Expression of interleukin 3 and granulocyte-macrophage colony-stimulating factor receptor common chain βc, βIT in normal haematopoiesis: Lineage specificity and proliferation-independent induction

Abstract

Interleukin 3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 5 (IL-5) exert their biological activities through interaction with cell-surface receptors that consist of two subunits, a specific α subunit and a common β transducing subunit (βc). We have evaluated the expression of βc on purified haematopoietic progenitor cells (HPCs) induced to unilineage differentiation/maturation through the erythroid (E), granulocytic (G), megakaryocytic (Mk) or monocytic (Mo) lineage, HPCs displayed low βc expression, which increased during the initial stages of HPC differentiation along the E, G, Mo or Mk lineages. At later stages of differentiation, βc chain expression increased in both G and Mo lineages, was expressed at low levels in the Mk lineage and declined to undetectable levels in the E lineage. Analysis of the full-length βc and intracytoplasmically truncated βc (βIT) mRNAs showed that the former was predominant in the G and Mo lineages, whereas the latter was prevalent in the E and Mk lineages. The βc induction takes place even in the absence of cell cycling. Thus, incubation of HPCs with graded amounts of IL-3 showed that the initial induction of βc expression is unrelated to cell proliferation. Furthermore, circulating monocytes and granulocytes exhibit a low level of βc expression that is greatly stimulated following incubation with either IL-3 or GM-CSF.