Inhibition of the PI3K/Akt pathway prevents induction of Mcl-1 and abrogates the protective effect of imm-IgM on fludarabine-induced PARP cleavage. (A) Schematic representation of the pathways activated by imm-IgM and their respective inhibitors. (B) Cells were preincubated for 2 hours with the IKK inhibitor BAY-11 (2 μM), PI3K inhibitor LY294002 (10 μM), or ERK inhibitor U0126 (10 μM) prior to the addition of imm-IgM. Fludarabine (20 μM) was added 3 hours later. Cells were collected after 40 hours and analyzed for Mcl-1 expression and PARP cleavage by immunoblotting. The experiment was performed with CLL cells from 3 different cases (2 with mutated and 1 with unmutated V_H genes), with similar results. One representative experiment is shown (case G31, U-CLL).