VEGF and Hypoxia Independently Induce MDR1 Expression to Promote Endothelial Cell Angiogenesis

Angiogenesis is a critical process in endothelial biology and tumor progression, primarily regulated by vascular endothelial growth factor (VEGF) and hypoxia. Multidrug resistance protein 1 (MDR1), best known for its role in drug efflux, has recently been implicated in endothelial function. This study aimed to investigate whether VEGF and hypoxia independently regulate MDR1 expression in human umbilical vein endothelial cells (HUVECs) and to elucidate the functional role of MDR1 in angiogenesis.

HUVECs were treated with VEGF or exposed to hypoxic conditions (1% O₂ or CoCl₂). MDR1 mRNA expression was assessed by quantitative real-time PCR, whereas MDR1 protein expression was evaluated by Western blotting, flow cytometry, and immunofluorescence. Functional assays, including migration, invasion, tube formation, and cell viability, were performed following MDR1 overexpression or siRNA-mediated knockdown. HIF-1α overexpression was used to examine hypoxia-mediated regulation.

VEGF induced MDR1 expression in a dose- and time-dependent manner. VEGF-induced MDR1 expression was predominantly localized intracellularly and did not significantly enhance drug efflux activity. MDR1 overexpression promoted endothelial migration, invasion, tube formation, and cell viability even in the absence of VEGF, whereas MDR1 knockdown attenuated VEGF-induced angiogenic responses. Hypoxia and hypoxia-inducible factor 1-alpha (HIF-1α) overexpression also significantly upregulated MDR1 expression independently of VEGF.

VEGF and hypoxia independently induce MDR1 expression in endothelial cells through distinct signaling pathways. MDR1 functions as a key mediator of angiogenesis independent of its classical drug efflux role, highlighting its potential as a therapeutic target in angiogenesis-related vascular diseases.