Brain Tumor Exosomes and Microvesicles: Pleiotropic Effects from Tiny Cellular Surrogates

Abstract

Extracellular signaling is a necessity for tissue and organ system development, maintenance, adaptation and survival. From the biologic unit of the cell to the complete organizational structure that is the organism, cell-cell, cell-tissue, tissue-organ, and organ-system communication are essential to keep the organism functioning, homeostatic, and proliferative. Cell-derived extracellular vesicles such as exosomes and microvesicles are vital players in these forms of proximal and distal messaging, acting as discrete packets of information capable of altering recipient cell phenotypes, activities, and responses. These vesicles are part of the normal biologic repertoire of the organism, but are particularly exploited by neoplasmic growths and cancers to change both the local and systemic environments to aid in tumor proliferation, invasion, and metastases, and in the defense of the tumor. This chapter will focus on exosomes and microvesicles from brain tumors, but similar stories may be told about such vesicles from almost any tumor type. Following this general introduction on exosomes and microvesicles we will discuss the experimentally determined and putative roles of exosomes in brain tumor biology, particularly in stress responses, metabolism, migration, immunology, and protection against chemotherapeutics.