Glycomic insights into microvesicle biogenesis
Cells can mediate intercellular communication by the secretion and uptake of microvesicles, nano-sized membranous particles that carry signaling molecules, antigens, lipids, mRNA and miRNA between cells. The biological function of these vesicles is dependent upon their composition and cellular origin which is regulated by mechanisms that are not well understood. Based on their molecular content, microvesicles may play a role in immune regulation, cancer progression, the spread of infectious agents and numerous other important normal and pathogenic processes. The proteomic content of microvesicles from diverse sources has been intensely studied. In contrast, little is known about their glycomic content. The glycosylation pattern of a protein or lipid plays a key role in determining its functional properties in several ways. Glycans can determine the trafficking of a protein to particular regions of the cell as well as the protein’s half life. In addition, the glycan-dervied oligomerization of glycolipids and glycoproteins is a known mechanism for the activation of receptors and recognition of ligands on the surface of the cell. Glycomic analysis may thus provide valuable insights into microvesicle function. I utilized lectin microarray technology to compare the glycosylation patterns of microvesicles derived from a variety of biological sources. When compared to cellular membranes, microvesicles were enriched in high mannose, polylactosamine, α2-6 sialic acid, and complex N-linked glycans but exclude terminal blood group A and B antigens. The polylactosamine signature in microvesicles from different cell lines derives from distinct glycoprotein cohorts. After treatment of Sk-Mel-5 cells with lactose to inhibit lectin-glycan interactions, secretion of microvesicle resident proteins was severely reduced. Taken together, this work provides evidence for a role of glycosylation in microvesicle-directed protein sorting.