RNA Editing of the Human Herpesvirus 8 Kaposin Transcript Eliminates Its Transforming Activity and Is Induced during Lytic Replication

Abstract

Human herpesvirus 8 is the etiologic agent associated with Kaposi's sarcoma and primary effusion lymphoma (PEL). The K12 RNA, which produces as many as three variants of the kaposin protein, as well as a microRNA, is the most abundant transcript expressed in latent Kaposi's sarcoma-associated herpesvirus infection, and yet it is also induced during lytic replication. The portion of the transcript that includes the microRNA and the kaposin A sequence has been shown to have tumorigenic potential. Genome coordinate 117990, which is within this transcript, has been found to be heterogeneous, primarily in RNAs but also among viral DNA sequences. This sequence heterogeneity affects an amino acid in kaposins A and C and the microRNA. The functional effects of this sequence heterogeneity have not been studied, and its origin has not been definitively settled; both RNA editing and heterogeneity at the level of the viral genome have been proposed. Here, we show that transcripts containing A at position 117990 are tumorigenic, while those with G at this position are not. Using a highly sensitive quantitative assay, we observed that, in PEL cells under conditions where more than 60% of cDNAs derived from K12 RNA transcripts have G at coordinate 117990, there is no detectable G in the viral DNA sequence at this position, only A. This result is consistent with RNA editing by one of the host RNA adenosine deaminases (ADARs). Indeed, we observed that purified human ADAR1 efficiently edits K12 RNA in vitro. Remarkably, the amount of editing correlated with the replicative state of the virus; editing levels were nearly 10-fold higher in cells treated to induce lytic viral replication. These results suggest that RNA editing controls the function of one segment of the kaposin transcript, such that it has transforming activity during latent replication and possibly another, as-yet-undetermined, function during lytic replication.

Editing of Epstein-Barr Virus-encoded BART6 MicroRNAs Controls Their Dicer Targeting and Consequently Affects Viral Latency*

“…Additional studies conducted more recently confirmed that this is indeed due to A-to-I editing at this site of the viral transcript harboring KSHV-miR-K12-10 by ADAR1 (56). Interestingly, the transcript could be processed into the viral miRNA as well as the mRNA coding for Kaposin A. A-to-I editing and consequent recoding of Kaposin A reduced its transforming activity (56). However, the significance of A-to-I editing of KSHV-miR-K12-10 RNAs remains unknown.…”

The fraction of RNA that folds into the correct branched secondary structure determines hepatitis delta virus type 3 RNA editing levels

“…Editing levels of a number of cellular and viral RNAs vary considerably, not only among different sites, but for the same site in different tissues, stages of development, and pathological settings (Bass 2002;Keegan et al 2004;Maas et al 2006;Gandy et al 2007;Cenci et al 2008;Riedmann et al 2008). As yet, the factors that determine these variations are not well understood.…”

Genomewide Mapping and Screening of Kaposi's Sarcoma-Associated Herpesvirus (KSHV) 3′ Untranslated Regions Identify Bicistronic and Polycistronic Viral Transcripts as Frequent Targets of KSHV MicroRNAs

“…KSHV pre-miR-K10 is derived from the coding region of ORF-K12 (59). Although there are several functional variants, the predominant mature miRNA in latent KSHV cells is miR-10a-3p, which can be switched to miR-10b-3p with a single point mutation during lytic replication through RNA editing (13,32,38,60,61). The ORF71-73 gene locus encodes three viral latent proteins, including vFLIP (ORF71), vCyclin (ORF72), and LANA (ORF73), that have diverse functions during viral latency.…”