Heparan sulfate as a mediator of herpes simplex virus binding to basement membrane

Extracellular acidosis enhances Zika virus infection both in human cells and ex-vivo tissue cultures from female reproductive tract

Zika virus (ZIKV) is a flavivirus transmitted by mosquitoes of the genus Aedes, but unlike other flaviviruses, ZIKV can be sexually transmitted by vaginal intercourse. The healthy vaginal pH ranges from 4.0 to 6.0, reaching values of 6.0-7.0 after semen deposition. Here, we report that low extracellular pH values (range 6.2-6.6) dramatically increase ZIKV infection on cell lines of different origin including some derived from the female genital tract and monocyte-derived macrophages. Furthermore, low pH significantly increased ZIKV infection of human ectocervix and endocervix cultured ex-vivo. Enhancement of infection by low pH was also observed using different ZIKV strains and distinct methods to evaluate viral infection, i.e. plaque assays, RT-PCR, flow cytometry, and fluorescence microscopy. Analysis of the mechanisms involved revealed that the enhancement of ZIKV infection induced by low pH was associated with increased binding of the viral particles to the heparan sulphate expressed on the target cell surface. Acidosis represents a critical but generally overlooked feature of the female genital tract, with major implications for sexual transmission diseases. Our results suggest that low vaginal pH might promote male-to-female transmission of ZIKV infection.

Role of heparan sulfate in the Zika virus entry, replication, and cell death

Zika virus (ZIKV) is an emerging arbovirus and its infection associates with neurologic diseases. Whether heparan sulfate (HS), an attachment factor for many viruses, plays a role in the ZIKV infection remains controversial. Our study generated several HS biosynthesis-deficient cell clones by disrupting SLC35B2, B3GAT3, or B4GALT7 gene using the CRISPR/Cas9 system. The HS deficiency did not affect the viral attachment and internalization of ZIKV, but reduced the attachment of Dengue virus (DENV) 2. The early RNA and protein levels of ZIKV and DENV2 were impaired in the HS deficient cells, while the viral yields were not accordingly reduced. Our data further showed that HS promoted the cell death induced by virus infection, and inhibition of cell death significantly increased the viral replication of ZIKV and DENV2. Collectively, our study described an unexpected role of HS in the viral attachment, replication and cell death induced by ZIKV.

Entry of Herpes Simplex Virus 1 into Epidermis and Dermal Fibroblasts Is Independent of the Scavenger Receptor MARCO

To enter host cells, herpes simplex virus 1 (HSV-1) initially attaches to cell surface glycosaminoglycans, followed by the requisite binding to one of several cellular receptors, leading to viral internalization. Although virus-receptor interactions have been studied in various cell lines, the contributions of individual receptors to uptake into target tissues such as mucosa, skin, and cornea are not well understood. We demonstrated that nectin-1 acts as a major receptor for HSV-1 entry into murine epidermis, while herpesvirus entry mediator (HVEM) can serve as an alternative receptor. Recently, the macrophage receptor with collagenous structure (MARCO) has been described to mediate adsorption of HSV-1 to epithelial cells. Here, we investigated the impact of MARCO on the entry process of HSV-1 into the two major cell types of skin, keratinocytes in the epidermis and fibroblasts in the underlying dermis. Using ex vivo infection of murine epidermis, we showed that HSV-1 entered basal keratinocytes of MARCO^-/- epidermis as efficiently as those of control epidermis. In addition, entry into dermal fibroblasts was not impaired in the absence of MARCO. When we treated epidermis, primary keratinocytes, or fibroblasts with poly(I), a ligand for class A scavenger receptors, HSV-1 entry was strongly reduced. As we also observed reducing effects of poly(I) in the absence of both MARCO and scavenger receptor A1, we concluded that the inhibitory effects of poly(I) on HSV-1 infection are not directly linked to class A scavenger receptors. Overall, our results support that HSV-1 entry into skin cells is independent of MARCO.IMPORTANCE During entry into its host cells, the human pathogen herpes simplex virus (HSV) interacts with various cellular receptors. Initially, receptor interaction can mediate cellular adsorption, followed by receptor binding that triggers viral internalization. The intriguing question is which receptors are responsible for the various steps during entry into the natural target tissues of HSV? Previously, we demonstrated the role of nectin-1 as a major receptor and that of HVEM as an alternative receptor for HSV-1 to invade murine epidermis. As MARCO has been described to promote infection in skin, we explored the predicted role of MARCO as a receptor that mediates adsorption to epithelial cells. Our infection studies of murine skin cells indicate that the absence of MARCO does not interfere with the efficiency of HSV-1 entry and that the inhibitory effect on viral adsorption by poly(I), a ligand of MARCO, is independent of MARCO.

