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Constitutive activation of the MAPK pathway mediates v-fes-induced mitogenesis in murine macrophages
E Rovida1, F Marra, M Baccarini
1Department of Experimental Pathology and Oncology, Università degli Studi di Firenze, Florence, Italy.
Abstract:
Fes is a nonreceptor tyrosine kinase expressed at the highest level in macrophages. We previously showed that the overexpression of c-fes in murine macrophages of the BAC-1.2F5 cell line renders these cells independent of macrophage colony-stimulating factor (MCSF) for survival and proliferation, although no direct relationship could be established between tyrosine-phosphorylated substrates of Fes- and MCSF receptor-dependent signaling and mitogenesis. In this study, we investigated whether the mitogen-activated protein kinase (MAPK) pathway is involved in the growth factor-independent growth of v-fes-overexpressing macrophages. We found a constitutively increased phosphorylation of extracellularly regulated kinase (ERK) in v-fes-overexpressing macrophages as compared with mock-infected cells. This finding was associated with activation of mitogen/extracellular signal-regulated kinase (MEK) and with constitutive localization of ERK in the nucleus. Treatment of v-fes-overexpressing cells with the MEK-specific inhibitor PD98059 markedly reduced cell growth, hyperphosphorylation, and nuclear localization of ERK, indicating that the MAPK pathway mediates the mitogenic effect of v-fes. (Blood. 2000;95:3959-3963)
Insights
Overexpression of the Fes tyrosine kinase in macrophages leads to growth factor-independent proliferation. This study reveals the mitogen-activated protein kinase (MAPK) pathway mediates this effect through extracellularly regulated kinase (ERK) activation.
Area of Science:
- Cell Biology
- Molecular Biology
- Oncology
Background:
- Fes is a nonreceptor tyrosine kinase highly expressed in macrophages.
- Previous studies showed Fes overexpression confers MCSF-independent survival and proliferation in macrophages.
- The signaling pathways linking Fes to mitogenesis remained unclear.
Purpose of the Study:
- To investigate the role of the mitogen-activated protein kinase (MAPK) pathway in the growth factor-independent growth of v-fes-overexpressing macrophages.
- To determine if MAPK pathway activation is a downstream consequence of v-fes overexpression.
Main Methods:
- Overexpression of v-fes in BAC-1.2F5 murine macrophage cell line.
- Analysis of extracellularly regulated kinase (ERK) phosphorylation and localization.
- Assessment of mitogen/extracellular signal-regulated kinase (MEK) activation.
- Treatment with the MEK-specific inhibitor PD98059.
Main Results:
- v-fes-overexpressing macrophages exhibited constitutively increased ERK phosphorylation compared to mock-infected cells.
- This was associated with MEK activation and constitutive nuclear localization of ERK.
- Inhibition of MEK with PD98059 significantly reduced cell growth, ERK hyperphosphorylation, and nuclear ERK localization.
Conclusions:
- The MAPK pathway, specifically through MEK and ERK, is crucial for the mitogenic effects of v-fes.
- Fes-mediated growth factor-independent macrophage proliferation is dependent on MAPK pathway activation.