Molecular Features Contributing to Virus-Independent Intracellular Localization and Dynamic Behavior of the Herpesvirus Transport Protein U(S)9

Reaching the right destination is of vital importance for molecules, proteins, organelles, and cargoes. Thus, intracellular traffic is continuously controlled and regulated by several proteins taking part in the process. Viruses exploit this machinery, and viral proteins regulating intracellular transport have been identified as they represent valuable tools to understand and possibly direct molecules targeting and delivery. Deciphering the molecular features of viral proteins contributing to (or determining) this dynamic phenotype can eventually lead to a virus-independent approach to control cellular transport and delivery. From this virus-independent perspective we looked at U(S)9, a virion component of Herpes Simplex Virus involved in anterograde transport of the virus inside neurons of the infected host. As the natural cargo of U(S)9-related vesicles is the virus (or its parts), defining its autonomous, virus-independent role in vesicles transport represents a prerequisite to make U(S)9 a valuable molecular tool to study and possibly direct cellular transport. To assess the extent of this autonomous role in vesicles transport, we analyzed U(S)9 behavior in the absence of viral infection. Based on our studies, Us9 behavior appears similar in different cell types; however, as expected, the data we obtained in neurons best represent the virus-independent properties of U(S)9. In these primary cells, transfected U(S)9 mostly recapitulates the behavior of U(S)9 expressed from the viral genome. Additionally, ablation of two major phosphorylation sites (i.e. Y(32)Y(33) and S(34)ES(36)) have no effect on protein incorporation on vesicles and on its localization on both proximal and distal regions of the cells. These results support the idea that, while U(S)9 post-translational modification may be important to regulate cargo loading and, consequently, virion export and delivery, no additional viral functions are required for U(S)9 role in intracellular transport.