Malignant melanoma is aggressive and has a high mortality rate. Toll-like receptor 4 (TLR4) has been linked to melanoma growth, angiogenesis and metastasis. However, signal transduction mediated by TLR4 for driving melanoma progression is not fully understood. Signal transducer and activator of transcription 3 (STAT3) has been identified as a major oncogene in melanoma progression. We found: that TLR4 expression positively correlates with activation/phosphorylation of STAT3 in human melanoma samples; that TLR4 ligands activate STAT3 through MYD88 and TRIF in melanoma cells; and that intratumoral activation of TLR4 increases STAT3 activation in the tumor and promotes tumor growth, angiogenesis, epithelial-mesenchymal transition (EMT) and the formation of an immunosuppressive tumor microenvironment in mice. Further, we found that the effects mediated by activating TLR4 are weakened by suppressing STAT3 function with a dominant negative STAT3 variant in melanoma. Collectively, our work identifies STAT3 activation as a key event in TLR4 signaling-mediated melanoma progression, shedding new light on the pathophysiology of melanoma.

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In this study, we aimed to investigate the anti-melanoma effects and the JAK2/STAT3 pathway-related mechanism of action of atractylenolide I in human melanoma cells. Our results showed that atractylenolide I effectively reduced viability, induced apoptosis and inhibited migration of melanoma cells. Meanwhile, atractylenolide I decreased the protein expression levels of phospho-JAK2 and phospho-STAT3, and in turn downregulated the mRNA levels of STAT3-targeted genes, including Bcl-xL, MMP-2 and MMP-9. Furthermore, the cytotoxic effect of atractylenolide I was attenuated in STAT3-overactivated A375 cells. These findings indicate that inhibition of JAK2/STAT3 signalling contributes to the anti-melanoma effects of atractylenolide I.

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