細胞膜上的死亡受體TRAIL-R1（DR4）在人參皂□Rh2誘導肺腺癌細胞凋亡的過程扮演重要的角色

A STUDY OF THE CITICAL ROLE OF TRAIL-R1 (DR4) IN RH2-TRIGGERED APOPTOSIS IN HUMAN LUNG ADENOCARCINOMA A549 CELLS

Rh2 是從紅參中萃取出來的一種二醇類人參皂{^FA6C^}，在過去的研究中發現其對於某些種類的癌細胞具有抑制癌細胞增殖（ antiproliferative effect）的作用，但其抗癌的分子作用機轉尚有未清楚之處，本文以肺腺癌（ A549）細胞作為研究，探討 Rh2 是否會對其生長造成影響，並進一步探討其分子作用機轉。 Rh2 處理後的肺腺癌細胞不論是在細胞形態上或是 TUNEL assay 及 DNA fragmentation analysis 都發現 Rh2 會造成肺腺癌細胞的凋亡，我們進一步探討其凋亡路徑，分析了 Bcl-2 家族相關分子，發現其表現量無多大的變化，其凋亡路徑與粒線體凋亡路徑的 Bcl-2家族無關。但分析了細胞膜上的死亡受體路徑，發現 TRAIL-R1（ DR4）的表現量增加，所以其凋亡路徑可能走的是細胞膜上的死亡受體路徑。在劊蛋白{^FAF0^}（ caspase）方面， caspase-2, -3及 -8 有被活化的現象，若加入 caspase-8 的抑制劑則會影響 caspase-2 及 -3 的活化，所以可能是先活化了 caspase-8，之後再活化 caspase-2 及 -3。Ginsenoside Rh2 (Rh2), a purified ginseng saponin, has been shown to have antiproliferative effects in certain cancer cell types. However, the molecular mechanisms of Rh2 on cell growth and death have not been fully clarified. In this study, the anti-proliferative effect of Rh2 in human lung adenocarcinoma A549 cells was investigated. Rh2-induced apoptosis was confirmed by TUNEL assay and DNA fragmentation analysis. Results show that the administration of Rh2 caused an increase in the expression level of TRAIL-R1 (DR4) death receptor but did not alter the level of other death receptors and Bcl-2 family molecules. Furthermore, the Rh2-induced apoptosis was significantly inhibited by DR4: Fc fusion protein, which inhibited the TRAIL-DR4-mediated apoptosis. In addition, the caspase-2, -3 and -8 were drastically activated upon Rh2 treatment. The inhibitors of caspase-2, -3, and caspase-8 markedly prevented the cell death induced by Rh2, and the inhibitor of caspase-8 also significantly inhibited the activation of caspase-2, -3 and -8. This suggest that the increase in the expression level of DR4-death receptor may play a critical role in the initiation of Rh2-triggered apoptosis, and the activation of caspase-8/caspase-3 cascade also acts as the executioner of the Rh2-induced death process.