Polysulfonate suramin inhibits Zika virus infection

Zika virus (ZIKV) is an arthropod-borne flavivirus that causes newborn microcephaly and Guillian-Barré syndrome in adults. No therapeutics are available to treat ZIKV infection or other flaviviruses. In this study, we explored the inhibitory effect of glycosaminoglycans and analogues against ZIKV infection. Highly sulfated heparin, dextran sulfate and suramin significantly inhibited ZIKV infection in Vero cells. De-sulfated heparin analogues lose inhibitory effect, implying that sulfonate groups are critical for viral inhibition. Suramin, an FDA-approved anti-parasitic drug, inhibits ZIKV infection with 3-5 log₁₀ PFU viral reduction with IC₅₀ value of ∼2.5-5 μg/ml (1.93 μM-3.85 μM). A time-of-drug-addition study revealed that suramin remains potent even when administrated at 1-24 hpi. Suramin inhibits ZIKV infection by preventing viral adsorption, entry and replication. Molecular dynamics simulation revealed stronger interaction of suramin with ZIKV NS3 helicase than with the envelope protein. Suramin warrants further investigation as a potential antiviral candidate for ZIKV infection. Heparan sulfate (HS) is a cellular attachment receptor for multiple flaviviruses. However, no direct ZIKV-heparin interaction was observed in heparin-binding analysis, and downregulate or removal of cellular HS with sodium chlorate or heparinase I/III did not inhibit ZIKV infection. This indicates that cell surface HS is not utilized by ZIKV as an attachment receptor.

Restrictions that control herpes simplex virus type 1 infection in mouse brain ex vivo

Elucidating the cellular and molecular factors governing herpes simplex virus type 1 (HSV-1) neurotropism is a prerequisite for understanding HSV-1 encephalitis and for targeting HSV-1-derived vectors for gene transfer to the brain. Earlier we had described an ex vivo system of mouse brain slices and demonstrated a selective and unique infection pattern, mostly around the ventricles. Here, we examined tissue factors controlling HSV-1 infection of brain slices. We demonstrated that heparan sulphate, while an important factor, does not determine the infection pattern. Hyaluronic acid, but not collagen, appears to enhance HSV-1 brain infection. To investigate whether tissue distribution of viral receptors determines the infection pattern, we examined transcription of herpes virus entry mediator and nectin-1 receptor genes in infected and uninfected brain regions. Both the infected and the uninfected regions express the receptors. We also explored the influence of intra-cellular factors. HSV-1 does not preferentially infect proliferating cells in the brain slices, despite its predilection to the ventricular zones. To delineate the step at which the HSV-1 infection cascade is restricted, mRNA was isolated following tissue infection, and transcription of the immediate-early and late viral genes was evaluated. The results indicated that HSV-1 genes are not expressed in regions that do not express a viral reporter gene. Therefore, we conclude that tissue resistance to infection is associated with a block at or prior to the immediate-early mRNA synthesis. Taken together, using the ex vivo system of organotypic culture we describe here extra-cellular and intra-cellular restriction levels of HSV-1 brain infection.

Virion-associated viral fibroblast growth factor stimulates cell motility

The Autographa californica M nucleopolyhedrovirus (AcMNPV) viral fibroblast growth factor (vFGF) has functional parallels to cellular FGFs. Deletion of the AcMNPV vfgf has no obvious phenotype in cell culture but delays the time of insect death. Here, we determined vFGF production during virus infection. vFGF was detected at 24 hours post infection and through the remainder of the infection cycle. Since vFGF is thought to be a secreted membrane-binding protein and virions acquire an envelope derived from the cell membrane, we examined virions for the presence of vFGF using microscopy, flow cytometry, and affinity chromatography. We found that vFGF associated with virions. Furthermore, budded virus carrying vFGF had more affinity to heparin than vFGF-deficient budded virus, consistent with the affinity of FGFs for heparan sulfate proteoglycans. Although the function of virion-associated vFGF is not clear, we found that virion-associated vFGF stimulated cell motility and affected virus attachment.

Oral keratinocytes support non-replicative infection and transfer of harbored HIV-1 to permissive cells

Background

Oral keratinocytes on the mucosal surface are frequently exposed to HIV-1 through contact with infected sexual partners or nursing mothers. To determine the plausibility that oral keratinocytes are primary targets of HIV-1, we tested the hypothesis that HIV-1 infects oral keratinocytes in a restricted manner.

