探討survivin 與p53 在honokiol所誘發人類大腸癌細胞凋亡之調控作用

Abstract

Honokiol 是一種從木蘭樹萃取的小分子之雙酚類化合物，發現對各種不同的癌症具有抗癌活性，但honokiol之分子抗癌機制仍不清楚。本篇研究我們發現survivin 與p53 在honokiol所誘發的大腸癌細胞之凋亡扮演相反作用。處理honokiol 後會誘發RKO人類大腸癌細胞之細胞死亡和凋亡。有趣地，我們發現honokiol會同時誘發細胞凋亡之內在及外在路徑。honokiol會活化內在路徑中的caspase 9，也會引起外在路徑的DR5和caspase 8之活化，最後honokiol會造成細胞凋亡的下游蛋白分子caspase 3 的活化及PARP 蛋白的分解。此外，honokiol 會顯著地減少抗細胞凋亡蛋白survivin 的蛋白質和基因表現，當轉殖survivin的表現質體時，會對honokiol 所誘發的細胞毒性產生抗性。同時honokiol會增加p53 及其下游蛋白PUMA 的蛋白質表現。在p53 功能正常的HCT116 人類大腸癌細胞對honokiol所誘發的細胞毒性、細胞凋亡和survivin 的抑制作用，會比喪失p53的HCT116細胞更加敏感。以上結果顯示survivin 及p53在人類大腸癌細胞，參與調控honokiol所誘發的細胞凋亡，並擔任相反的調控作用。

Honokiol is a small biphenolic compound isolated from Magnoliaceous plants, which exerts antitumor activities in various cancers. However, the anticancer mechanisms of honokiol remain unclear. In this study, we show survivin and p53 displaying opposite roles on the honokiol-induced apoptosis in the human colon cancer cells. Treatment with honokiol increased the cell death and apoptosis in RKO colon cancer cells. Interestingly, honokiol induced both intrinsic and extrinsic apoptotic pathways. The intrinsic pathway of caspase 9 was activated by honokiol. Honokiol also elicited the activation of DR5 and caspase 8 in the extrinsic death receptor pathway. The downstream targets of caspase 3 and PARP proteins were cleaved for apoptotic induction. Moreover, honokiol markedly reduced anti-apoptotic survivin protein and gene expression. Transfection with a survivin-expressed vector resisted the honokiol-induced cancer cell death. Meanwhile, honokiol increased tumor suppressor p53 protein expression and its downstream protein PUMA. Additionally, HCT116 p53-wild type colon cancer cells were exhibited greater cytotoxicity, apoptosis and survivin inhibition than the p53-null cells following treatment with honokiol. These findings suggest that survivin and p53 display the opposite roles on the regulation of honokiol-induced apoptosis in the human colon cancer cells.