CA9 and cancer: HIF-1α actively participates in metabolic adaptation of cancer cells to hypoxia by up-regulating the expression of genes encoding pyruvate dehydrogenase kinase 1 (PDK1), which inhibits the conversion of pyruvate into acetyl-CoA, glucose transporters (GLUT1 and GLUT3) and carbonic anhydrase IX (CA-IX) converting the metabolically generated CO2 into carbonic acid [83,84].