Extracellular Vesicles Shed by Melanoma Cells Contain a Modified Form of H1.0 Linker Histone and H1.0 mRNA-binding Proteins

Extracellular vesicles (EVs) are shed in the extracellular environment by both prokaryotes and eukaryotes. Although produced from both normal and cancer cells, malignant cells release a much higher amount of EVs, which also contain tumor-specific proteins and RNAs. We previously found that G26/24 oligodendroglioma cells shed EVs that contain the pro-apoptotic factors FasL and TRAIL1-2. Interestingly, G26/24 release, via EVs, extracellular matrix remodelling proteases3, and H1° histone protein4, and mRNA. To shed further light on the role of EVs in discarding proteins and mRNAs otherwise able to counteract proliferative signals, we studied a melanoma cell line (A375). We found that also these cancer cells produce H1° and release it into the extracellular space by EVs. Interestingly, H1° sorted to vesicles has a molecular mass higher than expected, and is probably sumoylated. By T1 RNase-protection assay with the H1° RNA, three main complexes were evidenced in EVs, the most abundant of which has a molecular mass of about 65 kDa. By using a biotinylated H1° RNA to fish interacting factors, we isolated from EVs a few proteins which have been then identified by mass spectrometry: the most abundant is a protein of about 60 kDa: myelin expression factor-2 (MYEF2). Western blot analyses confirmed the presence of MYEF2 in EVs released from A375 melanoma cells. 1. D’Agostino et al. 2006, Int J Oncol 29:1075-85. 2. Lo Cicero A et al. 2011, Int J Oncol 39:1353-57. 3. Lo Cicero A et al. 2012, Matrix Biol 31: 229-33. 4. Schiera G et al. 2013, Int J Oncol 43: 1771-76.