Extracellular vesicles released from melanoma cells contain H1° mRNA-binding proteins, one of which is (probably) MYEF2.

Abstract

Release of extracellular vesicles (EVs) is a process conserved from prokaryotes to eucaryotes. Although EVs are produced from both normal and cancer cells, malignant cells release a much higher amount of EVs, which contain tumour-specific proteins and RNAs. We previously found that G26/24 oligodendroglioma cells shed EVs that contain the pro-apoptotic factors FasL and TRAIL and are able to inhibit neurite outgrowth, and induce apoptosis in about 75% of rat cortical neurons [1] and 40% of astrocytes [2] in culture. By labelling proteins synthesized in one cell type, we also demonstrated EV-mediated horizontal transfer of proteins among brain cells. Interestingly, G2624 release, via EVs, extracellular matrix remodelling proteases [3], and H1° histone protein [4]. We suggested that by releasing H1°, a differentiation-specific histone, cancer cells may escape differentiation cues [4]. 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 EVs. Interestingly, H1° sorted to vesicles shows 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, recognized as 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 39:1353-7 [3] Lo Cicero A et al. 2012, Matrix Biol 31:229-33 [4] Schiera G et al. 2013, Int J Oncol 43:1771-6