在珍核細胞中，存在有一系列圍繞在細胞質及細胞核膜的胞器-內質網(endoplasmic reticulum, ER )-為雙層膜組合而成的構造。大部分的蛋白質皆在內質網內製造，這些新合成出來的蛋白質需要在內質網內經由完全的摺疊和適當的修飾，形成正確構形後，才會被送至目標地。當細胞受到某些刺激後，會造成內質網內的恆定被改變，使得許多不完全摺疊的蛋白質累積在內質網內，產生內質網壓力(ER stress)，為了修復此傷害，細胞便會啟動一連串的反應，這反應稱為不完全摺疊蛋白反應(unfolded protein response, UPR)或是一些促進生存的機制來對抗內質網壓力。倘若細胞一直處於內質網壓力下，便會啟動死亡的機制，造成細胞凋亡。而腫瘤抑制蛋白p53，在因應細胞遭受的危機事件中扮演一個非常重要的角色，所以我們有興趣探討p53是否參與在內質網壓力所引起的反應中。我們發現當利用內質網壓力誘導物-tunicamycin和brefeldin A處理MCF-7細胞，p53的表現量會先下降，與之前的文獻看到的現象一樣(Qu et al., 2004)，但是六小時後，p53便會開始大量表現在細胞中，而ser15的位置也有被磷酸化的情形，因此在內質網壓力下p53的表現有two-phases的情形。再用RNAi的技術抑制p53的表現，觀察到內質網所導致的死亡現象有適度減少的情形。接著，用Semiquantitative RT-PCR方法測試到在處理brefeldin A後，p53 mRNA表現量明顯的上升；且用cycloheximide抑制蛋白質新合成，內質網壓力所誘發的p53會被抑制。另外，利用NF-B的抑制物-Bay 11-7082，p53的表現量亦會被壓下來。再藉由染色體免疫沉澱實驗(chromatin immunoprecipitation assay)得知在內質網壓力下NF-B和p53本身可結合到p53 promoter上，可能調節p53的表現量。最後，我們觀察到brefeldin A處理細胞後，p53似乎不會促進目標基因的表現，但ser15被磷酸化的p53可移動至粒腺體上。綜合以上所觀察到的結果，我們推測p53可能參與在內質網壓力所誘發的細胞死亡反應中，且值得我們深入探討。

　Eukaryotic cells have a membranous labyrinth network called the endoplasmic reticulum (ER) that extends through the cytoplasm of the cell and is contiguous with the nuclear envelope. Proteins must be correctly folded and assembled in the ER prior to transit to intracellular organelles and the cell surface. A number of cellular stress conditions lead to accumulation of unfolded or misfolded proteins in the ER lumen. Cells responsed to excess of unfolded proteins in ER are through the well-characterized unfolded protein response (UPR) pathway. If the cells are exposed to prolonged or strong ER stress, the cells are destroyed by apoptosis. The p53 tumor suppressor is a key mediator of the cellular response to stress. Given the role of p53 in stress sensing and proapoptotic signaling, we are interested to investigate whether p53 plays a role in ER stress. Here, our data shows that the expression of p53 reduces in the first six hours after treated with tunicamycin and brefeldin A, two ER stress inducers, the same as a previous study. But interestingly, we find that the expression of p53 will increase six hours after ER stress and that p53 phosphorylation at serine 15 can also be observed 18 hr after ER stress. Ablation of p53 by RNA interference confers cells resistance to ER stress-induced cell death. Semiquantitative RT-PCR shows that the expression of p53 increases following brefeldin A and tunicamycin treatment and the expression can be abolished by treating with cycloheximide. Nuclear translocation of NF-B is observed during ER stress and the induction of p53 can be attenuated by IBkinase inhibitor Bay 11-7082. Indeed, chromatin immunoprecipitation (ChIP) assay demonstrates that NF-B and p53 itself may bind to p53 promoter to regulate p53 gene expression during ER stress. Furthermore, p53 has little effect on driving downstream genes expression, but phospho-ser15-p53 translocates to mitochondria is detected by western blotting after brefeldin A treatment. Altogether, these data suggest p53 may play a role in ER stress-induced cell death, and the mechanism should be further studied.

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