Crosstalk between protease-activated receptor 1 and platelet-activating factor receptor regulates melanoma cell adhesion molecule (MCAM/MUC18) expression and melanoma metastasis.

The cellular and molecular pathways that regulate platelet activation, blood coagulation, and inflammation are emerging as critical players in cancer progression and metastasis. Here, we demonstrate a novel signaling mechanism whereby protease-activated receptor 1 (PAR1) mediates expression of melanoma cell adhesion molecule MCAM/MUC18 (MUC18), a critical marker of melanoma metastasis, via activation of platelet-activating factor receptor (PAFR) and cAMP-responsive element-binding protein (CREB). We found that PAR1 silencing with small hairpin RNA inhibits MUC18 expression in metastatic melanoma cells by inhibiting CREB phosphorylation, activity, and binding to the MUC18 promoter. We further demonstrate that the PAF/PAFR pathway mediates MUC18 expression downstream of PAR1. Indeed, PAR1 silencing down-regulates PAFR expression and PAF production, PAFR silencing blocks MUC18 expression, and re-expression of PAFR in PAR1-silenced cells rescues MUC18 expression. We further demonstrate that the PAR1-PAFR-MUC18 pathway mediates melanoma cell adhesion to microvascular endothelial cells, transendothelial migration, and metastatic retention in the lungs. Rescuing PAFR expression in PAR1-silenced cells fully restores metastatic phenotype of melanoma, indicating that PAFR plays critical role in the molecular mechanism of PAR1 action. Our results link the two pro-inflammatory G-protein-coupled receptors, PAR1 and PAFR, with the metastatic dissemination of melanoma and suggest that PAR1, PAFR, and MUC18 are attractive therapeutic targets for preventing melanoma metastasis.

Long-term morpho-functional development of Helicobacter pylori-induced gastritis in Mongolian gerbils.

OBJECTIVE: Epidemiological studies have shown that Helicobacter pylori infection with associated chronic gastritis is the main risk factor for development of gastric cancer. The aim of this study was to investigate the long-term development of H. pylori-induced gastritis in Mongolian gerbils in terms of morphology, gastrin secretion, epithelial proliferation and gene expression of pro-inflammatory cytokines. MATERIAL AND METHODS: A total of 133 gerbils were inoculated with H. pylori and 62 served as controls. The gerbils were killed at different time-points between 6 and 94 weeks after inoculation. Serum concentrations of anti-H. pylori IgG and gastrin were determined by enzyme-linked immunoabsorbent assay (ELISA) and radioimmunoassay (RIA), respectively. Epithelial proliferation was evaluated immunohistochemically after labeling with 5-bromo-2'-deoxy-uridine. Gene expression of beta-actin, interleukin-1beta (IL-1beta) and tumor necrosis factor-alpha (TNF-alpha) were measured by real-time reverse transcriptase-polymerase chain reaction (RT-PCR). Histological parameters of gastritis were assessed semiquantitatively and expressed as a "gastritis score". RESULTS: Serum concentrations of anti-H. pylori IgG and gastrin increased over time. Epithelial proliferation in the antrum was increased 6 weeks after inoculation, followed by increased proliferation in the corpus 32 weeks after inoculation. Gene expression of IL-1beta and TNF-alpha were increased in H. pylori-infected gerbils. Beta-actin was not a reliable endogenous control for RT-PCR. With time, gastritis expanded from the antrum to the corpus and the gastritis score increased to reach a peak 32 weeks after inoculation. Pseudopyloric metaplasia (loss of specialized cells) was a characteristic feature in the corpus mucosa. Gastric ulcers, but neither dysplasia nor carcinoma, were observed during 94 weeks of infection. CONCLUSIONS: Long-term H. pylori infection in Mongolian gerbils led to progressive gastritis, glandular atrophy, hypergastrinemia, increased epithelial proliferation and elevated gene expression of pro-inflammatory cytokines.