2-aminopurine suppresses the TGF-β1-induced epithelial–mesenchymal transition and attenuates bleomycin-induced pulmonary fibrosis

Cell Death Discovery, Feb 2018

The epithelial–mesenchymal transition (EMT) is a multifunctional cell process involved in the pathogenesis of numerous conditions, including fibrosis and cancer. Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal disease characterized by fibroblast accumulation and collagen deposition in the lungs. The fibroblasts involved in this process partially originate from lung epithelial cells via the EMT. Evidence suggests that the EMT contributes to progression, invasion, and metastasis of various types of cancer. We screened a series of 80 compounds for the ability to interfere with the EMT and potentially be applied as a therapeutic for IPF and/or lung cancer. We identified 2-aminopurine (2-AP), a fluorescent analog of guanosine and adenosine, as a candidate in this screen. Herein, we demonstrate that 2-AP can restore E-cadherin expression and inhibit fibronectin and vimentin expression in TGF-β1–treated A549 lung cancer cells. Moreover, 2-AP can inhibit TGF-β1-induced metastasis of A549 cells. This compound significantly attenuated bleomycin (BLM)-induced pulmonary inflammation, the EMT, and fibrosis. In addition, 2-AP treatment significantly decreased mortality in a mouse model of pulmonary fibrosis. Collectively, we determined that 2-AP could inhibit metastasis in vitro by suppressing the TGF-β1-induced EMT and could attenuate BLM-induced pulmonary fibrosis in vivo. Results of this study suggest that 2-AP may have utility as a treatment for lung cancer and pulmonary fibrosis.

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2-aminopurine suppresses the TGF-β1-induced epithelial–mesenchymal transition and attenuates bleomycin-induced pulmonary fibrosis

Abstract The epithelial–mesenchymal transition (EMT) is a multifunctional cell process involved in the pathogenesis of numerous conditions, including fibrosis and cancer. Idiopathic pulmonary fibrosis (IPF) is a progressive and fatal disease characterized by fibroblast accumulation and collagen deposition in the lungs. The fibroblasts involved in this process partially originate from lung epithelial cells via the EMT. Evidence suggests that the EMT contributes to progression, invasion, and metastasis of various types of cancer. We screened a series of 80 compounds for the ability to interfere with the EMT and potentially be applied as a therapeutic for IPF and/or lung cancer. We identified 2-aminopurine (2-AP), a fluorescent analog of guanosine and adenosine, as a candidate in this screen. Herein, we demonstrate that 2-AP can restore E-cadherin expression and inhibit fibronectin and vimentin expression in TGF-β1–treated A549 lung cancer cells. Moreover, 2-AP can inhibit TGF-β1-induced metastasis of A549 cells. This compound significantly attenuated bleomycin (BLM)-induced pulmonary inflammation, the EMT, and fibrosis. In addition, 2-AP treatment significantly decreased mortality in a mouse model of pulmonary fibrosis. Collectively, we determined that 2-AP could inhibit metastasis in vitro by suppressing the TGF-β1-induced EMT and could attenuate BLM-induced pulmonary fibrosis in vivo. Results of this study suggest that 2-AP may have utility as a treatment for lung cancer and pulmonary fibrosis. Introduction The epithelial–mesenchymal transition (EMT) is a multifunctional cell process characterized by loss of cell polarity, loss of cell–cell adhesion, detachment from the basal lamina, cytoskeletal rearrangement, and migration into the provisional matrix1. These vast phenotypic shifts are accompanied by significant changes in molecular expression and signal transduction within cells, including downregulation of E-cadherin (a biomarker of epithelial cells) and upregulation of fibronectin and vimentin (biomarkers of mesenchymal cells)2. To ascertain the occurrence of the EMT, the following molecular hallmarks are commonly assessed: increased nuclear localization of β-catenin; increased expression of N-cadherin, fibronectin, vimentin, and Snail1/2; and decreased production of E-cadherin, desmoplakin, cytokeratin, and occludin3. TGF-β1 is a potent inducer of the EMT that is common to Smad and non-Smad signaling pathways. TGF-β1 signaling directly activates expression of the EMT-associated transcription factors Snail, Slug, and Twist14. A transcriptional complex comprising Smad3/Smad4 and Snail can bind to regulatory promoter sequences of the genes that encode the epithelial-junction proteins E-cadherin and occludin. This results in TGF-β1–mediated repression of gene expression5. In addition, TGF-β1 regulates the expression of matrix metalloproteinases (MMPs), such as MMP2 and MMP9, and of components of the extracellular matrix, such as fibronectin and collagens, by activating EMT-associated transcription factors6. TGF-β1-induced non-Smad signaling also promotes the EMT. Specifically, TGF-β1 activates the PI3K/Akt/mTOR pathway, thereby producing increased protein synthesis, motility, and cell invasion during the EMT by means of mTOR complex 17. Other growth factors also can synergize with TGF-β1 signaling to facilitate the EMT; these include epidermal growth factor and fibroblast growth factor, which act through receptor tyrosine kinases and are released into the epithelial cell microenvironment8. The EMT is crucial for in the pathogenesis of many conditions, including fibrosis and cancer. Idiopathic pulmonary fibrosis (IPF) is a chronic and often lethal disease that involves progressive scarring, or fibrosis, of the lungs. Patients with IPF have a mean survival time of 2–3 years from diagnosis9. In the United States, ~50,000 new cases of IPF are diagnosed each year, and as many as 40,000 Americans die from IPF annually9. Despite efforts to understand IPF, the etiology and epidemiology of this condition have not been elucidated fully. The excessive fibrosis in IPF is attributable, at least in part, to enhanced formation and survival of fibroblasts. These cells are the primary source of extracellular matrix proteins, such as fibronectin and collagens10. Accumulation of extracellular matrix proteins leads to irreversible destruction of the lung parenchyma and a progressive decline in lung function11. Because fibroblast expansion and concomitant deposition of collagen fibrils are key processes in IPF, much attention has been given to understanding molecular mechanisms that lead to fibroblast proliferation and synthesis of matrix proteins. In addition to proliferation of lung-resident fibroblasts, fibrogenic fibroblasts originate from lung epithelial cells via the EMT12, 13. Lung cancer is relatively common and is the leading cause of death among patients with cancer. Approximately 90% of lung cancer deaths (...truncated)


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Dong Weng, Jian-xia Chen, Hao-hao Li, Feng Liu, Li-dan Zhou, Hai-peng Liu, Rui-juan Zheng, Yan Jiang, Zhong-hua Liu, Baoxue Ge. 2-aminopurine suppresses the TGF-β1-induced epithelial–mesenchymal transition and attenuates bleomycin-induced pulmonary fibrosis, Cell Death Discovery, 2018, Issue: 4, DOI: 10.1038/s41420-017-0016-3