SIGNAL-TRANSDUCTION BY GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR AND INTERLEUKIN-3 RECEPTORS

Granulocyte-macrophage colony stimulating factor (GM-CSF) and Interleu kin-3 (IL-3) are cytokines which stimulate myeloid bone marrow progeni tor cell proliferation and maturation. GM-CSF also enhances the functi on of terminally differentiated effector cells including neutrophils, monocytes and eosinophils. Both growth factors exhibit similar biologi cal activities on overlapping cell populations which are mediated by h igh affinity receptors. These receptors share a common beta subunit ne cessary for signal transduction. The receptors for GM-CSF and IL-3 are members of the hematopoietin receptor superfamily and consequently la ck intrinsic tyrosine kinase activity. Several kinases, including JAK2 and raf-l, and other downstream molecules are likely to be responsibl e for the functional redundancy demonstrated by GM-CSF and IL-3 in fac tor-responsive cells. This review discusses recent findings which eluc idate the signaling pathways activated by these two cytokines.