細胞分裂中Cdk1對Repo-Man磷酸化對染色體濃縮的影響

Abstract

Cdk1在細胞週期和染色體濃縮中扮演一個重要的角色，然而其機制仍尚未明瞭。經由DNA微陣列的分析，我們發現Repo-Man過度表現在肝細胞癌中。先前研究指出Repo-Man是1號γ型蛋白去磷酸酶 (PP1γ)的結合伴侶，會在細胞分裂時調控染色體濃縮，但其功能如何調控目前尚未明瞭。 在本篇論文中，我們發現在細胞分裂早期Repo-Man會被Cdk1磷酸化。喪失磷酸化機能的突變型Repo-Man會在細胞分裂的前期和中期提前轉位至染色體上，抑制染色體濃縮。染色體濃縮遭到抑制會在細胞分裂後期和末期造成染色體橋，以及在細胞分裂結束後產生微細胞核。磷酸化的Repo-Man會於細胞分裂後期招攬PP1γ至染色體上。而突變形的Repo-Man 會於細胞分裂前期與中期提前招攬PP1γ至染色體，造成組蛋白H3 (Histone H3)於3號羥丁氨酸過早去磷酸化。我們的研究結果顯示Cdk1磷酸化的Repo-Man會於細胞分裂早期將Repo-Man-PP1γ複合體排除於染色體外，使得Histone H3 於3號羥丁氨酸可被磷酸化，進而導致細胞分裂早期的染色體濃縮。

Cyclin-dependent kinase 1 (Cdk1) is a key player in cell cycle regulation, yet the mechanism of regulating chromosome condensation is not fully known. Using microarray analysis, we found Repo-Man is a gene overexpressed in hepatocellular carcinoma. Repo-Man is originally identified as a binding partner for protein phosphatase 1γ. A previous study found Repo-Man is implicated in regulation of chromosome condensation during mitosis, but the mechanism is still unknown. We propose a novel finding that Repo-Man is phosphorylated by Cdk1 in early mitosis. Phosphorylation null Repo-Man prematurely translocates to chromosomes in prophase and metaphase and inhibits chromosome condensation. The inhibition of chromosome condensation results in chromosomal bridging in anaphase and telophase and micronuclei formation after mitosis. Phosphorylated Repo-Man recruits protein phosphatase 1γ (PP1γ) onto chromosome at the onset of anaphase. Phosphorylation null Repo-Man prematurely recruits PP1γ onto chromatin in prophase and metaphase, leading to premature dephosphorylation of Histone H3 Thr3. The data indicate that Cdk1 phosphorylates Repo-Man to exclude the binding of Repo-Man-PP1γ complex on chromosome in early mitosis and induces full phosphorylation of Histone H3 Thr3 to induce chromosome condensation in early mitosis.