Coagulation Factor Binding Orientation and Dimerization May Influence Infectivity of Adenovirus-Coagulation Factor Complexes

Abstract

d Adenoviruses (Ads) are promising vectors for therapeutic interventions in humans. When injected into the bloodstream, Ad vectors can bind several vitamin K-dependent blood coagulation factors, which contributes to virus sequestration in the liver by facilitating transduction of hepatocytes. Although both coagulation factors FVII and FX bind the hexon protein of human Ad serotype 5 (HAdv5) with a very high affinity, only FX appears to play a role in mediating Ad-hepatocyte transduction in vivo. To understand the discrepancy between efficacy of FVII binding to hexon and its apparently poor capacity for supporting virus cell entry, we analyzed the HAdv5-FVII complex by using high-resolution cryo-electron microscopy (cryo-EM) followed by molecular dynamic flexible fitting (MDFF) simulations. The results indicate that although hexon amino acids T423, E424, and T425, identified earlier as critical for FX binding, are also involved in mediating binding of FVII, the FVII GLA domain sits within the surface-exposed hexon trimer depression in a different orientation from that found for FX. Furthermore, we found that when bound to hexon, two proximal FVII molecules interact via their serine protease (SP) domains and bury potential heparan sulfate proteoglycan (HSPG) receptor binding residues within the dimer interface. In contrast, earlier cryo-EM studies of the Ad-FX interaction showed no evidence of dimer formation. Dimerization of FVII bound to Ad may be a contributing mechanistic factor for the differential infectivity of Ad-FX and Ad-FVII complexes, despite high-affinity binding of both these coagulation factors to the virus. V iral vectors based on adenoviruses (Ads) specific to human and animal species have been adapted widely for gene transfer applications both in vitro and in vivo. Extensive in vitro analyses have revealed a model of Ad cell infection whereby the initial virus attachment to a plasma membrane-localized receptor via the fiber protein is followed by virus penton interaction with integrins that mediate virion internalization into the cell (1, 2). To date, a number of cellular proteins that serve as functional high-affinity virus attachment receptors have been identified. For the most common vectors, based on species C human adenovirus serotype 5 (HAdv5), as well as for HAdv of species A, D, E, and F, it was found that a tight junction protein designated coxsackie and adenovirus receptor (CAR) can serve as a high-affinity attachment receptor (3-5). The species B Ads may utilize CD46 and/or DSG2 proteins to gain entry into host cells (6-8), while several species D Ads may utilize CD46, sialic acid, or GD1a glycan to enter the cell (9, 10). It was also shown that HAdv can bind a variety of integrin classes that interact with a penton RGD amino acid motif to trigger internalization of cell-bound virus particles into the cell (2).Although this canonical pathway of HAdv cell entry operates efficiently in vitro and explains the topology and functional interdependence between viral capsid proteins (11, 12), ...

A targeting ligand enhances infectivity and cytotoxicity of an oncolytic adenovirus in human pancreatic cancer tissues

“…If the same amount of virus was intravenously injected, a level of ectopic infection in distant organs should be comparable between AdSur-SYE and AdSur as previously reported [15]. It was recently reported that coagulation factor (F) X binds the hypervariable regions (HVR) of the hexon in an adenovirus, leading to liver infection [25,26]. The factor X enhances liver transduction by adenovirus vectors due to the protection of adenovirus from attack by the classical complementary pathway [27].…”

Recent advances in genetic modification of adenovirus vectors for cancer treatment

“…It was recently reported that coagulation factor (F) X binds the hypervariable regions (HVRs) of the adenovirus hexon, leading to enhanced liver infection . Therefore, insertion of mutations in the FX‐binding domain of HVR and its replacement with HVR of other serotype adenoviruses markedly decreased the liver sequestration of the adenoviruses (Fig.…”

Innate immunity to adenovirus: lessons from mice

“…Upon discovery of CAR as the principal cell-surface attachment receptor for HAdv-C5 [39,40], attempts have been made to reduce HAdv-C5 hepatocyte infection via introduction of mutations into the knob domain of the fiber to ablate virus interaction with CAR. Using a set of HAdv-C5-based vectors ablated for fiber-mediated receptor interactions in mice, it was found that blood coagulation factors, namely FVII, FIX, and FX, can support efficient infection of virus-resistant cells and hepatocytes in vitro or upon isolated liver perfusion ex vivo [7,15,16]. Furthermore, HAdv-C5-based vectors ablated for interactions with both the CAR and cellular integrins retained their capacity to efficiently transduce hepatocytes after intravenous administration [55,56].…”

“…An extensive search for the mechanisms mediating the hepatic tropism of HAdv-C5 revealed that Gla domain-containing blood coagulation factors bind to the major virus capsid protein hexon and that coagulation factors can mediate virus entry into hepatocytes independent of the canonical virus cell attachment receptors, which interact with the fiber knob domain [7][8][9]15]. It was established that although several blood coagulation factors (F), including FVII [16], FIX [7], and FX [8,9], can bind to HAdv-C5 hexon, coagulation FX binds HAdv-C5 hexon with the highest, near picomolar, affinity [8,9]. Analysis of stoichiometry of FX binding to HAdv-C5 showed that a single virus particle can bind 240 FX molecules, indicating that the entire HAdv-C5 virus capsid, which is composed of 240 hexon trimer capsomers [17], is covered by FX after intravenous virus administration [8,18].…”