Abstract
PURPOSE: Previously, we reported that quinacrine (QC) may cause apoptosis in breast and colon cancer cells by activating the death receptor 5 (DR5), resulting in autophagic cell death through p21 modulation. Here, we systematically evaluated the combined role of p21 and DR5 and their crosstalk in QC-mediated autophagy and apoptosis in breast cancer cells using in vitro and in vivo models. METHODS: Multiple breast cancer-derived cell lines (MCF-7, ZR-75-1, T47D, MDA-MB-231 and MCF-10A-Tr) and a mouse xenograft model were used. Also, multiple assays, including Western blotting, immunoprecipitation, staining for autophagy and apoptosis, gene silencing, hematoxylin and eosin staining, immunohistochemistry, cell viability assessment, fluorescence imaging and cell sorting were used. RESULTS: We found that QC activates p21 and DR5 in combination with the apoptosis inducer TRAIL in the breast cancer-derived cells tested. Combined TRAIL and QC treatment increased autophagy and apoptosis by increasing the interaction between, and co-localization of, p21 and DR5 in the death-inducing signaling complex (DISC). We found that this combination also inhibited the mTOR/PI3K/AKT signaling cascade and modulated reactive oxygen species (ROS) and nitric oxide (NO) production. Reductions in autophagy and apoptosis in DR5-knockout cells and a lack of change in p21-DR5-silenced cells were noted after TRAIL + QC treatment. This result explains dependence of the death (autophagy and apoptosis) cascade on these two key regulatory proteins. In addition, we found in an in vivo mouse xenograft model that increased expression and enhanced co-localization of p21 and DR5 after TRAIL + QC treatment supported a joint regulatory role of these proteins in the co-prevalence of autophagy and apoptosis. CONCLUSION: Our data suggest that a combined treatment of TRAIL and QC causes cell death in breast cancer-derived cells via autophagy and apoptosis by increasing the interaction of p21 and DR5, as indicated by both in vitro and in vivo studies.