Interplay between HCMV Protein pp65 and cGAS-STING Pathway: Modulating Viral Infectivity via Lipid Metabolism

The phosphoprotein 65 (pp65) constitutes a major component of the virion tegument in human cytomegalovirus (HCMV), despite its nonessential role in virion assembly. Nevertheless, pp65 plays a pivotal role in modulating and dampening host antiviral responses. This study seeks to elucidate the impact of pp65 on viral infectivity. We initially assessed the replication and infectivity of a mutant strain of HCMV TB40-BAC4, unable to express UL83-encoded pp65 (v65Stop), in comparison to its pp65 revertant counterpart (v65Rev), using primary human foreskin fibroblasts (HFFs), under multiplicity of infection (MOI) condition. No differences in replication were observed between v65Stop and v65Rev, consistent with existing literature. However, infecting HFFs with an equivalent number of v65Stop or v65Rev virions per cell revealed a significant reduction in v65Stop infectivity relative to v65Rev, underscoring the involvement of pp65 in viral infectivity. Viral infectivity is a multifaceted process, where lipid metabolism plays a crucial role. Hence, our focus turned to exploring how pp65 impacts fatty acid synthase (FASN), the rate-limiting enzyme of de novo lipogenesis. Our results demonstrated that HCMV infection significantly upregulates the FASN expression and lipid concentrations highlighting a regulatory role of pp65 in de novo lipogenesis. Furthermore, given the relevance of the cGAS-STING pathway in maintaining metabolic homeostasis, we generated cell lines with silenced cGAS and STING genes. Remarkably, we observed a restoration of v65Stop infectivity in silenced cells, supporting the relevance of the cGAS-STING pathway in lipid metabolism. Understanding the intricate connections between pp65, lipid metabolism, and the interferon pathway provides valuable insights into the molecular mechanisms driving HCMV infectivity and unveils potential targets for therapeutic interventions against HCMV infections.