Mechanisms of mRNP remodeling in mRNA turnover

描述（由申请人提供）：基因表达可在多个水平调控，包括mRNA降解。mRNA的降解速率可以有数量级的变化，并且可以通过细胞信号来调节，从而改变mRNA的水平，从而改变蛋白质的产生，以响应细胞条件的变化。mrna与蛋白质复合物存在于细胞中，形成信使核糖核蛋白（mrna）。mRNP复合物的蛋白质控制mRNA的活性并保护mRNA免于衰变。mRNA的靶向降解涉及RNA降解酶的募集-然而，mRNP的蛋白质被释放以允许mRNA降解酶进入mRNA的机制尚不清楚。我们最近发现了一种依赖于ATP水解的蛋白Upf1的活性，这种活性对于分解mRNP至关重要，从而允许mRNA降解靶向mRNA衰变途径，称为无义介导的衰变（NMD）。本研究的目的是通过以下具体目的来了解mRNP重塑和拆卸在各种人类mRNA衰变途径中的重要性和机制。首先，研究人员将测试Upf1过度磷酸化的能力，Upf1是NMD通路的核心成分，包含其激酶Smg1的多个磷酸化位点，在NMD通路中充当mRNA衰减放大器，通过增强mRNA衰减因子的募集，使NMD能够在mRNA衰减因子受限时与其他mRNA衰减通路竞争。其次，将测试Upf1的atp酶活性是否对组蛋白mRNA的重塑至关重要，从而使组蛋白mRNA在细胞周期s期结束时衰变。第三，我们将测试在RNA诱导沉默复合体（RISC）与microRNAs复合物激活的mRNA降解过程中，Upf1的同源物MOV10的ATPase活性是否需要RNP重塑。与公共卫生的相关性mRNA周转的放松与包括癌症在内的许多人类疾病有关。本文所述的研究旨在阐明人类细胞中mRNA降解的基本机制，这将有助于了解mRNA的降解在正常条件下是如何调节的，而在人类疾病中是如何解除调控的。

DESCRIPTION (provided by applicant): Gene expression can be regulated at multiple levels including mRNA degradation. The rate of degradation of mRNAs can vary by orders of magnitude and can be regulated by cellular cues, thus altering mRNA levels and thereby protein production in response to changes in cell conditions. mRNAs exist in cells in complex with proteins, forming the messenger ribonucleoproteins (mRNPs). The proteins of the mRNP complex control mRNA activity and protect the mRNA from decay. The targeting of an mRNA for degradation involves the recruitment of RNA degrading enzymes - however, the mechanism by which proteins of the mRNP are released to allow access for the mRNA decay enzymes to the mRNA is poorly understood. We have recently uncovered an activity dependent on ATP hydrolysis by the protein Upf1 that is critical for disassembling the mRNP to allow for degradation of mRNAs targeted to an mRNA decay pathway called nonsense-mediated decay (NMD). The objective of this research is to understand the importance and mechanism of mRNP remodeling and disassembly in various human mRNA decay pathways, through the following specific aims. First, it will be tested whether the ability to hyperphosphorylate Upf1, a central component of the NMD pathway that contains multiple phosphorylation sites for its kinase Smg1, serves as an mRNA decay amplifier in the NMD pathway that, via enhanced mRNA decay factor recruitment, enables NMD to compete with other mRNA decay pathways when mRNA decay factors are limiting. Second, it will be tested whether the ATPase activity of Upf1 is critical for remodeling of histone mRNPs to allow histone mRNA decay at the end of the cell cycle S-phase. Third, it will be tested whether ATPase activity of MOV10, a homolog of Upf1, is required for RNP remodeling during mRNA degradation activated by the RNA induced silencing complex (RISC) in complex with microRNAs. Relevance to Public Health Deregulation of mRNA turnover has been associated with a number of human disorders including cancers. The studies described here are aimed at elucidating fundamental mechanisms underlying the degradation of mRNA in human cells, which should provide insights into how mRNA decay is regulated under normal conditions and deregulated in human disorders. PUBLIC HEALTH RELEVANCE: The degradation of mRNA is an important point in regulation of gene expression and its mis- regulation is associated with multiple human disorders including cancers. Cellular mRNAs are coated with proteins in messenger ribonucleoprotein (mRNP) complexes, which control mRNA function and protect the mRNAs from degradation by mRNA decay enzymes. It has recently become clear that when an mRNA is targeted for decay, a critical and possibly regulated step is to strip the mRNP of associated proteins to allow access for mRNA decay enzymes. The goal of the studies of this proposal is to understand the mechanism by which various mRNA decay pathways achieve this.