Vol. 66, No. 1
JOURNAL
OF VIROLOGY, Jan. 1992, p. 226-234 0022-538X/92/010226-09$02.00/0 Copyright C) 1992, American Society for Microbiology
Human Immunodeficiency Virus Type 1 Vpu Protein Regulates the Formation of Intracellular gpl60-CD4 Complexes RONALD L. WILLEY, FRANK MALDARELLI, MALCOLM A. MARTIN, AND KLAUS STREBEL* Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases,
Bethesda, Maryland 20892 Received 21 August 1991/Accepted 9 October 1991
Intracellular transport and processing of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein, gpl60, proceeds via the endoplasmic reticulum and Golgi complex and involves proteolytic processing of gpl60 into the mature virion components, gpl20 and gp4l. We found that coexpression of gpl60 and human CD4 in HeLa cells severely impaired gpl20 production due to the formation of intracellular gpl60-CD4 complexes. This CD4-mediated inhibition of gpl60 processing was alleviated by coexpression of the HIV-1-encoded Vpu protein. The coexpression of Vpu and CD4 in the presence of gpl60 resulted in increased degradation of CD4. Although the precise mechanism(s) responsible for the Vpu effect is presently unclear, our findings suggest that Vpu may destabilize intracellular gpl60-CD4 complexes. precursor
Vpu is a 16-kDa phosphorylated membrane protein which has been shown to enhance the release of viral proteins and progeny virions from infected cells (26). Vpu appears to be located predominantly in the perinuclear region in virusproducing cells (16) but has not been found to be particle associated (25), which suggests that it might modulate an intracellular event(s) attending virus assembly and/or release. The Vpu open reading frame is located upstream of and overlapping the viral env gene. A recent report has suggested that Vpu and the envelope precursor glycoprotein, gpl60, are expressed from a single bicistronic mRNA (21). This unusual utilization of viral transcripts might reflect a requirement for the coordinate interaction of the two viral gene products. CD4, the receptor for the human lentiviruses, has previously been shown to interact with gpl60 in the endoplasmic reticulum (ER) (2, 4). In fact, the stable complex which forms blocks the transport and cell surface expression of CD4, a feature commonly associated with human immunodeficiency virus (HIV)-producing cells (6, 15). In a previous report, we suggested that the formation of gpl60-CD4 complexes might promote the intracellular degradation of gpl60 and result in the inefficient processing of gpl60 (
JOURNAL
OF VIROLOGY, Jan. 1992, p. 226-234 0022-538X/92/010226-09$02.00/0 Copyright C) 1992, American Society for Microbiology
Human Immunodeficiency Virus Type 1 Vpu Protein Regulates the Formation of Intracellular gpl60-CD4 Complexes RONALD L. WILLEY, FRANK MALDARELLI, MALCOLM A. MARTIN, AND KLAUS STREBEL* Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases,
Bethesda, Maryland 20892 Received 21 August 1991/Accepted 9 October 1991
Intracellular transport and processing of the human immunodeficiency virus type 1 (HIV-1) envelope glycoprotein, gpl60, proceeds via the endoplasmic reticulum and Golgi complex and involves proteolytic processing of gpl60 into the mature virion components, gpl20 and gp4l. We found that coexpression of gpl60 and human CD4 in HeLa cells severely impaired gpl20 production due to the formation of intracellular gpl60-CD4 complexes. This CD4-mediated inhibition of gpl60 processing was alleviated by coexpression of the HIV-1-encoded Vpu protein. The coexpression of Vpu and CD4 in the presence of gpl60 resulted in increased degradation of CD4. Although the precise mechanism(s) responsible for the Vpu effect is presently unclear, our findings suggest that Vpu may destabilize intracellular gpl60-CD4 complexes. precursor
Vpu is a 16-kDa phosphorylated membrane protein which has been shown to enhance the release of viral proteins and progeny virions from infected cells (26). Vpu appears to be located predominantly in the perinuclear region in virusproducing cells (16) but has not been found to be particle associated (25), which suggests that it might modulate an intracellular event(s) attending virus assembly and/or release. The Vpu open reading frame is located upstream of and overlapping the viral env gene. A recent report has suggested that Vpu and the envelope precursor glycoprotein, gpl60, are expressed from a single bicistronic mRNA (21). This unusual utilization of viral transcripts might reflect a requirement for the coordinate interaction of the two viral gene products. CD4, the receptor for the human lentiviruses, has previously been shown to interact with gpl60 in the endoplasmic reticulum (ER) (2, 4). In fact, the stable complex which forms blocks the transport and cell surface expression of CD4, a feature commonly associated with human immunodeficiency virus (HIV)-producing cells (6, 15). In a previous report, we suggested that the formation of gpl60-CD4 complexes might promote the intracellular degradation of gpl60 and result in the inefficient processing of gpl60 (
