Actin Polymerization Is Required for Filopodia Formation Supporting HSV-1 Entry into Activated T Cells

Impact of actin polymerization and filopodia formation on herpes simplex virus entry in epithelial, neuronal, and T lymphocyte cells

Herpes simplex virus type 1 (HSV-1) has been known as a common viral pathogen that can infect several parts of the body, leading to various clinical manifestations. According to this diverse manifestation, HSV-1 infection in many cell types was demonstrated. Besides the HSV-1 cell tropism, e.g., fibroblast, epithelial, mucosal cells, and neurons, HSV-1 infections can occur in human T lymphocyte cells, especially in activated T cells. In addition, several studies found that actin polymerization and filopodia formation support HSV-1 infection in diverse cell types. Hence, the goal of this review is to explore the mechanism of HSV-1 infection in various types of cells involving filopodia formation and highlight potential future directions for HSV-1 entry-related research. Moreover, this review covers several strategies for possible anti-HSV drugs focused on the entry step, offering insights into potential therapeutic interventions.

HPV16E1 downregulation altered the cell characteristics involved in cervical cancer development

The primary causes of cervical cancer are human papillomavirus type 16 (HPV16) and/or other high-risk (Hr -) HPV infections. Hr-HPVE5, E6, and E7 have been identified as oncoproteins that play roles in the development of cancer. However, other HPV proteins, especially E1, may also be involved in cancer development. In this study, the role of HPV16E1 in cervical carcinogenesis was examined by siRNA knockdown experiments using SiHa cells as a model. The results showed that HPV16E1 regulated P-FOXO3a and HPV16E7 expression. Various cell functions associated with the hallmarks of cancer, including cell viability, colony formation, invasion, and anchorage-independent cell growth, were altered when HPV16E1 was downregulated. However, no effect on cell migration and apoptosis properties was found. Moreover, HPV16E1 downregulation resulted in an increase in cisplatin susceptibility. In conclusion, this is the first demonstration that HPV16E1 might be regarded as a possible novel oncoprotein involved in several processes related to oncogenesis.

ICP4-Associated Activation of Rap1b Facilitates Herpes Simplex Virus Type I (HSV-1) Infection in Human Corneal Epithelial Cells

The strong contribution of RAS-related protein 1b (Rap1b) to cytoskeleton remodeling determines intracellular and extracellular physiological activities, including the successful infection of viruses in permissive cells, but its role in the HSV-1 life cycle is still unclear. Here, we demonstrated that the HSV-1 immediate early (IE) gene ICP4 inhibits protein kinase A (PKA) phosphorylation to induce Rap1b-activation-mediated viral infection. Rap1b activation and membrane enrichment begin at the early stage of HSV-1 infection and remain active during the proliferation period of the virus. Treating the cells with Rap1b small interfering RNA (siRNA) showed a dose-dependent decrease in viral infection levels, but no dose-dependent increase was observed after Rap1b overexpression. Further investigation indicated that the suppression of Rap1b activation derives from phosphorylated PKA and Rap1b mutants with partial or complete prenylation instead of phosphorylation, which promoted viral infection in a dose-dependent manner. Furthermore, the PKA agonist Forskolin disturbed Rap1b activation in a dose-dependent manner, accompanied by a decreasing trend in viral infection. Moreover, the HSV-1 IE gene ICP4 induced PKA dephosphorylation, leading to continuous Rap1b activation, followed by cytoskeleton rearrangement induced by cell division control protein 42 (CDC42) and Ras-related C3 botulinum toxin substrate 1 (RAC1). These further stimulated membrane-triggered physiological processes favoring virus infection. Altogether, we show the significance of Rap1b during HSV-1 infection and uncover the viral infection mechanism determined by the posttranslational regulation of the viral ICP4 gene and Rap1b host protein.