HIF1A and colon carcinoma: In colon carcinoma lines, hypoxia (1% O2) causes HIF-1α, the major regulator of the transcriptional response to hypoxia [37], [38], [39], to compete with TCF-4 for binding to β-catenin; this causes an increase in HIF-1α-mediated transcription while decreasing TCF-4 mediated transcription [40], which the authors suggest promote survival and adaptation to hypoxia and contribute to the cell cycle arrest induced by hypoxia, respectively.