GHF-1/Pit-1 functions as a cell-specific integrator of Ras signaling by targeting the Ras pathway to a composite Ets-1/GHF-1 response element.
Activation of the rat prolactin (rPRL) promoter by Ras is a prototypical example of tissue-specific transcriptional regulation in a highly differentiated cell type. Using a series of site-specific mutations and deletions of the proximal rPRL promoter we have mapped the major Ras/Raf response element (RRE) to a composite Ets-1/GHF-1 binding site located between positions -217 and -190. Mutation of either the Ets-1 or GHF-1 binding sites inhibits Ras and Raf activation of the rPRL promoter, and insertion of this RRE into the rat growth hormone promoter confers Ras responsiveness. We show that Ets-1 is expressed in GH4 cells and, consistent with their functional synergistic interaction, both Ets-1 and GHF-1 are able to bind specifically to this bipartite RRE. We confirm that Ets-1 or a related Ets factor is the nuclear target of the Ras pathway leading to activation of the rPRL promoter and demonstrate that Elk-1 and Net do not mediate the Ras response. Thus, the pituitary-specific POU homeodomain transcription factor, GHF-1, serves as a cell-specific signal integrator by functionally interacting with an Ets-1-like factor, at uniquely juxtaposed binding sites, thereby targeting an otherwise ubiquitous Ras signaling pathway to a select subset of cell-specific GHF-1-dependent genes.
Bradford
A P
AP
Department of Medicine, Program in Molecular Biology, and Colorado Cancer Center, University of Colorado Health Sciences Center, Denver, 80262, USA.
Conrad
K E
KE
Tran
P H
PH
Ostrowski
M C
MC
Gutierrez-Hartmann
A
A
D000818:Animals; D004268:DNA-Binding Proteins / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D015513:Oncogene Proteins; D010902:Pituitary Gland / Q000166:cytology / Q000378:metabolism; D011388:Prolactin / Q000235:genetics; D011401:Promoter Regions, Genetic; D050784:Proto-Oncogene Protein c-ets-1; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D050783:Proto-Oncogene Proteins c-ets; D016283:Proto-Oncogene Proteins p21(ras) / Q000378:metabolism*; D051381:Rats; D015398:Signal Transduction; D050817:Transcription Factor Pit-1; D014157:Transcription Factors / Q000378:metabolism*; D014161:Transduction, Genetic; D014407:Tumor Cells, Cultured; D050807:ets-Domain Protein Elk-1
D004268:DNA-Binding Proteins; C494114:Elk1 protein, rat; C086924:Elk3 protein, mouse; C494042:Ets1 protein, mouse; C494043:Ets1 protein, rat; D018398:Homeodomain Proteins; D015513:Oncogene Proteins; C494186:Pou1f1 protein, rat; D050784:Proto-Oncogene Protein c-ets-1; D011518:Proto-Oncogene Proteins; D050783:Proto-Oncogene Proteins c-ets; D050817:Transcription Factor Pit-1; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D011388:Prolactin; D016283:Proto-Oncogene Proteins p21(ras)