Restoration of apoptotic response to GrB after Bak gene transduction. (A) Bak expression, caspase-3 activation and PARP cleavage after adenoviral-mediated transduction of Bak. 24 h after infection of Bak-deficient cells with the indicated combinations of adenoviral vectors, cell extracts were assessed by immunoblotting for Bak expression. The membrane was stripped and reprobed for caspase-3 activation, stripped again, and reprobed with anti-PARP mAb. The p20 caspase-3 subunit in LacZ transduced cells represents the direct cleavage of caspase-3 by GrB. (B) Susceptibility of Bak-deficient cells to GrB 24 h after adenoviral transduction with Bak, but not with LacZ gene. The presence of apoptotic cells was assessed by annexin V staining of wild-type or Bak-deficient cells infected with the indicated combinations of adenoviral vectors and treated with GrB (1 μg/ml). Percentage of annexin V-positive cells is indicated.