br Acknowledgements br Introduction Lung cancer treatment st
Introduction Lung cancer treatment strategies, especially molecular targeted therapy, have progressed rapidly. However, most established treatments are for adenocarcinoma of the lung, not for squamous cell carcinoma (SQCC). SQCC constitutes approximately 30% of lung cancers, with a prognosis that is worse than that of adenocarcinoma , . The number of molecular alternations in SQCC is larger than in adenocarcinoma, presumably because SQCC comprises a larger proportion of smokers . A large comprehensive cohort study of lung SQCC patients was conducted as part of The Cancer Genome Atlas (TCGA) project ; in that study, the mean somatic mutation rate was 8.1 per megabase (Mb), higher than with acute myelogenous leukemia (0.56 per Mb), breast carcinoma (1.0 per Mb), and colorectal carcinoma (3.2 per Mb). Considering these findings, difficulty treating SQCC is thought to be due mainly to various genetic alterations, so that it is unlikely that driver mutations exist. Based on that, discoidin domain receptor (DDR) 2 mutations and FGFR1 amplification have recently been reported from single-platform studies as candidate targets for molecular therapy , . The DDR2 gene is located in 1q23.3, and its product is a tyrosine kinase receptor for fibrillar collagen , , , . Under normal physiological conditions, it acts in cutaneous wound healing mediated by proliferation, chemotactic migration, and secretion of metalloproteinases and collagen by skin fibroblasts, and it also acts in bone development . DDRs have also been implicated in cancer progression, and DDR2 mutations have been found in SQCCs . Some of these mutations promote colony formation by NIH-3T3 mecamylamine in soft agar with the ectopic expression system, and shRNA targeting DDR2 reduces proliferation in cell lines carrying DDR2 mutation, suggesting that some DDR2 mutations, such as L63V in the discoidin domain and I638F in the tyrosine kinase domain, have oncogenic properties . DDR2 mutations are found in 4–5% of SQCCs and are located in at least fifteen different regions including the discoidin domain and the tyrosine kinase domain , , . Although Dasatinib, second generated BCR-Abl inhibitor, has already been actually used in clinical practice for chronic myeloid leukemia, it also inhibits tumor growth of lung SQCC cell lines that have DDR2 mutations , . Based on these results, it is concluded that DDR2 is a candidate for molecular targeting in lung SQCCs. However, DDR2 expression and mutation status, as well as the precise role of DDR2 in lung SQCC, have yet to be clarified. In this paper, we describe our investigation of DDR2 mutation status and DDR2 protein level in patients with lung SQCC and our examination of the biological function of DDR2 in vitro and in animal model experiments. DDR2 was overexpressed in 29% of lung squamous cell carcinoma, and mutations were sporadically observed. DDR2 overexpression promoted SQCC cell invasion in vitro and metastasis in the animal model, and those activities were reduced with the T681I DDR2 mutation, which we found among 44 primary lung SQCC samples and 7 lung SQCC cell lines. DDR2 phosphorylation induced by collagen treatment increased gene expression of several genes, including MMP-1, and c-Jun phosphorylation. We discuss the implications of these results for the possible use of DDR2 as a molecular target in the treatment of lung SQCC.
Material and methods
Discussion In this study, DDR2 protein level was elevated in 29% of lung SQCC patients, and a mutation of DDR2, T681I, was observed. Ectopic expression of DDR2 promoted cancer cell invasion of human SQCC cell line H226B. In an animal model, lung metastasis was significantly enhanced after transplantation of cells overexpressing DDR2 wild type, but metastatic potential was lower with the T681I mutation. Ectopic expression of DDR2 wild type induced MMP-1 mRNA expression accompanied with phosphorylation of c-Jun, whereas T681I did not. These results suggest that DDR2 overexpression is involved in cancer progression, including invasion and metastasis, and that DDR2 T681I is an inactivating mutation.