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\ub0 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\ub0 and release it into the extracellular space by EVs. Interestingly, H1\ub0 sorted to vesicles has a molecular mass higher than expected, and is probably sumoylated. By T1 RNase-protection assay with the H1\ub0 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\ub0 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\u2019Agostino 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