Elucidating the molecular mechanism of ATP synthase inhibitor citreoviridin on anti-proliferative activity of breast cancer cells

ATP 合成酶在所有生物體中皆存在，且通常位於真核細胞粒線體的內膜上。我們先前的研究發現，相較於正常細胞，ATP合成酶在乳癌組織中表現量較高，且在腫瘤細胞表面上出現 (Journal of Proteome Research, 2008)。在此我們發現citreoviridin在MCF-7細胞中能顯著地抑制增生，原因可能為其具有促進細胞週期停滯之能力。為了能更清楚的闡述citreoviridin的機制，我們設計了一個結合二維電泳與基質輔助雷射脫附游離質譜儀的蛋白質體學實驗。藉由比較加入citreoviridin與對照組的蛋白質體，我們發現表現量出現明顯差異的蛋白質主要與蛋白質的摺疊有關。累積大量的未折疊蛋白在內質網的內膜上會活化未折疊蛋白質反應並造成細胞週期停滯在G0/G1期。我們證明citreoviridin可使細胞週期停滯在G0/G1期是藉由引發未折疊蛋白質反應，造成eIF2α的磷酸化並抑制轉譯，最後阻礙一般蛋白質合成，當中包括細胞週期調節因子cyclin D1和retinoblastoma蛋白。最後的結果證明citreoviridin這個ATP合成酶抑制劑是一具有潛力的乳癌治療藥物。ATP synthase presents in all organisms and usually located on the membrane of mitochondria of eukaryotic cells. Our previous study showed that ATP synthase was upregulated in breast cancer tissues and could be expressed on tumor cell surface more than on normal cell surface (Journal of Proteome Research, 2008). Here, we found that citreoviridin displayed significant anti-proliferative activity in MCF-7 cells, which may be attributed to its induction of cell cycle arrest. To further elucidate the mechanism of citreoviridin, we performed a proteomic study combining two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. By comparing citreoviridin-treated and control proteome profiles of MCF-7 cells, we found the major function of these differential expressed proteins was related to protein folding. Accumulation of unfolded proteins in the lumen of the ER could activate the unfolding protein response (UPR), which could induce cell cycle arrest at G0/G1 phase. We demonstrated that citreoviridin could induce cell cycle arrest at G0/G1 phase through triggering of UPR, the phosphorylation of eIF2α and induction of translational inhibition, thereby blocking general protein synthesis including the cell cycle regulator cyclin D1 and retinoblastoma protein. Our results showed that ATP synthase inhibitor citreoviridin could be a potential drug for breast cancer therapy