HCMV UL8 interaction with β-catenin and DVL2 regulates viral reactivation in CD34⁺ hematopoietic progenitor cells

Human cytomegalovirus (HCMV) is a species-specific virus that establishes a persistent/latent infection in CD34⁺ hematopoietic progenitor cells (HPCs). The ability of HCMV to reactivate from latency is exquisitely linked to changes in cell signaling, which result in HPC differentiation. The Wnt/β-catenin pathway is tightly linked to CD34⁺ HPC homeostasis and differentiation. The majority of the viral and cellular factors involved in the maintenance of HCMV latency and reactivation are still unknown. Our group previously discovered a viral hematopoietic cytokine (pUL7) that promotes cellular differentiation and viral reactivation. Here, we show that the UL7-related RL11 family member UL8 is also required for efficient viral reactivation in CD34⁺ HPCs by interacting with components of the (Wnt)/β-catenin pathway. Pull-down experiments demonstrate that UL8 and β-catenin interact with Dishevelled-2 (DVL2) through their PDZ-binding domains, and this interaction promotes β-catenin stabilization and transcriptional activation. Disrupting the interaction among UL8, β-catenin, and DVL2 blocks HCMV reactivation in vitro and in vivo, similar to deletion of UL8. This is the first observation that Wnt signaling components are essential for HCMV reactivation, unlike α- and γ-herpesvirus that require an active Wnt pathway to maintain latency. Detailed understanding of how the Wnt network is manipulated by herpesviruses will improve our ability to develop targeted therapeutics. IMPORTANCE CD34⁺ hematopoietic progenitor cells (HPCs) are an important cellular reservoir for latent human cytomegalovirus (HCMV). Several HCMV genes are expressed during latency that are involved with the maintenance of the viral genome in CD34⁺ HPC. However, little is known about the process of viral reactivation in these cells. Here, we describe a viral protein, pUL8, and its interaction and stabilization with members of the Wnt/β-catenin pathway as an important component of viral reactivation. We further define that pUL8 and β-catenin interact with DVL2 via a PDZ-binding domain, and loss of UL8 interaction with β-catenin-DVL2 restricts viral reactivation. Our findings will be instrumental in understanding the molecular processes involved in HCMV reactivation in order to design new antiviral therapeutics.