GRWD1-WDR5-MLL2 Epigenetic Complex Mediates H3K4me3 Mark and Is Essential for KSHV-Induced Cellular Transformation

Infection by Kaposi's sarcoma-associated herpesvirus (KSHV) is causally associated to the development of several cancers. Despite intensive studies, the mechanism of KSHV-induced oncogenesis remains unclear. By performing a genome-wide CRISPR-Cas9 screening in a model of KSHV-induced cellular transformation of primary cells, we have identified a set of cellular genes related to epigenetic regulation that are essential for KSHV-induced cellular transformation. The top 9 genes had positive effects on cell proliferation and survival of KMM but not MM cells with the most differences in CRISPR Scores between KMM and MM cells were selected. Examination of TCGA datasets revealed that the expression of these 9 genes predicts patient survival in different types of cancer. We revealed global epigenetic remodeling including H3K4me3 mark in KSHV-transformed cells (KMM) compared to the matched primary cells (MM). Knockdown of glutamate rich WD repeat containing 1 (GRWD1), a WD40 family protein upregulated by KSHV, not only inhibited cell proliferation, cellular transformation and tumor formation but also caused down-regulation of global H3K4me3 mark in KMM cells. GRWD1 interacted with WD repeat domain 5 (WDR5), the core protein of H3K4 methyltransferase complex, and several H3K4me3 methyltransferases including myeloid/lymphoid or mixed-lineage leukemia 2 (MLL2). Knockdown of WDR5 and MLL2 phenocopied GRWD1, and altered the expression of a similar set of genes and caused global reduction of H3K4me3 mark. RNA-seq and ChIP-seq analyses further identified common and distinct cellular genes and pathways that were regulated by GRWD1, WDR5 and MLL2. These results indicate that KSHV upregulates GRWD1 to hijack the GRWD1-WDR5-MLL2 epigenetic complex and increase H3K4me3 methylation, which is essential for KSHV-induced cellular transformation and tumorigenesis. Our work has identified an epigenetic complex as a novel therapeutic target for KSHV-induced cancers.