GSE99946
KSHV chromatin looping facilitates effective gene expression: high-resolution mapping of long-range chromatin interactions in the KSHV genome [Hi-C]
The three-dimensional structure of chromatin via formation of genomic loops allows cellular RNA polymerase II to access distal promoters, thus it has a significant impact on the outcome of gene expression. The Kaposi's sarcoma-associated herpesvirus (KSHV) entire lytic transcriptional program of 80 plus genes is initiated by a single viral transactivator, K-Rta. Here we examined the relationship between the KSHV genomic structure and K-Rta recruitment sites with unbiased Capture Hi-C analyses. The studies showed that KSHV forms a unique genomic structure, which coordinates a domain-specific viral gene expression program via K-Rta recruitment, and identified a number of direct physical, long-range, and dynamic genomic interactions. Chromatin immunoprecipitation-sequencing analyses identified a limited number of K-Rta recruitment sites in the KSHV genome, including the K12 and PAN RNA promoters. KSHV engineered to harbor point mutations in the K-Rta-responsive elements (RE) at these promoters significantly attenuated not only the direct downstream gene, but also distal viral gene expression in a domain-specific manner. Despite the long distance between two RE sites in the linear orientation, efficient recruitment of K-Rta to either promoter required intact K-Rta REs at both promoters. Finally, inducible genomic loops generated during KSHV reactivation occurred preferentially at K-Rta recruitment sites. Mutation of a K-Rta RE inhibited formation of inducible genomic loops, gene expression of its destination of looping genes, and KSHV replication in de novo infected human gingival epithelial cells. These results suggest that the KSHV genome is programed to form both stable and inducible chromatin hubs for effective KSHV gene expression, and partly explains why K-Rta has such a dominant effect on KSHV lytic gene transcription. Overall design: The overall goal of these studies was to define the long-range chromatin interactions occurring within the KSHV genome as well as between the KSHV and human host cell genomes both during latency and viral reactivation. These were defined in an unbiased manner using Hi-C analysis, which is chromosome conformation capture (3C) combined with next-generation sequencing (NGS). A modified protocol, referred to as Capture Hi-C, was utilized to selectively enrich interactions involving KSHV by performing target enrichment with a custom-designed KSHV genomic capture probe library. Experiments were performed in two cell lines, TREx-(F3H3)-K-Rta BCBL-1 and iSLK.r219 cells, in which KSHV can be reactivated via doxyclyine-induced expression of K-Rta. Accordingly, Capture Hi-C sequencing libraries were prepared from replicate cultures of each cell line cultured in the absence (i.e., latency) or presence (i.e., reactivation) of doxycycline for 24 hours.