title: Receptor complementation and mutagenesis reveal SR-BI as an essential HCV entry factor and functionally imply its intra- and extra-cellular domains.
abstract: HCV entry into cells is a multi-step and slow process. It is believed that the initial capture of HCV particles by glycosaminoglycans and/or lipoprotein receptors is followed by coordinated interactions with the scavenger receptor class B type I (SR-BI), a major receptor of high-density lipoprotein (HDL), the CD81 tetraspanin, and the tight junction protein Claudin-1, ultimately leading to uptake and cellular penetration of HCV via low-pH endosomes. Several reports have indicated that HDL promotes HCV entry through interaction with SR-BI. This pathway remains largely elusive, although it was shown that HDL neither associates with HCV particles nor modulates HCV binding to SR-BI. In contrast to CD81 and Claudin-1, the importance of SR-BI has only been addressed indirectly because of lack of cells in which functional complementation assays with mutant receptors could be performed. Here we identified for the first time two cell types that supported HCVpp and HCVcc entry upon ectopic SR-BI expression. Remarkably, the undetectable expression of SR-BI in rat hepatoma cells allowed unambiguous investigation of human SR-BI functions during HCV entry. By expressing different SR-BI mutants in either cell line, our results revealed features of SR-BI intracellular domains that influence HCV infectivity without affecting receptor binding and stimulation of HCV entry induced by HDL/SR-BI interaction. Conversely, we identified positions of SR-BI ectodomain that, by altering HCV binding, inhibit entry. Finally, we characterized alternative ectodomain determinants that, by reducing SR-BI cholesterol uptake and efflux functions, abolish HDL-mediated infection-enhancement. Altogether, we demonstrate that SR-BI is an essential HCV entry factor. Moreover, our results highlight specific SR-BI determinants required during HCV entry and physiological lipid transfer functions hijacked by HCV to favor infection.
authors.affiliation: Université de Lyon, UCB-Lyon1, IFR128, INSERM, U758, Ecole Normale Supérieure de Lyon, Lyon, France.
authors.forename: Marlène
authors.initials: M
authors.lastname: Dreux
authors.forename: Viet Loan
authors.initials: VL
authors.lastname: Dao Thi
authors.forename: Judith
authors.initials: J
authors.lastname: Fresquet
authors.forename: Maryse
authors.initials: M
authors.lastname: Guérin
authors.forename: Zélie
authors.initials: Z
authors.lastname: Julia
authors.forename: Géraldine
authors.initials: G
authors.lastname: Verney
authors.forename: David
authors.initials: D
authors.lastname: Durantel
authors.forename: Fabien
authors.initials: F
authors.lastname: Zoulim
authors.forename: Dimitri
authors.initials: D
authors.lastname: Lavillette
authors.forename: François-Loïc
authors.initials: FL
authors.lastname: Cosset
authors.forename: Birke
authors.initials: B
authors.lastname: Bartosch
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism; D016466:CHO Cells; D002460:Cell Line; D045744:Cell Line, Tumor; D062445:Claudin-1; D006224:Cricetinae; D003412:Cricetulus; D004285:Dogs; D016174:Hepacivirus / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D051379:Mice; D016296:Mutagenesis; D017434:Protein Structure, Tertiary; D051381:Rats; D011991:Receptors, Virus / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D051122:Scavenger Receptors, Class B / Q000235:genetics* / Q000378:metabolism; D060225:Tetraspanin 28; D053586:Virus Internalization
chemical_list: D015703:Antigens, CD; C554798:CD81 protein, human; C568108:CLDN1 protein, human; C554799:Cd81 protein, mouse; C554797:Cd81 protein, rat; D062445:Claudin-1; C568113:Cldn1 protein, mouse; C568114:Cldn1 protein, rat; D008565:Membrane Proteins; D011991:Receptors, Virus; D011993:Recombinant Fusion Proteins; C495124:SCARB1 protein, human; C495125:Scarb1 protein, rat; D051122:Scavenger Receptors, Class B; D060225:Tetraspanin 28