Abstract
Calretinin (CR) is used as a positive marker for human malignant mesothelioma (MM) and is essential for mesothelioma cell growth/survival. Yet, the putative role(s) of CR during MM formation in vivo, binding partners or CR’s influence on specific signaling pathways remain unknown. We assessed the effect of CR overexpression in the human MM cell lines MSTO-211H and SPC111. CR overexpression augmented the migration and invasion of MM cells in vitro. These effects involved the activation of the focal adhesion kinase (FAK) signaling pathway, since levels of total FAK and phospho-FAK (Tyr397) were found up-regulated in these cells. CR was also implicated in controlling epithelial-to-mesenchymal transition (EMT), evidenced by changes of the cell morphology and up-regulation of typical EMT markers. Co-IP experiments revealed FAK as a new binding partner of CR. CR co-localized with FAK at focal adhesion sites; moreover, CR-overexpressing cells displayed enhanced nuclear FAK accumulation and an increased resistance towards the FAK inhibitor VS-6063. Finally, CR downregulation via a lentiviral shRNA against CR (CALB2) resulted in a significantly reduced tumor formation in vivo in an orthotopic xenograft mouse model based on peritoneal MM cell injection. Our results indicate that CR might be considered as a possible target for MM treatment.
Highlights
Malignant mesothelioma (MM) is a highly aggressive neoplasm that arises from mesothelial cells covering the surfaces of the pleura, peritoneum, and pericardium and is prevalently associated with asbestos exposure [1]
Our results demonstrate the essential role of CR in promoting migration, invasion and epithelial-to-mesenchymal transition (EMT) in vitro, likely with an involvement of focal adhesion kinase (FAK) signaling, since FAK protein levels and the activated phosphorylated form p-FAK (Tyr397) were up-regulated in CR-overexpressing cells
Since transient CR expression in the mesenchyme occurs during normal embryonic development of the mouse lung [23], and CR expression is increased in mice subjected to bleomycin treatment resulting in EMT [24], we investigated the effect of long-term CR overexpression in MM cells on EMT
Summary
Malignant mesothelioma (MM) is a highly aggressive neoplasm that arises from mesothelial cells covering the surfaces of the pleura, peritoneum, and pericardium and is prevalently associated with asbestos exposure [1]. There is no effective treatment so far; median overall survival following frontline chemotherapy with pemetrexed and cisplatin is approximately 12 months [2], early diagnosis is critical, and prolonged survival can be best achieved among patients who are candidates for surgery [1]. The development of MM occurs after a long latency period, suggesting that multiple (genetic) events are required for tumorigenic conversion of mesothelial cells [3]. Overexpression of CR in immortalized mesothelial cells protects them from acute asbestos-induced cytotoxicity www.oncotarget.com in vitro; an increased survival of asbestos-exposed CR-expressing mesothelial cells may promote and favor MM development [8]. Regulation of CR expression is cell type-specific [9], yet little is known on the mechanisms and effects of CR up-regulation during early stages of mesotheliomagenesis
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