The work that I am proposing in this fellowship application arises from exciting, recent discoveries showing that cancer cells can communicate with other cancer cells, as well as with non-transformed cells, through the secretion of extracellular shed vesicles (ESVs), which are distinct from traditional secretory vesicles. Studies by our laboratory and others have suggested that ESVs can contribute to cancer progression in a number of important ways, and therefore are garnering a great deal of attention in both the cell biology and pharmaceutical communities because of the possibilities they present as new targets for therapeutic intervention, as well as diagnostic markers. ESVs fall into two primary categories based on their size. Those that have a diameter ranging from 0.2-2 micron are referred to as microvesicles (MVs), whereas, a smaller class of vesicles called exosomes range from 0.05-0.2 micron in diameter. Although these two classes of vesicles are often thought to be functionally interchangeable, it has been suggested that they are generated through different mechanisms and thus may have specific biological roles. Specifically, exosomes have been reported to be generated through the exocytosis of multi-vesicular bodies, whereas MVs are formed through a distinct mechanism occurring at the cell surface that involves actin filament rearrangements and Rho GTPase-dependent signaling. However, despite the potentially important roles that ESVs play in biology and disease, a number of questions still need to be answered regarding their formation, composition and function, including whether microvesicles and exosomes contain distinct types of protein and RNA cargo, and if so, how their specific cargo contributes to their biological activities. Thus, I am proposing to address these important questions in the context of brain cancer, as aggressive glioblastoma cell lines, as well as glioma initiating (stem) cells, constitutively generate and shed large amounts of EVSs. Specifically, I will set out to: 1) Take advantage of methods developed by our laboratory to resolve MVs from exosomes to compare the functional capabilities of these two classes of ESVs, shed by aggressive glioblastoma cells. In particular, I will compare the abilities of MVs and exosomes to alter the growth and survival of low-grade glioma cells and non-transformed cells (astrocytes). 2) I will compare the cargo present in MVs versus exosomes and identify the essential cargo for mediating the biological functions of these two classes of vesicles. As a longer term goal (Aim 3), I want to take advantage of the information obtained from these first two lines of study to tes whether MVs and/or exosomes can function as reliable tumor markers, using mouse models for glioblastoma that are being studied by our laboratory.