Tangeretin 抑制IL-1β誘發肺癌環氧化酵素(COX-2)表現之機制探討

Abstract

Tangeretin 為柑橘類果皮中含量最豐富的多甲氧基類黃酮 ( polymethoxylated flavonoid )。 在近幾年的研究中， tangeretin 已被發現具有抗細胞生長、抗癌細胞侵襲與轉移、以及抗氧化的功能。 然而在抗發炎部分的研究則不甚明瞭。 在本篇論文中，我們研究 tangeretin 及其構造相似物 nobiletin 對發炎反應高度相關的環氧化酵素(Cyclooxygenase-2 ,COX-2 )表現的調控。我們使用的細胞為 : 肺癌上皮細胞( A549 ) 和非小細胞型肺癌細胞 (H1299)。實驗結果發現，不論是tangeretin 或 nobiletin 都能有效抑制介白素-1β (IL-1β) 所引發的 COX-2 表現，而且 tangeretin 的抑制效果明顯優於 nobiletin。 同時我們發現 tangeretin 對抑制細胞內生性 COX-2 的表現也有同樣的效果。進一步的研究也看到tangeretin 能有效抑制 IL-1β 活化的細胞激酶 : p38、JNK、AKT，並且可藉由抑制 IL-1β 活化 p38 及 AKT 而調控轉錄因子 NF-kappaB 的活化，進一步達到抑制 COX-2 的效果。綜合我們的研究結果，我們推測 tangeretin 藉由抑制 p38 及 AKT 等激酶的活性，進而抑制轉錄因子 NF-kappaB 的活化，使得 COX-2 基因的轉錄受到部份抑制，最後造成肺癌細胞中 COX-2 蛋白表現量的下降。

Tangeretin (5,6,7,8,4’-pentamethoxyflavone) is a polymethoxylated flavonoid concentrated in the peel of citrus fruits. Recent studies have shown that tangeretin exhibits anti-proliferative, anti-invasive, anti-metastatic, and antioxidant activities. However, the anti-inflammatory properties of tangeretin are unclear. In this study, we examine the effects of tangeretin and its structure-related compound, nobiletin, on the expression of cyclooxygenases-2 (COX-2) in human lung epithelial carcinoma cells, A549, and human non-small cell lung carcinoma cells, H1299. Tangeretin exerts a much better inhibitory activity than nobiletin against IL-1beta-induced production of COX-2 in A549 cells, and it effectively represses the constitutively-expressed COX-2 in H1299. RT-PCR was used to investigate the transcriptional inhibition of COX-2 by tangeretin. COX-2 mRNA was rapidly induced by IL-1β in 3 h and markedly suppressed by tangeretin. IL-1β induced the activation of ERK, p38 MAPK, JNK, and AKT in A549 cells. COX-2 expression in response to IL-1beta was attenuated by pretreatment with SB203580, SP600125, and LY294002, but not with PD98059, suggesting the involvement of p38 MAPK, JNK, and PI3K in this response. Pretreatment of cells with tangeretin inhibited IL-beta-induced p38 MAPK, JNK, and AKT phosphorylation and the downstream activation of NF-kappaB. These results may reveal that the tangeretin inhibition of IL-1beta-induced COX-2 expression in A549 cells is, at least in part, mediated through suppression of NF-lappaB transcription factor as well as through suppression of the signaling proteins of p38 MAPK, JNK, and PI3K, but not of ERK.