HIF1A and renal carcinoma: To verify this, we switched the experimental set up and utilized the von Hippel-Lindau protein (pVHL)-deficient renal carcinoma cells (RCC4−pVHL), where HIF-1α levels are always upregulated regardless of whether the cells are grown under normoxia or hypoxia (Fig. 2b) [32,33] For comparative reasons, we also used RCC4 cells with reintroduced pVHL protein (RCC4pVHL).