| Herpes simplex virus type-1 (HSV-1) is a neurotropic alphaherpesvirus that promotes the development of a wide array of diseases, ranging from fever blisters and cold sores to more serious, life threatening diseases including keratitis, encephalitis, and meningitis. The ability of HSV-1 to infect a wide variety of cell types leads to the diverse manifestations seen in association with HSV-1 infection. Though molecular details of viral infection are not fully understood, it is believed HSV-1 entry receptors play a significant role. One receptor, heparan sulfate (HS), is a glycosaminoglycan ubiquitously expressed on the surface of virtually all cells. HS is unique in the fact that it plays a role in HSV-1 attachment, penetration, and spread. However, much remains unknown about its functions during infection. The purpose of our study was to further analyze the role of HS during HSV-1 entry and spread. Several critical functions of HS during HSV-1 infection were identified: (i) the enzyme 3-O-sulfotransferase-2, which is highly expressed in the brain, generates an HSV-1 gD binding form of 3-O-sulfated heparan sulfate (3-OS HS) that facilitates viral entry, which could be crucial for HSV-1 tropism in the brain and the development of encephalitis and meningitis. (ii) Cells expressing unique sets of 3OST isoforms show significantly reduced viral entry and a cell-type specific reduction in spread after 3-OS HS downregulation by siRNA treatment that suggests 3-OS HS may have additional function(s) besides its ability to bind gD. (iii) Unmodified HS negatively regulates HSV-1 mediated cell-cell fusion, which may be due to increased Rho GTPase activity in the absence of HS, which correlates with increased fusion. (iv) Live cell imaging of HSV-1 cell-cell fusion provides evidence of transient cell-cell fusion events that allow HSV-1 to spread without alerting the host immune system in the absence of syncytia formation. Together, these results have expanded our understanding of HS role in HSV-1 infection. HS function during HSV-1 attachment, penetration, and spread makes it an ideal target for the development of therapeutic agents that, by interfering with HS function during infection, may impede multiple processes, contributing significantly to inhibition of HSV-1 infection. |
