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Signal transducer and activator of transcription 3 (STAT3) signaling is constantly activated in human melanoma, and promotes melanoma metastasis. The dietary flavonoid apigenin is a bioactive compound that possesses low toxicity and exerts anti-metastatic activity in melanoma. However, the anti-metastasis mechanism of apigenin has not been fully elucidated. In the present study, we showed that apigenin suppressed murine melanoma B16F10 cell lung metastasis in mice, and inhibited cell migration and invasion in human and murine melanoma cells. Further study indicated that apigenin effectively suppressed STAT3 phosphorylation, decreased STAT3 nuclear localization and inhibited STAT3 transcriptional activity. Apigenin also down-regulated STAT3 target genes MMP-2, MMP-9, VEGF and Twist1, which are involved in cell migration and invasion. More importantly, overexpression of STAT3 or Twist1 partially reversed apigenin-impaired cell migration and invasion. Our data not only reveal a novel anti-metastasis mechanism of apigenin but also support the notion that STAT3 is an attractive and promising target for melanoma treatment.

BackgroundMelanoma is notorious for its propensity to metastasize, which makes treatment extremely difficult. Receptor tyrosine kinase c-Met is activated in human melanoma and is involved in melanoma progression and metastasis. Hepatocyte growth factor (HGF)-mediated activation of c-Met signaling has been suggested as a therapeutic target for melanoma metastasis. Quercetin is a dietary flavonoid that exerts anti-metastatic effect in various types of cancer including melanoma. In a previous report, we demonstrated that quercetin inhibited melanoma cell migration and invasion in vitro, and prevented melanoma cell lung metastasis in vivo. In this study, we sought to determine the involvement of HGF/c-Met signaling in the anti-metastatic action of quercetin in melanoma.MethodsTranswell chamber assay was conducted to determine the cell migratory and invasive abilities. Western blotting was performed to determine the expression levels and activities of c-Met and its downstream molecules. And immunoblotting was performed in BS3 cross-linked cells to examine the homo-dimerization of c-Met. Quantitative real-time PCR analysis was carried out to evaluate the mRNA expression level of HGF. Transient transfection was used to overexpress PAK or FAK in cell models. Student’s t-test was used in analyzing differences between two groups.ResultsQuercetin dose-dependently suppressed HGF-stimulated melanoma cell migration and invasion. Further study indicated that quercetin inhibited c-Met phosphorylation, reduced c-Met homo-dimerization and decreased c-Met protein expression. The effect of quercetin on c-Met expression was associated with a reduced expression of fatty acid synthase. In addition, quercetin suppressed the phosphorylation of c-Met downstream molecules including Gab1 (GRB2-associated-binding protein 1), FAK (Focal Adhesion Kinase) and PAK (p21-activated kinases). More importantly, overexpression of FAK or PAK significantly reduced the inhibitory effect of quercetin on the migration of the melanoma cells.ConclusionsOur findings suggest that suppression of the HGF/c-Met signaling pathway contributes to the anti-metastatic action of quercetin in melanoma.Electronic supplementary materialThe online version of this article (doi:10.1186/s12943-015-0367-4) contains supplementary material, which is available to authorized users.

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Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has attracted considerable attention owing to its selective killing of tumor cells but not normal cells. Melanoma shows weak response to TRAIL because of its low level of TRAIL death receptors. Here, we investigated whether indomethacin, a nonsteroidal anti-inflammatory drug, can potentiate TRAIL-induced apoptosis in melanoma cells. We showed that indomethacin was capable of promoting TRAIL-induced cell death and apoptosis in A375 melanoma cells. Mechanistically, indomethacin induced cell surface expression of death receptor 5 (DR5) in melanoma cells and also in various types of cancer cells. DR5 knockdown abolished the enhancing effect of indomethacin on TRAIL responses. Induction of the DR5 by indomethacin was found to be p53 independent but dependent on the induction of CCAAT/enhancer-binding protein homologous protein (CHOP). Knockdown of CHOP abolished indomethacin-induced DR5 expression and the associated potentiation of TRAIL-mediated cell death. In addition, indomethacin-induced reactive oxygen species (ROS) production preceded upregulation of CHOP and DR5, and consequent sensitization of cells to TRAIL. We also found that indomethacin treatment downregulated survivin via ROS and the NF-κB-mediated signaling pathways. Interestingly, indomethacin also converted TRAIL-resistant melanoma MeWo and SK-MEL-5 cells into TRAIL-sensitive cells. Taken together, our results indicate that indomethacin can potentiate TRAIL-induced apoptosis through upregulation of death receptors and downregulation of survivin.