Transduction of activation signal that follows HIV-1 binding to CD4 and CD4 dimerization involves the immunoglobulin CDR3-like region in domain 1 of CD4.
The role of CD4 during the human immunodeficiency virus type 1 (HIV-1) life cycle in T cells is not restricted to binding functions. HIV-1 binding to CD4 also triggers signals that lead to nuclear translocation of NF-kappaB and are important to the productive infection process. In addition to its cytoplasmic tail, in the ectodomain, the immunoglobulin (Ig) CDR3-like region of CD4 domain 1 seemed to play a role in this cascade of signals. We demonstrate in this work that the structural integrity of the CDR3-like loop is required for signal transduction. Substitutions of negatively charged residues by positively charged residues within the CDR3-like loop either inhibited NF-kappaB translocation after HIV-1 and gp120-anti-gp120 immune complexes binding to E91K,E92K mutants or induced its constitutive activation for E87K,D88K mutants. Moreover, A2.01-3B cells expressing the E91K,E92K mutant exhibited a lower HIV-1Lai replication. These cells, however, expressed p56(lck), demonstrated NF-kappaB translocation upon PMA stimulation, bound HIV-1Lai envelope glycoprotein with high affinity, and contained HIV-1 DNA 24 h after exposure to virus. E91K, E92K, and E87K,D88K mutant CD4 molecules were unable to bind a CD4 synthetic aromatically modified exocyclic, CDR3.AME-(82-89), that mimics the CDR3-like loop structure and binds to native cell surface CD4. This result together with molecular modeling studies indicates that the CDR3.AME-(82-89) analog binds to the CDR3-like loop of CD4 and strongly suggests that this region represents a site for CD4 dimerization. The negative charges on the CDR3-like loop thus appear critical for CD4-mediated signal transduction most likely related to CD4 dimer formation.
Briant
L
L
Laboratoire d'Immunologie des Infections Retrovirales, CNRS ERS155, Institut de Biologie, 34060 Montpellier, France.
Signoret
N
N
Gaubin
M
M
Robert-Hebmann
V
V
Zhang
X
X
Murali
R
R
Greene
M I
MI
Piatier-Tonneau
D
D
Devaux
C
C
D000595:Amino Acid Sequence; D015704:CD4 Antigens / Q000737:chemistry* / Q000502:physiology; D019281:Dimerization; D015497:HIV-1 / Q000502:physiology*; D006801:Humans; D007135:Immunoglobulin Variable Region / Q000737:chemistry; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection; D014779:Virus Replication; D019061:src-Family Kinases / Q000502:physiology
D015704:CD4 Antigens; D007135:Immunoglobulin Variable Region; D016328:NF-kappa B; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D019061:src-Family Kinases