Exosomes secreted under hypoxia enhance stemness in Ewing's sarcoma through miR-210 delivery.

Matthew J Kling,Shantaram S Joshi,Don W Coulter,J Graham Sharp,Varun Kesherwani,Nagendra K Chaturvedi,Timothy R Mcguire

doi:10.18632/oncotarget.27702

Matthew J Kling, Shantaram S Joshi + Show 5 more

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https://doi.org/10.18632/oncotarget.27702

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Abstract

Intercellular communication between tumor cells within the hypoxic microenvironment promote aggressiveness and poor patient prognoses for reasons that remain unclear. Here we show that hypoxic Ewing’s sarcoma (EWS) cells release exosomes that promote sphere formation, a stem-like phenotype, in EWS cells by enhancing survival. Analysis of the hypoxic exosomal miRNA cargo identified a HIF-1α regulated miRNA, miR-210, as a potential mediator of sphere formation in cells exposed to hypoxic exosomes. Knockdown of HIF-1α in hypoxic EWS cells led to decreased exosomal miR-210 levels and reduced the capacity of hypoxic exosomes to form spheres. Inhibition of miR-210 in hypoxic spheres attenuated sphere formation and overexpression of miR-210 in normoxic spheres significantly enhanced the number of EWS spheres. Our results indicate that hypoxic exosomal miR-210 targets the proapoptotic protein CASP8AP2 in recipient cells. Moreover, the suppression of CASP8AP2 led to a reduction in apoptotic cells and increased sphere formation. Together, the findings in this study suggest that hypoxic exosomes promote stemness in EWS cells by delivering enriched miR-210 that is capable of down-regulating apoptotic pathways, resulting in the survival of cells with increased sphere formation. Future studies will further investigate the effects of EWS derived exosomal miRNAs on target genes and the role these interactions play in driving aggressiveness in hypoxic EWS tumors.

Highlights

Ewing’s sarcoma (EWS) is an aggressive and highly malignant bone tumor that develops in children and adolescents [1]
Total exosomal protein was similar to total particle concentration and together, our findings suggest that EWS exosome secretion is dependent on proliferation rates which is consistent with the effects of hypoxia on cell proliferation
Aggressive tumors often consist of hypoxic regions capable of creating an environment that supports stem-like cancer cells [6, 7]

Summary

Introduction

Ewing’s sarcoma (EWS) is an aggressive and highly malignant bone tumor that develops in children and adolescents [1]. In 85% of patients, EWS is driven by a chromosomal translocation, t [11, 22] (q24; q12), that results in the fusion protein, EWS-FLI1, which has been shown to regulate key pathways involved in EWS tumorigenesis [2, 3] This pediatric tumor is treatable with a high degree of success if caught early, patients diagnosed with metastases or who relapse have a five-year survival rate of less than 25% and are considered to have the worst prognosis of all of the bone sarcomas [4]. Emerging evidence indicates intercellular communication between tumor cells in hypoxic and normoxic regions contributes to functional differences associated with hypoxic tumors [10,11,12]

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