there is discordance between the dividing cells and the cells with nuclear progesterone receptor expression. The release of paracrine growth factors from nuclear receptor-positive cells has been postulated as a mechanism, since in vitro studies show a lack of growth effect by progesterone in breast epithelial cells lacking nuclear receptors. This study examined possible nongenomic effects of progesterone in breast epithelia by using MCF-10A cells known to lack nuclear progesterone receptor expression. Treatment for 30-60 min with progesterone or the progestin, R5020, increased mitochondrial activity as shown by an increase in mitochondrial membrane potential (hyperpolarization) with a concordant increase in total cellular ATP. The reaction was inhibited by a specific progesterone receptor antagonist and not affected by the translation inhibitor cycloheximide. Progestin treatment inhibited apoptosis induced by activation of the FasL pathway, as shown by a decrease in sub-G(1) cell fraction during fluorescence-activated cell sorting and a decrease in caspase 3/7 levels. Progestin treatment did not alter the cell cycle over 48 h. Our study demonstrates a nongenomic action of progesterone on benign breast epithelial cells, resulting in enhanced cellular respiration and protection from apoptosis.