Moreover, it leads to differences in the expression of HIF-1α and HIF-2α in RCC that PHD is selective for modification of HIF-1α and HIF-2α (Koh et al., 2008), which may explain why a large number of VHL-defective ccRCC cell lines do not express HIF-1α, but express HIF-2α (Figure 1). This evidence concerns the gene VHL and renal cell carcinoma.