細胞中，粒線體負責許多重要的生化反應，包括能量的產生、脂質代謝、鈣離子訊息傳遞以及細胞凋亡路徑。粒線體同時也是內生性氧自由基主要產生者。在許多種癌細胞中，粒線體 DNA皆展現較高的突變率；在其他研究中亦指出，對化療藥物有抗藥性的細胞，其粒線體功能明顯低下。之前的研究發現到PC14PE6/ AS2 (萃取自老鼠肺積水的人類肺腺癌細胞株)對paclitaxel明顯較具抗性： PC14PE6/ AS2為一STAT 3持續活化的細胞株，在paclitaxel處理下，PC14PE6/ AS2細胞內STAT 3的活化情況更加顯著，PC14PE6/ AS2細胞內的氧自由基的數量亦明顯上升，而且此氧自由基主要來自粒線體；然而氧自由基以及粒線體本身在化療抗藥性機轉上所扮演的角色，目前仍不清楚。這次研究主要以PC14PE6/ AS2抗藥性細胞株為模式，來探討在肺腺癌細胞對化療藥物的反應中，氧自由基的參與途徑，以及粒線體所扮演的角色為何。結果顯示與其他肺癌細胞株相比 (A549, H460)，PC14PE6/ AS2細胞在粒線體DNA的D-loop區域明顯具有較高的突變率。利用DCFH螢光染劑，發現到PC14PE6/ AS2細胞亦具有較高量內生性氧自由基。在經過H2O2的處理下，MTT分析顯示氧化壓力並不會造成PC14PE6/ AS2細胞的死亡；PC4PE6/ AS2的STAT 3 變種細胞株AS2/ S3D對氧化壓力所誘發的細胞死亡較具抗性，顯示PC14PE6/ AS2的抗藥性機轉，STAT 3並非唯一構成因子。在分析PC14PE6/ AS2細胞內由氧化壓力所誘發的粒線體主導性細胞凋亡時，由Annexin V染色結果、caspase 3和caspase 9的活化數據顯示出和其他肺癌細胞 (A549, H460)相比，PC14PE6/ AS2細胞對氧化壓力所誘發的細胞凋亡較具抗性。以上結果顯示氧化壓力在PC14PE6/ AS2細胞的化療抗藥性的產生扮演重要的角色，並且進一步發現PC14PE6/ AS2細胞亦展現較低下的粒線體ATP生合成速率。已知Akt的活化會往下啟動相當多的利於細胞生存的訊息傳遞路徑，同時亦會阻斷細胞凋亡路徑，以提供細胞較佳的生存優勢。由結果顯示在處理H2O2後，細胞的Akt活化狀態更加明顯；當PC14PE6/ AS2細胞處在氧化壓力下，PI3K/ Akt 抑制劑 (LY294002)的加入會使PC14PE6/ AS2凋亡細胞增多。綜合以上結果，我們證實PC14PE6/ AS2具有較高的粒線體DNA突變率，承受較高的內生性氧化壓力；在面對氧化壓力所引起的細胞死亡，PC14PE6/ AS2細胞明顯較具抗性，並推測氧化壓力藉由活化PC14PE6/ AS2細胞內的如Akt等促進細胞生存的訊息傳導途徑，來提供PC14PE6/ AS2較佳的生長優勢。

Mitochondria play important roles in cellular metabolism, including energy supply, biochemical reactions, signal transduction and apoptosis. It is well documented that mitochondrial DNA mutation rates are significantly enhanced in cancer cells. Recent studies have shown that the cancer cells defective in mitochondrial functions are resistant to chemotherapeutic drugs. A lung adenocarcinoma cell line PC14PE6/ AS2, isolated from pleural effusion, has been reported resistant to chemotherapeutic drugs including paclitaxel. Recent studies found that in PC14PE6/ AS2 cells treated with paclitaxel abundant reactive oxygen species (ROS) were produced. In this study we investigated on the potential roles of mitochondria in response to chemotherapy. We found that the PC14PE6/ AS2 cells displayed higher mutation rates on the mitochondrial D loop than the other lung cancer cell lines did (A549, H460). The PC14PE6/ AS2 cells also displayed higher intracellular ROS levels, as shown by DCFH staining methods. However, the oxidative stress did not cause cell death in the PC14PE6/ AS2 cells, as they were
highly resistant to hydrogen peroxide treatment. The PC14PE6/ AS2 cells were also defective in oxidative stress-induced apoptosis and activations of caspases 3 and 9. And the deficiency of apoptotic pathway induced by ROS probably plays an important role for chemo-resistance of PC14PE6/ AS2 cells. PC14PE6/ AS2 cells with higher mitochondrial DNA mutation rates also displayed lower efficiency of mitochondrial ATP synthesis. It is known that oxidative stress activates Akt, which provides many survival signaling and stops apoptotic pathway. We found that in PC14PE6/ AS2 cell, the activation of Akt was much higher after hydrogen peroxide treatment. In PI3K/ Akt inhibitor-treated PC14PE6/ AS2 cells, the activation of Akt was inhibited and apoptotic cells were increased. These data indicated that pro-survival signalings (eg. Akt) activated by oxidative stress provided PC14PE6/ AS2 survival advantage, which was suggested as a contributor in chemo-resistance.

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