First Sentence

"Although it is presently not known exactly why loss of the VHL gene results in tumorigenesis, one of the first clues to the function of the VHL protein came with the discovery that clear cell renal carcinoma cells lacking a functional VHL gene misregulate and constitutively express hypoxia-inducible genes like glucose transporter-1 (GLUT1), vascular endothelial growth factor (VEGF), and transforming growth factor (TGF) (Gnarra et al., 1996; Iliopoulos et al., 1996; Siemeister et al., 1996; Knebelmann et al., 1998; de Paulsen et al., 2001)."