Differential localization and activity of the A- and B-forms of the human progesterone receptor using green fluorescent protein chimeras

Subcellular localization and transcriptional activity of green fluorescent protein-progesterone receptor A and B chimeras (GFP-PRA and GFP-PRB) were e xamined in living mammalian cells. Both GFP-PRA and B chimeras were found t o be similar in transcriptional activity compared with their non-GFP counte rparts. GFP-PRA and PRA were both weakly active, while GFP-PRB and PRE gave a 20- to 40-fold induction using a reporter gene containing the full-lengt h mouse mammary tumor virus long-terminal repeat linked to the luciferase g ene (pLTRluc). Using fluorescence microscopy, nuclear/cytoplasmic distribut ions for the unliganded and hormone activated forms of GFP-PRA and GFP-PRB were characterized. The two forms of the receptor were found to have distin ct intracellular distributions; GFP-PRA was found to be more nuclear than G FP-PRB in four cell lines examined. The causes for and implications of this differential localization of the A and B forms of the human PR are discuss ed.