The progesterone receptor (PR) protein is an inherent testicular protein and not a secretion of accessory reproductive organs. PR is expressed in human testis and in various reproductive tissues. It can serve as a marker to define the fertilizing potential of the spermatozoa. PR acts as an important marker for hormone dependence and disease prognosis. It is expressed in prostate stromal cells, where it regulates cell motility. Down-regulation of this protein in prostate stromal cancer cells, might lead to increased stromal derived factor-1 (SDF-1) and interlukin-6 (IL-6) levels, which in turn might promote tumor progression. In breast cancer, PGR and activator protein 1 (AP-1) nuclear interaction serves as a marker of favorable prognosis and overall patient survival, in cases treated with tamoxifen.
