Helmholtz-University-Group "Molecular RNA Biology & Cancer," German Cancer Research Center DKFZ & Institute of Pathology, University Hospital Heidelberg, Germany.
Hepatology. 2013 Nov;58(5):1703-12. doi: 10.1002/hep.26537. Epub 2013 Aug 7.
Selected long noncoding RNAs (lncRNAs) have been shown to play important roles in carcinogenesis. Although the cellular functions of these transcripts can be diverse, many lncRNAs regulate gene expression. In contrast, factors that control the expression of lncRNAs remain largely unknown. Here we investigated the impact of RNA binding proteins on the expression of the liver cancer-associated lncRNA HULC (highly up-regulated in liver cancer). First, we validated the strong up-regulation of HULC in human hepatocellular carcinoma. To elucidate posttranscriptional regulatory mechanisms governing HULC expression, we applied an RNA affinity purification approach to identify specific protein interaction partners and potential regulators. This method identified the family of IGF2BPs (IGF2 mRNA-binding proteins) as specific binding partners of HULC. Depletion of IGF2BP1, also known as IMP1, but not of IGF2BP2 or IGF2BP3, led to an increased HULC half-life and higher steady-state expression levels, indicating a posttranscriptional regulatory mechanism. Importantly, HULC represents the first IGF2BP substrate that is destabilized. To elucidate the mechanism by which IGF2BP1 destabilizes HULC, the CNOT1 protein was identified as a novel interaction partner of IGF2BP1. CNOT1 is the scaffold of the human CCR4-NOT deadenylase complex, a major component of the cytoplasmic RNA decay machinery. Indeed, depletion of CNOT1 increased HULC half-life and expression. Thus, IGF2BP1 acts as an adaptor protein that recruits the CCR4-NOT complex and thereby initiates the degradation of the lncRNA HULC.
Our findings provide important insights into the regulation of lncRNA expression and identify a novel function for IGF2BP1 in RNA metabolism.
已显示某些长链非编码 RNA（lncRNA）在致癌作用中发挥重要作用。尽管这些转录本的细胞功能可能多种多样，但许多 lncRNA 可调节基因表达。相比之下，控制 lncRNA 表达的因素在很大程度上仍未知。在此，我们研究了 RNA 结合蛋白对肝癌相关 lncRNA HULC（肝癌中高度上调）表达的影响。首先，我们验证了 HULC 在人肝癌中的强烈上调。为了阐明调节 HULC 表达的转录后调控机制，我们应用 RNA 亲和纯化方法来鉴定特定的蛋白相互作用伙伴和潜在的调节剂。该方法鉴定了 IGF2BPs（IGF2 mRNA 结合蛋白）家族为 HULC 的特异性结合伙伴。IGF2BP1（也称为 IMP1）的消耗，但不是 IGF2BP2 或 IGF2BP3 的消耗，导致 HULC 半衰期增加和稳态表达水平升高，表明存在转录后调控机制。重要的是，HULC 代表第一个被 IGF2BP 稳定化的 IGF2BP 底物。为了阐明 IGF2BP1 使 HULC 不稳定的机制，鉴定了 CNOT1 蛋白为 IGF2BP1 的新型相互作用伙伴。CNOT1 是人类 CCR4-NOT 脱腺苷酸酶复合物的支架，该复合物是细胞质 RNA 降解机制的主要组成部分。事实上，CNOT1 的消耗增加了 HULC 的半衰期和表达。因此，IGF2BP1 作为衔接蛋白，募集 CCR4-NOT 复合物，从而启动 lncRNA HULC 的降解。
我们的发现为 lncRNA 表达的调控提供了重要的见解，并确定了 IGF2BP1 在 RNA 代谢中的新功能。
