KSHV Terminal Repeat Regulates Inducible Lytic Gene Promoters
The Kaposi's sarcoma-associated herpesvirus (KSHV) genome consists of an approximately 140 kb unique coding region flanked by 30-40 copies of 0.8 kb terminal repeat (TR) sequence. KSHV genomes persist in latently infected cells as episomes via tethering to the host cell chromosomes, and KSHV latency associated nuclear antigen (LANA) plays a crucial role in latent episomal DNA replication and segregation during host cell mitosis by binding to TR. While TR's function in plasmid maintenance is well-established, TR's transcription regulatory roles as gene enhancer has not been fully explored. Gene enhancer harbors transcription enzymes via arrays of transcription factors bindings and often forms phase separate nuclear body in part through recruitment of BRD4 and MED1 that contain intrinsically disordered domain. Here we show KSHV TR possesses transcription regulatory function with LANA. A series of Cleavage Under Targets & Release Using Nuclease (CUT&RUN) demonstrated that TR fragments are occupied by histone modifying enzymes that are known to interact with LANA in naturally infected cells, and the TR possessed characteristic enhancer histone modifications. The H3K4me3 and H3K27Ac modification were also conserved in unique region of the KSHV genome among three PEL cells, and the KSHV Origin of lytic replication (Ori-Lyt) showed similar protein and histone modification occupancies with TR's. In the Ori-Lyt region, the LANA protein complex colocalizes with H3K27Ac-modified nucleosome along with paused RNA polymerase II, and the nucleosome is franked by two K-Rta recruitment sites. The isolated reporter assays demonstrated that neighboring TR fragments enhanced viral lytic gene promoter activity independent of orientation in KSHV-infected and non-infected 293FT cells. K-Rta transactivation function was drastically enhanced with TR, while LANA acquired promoter repression function when the reporter was ligated with TR. The deletion of LANA acidic repeat sequence, a highly-disordered protein domain, further increased gene repression functions. Combined, the TR region is (i) an epigenetically active DNA element that is stitched within 12.5 kb (20-40 copies), (ii) has an array of transcription factor (LANA) binding sites, (iii) recruited by transcription related enzymes including BRD4 (bromodomain containing 4), (iv) decorated by histone H3K27Ac marks, and (v) possesses orientation-independent transcription activation function. KSHV TR is therefore an enhancer domain for KSHV inducible genes. However, in contrast to cellular enhancers that are bound by multiple transcription factors, perhaps KSHV enhancer is predominantly regulated by the LANA nuclear body on the TR. We suggest that KSHV evolved a clever mechanism to tightly control the latency-lytic switch with the TR/LANA complex. Overall design: The goal of these studies was to utilize CUT&RUN in order to determine the lanscape of histone-modifying enzymes that interact with LANA and occupy the KSHV Terminal Repeat fragents in naturally infected cells . For this CUT&RUN was performed for BRD4, ADNP, MLL1, SMC1, SMARCA5, CTCF, RNA polymerase II, and histone modification marks (H327Ac, H3K4me1, H3K4me2, H3K27me3 ). Please note that the records have been updated with the additional *CPM_norm.bigWig files on Oct 19, 2023.