Phosphorylation of Axl is an upstream event of SFKactivation. (A) Inhibition of SFK phosphorylation does not alter Axl phosphorylation. Cell lysates from CLL B cells treated with the Src inhibitor (PP1) or PI3K inhibitor (wortmannin) or left untreated were examined for the detection of phosphorylated Axl, SFK, or PI3K by Western blot analysis. Actin was used as loading control. (B) Knockdown of Axl reduces phosphorylation of SFK. CLL B cells were transfected with scrambled siRNA (Sc-siRNA) as a control or Axl-specific siRNA, and cell lysates were analyzed for the detection of phosphorylated Axl and SFK in Western blot. Actin was used as loading control. Patients with CLL are indicated by arbitrary numbers.