Abstract

Vascular endothelial growth factor (VEGF) is an endothelial cell mitogen that promotes angiogenesis during embryonic development and the progression of certain pathologies. This study examined the regulation of VEGF expression by adenosine receptor (AR) activation in PC12 rat pheochromocytoma cells. Treatment of cells with the AR agonist CGS21680 reduced the VEGF mRNA level to ∼20% of that in control cells with an EC₅₀ value of 0.47 nM, indicative of mediation by the A_2AAR. Down-regulation of VEGF mRNA by CGS21680 was abolished by pretreatment of cells with the AR antagonist ZM241385. Additionally, ZM241385 alone increased VEGF mRNA by 2.8-fold above basal. RNase protection assays indicated that CGS21680 down-regulated VEGF₁₂₁, VEGF₁₆₅, and VEGF₁₈₉transcripts. VEGF protein secretion was similarly decreased by CGS21680. Under hypoxic conditions, VEGF mRNA expression was reduced by 85.7% after pretreatment with CGS21680. The down-regulation response appears to be mediated predominately by coupling of the A_2AAR to G_s because cholera toxin treatment also reduced VEGF expression. The decrease in VEGF mRNA steady-state levels after A_2AAR activation is apparently due to a decrease in the VEGF gene transcription rate and not to a decrease in mRNA stability. Thus, depending on the cell type, adenosine may have an inhibitory effect on VEGF production, which may have implications in blood vessel development.