Glioma cells enhance angiogenesis and inhibit endothelial cell apoptosis through the release of exosomes that contain long non-coding RNA CCAT2

Potential roles of tumor-derived exosomes in angiogenesis

INTRODUCTION

Tumor-derived exosomes (TEX) and their role in tumor progression by accelerating angiogenesis are of great current interest. A better understanding of the mechanisms underlying TEX-blood vessels cross-talk may lead to improvements in current diagnosis, prognosis and treatment of cancer. Areas covered: For solid tumors, an adequate blood supply is of critical importance for their development, growth and metastasis. TEX, virus-size vesicles which circulate freely throughout body fluids and accumulate in the tumor microenvironment (TME), have been recognized as a new contributor to angiogenesis. TEX serve as a communication system between the tumor and various normal cells and are responsible for functional reprogramming of these cells. The molecular and genetic cargos that TEX deliver to the recipient cells involved in angiogenesis promote its induction and progression. The targeted inhibition of TEX pro-angiogenic functions might be a novel therapeutic approach for control of tumor progression. Expert opinion: TEX circulating in body fluids of cancer patients carry a complex molecular and genetic cargo and are responsible for phenotypic and functional reprogramming of endothelial cells and other normal cells residing in the TME.

Tumor-derived extracellular vesicles in angiogenesis

Angiogenesis is crucial for tumor growth and metastasis. Recent studies revealed that tumor cells promote angiogenesis by secreting extracellular vesicles, which can be captured by endothelial cells. These tumor-derived extracellular vesicles carry microRNAs, long non-coding RNAs, and proteins, which activate pro-angiogenic signaling in endothelial cells. In this review, we will summarize the roles of tumor-derived extracellular vesicles in angiogenesis and the underlying molecular mechanisms.

The decade of exosomal long RNA species: an emerging cancer antagonist

Exosomes have emerged as a novel approach for the treatment and diagnosis of cancer after RNA content was discovered in exosomes in 2007. As important meditators of intercellular communication, exosomes have become a strong focus of investigation for researchers in the past decade, as witnessed through the exponential increase of research on exosomes. The capability of exosomes to transfer functionally active cargo highlights their importance as promising biomarkers and diagnostic molecules, as well as prospective drug delivery systems. The accessibility of exosomes in nearly all biofluids additionally alludes to its unprecedented ability in various types of cancers due to its extensive impact on tumor formation and progression. This review analyzes the role of exosomal long RNA species, which is comprised of mRNA, lncRNA, and circRNA, in tumor formation and progression, with an emphasis on their potential as future diagnostic biomarkers and treatment vectors in cancer biology. Their alignment with the development of exosomal databases is further examined in this review, in view of the accumulation of studies published on exosomes in the past decade.

Exosomal lncRNAs as new players in cell-to-cell communication

Neoplastic cells use various intercellular communication mechanisms in order to adapt to the local microenvironment, manipulate the immune system, and facilitate metastasis. Exosomes release is a new mechanism of cell-to-cell communication. These nanovesicles enclose various types of molecules including lipids, proteins, DNA, messenger RNA (mRNA) and non-coding RNAs [microRNA and long non-coding RNA (lncRNA)]. lncRNAs are over 200 nt long transcripts, that exhibit no coding potential, but are crucial regulators of physiological processes and are deregulated in cancer. In this review, we will discuss the role of exosomal lncRNAs in cancer, which is an incipient research field that could bring new insights to the vast domain of intercellular communication. Exosomal lncRNAs seem to be promising biomarkers for any type of cancer. The exact role of exosomal lncRNAs is not fully revealed. Several studies show that cancer derived exosomal lncRNAs are functional and can transmit to neighboring cells different phenotypic patterns, like drug resistance and increased angiogenesis. We further discuss the mechanistic function of exosomal lncRNAs, and hypothesize that the crowded exosomal content can be a suitable place of RNA species crosstalk. Finally, we assume that lncRNAs could be a loading vehicle for miRNAs, mRNAs and other complex molecules into the exosome but future studies are required to confirm these hypotheses.

Exosomes derived from cancerous and non-cancerous cells regulate the anti-tumor response in the tumor microenvironment

The tumor microenvironment (TME) is a unique platform of cancer biology that considers the local cellular environment in which a tumor exists. Increasing evidence points to the TME as crucial for either promoting immune tumor rejection or protecting the tumor. The TME includes surrounding blood vessels, the extracellular matrix (ECM), a variety of immune and regulatory cells, and signaling factors. Exosomes have emerged to be molecular contributors in cancer biology, and to modulate and affect the constituents of the TME. Exosomes are small (40-150 nm) membrane vesicles that are derived from an endocytic nature and are later excreted by cells. Depending on the cells from which they originate, exosomes can play a role in tumor suppression or tumor progression. Tumor-derived exosomes (TDEs) have their own unique phenotypic functions. Evidence points to TDEs as key players involved in tumor growth, tumorigenesis, angiogenesis, dysregulation of immune cells and immune escape, metastasis, and resistance to therapies, as well as in promoting anti-tumor response. General exosomes, TDEs, and their influence on the TME are an area of promising research that may provide potential biomarkers for therapy, potentiation of anti-tumor response, development of exosome-based vaccines, and exosome-derived nanocarriers for drugs.