| Summary: | 碩士 === 長庚大學 === 基礎醫學研究所 === 90 === Bradykinin (BK) is a nonapeptide that is released in response to inflammation. There is an elevated level of kinins in bronchoalveolar lavage (BAL) fluid of allergic asthmatic patients under allergen challenge. BK appears to be involved in the pathogenesis of asthma. Inhaled BK constricts the bronchus of asthmatic patients, however there is little or no effect in normal individuals, suggesting the possibility of airway epithelial cell involvements. Studies within the last decade have revealed that airway epithelial cells act not only as a physical barrier but also play a significant role in the inflammation process by generating inflammatory mediators including arachidonic acid metabolites. BK has been shown to increase the secretion of prostaglandins and expression of cyclooxygenase-2 (COX-2) in a variety of cells. However the mechanisms are not completely understood in tracheal epithelial cells (TECs). Thus, the experiments were designed to determine the mechanisms of COX-2 expression induced by BK in cultured canine TECs, using Western blot and specific antibodies. The results show that BK induced phosphorylation of p42/p44 MAPK and COX-2 expression in a concentration- and time-dependent manner. Pretreatment of the cells with Hoe 140 (an antagonist of B2 receptor), U73122 (an inhibitor of PI-PLC), D609 (an inhibitor of PC-PLC), BAPTA/AM plus EGTA (intra- and extra-cellular Ca2+ chelator), GF109203X (a PKC inhibitor), U0126 and PD98059 (MEK1/2 inhibitors), and wortmannin and LY294002 (PI3K inhibitors) attenuated the phosphorylation of p42/p44 MAPK and COX-2 expression. These responses were not affected by pretreatment with CTX (a Gs protein sensitive toxin) and PTX (a Gi protein sensitive toxin), suggesting that BK activates MAPK pathway via a Gq protein. These results suggest that BK induced COX-2 expression in cultured canine TECs may be mediated through activation of p42/p44 MAPK and were modulated by B2 receptor, Gq protein, PLC, Ca2+, PKC, MEK1/2, and PI3K. Finally, protein synthesis inhibitors cycloheximide and actinomycin D attenuated COX-2 expression, suggesting that protein synthesis is involved in the COX-2 expression induced by BK.
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