Classic and non-classic progesterone receptors are both expressed in human spermatozoa.

Progesterone is one of the physiological inducers of the acrosome reaction in mammalian spermatozoa. The receptor that responds to progesterone is not yet identified, and its properties differ in many aspects from the properties of the classic nuclear progesterone receptor, suggesting the participation of a novel or non-classic receptor. In this study, we investigated the expression of a novel progesterone-binding protein (hmPR1/PGMRC1) and its ortholog (hmPR2/PGMRC2), which have previously been identified in liver microsomes and are considered receptor candidates, along with the nuclear progesterone receptor. The purification procedure was optimized with special emphasis on the control of leukocyte contamination in single donor samples. The results indicate that all three proteins are expressed in human sperm, as transcripts have been detected in 46 %, 42 % and 37.5 % of individual samples, respectively (n = 24).