a Division of Life Science, Center for Cancer Research and State Key Lab for Molecular Neuroscience , Hong Kong University of Science and Technology , Hong Kong , China.
b Guangzhou HKUST Fok Ying Tung Research Institute , Guangzhou , China.
Cell Cycle. 2019 Mar;18(5):605-620. doi: 10.1080/15384101.2019.1578522. Epub 2019 Feb 17.
Noc3p (Nucleolar Complex-associated protein) is an essential protein in budding yeast DNA replication licensing. Noc3p mediates the loading of Cdc6p and MCM proteins onto replication origins during the M-to-G transition by interacting with ORC (Origin Recognition Complex) and MCM (Minichromosome Maintenance) proteins. FAD24 (Factor for Adipocyte Differentiation, clone number 24), the human homolog of Noc3p (hNOC3), was previously reported to play roles in the regulation of DNA replication and proliferation in human cells. However, the role of hNOC3 in replication licensing was unclear. Here we report that hNOC3 physically interacts with multiple human pre-replicative complex (pre-RC) proteins and associates with known replication origins throughout the cell cycle. Moreover, knockdown of hNOC3 in HeLa cells abrogates the chromatin association of other pre-RC proteins including hCDC6 and hMCM, leading to DNA replication defects and eventual apoptosis in an abortive S-phase. In comparison, specific inhibition of the ribosome biogenesis pathway by preventing pre-rRNA synthesis, does not lead to any cell cycle or DNA replication defect or apoptosis in the same timeframe as the hNOC3 knockdown experiments. Our findings strongly suggest that hNOC3 plays an essential role in pre-RC formation and the initiation of DNA replication independent of its potential role in ribosome biogenesis in human cells.
Noc3p（核仁复合物相关蛋白）是芽殖酵母 DNA 复制许可中的必需蛋白。Noc3p 通过与 ORC（起始识别复合物）和 MCM（微小染色体维持）蛋白相互作用，介导 Cdc6p 和 MCM 蛋白在 M 到 G 转换期间加载到复制起点。FAD24（脂肪细胞分化因子，克隆号 24）是 Noc3p（hNOC3）的人类同源物，先前报道在人类细胞中发挥调节 DNA 复制和增殖的作用。然而，hNOC3 在复制许可中的作用尚不清楚。在这里，我们报告 hNOC3 与多个人类前复制复合物（pre-RC）蛋白物理相互作用，并在整个细胞周期与已知的复制起点相关联。此外，在 HeLa 细胞中敲低 hNOC3 会破坏其他 pre-RC 蛋白（包括 hCDC6 和 hMCM）与染色质的关联，导致 DNA 复制缺陷并最终在有缺陷的 S 期发生细胞凋亡。相比之下，在 hNOC3 敲低实验的相同时间内，通过阻止 pre-rRNA 合成特异性抑制核糖体生物发生途径不会导致任何细胞周期或 DNA 复制缺陷或细胞凋亡。我们的研究结果强烈表明，hNOC3 在 pre-RC 形成和 DNA 复制起始中发挥重要作用，独立于其在人类细胞中核糖体生物发生中的潜在作用。
