Signalling properties of an HIV-encoded angiogenic peptide mimicking vascular endothelial growth factor activity

Abstract

HIV-1 expresses a multifunctional protein called TAT (trans-acting transcriptional activator), the function of which in vivo is tightly correlated with the incidence of Kaposi's sarcoma in AIDS patients. TAT is angiogenic and apparently binds to receptors specific for vascular endothelial growth factor (VEGF). Amino acids 46-60 of HIV-TAT, known as the basic peptide, have been shown to be responsible for its functional interaction with VEGF receptors. To characterize further the binding properties of this peptide, its coding sequence was fused to the reading frame of bacterial thioredoxin, allowing the production of large amounts of chimaeric polypeptides in bacteria in a biologically active form. Binding of chimaeric proteins to VEGF receptors was studied in vitro in endothelial cell cultures expressing either of the two receptors. Chimaeric thioredoxin proteins carrying the basic domain of TAT bound to both VEGF receptors with affinities similar to those of HIV-TAT or VEGF. Interestingly, these polypeptides competed only partially with VEGF for receptor binding, implying different binding sites for the TAT peptide and VEGF. This suggests that TAT binds VEGF receptors at new sites that might be useful targets for pharmacological intervention during pathological angiogenesis. The thioredoxin/basic-peptide chimaeras are functional agonists that mediate VEGF receptor signalling: (1) they stimulate the growth of endothelial cells; (2) together with basic fibroblast growth factor they cause tube formation of endothelial cells in collagen gels; (3) they induce blood vessel formation on the chicken chorioallantoic membrane; and (4) they activate VEGF receptor kinase and mitogen-activated protein kinase activity.

Targeting angiogenesis: Structural characterization and biological properties of a de novo engineered VEGF mimicking peptide

“…Many approaches have been pursued to modulate the VEGFreceptors interaction, and new molecular entities as peptides (14)(15)(16)(17)(18)(19)(20) and antibodies (21)(22)(23) have been reported to bind to the extracellular region of the VEGF receptors. A large number of them show an antagonist activity and only few behave as agonists (15).…”

Chemomechanical mapping of ligand–receptor binding kinetics on cells

“…These results also lay the groundwork for important and open questions, including whether this imaging approach and/or the binding kinetics are altered in mechanically stiff regions of cell surfaces; such work is ongoing. However, reasonable agreement of VEGFR2/cell with cell population-averaged levels (34,35) suggests that total receptor number is not grossly underestimated.…”

Role of Trophic Factors on Neuroimmunity in Neurodegenerative Infectious Diseases

“…Consequently, in addition to growth factors, cytokines, and chemokines ( Figures 3 and 4), we must also include viral proteins in our discussion of the role of trophic factors in the host's neuroimmune response ( Figure 5) (Barillari et al, 1999) (Mechtcheriakova et al, 2001;Scheidegger et al, 2001;Liu et al, 2000). Although numerous examples exist, HIV provides an excellent model for describing these signaling interactions in the context of neuronal protection and maintenance of the BBB Langford and Masliah, 2001).…”

“…HIV Tat mimics the effect of VEGF on endothelial cells via PAF-1 synthesis, activates the angiogenic process by binding to integrin receptors, and acts with bFGF to promote endothelial cell growth and angiogenesis (Scheidegger et al, 2001;Del Sorbo et al, 2001;Albini et al, 1996;Barillari et al, 1999) (Figure 5). Moreover, in recent reports, IL-8 has been presented as a key player in crosstalk between the HIV Tat protein and modulation of angiotrophic factors such as bFGF, VEGF, and endothelin-1 (Koch et al, 1992;Gershengorn et al, 1998) (Figures 5 and 6).…”