Extracellular membrane vesicles can mediate intercellular transfer of molecules

Abstract

Many eukaryotic cell types, including neural cells, release into the extracellular environment vesicles of different sizes and composition. Neurons and astrocytes shed extracellular vesicles which contain FGF2 and VEGF and could be involved in interaction with endothelial cells, to form the blood-brain barrier. Also brain tumor cells, such as glioblastomas, release vesicles in the extracellular space. Microvesicles (MVs) shed from G26/24 oligodendro¬glioma cells were previously reported to contain FAS-L and to cause a reproducible, dose-dependent, inhibitory effect on neurite outgrowth, and neuronal apoptosis, when added to primary cultures of rat cortical neurons. More recently, they were also shown to contain TRAIL. This finding suggests the possibility that Fas-L and TRAIL cooperate in inducing brain cell death. We labeled oligodendroglioma cells with radioactive methionine and, after purification of labeled vesicles, we added them to unlabeled astrocytes in culture. We found that labeled proteins were delivered to the test cells. To understand the role of MVs in apoptosis and their possible interaction with different brain cell types, we inves¬tigated their effects on primary astrocytes, which have been reported to be resistant to different stresses that are effective on neurons. These cells were clearly more resistant than neurons to microvesicle-induced damage: a high dose (40 μg) of shed MVs induced cell death in only about 40% of astrocytes. Furthermore, considering that some RNA binding proteins (RBPs) are involved in tumorigenesis, we searched for these proteins in MVs. RNase T1 protection analyses revealed indeed the presence, in MVs shed from melanoma cells, of RBPs of 64, 50 and 36 kDa that bind H1° RNA.