Effects of tumor microenviromental factors on VEGF expression

The expression of vascular endothelial growth factor (VEGF) is regulated by microenvironmental factors within the tumors, such as hypoxia, free radicals, pH imbalance and nutrient deficiency. The purpose of this study was to observe VEGF activity in tumor cells under different stress conditions. A plasmid was generated, consisting of green fluorescent protein (GFP) fused to a 1,217-bp sequence, which was located downstream and upstream of the transcriptional start site of VEGF, respectively. The plasmid was stably transfected into 4T1 mouse breast carcinoma cells. Cells were cultured in a medium with nitric oxide (NO) donor sodium nitroprusside (SNP), hypoxia-mimetic agent deferoxamine mesylate (DFX), H₂O₂, absence of serum and lowered or elevated pH, or were heat-shocked, followed by measurement of VEGF activity by reverse transcription polymerase chain reaction (RT-PCR) and ELISA. Hypoxia, SNP and H₂O₂ led to increments of VEGF mRNA and protein expression, as well as of GFP expression. The pH alterations, serum deprivation and heat shock reduced VEGF mRNA expression, but had little effect on GFP expression. The results demonstrated that VEGF expression may be influenced by a number of microenvironmental factors and these factors may play important roles in regulating VEGF expression during tumorigenesis.