Hdm2在過氧化氫所誘發的細胞老化中之角色探討

The role of Hdm2 in H2O2-induced senescence in WI38 human diploid fibroblast

蘇新棠(Shin-Tang Su)

指導教授 ： 柯逢春

國立臺灣大學/生命科學院/分子與細胞生物學研究所/碩士(2005年)

https://doi.org/10.6342/NTU.2005.01403

摘要

細胞老化屬於一種極度穩定的細胞週期停止運轉狀態，並且作為細胞遭遇壓力時的一套反應機制。目前已知有許多種壓力皆可以引發細胞老化，反應不同壓力的細胞老化機制是由兩個抑癌因子所控制: p53 和 Rb。在老化細胞中，Rb分子會促進形成一種特殊的異染色體結構稱為senescence associated heterochromatin foci (SAHF)。許多E2F所調控的與促進細胞增生相關的基因會被包裹進此特殊異染色體內而抑制其基因表現。人類致癌因子：Hdm2 是ㄧ個含有RING domain的 E3 ubiquitin ligase，已知其是p53的主要負調節因子並且也有能力與Rb做結合，因此Hdm2可能扮演細胞老化中p53 和 Rb兩個重要角色間的橋樑。
在此研究中，我們利用H2O2建立一個有效誘發細胞老化的方法並且藉此研究Hdm2在細胞老化中所扮演的角色。細胞經H2O2處裡過後，p53 pathway被活化，p53進ㄧ步去活化Hdm2的產生。Hdm2和p53兩個分子在細胞老化形成過程中都保持在啟動狀態。Upregulated Hdm2形成一個特殊的foci在細胞核內，並且在不同次的H2O2處理下當老化的細胞比例越高，形成Hdm2 foci的細胞所與之比例也越高。在H2O2處理下，Hdm2 和 Rb彼此間的結合也增加。我們也在2次處理H2O2後2天發現mono-ubiquitylation of histone H4明顯增加。在H2O2引發的細胞老化過程裡Hdm2 foci的形成可能屬於一套機制，此機制可能負責p53活性的維持並且與Rb-dependent SAHF相關。

關鍵字

細胞老化

並列摘要

Cellular senescence, an extremely stable form of cell cycle arrest that serve as a general cellular stress response program. Although diverse stress can induce a senescence response, they appear to be governed by the two tumor suppressor proteins, p53 and pRB. In senescent cell, Rb promotes a distinct heterochromatic structure formation, called senescence associated heterochromatin foci (SAHF). Several E2F target genes that promote cellular proliferation were repressed by packaging into SAHF in senescent cells. The human oncoprotein Mdm2 (Hdm2), a RING domain E3 ubiquitin ligase known as the major negative regulator of p53, also interact with pRB physically. Hdm2 may serve as a mediator between p53 and pRB in senescence response.
In this study, we optimize an effective H2O2-induced senescence protocol and study the role of Hdm2 in H2O2-induced senescence. After treated cell with H2O2, p53 pathways were activated with upregulate Hdm2 protein. Both p53 and Hdm2 are upregulated and sustained during the course of H2O2-induced senescence. The upregulated Hdm2 form the distinct nuclear foci and the ratio of Hdm2 foci is correlated to the ratio of SA-β-gal positive cells in different treatment protocols. Furthermore, H2O2 treatment promotes physical interaction between Hdm2 and Rb. We also find mono-ubiquitylation of histone H4 at second day under 2 × H2O2 treatment. Hdm2 foci formation may be a novel mechanism for p53 sustained activity during H2O2-induced senescence and a possible connection to Rb-dependent SAHF formation.

並列關鍵字

Hdm2 ； senescence

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