Nox2/ROS-dependent human antigen R translocation contributes to TNF-α-induced SOCS-3 expression in human tracheal smooth muscle cells

Elevated levels of TNF-α have been detected in the airway fluids, which may induce upregulation of inflammatory proteins. Suppressors of cytokine signaling (SOCS)-3 proteins can be induced by various cytokines and negatively regulated inflammatory responses. Although TNF-α has been shown to induce SOCS-3 expression, the mechanisms underlying TNF-α-induced SOCS-3 expression in human tracheal smooth muscle cells (HTSMCs) remain unclear. Here, we showed that TNF-α induced SOCS-3 expression, which was inhibited by pretreatment with the inhibitor of transcription level (actinomycin D), translation level (cycloheximide), JNK1/2 (SP600125), MEK1/2 (U0126), NADPH oxidase (Nox; apocynin and diphenyleneiodonium chloride), or reactive oxygen species (ROS; N-acetyl-L-cysteine) and transfection with siRNA of JNK1, p47^phox, p42, Nox2, or human antigen R (HuR). In addition, TNF-α-stimulated JNK1/2 and p42/p44 MAPK phosphorylation, Nox activation, and ROS generation were inhibited by pretreatment with U0126 or SP600125 and transfection with siRNA of JNK1 or p42. We further showed that TNF-α markedly induced HuR protein expression and translocation from the nucleus to the cytosol, which could stabilize SOCS-3 mRNA. Moreover, TNF-α-enhanced HuR translocation was reduced by transfection with siRNA of p42, JNK1, or p47^phox. These results suggested that TNF-α induces SOCS-3 protein expression and mRNA stabilization via a TNFR1/JNK1/2, p42/p44 MAPK/Nox2/ROS-dependent HuR signaling in HTSMCs. Lipopolysaccharide (LPS) has been shown to play a key role in inflammation via induction of adhesion molecules and then causes airway and lung injury. Moreover, we also demonstrated that overexpression of SOCS-3 protects against LPS-induced adhesion molecules expression and airway inflammation.