KB-3 cells were pretreated with or without 20 μM SP600125 for 30 min and were then untreated or treated with 30 nM vinblastine for the times indicated. A, whole cell extracts were prepared and subjected to immunoblotting for phospho-(Ser-63) c-Jun (P-c-Jun) and GAPDH as a loading control. B, cytosolic and mitochondrial fractions were prepared and subjected to immunoblotting for Bax, GAPDH and Cox II (Complex IV), respectively. C, cells were permeabilized, treated with digitonin in the presence of 1 mM DSP, and CHAPS-solubilized particulate fractions subjected to SDS-PAGE. Immunoblotting for Bax was performed with the monomeric (21-kDa) and oligomeric (42-kDa) forms shown. D, whole cell extracts were prepared and subjected to immunoprecipitation with anti-Bax 6A7 antibody (lanes 1 ~ 6), followed by immunoblotting for Bax. A precipitates prepared in the absence of 6A7 antibody (lane 7) and a whole cell extract (lane 8) were also examined as controls. E, whole cell extracts were prepared and subjected to immunoblotting for PARP, with uncleaved (116-kDa) and cleaved (85-kDa) species indicated. GAPDH was used as a loading control.