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Lymphotropic Herpesvirus saimiri uses the SMN complex to assemble Sm cores on its small RNAs.

ABSTRACT: The lymphotropic Herpesvirus saimiri (HVS) causes acute leukemia, T-cell lymphoma, and death in New World monkeys. HVS encodes seven small RNAs (HSURs) of unknown function. The HSURs acquire host Sm proteins and assemble Sm cores similar to those found on the spliceosomal small nuclear RNPs (snRNPs). Here we show that, like host snRNPs, HSURs use the SMN (survival of motor neurons) complex to assemble Sm cores. The HSURs bind the SMN complex directly and with very high affinity, similar to or higher than that of host snRNAs, and can outcompete host snRNAs for SMN-dependent assembly into RNPs. These observations highlight the general utility of the SMN complex for RNP assembly and suggest that infectious agents that engage the SMN complex may burden SMN-dependent pathways, possibly leading to a deleterious reduction in available SMN complex for essential host functions.

SUBMITTER: Golembe TJ

PROVIDER: S-EPMC543424 | biostudies-other | 2005 Jan

REPOSITORIES: biostudies-other

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Project description:In latently infected marmoset T cells, Herpesvirus saimiri (HVS) expresses six microRNAs (known as miR-HSURs [H. saimiri U-rich RNAs]). The viral miR-HSURs are processed from chimeric primary transcripts, each containing a noncoding U-rich RNA (HSUR) and a pre-miRNA hairpin. To uncover the functions of miR-HSURs, we identified mRNA targets in infected cells using high-throughput sequencing of RNA isolated by cross-linking immunoprecipitation (HITS-CLIP). HITS-CLIP revealed hundreds of robust Argonaute (Ago) binding sites mediated by miR-HSURs that map to the host genome but few in the HVS genome. Gene ontology analysis showed that several pathways regulating the cell cycle are enriched among cellular targets of miR-HSURs. Interestingly, miR-HSUR4-3p represses expression of the p300 transcriptional coactivator by binding the open reading frame of its mRNA. miR-HSUR5-3p directly regulates BiP, an endoplasmic reticulum (ER)-localized chaperone facilitating maturation of major histocompatibility complex class I (MHC-I) and the antiviral response. miR-HSUR5-3p also robustly downregulates WEE1, a key negative regulator of cell cycle progression, leading to reduced phosphorylation of its substrate, cyclin-dependent kinase (Cdk1). Consistently, inhibition of miR-HSUR5-3p in HVS-infected cells decreases their proliferation. Together, our results shed light on the roles of viral miRNAs in cellular transformation and viral latency.Viruses express miRNAs during various stages of infection, suggesting that viral miRNAs play critical roles in the viral life cycle. Compared to protein-coding genes, the functions of viral miRNAs are not well understood. This is because it has been challenging to identify their mRNA targets. Here, we focused on the functions of the recently discovered HVS miRNAs, called miR-HSURs. HVS is an oncogenic gammaherpesvirus that causes acute T-cell lymphomas and leukemias in New World primates and transforms human T cells. A better understanding of HVS biology will help advance our knowledge of virus-induced oncogenesis. Because numerous cellular miRNAs play crucial roles in cancer, viral miRNAs from the highly oncogenic HVS might also be important for transformation. Here, we found that the miR-HSURs preferentially modulate expression of host cell cycle regulators, as well as antiviral response factors. Our work provides further insight into the functions of herpesviral miRNAs in virus-induced oncogenesis and latency.

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Lymphotropic Herpesvirus saimiri uses the SMN complex to assemble Sm cores on its small RNAs.

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