中文摘要
前致癌蛋白c-Jun 是屬於轉錄因子AP-1 家族的一員，包含在調控細胞增殖、分化和死亡。如何維持c-Jun 蛋白質表現量在上皮細胞的增殖和死亡扮演很重要的角色。實驗室過去的研究證實將上皮細胞養在膠原蛋白凝膠上會導致細胞凋亡，是由於細胞接受到軟基質的物理性作用所致。我們發現軟性基質誘發c-Jun 降解所導致細胞刁亡只會發生在一般上皮細胞，而不會發生在癌細胞。因此我的研究方向主要在探討軟性基質導致c-Jun 降解的分子機制。我們證實軟性基質所導致c-Jun 降解可以受26S 蛋白解體抑制劑回復。此外，Cul1 泛素接合酶可以特異性的調控軟性基質所導致c-Jun 多次泛素化及降
解。在研究中我們發現軟性基質導致Cul1 neddylation 並活化Cul1所調控的多次泛素化，接著觀察到Cul1 可以和c-Jun 相互作用，免疫螢光染色也顯示軟性基質誘導Cul1 及26S 蛋白解體累積在細胞核裡，並且參與軟性基質所導致的c-Jun 降解。綜合實驗結果我們證實了軟性基質誘發Cul1 neddylation 可以導致c-Jun 多次泛素化，然後透過泛素-蛋白解體分解路徑在上皮細胞的細胞核中降解。

Abstract
The proto-oncoprotein c-Jun is a component of the transcription factor AP-1 (activator protein-1) involved in cellular proliferation, differentiation and death. Maintenance of c-Jun protein levels plays an important role in proliferation and survival of epithelial cells. Previous studies in our lab showed that epithelial cells cultured on collagen gel developed apoptosis due to low substratum rigidity. Low rigidity-induced cell apoptosis was mediated by degradation of c-Jun, which was observed only in epithelial, but not transformed cells. The purpose of my study was to delineate the underlying mechanism whereby low substratum rigidity induced degradation of c-Jun. The low rigidity-induced degradation of c-Jun could be reversed by 26S proteasome specific inhibitors. Here we showed that Cul1, a ring-domain ubiquitin ligase, had a specific physiological role in low rigidity-induced c-Jun degradation. Low substratum rigidity induced Cul1 neddylation and enhanced Cul1-mediated polyubiquitination. Under low substratum rigidity condition,
Cul1 physically interacted with c-Jun. Immunofluorescence study showed that low rigidity induced the accumulation of Cul1 in the nucleus, which was associated with degradation of c-Jun. In addition, low rigidity also triggered translocation of 26S proteasome into the nucleus. Taken together, we demonstrate that low substratum rigidity induces Cul1 neddylation which triggers c-Jun polyubiquitination and results in c-Jun degradation through ubiquitin-proteasome proteolysis in epithelial cells.

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