Thrombospondin-1 inhibits VEGF receptor-2 signaling by disrupting its association with CD47

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Thrombospondin-1 (TSP1) is known to inhibit angiogenesis through various mechanisms, including interactions with VEGF and endothelial cell receptors.
• While CD47 ligation by TSP1 affects downstream signaling of VEGF receptor-2 (VEGFR2), its direct impact on VEGFR2 activation has not been fully elucidated.

Purpose of the Study:

• To investigate the direct mechanism by which TSP1 inhibits VEGFR2 activation through its receptor CD47.
• To determine if CD47 ligation by TSP1 directly affects VEGFR2 phosphorylation and downstream signaling pathways.

Main Methods:

• Co-immunoprecipitation and Förster Resonance Energy Transfer (FRET) assays were used to assess the association between CD47 and VEGFR2.
• VEGFR2 phosphorylation and downstream signaling (e.g., Akt) were measured following CD47 ligation by TSP1.
• Experiments utilized human endothelial cells and murine CD47-null cells, along with recombinant TSP1 domains and peptides.

Main Results:

• CD47 constitutively associates with VEGFR2.
• TSP1 ligation of CD47 abolished FRET between CD47 and VEGFR2, inhibiting VEGFR2 and Akt phosphorylation.
• TSP1's inhibitory effect on VEGFR2 phosphorylation was dependent on CD47 expression and mediated by TSP1's CD47-binding domain.

Conclusions:

• TSP1 inhibits VEGFR2 activation through CD47 engagement, representing a potent anti-angiogenic mechanism.
• This pathway extends beyond nitric oxide signaling inhibition to a global suppression of VEGFR2 signaling.
• CD47 acts as a crucial mediator for TSP1-induced anti-angiogenic effects on endothelial cells.