Abstract 1108: B-cell lymphoma-derived exosomes are reservoirs of inhibitors of apoptosis

Abstract

Abstract B-cells, along with other normal and cancerous cells, secrete 50-150 nm vesicles called exosomes. Exosomes carry proteins, mRNA, and miRNA that can be functional upon cellular uptake and are often specific to cell of origin, offering potential as disease biomarkers. Our lab has identified within exosomes from solid tumor cells a cancer-specific protein, Survivin, which is a member of the Inhibitors of Apoptosis (IAP) family. Whether Survivin and other IAP family members such as XIAP, cIAP1 or cIAP2 are also expressed in exosomes from hematopoietic malignancies is yet to be determined. In this study, we aim to investigate the exosomes released from B-cell lymphoma cells and determine the IAP content under basal and sublethal stress conditions. Three human non EBV-transformed B-cell lymphoma lines developed at Wayne State University were used. WSU-FSCCL (follicular small cleaved cell), WSU-DLCL-2 (diffuse large cell), and WSU-WM (Waldenstrom Macroglobulinemia) represent different levels of aggressiveness. Cells were cultured for 24 or 48 hours before exosome isolation from the conditioned media using either ultracentrifugation on a sucrose cushion or ExoQuick (System Biosciences). Sublethal levels of UV irradiation were determined for each cell line by analyzing DNA content by propidium iodide staining with a FACSCalibur. Protein quantity of exosomes was measured using a BCA assay, and protein content was studied using Western blotting. Corresponding gene expression was identified using RT-PCR. Here we report IAP protein and mRNA (except XIAP) within exosomes from basal cells. We are currently probing exosomes from stressed cells for comparison. We hypothesize that the IAP exosomal profile may change under stressed conditions. The specificity and variability in exosomal content offers capabilities not only as disease biomarkers, but also in the immunomodulating activity of exosomes which have shown roles in both stimulating and inhibiting the immune system, We have found evidence that exosomal Survivin plays an immune role in skewing Th1/Th2 populations and decreasing cytotoxic function. Changes in exosome content between basal and stressed cells may have roles in the immunomodulation of the tumor microenvironment which facilitates the evasion of lymphoma cells to immune destruction, as well as possible prognostic benefit as to whether treatments are being effective or detrimental. Citation Format: Heather R. Ferguson Bennit, Malyn M. Asuncion Valenzuela, Jessica S. Jutzy, Nathan R. Wall. B-cell lymphoma-derived exosomes are reservoirs of inhibitors of apoptosis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1108. doi:10.1158/1538-7445.AM2014-1108