Progesterone receptor isoform A inhibits isoform B-mediated transactivation in human amnion

Human amnion cells were transfected with progesterone receptor A and/or B, and the progesterone-dependent reporter construct, mouse mammary tumor viru s promoter (MMTV), linked to a luciferase gene. In progesterone receptor B- expressing amnion that had been cultured before the onset of labour, treatm ent with progesterone resulted in an eightfold increase of the reporter act ivity, whereas in laboured cells, no such increase was seen. In contrast, p rogesterone receptor A was a weak activator of transcription in laboured an d non-laboured amniocytes. When the isoforms A and B of the progesterone re ceptor were co-transfected, progesterone receptor A exhibited a marked inhi bitory effect on progesterone receptor B-mediated transcription. These resu lts show that progesterone receptors A and B function differentially, and p rogesterone receptor A is a transdominant repressor of progesterone recepto r B-mediated transcription in human term amnion. (C) 2001 Published by Else vier Science B.V.