Regulation of proteolytic activity induced by inflammatory stimuli in lung epithelial cells

A large number of chronic lung diseases such as asthma bronchiale are associated with alveolar and/or bronchial inflammation accompanied by a damage of the alveolocapillary barrier. In this process proteolytic mechanisms may play a crucial role. The aim of the present study was to assess the role of TNF-alpha on the proteolytic activity of pulmonary epithelial cells and to find possible intracellular signaling pathways which may mediate the effect of TNF-alpha. For our studies we have used the A549 human lung epithelial cell line. Plasminogen activator and metalloproteinase activity was measured using zymography. TNF-alpha induced a time and concentration dependent activation of the urokinase type plasminogen activator (u-PA) and tissue type plasminogen activator (t-PA) activity in A549 cells. This effect could be blocked completely by dexamethasone and was reduced significantly by the Rho-kinase inhibitor Y27632. Similarily, an increased activity in the culture medium of the 72 kDa MMP-2 in response to TNF-alpha could be observed as well. This could be reduced by dexamethasone and Y27632. Our results show that TNF-alpha is at least partly responsible for an increased proteolytic activity and beside corticosteroids Rho-kinase may constitute a potential target for future therapeutical approaches.