A murine macrophage cell line, immortalized by v‐raf and v‐myc oncogenes, exhibits normal macrophage functions

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Abstract
In vitro immortalized cell lines with the morphology and phenotype of mature macrophages (MΦ) have been generated by infecting freshly isolated bone marrow cells from C3H/HeJ mice with a recombinant retrovirus carrying v‐raf and v‐myc oncogenes. All of the clones obtained had MΦ‐like phenotypes, and one such clone, GG2EE, has been compared to normal MΦ to ascertain the effects of immortalization on the expression of the biological functions of the lines. GG2EE cells expressed cytotoxic activity against L5178Y, P815 or RL 1 target cells in response to stimulation with interferon‐γ (IFN‐γ) and heat‐killed Listeria monocytogenes; in contrast, they failed to kill YAC‐1 target cells. GG2EE cells did not constitutively express I‐A or I‐E antigens; nevertheless, I region‐coded antigens could be induced by IFN‐γ treatment. GG2EE cells produced interleukin 1 upon stimulation with a T cell‐derived lymphokine; they were weakly phagocytic, yet became highly phagocytic following IFN‐γ treatment. Since c‐fos mRNA is augmented in peritoneal exudate MΦ by protein kinase C activators but not by IFN‐γ, we evaluated the effects of calcium ionophore, phorbol myristate acetate, L‐α‐1‐oleoyl‐2‐acetoyl‐sn‐3 glycerol (OAG) and IFN‐γ on the levels of c‐fos mRNA in GG2EE cells. We found that calcium ionophore, PMA and OAG stimulation enhanced the expression of c‐fos mRNA, but IFN‐γ treatment did not. The kinetics of c‐fos induction in GG2EE cells were also comparable to those observed in peritoneal exudate MΦ. Overall, the GG2EE cell line has the same biological properties as normal tissue MΦ. Because it is capable of both constitutive and inducible MΦ‐like functions, this cell line provides a valuable tool for studying the molecular mechanisms controlling induction and/or expression of biological activities in MΦ. It is striking that a cell line immortalized in vitro by two oncogenes, v‐raf and v‐myc, behaves, according to the criteria mentioned above, like a normal MΦ population.