Integrin stimulation mediates activation of SYK in CLL cells. (A) Stimulation of CLL samples (n = 10) for 15 seconds with human recombinant VCAM-1 increased phosphorylation of SYK at Y352 determined by the MFI (P < .01). (B) Immunoprecipitation of SYK with subsequent immunoblotting for phosphotyrosine (pY) revealed SYK phosphorylation on VCAM-1 contact as shown in the representative immunoblot and the densitometric evaluation of 9 different CLL samples displayed as relative expression after 15 minutes with or without VCAM-1 contact (mean ± SEM; P < .05; bottom). (C) Immunoblotting for the autophosphorylation site 525/526 for SYK revealed an increase induced by fibronectin contact as shown by a representative immunoblot and densitometric evaluation after normalization to β actin for 6 CLL samples (bottom). Displayed is the relative expression as mean ± SEM (P < .005).
