HIV-TAT PROTEIN IS A HEPARIN-BINDING ANGIOGENIC GROWTH-FACTOR

Transgenic animal studies have linked the expression of the HIV-1 tat gene to the appearance of Kaposi's sarcoma (KS)-like lesions. We have recently shown that recombinant tat is angiogenic in vivo, and that ta t angiogenic response is enhanced by heparin. Also in the rabbit corne a model, recombinant HIV-1 tat alone is poorly angiogenic, but gives a good response when combined with heparin. Like many angiogenic growth factors, tat has a basic domain similar to that of several heparin bi nding angiogenic factors, including FGF, VEGF and HGF, suggesting that this region is important in endothelial cell activation. We show that tat binds heparin sepharose with a high affinity, similar to bFGF. Bi nding of tat to the cell surface is also modulated by heparin. Biologi cal activities of tat, such as induction of endothelial cell growth, m igration and invasion in vitro are all enhanced by low concentrations and inhibited by high concentrations of heparin, as has been shown for other heparin-binding angiogenic factors. Heparan sulfate is also eff ective, whereas the unsulfated polysaccharide K5 does not enhance tat activity. Furthermore, a peptide encompassing the tat basic domain is able to induce growth and migration of endothelial cells, while an adj acent peptide is not. Our data indicate that the tat basic domain play s a key role in its vascular cell activation properties, and strongly suggest that extracellular HIV-tat is essentially a 'new' heparin-bind ing angiogenic factor.