Immunofluorescent localization of a novel progesterone receptor(s) in a T47D-Y breast cancer cell line lacking genomic progesterone receptor expression.

Objective: To identify a novel nongenomic progesterone receptor (PR), PR-M, in T47D-Y breast cancer cells lacking genomic PR expression.
Methods: Immunofluorescent staining of T47D and T47D-Y breast cancer cells with selective anti-PR antibodies and ligand binding. Transient transfection of breast cancer cells with a cDNA expressing PR-M with a carboxy terminal green fluorescent protein.
Results: In the T47D-Y cell line, lacking expression of genomic PR, plasma membrane-bound and intracellular PR(s) are identified with anti-PR antibodies directed to the hormone-binding domain but not with an antibody directed to the amino terminus. A plasma membrane PR is also evident by immunofluorescent ligand binding. Expression of a novel truncated PR (PR-M) tagged with green fluorescent protein showed intracellular localization.
Conclusions: These studies support the expression of a novel, truncated PR (PR-M) in a breast cancer cell line known to lack expression of genomic PR. This observation raises the possibility of progesterone action in breast cancer cells classically considered nonresponsive due to lack of genomic PR expression.