Arsenic is a well-known human carcinogen which is closely associated with lung cancer. However, the mechanism underlying the arsenic-induced carcinogenesis remains to be elucidated. The alterations of miRNAs profiles in cancers have profound implication in cancer development. However, it remains to be determined whether the alterations of miRNA signature in response to carcinogens such as arsenic may result in cell malignant transformation and tumor growth. In this study, we developed an in vitro model by transforming human lung epithelial BEAS-2B cells through long-term exposure to low concentration of arsenic. The BEAS-2B cells were malignantly transformed validated by cell proliferation, anchorage independent growth and tumor growth assay. By utilizing this model, we found that miR-199a-5p expression level was dramatically repressed in arsenic-transformed cells. Re-expression of miR-199a-5p impaired arsenic-induced tumor angiogenesis through directly targeting hypoxia inducible factor-1α (HIF-1α). Interestingly, we found another proangiogenic factor cyclooxygenase-2 (COX-2) that was also upregulated in arsenic-transformed cells and was predicted as a target of miR-199a-5p. It was confirmed by generating COX-2 3’UTR miRNA luciferase reporters with wild-type or mutant binding sites with miR-199a-5p. Overexpression of miR-199a-5p inhibited COX-2 protein expression. Functional study revealed that knockdown of COX-2 by siRNA in arsenic-transformed cells decreased tumor angiogenesis. We further showed that the COX-2 promoter contains a functional hypoxia response element (HRE). HIF-1α regulated COX-2 expression at the transcriptional level via direct binding to the HRE (-576/-584) located within the COX-2 promoter. Thus, arsenic-induced COX-2 activation is mediated by repression of miR-199a-5p and activation of HIF-1. Moreover, prostaglandin E2 (PGE2), a product of COX-2 regulated HIF-1 expression in a positive-feedback manner. In addition, arsenic-transformed cells have high levels of reactive oxygen species (ROS) for activating COX-2 pathway. Taken together, our results demonstrate that arsenic-induced angiogenesis through miR-199a-5p repression and pro-inflammatory responses induced by ROS. Both pathways lead to activation of HIF-1/COX-2 pathway. These findings establish critical roles of miR-199a-5p and its downstream targets HIF-1/COX-2 in arsenic-induced tumor angiogenesis. As miR-199a-5p is generally downregulated, whereas COX-2 is overexpressed in human lung cancer tissues, they may be used as new therapeutic targets for lung cancer treatment in the future.
Citation Format: Jun He, Richard Carpenter, Yue Jiang, Qing Xu, Bing-Hua Jiang. Roles of miR-199a-5p and COX-2 in arsenic-induced tumor angiogenesis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3592. doi:10.1158/1538-7445.AM2013-3592