IRES-dependent translation of the long non coding RNA meloe in melanoma cells produces the most immunogenic MELOE antigens

// Maud Charpentier 1 , Mikael Croyal 2, 3 , Delphine Carbonnelle 1 , Agnes Fortun 1 , Laetitia Florenceau 1, 4 , Catherine Rabu 1 , Michel Krempf 2, 3, 4 , Nathalie Labarriere 1, 4 , Francois Lang 1 1 CRCNA, INSERM, CNRS, Universite d’Angers, Universite de Nantes, Nantes, France 2 UMR INRA 1280, CHU, Nantes, France 3 West Human Nutrition Research Center, CHU, Nantes, France 4 CHU, Nantes, France Correspondence to: Francois Lang, email: francois.lang@univ-nantes.fr Keywords: melanoma, IRES, long non coding RNA, tumor antigens, immunotherapy Received: June 07, 2016      Accepted: July 20, 2016      Published: July 29, 2016 ABSTRACT MELOE-1 and MELOE-2, two highly specific melanoma antigens involved in T cell immunosurveillance are produced by IRES-dependent translation of the long « non coding » and polycistronic RNA, meloe . In the present study, we document the expression of an additional ORF, MELOE-3, located in the 5′ region of meloe . Data from in vitro translation experiments and transfection of melanoma cells with bicistronic vectors documented that MELOE-3 is exclusively translated by the classical cap-dependent pathway. Using a sensitive tandem mass spectrometry technique, we detected the presence of MELOE-3 in total lysates of both melanoma cells and normal melanocytes. This contrasts with our previous observation of the melanoma-restricted expression of MELOE-1 and MELOE-2. Furthermore, in vitro stimulation of PBMC from 6 healthy donors with overlapping peptides from MELOE-1 or MELOE-3 revealed a very scarce MELOE-3 specific T cell repertoire as compared to the abundant repertoire observed against MELOE-1. The poor immunogenicity of MELOE-3 and its expression in melanocytes is consistent with an immune tolerance towards a physiologically expressed protein. In contrast, melanoma-restricted expression of IRES-dependent MELOE-1 may explain its high immunogenicity. In conclusion, within the MELOE family, IRES-dependent antigens represent the best T cell targets for immunotherapy of melanoma.