RRM2 and neoplasm: 2b, P < 0.01). Hypoxia condition in tumor has been shown to be an important stimulus for VEGF gene expression as well as tumor angiogenesis. To determine the effect of RRM2 on VEGF expression under hypoxia, we compared VEGF mRNA and protein in KB-V and KB-M2-D cells. The results showed that hypoxia (1% oxygen for 16h) upregulated VEGF by ~2 fold at protein levels (Figure. 2c, P < 0.05) or ~4-fold at mRNA (Figure. 2d, P < 0.01) in both cells. Compared with that of KB-V, the production of VEGF in KB-M2-D was still significantly higher under both normoxia and hypoxia (Figure. 2c, d, P < 0.05).