SYK is involved in the CXCL12 pathway in CLL cells. (A) Stimulation of primary CLL samples (n = 8) for 15 seconds with human CXCL12 resulted in an increase of pY352 SYK, the activation site of SYK determined by the MFI (P < .001). (B) Concomitant SYK inhibition abrogated the phosphorylation of Akt induced by CXCL12 stimulation. Displayed is the MFI of CLL cells stained for pAkt after 30 seconds of stimulation with CXCL12 (n = 8; P < .01). A representative immunoblot is shown. (C) F-Actin formation after CXCL12 stimulation was determined by intracellular staining using Alexa488-labeled phalloidin and flow cytometric analysis of 7 different primary CLL samples. SYK inhibition alone did not significantly change F-actin formation, CXCL12 induced F-actin (P < .001), and R406 prevented up-regulation induced by CXCL12 (P < .05). (D) Transwell chemotaxis assays toward CXCL12 were performed without or with R406 for 7 CLL samples. The percentage of migrated cells in vehicle control was defined as 100% to determine the relative chemotaxis. R406 inhibited chemotaxis toward CXCL12 with a P value less than .001.