Differential regulation of macrophage differentiation in response to leukemia inhibitory factor/oncostatin-M/interleukin-6: the effect of enforced expression of the SCL transcription factor.

The physiologic program of macrophage differentiation normally proceeds in a coordinated manner in response to several different growth factors. Although the utilization of common receptor subunits may explain in part overlapping biologic functions, mechanisms by which unique actions are mediated remain obscure. We examined growth factor-induced macrophage differentiation in M1 leukemia cells that simultaneously display receptors for interleukin-6 (IL-6), leukemia inhibitory factor (LIF) and Oncostatin-M (OSM). Differentiation induced by all three factors was associated with decreased expression of transcription factors myb and SCL, increased expression of macrophage markers, and suppression of proliferation. Cell lines were established in which SCL expression was enforced. In the absence of growth factors, cells were indistinguishable from parental cells. However, LIF (or OSM)-induced macrophage differentiation was perturbed; there was failure to undergo morphologic differentiation, disturbed expression of lysozyme and Mac1 alpha, and failure to suppress proliferation. Surprisingly the perturbation of macrophage differentiation did not apply to induced expression of macrophage colony-stimulating factor (M-CSF) or granulocyte colony stimulating factor (G-CSF) receptors. This dissociation of elements normally coordinated in a macrophage differentiation program applied at a clonal level. There was no disturbance of IL-6-induced macrophage differentiation. These data directly implicate SCL in components of the macrophage differentiation program (suggesting that LIF receptor/gp130 heterodimers utilize an SCL-inhibitable pathway while gp130 homodimers do not) and demonstrate differential-regulation of components of the mature macrophage phenotype.