Differentiation of lactotrope precursor GHFT cells in response to fibroblast growth factor-2.
The mechanisms that control the emergence of different anterior pituitary cells from a common stem cell population are largely unknown. The immortalized GHFT cells derived from targeted expression of SV40 T antigen to mouse pituitary display characteristics of somatolactotropic progenitors in that they express the transcription factor GHF-1 (Pit-1) but not growth hormone (GH) or prolactin (PRL). We searched for factors capable of inducing lactotropic differentiation of GHFT cells. PRL gene expression was not observed in cells subjected to a variety of stimuli, which induce PRL gene expression in mature lactotropes. Only fibroblast growth factor-2 (FGF-2) was able to initiate the transcription, synthesis, and release of PRL in GHFT cells. However, induction of PRL expression was incomplete in FGF-2-treated cells, suggesting that additional factors are necessary to attain high levels of PRL transcription in fully differentiated lactotropes. We also show that the FGF-2 response element is located in the proximal PRL promoter. Stimulation of PRL expression by FGF-2 requires endogenous Ets factors and these factors as well as GHF-1 are expressed at low levels in the committed precursor, suggesting that these low levels are limiting for full PRL expression. Moreover, FGF-2 effect on lactotrope differentiation is mediated, at least partially, by stimulation of the Ras-signaling pathway. Our results suggest that, indeed, GHFT cells represent a valid model for studying lactotropic differentiation and that FGF-2 could play a key role both in initiating lactotrope differentiation and maintaining PRL expression.
López-Fernández
J
J
Department of Pharmacology and Center for Molecular Genetics, University of California, San Diego, La Jolla, California 92093-0636, USA.
Palacios
D
D
Castillo
A I
AI
Tolon
R M
RM
Aranda
A
A
Karin
M
M
D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000235:genetics; D002454:Cell Differentiation / Q000187:drug effects / Q000502:physiology*; D002461:Cell Line, Transformed; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D007700:Kinetics; D051379:Mice; D010903:Pituitary Gland, Anterior / Q000166:cytology / Q000187:drug effects* / Q000502:physiology; D011388:Prolactin / Q000235:genetics*; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D050783:Proto-Oncogene Proteins c-ets; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013539:Simian virus 40 / Q000235:genetics; D013234:Stem Cells / Q000166:cytology; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*
D000952:Antigens, Polyomavirus Transforming; D004268:DNA-Binding Proteins; D011388:Prolactin; D011518:Proto-Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D012333:RNA, Messenger; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; C494185:Pou1f1 protein, mouse