Int. J. Dev. Biol. 59: 391 - 398 (2015)
doi: 10.1387/ijdb.150213gb
© UPV/EHU Press

HA14-1 potentiates apoptosis in B-cell cancer cells sensitive to a peptide disrupting IP3 receptor / Bcl-2 complexes

Haidar Akl1, Rita M.L. La Rovere1,2, Ann Janssens3, Peter Vandenberghe4, Jan B. Parys*,1 and Geert Bultynck*,1

1KU Leuven, Lab. Molecular and Cellular Signaling, Dept. Cellular and Molecular Medicine, Leuven, Belgium, 2University “G. d’Annunzio”, Dept. Neuroscience Imaging and Clinical Sciences, Chieti, Italy and 3UZ Leuven, Dept. Hematology, Leuven, Belgium and 4KU Leuven, Dept. Human Genetics, Leuven, Belgium

ABSTRACT Anti-apoptotic B-cell lymphoma 2 (Bcl-2) is commonly upregulated in hematological cancers, including B-cell chronic lymphocytic leukemia (B-CLL) and diffuse large B-cell lymphoma (DLBCL), thereby protecting neoplastic cells from oncogenic-stress-induced apoptosis. Bcl-2 executes its anti-apoptotic function at two different sites in the cell. At the mitochondria, Bcl-2 via its hydrophobic cleft interacts with pro-apoptotic Bcl-2 family members to inhibit apoptosis. At the endoplasmic reticulum (ER), Bcl-2 via its Bcl-2 homology (BH)4 domain, prevents excessive Ca2+ signals by interacting with the inositol 1,4,5-trisphosphate receptor (IP3R), an intracellular Ca2+-release channel. A peptide tool (BIRD-2) that targets the BH4 domain of Bcl-2 reverses Bcl-2’s inhibitory action on IP3Rs and can trigger pro-apoptotic Ca2+ signals in B-cell cancer cells. Here, we explored whether HA14-1, a Bcl-2 inhibitor that also inhibits sarco/endoplasmic reticulum Ca2+-ATPases (SERCA), could potentiate BIRD-2-induced cell death. We measured apoptosis in Annexin V/7-AAD stained cells using flow cytometry and intracellular Ca2+ signals in Fura2-AM-loaded cells using an automated fluorescent plate reader. HA14-1 potentiated BIRD-2-induced Ca2+ release from the ER and apoptosis in both BIRD-2-sensitive DLBCL cell lines (SU-DHL-4) and in primary B-CLL cells. BIRD-2-resistant DLBCL cells (OCI-LY-1) were already very sensitive to HA14-1. Yet, although BIRD-2 moderately increased Ca2+ levels in HA14-1-treated cells, apoptosis was not potentiated by BIRD-2 in these cells. These results further underpin the relevance of IP3R-mediated Ca2+ signaling as a therapeutic target in the treatment of Bcl-2-dependent B-cell malignancies and the advantage of combination regimens with HA14-1 to enhance BIRD-2-induced cell death.

Keywords:

cancer, apoptosis, Bcl-2, IP3R, Ca2+

*Corresponding author e-mail: jan.parys@med.kuleuven.be ; geert.bultynck@med.kuleuven.be