Steroid hormone receptor expression and P4 responsiveness in St-T1b cells. A) Expression of PR and ERα was analyzed by RT-PCR in St-T1b cells and ESC cultured without or with P4 (1 μM) for 4 h. PR transcripts were amplified using primers recognizing specifically PR-B, a region common to PR-B and PR-A, or the ligand-binding domain (LBD). GAPDH mRNA was amplified as a loading control. B) Expression of P4 target genes was analyzed in St-T1b cells by RT-PCR, after 4 or 24 h treatment with the indicated doses of P4, dexamethasone or R5020. Controls received 0.001% ethanol as a vehicle control.