Type I Interferon and NF-κB Activation Elicited by Herpes Simplex Virus gH/gL via αvβ3 Integrin in Epithelial and Neuronal Cell Lines

Abstract

␣v␤3 integrin represents a novel sensing system which detects herpes simplex virus (HSV) and bacterial constituents. In cooperation with Toll-like receptor 2 (TLR2), it elicits an innate response that leads to activation of type I interferon (IFN), NF-B, and a specific set of cytokines. We report that this defensive branch is functional in cells which represent experimental models of epithelial, including keratinocytic, and neuronal cells. These are the major targets of HSV in vivo. HSV entered the three cell lines via distinct routes. Hence, the defensive response was independent of the route of virus entry. Soluble gH/gL sufficed to elicit type I IFN and NF-B activation and represents the viral pathogen-associated molecular pattern (PAMP) of this defense system. P attern recognition receptors (PRRs) are responsible for sensing pathogens and for initiating signaling cascades which culminate in the innate response, whose hallmarks are the production of interferons (IFNs) and proinflammatory cytokines and the activation of the transcription factor NF-B (1). Based on the nature of the pathogen-associated molecular pattern (PAMP) and the properties of the respective PRR, the innate response to herpesviruses can be divided into three main branches (for an indepth review, see reference 2). Thus, the Toll-like receptors (TLRs) localized at the plasma membranes, e.g., TLR2, recognize proteic or lipidic PAMPs. The endosomal TLR3 and TLR7, as well as the cytoplasmic RIG-I (RNA helicase retinoic acid-inducible gene I), sense single-or double-stranded RNAs. The endosomal TLR9 and a number of cytosolic molecules, such as DAI (DNAdependent activator of interferon-regulatory factor), IFI16 (gamma interferon-inducible protein 16), and AIM2 (absent in melanoma 2), etc., sense double-stranded DNA (2, 3).Until recently, the prevalent paradigm has been that the IFN production occurs in response to activation of the cytosolic sensors, whereas the TLRs located at the plasma membrane elicit a predominantly inflammatory response (4-6). In particular, until recently, TLR2 was known to sense bacteria and was thought not to be involved in recognition of viruses. When a role for TLR2 against herpes simplex virus (HSV) and other herpesviruses was documented, TLR2 was found to be polarized toward an inflammatory response (7,8). Kurt-Jones and coworkers (9) found that encephalitis caused by HSV was less severe in mice lacking TLR2, thus providing evidence for a role of TLR2 in the response to HSV and highlighting an inflammatory effect (10). In contrast with this view, Barbalat et al. (11) demonstrated that TLR2 was capable of inducing a type I IFN in response to viral ligands in inflammatory monocytes; the PAMPs remained elusive. Key to understanding the significance of the multiple, apparently redundant, innate defense branches against herpesviruses is the fact that they have been often demonstrated in highly specific cell types. For example, the TLR9 response was observed in plasmacytoid cells, the TLR9 and TLR2 responses were observed i...

Herpes Simplex Virus Internalization into Epithelial Cells Requires Na + /H + Exchangers and p21-Activated Kinases but neither Clathrin- nor Caveolin-Mediated Endocytosis

“…These results are consistent with previous studies in Vero, HEp-2, CHO-PILR␣, BHK, J-nectin1, C10 murine melanoma, J-HVEM, or the neuroblastoma SK-N-SH cells (27,30,32,77,78) and the fact that low pH does not account for conformational changes in gB during fusion (79,80). Indeed, in HEp-2 and PtK 2 cells, HSV-1 infection was even more efficient when endosomal acidification, and thus presumably virion degradation, had been inhibited.…”

“…Indeed, in HEp-2 and PtK 2 cells, HSV-1 infection was even more efficient when endosomal acidification, and thus presumably virion degradation, had been inhibited. In other cell lines, such as CHO-nectin1, CHO-HVEM, J-nectin1-integrin ␣v␤3/6/8 , HaCaT, HaCaT-integrin ␣v␤3 , and SK-N-SH-integrin ␣v␤3 cells, infection is reduced by baf (9,19,21,26,30,31,78,81). Furthermore, infection of a different HeLa line with a different KOS strain is inhibited by baf (26).…”

“…Furthermore, infection of a different HeLa line with a different KOS strain is inhibited by baf (26). The apparently conflicting results with different HeLa lines could arise from various amounts of crucial host factors such as integrin ␣v␤3 ; HSV-1 infection is reduced by baf in HeLaintegrin ␣v␤3 , HaCaT-integrin ␣v␤3 , or SK-N-SH-integrin ␣v␤3 cells but not after RNAi silencing of the ␤3 integrin subunit in these same cell lines (78). Therefore, viral entry pathways can be described only for a particular cell line, and general concepts can be obtained only after testing several host factors (75).…”

Dissociation of HSV gL from gH by αvβ6- or αvβ8-integrin promotes gH activation and virus entry

“…Integrins were silenced in SW480 cells by means of ON-TARGET plus, smart pools (Dharmacon), as previously described (49). Control cells were transfected with siRNA to E.coli-polA_0054 (20).…”

Herpes Simplex Virus Type 2 Glycoprotein H Interacts with Integrin αvβ3 To Facilitate Viral Entry and Calcium Signaling in Human Genital Tract Epithelial Cells

“…Glycoprotein H (which forms heteroligomers with gL) is also essential for viral entry and cell-to-cell spread and has been implicated in regulating the fusogenic activity of gB (12,13). Several studies suggest that gH-gL may interact with integrins at the plasma membrane, although the findings have been inconsistent (5,(14)(15)(16)(17)(18)(19)(20). Viruses can induce conformational changes and/or clustering of integrins to elicit cell signaling, cytoskeletal rearrangement, and viral internalization (21).…”