High Glucose Promotes Tumor Invasion and Increases Metastasis Associated Protein Expression in Human Lung Epithelial Cells by Upregulating Heme Oxygenase 1 via Reactive Oxygen Species or the TGF b1/PI3K/Akt Signaling Pathway
Background: Growing evidence indicates that heme oxygenase 1 (HO 1) is up regulated in malignancies and subsequently alters tumor aggressiveness and various cancer related factors, such as high glucose (HG) levels. HO 1 expression can be induced when glucose concentrations are above 25 mM; however, the role of HO 1 in lung cancer patients with diabetes remains unknown. Therefore, in this study we investigated the promotion of tumor cell invasion and the expression of metastasis associated proteins by inducing the up regulation of HO 1 expression by HG treatment in A549 human lung epithelial cells. Methods: The expression of HO 1and metastasis associated protein expression was explored by western blot analysis. HO 1 enzymatic activity, reactive oxygen species (ROS) production and TGF b1 production were examined by ELISA. Invasiveness was analyzed using a Transwell chamber. Results: HG treatment of A549 cells induced an increase in HO 1 expression, which was mediated by the HG induced generation of reactive oxygen species (ROS) and transforming growth factor b1 (TGF b1) in a concentration and time dependent manner. Following the increase in HO 1 expression, the enzymatic activity of HO 1 also increased in HG treated cells. Pretreatment with N acetyl L cysteine (NAC) or with phosphatidylinositol 3 kinase (PI3K)/Akt inhibitors attenuated the HG induced increase in HO 1 expression. HG treatment of A549 cells enhanced the invasion potential of these cells, as shown with a Transwell assay, and increased metastasis associated protein expression. However, HO 1 siRNA transfection significantly decreased these capabilities. Conclusion: this study is the first to demonstrate that HG treatment of A549 human lung epithelial cells promotes tumor cell invasion and increases metastasis associated protein expression by up regulating HO 1 expression via ROS or the TGF b1/PI3K/Akt signaling pathway.
Cellular Physiology and Biochemistry