Activation of the Kaposi's Sarcoma-Associated Herpesvirus Major Latency Locus by the Lytic Switch Protein RTA (ORF50)

Abstract

Kaposi's sarcoma-associated herpesvirus (KSHV) maintains a latent infection in primary effusionWe identified a minimal cis-regulatory region, which overlaps with the promoter for the bicistronic K14/v-GPCR delayed early gene that is transcribed in the opposite direction. In addition to a TATA box at ؊30 relative to the LT i mRNA start sites, we identified three separate RTA response elements that are also utilized by the K14/v-GPCR promoter. Interestingly, LT i is unresponsive to sodium butyrate, a potent inducer of lytic replication. This suggests there is a previously unrecognized class of RTA-responsive promoters that respond to direct, but not indirect, induction of RTA. These studies highlight the fact that induction method can influence the precise program of viral gene expression during early events in reactivation and also suggest a mechanism by which RTA contributes to establishment of latency during de novo infections.

Cytoplasmic isoforms of Kaposi sarcoma herpesvirus LANA recruit and antagonize the innate immune DNA sensor cGAS

“…It has been shown that expression of LANA can be directed from two different promoters that generate different 5′ UTRs of LANA mRNA. Although the constitutive (latent) promoter generates a longer 5′ UTR that occurs in a spliced or unspliced form, the lytic LANA promoter, localized in the intron within the LANA 5′ UTR, directs the expression of an unspliced mRNA with a shorter 5′ UTR (4,57,58). One could envisage that the shorter 5′ UTR generated during lytic reactivation could favor, as a result of a different RNA structure fold, the use of internal start codons in the LANA NTD and thereby the generation of LANA variants lacking the N-terminal NLS (4,5), which localize to the cytoplasm.…”

A combined computational and microarray-based approach identifies novel microRNAs encoded by human gamma-herpesviruses

“…The region deleted in the B95-8 strain of EBV is indicated. (Dittmer et al 1998;Sadler et al 1999;Li et al 2002;Matsumura et al 2005;Pearce et al 2005). The question mark indicates a2.3-kb ''Kaposin'' mRNA (Sadler et al (1999); it is unclear to what extent this transcript contributes to the overall abundance of Kaposin-encompassing transcripts in latently infected cells.…”

Transcripts Encoding K12, v-FLIP, v-Cyclin, and the MicroRNA Cluster of Kaposi's Sarcoma-Associated Herpesvirus Originate from a Common Promoter

“…Recent work from our laboratory has characterized a second promoter (LT i ) that is located between LT c and the initiation codon of ORF 73 (35). In latent cells, LT i is inactive but can be induced by the lytic switch protein RTA encoded by ORF 50.…”

“…In latent cells, LT i is inactive but can be induced by the lytic switch protein RTA encoded by ORF 50. Using a PEL-derived cell line (TRExBCBL1-Rta) that has been engineered to allow regulated expression of the lytic switch protein RTA in the presence of doxycycline (38), we observed a fiveto sevenfold induction of both the 5.4-and 1.7-kb LT mRNAs, accompanied by a small but appreciable decrease in average transcript length to approximately 1.5 kb (35).…”

“…A constitutively active promoter (LT c ) gives rise to a precursor RNA (dotted line) that undergoes polyadenylation/cleavage and alternative splicing to produce ϳ5.7-kb and ϳ5.4-kb tricistronic (ORFs 71, 72, and 73) and ϳ1.7-kb dicistronic (ORFs 71 and 72) mRNAs (14,47,50). Expression of the lytic activator RTA induces a second promoter (LT i ) located between ORF 73 and LT c , giving rise to a 5.5-kb mRNA spanning all three ORFs (35). A 2.3-to 2.5-kb spliced mRNA corresponding to ORF K12, encoding multiple isoforms of kaposin, is transcribed during latency from a promoter at the 3Ј end of ORF 73 and is induced further during lytic replication (27,45).…”