TGF-β/Activin/Nodal 信號通路調節了許多重要的細胞生物學過程,例如,細胞分裂,增殖,分化,遷移和衰老凋亡。此外,它也在胚胎髮育,損傷修復,腫瘤發生,組織纖維化,糖尿病發生及其免疫方面也扮演了重要的角色。TGF-β家族信號分子,包括TGF-β, Activin 和 Nodal,通過結合到它們各自的受體從而啟動它們,而啟動後的受體又可以通絡磷酸化作用進一步激活Smad2 和Smad3 蛋白,激活後的Smad2 和Smad3 蛋白可以和Smad4 蛋白形成複合體,一起從細胞膜轉移到細胞核內調節下游基因的表達。 / 在人的胚胎幹細胞中,TGF-β/Activin/Nodal signaling 做為最關鍵的信號分子,調節了人胚胎幹細胞的自我更新以及胚胎幹細胞多能性的維持。而在小鼠胚胎幹細胞中,該信號通路的功能並沒有清楚的研究。在本論文中,我們分離以及建立了Smad3 突變體的小鼠胚胎幹細胞系(Smad3-/-),該突變體細胞能夠維持正常小鼠胚胎幹細胞的形態,在自我增殖更新方面也沒有缺。此外,幹細胞多能性相關的標記基因以及組織標記基因表達水準也與野生型細胞非常相似,但是,在擬胚體的生長過程中,Smad3 被敲除後導致了組織發育相關的標記基因出現了差異性的表達。與野生型相比,中胚層標記基因（T 和GSC）的表達明顯受到了抑制。另外令人驚奇的是,將Smad3 基因敲除的胚胎幹細胞皮下注射裸鼠後長出了惡性的未完全成熟的畸胎瘤,而野生型的幹細胞則更傾向于長成成熟的良性畸胎瘤。進一步的分析發現,Smad3 功能性缺失後,細胞的增殖速率明顯增加了;紫外(UV)誘變後,相對於野生型,突變體細胞的抗凋亡能力也明顯增強了;並且在分化過程中,突變體細胞的遷移能力也要明顯強于野生型細胞。所有以上的細胞特徵可以解釋為什麼Smad3 基因敲除後會長出惡性的畸胎瘤。 / Microarray 分析結果發現,一個DNA 損傷修復基因Rif1,在Smad3 突變體細胞中呈現出了很高的上調,這個基因的上調現象已經發現是和侵蝕性腫瘤的發生是相關的,而且該基因的上調水準也與乳腺癌的浸潤程度是非常相關的。染色質免疫共沉澱和螢光素酶活性實驗進一步證實了Smad3 可以結合到Rif1 的啟動子領域從而直接抑制該基因的表達。這些實驗進一步說明了Smad3 可能通過下調Rif1 基因的表達,從而抑制了小鼠胚胎幹細胞長出惡性畸胎瘤的發生。 / 總之,我們建立了Smad3-/-基因敲除的小鼠胚胎幹細胞系,並且發現該突變體細胞傾向于長出惡性的畸胎瘤。我們推測,在正常的情況下,Smad3 正是通過抑制了DNA 損傷修復因數基因Rif1 的表達,從而阻止了惡性畸胎瘤的發生。這些研究的結果不僅開闊了我們對於惡性腫瘤發生的認識,而且為我們在幹細胞或誘導多能幹細胞治療應用中防止畸胎瘤的發生提供了新的思路和策略。 / TGF-β/Activin/Nodal signaling controls many important biological procedures in cells, such as cell division, proliferation, differentiation, migration and apoptosis in mammalian cells. It also plays a critical role in embryo development, wound healing, tumorigenesis, tissue fibrosis, diabetes and immunity. TGF-β superfamily ligands, such as TGF-β, Activin and Nodal bind to their respective ligand receptors and activate them, which in turn activate the receptor related SMAD proteins by phosphorylation, including Smad2 and Smad3. Once phosphorylated, they can cooperate with Smad4 and enter nucleus to bind promoter DNA sequence and regulate the target gene expression. / In human embryonic stem (ES) cells, TGF-β/Activin/Nodal signaling has been demonstrated to be the most critical pathways for ES cell self-renewal and maintenance of undifferentiated state. However, in mouse ES cells, its role is yet to be clearly exploited. In this study, we reported the derivation and establishment of mouse Smad3 knockout embryonic stem cell lines (Smad3-/- ES cells). Smad3-/- ES cells maintain normal ES cell morphology and express higher level of mouse ES cell markers, alkaline phosphatase (AP) and stage-specific embryonic antigen 1(SSEA1), and display no defect on self-renewal capacity. In addition, both of them show similar expression profiles of pluripotent and lineage marker genes compared to wild type ES cells. However, Smad3 ablation results in transient different expression of germ layer markers during embryoid body (EB) development. The expression of mesoderm lineage marker, like T and GSC, is significantly reduced in the EBs developed by Smad3-/- ES cells compared to EBs formed by wild type ES cells. More interestingly, to investigate the differentiation potential of Smad3-/- ES in