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PR-A/PR-B Ratio

Meaning

The PR-A/PR-B Ratio refers to the relative expression levels of the two main isoforms of the progesterone receptor, Progesterone Receptor A (PR-A) and Progesterone Receptor B (PR-B), within a specific target tissue. These two isoforms are transcribed from the same gene but differ in their N-terminal domains, resulting in distinct functional properties and transcriptional activities. PR-B is generally considered the full-length, classical activator of progesterone-responsive genes, while PR-A often acts as a dominant negative regulator, repressing the transcriptional activity of both PR-B and other steroid receptors. The precise ratio of PR-A to PR-B is a critical determinant of a tissue’s sensitivity and specific response to progesterone, with imbalances implicated in conditions like endometriosis and breast cancer.