Binding of Bim to Bcl-x_L and Bcl-2 in myeloma cell correlates with codependence and sensitivity to ABT-737. (A) Coimmunoprecipitation of proapoptotic proteins with Mcl-1, Bcl-x_L, and Bcl-2 was determined by Western blot analysis after lysing all 6 cell lines in 2% 3(3-cholamidopropyl) dimethylammonio-1-propane sulfonate buffer and immunoprecipitating with specific monoclonal antibodies as described in “Antibodies.” and “Coimmunoprecipitation studies.” Lysates and supernatant contain 7%, whereas the immunoprecipitated proteins contain 60% of the input. (B) CD138⁺ myeloma cells were isolated, and 1 million cells were subjected to lysis and immunoprecipitation with anti–Bcl-x and anti–Mcl-1 antibodies as described in “Antibodies” and “Coimmunoprecipitation studies.” Immunoprecipitates were subjected to SDS-PAGE and Western blot analysis performed for Bcl-x_L, Mcl-1, and Bim. Two of 6 patient samples tested are shown, and each experiment was performed in parallel with MM.1s as a reference.