Constitutive IP 3 signaling underlies the sensitivity of B-cell cancers to the Bcl-2/IP 3 receptor disruptor BIRD-2

• Published in: Cell death and differentiation 2019-03, Vol.26 (3), p.531
• Main Authors: Bittremieux, Mart, La Rovere, Rita M, Akl, Haidar, Martines, Claudio, Welkenhuyzen, Kirsten, Dubron, Kathia, Baes, Myriam, Janssens, Ann, Vandenberghe, Peter, Laurenti, Luca, Rietdorf, Katja, Morciano, Giampaolo, Pinton, Paolo, Mikoshiba, Katsuhiko, Bootman, Martin D, Efremov, Dimitar G, De Smedt, Humbert, Parys, Jan B, Bultynck, Geert
• Format: Article
• Language: English
• ISSN: 1476-5403
• DOI: 10.1038/s41418-018-0142-3

Anti-apoptotic Bcl-2 proteins are upregulated in different cancers, including diffuse large B-cell lymphoma (DLBCL) and chronic lymphocytic leukemia (CLL), enabling survival by inhibiting pro-apoptotic Bcl-2-family members and inositol 1,4,5-trisphosphate (IP ) receptor (IP R)-mediated Ca -signaling. A peptide tool (Bcl-2/IP R Disruptor-2; BIRD-2) was developed to abrogate the interaction of Bcl-2 with IP Rs by targeting Bcl-2's BH4 domain. BIRD-2 triggers cell death in primary CLL cells and in DLBCL cell lines. Particularly, DLBCL cells with high levels of IP R2 were sensitive to BIRD-2. Here, we report that BIRD-2-induced cell death in DLBCL cells does not only depend on high IP R2-expression levels, but also on constitutive IP signaling, downstream of the tonically active B-cell receptor. The basal Ca level in SU-DHL-4 DLBCL cells was significantly elevated due to the constitutive IP production. This constitutive IP signaling fulfilled a pro-survival role, since inhibition of phospholipase C (PLC) using U73122 (2.5 µM) caused cell death in SU-DHL-4 cells. Milder inhibition of IP signaling using a lower U73122 concentration (1 µM) or expression of an IP sponge suppressed both BIRD-2-induced Ca elevation and apoptosis in SU-DHL-4 cells. Basal PLC/IP signaling also fulfilled a pro-survival role in other DLBCL cell lines, including Karpas 422, RI-1 and SU-DHL-6 cells, whereas PLC inhibition protected these cells against BIRD-2-evoked apoptosis. Finally, U73122 treatment also suppressed BIRD-2-induced cell death in primary CLL, both in unsupported systems and in co-cultures with CD40L-expressing fibroblasts. Thus, constitutive IP signaling in lymphoma and leukemia cells is not only important for cancer cell survival, but also represents a vulnerability, rendering cancer cells dependent on Bcl-2 to limit IP R activity. BIRD-2 seems to switch constitutive IP signaling from pro-survival into pro-death, presenting a plausible therapeutic strategy.