我們實驗室過去已經證實collagen gel製造的軟性基質所引起的上皮細胞凋亡，主要是透過AP-1蛋白的表現失衡以及endoplasmic reticulum stress所造成的鈣離子恆定性的失衡所引起。為了進一步探討軟性基質所引起的上皮細胞凋亡的機制，我們利用polyacrylamide (PA) gel製造出不同軟硬度的基質。我們首先確認軟性基質所引起的細胞凋亡，只會發生在上皮細胞。我們發現PA gel所引起的上皮細胞凋亡的比率，會隨著細胞培養的基質軟硬度增加而減少， 1000 Pa大概是造成上皮細胞凋亡的基質軟硬度界限。軟性基質所造成的上皮細胞凋亡，與c-Jun蛋白的量的減少有關。而細胞中c-Jun蛋白的減少，主要是透過c-Jun ubiquitination的過程所造成，此一結果也與過去實驗室的發現一致。與過去研究結果略有不同的是，當上皮細胞培養在PA gel上，隨著軟硬度增加，細胞中的c-Fos、JNK蛋白的以及JNK的磷酸化程度均會隨之增加。此外基質軟硬度增加亦會提升上皮細胞中的c-Jun的量以及c-Jun磷酸化的程度，並與JNK的活性有關。利用phosphatase inhibitor抑制去磷酸化，可以避免軟性基質造成c-Jun量的減少。綜合上述實驗結果，我們發現軟性基質引發的上皮細胞凋亡，主要是透過減少JNK-c-Jun路徑的訊息傳遞而造成的。雖然PA gel與collagen gel對細胞凋亡有相同的效果，但是上皮細胞培養在PA gel上還可以引起與在collagen gel上完全不同的訊息傳遞機制。

Our previous studies have demonstrated that low-stiffness of collagen gel-induced epithelial cells apoptosis is mediated by deregulation of AP-1 proteins and endoplasmic reticulum stress-mediated disturbance of Ca2+ homeostasis. In order to elucidate to what extent and by what mechanism low rigidity induces apoptosis, we employed polyacrylamide (PA) gel to control substratum flexibility. We confirmed that low rigidity-induced apoptosis was only observed in epithelial cells. PA gel-induced apoptosis ratio was inversely correlated with substratum rigidity, and the threshold of substratum rigidity in triggering epithelial cell apoptosis was one thousand Pascal. In addition, low-rigidity of PA gel also induced c-Jun down-regulation, which is associated with c-Jun ubiquitination similar to the results observed by collagen gel. Interestingly, when cells were cultured on polyacrylamide gel, an increase in substratum rigidity augmented levels of c-Fos, JNK, and phosphorylation of JNK, unlike what was observed in cells cultured on collagen gel. Enhancement of substratum rigidity also up-regulated levels of c-Jun as well as phosphorylated c-Jun, which was dependent on JNK activation. In addition, augmentation of c-Jun phosphorylation by phosphatase inhibitor could prevent the degradation of c-Jun at various substratum rigidity. Taken together, these results indicate that low substratum rigidity triggers epithelial cell apoptosis through downregulation of JNK-c-Jun axis. As well as c-Jun ubiquitination and degradation, polyacrylamide gel elicits distinctive signal transduction mechanism from collagen gel.

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