RESUMO
HIV-1 entry into host cells starts with interactions between the viral envelope glycoprotein (Env) and cellular CD4 receptors and coreceptors. Previous work has suggested that efficient HIV entry also depends on intracellular signaling, but this remains controversial. Here we report that formation of the pre-fusion Env-CD4-coreceptor complexes triggers non-apoptotic cell surface exposure of the membrane lipid phosphatidylserine (PS). HIV-1-induced PS redistribution depends on Ca2+ signaling triggered by Env-coreceptor interactions and involves the lipid scramblase TMEM16F. Externalized PS strongly promotes Env-mediated membrane fusion and HIV-1 infection. Blocking externalized PS or suppressing TMEM16F inhibited Env-mediated fusion. Exogenously added PS promoted fusion, with fusion dependence on PS being especially strong for cells with low surface density of coreceptors. These findings suggest that cell-surface PS acts as an important cofactor that promotes the fusogenic restructuring of pre-fusion complexes and likely focuses the infection on cells conducive to PS signaling.
Assuntos
Infecções por HIV/virologia , HIV-1/fisiologia , HIV-1/patogenicidade , Fusão de Membrana/fisiologia , Fosfatidilserinas/metabolismo , Ativação Viral/fisiologia , Internalização do Vírus , Amidas/antagonistas & inibidores , Anoctaminas/metabolismo , Anticorpos Monoclonais , Benzilaminas , Antígenos CD4/metabolismo , Cálcio/metabolismo , Linhagem Celular , Membrana Celular/metabolismo , Ciclamos , Células HEK293 , Células HeLa , Compostos Heterocíclicos/antagonistas & inibidores , Interações Hospedeiro-Patógeno/fisiologia , Humanos , Proteínas de Transferência de Fosfolipídeos/metabolismo , Compostos de Amônio Quaternário/antagonistas & inibidores , Receptores CCR5/efeitos dos fármacos , Receptores CCR5/imunologia , Receptores CXCR4/efeitos dos fármacos , Transdução de Sinais , Proteínas do Envelope Viral/metabolismo , Ligação Viral , Replicação Viral/fisiologiaRESUMO
According to one prominent model, each protomer in the activated nucleoprotein filament of homologous recombinase RecA possesses two DNA-binding sites. The primary site binds (1) single-stranded DNA (ssDNA) to form presynaptic complex and (2) the newly formed double-stranded (ds) DNA whereas the secondary site binds (1) dsDNA of a partner to initiate strand exchange and (2) the displaced ssDNA following the strand exchange. RecA protein from Pseudomonas aeruginosa (RecAPa) promotes in Escherichia coli hyper-recombination in an SOS-independent manner. Earlier we revealed that RecAPa rapidly displaces E.coli SSB protein (SSB-Ec) from ssDNA to form presynaptic complex. Here we show that this property (1) is based on increased affinity of ssDNA for the RecAPa primary DNA binding site while the affinity for the secondary site remains similar to that for E.coli RecA, (2) is not specific for SSB-Ec but is also observed for SSB protein from P.aeruginosa that, in turn, predicts a possibility of enhanced recombination repair in this pathogenic bacterium.