PIT-1 GHF-1 TRANSCRIPTION FACTOR EXPRESSION IN RODENT PITUITARIES/

The Pit-1/GHF-1 (Pit-1) transcription factor is important for the deve lopment of anterior pituitary cells that produce GH and PRL. We examin ed the expression of Pit-1 mRNA in pituitary tissues from rats and mic e. Analysis of pituitaries from normal and GHRH transgenic mice showed that Pit- 1 transcripts were readily detected in normal, hyperplastic , and neoplastic pituitaries. A cell line (GHRH-CL1) established from a GhRH transgenic mouse pituitary tumor in our laboratory also express ed Pit-1 mRNA Normal rat pituitaries and those with estrogen-induced P RL cell hyperplasia expressed Pit-1 mRNA There was a decrease in Pit-1 mRNA in hyperplastic rat pituitaries concomitant with a decrease in G H mRNA amounts and an increase in PRL mRNA amounts after estrogen trea tment. Similarly, analysis of GH3 cells in vitro showed that estrogen and bFGF modulated PRL but not Pit-1 mRNA levels. Pit-1 mRNA was local ized by combined in situ hybridization and immunohistochemistry to pre dominantly GH and PRL cells, although some TSH and LH cells in the rat pituitary also expressed Pit-1 mRNA, indicating wide distribution of the mRNA for this transcription factor in various anterior pituitary c ell types. Analysis of cell proliferation in normal rat pituitary and GH3 cells revealed that estrogen and bFGF stimulated cell proliferatio n in normal pituitaries but inhibited proliferation in GH3 cells, wher eas Pit-1 transcripts remained unchanged in both groups of cultured ce lls. These results indicate that Pit-1 mRNA is readily detected in nor mal, hyperplastic, and neoplastic rodent pituitaries. Changes in Pit-1 mRNA amounts appear to correlate more closely with changes in GH than PRL mRNA levels in cultured pituitary cells.