Thrombospndin 1 accelerates VEGFR2 trafficking and directs towards lysosomes for degradation

Abstract

In a recent study we found that CD47 constitutively associates with VEGFR2 based on FRET and receptor co-localization. CD47 ligation with either TSP1 or a peptide derived from the CD47 binding site of TSP1 (7N3) abolishes FRET and co-localization with VEGFR2, and inhibits phosphorylation of VEGFR2 at Y1175 and its downstream target Akt at S473. We found that association of VEGFR2 with the early endosomal markers EEA1 and Rab5 is decreased with TSP1 treatment, whereas association with LAMP1 and Rab7 in late endosomes is enhanced. Confocal live imaging showed that TSP1 directs VEGFR2 to the lysosomal compartment and can be inhibited with NH4Cl. Surface labeling with biotin and cycloheximide treatment showed that VEGFR2 degrades faster in TSP1-treated cells in the presence of VEGF. This indicates that TSP1 binding to CD47 inhibits VEGFR2 signaling by accelerating trafficking of the VEGF-VEGFR2 complex towards lysosomes. Current antiangiogenic therapies are directed towards inhibition of VEGF signaling. The data presented here indicates that VEGF signaling can also be blocked be enhancing VEGFR2 degradation by TSP1 treatment or using a CD47 binding peptide. This provides a new mechanism for the anti-angiogenic activity of TSP1. Analogs of the 7N3 peptide could be useful small molecule adjuvants to current anti-angiogenic therapies.