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.
Laboratoire de Rétrovirologie Humaine, Département de Microbiologie et Immunologie, Université de Montréal, Québec H3C 3J7, Canada.
Karine
K
Levesque
Yong-Sen
YS
Zhao
Eric A
EA
Cohen
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