Figure 2.

Progestin binding to plasma membranes and G protein activation in MDA-MB-231 cells stably transfected with PGRMC1 (PG). A, Specific [³H]P4 binding to PG- and vector (V)-transfected cell membranes in a single point assay. B, Representative saturation curve and Scatchard plot of specific [³H]P4 binding to plasma membranes of PG cells. C, Representative competition curves for progestin binding expressed as a percentage of maximum progesterone binding. D, Specific membrane binding of [³⁵S]GTPγS in response to 100 nM progesterone. E, Effects of transfection of PG cells with mPRα siRNA on membrane mPRα expression (upper) and specific [³H]P4 membrane binding (lower). F. Effects of transfection of PG cells with mPRα siRNA on specific membrane binding of [³⁵S]GTPγS in response to progesterone. G, Effects of transfection of PG cells with mPRα siRNA on progesterone attenuation of serum starvation-induced apoptosis. P4, progesterone; 02–0, Org OD 02–0; R5020, promegestone; Cort, cortisol; Cst, corticosterone; veh, vehicle control. D, mPRα, MDA-MB-231 cells stably transfected with mPRα. E, mPRα, PG cells transfected with mPRα siRNA; nontarget, PG cells transfected with control pool of siRNA. P < .05 compared with V (A), corresponding vehicle-treated (D, F, and G), compared with nontarget (E), n = 6 (Students t test). All the experiments were repeated 3 or more times and similar results were obtained in each experiment.