Viral RNPs, mRNA Stability and Export

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The roles of non-coding RNAs in lymphoid cells harboring three transforming herpesviruses are being investigated. Epstein-Barr virus (EBV) infects and transforms humanB cells; it is the causative agent of infectious mononucleosis and is associated with several human cancers. Herpesvirus saimiri (HVS) induces fatal lymphomas and leukemias in New World monkeys and transforms human and monkey T lymphocytes in culture, generating a mature; activated phenotype. Kaposi's sarcoma-associated herpesvirus (KSHV) afflicts immunocompromised individuals and persists in a latent form until lytic activation. The two EBVencoded EBERs, as well as >23 newly identified microRNAs, and the seven HVS-encoded HSURs are expressed in virally transformed cells. Upon induction, KSHV produces PAN, a capped, polyadenylated RNA that does not leave the nucleus. These viral RNAs are all small (from 21 nts to 1.1 kb), abundant, conserved, and associate with host proteins to form RNPs. Studying their functions has,already contributed important insights into host cell pathways perturbed during viral transformation or lytic growth. Proposed aims will test the hypotheses that EBERs, HSURs and PAN manipulate cellular metabolism by sequestering host proteins or microRNAs, or that the resulting RNPs perform a critical viral function. We recently found that HSUR RNPs bind certain host microRNAs; interference with their regulatory roles in transformed T cells will be examined. The possibility that EBERs likewise bind host microRNAs will be tested. Our discovery that microRNAs in quiescent cells activate rather than repress translation will be exploited to investigate the EBV-encoded microRNAs since many transformed B cells exist in a quiescent state in the body. We showed that PAN RNA accumulates to very high nuclear levels in KSHV-reactivated cells because an element (the ENE) near its 3' end engages the polyA tail to prevent RNA decay. Structural studies of the ENE +/- oligoA, as well as complexed with polyA binding protein (PABPC1), will provide mechanistic insights. Our observation that PAN RNA is involved in relocalization of host PABPC1 to the nucleus, suggesting collaboration with the KSHV SOX protein in host mRNA shut off, will be investigated