Functional Expression of Interleukin 2 Receptor in a Human Factor-dependent Megakaryoblastic Leukemia Cell Line: Evidence That Granulocyte-Macrophage Colony-stimulating Factor Inhibits Interleukin 2 Binding to Its Receptor¹

Human interleukin 2 (IL-2) is a member of the class of crucial regulators of lymphocyte proliferation. The action of IL-2 is known to be mediated through binding to a specific IL-2 receptor (IL-2R) which comprises at least two distinct proteins: IL-2Rα (p55) and IL-2Rβ (p70–75). However, the expression and function of IL-2R are largely unknown in acute myeloblastic leukemia cells. In a human granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-3, or stem cell factor-dependent myeloid leukemia cell line (M07E), IL-2 was found to stimulate proliferation in a dose-dependent manner and to augment GM-CSF- and stem cell factor-induced proliferation of M07E cells. The expression of IL-2Rβ on M07E cells was detectable with ¹²⁵I-IL-2 binding and affinity cross-linking analyses and with a monoclonal antibody against IL-2Rβ, Mik-β1. Although the expression of IL-2Rβ was not down-regulated but somewhat up-regulated by treatment with GM-CSF in both mRNA and protein levels, GM-CSF was found to compete (75%) with radiolabeled IL-2 for binding to IL-2R on M07E cells, whereas no competition of GM-CSF binding was observed with IL-2 even at a 400-fold molar excess. These results suggest that IL-2R may be functionally expressed in some cases of acute myeloblastic leukemia cells and raise the possibility that IL-2 may have some effects on human myelopoiesis.