Stomatin is highly expressed in exosomes of different origin and is a promising candidate as an exosomal marker

Proteins involved in the organizing of lipid rafts can be found in exosomes, as shown for caveolin‐1, and they could contribute to exosomal cargo sorting, as shown for flotillins. Stomatin belongs to the same stomatin/prohibitin/flotillin/HflK/C family of lipid rafts proteins, but it has never been studied in exosomes except for extracellular vesicles (EVs) originating from blood cells. Here we first show the presence of stomatin in exosomes produced by epithelial cancer cells (non–small cell lung cancer, breast, and ovarian cancer cells) as well as in EVs from biological fluids, including blood plasma, ascitic fluids, and uterine flushings. A high abundance of stomatin in EVs of various origins and its enrichment in exosomes make stomatin a promising exosomal marker. Comparison with other lipid raft proteins and exosomal markers showed that the level of stomatin protein in exosomes from different sources corresponds well to that of CD9, while it differs essentially from flotillin‐1 and flotillin‐2 homologs, which in turn are present in exosomes in nearly equal proportions. In contrast, the level of vesicular caveolin‐1 as well as its EV‐to‐cellular ratio vary drastically depending on cell type. Extracellular vesicles (EVs) raise a growing interest both in the context of the intercellular distant communication and in terms of the prospects for their use in the diagnostics and treatment of various pathologies, including cancer. One of the mechanisms of exosomes biogenesis is supposed to be associated with lipid rafts, structures that organize membranes, and participate in the assembly of signal complexes. Lipid rafts organizing proteins include members of stomatin/prohibitin/flotillin/HflK/C family proteins, such as flotillins and stomatin (flat rafts) and caveolin‐1 (invaginated rafts). However, stomatin, unlike flotillins, has never been studied previously in exosomes secreted by cancer cells. Here we first show that stomatin unlike caveolin‐1 is highly expressed in exosomes of different origins, including exosomes produced by different cells in culture and exosomes from various biological fluids (blood plasma and ascitic fluids). Moreover, we found that EVs are enriched in stomatin compared to producer cells, with the highest levels of stomatin found in smaller vesicles corresponding to exosomes compared to larger microvesicles. All this together indicates that stomatin can be considered a new specific exosomal marker.