大腸癌細胞中 Cten 蛋白質在 Beta-catenin 介導訊息路徑中所扮演角色及其進入細胞核之機制探討

Studies on the β-catenin-dependent Roles and the Nuclear Targeting Mechanisms of Cten in Colon Cancer Cells

高芸歆(Yung-Hsin Kao)

指導教授 ： 廖憶純

國立臺灣大學/生命科學院/生化科技學系/碩士(2012年)

https://doi.org/10.6342/NTU.2012.10761

摘要

Cten (C-termial tensin-like)是 tensin 蛋白質家族中分子量最小的成員。它 是一個集中附著點(focal adhesion)蛋白質,並且在細胞附著、遷移和癌症發生過程中扮演重要角色。Cten 在各個時期的大腸癌中皆有表現量上升的現象,且過量表現的 Cten 蛋白質能夠增強大腸癌細胞的生長、轉移、侵略等癌症特性。

本研究顯示在人類大腸癌細胞株 SW480 中,除了細胞質的集中附著點外, Cten 還能進入細胞核,並在細胞質及細胞核內和 β-catenin 蛋白質發生交互作用。 β-catenin 蛋白質是 Wnt 訊息傳導路徑中的核心分子。很高比例的大腸癌中都在此路徑上發生變異,最後造成 β-catenin 不正常地累積於細胞核內,活化與癌症相關基因的轉錄。本研究使用冷光報導系統發現當 Cten 能夠進入細胞核中時,似乎會對 β-catenin 之轉錄功能稍有增強作用。此觀察為 Cten 具有促進大腸癌發生之活性的分子機轉,提供了一可能解釋。

此外,本研究也探討 Cten 在細胞中分佈的機制,發現 Cten 與 β-catenin 的存在、及兩者間的交互作用,對於彼此進入細胞核皆非必需。然而,我們發現細胞核中的 Cten 似乎具有較高的磷酸化程度,而且當六個保守性磷酸化位置受到突變時,Cten 便不再能夠進入核中。這些結果說明磷酸化可能在 Cten 於細胞中分 佈調控中扮演重要角色。最後,我們以 Kinasephos2.0 網站預測可能磷酸化這些位點的蛋白質激酶,做為未來研究方向之參考。

關鍵字

Cten 蛋白質 ； β-catenin 蛋白質 ； 大腸癌 ； 細胞核 ； 磷酸化

並列摘要

C-terminal tensin-like (Cten) protein, the smallest member of the tensin protein family, is a focal adhesion molecule that plays a role in cell adhesion, migration and the development of malignancies. Elevated Cten level has been detected in all stages of colon cancer, and Cten overexpression promotes the tumorigenicity of colon cancer cells.

In this study, we demonstrated that besides focal adhesions, a high population of Cten is present in the nucleus of human colon cancer SW480 cells, and that Cten binds to β-catenin in both the cytoplasm and the nucleus. β-catenin is the central mediator of Wnt signaling, a pathway whose over-activation is highly involved in colon cancer development. Ultimately, such aberrant activation results in improper accumulation of β-catenin in the nucleus, where it triggers the transcription of cancer-associated genes. Using the dual-luciferase reporter system, we showed that Cten may mildly promote β-catenin-dependent transcription in a nuclear-targeting-dependent manner, suggesting one possible explanation for its oncogenic activity in colon cancers.

Exploring the mechanisms underlying Cten’s unexpected nuclear entry, our results implied that the presence of and interaction with β-catenin may not be necessary for the nuclear targeting of Cten. However, we discovered that Cten appeared to be more heavily phosphorylated in the nucleus, and that mutation of six conserved potential phosphorylation sites inhibits the nuclear accumulation of Cten, indicating a role for phosphorylation in specifying Cten’s subcellular distribution. In the end, in silico analysis was carried out to identify kinases that might be responsible for phosphorylations of these mutated residues.

並列關鍵字

Cten ； β-catenin ； colon cancer ； nuclear targeting ； phosphorylation

參考文獻

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