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Transformation of murine fibroblasts by a retrovirus encoding the murine c-fms proto-oncogene
L R Rohrschneider1, V M Rothwell, N A Nicola
1Fred Hutchinson Cancer Research Center, Cell Biology Department, Seattle, Washington 98104.
Abstract:
The c-fms proto-oncogene is the growth factor receptor for the macrophage colony stimulating factor, M-CSF. In this paper we have investigated the inappropriate expression of c-fms within a species as a relevant model for analysing transformation, growth, and differentiation promoting activities of c-fms. A retroviral vector was constructed for the expression of the murine c-fms proto-oncogene in murine cells. Initial characterization of this vector was performed in fibroblasts. Infection of Balb/c 3T3 cells with the murine c-fms retrovirus resulted in high level expression of the gp140c-fms precursor and the gp165c-fms mature receptor protein on the cell surface and both proteins exhibited kinase activity. Up to 3.3 x 10(4) M-CSF receptors per cell were detectable. The c-fms retrovirus induced foci of morphologically transformed Balb/c cells that exhibited anchorage independent growth in soft agar and produced progressively growing tumors in syngeneic animals. The Balb/c cells synthesize and secrete M-CSF and therefore these results suggest an autocrine mechanism of transformation caused solely by the expression of a normal growth factor receptor in an inappropriate, endogenous M-CSF-producing cell.
Insights
Overexpressing the c-fms proto-oncogene in cells triggers transformation, promoting growth and differentiation. This study reveals an autocrine mechanism driving cancer through inappropriate c-fms receptor activity.
Area of Science:
- Molecular Biology
- Cell Biology
- Oncology
Background:
- The c-fms proto-oncogene encodes the receptor for macrophage colony-stimulating factor (M-CSF).
- Aberrant c-fms expression is implicated in cellular transformation, growth, and differentiation.
- Investigating c-fms in an endogenous system provides insights into oncogenesis.
Purpose of the Study:
- To explore the consequences of inappropriate c-fms proto-oncogene expression in murine cells.
- To establish a model for analyzing the transformation, growth, and differentiation activities of c-fms.
- To elucidate the role of autocrine signaling in c-fms-mediated transformation.
Main Methods:
- Construction of a retroviral vector for murine c-fms expression.
- Infection of Balb/c 3T3 fibroblasts with the c-fms retrovirus.
- Analysis of cell surface receptor expression, kinase activity, and M-CSF receptor numbers.
- Assessment of morphological transformation, anchorage-independent growth, and tumor formation in vivo.
Main Results:
- High-level expression of gp140c-fms precursor and gp165c-fms mature receptor with kinase activity was achieved.
- Balb/c 3T3 cells displayed up to 3.3 x 10(4) M-CSF receptors per cell.
- Retroviral c-fms expression induced morphological transformation, anchorage-independent growth, and tumor formation.
- Transformed cells synthesized and secreted endogenous M-CSF.
Conclusions:
- The expression of a normal growth factor receptor (c-fms) in an inappropriate cellular context can drive transformation.
- An autocrine mechanism, driven by endogenous M-CSF and overexpressed c-fms, is sufficient for cellular transformation.
- This study provides a model for understanding oncogenic signaling pathways involving growth factor receptors.