Inhibition of HIV-1 Replication by Mutant Tat Peptides
The HIV-1 Tat protein is a potent transactivator that is essential for virus replication. We reported previously that chemically synthesized Tat minimal domain peptides and full length Tat (Tat86), in which alanine is substituted for Lys-41, are taken up by cells and antagonize the expression of microinjected HIV-LTR driven CAT gene. We find that several Tat mutant peptides inhibit HIV-1 (HTLV-IIIB) replication. Tat86,41Ala, the most active peptide, inhibits virus replication 95–99% in acutely infected cells when added to the culture medium at concentrations of 10−6 M to 10−7 M; chronically infected cells are also inhibited but to a lesser extent. Tat86,41Ala protects HIV-1 infected cells from virus-induced cytopathogenicity and inhibits syncytia formation. The mechanism of inhibition by Tat mutant peptides is unknown. Unexpectedly, co-transfection of a Tat86 expressing plasmid with plasmids expressing Tat86,41Ala does not inhibit transactivation of endogenous HIV-LTRCAT in HeLa cells. Thus the Tat86,41Ala peptide, when added to cells together with Tat86 can block HIV-LTRCAT transactivation, but not when expressed endogenously from a plasmid. These results imply a novel mechanism of Tat antagonism.
KeywordsHuman Immunodeficiency Virus Transactivation Activity Molt4 Cell Syncytium Formation Fusion Index
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