Up-Regulation of Death Receptor 5 and Bax Translocation Is Necessary To Induce Apoptosis by Sanguinarine in Primary Effusion Lymphoma.

Primary effusion lymphoma (PEL) is an aggressive and fatal type of cancer. PEL cells produce a variety of autocrine cytokines and growth factors, which provides cyto-protection against conventional chemotherapeutic agents. In efforts to identify novel approaches to block the proliferation of PEL cells, we found that Sanguinarine, a natural compound isolated from the root plant Sanguinaria canadendid, that is being used as an anti-microbial agent, inhibited cell proliferation and induced apoptosis in a dose dependent manner in several PEL cell lines through a bax-dependent signaling pathway. Five PEL cell lines used in this study were treated with various doses of Sanguinarine ranging between 0.5–4μM inhibited cell proliferation in all the cell lines in a dose dependent manner (BC1 40–97%, BC3 46–93%, BCBL1 11–94%, BCP1 20–97% and HBL6 7–95%). Treatment with varying doses of Sanguinarine also induced apoptosis in all cell lines as determined by cell cycle analysis, annexinV/PI dual staining, TUNEL assay and DNA laddering. Sanguinarine treatment resulted in up-regulation of death receptor 5 (DR5) expression, activation of caspase-8 and Bid leading to Bax conformational changes and translocation to the mitochondrial causing loss of mitochondrial membrane potential as measured by JC1 staining and release of cytochrome c to the cytosole. Sanguinarine induced release of cytochrome c resulted in activation of caspase-3, followed by polyadenosin-5′-diphosphate-ribose polymerase (PARP) cleavage leading to inhibition of proliferation and induction of caspase-dependent apoptosis. Furthermore, pre-treatment of PEL cells with z-VAD-fmk, a universal inhibitor of caspases, abrogated caspase-3 and PARP activation and prevented cell death induced by Sanguinarine. Inhibitor of apoptosis proteins (IAPs), play an important role in protecting cells against apoptosis through their direct action on caspases-9 and -3. Treatment of PEL cells with Sanguinarine down-regulated the expression of IAPs; XIAP, cIAP1 and cIAP2. Taken altogether, our findings suggest that Sanguinarine induces apoptosis via up-regulation of DR5, activation of Bax in a caspase-dependent pathway and down-regulation of IAPs. These results provide the molecular basis and preliminary data for new treatment strategies that may incorporate Sanguinarine in regimens for primary effusion lymphoma treatment.