UP-REGULATION OF LINEAGE-SPECIFIC RECEPTORS AND LIGANDS IN MULTIPOTENTIAL PROGENITOR CELLS IS PART OF AN ENDOGENOUS PROGRAM OF DIFFERENTIATION

Multipotent hematopoietic progenitor cell lines (FDCP-Mix) infected wi th a retroviral vector expressing the GM-CSF gene show functional down regulation of the GM-CSF receptor when maintained in IL-3 and activati on of the receptor resulting in synchronous differentiation into matur e granulocytes and macrophages on withdrawal of IL-3. This system has now been used to investigate whether or not receptors for some of the other growth factors are also influenced as a consequence of different iation. We show here the lineage specific receptors for M-CSF, G-CSF a nd erythropoietin are all upregulated, regardless of whether or not di fferentiation is induced by GM-CSF or by other conditions. Concomitant induction of the mRNA coding for the ligands M-CSF and G-CSF, but not for erythropoietin, suggests that M-CSF and possibly G-CSF facilitate macrophage or granulocyte differentiation by an autocrine stimulation of the lineage specific receptors. FDCP Mix mutants that are blocked in their ability to differentiate on exposure to GM-CSF, but that stil l require GM-CSF for proliferation, do not express increased levels of M-CSF receptor nor M-CSF. Based on these data, we suggest that expres sion of these lineage specific receptors is part of the intrinsic endo genous program of myeloid differentiation.