title: Modulation of HIV-1 infectivity and cyclophilin A-dependence by Gag sequence and target cell type.
abstract: BACKGROUND
  HIV-1 Gag proteins are essential for virion assembly and viral replication in newly infected cells. Gag proteins are also strong determinants of viral infectivity; immune escape mutations in the Gag capsid (CA) protein can markedly reduce viral fitness, and interactions of CA with host proteins such as cyclophilin A (CypA) and TRIM5alpha can have important effects on viral infectivity. Little information, however, is available concerning the extent that different primary Gag proteins affect HIV-1 replication in different cell types, or the impact on viral replication of differences in the expression by target cells of proteins that interact with CA. To address these questions, we compared the infectivity of recombinant HIV-1 viruses expressing Gag-protease sequences from primary isolates in different target cells in the presence or absence of agents that disrupt cyclophilin A - CA interactions and correlated these results with the viral genotype and the expression of cyclophilin A and TRIM5alpha by the target cells.
  
  
  RESULTS
  Viral infectivity was governed by the nature of the Gag proteins in a target cell-specific fashion. The treatment of target cells with agents that disrupt CypA-CA interactions often produced biphasic dose-response curves in which viral infectivity first increased and subsequently decreased as a function of the dose used. The extent that treatment of target cells with high-dose CypA inhibitors impaired viral infectivity was dependent on several factors, including the viral genotype, the nature of the target cell, and the extent that treatment with low-dose CypA inhibitors increased viral infectivity. Neither the presence of polymorphisms in the CA CypA-binding loop, the level of expression of CypA, or the level of TRIM5alpha expression could, alone, explain the differences in the shape of the dose-response curves observed or the extent that high-dose CypA inhibitors reduced viral infectivity.
  
  
  CONCLUSIONS
  Multiple interactions between host-cell factors and Gag can strongly affect HIV-1 infectivity, and these vary according to target cell type and the origin of the Gag sequence. Two of the cellular activities involved appear to be modulated in opposite directions by CypA-CA interactions, and Gag sequences determine the intrinsic sensitivity of a given virus to each of these cellular activities.
authors.affiliation: INSERM U941, Paris 75010, France. saori.matsuoka@inserm.fr
authors.forename: Saori
authors.initials: S
authors.lastname: Matsuoka
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Dam
authors.forename: Denise
authors.initials: D
authors.lastname: Lecossier
authors.forename: François
authors.initials: F
authors.lastname: Clavel
authors.forename: Allan J
authors.initials: AJ
authors.lastname: Hance
mesh_terms: D000090103:Antiviral Restriction Factors; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D021984:Cyclophilin A / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D016572:Cyclosporine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D015658:HIV Infections / Q000235:genetics / Q000378:metabolism*; D015497:HIV-1 / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D054884:Host-Pathogen Interactions / Q000187:drug effects; D006801:Humans; D011485:Protein Binding / Q000187:drug effects; D000070584:Tripartite Motif Proteins; D044767:Ubiquitin-Protein Ligases; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000235:genetics / Q000378:metabolism*
chemical_list: D000090103:Antiviral Restriction Factors; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D000070584:Tripartite Motif Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus; D016572:Cyclosporine; C477346:TRIM5 protein, human; D044767:Ubiquitin-Protein Ligases; D021984:Cyclophilin A; C499715:alisporivir