Fig. 7: Impact on the sequestration of pro-apoptotic proteins by BCL2 or MCL1 after BH3 mimetic treatment.

A Redistribution of pro-apoptotic proteins following BH3 mimetic treatment. The amount of BIM, PUMA or BAX bound to BCL2 or to MCL1 in KMS-12-PE after treatment with 1 µM VEN, MCL1i or both inhibitors were examined by co-immunoprecipitation; the cells were co-treated with the broad-spectrum caspase inhibitor Q-VD-OPh (10 µM). Original uncropped immunoblots are provided with Supplemental materials. B Levels of BCL2 family proteins after treatment with BH3 mimetics. Lysates prepared from KMS-12-PE cells after treatment with 1 µM VEN, MCL1i or both for 0–24 h were blotted for the indicated proteins; as in (A), the experiments were performed with the addition of Q-VD-OPh. Original uncropped immunoblots are provided with Supplementary materials. C Working model for the indirect impact on MCL1 triggered by targeting BCL2 with venetoclax in CLL cells. The capacity of BCL2/MCL1 to sequester BAX/BAK in CLL cells is influenced by the abundance of prevailing endogenous BH3-only proteins (e.g., BIM, PUMA). Targeting BCL2 directly with venetoclax could indirectly inhibit MCL1 (and other pro-survival proteins) because of the displacement of BH3-only proteins from BCL2 caused by venetoclax [49] or redistribution of newly synthesized new proteins Co-targeting BCL2 and MCL1 frees the pro-apoptotic proteins from control by both pro-survival protein maximizing cell killing. Blots in (A) and (B) are representatives of 2 independent experiments; blotting for GAPDH served as loading controls.