AIP and growth hormone-producing pituitary gland neoplasm: With respect to the relatively insensitive response of some somatotropinomas to somatostatin analogs, the decreased changes in expression of the antiproliferative gene zinc-finger regulator of apoptosis and cell-cycle arrest (ZAC-1; also known as PLAGL1) by AIP inactivation has been suggested to be a mechanism [14, 15].