UCLA

Adenovirus e1a expression in contact-inhibited cells forces G1 to S phase transition in preparation to create suitable cellular environment for viral replication. To determine genomic regions targeted by e1a to bind and manipulate chromatin landscape of host cells, ChIP-seq of e1a was performed in e1a-expressing primary fibroblast cells at 6 and 24 hours post infection. Critical regions in the genome are occupied by e1a proteins since early in infection including active enhancers, gene body of growth inhibition genes, and cell cycle gene promoters. Binding of e1a at active enhancers results in drastic reduction of H3K18ac and H3K27ac histone modifications. Through co-localization with massive levels of P300/CBP, activators of TGF-beta pathway are strongly repressed with high density of e1a binding throughout gene promoter and gene body to prevent G1 arrest. Finally, promoters of cell cycle genes bound by Rb in contact-inhibited cells are targeted by e1a at both 6 and 24 hours post infection to relieve Rb repression of E2F-regulated cell cycle genes. Overall, highly-expressed cell-type-specific genes are repressed by e1a binding and genes promoting S phase entry are stimulated by e1a. Surprisingly, e1a binding sites at both 6 and 24 hours PI are also early replication origin found in growing normal fibroblast cells. Furthermore, e1a represses host cell replication as 95% of newly synthesized DNA in e1a expressing cells originated from viral genome. By binding to host cell chromatin, e1a creates S phase environment in host cell to stimulate viral replication.