Dual Role of RACK1 in Airway Epithelial Cells: A Concomitant Regulator of TGF-β1 Induced Apoptosis and Epithelial Mesenchymal Transition

Background: Airway epithelial apoptosis and epithelial mesenchymal transition (EMT) are two crucial components of asthma pathogenesis, concomitantly mediated by TGF-β1. RACK1 is a downstream target gene of TGF-β1 shown to enhancement in asthma mice in our previous study. Methods: The Balb/c mice were sensitized with OVA twice and challenged with OVA every day for 7 days. Transformed human bronchial epithelial cells, BEAS-2B cells were cultured and exposure to recombinant soluble human TGF-β1 to induced apoptosis (30 ng/ml, 72 h) and EMT (10 ng/ml, 48 h) in vitro, respectively. siRNA and pharmacological inhibitors were used to evaluate the regulation of RACK1 protein in apoptosis and EMT. Western blotting analysis and immunostaining were used to detect the protein expressions in vivo, and in vitro. Findings: Our data showed that RACK1 protein levels were significantly increased in OVA challenged mice and TGF-β1 induced apoptosis and EMT of BEAS-2B cells. Knockdown of RACK1 (siRACK1) significantly inhibited apoptosis and decreased TGF-β1 up-regulated EMT related protein levels (N-cadherin and Snail) in vitro via suppression of JNK and Smad3 activation. Moreover, siSmad3 or siJNK impaired TGF-β1 induced N-cadherin and Snail up-regulation in vitro. Importantly, JNK gene silencing (siERK) also impaired the regulatory effect of TGF-β1 on Smad3 activation. Interpretation: Our present data demonstrate that RACK1 is a concomitant regulator of TGF-β1 induces airway apoptosis and EMT via JNK/Smad/Snail signaling axis. Therefore, our findings may provide a new insight into understanding the regulation mechanism of RACK1 in asthma pathogenesis. Funding Statement: This study was supported by the National Natural Science Foundation of China (No. 81470224 to Lihong Wan). Declaration of Interests: The authors declare no conflict of interest. Ethics Approval Statement: Animal ethics approval has been obtained from West China School of Basic Medical Sciences and Forensic Medicine.