The Basic Domain in HIV-1 Tat Protein as a Target for Polysulfonated Heparin-mimicking Extracellular Tat Antagonists

Heparin binds extracellular HIV-1 Tat protein and modulates its HIV long terminal repeat (LTR)-transactivating activity (M. Rusnati, D. Coltrini, P. Oreste, G. Zoppetti, A. Albini, D. Noonan, F. d’Adda di Fagagna, M. Giacca, and M. Presta (1997) J. Biol. Chem. 272, 11313–11320). On this basis, the glutathione S -transferase (GST)-Tat R49/52/53/55/56/57A mutant, in which six arginine residues within the basic domain of Tat were mutagenized to alanine residues, was compared with GST-Tat for its capacity to bind immobilized heparin. Dissociation of the GST-Tat R49/52/53/55/56/57A ·heparin complex occurred at ionic strength significantly lower than that required to dissociate the GST-Tat·heparin complex. Accordingly, heparin binds immobilized GST-Tat and GST-Tat R49/52/53/55/56/57A with a dissociation constant equal to 0.3 and 1.0 μ m , respectively. Also, the synthetic basic domain Tat-(41–60) competes with GST-Tat for heparin binding. Suramin inhibits [ 3 H]heparin/Tat interaction, 125 I-GST-Tat internalization, and the LTR-transactivating activity of extracellular Tat in HL3T1 cells and prevents 125 I-GST-Tat binding and cell proliferation in Tat-overexpressing T53 cells. The suramin derivative 14 C-PNU 145156E binds immobilized GST-Tat with a dissociation constant 5 times higher than heparin and is unable to bind GST-Tat R49/52/53/55/56/57A . Although heparin was an antagonist more potent than suramin, modifications of the backbone structure in selected suramin derivatives originated Tat antagonists whose potency was close to that shown by heparin. In conclusion, suramin derivatives bind the basic domain of Tat, prevent Tat/heparin and Tat/cell surface interactions, and inhibit the biological activity of extracellular Tat. Our data demonstrate that tailored polysulfonated compounds represent potent extracellular Tat inhibitors of possible therapeutic value.