Molecular Medicine Laboratory, International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
PLoS One. 2010 Nov 9;5(11):e13720. doi: 10.1371/journal.pone.0013720.
The retinoblastoma protein (Rb) is a crucial regulator of cell cycle progression by binding with E2F transcription factor and repressing the expression of a variety of genes required for the G1-S phase transition.
METHODOLOGY/PRINCIPAL FINDINGS: Here we show that Rb and E2F1 directly participate in the control of initiation of DNA replication in human HeLa, U2OS and T98G cells by specifically binding to origins of DNA replication in a cell cycle regulated manner. We show that, both in vitro and inside the cells, the largest subunit of the origin recognition complex (Orc1) specifically binds hypo-phosphorylated Rb and that this interaction is competitive with the binding of Rb to E2F1. The displacement of Rb-bound Orc1 by E2F1 at origins of DNA replication marks the progression of the G1 phase of the cell cycle toward the G1-S border.
CONCLUSIONS/SIGNIFICANCE: The participation of Rb and E2F1 in the formation of the multiprotein complex that binds origins of DNA replication in mammalian cells appears to represent an effective mechanism to couple the expression of genes required for cell cycle progression to the activation of DNA replication.
视网膜母细胞瘤蛋白（Rb）通过与 E2F 转录因子结合并抑制 G1-S 期转化所需的多种基因的表达，从而成为细胞周期进程的关键调节因子。
方法/主要发现：在这里，我们表明 Rb 和 E2F1 通过在细胞周期调控方式下特异性结合 DNA 复制起始点，直接参与控制人 HeLa、U2OS 和 T98G 细胞中 DNA 复制的起始。我们表明，在体外和细胞内，起始识别复合物（Orc1）的大亚基特异性地结合低磷酸化的 Rb，并且这种相互作用与 Rb 与 E2F1 的结合具有竞争性。E2F1 在 DNA 复制起始点取代与 Rb 结合的 Orc1，标志着细胞周期的 G1 期向 G1-S 边界的进展。
结论/意义：Rb 和 E2F1 参与在哺乳动物细胞中形成与 DNA 复制起始点结合的多蛋白复合物的过程，似乎代表了一种将细胞周期进程所需基因的表达与 DNA 复制的激活相耦合的有效机制。
