Abstract 5089: Extracellular Survivin uptake by cancer cells via receptor-mediated endocytosis

The tumor microenvironment is a crucial player in tumorigenesis, proliferation, and survival. Communication between its various components through microvesicular trafficking is central to the interaction between tumor cells and the surrounding milieu. Exosomes, nanovesicles released by all cell types, carry various proteins and nucleic acids. Once released into the extracellular environment, exosomes are taken up by surrounding cells or the exosomes travel in various bodily fluids to reach distant parts of the body. Those exosomes derived from tumor cells contain proteins and nucleic acids essential to the development and maintenance of tumors. One such protein, Survivin, a member of the Inhibitor of Apoptosis (IAP) protein family, has been identified in virtually all cancer cells. Survivin function is closely linked with subcellular location. Nuclear Survivin plays a key role in cell division and cell cycle regulation as a member of the chromosome passenger complex. Cytosolic and mitochondrial Survivin primarily facilitate the inhibition of apoptosis. Recent research has identified a unique pool of Survivin in the extracellular environment. Functions tied to this location are as yet undefined, however, evidence suggests that this population may contribute to increased proliferation, invasiveness and therapeutic resistance when taken into recipient cancer cells. Using tandem affinity purification we have identified a relationship between Survivin and TNF receptor 1 (TNFR1), as well as transferrin receptor 2 (TfR2). Both of these receptors play a role in endocytosis of extracellular proteins. Transferrin receptors are upregulated on cancer cells to facilitate the increased iron demand of proliferating cells. We therefore hypothesize that exosomal Survivin is taken up by adjacent cancer cells via receptor-mediated endocytosis. We have shown that in the presence of antibodies to these receptors, there is a decreased uptake of extracellular Survivin (from conditioned media). Results were similar when conditioned media was introduced to HeLa cells with siRNA knockdowns of each receptor, as well as to CHO cells deficient in these receptors. We conclude that uptake of extracellular Survivin into cancer cells is dependent upon these two endocytosis receptors. The relationship of Survivin and exosomes in the extracellular environment is indicative that exosomes transport Survivin out of tumor cells and into the surroundings. These results suggest that exosomal Survivin enters cancer cells by way of receptor-mediated endocytosis. Understanding this mechanism of signaling between cancer cells shows the potential intercellular trafficking of oncoproteins may play in tumor maintenance and progression. It also provides us with a novel means to combat the resulting enhanced aggressive nature of the disease. Citation Format: Amber Gonda, Salma Khan, Heather R. Ferguson Bennit, Ron B. Moyron, Nathan R. Wall. Extracellular Survivin uptake by cancer cells via receptor-mediated endocytosis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5089.