hnRNP-A1 binds to the IRES of MELOE-1 antigen to promote its translation in stressed melanoma cells.

The major challenge in antigen-specific immunotherapy of cancer is to select the most relevant tumor antigens to target. To this aim, understanding their mode of expression by tumor cells is critical. We previously identified a melanoma-specific antigen, melanoma-overexpressed antigen 1 (MELOE-1) - coded for by a long non-coding RNA - whose internal ribosomal entry sequence (IRES)-dependent translation is restricted to tumor cells. This restricted expression is associated with the presence of a broad specific T cell repertoire that is involved in tumor immunosurveillance in melanoma patients. In the present work, we explored the translation control of MELOE-1 and provide evidence that heterogeneous nuclear ribonucleoprotein A1 (hnRNP-A1) binds to the MELOE-1 IRES and acts as an IRES trans-activating factor (ITAF) to promote the translation of MELOE-1 in melanoma cells. In addition, we showed that endoplasmic reticulum (ER) stress induced by thapsigargin, which promotes hnRNP-A1 cytoplasmic translocation, enhances MELOE-1 translation and recognition of melanoma cells by a MELOE-1-specific T cell clone. These findings suggest that pharmacological stimulation of stress pathways may enhance the efficacy of immunotherapies targeting stress-induced tumor antigens such as MELOE-1.