Date of this Version
Kaposi’s sarcoma-associated herpesvirus (KSHV) is a member of the gamma-herpesvirinae subfamily and displays two distinct life phases, latency and lytic replication. Infection with KSHV mostly results in a latent state. A small population of infected cells can spontaneously undergo lytic phase, which is marked by abundant viral gene expression and production of infectious viral progeny. Lytic replication is important for transmission of KSHV in the population and development of diseases. RTA (replication and transcription activator) is a master regulator of KSHV lytic replication. Expression of RTA alone is sufficient to disrupt KSHV latency and initiate the lytic replication cascade. The objective of this research is to understand how RTA stimulates lytic replication.
RTA utilizes its DNA binding ability and /or cooperates with co-activators to up-regulate vial lytic gene expression for lytic replication. In the present and previous studies, we identified three distinct RTA responsive elements (RREs) in an early gene (ORF57) promoter, and all of them are located in close proximity to each other in the ORF57 promoter. Current study demonstrated that two adjacent RREs and a co-activator (RBP-Jκ) binding site are required for optimal transactivation of the ORF57 promoter by RTA. These results present the first evidence that RTA targets multiple DNA motifs in responsive viral promoter to achieve full transactivation.
We demonstrated that RTA is able to enhance the autophagy pathway through interference of the interaction between an autophagy-related protein Beclin 1 and an anti-apoptotic protein Bcl-2 by inducing Bcl-2 phosphorylation. This post-translational modification is a result of the induction of c-JUN N-terminal kinase (JNK) signaling pathway by RTA. In addition, a defective autophagy pathway specifically reduces RTA-mediated transactivation of lytic gene promoters. These results indicate that RTA activates autophagy to stimulate lytic gene expression and initiate lytic reactivation.
In conclusion, multiple non-conserved RREs and a co-activator binding site are required for RTA-mediated transactivation, indicating that a complex mechanism exists by which RTA transactivates lytic cycle gene expression. Additionally, RTA-induced autophagy may provide an optimal condition for RTA to mediate lytic gene expression and KSHV lytic activation, demonstrating that KSHV adopts cellular machinery for its viral DNA replication.