Abstract 121: Characterization of an extracellular, cell permeable pool of the inhibitor of apoptosis (IAP) protein survivin

Abstract

Abstract Inhibitor of apoptosis (IAP) and Heat shock proteins (HSPs) provide assistance in protecting cells from the stresses of hypoxia, imbalanced pH, and altered metabolic and redox states commonly found in the microenvironmental mixture of tumor and nontumor cells. HSPs are upregulated, cell-surface displayed and released extracellularly in some types of tumors, a finding that until now was not shared by members of the IAP family. The IAP, Survivin, has been implicated in apoptosis inhibition and the regulation of mitosis in cancer cells. Survivin exists in a number of subcellular locations such as the mitochondria, cytoplasm, nucleus, and most recently, the extracellular space. Our previous work showing that extracellular survivin was able to enhance cellular proliferation, survival and tumor cell invasion provided evidence that survivin might be secreted via an unidentified exocytotic pathway. In the present study, we describe for the first time the exosome-release of survivin to the extracellular space both basally and after proton irradiation-induced stress. To examine whether exosomes contributed to survivin release from cancer cells, exosomes were purified from HeLa cervical carcinoma cells and exosome quantity and survivin content were determined. We demonstrate that although proton irradiation does not influence the exosomal secretory rate, the survivin content of exosomes isolated from HeLa cells treated with a sublethal dose of proton irradiation (3Gy) is significantly higher than control. These data identify a novel secretory pathway by which survivin can be actively released from cells in both the basal and stress-induced state. The quantitation of exosomal survivin from blood or sera may be used to identify the presence of cancer. It may also be feasible to positively impact cancer therapy by targeting exosome-associated protein release, and thus prohibit stress-activated, anti-apoptotic proteins like survivin from impacting the tumor microenvironment and ultimately a patient's response to therapy. 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 121.