氏 名 野口
ノ グ チあや
ア ヤ所 属 理工学研究科 生命科学専攻 学 位 の 種 類 博士（理学）
学 位 記 番 号 理工博 第
262号 学 位 授 与 の 日 付 平成
30年
3月
25日 課 程 ・ 論 文 の 別 学位規則第
4条第
1項該当
学 位 論 文 題 名
RNA-binding protein ZFP36L2 is a novel regulator of cell cycle細胞周期制御における
RNA結合タンパク質
ZFP36L2の新機能（英 文）
論 文 審 査 委 員 主査 教授 川原 裕之 委員 教授 久永 眞市 委員 教授 相垣 敏郎
【論文の内容の要旨】
Messenger RNA (mRNA) turnover is an important mechanism for regulating prompt and accurate gene expression. Half-lives of each mRNA is mainly determined by cis-acting elements within the untranslated region. AU-rich element (ARE) located in the 3'UTR is a major determinant of mRNA stability. ARE binding proteins recognize the element and induce degradation of mRNAs.
Tandem CCCH zinc-finger domains allow ZFP36L2 to bind to the ARE directly.
ZFP36L2 binding to target ARE-mRNAs promotes mRNA decay by recruiting enzyme complexes such as Ccr4-Not. ZFP36L2 null mice display failure of hematopoiesis and die in shortly after birth. Deletion of the first exon of ZFP36L2 in mice leads to female sterility. About 8% of all mRNAs have ARE, but few have been identified as targets of ZFP36L2. Although ZFP36L2 plays critical roles in biological processes, little is known about mechanism. As excess of human ZFP36L2 in HeLa cells induces the delay in cell proliferation, I hypothesized that ZFP36 might have a role in controlling the cell cycle progression via mRNA degradation.
At first, I assessed the expression profile of ZFP36L2 in cell cycle, and found that ZFP36L2 shows cell cycle dependent change in its protein expression level. ZFP36L2 expression was repressed by protein degradation in interphase. Substitution of specific serine residue in the C-terminus to alanine stabilized ZFP36L2, suggesting that this residue is critical for ZFP36L2 degradation.
Next, I tried to identify target mRNAs of ZFP36L2 in cell cycle regulation. A group of potential ZFP36L2 target transcripts was chosen by intersecting the cell cycle genes with the group of genes containing ARE in their 3'UTR and the group of genes binding to ZFP36L2. I performed quantitative RT-PCR analysis on selected candidate ZFP36L2 target mRNAs, and found that ZFP36L2 knock down cells show increased expression of G1-S Cyclin mRNAs, such as CCNA2, CCND1 and CCNE2. This result indicated that ZFP36L2 might represses the cell cycle progression by mRNA decay. Contrary to this prediction, I found that ZFP36L2 knock down did not affect cell cycle progression in HCT116 cells.
Repression of G1-S cyclins is essential for cell cycle arrest induced by DNA damage.
Therefore, ZFP36L2 might have a role in DNA damage response. To investigate this possibility, I examined the effect of ZFP36L2 knock down on both cell cycle distribution and apoptosis in DNA damage induced cells. Cisplatin was used as a DNA damage inducing agent, as it induces S phase arrest. In DNA damage induced cells, lack of ZFP36L2 led to a decrease in the S phase arrested population. Moreover, ZFP36L2 knock down resulted in an increased apoptosis in DNA damage induced cells. These results indicate that ZFP36L2 assists cell cycle arrest by suppressing mRNAs such as Cyclin A2 and Cyclin D3 as a DNA damage response, and reduces apoptosis.
In conclusion, I presented evidence that ZFP36L2 is a novel cell cycle regulator, and acts as a key factor to decide a destiny of cells with DNA damage.
