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Mol. Cell. Biol., 05 1995, 2849-2857, Vol 15, No. 5
AP Bradford, KE Conrad, C Wasylyk, B Wasylyk and A Gutierrez-Hartmann
The mechanism by which activation of common signal transduction pathways
can elicit cell-specific responses remains an important question in
biology. To elucidate the molecular mechanism by which the Ras signaling
pathway activates a cell-type-specific gene, we have used the
pituitary-specific rat prolactin (rPRL) promoter as a target of oncogenic
Ras and Raf in GH4 rat pituitary cells. Here we show that expression of
either c-Ets-1 or the POU homeo-domain transcription factor GHF-1/Pit-1
enhance the Ras/Raf activation of the rPRL promoter and that coexpression
of the two transcription factors results in an even greater synergistic Ras
response. By contrast, the related GHF-1- dependent rat growth hormone
promoter fails to respond to Ras or Raf, indicating that GHF-1 alone is
insufficient to mediate the Ras/Raf effect. Using amino-terminal
truncations of c-Ets-1, we have mapped the c-Ets-1 region required to
mediate the optimal Ras response to a 40- amino-acid segment which contains
a putative mitogen-activated protein kinase site. Finally,
dominant-negative Ets and GHF constructs block Ras activation of the rPRL
promoter, and each blocks the synergistic activation mediated by the other
partner protein, further corroborating that a functional interaction
between c-Ets-1 and GHF-1 is required for an optimal Ras response. Thus,
the functional interaction of a pituitary-specific transcription factor,
GHF-1, with a widely expressed nuclear proto-oncogene product, c-Ets-1,
provides one important molecular mechanism by which the general Ras
signaling cascade can be interpreted in a cell-type-specific manner.
Copyright © 1995, American Society for Microbiology
Functional interaction of c-Ets-1 and GHF-1/Pit-1 mediates Ras activation of pituitary-specific gene expression: mapping of the essential c-Ets-1 domain
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262, USA.
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