Where is the receptor for progesterone located?

Classical nuclear progesterone receptor (nPR) exists as two main protein isoforms (types of protein from a single gene) PR-A and PR-B. Progesterone is a steroid hormone allowing diffusion through the lipid membrane of mammalian cells. Therefore nPR-A and B are located in the cytoplasm. They move to the nucleus after ligand (progesterone) binding to control gene expression. Literature also exists to suggest that progesterone receptors exist at the cell surface, both alternative isoforms of nPR and structurally unrelated mPR proteins from a different gene.