熊果酸抗癌活性作用機轉之探討

Anti-cancer mechaniams of ursolic acid:characterization of cell cycle arrest and apoptotic machinery

鄭琪云(Chi-Yun Cheng)

指導教授 ： 吳永昌

高雄醫學大學/藥學院/天然藥物研究所碩士班/碩士(2007年)

摘要

本研究係利用天然藥用植物白花蛇舌草之成分熊果酸 (ursolic acod，UA)處理人類血癌細胞株(K562)的抗癌活性作用機轉。實驗結果顯示隨著UA濃度的上升和加藥時間的延長，UA確實抑制血癌細胞存活率。UA可以藉由活化p21及p27，而降低Cdk1的表現，在無法與cyclin A、B形成complex的情況下，使得細胞週期停滯在G2/M期。在細胞凋亡的誘導方面，藉由死亡受體 DR4 and DR5/caspase-8系統的活化，啟動粒線體相關的細胞凋亡途徑，其作用包括增加Bax的表現、降低Bcl-2及Bcl-xL的表現量並改變粒線體之結構而造成膜電位的瓦解，導致促進細胞凋亡的分子之釋放而引發下游的反應，包括促使Apaf-1和procaspase-9形成複合物，再活化下游之procaspase-3成活化之caspase-3，並且導致PARP cleavage，並誘發細胞凋亡，最終造成細胞死亡，進而抑制細胞的存活率。在MAPK訊息調控方面，UA會抑制p-38的磷酸化而促進JNK的磷酸化，利用特定MAPK的抑制劑前處理確實會降低UA的抗癌作用。綜上所述，UA是經由粒線體和死亡受體傳遞及MAPK訊息調控路徑誘發細胞凋亡，以達到具有抗血癌活性的作用。

關鍵字

rsolic acid ； G2/M細胞週期停滯 ； 細胞凋亡 ； 血癌細胞 ； MAPK

並列摘要

Ursolic acid (UA) is a pentacyclic triterpene compound which naturally occurs in a large variety of vegetarian foods, medicinal herbs and plants, such as Hedyotis diffusa Willd. We demonstrated that treatment of UA resulted in a significant decrease of the viability of K562 cells in a time- and dose-dependent manner with IC50 value of 23 µM, which was revealed as apoptosis accompanying with nuclear fragmentation and an increase in sub-G0/G1 fraction. UA suppressed the proliferation of cells, producing cell cycle arrest at G2/M phase, and this effect through the down-regulation of cyclin A, D, E, cdk1, cdc25B, cdc25C and up-regulation of cyclin B, cdk2, p21, and p27. In addition, catalytic activation of caspase-9, a characteristic phenomenon of mitochondrial dysfunction, including mitochondrial membrane potential (∆Ψm) transition, and decreased expression of anti-aptototic Bcl-2 and Bcl-xL proteins were observed in UA-treated cells. Catalytic activation of caspase-3 by UA was further confirmed by cleavage of pro-caspase-3 and intracellular substrates, including poly (ADP-ribose) polymerase (PARP). In contrast to the lack of appreciable effect on the phosphorylation of ERK and p38, activation of JNK was noted when K562 cells were exposed to UA. Taken together, these findings suggest that UA induces the apoptosis of K562 cells through signaling cascade of caspases pathway and the activation of MAPKs signaling pathways, followed by the induction cell cycle arrest and apoptosis, might be responsible for anticancer activities of UA.

並列關鍵字

Ursolic acid ； G2/M arrest ； apoptosi ； K562 cells ； MAPK

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