探討丙戊酸活化Oct4啟動子的機制

細胞經由表達特定的轉錄因子，包含Oct4、SOX2、Klf4、c-Myc，使得細胞能夠重新編程產生誘導型多能性幹細胞，這類型的細胞可用來修補受損的組織，治療目前無法以傳統醫療治癒的疾病，例如：杜顯氏肌肉萎縮症，這項技術的優點在於避免了器官移殖可能發生的病人免疫排斥和傳統使用胚胎幹細胞的倫理道德問題，然而目前體細胞重新編程的技術仍存在一些待克服的問題，例如，使用反轉錄病毒作為載體，可能造成外源基因隨機插入染色體，進而干擾內源基因正常的表達，另一個潛在的問題則是產生誘導型多能性幹細胞的效率依然很低。因此，近年來有文獻指出加入小分子化合物-丙戊酸 (VPA)，是一種組蛋白去乙醯酶抑制劑能夠增加體細胞重新編程的效率。在我們實驗室先前的研究中證實，丙戊酸會作用在Oct4啟動子的賀爾蒙反應調控區域 (HRE) 來活化Oct4啟動子的活性，但丙戊酸調控Oct4啟動子的機制還不清楚。因此，在這篇研究中，我們證明丙戊酸不是經由抑制組蛋白去乙醯化來調控Oct4啟動子的活性，我們發現丙戊酸會經由誘發PI3K/Akt/mTOR訊息傳遞來活化Oct4啟動子，更進一步我們證明，對丙戊酸會影響某些特定核受體 (NRs)，例如，減緩TR2和COUP-TFΠ對Oct4啟動子的抑制，以及增強PPARδ對Oct4啟動子的活性，來活化Oct4啟動子。我們認為在體細胞重新編程的過程中，丙戊酸是透過活化PI3K/Akt/mTOR訊息傳遞來活化Oct4啟動子進而提升產生誘導型多能性幹細胞的效率。

關鍵字

丙戊酸

並列摘要

Reprograming of somatic cells into induced pluripotent stem cells (iPSC) by expressing Oct4, Sox2, Klf4, and c-Myc has paved the way for producing patient-specific pluripotent cells to treat inherited diseases, such as Duchenne muscular dystrophy. However, current reprogramming approach has some risks, such as viral transduction caused random integration of multiple pro-viral copies and low efficiency. Recently, it was shown that a small compound called valporic acid (VPA), a histone deacetylase (HDAC) inhibitor, could improve reprogramming efficiency. Our previous study had shown that VPA can enhance Oct4 promoter activity by targeting its proximal hormone response element (HRE), but the underlying mechanism is not clearly defined. In this study, we found that inhibition of HDACs might play a minor role in the VPA mediated activation of Oct4 promoter. We discovered that VPA activated Oct4 promoter through inducing the PI3K/Akt/mTOR signaling pathway. The proximal HRE of Oct4 promoter was targeted by several nuclear receptors and we found that VPA reversed the repressive effect of some NRs, such as TR2 (nuclear receptor subfamily 2, group C, member 1) and COUP-TFII (nuclear receptor subfamily 2, group F, member 2), but enhanced the inducing effect of other NRs, including PPARδ (peroxisome proliferator activator receptor delta). We concluded that VPA triggered PI3K/Akt/mTOR signaling plays critical role in activating Oct4 promoter activity during somatic reprogramming.

並列關鍵字

VPA ； Oct4 ； TR2 ； PPARδ ； PI3K/Akt/mTOR

參考文獻

Barnea, E., and Bergman, Y. (2000). Synergy of SF1 and RAR in activation of Oct-3/4 promoter. The Journal of biological chemistry 275, 6608-6619.

Brehm, A., Ohbo, K., and Scholer, H. (1997). The carboxy-terminal transactivation domain of Oct-4 acquires cell specificity through the POU domain. Molecular and cellular biology 17, 154-162.

Briggs, R., and King, T.J. (1952). Transplantation of Living Nuclei From Blastula Cells into Enucleated Frogs' Eggs. Proceedings of the National Academy of Sciences of the United States of America 38, 455-463.

Chen, G., Huang, L.D., Jiang, Y.M., and Manji, H.K. (1999). The mood-stabilizing agent valproate inhibits the activity of glycogen synthase kinase-3. Journal of neurochemistry 72, 1327-1330.

Chuang, Y.S., Huang, W.H., Park, S.W., Persaud, S.D., Hung, C.H., Ho, P.C., and Wei, L.N. (2011). Promyelocytic leukemia protein in retinoic acid-induced chromatin remodeling of Oct4 gene promoter. Stem cells 29, 660-669.

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探討丙戊酸活化Oct4啟動子的機制

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