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 b inding to CD4 also triggers signals that lead to nuclear translocation of NF-kappa B and are important to the productive infection process, In addition to its cytoplasmic tail, in the ectodomain, the immunoglob ulin (Ig) CDR3-like region of CD4 domain 1 seemed to play a role in th is 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 res idues within the CDR3-like loop either inhibited NF-kappa B translocat ion after HIV-1 and gp120-anti-gp120 immune complexes binding to E91K, E92K mutants or induced its constitutive activation for E87K,D88K muta nts, Moreover, A2.01-3B cells expressing the E91K,E92K mutant exhibite d a lower HIV-1(Lai) replication, These cells, however, expressed p56( lck), demonstrated NF-kappa B translocation upon PMA stimulation, boun d HIV-1(Lai) envelope glycoprotein with high affinity, and contained H IV-1 DNA 24 h after exposure to virus. E91K, E92K, and E87K,D88K mutan t CD4 molecules were unable to bind a CD4 synthetic aromatically modif ied exocyclic, CDR3.AME-(82-89), that mimics the CDR3-like loop struct ure and binds to native cell surface CD4, This result together with mo lecular modeling studies indicates that the CDR3.AME-(82-89) analog bi nds to the CDR3-like loop of CD4 and strongly suggests that this regio n represents a site for CD4 dimerization, The negative charges on the CDR3-like loop thus appear critical for CD4-mediated signal transducti on most likely related to CD4 dimer formation.