Tumor Necrosis Factor–α (TNF-α) Induces Upregulation of RhoA via NF-κB Activation in Cultured Human Bronchial Smooth Muscle Cells

Abstract

RhoA plays an important role in Ca²⁺ sensitization of bronchial smooth muscle in antigen-induced airway hyperresponsiveness (AHR). Tumor necrosis factor–α (TNF-α), a major proinflammatory cytokine, is capable of inducing AHR, but the mechanisms for this are still unknown. In the present study, the effect of TNF-α on RhoA protein expression was examined in cultured human bronchial smooth muscle cells (hBSMCs). To investigate the role of NF-κB in the TNF-α–induced upregulation of RhoA, the effects of an inhibitor of IκB kinase (IKK), BMS-345541, were also determined. Both immunoblot and immunocytochemical analyses revealed that incubation of the hBSMCs with TNF-α caused an activation of NF-κB (determined by a translocation of p65 proteins to nuclei): the peak response was observed when cells were incubated with 10 ng/mL of TNF-α for 30 min. An upregulation of RhoA protein was also observed at 12 – 24 h after the incubation with TNF-α (10 ng/mL). Both the activation of NF-κB and upregulation of RhoA were concentration-dependently inhibited by the co-incubation with BMS-345541. These results suggest that TNF-α–induced upregulation of RhoA might be mediated by an activation of NF-κB in hBSMCs.