vivo, we subcutaneously injected both wild type and Smad3-/- ES cells into nude mice, and observed that Smad3-/- ES cells are prone to grow malignant immature teratomas, while wild type ES cells develop normal mature teratomas. Further characterization of Smad3-/- ES cells demonstrates that depletion of Smad3 increases ES cell proliferation; Smad3-/- ES cells show higher capacity of the anti-apoptosis after UV irradiation and the migration potential of Smad3-/- ES cell differentiated cells is enhanced compared to wild type ES cells in the wound healing assay. Therefore, Smad3-/- ES cells exhibit enhanced malignancy, which may underlie their teratoma malignancy. / Microarray analysis shows that Rif1, a DNA repair factor is highly upregulated in Smad3-/- ES cells. Upregulation of DNA repair factor is found to be associated with invasive tumor. And the expression level of Rif1 is linked to the invasive degree of breast cancer at certain level. Chromatin immunoprecipitation (ChIP) assay and luciferase assay confirm that Smad3 binds to Rif1 promoter region and directly represses its expression; knockdown Rif1 in Smad3-/- ES cells rescues the expression level of Ccnd2 and migration potential to wild type ES cell level. Taken together, all these data suggests that Smad3 may suppress the malignancy of mouse embryonic stem cell formed teratoma through downregulating Rif1 expression in normal condition. / In summary, we reported the establishment of Smad3-/- ES cells and characterization of these cells. We discovered that Smad3-/- ES cells are prone to grow malignant teratomas compared to wild type ES cells. We hypothesized that Smad3 may suppress the malignancy of teratoma through repressing a DNA repair factor, Rif1. This information will not only broaden our general knowledge of malignant teratomas, but also help us to develop strategies to prevent malignant teratoma formation in ES/iPS cell therapy. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Li, Peng. / Thesis (Ph.D.) Chinese University of Hong Kong, 2014. / Includes bibliographical references (leaves 149-181). / Abstracts also in Chinese.
| Identifer | oai:union.ndltd.org:cuhk.edu.hk/oai:cuhk-dr:cuhk_1077662 |
| Date | January 2014 |
| Contributors | Li, Peng , active 2014 (author.), Yuan, Ping , active 2014 (thesis advisor.), Chinese University of Hong Kong Graduate School. Division of Chemical Pathology, (degree granting institution.) |
| Source Sets | The Chinese University of Hong Kong |
| Language | English, Chinese |
| Detected Language | English |
| Type | Text, bibliography, text |
| Format | electronic resource, electronic resource, remote, 1 online resource (181 leaves) : illustrations (some color), computer, online resource |
| Rights | Use of this resource is governed by the terms and conditions of the Creative Commons “Attribution-NonCommercial-NoDerivatives 4.0 International” License (http://creativecommons.org/licenses/by-nc-nd/4.0/) |
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