PR activation promotes GATA3 downregulation. A) T47D, BT474 or C4HD cells were pretreated or not with the antiprogestin RU486 (10 nM) for 30 minutes and then coincubated with MPA (10 nM) for the indicated time. Total protein lysates were prepared and GATA3 expression was measured by western blot (WB). GATA3 bands underwent densitometry and values were normalized to GAPDH protein bands setting the value of untreated cells as 1.0. B) T47D, BT474 or C4HD cells were transfected with control siRNA or with siRNA targeting PR (siRNA PR). Cells were starved for 24 hours and treated with MPA for the indicated time, total protein lysates were prepared and GATA3 expression was measured by WB. Bands were quantified as described in panel A. C) T47D cells, PR-null T47D-Y cells or T47D-Y cells transfected with either PR-A (T47D-YA) or PR-B (T47D-YB) isoforms were treated with MPA for 18 hours. Bands were quantified as described in panel A. MPA, medroxyprogesterone acetate; PR, progesterone receptor.