Human umbilical vein endothelial cells (HUVECs) were maintained in endothelial cell growth medium including supplements (EBM-2; Lonza, Allendale, NJ, USA) and harvested with immunoprecipitation lysis buffer (Pierce/Thermo Fisher Scientific, Waltham, MA, USA). Two milligrams of total protein from cell lysates was cleared with protein A/G beads and incubated with anti-MMP14 antibody (Abcam Inc., Cambridge, MA, USA) overnight in a cold room. The next day, 30 μL protein A/G agarose was added to the mixture and incubated for 4 hours. After the reaction, the agarose was washed with lysis buffer and boiled with loading dye with 100 mM β-mercaptoethanol as a reducing agent before being subjected to SDS-PAGE for Western blotting. For Western blot analyses, separated proteins on SDS-PAGE gels were transferred to nitrocellulose (NC) membranes and blocked using 5% milk or 3% bovine serum albumin. Vascular endothelial growth factor receptor 1, R2, and R3 were detected with specific antibodies (VEGFR1, R&D Systems Inc., Minneapolis, MN, USA; VEGFR2, Cell Signaling Technology, Danvers, MA, USA; VEGFR3, eBiosciences, San Diego, CA, USA). Membranes were incubated with primary antibodies for 1 hour and then washed with 0.05% Tween-20 in Tris-buffered saline. Then the NC membranes were incubated with fluorescence-conjugated secondary antibody (Li-Cor, Lincoln, NE, USA), and protein bands were detected using the Li-Cor Odyssey system (Li-Cor).