Sialic Acid Associated with αvβ3 Integrin Mediates HIV-1 Tat Protein Interaction and Endothelial Cell Proangiogenic Activation

Sialic acid (NeuAc) is a major anion on endothelial cells (ECs) that regulates different biological processes including angiogenesis. NeuAc is present in the oligosaccharidic portion of integrins, receptors that interact with extracellular matrix components and growth factors regulating cell adhesion, migration, and proliferation. Tat is a cationic polypeptide that, once released by HIV-1(+) cells, accumulates in the extracellular matrix, promoting EC adhesion and proangiogenic activation by engaging alpha(v)beta(3). By using two complementary approaches (NeuAc removal by neuraminidase or its masking by NeuAc-binding lectin from Maackia amurensis, MAA), we investigated the presence of NeuAc on endothelial alpha(v)beta(3) and its role in Tat interaction, EC adhesion, and proangiogenic activation. alpha(v)beta(3) immunoprecipitation with biotinylated MAA or Western blot analysis of neuraminidase-treated ECs demonstrated that NeuAc is associated with both the alpha(v) and the beta(3) subunits. Surface plasmon resonance analysis demonstrated that the masking of alpha(v)beta(3)-associated NeuAc by MAA prevents Tat/alpha(v)beta(3) interaction. MAA and neuraminidase prevent alpha(v)beta(3)-dependent EC adhesion to Tat, the consequent FAK and ERK1/2 phosphorylation, and EC proliferation, migration, and regeneration in a wound-healing assay. Finally, MAA inhibits Tat-induced neo-vascularization in the ex vivo human artery ring sprouting assay. The inhibitions are specific because the NeuAc-unrelated lectin from Ulex europaeus is ineffective on Tat. Also, MAA and neuraminidase affect only weakly integrin-dependent EC adhesion and proangiogenic activation by fibronectin. In conclusion, NeuAc is associated with endothelial alpha(v)beta(3) and mediates Tat-dependent EC adhesion and proangiogenic activation. These data point to the possibility to target integrin glycosylation for the treatment of angiogenesis/AIDS-associated pathologies.