BCLXL acts as a sink to capture freed proapoptotic proteins from MCL1 under A1210477 treatment in MCL1 nondependent cell lines. (A) MM1S and (B) U266 A1210477-resistant HMCLs were treated with A1210477 (2 μM) for the indicated times. Immunoprecipitation reactions of MCL1 were performed followed by western blotting analysis of BAK and BIM. # A minor BIM isoform other than EL, L or S associated with MCL1 in MM1S. Quantification of bound BAK and BIM proteins to MCL1 was done using ImageJ software. ][An empty space has been removed from the original image. (C-D) Free-MCL1 lysates of MM1S and U266 cell lines were then subjected to BCLXL immunoprecipitation reactions followed by western blotting analysis of BAK and BIM. *Ab light chain. Quantification of bound BAK and BIM proteins to BCLXL was done as in A and B.