Bcl-xL acts as an inhibitor of IP3R channels, thereby antagonizing Ca2+-driven apoptosis

• Published in: Cell death and differentiation Vol. 29; no. 4; pp. 788 - 805
• Main Authors: Rosa, Nicolas, Ivanova, Hristina, Wagner, Larry E., Kale, Justin, La Rovere, Rita, Welkenhuyzen, Kirsten, Louros, Nikolaos, Karamanou, Spyridoula, Shabardina, Victoria, Lemmens, Irma, Vandermarliere, Elien, Hamada, Kozo, Ando, Hideaki, Rousseau, Frederic, Schymkowitz, Joost, Tavernier, Jan, Mikoshiba, Katsuhiko, Economou, Anastassios, Andrews, David W., Parys, Jan B., Yule, David I., Bultynck, Geert
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01-04-2022; Nature Publishing Group
• Subjects: 13/2; 14/34; 14/35; 14/63; 38/109; 38/44; 38/70; 38/79; 42/34; 42/44; 631/337; 631/67; 631/80; 82/1; 82/103; 82/29; 82/80; 82/83; 96/2; Apoptosis; Bcl-2 protein; Bcl-x protein; Biochemistry; Biomedical and Life Sciences; Breast cancer; Calcium (reticular); Calcium channels; Calcium signalling; Cell Biology; Cell Cycle Analysis; Cell death; Endoplasmic reticulum; Inositol 1,4,5-trisphosphate receptors; Life Sciences; Mitochondria; Mutagenesis; Oscillations; Staurosporine; Stem Cells
• ISSN: 1350-9047; 1476-5403
• DOI: 10.1038/s41418-021-00894-w

Anti-apoptotic Bcl-2-family members not only act at mitochondria but also at the endoplasmic reticulum, where they impact Ca
2+
dynamics by controlling IP
3
receptor (IP
3
R) function. Current models propose distinct roles for Bcl-2
vs.
Bcl-xL, with Bcl-2 inhibiting IP
3
Rs and preventing pro-apoptotic Ca
2+
release and Bcl-xL sensitizing IP
3
Rs to low [IP
3
] and promoting pro-survival Ca
2+
oscillations. We here demonstrate that Bcl-xL too inhibits IP
3
R-mediated Ca
2+
release by interacting with the same IP
3
R regions as Bcl-2. Via
in silico
superposition, we previously found that the residue K87 of Bcl-xL spatially resembled K17 of Bcl-2, a residue critical for Bcl-2’s IP
3
R-inhibitory properties. Mutagenesis of K87 in Bcl-xL impaired its binding to IP
3
R and abrogated Bcl-xL’s inhibitory effect on IP
3
Rs. Single-channel recordings demonstrate that purified Bcl-xL, but not Bcl-xL
K87D
, suppressed IP
3
R single-channel openings stimulated by sub-maximal and threshold [IP
3
]. Moreover, we demonstrate that Bcl-xL-mediated inhibition of IP
3
Rs contributes to its anti-apoptotic properties against Ca
2+
-driven apoptosis. Staurosporine (STS) elicits long-lasting Ca
2+
elevations in wild-type but not in IP
3
R-knockout HeLa cells, sensitizing the former to STS treatment. Overexpression of Bcl-xL in wild-type HeLa cells suppressed STS-induced Ca
2+
signals and cell death, while Bcl-xL
K87D
was much less effective in doing so. In the absence of IP
3
Rs, Bcl-xL and Bcl-xL
K87D
were equally effective in suppressing STS-induced cell death. Finally, we demonstrate that endogenous Bcl-xL also suppress IP
3
R activity in MDA-MB-231 breast cancer cells, whereby Bcl-xL knockdown augmented IP
3
R-mediated Ca
2+
release and increased the sensitivity towards STS, without altering the ER Ca
2+
content. Hence, this study challenges the current paradigm of divergent functions for Bcl-2 and Bcl-xL in Ca
2+
-signaling modulation and reveals that, similarly to Bcl-2, Bcl-xL inhibits IP
3
R-mediated Ca
2+
release and IP
3
R-driven cell death. Our work further underpins that IP
3
R inhibition is an integral part of Bcl-xL’s anti-apoptotic function.