Teitur Sævarsson and Berglind Ósk Einarsdóttir
Introduction
Melanoma cells frequently dedifferentiate in response to inflammation. This process occurs through downregulation of MITF, the master regulator of the melanocytic lineage. Melanoma dedifferentiation can result in altered immune related gene expression. We have previously identified a context dependent mechanism in which dedifferentiating melanoma cells increase their expression of the immune checkpoint ligand PD-L1 and several immune modulating cytokines in response to IFN-γ, which is a clinically relevant inflammatory cytokine. We aim to characterize the molecular mechanism and biological impact of this effect.
Methods
MITF expression of the human melanoma cell line 624Mel was knocked down via siRNA transfection to induce dedifferentiation, and cells subsequently stimulated with IFN-γ. The mechanism facilitating increased PD-L1 expression was characterized using small molecule inhibitors and siRNA mediated knockdown of relevant signaling pathway components, determined via qPCR and western blotting. Through ATAC-sequencing, we will determine how changes in accessible chromatin during dedifferentiation contribute to this mechanism. Via co-culture experiments using TCR-redirected T cells, we will determine the functional activity of this increased PD-L1 expression.
Results
Increased PD-L1 expression in dedifferentiated melanoma cells appears mediated through the JAK-STAT1-IRF1 axis, indicating enhanced canonical IFN-γ signaling following dedifferentiation. ATAC-seq is currently being performed. Co-culture experiments are scheduled for in the fall of 2024 and spring of 2025.
Conclusions
Dedifferentiated melanoma cells have increased expression of many immunomodulatory genes, indicating increased immune evasion capabilities. However, the functional activity of this mechanism remains to be determined.
