Papel de la serín-proteasa de membrana TMPRSS4 en el desarrollo de cáncer de pulmón

Resumen

Lung cancer is the most lethal type of cancer with a 5-year overall survival rate at around 15% of the cases, despite the implementation of novel targeted therapies. The high mortality rates of lung cancer are the consequence of late detection and the fact that current therapeutic regimes are not sufficiently effective to increase survival. Therefore, it seems clear that there is a need for the identification of novel therapeutic targets. TMPRSS4 is a serine-protease that is overexpressed in many tumors such as non-small cell lung cancer (NSCLC). The goal of the present study was to validate the prognostic value of TMPRSS4 in non-small cell lung cancer (NSCLC) and to study different aspects related to its protumorigenic role, as well as the regulation of its expression. Immunhistochemical studies in a series of 96 patients showed that high TMPRSS4 levels were significantly associated with lower disease-free survival (DFS) and overall survival (OS) at early stages. Overexpression of TMPRSS4 in cell lines resulted in increased invasion, migration, acquisition of both epithelial to mesenchymal (EMT) and cancer stem cell (CSC) phenotypes and tumor growth in vivo, thus demonstrating that this protease plays a protumorigenic role. The same results were obtained in both in vitro and in vivo experiments where murine TMPRSS4 was overexposed in lung cancer cells from a mouse model. We also studied the relationship between TMPRSS4 and miR-205, a microRNA regulated by this protease that promotes an epithelial phenotype. One striking result was that a group of phosphodiesterases (PDEs) were down-regulated in miR-205-overexpressing cells. We focused our study on PDE4D because this PDE is a potential target of miR-205, and because previous studies had shown high levels of PDE4D in lung cancer and its involvement in the acquisition of an EMT phenoype. We first validated that PDE4D was down-regulated in lung cancer cells with high miR-205 levels and that TMPRSS4 was down-regulated in these cells as well. By cloning the 3¿UTR (wild type and mutant sequences) and performing luciferase assays, we demonstrated that PDE4D is a direct target of miR-205. Finally, to study the regulation of TMPRSS4, we focused our experiments on studying its promoter. Promoter methylation analysis revealed that TMPRSS4 underwent aberrant hypomethylation in lung cancer specimens, as compared to non-malignant tissues. Hypomethylation status was significantly correlated with reduced DFS. Promoter hypomethylation was also found in a series of NSCLC cell lines, which inversely correlated with high TMPRSS4 expression (p<0.001). Such correlation was also found in patients. Treatment with the demethylating agent 5¿-Aza-2¿-Deoxycytidine in cells with promoter hypomethylation caused reexpression of TMPRSS4. Our results show that TMPRSS4 overexpression, which may be the consequence of promoter hypomethylation, increases malignancy and associates with poor prognosis in NSCLC.