過去報導指出去泛素酶可以透過調節一些重要的生理功能之蛋白質來影響包含細胞週期、細胞凋亡、DNA損壞反應等重要的生理功能而在癌症發展中扮演重要的角色。泛素特異性胜肽酶二十四 (Ubiquitin-specific peptidase 24, USP24) 是去泛素酶的成員之一。過去對於USP24在癌症中的研究很少，而目前一些初步實驗結果發現USP24參與腫瘤形成及轉移。然而，對於USP24影響癌症的詳細機轉仍不清楚，因此我們想要透過了解與USP24交互作用的蛋白質來推論USP24在癌症發展中的角色。本篇研究目標為利用系統性分析找出潛在會與USP24交互作用的蛋白質，並利用生物資訊軟體分析釣到的標的蛋白質來推測出USP24在癌症發展中所可能影響的功能，最後在癌細胞實驗中證實USP24的功能。首先以USP24為餌利用酵母菌雙雜合系統 (yeast two hybrid) 篩選出超過兩百個蛋白質，將與USP24交互作用的蛋白質做功能上分析後發現篩選出的蛋白質參與在許多重要的生理功能，包括腫瘤、細胞週期調控、DNA損壞反應、細胞凋亡、蛋白質降解等，暗示USP24透過與這些蛋白質交互作用而調控重要生理功能，進而影響癌症發展。過去實驗發現當在細胞內過度表現USP24時會增加細胞凋亡，因此我們想要進一步探討USP24在細胞凋亡的重要性。分析從酵母菌雙雜合系統篩到的蛋白質時，發現Ku70在過去報導中指出會藉由調控Bax而參與細胞凋亡，我們進一步利用免疫沉澱法確認USP24和Ku70及Bax間的交互作用，並且發現USP24會穩定Bax蛋白質而造成表現量增加，進而促使細胞走向凋亡。

Deubiquitinating enzymes (DUBs) play a key role in cancer development through modulating cell cycle progression, apoptosis, and the response to DNA damage. Ubiquitin-specific peptidase (USP) 24 is one of DUB members, and rare studies related to USP24 in cancer were studied previously. Recently, we found that USP24 was involved in tumorigenesis and metastasis of cancer. However, it is lack of evidence clarifying which cancer-related proteins are direct interacted with USP24 in the tumorigenic process. In this study, initially, we used USP24 as bait to probe its interacted proteins, and more than 200 proteins were probed. After functional grouping with pathway analysis using MetaCoreTM software, data indicated that these interacted proteins were involved in cancer neoplasms, cell cycle regulation, DNA damage response, lung cancer progression, apoptosis, and protein degradation, implying that USP24 may regulate these pathways through interacting with these proteins thereby affecting cancer progression. To confirm the importance of USP24 in cell survival, we choose one of the pathways, apoptosis, to study further. First, knockdown of USP24 decreased cell death, and overexpression of USP24 increased cellular apoptosis. Second, to study the USP24-mediated apoptotic pathways, several apoptotic related factors were evaluated, such as Ku70, Bax and caspase 3. Knockdown of USP24 decreased Ku70-regulated protein, Bax, through reducing protein stability in a proteasome- dependent manner, suggesting that USP24 stabilizes Bax level, leading to the increase in transportation of Bax to mitochondria for apoptosis. In conclusion, this study uncovers the role of USP24 in cancer progression by systemic screening its interacted proteins.

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