Abstract
Airway epithelial apoptosis and epithelial mesenchymal transition (EMT) are two crucial components of asthma pathogenesis, concomitantly mediated by TGF‐β1. RACK1 is the downstream target gene of TGF‐β1 shown to enhancement in asthma mice in our previous study. Balb/c mice were sensitized twice and challenged with OVA every day for 7 days. Transformed human bronchial epithelial cells, BEAS‐2B cells were cultured and exposed to recombinant soluble human TGF‐β1 to induced apoptosis (30 ng/mL, 72 hours) and EMT (10 ng/mL, 48 hours) 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. Our data showed that RACK1 protein levels were significantly increased in OVA‐challenged mice, as well as 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. Our present data demonstrate that RACK1 is a concomitant regulator of TGF‐β1 induces airway apoptosis and EMT via JNK/Smad/Snail signalling axis. Our findings may provide a new insight into understanding the regulation mechanism of RACK1 in asthma pathogenesis.
Highlights
Asthma is a complicated airway inflammatory disease characterized by airway remodelling resulting from epithelial damage, glandular hyperplasia and subepithelial fibrosis.[1]
We found that and Jun N-terminal kinase (JNK)/Smad[3] pathway contributed to Receptor for activated protein kinase C 1 (RACK1)-mediated airway epithelial mesenchymal transition (EMT) and epithelial apoptosis, while ERK pathway is mainly involved in regulating TGF-β1-induced EMT
We found that without TGF-β1 exposure, siRACK1 treatment had no effect on the protein expressions of epithelial and mesenchymal markers (E-cadherin, N-cadherin, α-SMA and Snail), suggesting that RACK1 did not induce EMT alone
Summary
Asthma is a complicated airway inflammatory disease characterized by airway remodelling resulting from epithelial damage, glandular hyperplasia and subepithelial fibrosis.[1]. To initiate tissue repair process, amounts of TGF-β1 secreted from eosinophil and bronchial epithelial cell increase epithelial vulnerability to allergens and trigger the activation of EMT,[10] which contributes to the subepithelial fibrosis in airway remodelling.[11]. Both of airway epithelial apoptosis and EMT are potently stimulated by TGF-β, even simultaneously regulated by TGF-β.6,12. To investigate the potential dual role of RACK1 in apoptosis and EMT of airway epithelial cells and the underlying mechanisms, OVAchallenged mice and TGF-β1-induced apoptosis and EMT model in BEAS-2B cells were used in this study. The data presented suggest that RACK1 is a novel concomitant regulator in modulating airway epithelial apoptosis and EMT in response to TGF-β1 stimulation via JNK/Smad[3]
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