High-Affinity Laminin Receptor Isa Receptor forSindbis VirusinMammalian Cells

Sindbis virus isan alphavirus witha verywidehost range,being abletoinfect many birds andmammalsas well asmosquitoes. We haveisolated a monoclonal antibody thatlargely blocks virus binding tomammalian cells. Thisantibody was foundtobedirected against theC-terminal domainofthehigh-affinity laminin receptor, a 67-kDaprotein present on thecell surface thatbinds withhighaffinity tobasement membrane laminin andthatisknowntobeimportant indevelopment andintumorinvasion. Thisreceptor isbelieved to beformedfroma 295-amino-acid polypeptide thatismodified insome unknownway after translation. The primary sequenceofthis 295-amino-acid protein ishighly conserved among mammals. We foundthehamster aminoacid sequencetobeidentical toa mouse sequenceandtodiffer atonlytwoaminoacids froma human sequenceandattwoaminoacids fromabovine sequence.Toverify theimportance ofthelaminin receptor for infection bySindbis virus, hamster cells were stably transfected withthegeneencoding the295-amino-acid protein underthecontrol ofa high-efficiency promoter. Suchtransfected hamster cells overexpressed the laminin receptor atthecell surface, boundseveralfold more Sindbis virions thandidtheparental cells, and becameinfected bySindbis virus withahigher efficiency. Incontrast, cells transfected withtheantisense gene expressed less laminin receptor onthesurface andwere less susceptible tothevirus. Binding ofthevirus varied linearly withtheamountoflaminin receptor on thecell surface, whereas infectivity measured witha plaque assayvaried withthe1.4powerofthereceptor concentration, suggesting thatinteraction withmore thanone receptor aidsvirus penetration. Bythese criteria, thelaminin receptor functions asthemajorreceptor for Sindbis virus entryintomammaliancells. We alsofoundthattheanti-laminin receptor antibody partially blocked Sindbis virus binding tomosquito cells, suggesting that thelaminin receptor isconserved inmosquitoes andfunctions asa Sindbis virus receptor inthis host. Thewidedistribution ofthishighly conserved receptor may beinpartresponsible forthebroadhostrangeexhibited bythevirus, whichinfects a widerangeof mammalsandbirds aswell asitsmosquito vector andcaninfect many different tissues within these hosts. Part ofthebroadhost rangeofSindbis virus also appearstoresult froman ability ofthevirus toutilize more than one different protein receptor, however, because themajorreceptor usedbythevirus toenterchicken cells appearstobea 63-kDaprotein thatisnotthelaminin receptor (K.-S. Wang,A.L.Schmaljohn, R.J.Kuhn, andJ.H.Strauss, Virology 181:694-702, 1991). Theinitial eventintheinteraction ofavirus withthehost cell istheattachment ofthevirus toreceptors intheplasma membrane, andthepresence ofspecific cellular receptors is adeterminant ofthespecies andtissue tropism ofavirus and ofitspathogenesis. The26registered alphaviruses (family Togaviridae) infect awidevariety ofvertebrate hosts, in- cluding manyspecies ofbirds andmammals, andaretrans- mitted bymosquitoes, inwhichtheyalso replicate (6). Many arepathogenic forhumansanddomestic animals, causing fever, arthralgia, orencephalitis (39). Theviruses notonly caninfect verydivergent organisms butcaninfect awide variety ofcells within theorganism, including neurons and glial cells, striate andsmoothmusclecells, lymphcells, synovial cells, brownfatcells, hepatocytes, andothers (19, 39). Themechanisms bywhichtheviruses caninfect sucha spectrum ofcells andorganisms isofconsiderable interest. Possible mechanisms include useofareceptor that ishighly conserved across phylogenetic boundaries, theability touse multiple receptors, orboth.Influenza virus attaches tothe widely distributed sialic acidandiscapable ofinfecting a