IFN-α and -β induce caspase activation in MM cells.

U266 cells were collected at the indicated times (T) after IFN treatment and analyzed by protease activity assays for caspase 8 and caspase 3 by using the specific IETD and DEVD-pNA substrates (A) and Western blotting for caspase 3 cleavage (B). Data were representative of 3 separate experiments. (C) IFN-α and -β, but not -γ, induced caspase 3 cleavage in freshly isolated MM plasma cells (patient No. 2). Primary MM cells were isolated from bone marrow aspirates of patients, as described in “Materials and methods,” treated for 48 hours with IFNs, then subjected to Western blotting for caspase 3. The p32 kD band represents pro-caspase 3, whereas p17 represents its activated form.