Along similar lines, a HIF chimeric protein that contains the bHLH-PAS of HIF1α coupled to the NTAD/CTAD region of HIF2α cannot induce CAIX or PGK1 gene expression in HEK293 cells or RCC cells [13,31,32], highlighting the relevance of the HIF1α NTAD/CTAD region to explain HIF1α target selectivity. This evidence concerns the gene CA9 and renal cell carcinoma.