Binding of human immunodeficiency virus type 1 to CD4 induces association of Lck and Raf-1 and activates Raf-1 by a Ras-independent pathway.
We have analyzed CD4-mediated signaling during the early stages of human immunodeficiency virus type 1 (HIV-1) infection. Binding of purified HIV-1 virions or recombinant HIV-1 glycoprotein gp120 to CD4 receptors resulted in association and tyrosine phosphorylation and activation of tyrosine kinase Lck and serine/threonine kinase Raf-1. The association between Lck and Raf-1 was mediated by stimulation of the CD4 receptors, since it was abolished by preincubation of the virus with soluble CD4 and was not detected in CD4-negative A201 T cells. However, the Lck-Raf-1 association was restored in A201 cells permanently transfected with human CD4 cDNA and stimulated with anti-CD4 antibodies. In addition, a catalytically active Lck was required for the association of Lck and Raf-1. Surprisingly, the CD4-mediated signaling, induced by the HIV-1 binding, did not result in stimulation of the Ras GTP-binding activity or its association with Raf-1, indicating that the signaling pathway generated by the HIV-1 binding is not identical to the classical Ras/Raf-1 pathway. Furthermore, overexpression of activated Raf-1 in Jurkat T cells stimulated the HIV long terminal repeat promoter activity and significantly enhanced HIV-1 replication. This suggests that the Lck-Raf-1 pathway, rapidly stimulated by the binding of HIV-1 or gp120 to CD4 receptors, may play an essential role in the transcriptional activation of the integrated HIV-1 provirus as well as in its pathogenicity.
Oncology Center, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21231, USA.
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D000906:Antibodies; D015703:Antigens, CD / Q000502:physiology; D015704:CD4 Antigens / Q000502:physiology*; D002460:Cell Line; D004789:Enzyme Activation; D015699:HIV Envelope Protein gp120 / Q000378:metabolism*; D016325:HIV Long Terminal Repeat; D015497:HIV-1 / Q000502:physiology*; D006801:Humans; D007700:Kinetics; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D011994:Recombinant Proteins / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014771:Virion / Q000502:physiology; D014779:Virus Replication; D018631:ras Proteins / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism*
D000906:Antibodies; D015703:Antigens, CD; D015704:CD4 Antigens; D015699:HIV Envelope Protein gp120; D011518:Proto-Oncogene Proteins; D011994:Recombinant Proteins; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D019061:src-Family Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D018631:ras Proteins