Effects of protease inhibitors on lamin B₁ cleavage. Cells were incubated for 6 hours in the absence or presence of 10 μmol/L methylprednisolone with or without 10 μmol/L zAPFcmk or 25 μmol/L BACMK, and lamin B₁ was detected by immunoblotting. DNA fragmentation levels in these samples were quantified in parallel (by the diphenylamine assay) and are as follows: control, 8%; zAPFcmk, 3%; BACMK, 3%; MPS, 33%; MPS + zAPFcmk, 10%; MPS + BACMK, 5%. Arrows indicate positions of intact lamin B₁ and two characteristic lamin fragments. Results of one experiment typical of three independent replicates.