Cutaneous melanoma is one of the most aggressive cancers characterized by a high plasticity, a propensity for metastasis, and drug resistance. Melanomas are composed of phenotypically diverse subpopulations of tumor cells with heterogeneous molecular profiles that reflect intrinsic invasive abilities. In an attempt to identify novel factors of the melanoma invasive cell state, we previously investigated the nature of the invasive secretome by using a comparative proteomic approach. Here, we have extended this analysis to show that PTX3, an acute phase inflammatory glycoprotein, is one such factor secreted by invasive melanoma to promote tumor cell invasiveness. Elevated PTX3 production was observed in the population of MITFlow invasive cells but not in the population of MITFhigh differentiated melanoma cells. Consistently, MITF knockdown increased PTX3 expression in MITFhigh proliferative and poorly invasive cells. High levels of PTX3 were found in tissues and blood of metastatic melanoma patients, and in BRAF inhibitor-resistant melanoma cells displaying a mesenchymal invasive MITFlow phenotype. Genetic silencing of PTX3 in invasive melanoma cells dramatically impaired migration and invasion in vitro and in experimental lung extravasation assay in xenografted mice. In contrast, addition of melanoma-derived or recombinant PTX3, or expression of PTX3 enhanced motility of low migratory cells. Mechanistically, autocrine production of PTX3 by melanoma cells triggered an IKK/NFκB signaling pathway that promotes migration, invasion, and expression of the EMT factor TWIST1. Finally, we found that TLR4 and MYD88 knockdown inhibited PTX3-induced melanoma cell migration, suggesting that PTX3 functions through a TLR4-dependent pathway. Our work reveals that tumor-derived PTX3 contributes to melanoma cell invasion via targetable inflammation-related pathways. In addition to providing new insights into the biology of melanoma invasive behavior, this study underscores the notion that secreted PTX3 represents a potential biomarker and therapeutic target in a subpopulation of MITFlow invasive and/or refractory melanoma.
Bibliographical noteFunding Information:
Acknowledgements We thank RS Lo and R Ballotti for melanoma cells. We acknowledge the C3M animal and imaging (Microscopy and Imaging platform Côte d’Azur, MICA) facilities. This work was supported by Ligue Contre le Cancer, Fondation ARC, Fondation de France and the French Government (National Research Agency, ANR) through the “Investments for the Future” LABEX SIGNALIFE: program reference # ANR-11-LABX-0028-01. We also thank financial supports by Conseil Général des Alpes-Maritimes, Canceropôle PACA and Région PACA. MR was a recipient of a post-doctoral fellowship from Fondation ARC. The Marseille Proteomic facility (MaP; http:// map.univmed.fr/) is supported by IBiSA (Infrastructures Biologie Santé et Agronomie), Canceropôle PACA, Région PACA, and Institut Paoli-Calmettes.