Abstract 4109: The unfolded protein response promotes tolerance to extreme hypoxia through autophagy dependent maintenance of cellular metabolism

Abstract

Abstract Oxygenation patterns in solid human tumors are highly heterogeneous both amongst and within tumors, and individual cells can be exposed to mild or extreme hypoxia. Hypoxia is known to influence the behavior of tumor cells in an adverse manner, resulting in poor response to radiotherapy, chemotherapy, and an increased metastatic capacity. The ability of cells to tolerate extreme hypoxia and the unusual metabolic environments found within tumors are not fully understood, but cell phenotype is influenced through at least three important oxygen-sensing pathways: HIF, mTOR and the unfolded protein response (UPR). Previously we have shown that the PERK-eIF2α arm of UPR, which is activated rapidly in response to extreme hypoxia, contributes to hypoxia tolerance in both cell lines and in human tumor xenografts. Furthermore, we found that signaling through PERK results in increased capacity for autophagy through direct transcriptional regulation of the autophagy genes ATG5 and LC3b during hypoxic exposure. We hypothesize that autophagy promotes survival during hypoxia through regulation of metabolic homeostasis and control of proteotoxicity. To elucidate the contribution of PERK signaling and autophagy to cell survival and metabolic homeostasis we created a series of isogenic cell lines with inducible expression of transgenes that cause PERK or autophagy signaling deficiency. We analyzed the changes in metabolism and in global metabolite levels during exposure to extreme hypoxia in wild type, PERK deficient, and autophagy deficient variants. Using liquid chromatography mass spectrometry, we identified a series of metabolites whose concentration varied in a time-dependent manner during hypoxia. Importantly, we found that cells defective in PERK signaling decreased levels of amino acids, increased fatty acids and evidence of oxidative stress products. Both, PERK signaling and autophagy deficiency resulted in accelerated glucose metabolism as evidenced by increased consumption and lactate production during hypoxia compared to controls. Together, these results suggest that PERK-dependent regulation of autophagy contributes to maintenance of bio-energetic status, preventing increased glucose flux and production of reactive oxygen species. Our data also demonstrate that aggressive, therapy resistant hypoxic cells may be selectively targeted by therapies that exploit the dependency of these cells on autophagy for survival. 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 4109. doi:1538-7445.AM2012-4109