BH3 mimetic-elicited Ca
2+ signals in pancreatic acinar cells are dependent on Bax and can be reduced by Ca
2+-like peptides.
Cell Death Dis 2017;
8:e2640. [PMID:
28252652 PMCID:
PMC5386550 DOI:
10.1038/cddis.2017.41]
[Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2016] [Revised: 12/20/2016] [Accepted: 01/11/2017] [Indexed: 02/07/2023]
Abstract
BH3 mimetics are small-molecule inhibitors of B-cell lymphoma-2 (Bcl-2) and Bcl-xL, which disrupt the heterodimerisation of anti- and pro-apoptotic Bcl-2 family members sensitising cells to apoptotic death. These compounds have been developed as anti-cancer agents to counteract increased levels of Bcl-2 proteins often present in cancer cells. Application of a chemotherapeutic drug supported with a BH3 mimetic has the potential to overcome drug resistance in cancers overexpressing anti-apoptotic Bcl-2 proteins and thus increase the success rate of the treatment. We have previously shown that the BH3 mimetics, BH3I-2' and HA14-1, induce Ca2+ release from intracellular stores followed by a sustained elevation of the cytosolic Ca2+ concentration. Here we demonstrate that loss of Bax, but not Bcl-2 or Bak, inhibits this sustained Ca2+ elevation. What is more, in the absence of Bax, thapsigargin-elicited responses were decreased; and in two-photon-permeabilised bax-/- cells, Ca2+ loss from the ER was reduced compared to WT cells. The Ca2+-like peptides, CALP-1 and CALP-3, which activate EF hand motifs of Ca2+-binding proteins, significantly reduced excessive Ca2+ signals and necrosis caused by two BH3 mimetics: BH3I-2' and gossypol. In the presence of CALP-1, cell death was shifted from necrotic towards apoptotic, whereas CALP-3 increased the proportion of live cells. Importantly, neither of the CALPs markedly affected physiological Ca2+ signals elicited by ACh, or cholecystokinin. In conclusion, the reduction in passive ER Ca2+ leak in bax-/- cells as well as the fact that BH3 mimetics trigger substantial Ca2+ signals by liberating Bax, indicate that Bax may regulate Ca2+ leak channels in the ER. This study also demonstrates proof-of-principle that pre-activation of EF hand Ca2+-binding sites by CALPs can be used to ameliorate excessive Ca2+ signals caused by BH3 mimetics and shift necrotic death towards apoptosis.
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