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

Introduction: Phosphoprotein 65 (pp65) is a key component of the virion tegument in human cytomegalovirus (HCMV). While nonessential for virion assembly, pp65 plays a critical role in modulating and dampening host antiviral responses. Viral infectivity is a complex process in which lipid metabolism is crucial. The cGAS-STING pathway, essential for maintaining metabolic homeostasis, is modulated by pp65 during infection. This study investigates the interplay between pp65, the cGAS-STING pathway, and lipid metabolism to understand their collective role in HCMV infectivity. Objectives: This study aims to elucidate the impact of pp65 on HCMV infectivity, and on de novo lipogenesis, focusing on fatty acid synthase (FASN). Additionally, it explores the involvement of the cGAS-STING pathway in pp65-associated infectivity and its link to lipid metabolism. Materials & Methods: Two HCMV strains were used: a mutant strain (v65Stop) lacking UL83-encoded pp65 and its revertant counterpart (v65Rev). Primary human foreskin fibroblasts (HFFs) were infected under equivalent experimental conditions. Viral replication and infectivity were assessed to evaluate pp65's role. Lipid metabolism was analyzed by measuring FASN expression and lipid concentrations post-infection. To examine the role of the cGAS-STING pathway, HFF cell lines with silenced cGAS and STING genes were generated and infected with v65Stop and v65Rev strains. Results: No differences in viral replication were observed between v65Stop and v65Rev at the same multiplicity of infection (MOI). However, when equal numbers of virions were used to infect HFFs, v65Stop showed significantly reduced infectivity compared to v65Rev, emphasizing pp65's importance in infectivity. HCMV infection increased FASN expression and lipid concentration, effects diminished in v65Stop-infected cells, indicating pp65's regulatory role in de novo lipogenesis. Remarkably, silencing cGAS and STING restored v65Stop infectivity, demonstrating the cGAS-STING pathway's critical involvement in lipid metabolism and infectivity. Conclusion: pp65 enhances HCMV infectivity by regulating lipid metabolism and modulating cGAS-STING-mediated responses. Its regulation of FASN and lipid synthesis is essential during infection. These findings reveal the intricate connections between pp65, lipid metabolism, and the cGAS-STING pathway, offering potential targets for therapeutic strategies against HCMV infections.