Temporally designed treatment of melanoma cells by ATRA and polyI: C results in enhanced chemokine and IFNß secretion controlled differently by TLR3 and MDA5.

ABSTRACT

In the last three decades, the incidence of melanoma has increased worldwide and no effective treatment modalities have been developed yet. All-trans retinoic acid (ATRA) and polyinosinicpolycytidylic acid (polyIC) are strong inducers of toll-like receptor 3 (TLR3) and MDA5 expression, and polyIC-induced TLR3 and MDA5 signaling specifically causes cell death in melanoma cells in vitro. We addressed the question of whether ATRA pretreatment could enhance the efficacy of polyIC and, if so, would ATRA have any additional effects on this process. We found that the combined treatment of human melanoma cells with ATRA and polyIC strongly increased the expression of TLR3 and MDA5 in both WM35 and WM983A cells associated with significantly higher mRNA and secreted levels of interferon ß (IFNß), CXCL1, CXCL8/IL-8, CXCL9, and CXCL10 than cells treated with either ATRA or polyIC. Silencing of MDA5 by siRNA moderately affected IFNß secretion, whereas TLR3 knockdown interfered with both CXCL chemokine and IFNß production. Furthermore, the supernatants of ATRA+polyIC-activated cultures increased the migration of both human monocyte-derived macrophages and CD1a dendritic cells significantly as compared with the supernatants of cells treated with either ATRA or polyIC, and this effect occurred in a TLR3-dependent manner. In conclusion, consecutive treatment with ATRA and polyIC results in strong, TLR3/MDA5-mediated chemokine and IFN responses in cultured human melanoma cells, which triggers a functional migratory response in professional antigen-presenting cells. This novel mode of concomitant activation may represent a more efficient treatment option for future melanoma therapy.