Long non-coding RNA GRASLND affects melanoma phenotypic switch and modulates immunogenicity by inhibition of the IFNγ signaling pathway (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, IFNγ 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 IFNγ enhanced the expression of IFNγ-stimulated genes, including HLA-I antigen presentation, demonstrating suppressive activity of GRASLND on IFNγ signaling. Based on our findings, we hypothesize an adaptive resistance mechanism of melanoma cells evading the immune system via inhibition of IFNγ signaling by GRASLND overexpression and highlight its value as a negative prognostic factor for melanoma. To investigate effects of GRASLND knockdown on 501Mel melanoma cells, we generated dox-inducible shRNA knockdown cell lines with one control shRNA (lacZ) and 2 GRASLND-targeting shRNAs (sh4 and sh8)