Pituitary specific transcription factor messenger ribonucleic expression in adenomatous and nontumorous human pituitary tissues

Abstract

Background: The pituitary-specific transcription factor, Pit-1/GHF-1 (Pit-1) is a member of the POU family of homeobox genes. This transacting factor has a role in the development and expression of selected anterior pituitary cells including prolactin, growth hormone (GH), and thyrotropin, cell types in rodent pituitary. The expression of Pit-1 mRNA in human pituitaries has not been previously analyzed and the role of specific secretagogues in the regulation of Pit-1 transcripts in human pituitary adenomas has not been examined. Analysis of Pit-1 expression in normal and neoplastic human pituitaries may provide insight into the specificity of this transcription factor for pituitary cell types and the role of Pit-1 in human pituitary function.

Experimental design: In situ and Northern hybridization analyses were used to study the expression of Pit-1 mRNA in surgically removed human pituitary adenomas and nontumorous pituitaries obtained within 6 hours postmortem. A cultured GH surgically removed adenoma was used to analyze the regulation of GH and Pit-1 in vitro.

Results: In situ hybridization localized Pit-1 mRNA in all pituitary adenomas, although the mRNA levels in GH and prolactin adenomas were significantly higher than those in ACTH, null cell and gonadotroph tumors. Northern hybridization analysis revealed a 2.4 and a 1.2 kb mRNA transcript for Pit-1. Although GH mRNA transcript was markedly changed by dexamethasone and phorbol 12-myristate 13-acetate in vitro, Pit-1 mRNA transcripts were not changed significantly by these secretagogues.

Conclusions: Pit-1 mRNA transcripts are expressed mainly in prolactin and GH pituitary adenomas, but are also found in other adenomas and in the nontumorous adult human pituitary. Pit-1 mRNA transcript levels are not readily modulated in cultured GH adenoma cells by various secretagogues in vitro compared with the marked modulation of GH mRNA transcripts by these same secretagogues.