Rates of mutation to growth factor autonomy and tumorigenicity differ in hematopoietic stem and precursor cells expressing the multilineage colony-stimulating factor gene

Independently arising macrophage mutants dissociate growth factor-regulated survival and proliferation

Analysis of a simian virus 40-immortalized colony-stimulating factor 1 (CSF-1) -dependent macrophage cell line (BAC1.2F5) and independently arising autonomous mutants derived from it (aut4A, aut4A.1, aut2A, and aut2A.1) revealed distinct phenotypes. The parental line, BAC1.2F5, is dependent on CSF-1 for survival and growth. Of the mutants derived from BAC1.2F5, aut4A has lost the requirement of CSF-1 for survival; aut4A.1 (derived from aut4A) and aut2A grow in the absence of growth factor but proliferate more rapidly in its presence, and aut2A.1 (derived from aut2A) produces CSF-1 and proliferates as rapidly in the presence as in the absence of exogeneous CSF-1. The separation of the CSF-1 requirement for survival and proliferation observed in aut4A is also observed in a temperature-sensitive (ts) mutant tsgro1. At the nonpermissive temperature, tsgro1 cell proliferation is arrested, but the cells survive provided CSF-1 is present. The four cellular phenotypes observed--immortalization, loss of growth factor requirement for survival, loss of growth factor requirement for proliferation, and loss of growth factor-stimulated proliferation--indicate a divergence of the pathways of growth factor-regulated survival and proliferation and may represent phenotypes occurring at intermediate stages in tumor-cell progression.