title: Enhanced CD4 down-modulation by late stage HIV-1 nef alleles is associated with increased Env incorporation and viral replication.
abstract: Three viral proteins participate in the down-modulation of CD4 in human immunodeficiency virus type 1 (HIV-1)-infected cells. The underlying mechanisms have been extensively investigated. However, the physiological relevance of this phenomenon remains poorly understood. To address the role of CD4 down-modulation in HIV-1 pathogenesis in vivo, we have characterized the functional properties of nef alleles isolated from seven HIV-1-infected patients at either the stage of AIDS (late alleles) or during the asymptomatic phase of infection (early alleles). HIV-1 variants carrying these nef alleles showed striking differences in CD4 down-modulation, virus infectivity, and replication properties. Infection of T cells with late strains resulted in production of viral particles with enhanced infectivity, as compared with variants carrying early nef alleles. These differences in infectivity were observed only when viruses were produced in cells with high levels of the viral receptor, suggesting a functional link between CD4 levels and the ability of Nef to down-modulate CD4 and to enhance viral infectivity. Similarly, late nef alleles were substantially more active than early nef genes in stimulating HIV-1 replication in high CD4-positive cells, including primary lymphocytes, but not in cells expressing low levels of the CD4 receptor. Single-round assays showed that differences in infectivity between late and early strains are largely reduced when evaluated in target cells with high levels of CD4, suggesting that the inhibitory effect occurs at the entry step. Supporting this, enhanced CD4 down-modulation by late nef alleles was associated with higher levels of envelope incorporation into viral particles, a phenomenon that likely accounted for the augmented infectivity. Our data suggest a mechanistic link between the Nef-mediated CD4 down-modulation and the enhancement of replication in CD4-positive lymphocytes. As progression to disease occurs, HIV-1 Nef variants with enhanced ability to down-modulate CD4 are selected. These strains efficiently overcome the deleterious effects of CD4 and replicate more aggressively in CD4-positive primary lymphocytes. These results highlight the importance of the virus-induced CD4 down-modulation in HIV-1 pathogenesis.
authors.affiliation: Department of Medicine, School of Medicine, University of California, La Jolla, 92093, USA.
authors.forename: Enrique R
authors.initials: ER
authors.lastname: Argañaraz
authors.forename: Michael
authors.initials: M
authors.lastname: Schindler
authors.forename: Frank
authors.initials: F
authors.lastname: Kirchhoff
authors.forename: María J
authors.initials: MJ
authors.lastname: Cortes
authors.forename: Juan
authors.initials: J
authors.lastname: Lama
mesh_terms: D000483:Alleles; D015704:CD4 Antigens / Q000096:biosynthesis / Q000378:metabolism / Q000502:physiology*; D002460:Cell Line; D002478:Cells, Cultured; D015536:Down-Regulation; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D015686:Gene Products, env / Q000378:metabolism*; D015693:Gene Products, nef / Q000235:genetics / Q000378:metabolism*; D015658:HIV Infections / Q000276:immunology / Q000821:virology; D015497:HIV-1 / Q000378:metabolism; D006801:Humans; D019169:Jurkat Cells; D007963:Leukocytes, Mononuclear / Q000378:metabolism; D008214:Lymphocytes / Q000821:virology; D013997:Time Factors; D014162:Transfection; D054311:nef Gene Products, Human Immunodeficiency Virus
chemical_list: D015704:CD4 Antigens; D015686:Gene Products, env; D015693:Gene Products, nef; D054311:nef Gene Products, Human Immunodeficiency Virus