Abstract 1197: The role of mitochondrial permeability transition pore complex proteins VDAC1, ANT, and cyclophilin D in prednisolone-induced apoptosis in B-Lineage acute lymphoblastic leukemia (ALL)

Abstract

Abstract The loss of mitochondrial membrane permeability is central to apoptosis. The mitochondrial permeability transition pore (PTP) complex, comprising of at least voltage-dependent anion channel 1 (VDAC1), adenine nucleotide transporter (ANT) and cyclophilin D (CyD), mediates the permeability of the mitochondrial membranes. We investigated the involvement of VDAC1, ANT and CyD in prednisolone (PRED)-induced apoptosis in 2 ALL cell lines: Sup-B15 (sensitive) and REH (resistant). After 24h exposure to PRED (10.0µg/ml), VDAC1 protein was consistently upregulated only in PRED-sensitive cell line, but remained unchanged in the resistant one. Co-administration of non-specific VDAC1 inhibitor, 4, 4′-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) with PRED, blocked PRED-induced apoptosis and caspase-3 activity only in sensitive cell line. Surprisingly, complete VDAC1 silencing using siRNA (Dharmacon) failed to abrogate PRED-induced apoptosis, suggesting that VDAC1 is not critical. We next investigated the other members of the PTP complex i.e., ANT and CyD. Co-administration of PRED and bongkrekic acid (BA) a specific inhibitor of ANT, also resulted in a dose-dependent inhibition of apoptosis and the caspase-3 activity. The combination of DIDS and BA, even at reduced doses by 60% and 96% respectively, is highly synergistic in inhibiting PRED-induced apoptosis and surprisingly reduced VDAC1 upregulation in PRED-induced apoptosis, unlike each agent alone. PRED did not alter the level of CyD protein and administration of specific CyD inhibitor, cyclosporine A (CsA), did not affect PRED-induced apoptosis. We conclude that ANT protein is central in the mitochondrial PTP mediated apoptosis during PRED treatment of ALL; VDAC1 and CyD are dispensable. ANT is upstream to VDAC1 and it upregulates VDAC1 during PTP activation in PRED-induced apoptosis. Our investigation provides the basis for looking at the role of mitochondrial PTP complex proteins especially ANT in PRED treatment in childhood ALL. This may provide new avenues to reverse resistance to therapy in patients with relapsed ALL. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1197.