E2F1 and ACTH-producing pituitary gland adenoma: In cultured ACTH-secreting adenoma cells, USP8 dysregulation is associated with an increased expression of EGFR and other proteins involved in EGF signaling including CMTM8, MAPK15, and E2F1 transcription factor, which contribute to the genesis of corticotrope adenomas and sustain ACTH and POMC secretion [15,19,20,21].