- The VHL gene is commonly mutated or inactivated in RCC tumors and VHL activity regulated the expression and activity of not only CAIX but also CAXII as well as other genes critical for tumor angiogenesis such as vascular endothelial growth factor (VEGF), glucose transporter 1 (GLUT1), glucose transporter 3 (GLUT 3) and platelet derived growth factor (PDGF).