CXCR4 and B-cell chronic lymphocytic leukemia: As a control to ensure that the phosphorylation was dependent on CXCL12/CXCR4 signaling and to determine if the effects were dependent on signaling through the G-protein, Gi, CLL cells were pretreated with the small molecule CXCR4 antagonist, AMD3100, or the Gi-inhibitor, pertussis toxin (PTx) prior to a 3 min stimulation with CXCL12.