The Rab-effector protein RABEP2 regulates endosomal trafficking to mediate vascular endothelial growth factor receptor-2 (VEGFR2)-dependent signaling

As a master regulator of endothelial cell function, vascular endothelial growth factor receptor-2 (VEGFR2/KDR/Flk-1) activates multiple downstream signaling pathways that are critical for vascular development and normal vessel function. VEGFR2/KDR/Flk-1 trafficking through various endosomal compartments modulates its signaling output. Accordingly, proteins that regulate the speed and direction by which VEGFR2/KDR/Flk-1 traffics through endosomes have been demonstrated to be particularly important for arteriogenesis. However, little is known about how these proteins control VEGFR2/KDR/Flk-1 trafficking and about the implications of this control for endothelial cell function. Here, we show that Rab GTPase-binding effector protein 2 (RABEP2), a Rab-effector protein implicated in arteriogenesis, modulates VEGFR2/KDR/Flk-1 trafficking. By employing high-resolution microscopy and biochemical assays, we demonstrate that RABEP2 interacts with the small GTPase Rab4 and regulates VEGFR2/KDR/Flk-1 endosomal trafficking to maintain cell-surface expression of VEGFR2/KDR/Flk-1 and VEGF signaling. Lack of RABEP2 also led to prolonged retention of VEGFR2/KDR/Flk-1 in Rab5-positive sorting endosomes, which increased VEGFR2's exposure to phosphotyrosine Phosphatase 1b (PTP1b), causing diminished VEGFR2/KDR/Flk-1 signaling. Finally, the loss of RABEP2 increased VEGFR2/KDR/Flk-1 degradation by diverting VEGFR2/KDR/Flk-1 to Rab7-positive endosomes destined for the lysosome. These results implicate RABEP2 as a key modulator of VEGFR2/KDR/Flk-1 endosomal trafficking, and demonstrate the importance of RABEP2 and Rab4 for VEGFR2/KDR/Flk-1 signaling in endothelial cells.

Rab; angiogenesis; endothelial cell; receptor endocytosis; vascular endothelial growth factor (VEGF).