TopBP1 Deficiency Causes an Early Embryonic Lethality and Induces Cellular Senescence in Primary Cells
TopBP1 Deficiency Causes an Early Embryonic Lethality and Induces Cellular Senescence in Primary Cells
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DOI：
10.1074/jbc.m110.189704
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发表时间：
2011-02-18
影响因子：
4.8
通讯作者：
Hwang, Deog Su
中科院分区：
文献类型：
--
作者：
Jeon, Yoon;Ko, Eun;Hwang, Deog Su
TopBP1在脊椎动物的染色体复制、DNA损伤应答等细胞调控功能中发挥重要作用。虽然TopBP1的作用主要研究于癌细胞系，但其在小鼠和未转化细胞中的生理功能尚不清楚。我们产生了条件敲除小鼠，其中TopBP1基因的外显子5和6两侧是loxP序列。虽然缺乏topbp1的胚胎发育到囊胚期，但在E8.5及以上没有恢复到纯合子突变胚胎，在E7.5时有完全吸收的胚胎，这表明突变胚胎在着床期趋于死亡。这一发现表明，TopBP1在早期胚胎发生过程中对细胞增殖至关重要。使用表达Cre重组酶的逆转录病毒消融TopBP1（flox/flox）小鼠胚胎成纤维细胞和3T3细胞中的TopBP1，可在G(1)、S和G(2)/M期阻止细胞周期进程。topbp1消融小鼠细胞显示H2AX和Chk2磷酸化，表明细胞含有DNA断裂。topbp1消融后小鼠细胞进入细胞衰老。RNA干扰介导的TopBP1的下调虽然在人原代细胞中诱导细胞衰老，但在癌细胞中诱导细胞凋亡。因此，未转化的小鼠和人原代细胞缺乏TopBP1会导致细胞衰老而不是凋亡。这些结果表明，TopBP1对细胞增殖和维持染色体完整性至关重要。
TopBP1 plays important roles in chromosome replication, DNA damage response, and other cellular regulatory functions in vertebrates. Although the roles of TopBP1 have been studied mostly in cancer cell lines, its physiological function remains unclear in mice and untransformed cells. We generated conditional knock-out mice in which exons 5 and 6 of the TopBP1 gene are flanked by loxP sequences. Although TopBP1-deficient embryos developed to the blastocyst stage, no homozygous mutant embryos were recovered at E8.5 or beyond, and completely resorbed embryos were frequent at E7.5, indicating that mutant embryos tend to die at the peri-implantation stage. This finding indicated that TopBP1 is essential for cell proliferation during early embryogenesis. Ablation of TopBP1 in TopBP1(flox/flox) mouse embryonic fibroblasts and 3T3 cells using Cre recombinase-expressing retrovirus arrests cell cycle progression at the G(1), S, and G(2)/M phases. The TopBP1-ablated mouse cells exhibit phosphorylation of H2AX and Chk2, indicating that the cells contain DNA breaks. The TopBP1-ablated mouse cells enter cellular senescence. Although RNA interference-mediated knockdown of TopBP1 induced cellular senescence in human primary cells, it induced apoptosis in cancer cells. Therefore, TopBP1 deficiency in untransformed mouse and human primary cells induces cellular senescence rather than apoptosis. These results indicate that TopBP1 is essential for cell proliferation and maintenance of chromosomal integrity.