黃芩素經由泛素-蛋白分解體降解路徑抑制survivin 蛋白的表現

Abstract

Survivin是一種抗細胞凋亡的蛋白，具有促進癌細胞存活與增生的功能。黃芩素會誘發癌細胞生長停止及促進細胞凋亡的作用，然而黃芩素調控survivin蛋白表現的機制仍然不清楚。在本研究中，我們探討BFTC905人類膀胱癌細胞處理黃芩素後，survivin的角色與調控機制。處理黃芩素明顯地抑制BFTC905細胞中survivin蛋白的表現。雖然如此，利用反轉錄聚合酶鏈反應與即時聚合酶鏈反應分析，發現黃芩素並不會影響survivin mRNA的表現量。利用蛋白質合成抑制劑cycloheximide處理後，會促進黃芩素減少survivin蛋白的表現量。相反地，處理一種蛋白分解體的抑制劑MG132，能部分回復黃芩素所抑制的survivin蛋白表現，並且MG132會降低黃芩素所誘發的細胞凋亡。有趣地，利用免疫沉澱分析發現黃芩素會誘發survivin蛋白進行泛素化作用，泛素化的survivin蛋白被黃芩素大量誘發。此外，共同處理黃芩素與oxaliplatin會加強對BFTC905細胞的毒殺作用及抑制survivin蛋白的表現。綜合以上結果，我們推測黃芩素抑制人類膀胱癌細胞中survivin蛋白表現，是經由泛素-蛋白分解體的降解路徑。

Survivn is an anti-apoptosis protein that plays the roles in promoting cancer cell survival and proliferation. Baicalein has been shown to induce growth inhibition and apoptosis in cancer cells; however, the regulation of survivin protein expression by baicalein remains unclear. In this study, we investigated the role and regulation of survivin following baicalein treatment in the BFTC905 human bladder cancer cells. Treatment with baicalein markedly inhibited survivin protein expression in BFTC905 cells. Nevertheless, the survivin mRNA level did not alter with baicalein treatment using reverse transcription-polymerase chain reaction (RT-PCR) and real-time PCR. Treatment with a protein synthesis inhibitor (cycloheximide) increased the decrease of survivin protein level in the baicalein-treated cells. In contrast, a specific proteasome inhibitor (MG132) partially restored baicalein-inhibited survivin protein expression. Moreover, MG132 can reduce apoptosis induction by baicalein. Interestingly, baicalein induced the protein ubiquitination of survivin using immunoprecipitation assays. The ubiquitinated survivin proteins were increased by baicalein. Besides, co-treatment of baicalein and oxaliplatin enhanced the cytotoxicity and survivin protein inhibition in BFTC905 cells. As a consequence, we suggest that baicalein inhibits survivn protein expression through the ubiquitin-proteasome degradation pathway in the human bladder cancer cells.