PIT-1 GROWTH-HORMONE-FACTOR-1 SPLICE VARIANT EXPRESSION IN THE RHESUS-MONKEY PITUITARY-GLAND AND THE RHESUS AND HUMAN PLACENTA

We have examined the expression of Pit-1 messenger RNA (mRNA) splice v ariants in the nonhuman primate pituitary and in rhesus and human plac enta. Full-length complementary DNAs (cDNAs) representing Pit-1 and th e Pit-1 beta splice Variants were cloned from a rhesus monkey pituitar y cDNA library and were readily detectable by RT-PCR with rhesus pitui tary gland RNA. The Pit-1T variant previously reported in mouse pituit ary tumor cell lines was not detectable in normal rhesus pituitary tis sue, although two novel splice variants were detected. A cDNA approxim ating the rat Pit-1 Delta 4 variant was cloned but coded for a truncat ed and presumably nonfunctional protein. Only by using a nested RT-PCR approach were Pit-1 and Pit-1 beta variants consistently detectable i n both human and rhesus placental tissue. The Pit-1 beta variant mRNA was not detectable in JEG-3 choriocarcinoma cells unless the cells wer e stimulated with 8-Br-cAMP. Immunoblot studies with nuclear extracts from primary rhesus syn cytiotrophoblast cultures or JEG-3 choriocarci noma cells indicated that although mRNA levels were very low, Pit-1 pr otein was detectable in differentiated cytotrophoblasts, and levels in creased after treatment with 8-Br-cAMP. Two major species of Pit-1 pro tein were detected that corresponded to the two major bands in rat pit uitary GH3 cell nuclear extracts. Low levels of slightly larger bands also were seen, which may represent Pit-1 beta protein or phosphorylat ed species. We conclude that Pit-1 splice variants expressed in the pr imate pituitary gland differ from those in the rodent gland and that t he Pit-1 and Pit-1 beta mRNAs expressed in the placenta give rise to a pattern of protein expression similar to that seen in pituitary cells , which is inducible by treatment with 8-Br-cAMP.