FGF2 and Kaposi's sarcoma: Binding of HIV-1 Tat to heparan sulfate proteoglycans is competed out by the heparin-binding factor bFGF; Cell membrane heparin sulfate proteoglycans bind to the basic region of HIV-1 Tat (amino acids 49–57) and act as receptors for extracellular Tat uptake, an effect that may contribute to the angiogenic properties of Tat in promoting Kaposi's sarcoma