Intracellular membrane traffic of human immunodeficiency virus type 1 envelope glycoproteins: vpu liberates Golgi-targeted gp160 from CD4-dependent retention in the endoplasmic reticulum.
The membrane traffic of human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins has been investigated in COS-1 cells transiently expressing the HIV-1 env, vpu, and rev genes. Analysis of oligosaccharide processing revealed that the majority of gp160 remained fully endo-H sensitive throughout a 21-h chase period, and hence cleavage of gp160 to gp120-gp41 took place prior to the creation of hybrid and complex oligosaccharides on gp120. Immunofluorescence microscopy demonstrated that in the absence of CD4 both gp160 and Vpu are targeted to the Golgi apparatus, that can be stained with wheat germ agglutinin or antibodies to the human KDEL receptor. In contrast, gp160 complexed with CD4 was retained in the ER and thus failed to reach the cis-Golgi compartment. Although gp160-bound CD4 has its own half life of 4 h 35 min in the endoplasmic reticulum (ER), co-expression of Vpu accelerated the turnover of CD4 by 5.5-fold and thereby enabled gp160 to be translocated out of the ER to the cis-Golgi compartment. We concluded that Vpu prevents the formation of stable CD4-gp160 complexes in the ER and thus indirectly allows gp160 to accumulate in the Golgi apparatus, where it is selectively retained to produce gp120-gp41.
Department of Microbiology, Kansai Medical University, Osaka.
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Kimura
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Nishikawa
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Ohyama
D001692:Biological Transport; D015704:CD4 Antigens; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000276:immunology / Q000378:metabolism*; D015686:Gene Products, env / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D006678:HIV / Q000378:metabolism*; D015699:HIV Envelope Protein gp120 / Q000378:metabolism*; D019302:HIV Envelope Protein gp160; D006367:HeLa Cells; D006596:Hexosaminidases; D054298:Human Immunodeficiency Virus Proteins; D006801:Humans; D007150:Immunohistochemistry; D007425:Intracellular Membranes / Q000378:metabolism*; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D009844:Oligosaccharides / Q000378:metabolism; D011498:Protein Precursors / Q000378:metabolism*; D054334:Viral Regulatory and Accessory Proteins / Q000502:physiology*; D000086082:Viroporin Proteins
D015704:CD4 Antigens; D015686:Gene Products, env; D015699:HIV Envelope Protein gp120; D019302:HIV Envelope Protein gp160; D006596:Hexosaminidases; D054298:Human Immunodeficiency Virus Proteins; D017038:Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase; D009844:Oligosaccharides; D011498:Protein Precursors; D054334:Viral Regulatory and Accessory Proteins; C514859:vpu protein, Human immunodeficiency virus 1; D000086082:Viroporin Proteins