Targeting Bcl-2-IP3 Receptor Interaction to Reverse Bcl-2's Inhibition of Apoptotic Calcium Signals

Abstract

SUMMARY The antiapoptotic protein Bcl-2 inhibits Ca2+ release from the endoplasmic reticulum (ER). One proposed mechanism involves an interaction of Bcl-2 with the inositol 1,4,5-trisphosphate receptor (IP3R) Ca2+ channel localized with Bcl-2 on the ER. Here we document Bcl-2-IP3R interaction within cells by FRET and identify a Bcl-2 interacting region in the regulatory and coupling domain of the IP3R. A peptide based on this IP3R sequence displaced Bcl-2 from the IP3R and reversed Bcl-2-mediated inhibition of IP3R channel activity in vitro, IP3-induced ER Ca2+ release in permeabilized cells, and cell-permeable IP3 ester-induced Ca2+ elevation in intact cells. This peptide also reversed Bcl-2’s inhibition of T cell receptor-induced Ca2+ elevation and apoptosis. Thus, the interaction of Bcl-2 with IP3Rs contributes to the regulation of proapoptotic Ca2+ signals by Bcl-2, suggesting the Bcl-2-IP3R interaction as a potential therapeutic target in diseases associated with Bcl-2’s inhibition of cell death.

Intramitochondrial calcium regulation by the FHIT gene product sensitizes to apoptosis

“…The ER and mitochondria are thus crucial nodes at which intracellular Ca 2ϩ fluxes and functional outcomes are governed (20). Their relevance to the control of cell survival is supported by several reports showing that modulation of mitochondrial Ca 2ϩ accumulation (because of modification of the molecular repertoire of the cells) modifies cellular sensitivity to Ca 2ϩ -mediated apoptotic stimuli (12)(13)(14).…”

“…Indeed, mitochondria are at the crossroad of numerous apoptotic pathways that synergize in triggeringthemorphologicaltransitionsunderlyingthereleaseofproapoptotic factors into the cytoplasm (9-11). In most cases, Ca 2ϩ acts as a fundamental sensitizing factor, and anti-apoptotic proteins, such as Bcl-2, have been shown to reduce ER Ca 2ϩ levels, and agonistdependent release and mitochondrial loading (12)(13)(14).Different agents induce Ca 2ϩ release from the ER Ca 2ϩ store through the IP 3 R Ca 2ϩ release channel (15). Consequent mitochondrial Ca 2ϩ uptake, via a yet unidentified Ca 2ϩ channel of the inner mitochondrial membrane (the mitochondrial Ca 2ϩ uniporter, MCU), regulates different processes: Aerobic metabolism (16), release of caspase cofactors (17), and feedback control of neighboring ER or plasma membrane Ca 2ϩ channels (18,19).…”

“…Indeed, mitochondria are at the crossroad of numerous apoptotic pathways that synergize in triggeringthemorphologicaltransitionsunderlyingthereleaseofproapoptotic factors into the cytoplasm (9-11). In most cases, Ca 2ϩ acts as a fundamental sensitizing factor, and anti-apoptotic proteins, such as Bcl-2, have been shown to reduce ER Ca 2ϩ levels, and agonistdependent release and mitochondrial loading (12)(13)(14).…”

Intracellular localization of the BCL-2 family member BOK and functional implications

“…2,9 However, several members, including BCL-2, BAX and BAK, are also present on other organelles, most notably the endoplasmic reticulum (ER), where they have been reported to be involved in the regulation of calcium homeostasis, autophagy and ER stress responses. 2,[10][11][12][13][14][15] BOK (BCL-2-related ovarian killer) was identified in a yeast two-hybrid screen using MCL-1 as bait and was shown to selectively interact with MCL-1 and BFL-1/A1 but not with BCL-2 or BCL-X L . 16,17 Among the BCL-2 family members, BOK shows the highest evolutionary conservation.…”

Biphasic regulation of InsP 3 receptor gating by dual Ca 2+ release channel BH3-like domains mediates Bcl-x L control of cell viability

“…Conversely, the Bcl-x L BH4 domain may lack this interaction (36). Inhibition of the Bcl-2 BH4 domain interaction with the channel enhanced InsP 3 R-mediated Ca 2+ signals and apoptosis sensitivity in white blood cells (18,35,37).…”