HIV-Tat dependent chemotaxis and invasion, key aspects of tat mediated pathogenesis.

Extracellular Tat acts as a pleiotropic molecule inducing several biological effects on different target cells. Tat stimulates the chemotaxis of numerous cell types and it appears to have oncogenic activities, including acting as a co-factor for Kaposi's sarcoma. The Tat protein has been shown to bind integrins through an RGD amino acid motif. Tat is an angiogenic factor able to induce the migration and invasion of endothelial and KS cells through the interaction of its basic domain with the VEGF receptor VEGFR2 (Flk-1/KDR). We have also found that Tat is able to mimic chemokines, activating monocyte migration through the chemokine like' cysteine-core domain. Tat is a chemoattractant for dendritic cells, and both the RGD and basic domains appear to be involved in this response. In a recent study we demonstrated that Tat is chemotactic for PMN and induces Ca2+ mobilization in vitro. Experiments using synthetic peptides showed that Tat activities on PMN are mediated by the chemokine like' region. Finally Tat is also able to induce B cell chemotaxis, while its activity on helper T cells has not yet been clarified. Here we review data on Tat-dependent chemotaxis and discuss the possible implications in Tat mediated pathogenesis.