Inhibition of Hsp90 impairs B-cell receptor (BCR) signaling in ZAP-70⁺ CLL cells. ZAP-70⁺ CLL cells were preincubated with 17-AAG for 24 and 72 hours and then treated for 10 minutes with F(ab')₂ anti-μ antibodies to induce cellular activation. Protein lysates were immunoprecipitated (IP) with specific anti-p72^Syk antibody and assessed by Western blot (WB) for tyrosine phosphorylation using 4G10 antibody and p72Syk expression. Protein lysates from the same samples were evaluated by Western blot using the indicated antibodies. Activation of NF-κB was assessed by degradation of IκB-α. These results were reproduced more than 3 times.