Vpu exerts a positive effect on HIV-1 infectivity by down-modulating CD4 receptor molecules at the surface of HIV-1-producing cells.
Human immunodeficiencey virus, type 1 (HIV-1) encodes three proteins, Nef, Vpu, and gp160, that down-modulate surface expression of the CD4 receptor during viral infection. In the present study, we have investigated the role of CD4 down-modulation in the HIV-1 infection cycle, primarily from the perspective of Vpu function. We report here that, like Nef, Vpu-mediated CD4 degradation modulates positively HIV-1 infectivity. Our data reveal that accumulation of CD4 at the cell surface of Vpu-deficient HIV-1-producing cells leads to an efficient recruitment of CD4 into virions and to an impairment of viral infectivity. This CD4-mediated inhibition of viral infectivity was not observed when a CD4 mutant unable to bind Env gp120 was used or when VSV-G glycoprotein was utilized to pseudotype viruses, suggesting that an interaction between CD4 and gp120 is required for interference. Indeed, protein analysis of Vpu-defective viral particles reveals that CD4 recruitment is associated with an increased formation of gp120-CD4 complexes at the virion surface. Interestingly, we did not detect any difference at the level of total virion-associated Env glycoproteins between wild-type and Vpu-defective virus, indicating that accumulation of CD4 at the cell surface and recruitment of CD4 into Vpu-defective HIV-1 particles exert a negative effect on viral infectivity, most likely by promoting the formation of nonfunctional gp120-CD4 complexes at the virion surface. Finally, we show that both Vpu- and Nef-induced CD4 down-modulation activities are required for production of fully infectious particles in CD4+ T cell lines and primary cells, an observation that has clear implications for viral spread in vivo.
Levesque
Karine
K
Laboratoire de Rétrovirologie Humaine, Département de Microbiologie et Immunologie, Université de Montréal, Québec H3C 3J7, Canada.
Zhao
Yong-Sen
YS
Cohen
Eric A
EA
D015153:Blotting, Western; D015704:CD4 Antigens / Q000096:biosynthesis / Q000502:physiology*; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism / Q000821:virology; D002462:Cell Membrane / Q000378:metabolism / Q000821:virology*; D015536:Down-Regulation; D005434:Flow Cytometry; D015693:Gene Products, nef / Q000378:metabolism; D015699:HIV Envelope Protein gp120 / Q000378:metabolism; D015497:HIV-1 / Q000378:metabolism* / Q000472:pathogenicity*; D006367:HeLa Cells; D054298:Human Immunodeficiency Virus Proteins; D006801:Humans; D019169:Jurkat Cells; D007963:Leukocytes, Mononuclear / Q000378:metabolism / Q000821:virology; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D013997:Time Factors; D014162:Transfection; D054334:Viral Regulatory and Accessory Proteins / Q000502:physiology*; D054311:nef Gene Products, Human Immunodeficiency Virus; D000086082:Viroporin Proteins
D015704:CD4 Antigens; D015693:Gene Products, nef; D015699:HIV Envelope Protein gp120; D054298:Human Immunodeficiency Virus Proteins; D054334:Viral Regulatory and Accessory Proteins; D054311:nef Gene Products, Human Immunodeficiency Virus; C514859:vpu protein, Human immunodeficiency virus 1; D000086082:Viroporin Proteins