Results

To study the fate of HIV-1, immortalized oral keratinocytes (OKF6/TERT-2; TERT-2 cells) were characterized for the fate of HIV-specific RNA and DNA. At 6 h post inoculation with X4 or R5-tropic HIV-1, HIV-1gag RNA was detected maximally within TERT-2 cells. Reverse transcriptase activity in TERT-2 cells was confirmed by VSV-G-mediated infection with HIV-NL4-3Δenv-EGFP. AZT inhibited EGFP expression in a dose-dependent manner, suggesting that viral replication can be supported if receptors are bypassed. Within 3 h post inoculation, integrated HIV-1 DNA was detected in TERT-2 cell nuclei and persisted after subculture. Multiply spliced and unspliced HIV-1 mRNAs were not detectable up to 72 h post inoculation, suggesting that HIV replication may abort and that infection is non-productive. Within 48 h post inoculation, however, virus harbored by CD4 negative TERT-2 cells trans infected co-cultured peripheral blood mononuclear cells (PBMCs) or MOLT4 cells (CD4+ CCR5+) by direct cell-to-cell transfer or by releasing low levels of infectious virions. Primary tonsil epithelial cells also trans infected HIV-1 to permissive cells in a donor-specific manner.

Conclusion

Oral keratinocytes appear, therefore, to support stable non-replicative integration, while harboring and transmitting infectious X4- or R5-tropic HIV-1 to permissive cells for up to 48 h.

Cell-surface heparan sulfate facilitates human immunodeficiency virus Type 1 entry into some cell lines but not primary lymphocytes

Many viruses have evolved to exploit cell-surface glycosaminoglycans (GAG), particularly heparan sulfate, to facilitate their attachment and infection of host cells. Here, the case for the involvement of heparan sulfate GAG in cellular infection by human immunodeficiency virus Type 1 (HIV-1) compared with herpes simplex virus Type 1 (HSV-1) is re-examined. It is shown that HIV-1 infection is facilitated by heparan sulfate GAG in only one of three highly permissive cell lines tested, whereas HSV-1 infection is facilitated to varying extents in all three. To evaluate the physiological relevance of these findings, primary peripheral blood lymphocytes (PBL), the physiological host for HIV-1, were examined. It was found that treatment of PBL with heparitinase, to remove any traces of heparan sulfate GAG, did not alter their sensitivity to infection by either lymphocyte-tropic, X4-type strain HIV-1IIIB, nor the monocyte-tropic, R5-type strain, HIV-1Ba-L. It is concluded that heparan sulfate GAG has little physiological role in the infection of lymphocytes by HIV-1 and that evidence derived from studies on immortalized cell lines suggesting a significant role must be interpreted with caution.

Characteristics of HIV-1 gp120 glycoprotein binding to glycolipids

We examined the binding of the gp120 envelope glycoprotein (gp120) of the human immunodeficiency virus (HIV-1) to sulfatide (GalS), galactocerebroside (GalC), and GM1-ganglioside (GM1). The gp120 glycoprotein bound to GalS but not to GalC or GM1 by enzyme-linked immunosorbent assay (ELISA) and by an immunospot assay on nitrocellulose paper. However, it bound to all three glycolipids by an immunospot assay on thin layer chromatography (TLC) plates. In studies to determine whether GalS could be a receptor for gp120 on the surface of cells, gp120 bound to GalS incorporated into the plasma membrane of lymphoid cells as determined by cytofluorometric analysis and immunofluorescence microscopy. These studies indicate that GalS may function as a receptor for gp120 and HIV-1.

Inhibition of herpes simplex virus replication by genistein, an inhibitor of protein-tyrosine kinase

Genistein, an inhibitor of protein-tyrosine kinase, inhibited the replication of herpes simplex virus type 1 (HSV-1) at genistein concentrations of more than 25 microM, whereas the related compounds, which do not inhibit protein-tyrosine kinases, did not affect the replication of HSV-1. In the presence of genistein, the phosphorylation of tyrosine residues in specific viral polypeptides was markedly reduced. These results indicate that the phosphorylation of tyrosine residues in viral polypeptides may be essential for the replication of HSV-1.

Anti-viral activity of human recombinant heparin-binding proteins HBNF and MK

Herpes simplex viruses bind to cell surface heparan sulfate proteoglycans, as a first step of viral infection. We report here that two recombinant heparin-binding proteins HBNF and MK inhibit infectivity of human herpes simplex viruses types 1 and 2 and human cytomegalovirus. Carboxymethylated HBNF and MK, which retain affinity for heparin-Sepharose, do not exhibit anti-viral activities. Arguments are presented that anti-viral effects of HBNF and MK are due to the competition for the specific binding to the cell surface heparan sulfate proteoglycans.