Abstract 246: Calmodulin binding to death receptor-5 regulates pancreatic cancer apoptosis

Abstract

Abstract Targeting the extrinsic apoptosis pathway initiated by death receptors has been shown to be a promising therapy for pancreatic cancer. TRA-8, a humanized activating antibody for the death receptor 5 (DR5), is a potent therapeutic reagent for pancreatic cancer. However, several pancreatic cell lines are resistant to TRA-8-induced cell death. We have previously demonstrated that calmodulin (CaM) is recruited into the death-inducing signaling complex (DISC) by Fas death receptor activation, and that antagonists of CaM regulate DISC formation. Therefore, we determined the function of CaM in DR5-induced apoptosis of pancreatic cancer cells. We found that trifluoperazine (TFP), a CaM antagonist, enhanced TRA-8-induced cell death of pancreatic cells, PANC-1 and S2VP10, by 55% and 45% respectively. Consistent with the increased apoptosis, TFP increased TRA-8-induced activation of caspase 8 and caspase 3 in these cells. To determine the underlying molecular mechanisms, we analyzed the DR5-induced DISC. Interaction of CaM and DR5 was demonstrated by co-immunoprecipitation by using DR5 antibody. Activation of DR-5 by TRA-8 increased recruitment of CaM into the DISC which was inhibited by treatment with TFP. In addition, TFP decreased recruitment of the adaptor protein, FADD, and recruitment of other DISC proteins that regulate cell survival, including Src and FLICE-like inhibitory protein (FLIP), an inhibitor of caspase-8. These results suggest an important role for CaM in DR5-induced DISC formation in pancreatic cancer cells, regulating DR5-mediated survival and apoptotic signaling. In summary, we have demonstrated that CaM antagonism sensitizes pancreatic cancer cell to TRA 8-induced cell death, and that CaM binding to DR5 regulates DR5-induced DISC formation. Defining the function of CaM in regulating DR5-induced signaling pathways may lead to novel therapeutic strategies for pancreatic cancer therapy including possible combination therapy with TRA-8 and calmodulin antagonists. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 246. doi:1538-7445.AM2012-246