ABSTRACT
Melanoma is a rapidly growing and highly metastatic cancer with high mortality rates, for which a resolutive treatment is lacking. Identification of novel therapeutic strategies and biomarkers of tumour stage is thus of particular relevance. We report here on a novel biomarker and possible candidate therapeutic target, the sphingolipid metabolising enzyme acid sphingomyelinase (A-SMase). A-SMase expression correlates inversely with tumour stage in human melanoma biopsies. Studies in a mouse model of melanoma and on cell lines derived from mouse and human melanomas demonstrated that A-SMase levels of expression actually determine the malignant phenotype of melanoma cells in terms of pigmentation, tumour progression, invasiveness and metastatic ability. The action of A-SMase is mediated by the activation of the extracellular signal-regulated kinase, the subsequent proteasomal degradation of the Microphtalmia-associated transcription factor (Mitf) and inhibition of cyclin-dependent kinase 2, Bcl-2 and c-Met, downstream targets of Mitf involved in tumour cell proliferation, survival and metastatisation.
Subject(s)
Melanoma/pathology , Microphthalmia-Associated Transcription Factor/metabolism , Signal Transduction , Sphingomyelin Phosphodiesterase/metabolism , Animals , Cell Line, Tumor , Cell Movement , Cell Proliferation , Cyclin-Dependent Kinase 2/metabolism , Disease Progression , Down-Regulation , Female , Humans , Lung Neoplasms/pathology , Lung Neoplasms/secondary , Melanoma/metabolism , Melanoma, Experimental/metabolism , Melanoma, Experimental/mortality , Melanoma, Experimental/pathology , Mice , Mice, Inbred C57BL , Pigmentation , Proto-Oncogene Proteins c-bcl-2/metabolism , Proto-Oncogene Proteins c-met/metabolism , Sphingomyelin Phosphodiesterase/antagonists & inhibitors , Sphingomyelin Phosphodiesterase/geneticsABSTRACT
Scavenger phagocytes are mostly responsible for the in vivo clearance of activated or senescent platelets. In contrast to other particulate substrates, the phagocytosis of platelets does not incite proinflammatory responses in vivo. This study assessed the contribution of macrophages and dendritic cells (DCs) to the clearance of activated platelets. Furthermore, we verified whether antibodies against the beta2 Glycoprotein I (beta2GPI), which bind to activated platelets, influence the phenomenon. DCs did not per se intemalise activated platelets. In contrast, macrophages efficiently phagocytosed platelets. In agreement with the uneventful nature of the clearance of platelets in vivo, phagocytosing macrophages did not release IL-1beta, TNF-alpha, or IL-10, beta2GPI bound to activated platelets and was required for their recognition by anti-beta2GPI antibodies. DCs internalised platelets opsonised by anti-beta2GPI antibodies. The phagocytosis of opsonised platelets determined the release of TNF-alpha and IL-1beta by DCs and macrophages. Phagocytosing macrophages, but not DCs, secreted the antiinflammatory cytokine IL-10. We conclude that anti-beta2GPI antibodies cause inflammation during platelet clearance and shuttle platelet antigens to antigen presenting DCs.
Subject(s)
Antibodies/pharmacology , Dendritic Cells/immunology , Glycoproteins/immunology , Inflammation/chemically induced , Antibodies/isolation & purification , Blood Platelets/metabolism , Dendritic Cells/drug effects , Dendritic Cells/metabolism , Glycoproteins/metabolism , Humans , Immunoglobulin G/isolation & purification , Immunoglobulin G/pharmacology , Interleukin-1/analysis , Interleukin-1/metabolism , Interleukin-10/analysis , Interleukin-10/metabolism , Macrophages/immunology , Macrophages/metabolism , Macrophages/physiology , Phagocytosis/immunology , Platelet Activation , Tumor Necrosis Factor-alpha/analysis , Tumor Necrosis Factor-alpha/metabolism , beta 2-Glycoprotein IABSTRACT
OBJECTIVE: To verify whether the prototypical long pentraxin PTX3 represents an indicator of the activity of small-vessel vasculitis. METHODS: Concentrations of PTX3, a pentraxin induced in endothelium by cytokines, were measured by enzyme-linked immunosorbent assay in the sera of 43 patients with Churg-Strauss syndrome, Wegener's granulomatosis, and microscopic polyangiitis. PTX3 was also measured in the sera of 28 patients with systemic lupus erythematosus (SLE), 22 with rheumatoid arthritis, and 16 with CREST syndrome (calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly, telangiectasias). Serum concentrations of C-reactive protein (CRP) were measured by immunoturbidimetry. The cells involved in PTX3 production in vivo were identified in skin biopsy samples. RESULTS: Patients with active vasculitis had significantly higher concentrations of PTX3 than did those with quiescent disease (P < 0.001). PTX3 levels in the latter group were similar to those in healthy controls. PTX3 levels were higher in patients with untreated vasculitis and lower in patients who underwent immunosuppressive treatments (P < 0.005). In contrast, patients with active SLE had negligible levels of the pentraxin. PTX3 levels did not correlate with CRP levels in vasculitis patients. Endothelial cells produced PTX3 in active skin lesions. CONCLUSION: PTX3 represents a novel acute-phase reactant produced at sites of active vasculitis.
