Pituitary tumors are common intracranial neoplasms that often result in endocrine dysfunction due to hormone overproduction or deficiencies from mass effects. Gonadotrope cell or gonadotropinomas are tumors that produce LH and/or FSH and represent 40% of macroadenomas. Little is known about their underlying pathogenic mechanisms. We compared expression profiles of 10 gonadotropinomas to 9 normal pituitaries by cDNA array and identified bone morphogenetic protein (BMP) and retinoic acid (RA) inducible neural specific protein-3 (BRINP3) as overexpressed in tumors compared with normals. BRINP3 is a novel, normally brain restricted protein of unknown function. BRINP3 mRNA was expressed selectively in gonadotropinomas. Subcellular localization studies showed that BRINP3 was targeted to the mitochondria, but BRINP3 overexpression was unable to protect pituitary cells against programed cell death induced by growth factor withdrawal. However, BRINP3 overexpression in pituitary gonadotrope cells promoted proliferation, migration and invasion. A BRINP3 antibody was raised that demonstrated clustered expression of BRINP3 protein in gonadotropinomas and not in normal human pituitary samples. Thus, BRINP3 is a mitochondrially localized protein that is selectively up-regulated in human gonadotropinomas. Its actions to increase proliferation, migration and invasion suggest it may play an important role in pituitary tumorigenesis.