For example, in the RCC cell line Caki-1 which is VHL-proficient, relative HIF-1α and HIF-2α protein levels increased with subsequent decreased oxygen conditions starting at 10% oxygen for HIF-1α and 1% for HIF-2α with highest detection for both HIF-α subunits at 0.1% oxygen, suggesting HIF-1α preference at higher oxygen concentrations [67]. This evidence concerns the gene VHL and renal cell carcinoma.