Blocking CXCR4 inhibited PGE₂-induced tubular formation by HMECs. (A-B) HMECs were stimulated with VEGF (10 ng/mL) and bFGF (50 ng/mL) for 24 hours, and then tubular formation assay was performed on Matrigel in the presence (B) or absence (A) of SDF-1α. (C-D) Nonstimulated HMECs were plated on SDF-1α–containing Matrigel with (D) or without PGE₂ (C). As depicted by the figure, PGE₂ enhanced tubular formation. (E-F) PGE₂-stimulated HMECs were plated on SDF-1α–containing Matrigel in the presence of anti-CXCR4 20 μg/mL (E) or control antibody (F). Microphotographs were taken at × 10 original magnification. (G-I) Effect of COX inhibitors on VEGF- and bFGF-induced tubular formation. Quantitation of the number of the junctions in at least 3 fields under different treatments was determined by using the Bioquant program. Statistical analysis was performed using ANOVA test. The data shown in panels G and H represent the mean + SEM of 3 experiments; *P < .005. Panel I shows one representative experiment of 2 performed; *P < .005; **P < .01; ***P < .05.