| 摘要: | Peptidoglycan (PGN)革蘭氏陽性菌細胞壁上的主要成份，與大家所
熟知的革蘭氏陰性菌細胞壁成分lipopolysaccharide (LPS)一樣皆可造成發炎反應的物質，在免疫反應方面扮演著重要的角色。我們先前的研究已知PGN 在RAW 264.7 巨噬細胞誘導環氧化酶-2(cyclooxygenase-2, COX-2)的表現，可經由Ras/Raf-1/ERK 及NF-kB 的訊息傳遞而來(J. Biol. Chem., 279: 20889-20897, 2004)。本論文主要探討主題為Ras/PI3K/Akt 及p38 MAPK/MSK1 在PGN 誘導RAW 264.7巨噬細胞COX-2 蛋白表現中所扮演著的角色。PGN 誘導COX-2 表現會被PI3K抑制劑(wortmannin, LY 294002)，Ras 抑制劑manumycin A，Akt 抑制劑1L-6-Hydroxymethyl-chiro-inositol-2[(R)-2-O-methyl-3-octadecyl-
carbonate](Akt inh.)，p38 MAPK 抑制劑(SB 203580)和MSK1 抑制劑(Ro 318220)所抑制。而且PGN 會有時間相關性誘導IKK alpha/beta
，p38 MAPK 和MSK1 的活性及Akt Ser473、p65 Ser536 和Ser276 磷酸化的現象。加入manumycin A,LY 294002 及Akt inh.皆可抑制PGN 誘導Akt Ser473 和IKK alpha/beta磷酸化之現象，但是加入了manumycin A, LY 294002 和Akt inh.，並不會抑制PGN 誘導p65 Ser536的磷酸化。此外， p38 MAPK 抑制劑SB 203580 不同的濃度也不會抑制PGN 誘導p65 Ser536 的磷酸化；相反的， p38 MAPK 抑制劑SB203580 和MSK1 抑制劑Ro 318220，卻可以抑制PGN所誘導p65 Ser276磷酸化的現象。我們也利用轉染及報告基因的方法證實wortmannin,LY 294002, Akt inh, SB 203580 及Ro 318220 皆可以抑制由PGN 誘導kB-luciferase 的活性。接著我們更進一步證實PGN 可以依循時間相關性的誘導p85 alpha及Ras 與toll-like receptor 2 (TLR2)的結合。綜合以上的實驗結果，我們可以推測出PGN 可經由Ras/PI3K/Akt 的路徑活化IKK alpha/beta再活化NF-kB 來調控COX-2 蛋白表現，且又可經由p38 MAPK/MSK1這一條路徑經由p65 Ser276 的磷酸化，同樣活化NF-kB 來調控COX-2蛋白表現。
Peptidoglycan (PGN), a cell wall component of Gram-positive bacteria,can induce multiple similar responses in immune system as same as lipopolysaccharide (LPS) which is well known as a main cell wall component of Gram-negative bacteria caused inflammations. Our previous study shown that PGN induced cyclooxygenase-2 (COX-2) expression via Ras/Raf-1/ERK and NF-B signaling pathway in RAW 264.7 macrophages (J. Biol. Chem., 279:20889-20897, 2004). In this study, we investigated the roles of Ras/PI3K/Akt and p38MAPK/MSK1 on PGN-induced COX-2 expression in RAW 264.7 macrophages. PGN-induced COX-2 expression was inhibited by specific inhibitors of PI3K (wortmannin and LY294002), Ras inhibitor (manumycin A), Akt inh. (1L-6-Hydroxymethylchiro-inositol-2[(R)-2-O-methyl-3-O-octadecylcarbonate], p38 MAPK inhibitor (SB 203580) and MSK1 inhibitor (Ro 318220). Moreover, PGN induced IKK alpha/beta, p38 MAPK and MSK1 activity and increases in phosphorylation of Akt Ser473, p65 Ser536 and Ser276 in a time-depenednt manner. PGN induced increases in phosphorylation of Akt Ser473 and IKK alpha/beta on PGN-induced was inhibited by manumycin A, LY 294002 and Akt inh.. However, manumycin A, LY 294002 and Akt inh. did not inhibit PGN-induced p65 Ser536 phosphorylation. Inversely,PGN-induced p65 Ser276 phosphorylation was reduced by SB 203580 and Ro 318220 in RAW 264.7 macrophages. Moreover, PGN-induced kB-luciferase activity was inhibited by wortmannin, LY 294002, Akt inh., SB 203580 and Ro 318220. Further studies reveals that PGN induced the recruitment of p85 alpha and Ras to Toll-like receptor 2 (TLR2) in time-dependent manner. This propose demonstrate that two pathway
cross-link between Ras/PI3k/Akt and p38 MAPK/MSK1 to induce
IKK alpha/beta activity, p65 Ser536 and Ser276 phosphorylation and NF-kB activation, respectively and ultimately induce COX-2 expression in RAW 264.7 macrophages. |
