Author: Ramesh - Singh

Publisher:

Published: 2015

Total Pages: 118

ISBN-13:

Exosomes are nano-vesicles released into the microenvironment by different cell types including normal and cancer cells. Initial studies showed that these extracellular vesicles are used by cells to get rid of obsolete cellular molecules, toxic end products and drugs. Exosomes have acquired a lot of attention because of their ability to act as mediator of cell-cell communication. They have tetraspanin proteins on their membrane and contain lipids, proteins, mRNAs and non-coding RNAs. In this work we explore the potential of exosomal microRNAs and IncRNAs as mediators of cell communication. In this study, we demonstrate that exosomes carrying non-coding RNA can be transferred among different cell lines through direct uptake. We show that miR-10b, highly expressed in metastatic breast cancer MDA-MB-231 cells as compared to non-metastatic breast cancer cells or nonmalignant breast cells, is actively secreted into conditioned medium via exosomes. In particular, nSMase2 or ceramide promotes the exosome-mediated miR-10b secretion whereas ceramide inhibitor suppresses this secretion. Moreover, upon uptake, miR-10b can suppress the protein level of its target genes such as HOXD10 and KLF4, indicating its functional significance. Finally, treatment with exosomes derived from MDA-MB-231 cells could induce the invasion ability of nonmalignant HMLE cells. We also found that IncRNA BC200 is upregulated in breast cancer and actively secreted by cancer cells. BC200 is transcriptionally induced by estradiol (E2) in ER positive breast cancer cell lines and is vital for cell growth and viability. BC200 knockout, generated using CRISPR/Cas9 technique induces growth inhibition and cell apoptosis. Of great interest, BC200 knockout enhances expression of pro-apoptotic bcl-XS variant at both mRNA and protein level. Further studies confirmed that BC200 binds with hnRNP A2/B1 and thereby facilitates binding of hnRNP A2/B1 with bcl-X mRNA. In vivo study in mice shows that BC200 knockout MCF-7 cells had a marked reduction in tumor weight as compared to donor control tumor. The regulation of bd-X alternative splicing depends upon endogenous expression of BC200 that would help hnRNP A2/B1 to position itself on bd-X mRNA and modulate splicing in favor of bcl-XL. Thus, loss of BC200 leads to generation of bcl-XS protein synthesis and apoptosis. Together, these results suggest that BC200 functions as a negative regulator of apoptosis in breast cancer and thus, it may serve as a potential target for cancer therapies. Work done in this study suggests that a set of specific non-coding RNAs may play an important role in modulating tumor microenvironment through exosomes. Thus, a better understanding of this process may aid in the development of novel therapeutic agents.