Characterization of membrane nongenomic receptors for progesterone in human spermatozoa

Rapid, nongenomic actions of steroid hormones have been characterized only recently. They may be mediated by interaction with a poorly characterized membrane receptor, by classic receptor located to the plasma membrane, or by interaction of the classic receptor with other signaling effectors. Among these, rapid effects of progesterone on human spermatozoa have been shown to be mediated by interaction with one or more membrane receptors. Two proteins, respectively of 57 and 28 kDa, representing the possible surface progesterone receptors in human spermatozoa, have been identified by our group employing an antibody (c-262) directed against the progesterone binding domain of the genomic receptor. The two proteins have been immunoprecipitated using c-262, isolated by 2D gel electrophoresis and analyzed by Maldi-Tof. Preliminary results of the analysis in data bank of the obtained masses suggest that the two proteins represent previously unidentified ones since they do not match with any protein in the database. We have also performed RT-PCR analysis with RNA extracted from human spermatozoa, utilizing various oligoprimers in different regions of the human progesterone genomic receptor. Results indicate the presence of transcripts for the complete genomic receptor. However, several previously published studies in the literature indicate the absence of expression of the genomic receptor in human spermatozoa. In this light posttranscriptional/posttraductional modifications of the receptor can be hypothesized. Interestingly, with primers amplifying in the DNA-binding domain of the progesterone receptor gene, we detected a higher molecular weight transcript when compared to the placenta. Further studies are needed to determine whether the sequences of the transcripts obtained by RT-PCR analysis of human sperm RNA match exactly with the human genomic receptor gene and to define the sequence of the higher molecular weight transcript detected in the DNA-binding region.