Life-Death Trade-offs: HSV-1 ICP27 Differentially Modulates Intrinsic Apoptotic Signaling in Epithelial and Neuron-Like Cells

Abstract

Herpes simplex virus type 1 (HSV-1) is a well-established model to investigate virus-host interactions due to its ability to modulate cell fate and establish lifelong persistence. Among the immediate-early genes, the multifunctional regulatory protein ICP27, encoded by the UL54 gene, plays a central role in viral mRNA processing, nuclear export, and reprogramming host gene expression. This study investigates the role of ICP27 in modulating the intrinsic apoptotic pathway in two cell models representative of different stages of infection: hTert RPE-1 epithelial cells, modeling the lytic replication, and SH-SY5Y neuroblastoma cells, used as a neuron-like model to approximate a neuronal microenvironment. To dissect the specific contribution of HSV-1 ICP27 to apoptosis regulation, cells infected with wild-type HSV-1 (HSV-1 w.t.) were compared with a viral vector lacking ICP27 (HSV-1ΔICP27). A multi-layered experimental approach was employed to characterize infection-induced cellular responses. Analyses were conducted using RT-qPCR for gene quantification, western blotting for protein evaluation, enzymatic assays to measure caspase activity, flow cytometry to determine reactive oxygen species (ROS) production and mitochondrial functionality, and quantitative proteomic approaches for the global characterization of infection-induced protein changes. ICP27 is associated with the modulation of apoptotic signal in a cell type-dependent manner. In epithelial cells, the presence of ICP27 is linked to intensified pro-apoptotic markers, including activation of caspase-9 and effector caspases (3/7), increased ROS generation, altered mitochondrial function, and elevated Bax/Bcl-2 ratio, indicative of mitochondrial pathway activation. Conversely, in neuron-like cells, ICP27 expression appears to correlate with reduced apoptotic signaling, characterized by lower caspase activity, limited oxidative stress, and preserved mitochondrial integrity. Overall, our findings indicate that ICP27 differentially modulates apoptotic signaling depending on the cellular context, enhancing pro-apoptotic features in epithelial cells while limiting intrinsic pathway activation in neuron-like cells. This dual behaviour underscores HSV-1 adaptability across microenvironments, with implications for viral pathogenesis and therapeutic targeting.