Characterization of CLL exosomes reveals a distinct microRNA signature and enhanced secretion by activation of BCR signaling

Abstract

Key Points• CLL exosomes exhibit a disease-relevant microRNA signature.• B-cell receptor signaling enhances exosome secretion in CLL that can be antagonized by ibrutinib.Multiple studies show that chronic lymphocytic leukemia (CLL) cells are heavily dependent on their microenvironment for survival. Communication between CLL cells and the microenvironment is mediated through direct cell contact, soluble factors, and extracellular vesicles. Exosomes are small particles enclosed with lipids, proteins, and small RNAs that can convey biological materials to surrounding cells. Our data herein demonstrate that CLL cells release significant amounts of exosomes in plasma that exhibit abundant CD37, CD9, and CD63 expression. Our work also pinpoints the regulation of B-cell receptor (BCR) signaling in the release of CLL exosomes: BCR activation by a-immunoglobulin (Ig)M induces exosome secretion, whereas BCR inactivation via ibrutinib impedes a-IgM-stimulated exosome release. Moreover, analysis of serial plasma samples collected from CLL patients on an ibrutinib clinical trial revealed that exosome plasma concentration was significantly decreased following ibrutinib therapy. Furthermore, microRNA (miR) profiling of plasma-derived exosomes identified a distinct exosome microRNA signature, including miR-29 family, miR-150, miR-155, and miR-223 that have been associated with CLL disease. Interestingly, expression of exosome miR-150 and miR-155 increases with BCR activation. In all, this study successfully characterized CLL exosomes, demonstrated the control of BCR signaling in the release of CLL exosomes, and uncovered a disease-relevant exosome microRNA profile. (Blood. 2015;125(21):3297-3305) IntroductionChronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia in the western world and remains incurable with current therapies. Understanding the different contributors to pathogenesis in CLL represents a path by which improved therapeutic options can be proposed. Although the pathogenesis of CLL for many years has been attributed to defective apoptosis of tumor cells, robust death is typically noted when these are removed from the body, suggesting a strong role of nurturing in the tumor microenvironment.1 In vivo, CLL cells reside in close contact with T lymphocytes, stromal cells, monocyte-derived nurse-like cells, follicular dendritic cells, and macrophages, collectively referred to as the "microenvironment." Interactions between these components result in CLL cell trafficking, survival, proliferation, and the increase of the apoptotic threshold, which may be partly dependent on direct physical cell-to-cell contact or mediated through soluble factors. This crosstalk between CLL and the microenvironment is bidirectional; thus, CLL cells are not only being supported by the microenvironment but also are capable of activating and signaling through the secretion of mediators that sustain and promote their survival advantage. In vitro models and gene expression profiles have identified important pathways for the...

Extracellular vesicle miR-7977 is involved in hematopoietic dysfunction of mesenchymal stromal cells via poly(rC) binding protein 1 reduction in myeloid neoplasms

“…Recently, it was demonstrated that EVs derived from BM MSCs facilitated the progression of multiple myeloma, 44 and those derived from CML and chronic lymphocytic leukemia cells facilitated the progression through an autocrine mechanism. 19,21 Moreover, primary AML cells released EVs which were possibly enriched for both coding and non-coding RNAs. 17,45 These findings led us to explore the possibility of EVs-mediated communication between leukemic cells and MSCs.…”

Extracellular vesicles released from chronic lymphocytic leukemia cells exhibit a disease relevant mRNA signature and transfer mRNA to bystander cells

“…3 Recently the relevance of extracellular vesicles (EV) to the intercellular cross-talk and the establishment of a tumor-promoting CLL microenvironment was investigated in several studies. [4][5][6][7] EV are either shed from the cell surface or released as exosomes via exocytosis upon generation in multivesicular bodies. Tumor cell-derived EV enable the transfer of cancer-associated proteins and RNA which are able to alter the phenotype Supplementary Table S1A for the patients' characteristics).…”

Exosomes and CAFs: partners in crime

“…This contributes to increasing evidence that the ability of tumor cells to induce CAFs is a universal feature of progression in both solid 8 and blood 7,10 cancers. These data also provide incentive for detailed mechanistic investigation of the role exosomes play in pathogenic signaling processes 6 and regulating the understudied CLL-TME. Examining the contribution of exosomes and their content in predicting response (biomarkers) to different therapeutic agents including newly targeted kinase inhibitors will be of interest.…”

“…Proplatelet formation and maturation are heavily dependent on the membrane and cytoplasmic skeletal machinery, which include microtubule, actin, and spectrin. 5,6 Although microtubules and actin function as engines to power platelet formation and elongation, spectrin is necessary for the ultimate shape changes that occur when proplatelets mature For personal use only. on May 10, 2018. by guest www.bloodjournal.org From…”

“…Notably, some of these miRNAs (miR-150 and miR-155) were previously identified in circulating miRNA 5 and plasma-derived exosomes from CLL patients. 6 In addition, abundant miRNAs (miR-21, miR-146a) have been shown to regulate the induction of aberrant stromal cells. Exosome miRNAs were shown to transfer to MSCs and retain their functional activity.…”