The BRAF-MAPK signaling pathway is essential for cancer-immune evasion in human melanoma cells.
The mitogen-activated protein kinase (MAPK) pathway is frequently activated in human cancers, leading to malignant phenotypes such as autonomous cellular proliferation. Here, we demonstrate a novel role of the activated MAPK pathway in immune evasion by melanoma cells with the mutation of BRAF, which encodes a MAPKKs, (BRAF(V600E)). MEK inhibitor U0126 or RNA interference (RNAi) for BRAF(V600E) decreased production of the immunosuppressive soluble factors interleukin (IL)-10, VEGF, or IL-6 from melanoma cells to levels comparable to those after signal transducer and activator of transcription (STAT)3 inactivation. The suppressive activity of the culture supernatants from the melanoma cells on the production of inflammatory cytokines IL-12 and tumor necrosis factor alpha by dendritic cells upon lipopolysaccharide stimulation was markedly reduced after transduction with BRAF(V600E) RNAi, comparable to the effects observed with STAT3 RNAi transduction. No additive or synergistic effects were observed by the simultaneous transduction of RNAi for both BRAF(V600E) and STAT3. Furthermore, specific DNA binding and transcriptional activity of STAT3 were not affected by down-regulation of the MAPK signaling with the BRAF RNAi. These results indicate that the MAPK signal, along with the STAT3 signal, is essential for immune evasion by human melanomas that have constitutively active MAPK signaling and is a potential molecular target for overcoming melanoma cell evasion of the immune system.
Sumimoto
Hidetoshi
H
Division of Cellular Signaling, Institute for Advanced Medical Research, Keio University School of Medicine, Tokyo 160-8582, Japan.
Imabayashi
Fumie
F
Iwata
Tomoko
T
Kawakami
Yutaka
Y
D045744:Cell Line, Tumor; D006801:Humans; D007108:Immune Tolerance; D020935:MAP Kinase Signaling System / Q000276:immunology*; D008545:Melanoma / Q000201:enzymology* / Q000235:genetics / Q000276:immunology* / Q000517:prevention & control; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000502:physiology*; D050796:STAT3 Transcription Factor / Q000502:physiology
D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D020928:Mitogen-Activated Protein Kinases