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Alterations in CSF-1 receptor expression and protein tyrosine phosphorylation in autonomous mutants of a CSF-1
P Dello Sbarba1, J W Pollard, E R Stanley
1Department of Developmental Biology and Cancer, Albert Einstein College of Medicine, Bronx, New York 10461.
Abstract:
One approach to the problem of growth factor signal transduction is to identify alterations in growth factor-regulated events in mutants possessing an altered proliferative response. This approach was used in a study of the alterations in protein tyrosine phosphorylation in 22 independently-arising autonomous mutants of the CSF-1-dependent mouse macrophage cell line, BAC1.2F5. Only 4 of the mutants produced CSF-1 and/or factors that were capable of down-regulating the CSF-1 receptor (CSF-1R), suggesting that the majority were altered in the signal transduction pathway for proliferation. All of the mutants possessed lower numbers (13-89%) of cell surface CSF-1Rs than wild type cells. With two possible exceptions, the phosphorylation of the anti-phosphotyrosine-reactive cell surface CSF-1Rs from CSF-1 stimulated cells was directly proportional to cell surface CSF-1R number. In the absence of CSF-1, three of the 22 mutants exhibited tyrosine phosphorylation of proteins that was not observed in wild type cells under the same conditions. The results indicate that this approach will be useful in the analysis of the growth factor regulated pathway for cell proliferation.
Insights
This study investigated protein tyrosine phosphorylation in macrophage cell mutants to understand growth factor signaling. Most mutants showed altered cell surface receptors, impacting proliferation pathways.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- Growth factor signal transduction is crucial for cell proliferation.
- Understanding alterations in signaling pathways is key to identifying mechanisms of uncontrolled cell growth.
- Colony-stimulating factor 1 (CSF-1) regulates macrophage proliferation via its receptor (CSF-1R).
Purpose of the Study:
- To identify alterations in protein tyrosine phosphorylation in CSF-1-dependent macrophage mutants with altered proliferative responses.
- To investigate the role of CSF-1 receptor (CSF-1R) number and phosphorylation in these mutants.
- To explore potential defects in the CSF-1 signal transduction pathway for proliferation.
Main Methods:
- Analysis of 22 independently-arising autonomous mutants of the BAC1.2F5 mouse macrophage cell line.
- Assessment of CSF-1 production and CSF-1R down-regulation.
- Quantification of cell surface CSF-1R numbers.
- Measurement of protein tyrosine phosphorylation in response to CSF-1 stimulation.
Main Results:
- The majority of mutants (18/22) showed alterations in the signal transduction pathway for proliferation, not CSF-1 production.
- All mutants exhibited reduced cell surface CSF-1R numbers (13-89% of wild type).
- Phosphorylation of CSF-1R was generally proportional to receptor number; however, three mutants showed aberrant tyrosine phosphorylation in the absence of CSF-1.
Conclusions:
- The approach of studying growth factor-regulated events in mutants is effective for analyzing proliferation pathways.
- Mutations affecting CSF-1R number and/or downstream signaling components are critical for altered macrophage proliferation.
- Aberrant protein tyrosine phosphorylation in the absence of CSF-1 suggests potential dysregulation of signaling pathways.