Expression of activated mutants of the human interleukin-3/interleukin- 5/granulocyte-macrophage colony-stimulating factor receptor common β subunit in primary hematopoietic cells induces factor-independent proliferation and differentiation

To date, several activating mutations have been discovered in the common signal-transducing subunit (hβc) of the receptors for human granulocyte- macrophage colony-stimulating factor, interleukin-3, and interleukin-5. Two of these, FIΔ and 1374N, result in a 37 amino acid duplication and a single amino acid substitution in the extracellular domain of hβc, respectively. A third, V449E, results in a single amino acid substitution in the transmembrane domain. Previous studies comparing the activity of these mutants in different hematopoietic cell lines imply that the transmembrane and extracellular mutations act by different mechanisms and suggest the requirement for cell type-specific molecules in signalling. To characterize the ability of these mutant hβc subunits to mediate growth and differentiation of primarycells and hence investigate their oncogenic potential, we have expressed all three mutants in primary murine hematopoletic cells using retroviral transduction. It is shown that, whereas expression of either extracellular hβc mutant confers factor-independent proliferation and differentiation on cells of the neutrophil and monocyte lineages only, expression of the transmembrane mutant does so on these lineages as well as the eosinophil, basophil, megakaryocyte, and erythroid lineages. Factor-independent myeloid precursors expressing the transmembrane mutant display extended proliferation in liquid culture and in some cases yielded immortalized cell lines.