_v3-integrin-dependent activation of focal adhesion kinase mediates NF-B activation and motogenic activity by HIV-1 Tat in endothelial cells

Once in the extracellular environment, the transactivator protein HIV-1 Tat exerts several pleiotropic effects by interacting with different cellular receptors, including integrin _v3. Real-time surface plasmon resonance analysis reveals that Tat/_V3 interaction occurs with rapid kinetics (association and dissociation rates equal to 1.16x10⁷ M^-1 s^-1 and 3.78x10^-1 s^-1, respectively) and high affinity (dissociation constant = 32 nM). Through this interaction, substratum-immobilized Tat promotes adhesion and motogenic activity in endothelial cells. Also, _v3/Tat interaction triggers the activation of focal adhesion kinase, RhoA and pp60^src. Overexpression of the dominant negative form of focal adhesion kinase, but not of an inactive Leu₁₀₃₄Ser substitution mutant isoform, impairs the activation of focal adhesion kinase and RhoA, but not that of pp60^src, without affecting endothelial cell adhesion and spreading. _v3/Tat interaction triggers the activation of NF-B in endothelial cells in a focal adhesion kinase-, RhoA- and pp60^src-dependent manner, as shown in dominant negative focal adhesion kinase transfectants or using specific pharmacological inhibitors. Finally, the activation of focal adhesion kinase, RhoA, NF-B and pp60^src are required to mediate the motogenic activity of Tat in endothelial cells.

Since Tat accumulates in an immobilized form in the extracellular matrix, these results provide new biochemical and biological insights about _v3/Tat interaction exploitable for the design of anti-Tat strategies.