KSHV genome harbors both constitutive and lytically induced enhancers

Abstract

Kaposis sarcoma-associated herpesvirus (KSHV) belongs to the gamma-herpesvirus family and is a well-known human oncogenic virus. In infected cells, the viral genome of 165 kbp is circular DNA wrapped in chromatin. The tight control of gene expression is critical for latency, the transition into the lytic phase, and the development of viral-associated malignancies. Distal cis-regulatory elements (CRE), such as enhancers and silencers, can regulate gene expression in a position and orientation-independent manner. Open chromatin is another characteristic feature of enhancers. To systematically search for enhancers, we cloned all the open chromatin regions in the KSHV genome downstream to the luciferase gene and tested their enhancer activity in infected and uninfected cells. A silencer was detected upstream of the latency promoter (LANAp). Two constitutive enhancers were identified in the K12p-OriLyt-R and ORF29 Intron region, where ORF29 Intron is a tissue-specific enhancer. The following promoters: OriLyt-L, PANp, ALTp, and the Terminal Repeats (TRs) acted as lytically induced enhancers. Expression of the Replication and Transcription Activator (RTA), the master regulator of the lytic cycle, was sufficient to induce the activity of lytic enhancers in uninfected cells. We propose that the TRs that span about 24 kbp region serve as a "viral super-enhancer" that integrates the repressive effect of the latency protein LANA with the activating effect of RTA. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers and their regulated genes. The silencer and enhancers described here provide an additional layer to the complex gene regulation of herpesviruses. ImportanceIn this study, we performed a systematic functional assay to identify cis-regulatory elements within the genome of the oncogenic herpesvirus, Kaposi sarcoma-associated herpesvirus (KSHV). Similar to other herpesviruses, KSHV presents both latent and lytic phases. Therefore, our assays were performed in uninfected cells, during latent infection, and under lytic conditions. We identified two constitutive enhancers, where one seems to be a tissue- specific enhancer. In addition, four lytically induced enhancers, which are all responsive to the Replication and Transcription Activator (RTA), were identified. Furthermore, a silencer was identified between the major latency promoter and lytic genes locus. Utilizing CRISPR activation and interference techniques, we determined the connections between these enhancers with their regulated genes. The terminal repeats spanning a region of about 24 kbp, seem like a "viral super-enhancer" that integrates the repressive effect of the latency protein LANA with the activating effect of RTA to regulate latency to lytic transition.