Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA.
Mol Cell Biol. 2011 Aug;31(16):3472-84. doi: 10.1128/MCB.05587-11. Epub 2011 Jun 20.
Transcriptional silencing selectively impedes gene expression. Silencing is often accompanied by replication delay and can be prevented by replicator sequences. Here we report a replicator-binding protein complex involved in the prevention of transcriptional silencing. The protein complex interacts with an essential asymmetric region within the human β-globin Rep-P replicator and includes hnRNP C1/C2, SWI/SNF complex, and MeCP1, which are members of the locus control region (LCR)-associated remodeling complex (LARC). Interaction between LARC and Rep-P prevented transcriptional silencing and replication delay. Transgenes that did not contain the asymmetric LARC-binding region of Rep-P replicated late and exhibited stable silencing that could not be affected by a DNA methylation inhibitor. In contrast, transgenes that contain a mutation of the asymmetric region of Rep-P that could not bind LARC exhibited a silent state that could transiently be reactivated by DNA demethylation. The effect of DNA demethylation was transient, and prolonged exposure to a methylation inhibitor induced distinct, stable, methylation-independent silencing. These observations suggest that the interaction of LARC complex with replicators plays a role in preventing gene silencing and provides support for a novel, epigenetic mechanism of resistance to methylation inhibitors.
转录沉默选择性地阻碍基因表达。沉默通常伴随着复制延迟，并且可以通过复制子序列来预防。在这里，我们报告了一种参与预防转录沉默的复制子结合蛋白复合物。该蛋白复合物与人类β-珠蛋白 Rep-P 复制子内的一个必需非对称区域相互作用，包括 hnRNP C1/C2、SWI/SNF 复合物和 MeCP1，它们是基因座控制区 (LCR) 相关重塑复合物 (LARC) 的成员。LARC 与 Rep-P 之间的相互作用可防止转录沉默和复制延迟。不包含 Rep-P 的不对称 LARC 结合区域的转基因复制延迟，并表现出稳定的沉默，不能被 DNA 甲基化抑制剂影响。相比之下，含有不能结合 LARC 的 Rep-P 不对称区域突变的转基因表现出沉默状态，这种沉默状态可以通过 DNA 去甲基化短暂激活。DNA 去甲基化的效果是短暂的，长时间暴露于甲基化抑制剂会诱导出明显的、稳定的、与甲基化无关的沉默。这些观察结果表明，LARC 复合物与复制子的相互作用在防止基因沉默中起作用，并为抵抗甲基化抑制剂的新型表观遗传机制提供了支持。
