Functional interactions between colony-stimulating factors and the insulin family hormones for human myeloid leukemic...

We investigated functional interactions between granulocyte-monocyte-colony-stimulating factor (GM-CSF) and the insulin family hormones using the GM-CSF- and insulin-dependent human acute myeloid leukemia cell line AML-193. Recombinant human GM-CSF and insulin enhanced AML-193 cell proliferation 3- and 5-fold, respectively, and showed a synergistic 10-fold increase when added in combination. Insulin-like growth factors I and II (IGFI and IGFII) increased AML-193 cell proliferation 4-fold and 2-fold, respectively, and also demonstrated synergy when combined with GM-CSF. Blocking experiments with monoclonal antibodies against the insulin and IGFI receptors indicated that the proliferative effects of insulin and IGFI were mediated through both their homologous and heterologous receptors. Pertussis toxin and cholera toxin, which ADP ribosylate GTP-binding proteins (G proteins), and the cyclic AMP analogue, dibutyryl cyclic AMP, decreased the proliferation induced by GM-CSF or insulin. Specific receptor binding of 125I-insulin, -IGFI, and -GM-CSF to AML-193 cells was demonstrated and not affected by preincubation with pertussis toxin or cholera toxin. Radiolabeled GM-CSF, insulin, and IGFI did not cross-compete with the heterologous ligands for receptor binding. These studies demonstrate (a) association between receptor binding and proliferative effects of GM-CSF and the insulin family hormones, (b) involvement of the G proteins in signal transduction provoked by these hormones which occurs at a postreceptor-binding level, and (c) synergistic mitogenic interactions between GM-CSF and the insulin family hormones, suggesting that their receptors are linked to divergent signaling mechanisms in addition to sharing G protein-coupled pathways.