Involvement of the pituitary-specific transcription factor pit-1 in somatolactotrope cell growth and death: an approach using dominant-negative pit-1 mutants.
The anterior pituitary-specific transcription factor Pit-1 was initially identified and cloned as a transactivator of the prolactin (PRL) and GH genes and later as a regulator of the TSHb gene. It was found to be a major developmental regulator, because natural Pit-1 gene mutations cause a dwarf phenotype in mice and cause combined pituitary hormone deficiency associated with pituitary hypoplasia in humans. To further investigate the growth-promoting effects of Pit-1, we used a strategy based on the use of dominant-negative Pit-1 mutants as an alternative means of inactivating endogenous Pit-1 functions. R271W, a Pit-1 mutant identified in one allele in patients with severe combined pituitary hormone deficiency, and Pit-1Delta1-123, a deletion mutant in which only the DNA binding domain of Pit-1 is conserved, were generated, and their ability to abolish the effects of the endogenous native Pit-1 in the differentiated proliferating somatolactotrope GH4C1 cell line was investigated. Enforced expression of the dominant-negative mutants in GH4C1 cells using recombinant lentiviral vectors decreased the levels of expression of known Pit-1 target genes such as PRL and GH, abolished the hormone release, and reduced cell viability by decreasing the growth rate and inducing apoptosis via a caspase-independent pathway. These results show for the first time that the growth-promoting effects of Pit-1 are at least partly due to the fact that this transcription factor prevents apoptotic cell death.
Pellegrini
Isabelle
I
Laboratoire Interactions Cellulaires Neuroendocriniennes, Centre National de la Recherche Scientifique Unité Mixte de Recherche 6544, Université de la Méditerranée, France.
Roche
Cathy
C
Quentien
Marie-Helene
MH
Ferrand
Mireille
M
Gunz
Ginette
G
Thirion
Sylvie
S
Bagnis
Claude
C
Enjalbert
Alain
A
Franc
Jean-Louis
JL
D017209:Apoptosis / Q000235:genetics*; D016923:Cell Death / Q000235:genetics; D049109:Cell Proliferation; D002478:Cells, Cultured; D004393:Dwarfism, Pituitary / Q000235:genetics*; D005786:Gene Expression Regulation; D018014:Gene Transfer Techniques; D006801:Humans; D016086:Lentivirus / Q000235:genetics; D009154:Mutation; D010907:Pituitary Hormones / Q000172:deficiency* / Q000378:metabolism; D050817:Transcription Factor Pit-1 / Q000235:genetics / Q000502:physiology*; D014162:Transfection
D010907:Pituitary Hormones; D050817:Transcription Factor Pit-1