Differential expression of c-fos in hematopoietic cells: correlation with differentiation of monomyelocytic cells in vitro.

Among various neonatal mouse tissues, elevated levels of c-fos transcripts have been detected in crude preparations of bone. Here, we show that c-fos expression originates in the bone marrow, and to a lesser extent in adherent cells (macrophages). High levels of c-fos expression were also detected in primary cultures of differentiated bone marrow-derived macrophages, but not in cell lines resembling immature hematopoietic cells. However, when the human promyelocytic cell line HL60 was induced in vitro to differentiate into macrophages, c-fos expression was readily detectable. These findings suggest that c-fos expression in mononuclear phagocytic cells is restricted to late stages of differentiation. This pattern of c-fos expression is in marked contrast to those of the c-myb and c-myc genes which are transcriptionally active predominantly in precursor cells. In the amnion, where c-fos expression increases to high levels at late stages of gestation, synthesis of c-fos protein occurs in cells that do not resemble macrophages. It thus appears that c-fos expression in several distinct cell types is correlated with differentiation processes.