| Background and objectiveLung cancer is the most common cancer as well as the leading cause of cancer-related mortality in the world. It is a serious threat to human health. As the most common kind of lung cancer, lung adenocarcinoma has an increasing frequency in recent years. Approximately60to70percent of patients with lung adenocarcinoma already have a malignant pleural diffusion or distant metastasis at the time of diagnosis with poor prognosis. Metastatic lung adenocarcinoma cancer is responsible for the majority of lung cancer-related deaths. Nowadays, intensive efforts are underway to study the possible molecular mechanisms and develop therapeutics for the treatment of lung cancer metastasis. Hypoxia, defined as reduced O2levels, exists within a majority of solid tumor, including lung cancer. There is evidence that hypoxia is involved in in increased malignancy and distant metastasis. Cell migration is a key step of cancer metastatic progression. CapG was first isolated as a ubiquitous actin-binding protein and its over expression in endothelial cells and fibroblasts led to increased motility. In addition, our previous study showed that CapG protein could be significantly induced by hypoxia in hPASMCs. The expression of CapG in pancreatic cancer, oral squamous-cell carcinoma and ovarian carcinoma has been reported with different conclusions. The role of CapG in lung adenocarcinoma is contentious. In this study, we first detected the effect of hypoxia on CapG expression in lung adenocarcinoma cells and then evaluated the effect of inhibiting CapG expression by RNA interference on migration trait of these cells. Besides, the expression pattern of CapG protein in lung adencarcinoma tissues was analyzed.MethodsA549and H358cells were exposed to hypoxia in a hypoxia incubator (1%O2,94%N2, and5%CO2) for12h,24h,48h respectively, and then HIF-la and CapG expression were detected by western blot. Cells were transiently transfected with siRNA against CapG using lipofectamine-2000, and then the effect on migration and proliferation ability of cells under normoxia or hypoxia conditions was examined by Wound-healing assay, transwell chamber assay and MTT assay respectively. In addition, five μm thick microarray sections containing matched tumor tissue and adjacent non-tumor tissue cores from75patients were prepared from the paraffin-embedded tissues. Then the expression pattern and clinical significance of CapG protein in lung adencarcinoma tissues was analyzed by immunohistochemistry.ResultsCells were exposed to either normoxia or hypoxia (1%) for12h,24h and48h as indicated. CapG protein and HIF-1a protein were detected by western blot assay with GAPDH as loading control. HIF-la protein was served as a marker protein for effectiveness of hypoxia. The CapG protein expression level was remarkably increased in A549and H358cells after incubation under hypoxia for24h when compared with corresponding normoxia controls. The expression remains elevated until48h. As we found in wound healing assay and cell migration assay, cells transfected with si-CapG showed slower healing of the wound and reduced migration ability compared with negative control respectively, especially under hypoxia condition, while MTT assay showed no differences after transient transfection. Moreover, the excised lung adenocarcinoma tissues showed significantly increased immunoreactivity for CapG, compared to the adjacent tumor-free tissues. Overexpression of CapG is significantly associated with male sex (x2=5.195,p=0.033) and lymph node metastasis (x2=5.58, p=0.021). Likewise, CapG overexpression was observed with advanced tumor stages (Ⅲ and IV,16/31), compared with early tumor stages (Ⅰ and Ⅱ,14/44), but the difference was not statistically significant.ConclusionThe present study is the first to demonstrate that CapG expression is upregulated in human lung cancer cell lines under hypoxia and that CapG contributes to the migration ability of these cells. It is suggested that the interaction between the induction of CapG expression and the actin cytoskeleton may be involved in hypoxia-induced tumour cell migration. In addition, expression of CapG was significantly increased in lung adenocarcinoma tissues, compared to adjacent tumor-free tissues. The level of CapG expression also correlated with lymph node metastasis. Accordingly, CapG may play a play a critical role in the development and progression of lung adenocarcinoma cancer. It may be a promising target for therapy and a potential biomarker for predicting the prognosis of lung adenocarcinoma. |
PDF Full Text Request