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

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.

Emerging role of long noncoding RNA-encoded micropeptides in cancer

“…Researchers demonstrated that the lncRNA MELOE produced three polypeptides, MELOE-1, MELOE-2, and MELOE-3, of 39, 44, and 54 aa long, respectively [55][56][57]. MELOE RNA was shown to be polycistronic, and translation of MELOE-1 and MELOE-2 depends on internal ribosome entry site (IRES) sequences [58], while MELOE-3 is translated via a classical cap-dependent mechanism.…”

Potential Regulatory Roles of MicroRNAs and Long Noncoding RNAs in Anticancer Therapies

“… 33 Indeed, by transferring miR-503 from the endothelium to the tumor microenvironment, thus interfering with interaction between breast cancer (BC) cells and the microenvironment, endothelial exosomes contribute to chemotherapeutic response in BC. 25 In addition, exosome-transferred miR-21 derived from M2-polarized macrophages confer cisplatin resistance in GC, suggesting a new therapeutic strategy for GC patients 34 , 35 , 36 ( Table 1 ).…”

Mammalian Polycistronic mRNAs and Disease

“…As a result, ITAFs play an important role in determining the cell- or tissue-specific expression of polycistronic transcripts with IRESs. For example, in meloe, two IRESs code for T-cell antigens that are selectively expressed in melanoma cells but are absent in melanocytes, suggesting that ITAFs are silenced in normal melanocytes [15, 16]. In tissues that do not express or sequester ITAFs critical for IRES function, it would be expected that the polycistronic gene would function in a monocistronic manner, highly reliant on cap-dependent translation.…”

“…Differential expression of ITAFs between normal melanocytes and melanoma cells could also account for the activation of these antigens selectively in cancer cells [15]. Furthermore, an additional ORF was identified in the 5’ region of meloe coding for MELOE-3, translated by a cap-dependent pathway [16]. MELOE-3 was found to have poor immunogenicity, suggesting the importance of targeting the IRES-dependent proteins MELOE-1 and MELOE-2 for immunotherapy of melanoma.…”