Nucleolin在細胞具有許多的功能，包含了調控細胞增生、細胞凋亡及mRNA的穩定性等。先前的研究已經指出nucleolin會在腫瘤細胞中大量表現，而我們也在纖維母細胞IMR90及CL系列的肺癌細胞中看到同樣的現象。在實驗室先前的研究發現到nucleolin會結合到許多基因的3-UTR上，導致mRNA穩定性增加的情形。而在本篇論文，我們發現到在invasive能力比較強的CL1-1與CL1-0的比較之下，c-nucleolin (cleaved nucleolin)，尤其是nucleolin(70kDa)及nucleolin(55kDa)皆有顯著性的增加，但是nucleolin(wt)則沒有太大的差異。根據這個結果，我們就假設c-nucleolin會參與在肺癌細胞metastasis的過程當中。 為了證實這個假說，首先我們先找出nucleolin(55kDa)為nucleolin第270到710個胺基酸，並且架構nucleolin(270-710)載體。在HeLa細胞內轉染nucleolin(270-710)之後的確可以發現到細胞migratory及invasive的能力有顯著性的增加。而先前的實驗發現到nucleolin(wt)會保護HDAC11 mRNA，而HDAC11被報導為可能的腫瘤抑制基因。於是我們也在HeLa及H1299分別轉染HDAC11後，發現到細胞的migratory及invasive能力下降了。而為了更進一步了解nucleolin(55kDa)與HDAC11之間的關係，我們使用了RNA-IP發現到nucleolin(55kDa)會與nucleolin(wt)競爭結合到HDAC11的mRNA，並且導致HDAC11的表現量下降。綜合以上結果，nucleolin在腫瘤生成的早期就會開始大量累積，促使細胞增生；而當腫瘤持續惡化時，nucleolin就會被切割形成c-nucleolin，並且促使細胞轉移的現象。

Nucleolin has multiple functions such as anti-apoptosis and regulation of mRNA stability. Previous studies demonstrate that nucleolin is overexpression in tumor cells. Indeed, we also observed that nucleolin in IMR90, which is fibroblast less than that in CL series lung cancer cell line. Our previous study indicated that several important genes could be up-regulated by increasing their RNA stability through recruitment of nucleolin to the 3-UTR. In this study, we found that the level of nucleolin cleavage form in CL1-0 is less than that in CL1-1, whose invasive ability is stronger than CL1-0, but no significant difference in full-length nucleolin. According to these data, we hypothesize that nucleolin cleavage form might be involved in metastasis of lung tumor. To clarify the hypothesis, we identified one of the nucleolin cleavage forms, which is 55kDa. To determine the functional role of truncated nucleolin, the migratory and invasive ability of HeLa cells overexpressing the truncated nucleolin were analyzed. Our data indicated that both of cell migration and invasion were enhanced by truncated nucleolin significantly. To further investigate the mechanism on how full-length and truncated nucleolin modulate tumor cell metastasis activity, we used RNA-IP to study the recruitment of full-length and truncated nucleolins, and found that truncated nucleolin could compete the binding site of 3-UTR with full-length nucleolin to destabilize HDAC11 (Histone deacetylase 11) mRNA. In previous study we identified several novel genes were protected by nucleolin, including HDAC11. However, the function of HDAC11 in cancer is not well studied. Thus, we investigated whether truncated nucleolin-regulated metastasis is mediated by HDAC11. We found that the migration was decreased with transfection of increasing doses of HDAC11. Taken together, at early stage of tumor progression, full-length nucleolin accumulation contributes to cell proliferation. As the tumor progression to late stage, nucleolin was cleavage to be of truncated form to facilitate the metastasis activity. These data highlight the importance of nucleolin during tumorigenesis.

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