Long non-coding RNA GRASLND affects melanoma phenotypic switch and modulates immunogenicity by inhibition of the IFN? signaling pathway (IFNg treatment and GRASLND KD).

Melanoma is a highly malignant tumor, that stands as the most lethal form of skin cancer and is characterized by notable phenotypic plasticity and intratumoral heterogeneity. Melanoma plasticity is involved in tumor growth, metastasis and therapy resistance. Long non-coding RNAs (lncRNAs) could influence plasticity due to their regulatory function. However, their role and mode of action are poorly studied. Here, we show a relevance of lncRNA GRASLND in melanoma phenotypic switch, IFN? signaling and immunogenicity. GRASLND knockdown revealed switching towards a dedifferentiated, slow-proliferating and highly-invasive cell state. Interestingly, GRASLND is overexpressed in differentiated melanomas and associated with poor prognosis. Accordingly, we found GRASLND expressed in immunological “cold” tumors and it negatively correlates with gene signatures of immune response activation. In line, silencing of GRASLND under IFN? enhanced the expression of IFN?-stimulated genes, including HLA-I antigen presentation, demonstrating suppressive activity of GRASLND on IFN? signaling. Based on our findings, we hypothesize an adaptive resistance mechanism of melanoma cells evading the immune system via inhibition of IFN? signaling by GRASLND overexpression and highlight its value as a negative prognostic factor for melanoma. Overall design: To investigate a potential effect of GRASLND on the transcription of IFN?-stimulated genes, doxycycline-inducible GRASLND knockdown melanoma cells (501Mel) were generated, cell lines with control shRNA (lacZ) and 2 GRASLND-targeting shRNAs (sh4 and sh8). These GRASLND knockdown or lacZ control cells were treated with IFN? and were either uninduced or induced with doxycycline.