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J. Biol. Chem., Vol. 277, Issue 35, 31972-31979, August 30, 2002
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From the Howard Hughes Medical Institute, Department of
Biochemistry and Cell Biology, Rice University,
Houston, Texas 77005-1892
In Dictyostelium discoideum, cell
density is monitored by levels of a secreted protein, conditioned
medium factor (CMF). CMFR1 is a putative CMF receptor necessary for
CMF-induced G protein-independent accumulation of the SP70 prespore
protein but not for CMF-induced G protein-dependent
inositol 1,4,5-trisphosphate production. Using recombinant fragments of
CMF, we find that stimulation of the inositol 1,4,5-trisphosphate
pathway requires amino acids 170-180, whereas SP70 accumulation does
not, corroborating a two-receptor model. Cells lacking CMFR1 do not
aggregate, due to the lack of expression of several important early
developmentally regulated genes, including gp80. Although
many aspects of early developmental cAMP-stimulated signal transduction
are mediated by CMF, CMFR1 is not essential for cAMP-stimulated cAMP
and cGMP production or Ca2+ uptake, suggesting the
involvement of a second CMF receptor. Exogenous application of
antibodies against either the region between a first and second or a
second and third possible transmembrane domain of CMFR1 induces SP70
accumulation. Antibody- and CMF-induced gene expression can be
inhibited by recombinant CMFR1 corresponding to the region between the
first and third potential transmembrane domains, indicating that this
region is extracellular and probably contains the CMF binding site.
These observations support a model where a one- or two-transmembrane
CMFR1 regulates gene expression and a G protein-coupled CMF receptor
mediates cAR1 signal transduction.
A Single Cell Density-sensing Factor Stimulates Distinct Signal
Transduction Pathways through Two Different Receptors*
*
The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
An Investigator of the Howard Hughes Medical Institute. To whom
correspondence should be addressed: Howard Hughes Medical Institute,
Dept. of Biochemistry and Cell Biology, MS-140, Rice University, 6100 S. Main St., Houston, TX 77005-1892. Tel.: 713-348-4872; Fax:
713-348-5154; E-mail: richard@rice.edu.
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