"BCAS2,前列腺癌大量表現的蛋白質，可與NBS1結合以促進雙股DNA斷裂修復之研究"

Abstract

BCAS2在調控pre-mRNA剪接、有絲分裂時的紡錘絲形成，以及雄激素受體轉錄時都扮演關鍵的角色。也有之前的研究提及BCAS2參與DNA的修復作用，但詳細的機制還不清楚。我們實驗室提供證據顯示在人類前列腺癌細胞株中，BCAS2的表現可以保護細胞抵抗游離輻射 (IR) 造成的雙股DNA斷裂損害。我們也用果蠅翅成蟲盤組織做模式，證明BCAS2大量表現能夠舒緩輻射線造成的細胞凋亡。為了進一步探討BCAS2對雙股DNA斷裂修復的機制，實驗結果指出，BCAS2對於兩種主要的修復途徑，非同源末端连接 (non-homologous end joint, NHEJ) 以及同源重组修復 (Homologous Recombination, HR) 分別都有促進的作用。我們也證明BCAS2能夠用其N端片段與NBS1的N段及C端直接結合，NBS1是MRN complex (MRE11/RAD50/NBS1) 的一員，在DNA修復及細胞生理週期調控都是不可或缺的。因此我們提出，BCAS2經由結合並促進NBS1聚集到DNA斷裂點，增進雙股DNA修復的效率。最後我們發現在前列腺癌患者樣本上，BCAS2與另一個腫瘤生物標記β-catenin，都在惡性腫瘤上有較高的表現；另外在癌症基因庫的比對也顯示，BCAS2 mRNA表現量與前列腺癌患者存活率呈現正相關。綜合我們的研究成果，BCAS2經由與NBS1結合以協助雙股DNA斷裂修復機制，並促進前列腺癌的惡化進展。

Breast cancer amplified sequence 2 (BCAS2) plays crucial roles in regulating pre-mRNA splicing, spindle formation during mitosis, and androgen receptor transcription. Previous studies suggest that BCAS2 is involved in DNA repairs, but the details and mechanisms remain to be characterized. We provide evidence here to show that BCAS2 expression protected human prostate cancer cells from the DNA damage of ionizing radiation (IR). To support the results, we also demonstrate that dBCAS2 alleviated IR-induced cell apoptosis in Drosophila wing discs. Mechanistically, BCAS2 was able to enhance the in vitro and in vivo non-homologous end joint (NHEJ) efficiency in double-strand breaks (DSBs) repairs; in parallel, BCAS2 upregulated the homologous recombination (HR) ability during DSBs repairs. Furthermore, we prove that through its N-terminus domain, BCAS2 directly interacted with both the N- and C-terminal domains of NBS1, an indispensable component of the DNA repair/checkpoint complex MRE11-RAD50-NBS1 (MRN). Thus, BCAS2 may positively regulate DNA repairs through facilitating NBS1 recruitment to DSBs. Finally, we found that the expression levels of BCAS2 protein correlated well with that of β-catenin and high expression of BCAS2 was found more frequently in higher-stage human prostate cancer tissues. In addition, the survival analysis showed that high levels of BCAS2 mRNA in PCa tissues were significantly correlated with shorter survival in patients with PCa. Together, our results demonstrate that BCAS2 participates in more than one pathway of DSBs repairs through interaction with NBS1, and may possibly affect prostate cancer progression.