Induction of Ca²⁺-driven apoptosis in chronic lymphocytic leukemia cells by peptide-mediated disruption of Bcl-2-IP₃ receptor interaction.

Bcl-2 contributes to the pathophysiology and therapeutic resistance of chronic lymphocytic leukemia (CLL). Therefore, developing inhibitors of this protein based on a thorough understanding of its mechanism of action is an active and promising area of inquiry. One approach centers on agents (eg, ABT-737) that compete with proapoptotic members of the Bcl-2 protein family for binding in the hydrophobic groove formed by the BH1-BH3 domains of Bcl-2. Another region of Bcl-2, the BH4 domain, also contributes to the antiapoptotic activity of Bcl-2 by binding to the inositol 1,4,5-trisphosphate receptor (IP?R) Ca2(+) channel, inhibiting IP(3)-dependent Ca2(+) release from the endoplasmic reticulum. We report that a novel synthetic peptide, modeled after the Bcl-2-interacting site on the IP?R, binds to the BH4 domain of Bcl-2 and functions as a competitive inhibitor of the Bcl-2-IP?R interaction. By disrupting the Bcl-2-IP?R interaction, this peptide induces an IP?R-dependent Ca2(+) elevation in lymphoma and leukemia cell lines and in primary CLL cells. The Ca2(+) elevation evoked by this peptide induces apoptosis in CLL cells, but not in normal peripheral blood lymphocytes, suggesting the involvement of the Bcl-2-IP?R interaction in the molecular mechanism of CLL and indicating the potential merit of targeting this interaction therapeutically.