Viral lncRNA: A regulatory molecule for controlling virus life cycle

Wang, Ziqiang; Zhao, Yiwan; Zhang, Yaou

As a mediator of gene expression, lncRNAs can generate small ncRNAs less than 200 nts in length, such as tRNAs and miRNAs, to enlarge their regulatory power. MALAT1 (metastasis-associated lung adenocarcinoma transcript 1) is a lncRNA that is specifically retained in the nucleus [71] and has been found to be involved in not only the assembly, modification and/or storage of the pre-mRNA processing machinery [72] but also the generation of a short tRNA-like ncRNA [MALAT1-associated small cytoplasmic RNA (mascRNA)] through cleavage by RNase P and RNase Z. After processing, the long MALAT1 transcript remains in the nucleus, whereas mascRNA is exported to the cytoplasm [73] . This regulatory mechanism may allow cytoplasmic components to sense the differential MALAT1 expression in the nucleus and may be involved in translational regulation by serving as a tRNA mimic. As another example, H19 appears to be a bi-functional RNA acting as both an lncRNA and a miRNA precursor that is subsequently processed into miR-675 by cleavage by the RNase III enzymes Drosha and Dicer [74] . Although H19 and miR-675 are regarded as a tumor suppressor and an oncogene, respectively [75] , the mechanism by which H19 exerts its functions through the generation of miRNAs raises the possibility that some other lncRNAs might also perform their biological roles by giving rise to miRNAs.