Abstract 96: Conformational and thermodynamics analyses of the regulation of trifluoperazine on camodulin binding to Fas: Implications for cancer chemotherapy

Abstract

Abstract Fas-mediated signaling pathway is an important mechanism for apoptosis in a variety of cells, including cholangiocarcinoma and other cancer cells. The formation of death inducing signaling complex (DISC) is a critical step for Fas-mediated signaling. Recent experimental studies showed that calmodulin (CaM) binds to Fas and regulates Fas-mediated DISC formation and the binding of CaM to Fas is inhibited by the CaM antagonist, trifluoperazine (TFP) (J Cell Biochem, 103:788, 2008). The present study sought to determine the structural basis and molecular mechanisms of TFP regulation of Fas-mediated DISC formation. We used a combination of molecular dynamics simulations and binding free energy analyses to investigate the effect of TFP on CaM-Fas binding. We studied the interactions of different number(s) of TFP(s) with CaM and the effect of the resulting conformational changes of CaM on CaM/Fas binding. We found that the binding affinity of one TFP with CaM was affected by the sequential binding of other TFP(s) to CaM, which was consistent with near-UC circular dichroism data (Biochemistry 37:15300, 1998). The number of TFP(s) bound to CaM was shown to affect the conformational and motion changes of CaM, and thus directly affect CaM binding to Fas. Consistent with previous experimental observations that CaM-Fas binding was affected by TFP concentrations (J Biol Chem, 280:29964, 2005), we demonstrated that one TFP bound to CaM inhibited CaM-Fas binding while the subsequent two TFPs or four TFPs bound to CaM resulted in the recovery of CaM-Fas binding (Table 1). Results also showed that conformational and motional changes of Fas by binding to CaM were directly related to the number of TFPs bound to CaM, which could further affect Fas recruitment of FADD to the DISC. This study provides structural and thermodynamics evidence elucidating the role of the CaM antagonist, TFP, in regulating CaM-Fas binding and Fas-mediated DISC formation and apoptosis.Table 1.The change of CaM-Fas binding affinity by the CaM antagonist, TFP. CaM_Fas_WTCaM_1TFP_FasCaM_2TFPs_FasCaM_4TFPs_FasΔG−7.11±4.67−1.32±0.99−6.96±3.47−6.42±1.06ΔΔG 5.79*0.150.69All values in this table were expressed in terms of kcal/mol. ΔG is the binding free energy for the complex, and ΔΔG is the relative binding free energies with respect to the CaM-Fas complex without CaM antagonist TFP(s). * Differences are statistically significant (Student's t-test, p<0.05) 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 96.