Introduction of a human colony stimulating factor-1 gene into a mouse macrophage cell line induces CSF-1 independence but not tumorigenicity

The SV40-immortalized mouse macrophage cell line, BAC1.2F5, is strictly dependent on CSF-1 for its survival and proliferation in culture. Introduction of a retroviral vector containing a 1.6 kilobase (kb) pair human CSF-1 cDNA into these cells abrogated their growth factor dependence but did not render the cells tumorigenic in nude mice. The infected macrophages contained multiple copies of the vector provirus, expressed both membrane-bound and secreted forms of CSF-1, and exhibited constitutive down modulation of the murine CSF-1 receptor. Because insertion of the v-fms gene has previously been shown to abrogate factor dependence and induce tumorigenicity in BAC1.2F5 macrophages, the failure of these cells to express a fully transformed phenotype after persistent stimulation by endogenous CSF-1 suggests that the v-fms and c-fms gene products provide different signals for cell proliferation.