Selective regulation of IP 3-receptor-mediated Ca 2+ signaling and apoptosis by the BH4 domain of Bcl-2 versus Bcl-Xl

Abstract

Antiapoptotic B-cell lymphoma 2 (Bcl-2) targets the inositol 1,4,5-trisphosphate receptor (IP 3R) via its BH4 domain, thereby suppressing IP 3R Ca 2+-flux properties and protecting against Ca 2+-dependent apoptosis. Here, we directly compared IP 3R inhibition by BH4-Bcl-2 and BH4-Bcl-Xl. In contrast to BH4-Bcl-2, BH4-Bcl-Xl neither bound the modulatory domain of IP 3R nor inhibited IP 3-induced Ca 2 release (IICR) in permeabilized and intact cells. We identified a critical residue in BH4-Bcl-2 (Lys17) not conserved in BH4-Bcl-Xl (Asp11). Changing Lys17 into Asp in BH4-Bcl-2 completely abolished its IP 3R-binding and-inhibitory properties, whereas changing Asp11 into Lys in BH4-Bcl-Xl induced IP 3R binding and inhibition. This difference in IP 3R regulation between BH4-Bcl-2 and BH4-Bcl-Xl controls their antiapoptotic action. Although both BH4-Bcl-2 and BH4-Bcl-Xl had antiapoptotic activity, BH4-Bcl-2 was more potent than BH4-Bcl-Xl. The effect of BH4-Bcl-2, but not of BH4-Bcl-Xl, depended on its binding to IP 3Rs. In agreement with the IP 3R-binding properties, the antiapoptotic activity of BH4-Bcl-2 and BH4-Bcl-Xl was modulated by the LysAsp substitutions. Changing Lys17 into Asp in full-length Bcl-2 significantly decreased its binding to the IP 3R, its ability to inhibit IICR and its protection against apoptotic stimuli. A single amino-acid difference between BH4-Bcl-2 and BH4-Bcl-Xl therefore underlies differential regulation of IP 3Rs and Ca 2+-driven apoptosis by these functional domains. Mutating this residue affects the function of Bcl-2 in Ca 2+ signaling and apoptosis. © 2012 Macmillan Publishers Limited All rights reserved.