The Herpesvirus saimiri Small Nuclear RNAs Recruit AU-Rich Element-Binding Proteins but Do Not Alter Host AU-Rich Element-Containing mRNA Levels in Virally Transformed T Cells

Abstract

Herpesvirus saimiri (HVS) encodes seven Sm-class small nuclear RNAs, called HSURs (for Herpesvirus saimiri U RNAs), that are abundantly expressed in HVS-transformed, latently infected marmoset T cells but are of unknown function. HSURs 1, 2, and 5 have highly conserved 5′-end sequences containing the AUUUA pentamer characteristic of AU-rich elements (AREs) that regulate the stability of many host mRNAs, including those encoding most proto-oncogenes and cytokines. To test whether the ARE-containing HSURs act to sequester host proteins that regulate the decay of these mRNAs, we demonstrate their in vivo interaction with the ARE-binding proteins hnRNP D and HuR in HVS-transformed T cells using a new cross-linking assay. Comprehensive Northern and microarray analyses revealed, however, that the levels of endogenous ARE-containing mRNAs are not altered in T cells latently infected with HVS mutants lacking HSURs 1 and 2. HSUR 1 binds the destabilizing ARE-binding protein tristetraprolin induced following activation of HVS-transformed T cells, but even in such stimulated cells, the levels of host ARE-containing mRNAs are not altered by deletion of HSURs 1 and 2. Instead, HSUR 1 itself is degraded by an ARE-dependent pathway in HVS-transformed T cells, suggesting that HVS may take advantage of the host ARE-mediated mRNA decay pathway to regulate HSUR expression. This is the first example of posttranscriptional regulation of the expression of an Sm small nuclear RNA.

We are most grateful to Ronald Desrosiers and Daniel Silva for the creation of the wild-type and mutant HVS-transformed marmoset T-cell lines examined in this study. We thank Irena Tikhonova and Aiping Lin at the Keck microarray facility for expert assistance with the microarrays and biostatistical analyses. We thank William Rigby for generously providing anti-TTP antibody. We thank Jens Lykke-Andersen and members of the Steitz lab, especially Nick Conrad, for essential materials and valuable advice and discussion throughout this work.

The Keck DNA Microarray Resource at Yale University is supported by the Anna and Argall Hull Fund, the NIH/NIDDK Microarray Biotechnology Center Grant (NIH 5 U24 DK58776; Principal Investigator, Kenneth Williams), the C. G. Swebilius Trust U.W., and the Yale University Department of Pathology. H.L.C. was a Howard Hughes Medical Institute Predoctoral Fellow, and J.A.S. is an investigator of the Howard Hughes Medical Institute. This work was supported by grant CA 16038 from the NIH.