ABCG2 and pancreatic neoplasm: For instance, hypoxia induces extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation to activate HIF-1α, which directly binds to the promoter of ABCG2 gene and subsequently enhances ABCG2 transcription, leading to gemcitabine chemoresistance in pancreatic cancer cells (He et al., 2016).