Group B coxsackieviruses (CVB) belonging to the family of nonenveloped picornaviruses utilize the coxsackievirus-adenovirus receptor (CAR) to bind to and enter into host cells (5). Small depressions surrounding the fivefold axis, the so-called canyons formed by the viral capsid proteins VP1, VP2, and VP3, bind the CAR (24). Receptor binding induces conformational changes which facilitate the internalization of viral RNA into host cells (18,26). Additionally, human decay accelerating factor (hDAF/CD55) functions as an attachment but not an entry receptor for CVB1, -3, and -5 (6, 32). Recently, cell surface heparan sulfate proteoglycans (HSPG) were identified as additional receptors for the CVB3 variant PD (CVB PD) (38). Using HSPG for infection, CVB3 PD also replicates in CAR-lacking cell lines, e.g., CHO-K1, BHK-21, RD, and L929 (29).HSPG consist of a polydisaccharide chain tethered to serine residues of defined core proteins by a linking tetrasaccharide composed of xylose-galactose-galactose-glucuronic acid (12). NAcetyl-D-glucosamine (GlcNAc) and D-glucuronic acid (GlcA) residues are added alternatingly to the linker tetrasaccharide. Several steps of modifications of GlcNAc and GlcA then follow, including N-deacetylation and N-sulfation of GlcNAc, C-5 epimerization of GlcA to L-idoronic acid (IdoA), 2-O-sulfation of the uronic acid, and 6-O-and 3-O-sulfation of D-glucosamine (GlcN) residues. The resulting high molecular diversity of heparan sulfate (HS) chains enables many specific interactions with very different proteins and glycoproteins, e.g., growth factors, cytokines, and human pathogens, including enveloped viruses (13,22,36). Cell surface HS were also shown to bind nonenveloped viruses, e.g., a variant of human rhinovirus 89 (HRV89) (37), echoviruses (15), swine vesicular disease virus (11), and Theiler's murine encephalomyelitis virus (25), belonging, like CVB3 PD, to the picornavirus family. The sulfated structural motifs of HS mediating binding or entry of picornaviruses are poorly known. Strong differences in viral replication in CHO cell mutants with different defects in heparan sulfate synthesis led to the assumption that CVB3 PD binds to specifically sulfated HS moieties.During this study, the following tasks were performed: (i) the structural requirements, especially the sulfation pattern of HS necessary for CVB3 PD entry, were examined by using competition assays with growth factors binding to specifically sulfated HS sequences as well as with specifically desulfated heparins; (ii) the entry pathway of CVB3 PD while using HS was studied; and (iii) the kinetics of viral entry and the viral life cycle depending on the presence of CAR or HS as the receptor were investigated.
MATERIALS AND METHODSCell lines and viruses. Chinese hamster ovary cells (CHO-K1; German Collection of Microorganism and Cell Cultures no. ACC-110) and heparan sulfatenegative, human CAR-transfected pgsD-677-hCAR cells (38) were grown in Dulbecco's modified Eagle's medium (Cambrex, Belgium) supplemented with 10% fetal bovine...