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標題: | 新穎蛋白BCAS2受抑癌分子p53轉錄調控之研究 Study on the Transcription Regulation of Breast Cancer Amplified Sequence 2 (BCAS2) by p53 Tumor Suppressor |
作者: | Yi-Hsuan Lin 林奕瑄 |
指導教授: | 陳小梨(Show-Li Chen) |
關鍵字: | p53,BCAS2,轉錄壓抑,負調控因子,相互抑制, p53,BCAS2,transcription repression,negative regulator,reciprocal inhibition, |
出版年 : | 2008 |
學位: | 碩士 |
摘要: | 新穎分子BCAS2已被發現在乳癌細胞株MCF7及MDA-MB-231,以及一些乳癌患者之臨床組織切片中,發現有基因放大或過度表現的的現象,並可能與乳癌細胞的侵襲性和遠端轉移有關。在本實驗室的研究中,發現默化BCAS2會導致MCF7細胞發生細胞凋亡,且細胞聚落形成能力降低。並發現BCAS2可以和抑癌蛋白p53結合,阻礙p53對下游目標基因如p21的轉錄活化,因此是一個p53的負向調控分子。
p53為細胞中最重要的抑癌分子之一,約有百分之五十以上的癌症被發現含有突變的p53,其餘大多數亦與p53的調控或訊息傳導途徑相關。p53由其轉錄調控因子的功能,辨認特定的DNA序列並與之結合,並影響目標基因的轉錄活化或抑制;或是藉由其下游基因間接調控其他基因。p53下游的基因在細胞週期、細胞凋亡、老化等細胞重要反應上,都扮演相當重要的角色。 在本研究中,我們發現BCAS2可受到p53的轉錄壓抑作用。在胚胎腎細胞株293T、乳癌細胞株MCF7及肺癌細胞株H1299中皆可觀察到p53的活化或大量表現,將導致BCAS2蛋白質表現量降低的現象。後續實驗則發現p53可壓抑BCAS2基因啟動子的活性,以及其mRNA的表現。染色質免疫沉澱分析的結果則說明p53可結合至BCAS2啟動子上。然而對於p53乃辨認BCAS2啟動子中哪一段序列做為結合位,目前仍尚未釐清。 本研究證明BCAS2是抑癌蛋白p53下游進行轉錄抑制的目標基因之一,然而先前研究中BCAS2亦為p53的負向調控因子,因此在BCAS2與p53之間存在著相互抑制的互動關係。在細胞處於正常環境下,BCAS2可以抑制p53的活性,使細胞得以正常地生長分裂;BCAS2的過量表現甚至可能是癌細胞中,p53無法正常作用的原因之一。然而一旦p53受到活化,則可以抑制BCAS2的表現,且此壓抑作用可使p53活性更加增強,形成正回饋的效果。未來可以此機制,作為癌症治療的目標之一;且BCAS2與p53之間的互動,也可以成為未來研究p53與負向調控因子之間的模式之一。 A novel protein named BCAS2 has been reported overexpressed or gene amplified in breast cancer cell lines MCF7 and MDA-MB-231, as well as some of the clinical breast cancer samples. Overexpression of BCAS2 may associate with gaining of invasiveness and metastasis ability in breast cancer cells. Previous studies of our lab showed that silencing BCAS2 expression cause apoptosis in MCF7, and the colony-forming ability was dampened. BCAS2 was found to physically interact with the tumor suppressor p53.The interaction blocked the ability of p53 to transcribe target genes such as p21. Thus, we identified BCAS2 as a negative regulator of p53. p53 is one of the most crucial tumor suppressors in cells. It was reported that p53 mutations occurred in more than fifty percent of human cancers, and most of the rest were associated with the regulation or signaling pathways of p53. As a transcription regulator, p53 can recognize and bind to a specific DNA sequence and therefore activate or repress the transcription activity of its target genes. Some indirect regulation can be achieved through its downstream pathway. The target genes of p53 participate in many central cellular events such as cell cycle regulation, apoptosis, and cell senescence. In this study, we demonstrated that p53 can transcriptionally repress BCAS2 expression. Overexpression or activation of p53 cause the decrease of protein expression of BCAS2 in human embryonic kidney cell 293T, the breast cancer cell line MCF7 and also the lung cancer cell line H1299. Further analysis showed the promoter activity of BCAS2 gene could be repressed by p53, followed by the decrease of mRNA expression. Chromatin immunoprecipitation was performed to verified that p53 associated with BCAS2 promoter. However, it has not yet been clarified which region within BCAS2 promoter could interact with p53. In this report we identified BCAS2 as one of the target gene of p53-mediated transcription repression. We have also shown that BCAS2 can negatively regulate the activity of p53 previously. Taking together, there might exist a reciprocal inhibition between p53 and BCAS2. Cells under normal condition can grow and proliferate normally in result of p53 inactivation by BCAS2 negative regulator. Moreover, overexpression of BCAS2 might therefore promote tumor progression. Nevertheless, once p53 is activated, it can repress BCAS2 expression, thus elevate its own activity. This mechanism can be a tumor therapeutic target in the future, as well as a model to investigate the relationship between p53 and some of its negative regulators. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/37278 |
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