Unraveling a cytoplasmic role for hnRNP D in the in vivo mRNA destabilization directed by the AU-rich element
Unraveling a cytoplasmic role for hnRNP D in the in vivo mRNA destabilization directed by the AU-rich element
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DOI：
10.1101/gad.13.14.1884
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发表时间：
1999-07-15
影响因子：
10.5
通讯作者：
Shyu, AB
中科院分区：
文献类型：
--
作者：
Loflin, P;Chen, CYA;Shyu, AB
富含AU的RNA去稳定化元件（战神）已成为研究哺乳动物细胞胞质mRNA周转的范例。虽然许多RNA结合蛋白已被证明在体外结合到战神，反式作用因子，参与在体内的细胞质RNA的ARE不稳定仍然是未知的。进行实验以研究细胞机制并鉴定ARE指导的mRNA衰变的潜在反式作用因子。这些实验鉴定了hnRNP D，一种能够在细胞核和细胞质之间穿梭的异质核核糖核蛋白（hnRNP），作为ARE介导的快速mRNA衰变中体内RNA去稳定蛋白。我们的研究结果表明，ARE不稳定的功能显着阻碍氯化血红素诱导的红系分化，而不是在TPA诱导的巨核细胞分化的人红白血病K562细胞。hnRNP D螯合成氯化血红素诱导的蛋白质复合物，称为氯化血红素调节因子或HRF，与细胞质中ARE去稳定功能的丧失密切相关。进一步的实验表明，在氯化血红素处理的细胞中，hnRNP D的异位表达恢复了由ARE指导的快速衰减。hnRNP D的四种亚型的不稳定作用的程度不同，p37和p42显示最深刻的影响。这些结果证明了hnRNP D在ARE介导的衰变途径中作为RNA去稳定蛋白的特异性胞质功能。这些体内发现支持了一个新的观点，即穿梭的hnRNP蛋白在mRNA代谢中不仅具有核功能，而且还具有细胞质功能。这些数据进一步表明，穿梭hnRNP蛋白定义，至少部分，单个mRNA的核历史，从而影响其细胞质的命运。
AU-rich RNA-destabilizing elements (AREs) have become a paradigm for studying cytoplasmic mRNA turnover in mammalian cells. Though many RNA-binding proteins have been shown to bind to AREs in vitro, trans-acting factors that participate in the in vivo destabilization of cytoplasmic RNA by AREs remains unknown. Experiments were performed to investigate the cellular mechanisms and to identify potential trans-acting factors for ARE-directed mRNA decay. These experiments identified hnRNP D, a heterogeneous nuclear ribonucleoprotein (hnRNP) capable of shuttling between the nucleus and cytoplasm, as an RNA destabilizing protein in vivo in ARE-mediated rapid mRNA decay. Our results show that the ARE destabilizing function is dramatically impeded during hemin-induced erythroid differentiation and not in TPA-induced megakaryocytic differentiation of human erythroleukemic K562 cells. A sequestration of hnRNP D into a hemin-induced protein complex, termed hemin-regulated factor or HRF, correlates well with the loss of ARE-destabilizing function in the cytoplasm. Further experiments show that in hemin-treated cells, ectopic expression of hnRNP D restores the rapid decay directed by the ARE. The extent of destabilizing effect varies among the four isoforms of hnRNP D, with p37 and p42 displaying the most profound effect. These results demonstrate a specific cytoplasmic function for hnRNP D as an RNA-destabilizing protein in ARE-mediated decay pathway. These in vivo findings support an emerging idea that shuttling hnRNP proteins have not only a nuclear but also a cytoplasmic function in mRNA metabolism. The data further imply that shuttling hnRNP proteins define, at least in part, the nuclear history of individual mRNAs and thereby influence their cytoplasmic fate.