| Summary: | 碩士 === 台北醫學院 === 生物醫學技術研究所 === 90 === In this study, we investigated the role of cyclooxygenase-2 (COX-2) expression on lipoteichoic acid (LTA)-mediated nitric oxide synthase (iNOS) expression and NO release in murine RAW 264.7 macrophages. LTA caused concentration- and time-dependent increases in COX-2 expression and PGE2 release. LTA also induced iNOS expression and NO release; these events were inhibited by COX-2 inhibitors (indomethacin and NS-398), adenylyl cyclase (AC) inhibitor (DDA) or protein kinase A (PKA) inhibitor (KT-5720). Furthermore, PGE2 and cAMP analog (dibutyryl-cAMP) induced iNOS expression in dose- and time-dependent manners. Moreover, LTA caused time-dependent increases in NF-kB activation; this stimulatory effect was inhibited by indomethacin, NS-398 or KT-5720. These results suggest that LTA induced COX-2 expression and PGE2 release which in turn result in iNOS expression and NO release via the pathway of adenylyl cyclase, PKA and NF-kB. In addition to NF-kB activation, we further investigated the role of PGE2/PKA on the p44/42 and p38 mitogen-activated protein kinase (MAPK) activation caused by LTA. LTA induced p44/42 and p38 MAPK activation. Indomethacin and NS-398 reduced LTA-induced p44/42 MAPK and p38 MAPK activation. PGE2 and dibutyryl-cAMP also resulted in activations of p44/42 and p38 MAPK. However, dideoxyadenosine and KT-5720 reduced the PGE2-induced p38 MAPK activation, but not p44/42 MAPK. We demonstrate that LTA-induced COX-2-dependent PGE2 release and PKA activation contribute to p38 MAPK activation, but not p44/42 MAPK. Taken together, Lta might induce COX-2 expression and PGE2 release which in turn upregulates NF-kB activation, and finally induced iNOS expression and NO release. PGE2 might induce NF-kB activation or p38 MAPK activation via cAMP-PKA, which also resulted in p44/42 MAPK activation without cAMP-PKA pathway.
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