Extensive research has demonstrated a tumor‐promoting role of increased WNT5A expression in malignant melanoma.,However, very little light has been shed upon how WNT5A expression is up‐regulated in melanoma.,A potential regulator of WNT5A expression is the pro‐inflammatory cytokine Interleukin (IL)‐6, which shares the ability of WNT5A to increase melanoma cell invasion.,Here, we investigate whether IL‐6 can promote melanoma cell motility through an increased expression of WNT5A.,We clearly demonstrate that the WNT5A‐antagonistic peptide Box5 could inhibit IL‐6‐induced melanoma cell migration and invasion.,Furthermore, IL‐6 stimulation of the human melanoma cell lines HTB63 and A375 increased the expression of WNT5A in a dose‐dependent manner.,To identify the signaling mechanism responsible for this up‐regulation, we explored the involvement of the three main signals induced by IL‐6; STAT3, Akt and ERK 1/2.,Of these, only STAT3 was activated by IL‐6 in the melanoma cell lines tested.,However, the STAT3 inhibitor S3I‐201 failed to inhibit IL‐6‐induced WNT5A up‐regulation in HTB63 and A375 cells.,Nor did STAT3 siRNA silencing affect the expression of WNT5A.,In search of an alternative signaling mechanism, we detected IL‐6‐induced activation of p38‐MAPK in HTB63 and A375 cells.,The p38‐MAPK inhibitor SB203580 abolished the IL‐6‐induced WNT5A up‐regulation and blocked IL‐6‐induced melanoma cell invasion.,The latter effect could be rescued by the addition of recombinant WNT5A.,Notably, immunoprecipitation analysis revealed that only the p38α‐MAPK isoform was activated by IL‐6, and subsequent siRNA silencing of p38α‐MAPK abolished the IL‐6‐induced up‐regulation of WNT5A.,Taken together, we demonstrate a novel link between the two melanoma pro‐metastatic agents IL‐6 and WNT5A explaining how IL‐6 can increase melanoma cell invasion and thus promote the metastatic process.,This finding provides a basis for future therapeutic intervention of melanoma progression.,We provide a novel link between the melanoma pro‐metastatic agents IL‐6 and WNT5A.WNT5A signaling plays an important role in IL‐6‐induced melanoma cell motility.IL‐6 can increase WNT5A expression by STAT3‐independent signaling in melanoma cells.IL‐6‐induced WNT5A expression is mediated through p38α‐MAPK activation.,We provide a novel link between the melanoma pro‐metastatic agents IL‐6 and WNT5A.,WNT5A signaling plays an important role in IL‐6‐induced melanoma cell motility.,IL‐6 can increase WNT5A expression by STAT3‐independent signaling in melanoma cells.,IL‐6‐induced WNT5A expression is mediated through p38α‐MAPK activation.
Pigment epithelium-derived factor (PEDF), a member of the serine protease inhibitor (SERPIN) superfamily, displays a potent antiangiogenic and antimetastatic activity in a broad range of tumor types.,Melanocytes and low aggressive melanoma cells secrete high levels of PEDF, while its expression is lost in highly aggressive melanomas.,PEDF efficiently abrogates a number of functional properties critical for the acquisition of metastatic ability by melanoma cells, such as neovascularization, proliferation, migration, invasiveness and extravasation.,In this study, we identify hypoxia as a relevant negative regulator of PEDF in melanocytes and low aggressive melanoma cells.,PEDF was regulated at the protein level.,Importantly, although downregulation of PEDF was induced by inhibition of 2-oxoglutarate-dependent dioxygenases, it was independent of the hypoxia inducible factor (HIF), a key mediator of the adaptation to hypoxia.,Decreased PEDF protein was not mediated by inhibition of translation through untranslated regions (UTRs) in melanoma cells.,Degradation by metalloproteinases, implicated on PEDF degradation in retinal pigment epithelial cells, or by the proteasome, was also excluded as regulatory mechanism in melanoma cells.,Instead, we found that degradation by autophagy was critical for PEDF downregulation under hypoxia in human melanoma cells.,Our findings show that hypoxic conditions encountered during primary melanoma growth downregulate antiangiogenic and antimetastasic PEDF by a posttranslational mechanism involving degradation by autophagy and could therefore contribute to the acquisition of highly metastatic potential characteristic of aggressive melanoma cells.