Abstract 1671: A genome-wide RNA interference screen identifies autophagy mediators with therapeutic implications in chronic myeloid leukemia.

Abstract

Abstract Autophagy plays a critical role in cancer formation and therapeutic resistance. However, little is known about how autophagy is regulated in cancer and how it mediates therapeutic resistance. Here we elect to use chronic myeloid leukemia (CML) as a cancer model to study autophagy in that it is driven by a single onco-protein BCR-ABL, whose activity can be selectively blocked by imatinib a front-line treatment for CML. Moreover, imatinib resistance frequently occurs in CML patients. Thus, unraveling autophagy regulation in CML and its role in overcoming imatinib resistance has substantial therapeutic benefits not only for CML but also for other cancers that can be treated by imatinib. In this report, we performed a genome-wide RNA interference screen in K562 human CML cells using monodansylcadaverine (MDC) that marks autolysosomes followed by fluorescence-activated cell sorting to label and isolate autophagic cells. We have identified 336 candidate genes, knockdown of which significantly increased MDC fluorescence. Our further validation utilized Cyto-IDTM Green dye that selectively stains autophagy vacuoles and quantitative RT-PCR that measures knockdown efficiency of shRNAs. We have uncovered a set of genes acting as autophagy mediators in K562 cells. To study their role in imatinib resistance, we measured the effect of imatinib in combination with the knocking down of autophagy mediators. Our results showed that the shRNA of VAMP7, a pivotal factor in vesicle transportation, substantially sensitized K562 cells to imatinib. Intriguingly, our further work revealed that depletion of VAMP7 blocked the activity of key autophagy suppressors AKT and mTOR, suggesting that VAMP7 and perhaps other autophagy mediators regulate imatinib sensitivity through signaling pathways that inhibit autophagy. In conclusion, a set of genes revealed by a genome-wide RNA interference screen mediates autophagy in CML cells and, more importantly, some of these genes render CML cells resistant to imatinib thereby becoming appealing drug targets. Citation Format: Zhi Sheng, Sujuan Guo, Susan Murphy, Hanne Varmark, Amy Virbasius, Michael Green. A genome-wide RNA interference screen identifies autophagy mediators with therapeutic implications in chronic myeloid leukemia. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1671. doi:10.1158/1538-7445.AM2013-1671