Proteasome inhibition leads to release of cytochrome c from mitochondria. Cells were incubated in the absence (control) or presence of 10 μmol/L MG132, 25 μmol/L zAPFcmk, or 10 μmol/L methylprednisolone for 6 hours, and cytosolic cytochrome c was measured in digitonin-permeabilized cells by immunoblotting. Lane 1, 0 hours control; lane 2, 6 hours control; lane 3, MG132; lane 4, zAPFcmk; lane 5, methylprednisolone. Results are typical of three independent experiments with different CLL isolates.