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A single cell density-sensing factor stimulates distinct signal transduction pathways through two different receptors
William J Deery1, Tong Gao, Robin Ammann
1Howard Hughes Medical Institute, Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005-1892, USA.
The Journal of Biological Chemistry
|June 19, 2002
Summary
Dictyostelium discoideum uses conditioned medium factor (CMF) to monitor cell density. A novel receptor, CMFR1, regulates gene expression, while another receptor likely mediates G protein signaling, suggesting a dual-receptor system for CMF.
Area of Science:
- Cellular and Molecular Biology
- Developmental Biology
- Biochemistry
Background:
- Cell density signaling in Dictyostelium discoideum is crucial for development.
- Conditioned medium factor (CMF) is a key secreted protein involved in this process.
- The precise mechanisms and receptors mediating CMF's diverse functions are not fully understood.
Purpose of the Study:
- To investigate the role of the putative CMF receptor, CMFR1, in Dictyostelium discoideum development.
- To elucidate the distinct signaling pathways regulated by CMF and identify potential multiple receptors.
- To characterize the CMF binding site on CMFR1.
Main Methods:
- Utilized recombinant CMF fragments to map functional domains.
- Generated and analyzed CMFR1 knockout cells.
- Employed antibodies against CMFR1 to probe its function.
- Assessed gene expression and signaling pathway activation (e.g., inositol trisphosphate production, cAMP/cGMP levels, Ca2+ uptake).
Main Results:
- CMFR1 is essential for CMF-induced SP70 prespore protein accumulation and the expression of early developmental genes like gp80, but not for G protein-dependent inositol trisphosphate production.
- Distinct CMF regions are required for inositol trisphosphate pathway stimulation versus SP70 accumulation, supporting a two-receptor model.
- CMFR1 is not required for cAMP-stimulated cAMP/cGMP production or Ca2+ uptake, further suggesting a second CMF receptor.
- Antibodies targeting specific CMFR1 domains induced SP70 accumulation, and recombinant CMFR1 inhibited antibody- and CMF-induced gene expression, indicating an extracellular CMF binding site.
Conclusions:
- A model is proposed where CMFR1, a one- or two-transmembrane receptor, regulates gene expression.
- A separate G protein-coupled receptor likely mediates CMF-induced cAR1 signal transduction.
- Dictyostelium discoideum employs a dual-receptor system for sensing and responding to conditioned medium factor (CMF).