CXCR3, known to have four ligands (IFN-gamma inducible protein 10 (gamma IP-10), monokine induced by IFN-gamma (Mig), I-TAC, and 6Ckine), is predominantly expressed on memory/activated T lymphocytes. We recently reported that GM-CSF induces CXCR3 expression on CD34(+) hemopoietic progenitors, in which gamma IP-10 and Mig induce chemotaxis and adhesion. Here we further report that stimulation with GM-CSF causes phosphorylation of Syk protein kinase, but neither Casitas B-lineage lymphoma (Cbl) nor Cbl-b in CD34(+) hemopoietic progenitors can be blocked by anti-CD116 mAb. Specific Syk blocking generated by PNA antisense completely inhibits GM-CSF-induced CXCR3 expression in CD34(+) progenitors at both mRNA and protein as well as at functional levels (chemotaxis and adhesion). Cbl and Cbl-b blocking have no such effects. Thus, GM-CSF binds to its receptor CD116, and consequently activates Syk phosphorylation, which leads to induce CXCR3 expression. gamma IP-10 and Mig can induce Syk, Cbl, and Cbl-b phosphorylation in CD34(+) progenitors by means of CXCR3. gamma IP-10 or Mig has induced neither chemotaxis nor adhesion in GM-CSF-stimulated Cbl-b-blocked CD34(+) hemopoietic progenitors, whereas SDF-1alpha induces both chemotaxis and adhesion in these cells. Interestingly, gamma IP-10 and Mig can induce chemotaxis and adhesion in GM-CSF-stimulated Syk- or Cbl-blocked CD34(+) hemopoietic progenitors. Thus, Cbl-b, but not Syk and Cbl phosphorylation, is essential for gamma IP-10- and Mig-induced chemotaxis and adhesion in CD34(+) hemopoietic progenitors. This study provides a useful insight into novel signaling transduction pathways of the functions of CXCR3/gamma IP-10 and Mig, which may be especially important in the cytokine/chemokine environment for mobilization, homing, and recruitment during proliferation, differentiation, and maturation of hemopoietic progenitor cells.