Abstract IA20: Autophagy in alveolar soft part sarcomagenesis

Abstract

Abstract Altered metabolism is considered to be one of the new hallmarks of cancer. Autophagy is one major avenue of altered cancer metabolism, enabling cell survival under metabolic stress and promoting chemoresistance. The nuclear localization of MiTF/TFE3 family transcription factors has associated with upregulated transcription of autophagy genes in pancreatic cancer. Alveolar soft part sarcoma is a rare but deadly soft-tissue sarcoma, with a predilection for adolescent and young adult victims. Alveolar soft part sarcoma is noteworthy for its resistance to traditional cytotoxic chemotherapies. It consistently associates with a t(X;17) chromosomal translocation that produces the ASPSCR1-TFE3 target gene, bearing the DNA-binding domain from TFE3 and protein interaction domains from ASPSCR1. We have demonstrated that conditional expression of ASPSCR1-TFE3 is sufficient to drive alveolar soft part sarcomagenesis in the mouse with complete penetrance. Mouse tumors recapitulate human alveolar soft part sarcoma histology and transcriptomes faithfully. While direct targets of ASPSCR1-TFE3 have been studied in a renal cell carcinoma cell line, they have not been studied in alveolar soft part sarcoma. We report not only the first genome-wide localization of the ASPSCR1-TFE3 oncoprotein on chromatin from alveolar soft part sarcoma cell lines and mouse tumors, but also its association with actively transcribed genes. Among these are found many genes related to autophagy, especially those related specifically to the nutrient responsive pathways that drive autophagy. We demonstrate high expression of autophagy-related lysosomes and proteins at baseline conditions in human tumors and cell lines and mouse tumors. We also demonstrate active autophagic flux even in the absence of stress conditions. Inhibition of autophagy has no apparent impact on the survival of alveolar soft part sarcoma cells alone, but profoundly impacts their protein degradation pathways and the availability of amino acids for protein assembly in stress. Inhibition of autophagy strongly synergizes with chemotherapy to kill alveolar soft part sarcoma cells, suggesting it was a source mechanism for resistance. We have therefore demonstrated the direct targets of ASPSCR1-TFE3 in alveolar soft part sarcomas, including a number of autophagy genes that are expressed in these tumors, independently from nutrient deprivation or stress, rendering cells particularly resistant to many therapy-induced stresses. Citation Format: Kevin B. Jones. Autophagy in alveolar soft part sarcomagenesis [abstract]. In: Proceedings of the AACR Conference on Advances in Sarcomas: From Basic Science to Clinical Translation; May 16-19, 2017; Philadelphia, PA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(2_Suppl):Abstract nr IA20.