THE LCK PROTEIN-TYROSINE KINASE IS NOT INVOLVED IN ANTIBODY-MEDIATED CD4 (CDR3-LOOP) SIGNAL-TRANSDUCTION THAT INHIBITS HIV-1 TRANSCRIPTION

Monoclonal antibodies (mAb) that bind to the immunoglobulin CDR3-like region in the D1 domain of the CD4 molecule can inhibit the HIV-1 life cycle in CD4-positive T cells and lymphoblastoid cell lines at the st age of transcription. This antiviral effect requires the integrity of the cytoplasmic tail of CD4 which is known to act as a signal transduc tion region through its association with the protein tyrosine kinase ( PTK) p56(lck). In this study, we investigated the putative role of thi s PTK in transducing inhibitory signals that act on HIV-1 replication after triggering by anti-CDR3-like region antibody treatment of infect ed T cell lines. CEM (CD4(+)/p56(lck+inducible)), MT2 (CD4(+)/p56(lck- repressed)), HSB-2 (CD4(-)/p56(lck+constitutively)), HSB-2 WTCD4 (CD4( +)/p56(lck+constitutively)), HSB-2 CD4.402 (CD4(+truncated form which lacks the cytoplasmic domain)/p56(lck+constitutively)), and HSB-2 CD4m ut (CD4(+unable to bind lck)/p56(lck+constitutively)) were exposed to HIV-1 and cultured in medium supplemented with an anti-CDR3-like regio n-specific antibody or a control anti-CD4 mAb which does not inhibit H IV-1 transcription. We found that CDR3-loop-mediated inhibitory signal s are efficiently transduced in CD4-positive cells which demonstrate a constitutive activation of p56(lck) or in CD4-positive cells lacking p56(lck) expression. Moreover, inhibitory signals were transduced in H SB-2 CD4mut cells expressing a cell surface CD4 with a double cysteine mutation in its cytoplasmic tail that renders the molecule unable to bind p56(lck), but not HSB-2 CD4.402 cells expressing a truncated form of CD4 which lacks the cytoplasmic domain. These results indicate tha t the p56(lck) plays no direct role in this process and suggests the e xistence of another signaling partner for CD4.