description) Human immunodeficiency virus type-1 (HIV-1)Tat is a potent transcriptional transactivator of both viral and cellular gene expression that possesses angiogenic properties. Tat cooperates with basic fibroblast growth factor(bFGF) in increasing the development of angiogenic lesions of Kaposi's sarcoma (KS) in HIV-1 infected individuals. Preliminary data suggest that this effect of Tat is triggered in vivo by inflammatory cytokines (IC)present in KS, including interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha) and gamma-interferon (gamma-IFN). Although both bFGF and vascular endothelial growth factor (VEGF) are expressed by KS cells in vivo and in vitro and IC upregulate the expression of both of these angiogenic factors, Tat exerts its angiogenic effects only with bFGF. The angiogenic process is complex, involving vascular endothelial cell growth, adhesion, migration, invasion and differentiation. To dissect the mechanism(s) for Tat-mediated angiogenic effects during each of these steps, in vitro and in vivo assays in which Tat, Tat mutants and Tat peptides are active have been developed. The central hypothesis of this proposal is that specific functional domains of Tat modulate proliferative, migratory and/or morphogenic effects on primary vascular endothelial cells during angiogenesis through a bFGF-mediated pathway. Toward this end, preliminary studies suggest that the ability of Tat to promote angiogenesis in synergy with bFGF is mediated, in part, by the selective interaction of the RGD domain of Tat with specific integrins (alpha5 beta1 and alphav Beta3) that are induced by bFGF. Through this interaction, the RGD domain of Tat promotes the locomotion and adhesion of KS and cytokine-activated primary vascular endothelial cells. In addition, the basic region of Tat retrieves extracellular bound bFGF into a soluble form that mediates cellular growth induced by Tat. Thus, Tat, a key regulatory protein of HIV-1 that can be released extracellularly from HIV-1-infected cells, upregulates angiogenesis, in part, by mimicking the functions of extracellular matrix proteins. The angiogenic effects of intracellular Tat are not known and determining this is a major focus of this proposal.
The aims of the studies proposed herein are to determine whether (1) the transcriptional activating function of Tat, along with the RGD and basic region domains of Tat, plays a role during angiogenesis, (2) an endothelial cell-derived cyclin-dependent kinase, TAK/pTEF-b, activity that is essential for Tat transactivation, is induced through activation of primary human vascular endothelial cells by inflammatory cytokines or angiogenic factors that mediate Tat-enhanced angiogenesis and (3) Tat transactivates Bcl-2 gene expression in vascular endothelial cells stimulated to undergo angiogenesis, an effect that may involve the cellular Tat cofactor, TAK/pTEF-b.
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