Tetraspanins in Extracellular Vesicle Formation and Function

Abstract

Extracellular vesicles (EVs) represent a novel mechanism of intercellular communication as vehicles for intercellular transfer of functional membrane and cytosolic proteins, lipids, and RNAs. Microvesicles, ectosomes, shedding vesicles, microparticles, and exosomes are the most common terms to refer to the different kinds of EVs based on their origin, composition, size, and density. Exosomes have an endosomal origin and are released by many different cell types, participating in different physiological and/or pathological processes. Depending on their origin, they can alter the fate of recipient cells according to the information transferred. In the last two decades, EVs have become the focus of many studies because of their putative use as non-invasive biomarkers and their potential in bioengineering and clinical applications. In order to exploit this ability of EVs many aspects of their biology should be deciphered. Here, we review the mechanisms involved in EV biogenesis, assembly, recruitment of selected proteins, and genetic material as well as the uptake mechanisms by target cells in an effort to understand EV functions and their utility in clinical applications. In these contexts, the role of proteins from the tetraspanin superfamily, which are among the most abundant membrane proteins of EVs, will be highlighted.

Time-dependent release of extracellular vesicle subpopulations in tumor CABA I cells

“…We therefore analyzed two transmembranes (CD63 and HLA), one intracellular (Ago-2) and two extracellular (gelatinases and plasminogen activators) proteins. CD63, particularly, was long considered a specific EXOs marker, but not more nowadays (35)(36)(37). CD63 and HLA expression is more evident in EVs obtained after 18 h of stimulation as compared to Ago-2, which seems to be slightly more expressed in EVs obtained after 30 min.…”

Extracellular vesicles and viruses: Are they close relatives?

“…Specific combinations of lipids and proteins, in particular, tetraspanins (22), in the EV membrane can mediate specific targeting of vesicles to recipient cells and may determine the ability of vesicles to fuse with cellular membranes. These molecules, as well as genetic material and proteins enclosed in EVs (e.g., transcription factors and cytokines), constitute molecular signals that can affect the function of recipient cells.…”

Resolving sorting mechanisms into exosomes

“…Interestingly, heparanase activity also facilitated the recruitment of CD63 into exosomes, in a syntenindependent manner [6,7]. Sorting of many membrane proteins into exosomes coincides with their association with tetraspanin membrane proteins [8]. Webs of interacting tetraspanins and associated proteins are stabilized by protein palmitoylation, and lipids also play an important role in the forma-npg tion of tetraspanin webs, conceivably explaining the relative enrichment of cholesterol and glycosylceramides in exosomes, as well as the dependency on sphingomyelinase activity for exosome formation [9].…”

“…Webs of interacting tetraspanins and associated proteins are stabilized by protein palmitoylation, and lipids also play an important role in the forma-npg tion of tetraspanin webs, conceivably explaining the relative enrichment of cholesterol and glycosylceramides in exosomes, as well as the dependency on sphingomyelinase activity for exosome formation [9]. Non-tetraspanin membrane proteins may in this way piggyback onto tetraspanin webs for their sorting into exosomes [8]. Interestingly, the tetraspanin CD63, which is highly enriched in exosomes and considered to be important for chaperoning cargo into exosomes [10], can also be recruited by syntenin [11].…”