AIP and pituitary tumor: For example, investigation of the Aip+/− mouse model has revealed that the associated pituitary tumours have activation of a hypoxic response, with induction of HIF-1α expression, and that signalling through the HIF-1α binding partners aryl hydrocarbon receptor nuclear translocator (ARNT) and ARNT2 is a key factor in the development of pituitary tumours, after loss of Aip (Raitila et al., 2010).