EXPRESSION OF PIT-1 MESSENGER-RIBONUCLEIC-ACID AND PROTEIN IN THE HUMAN PLACENTA

It is well established that the human placenta produces a wide range o f hormones similar to those secreted by the pituitary ant; hypothalamu s. However, the physiological role and regulation of placental hormone synthesis and release are still largely unknown. CH (GH-N) is express ed in the pituitary, where it requires the tissue-specific transcripti on factor Pit-1. Chorionic somatomammotropin A (CS-A) and CS-B as well as the placental GH variant (GH-V), which also belong to the GH gene family and are located in the same chromosomal cluster, are expressed in the placental syncytiotrophoblast. The presence of Pit-1-binding si tes in the CS-A and GH-V promoter regions predicts that Pit-1 may be e xpressed in the placenta. However, this has not yet been demonstrated. To examine possible similarities in the regulation of these genes in the pituitary and placenta, we studied the expression of pit-1 messeng er ribonucleic acid (mRNA) in the human placenta, transformed human pl acental cells, and the JEG-3 choriocarcinoma cell line. Polymerase cha in reaction (PCR) products of the expected size were amplified;from fi rst and third trimester placentas, transformed placental cells, and JE G-3 complementary DNA by reverse transcription-PCR, The pit-1-specific sequence was confirmed by restriction endonuclease digestion, Souther n hybridization, and DNA sequencing. Human pituitary tissue was used a s a positive control; no PCR product was obtained from hippocampus (ne gative control). In situ hybridization of placental tissue sections re vealed the presence of pit-1 mRNA in first and third trimester syncyti otrophoblast. Pit-1 protein was localized by immunohistochemistry with the same tissue distribution and a nuclear localization pattern. Thes e data demonstrate expression of pit-1 mRNA and Pit-1 protein in the h uman placenta, thus questioning its role as a pituitary-specific regul ator of GH-N gene transcription. The es pression of Pit-1 in the place nta, together with its previously demonstrated capability to bind to a nd activate the CS-A and the GH-V promoters, suggests that it may play a role in the regulation of hormones belonging to the GH gene family in both pituitary and placenta.