AIP Mutations are not identified in patients with sporadic pituitary adenomas.

The pathogenesis of pituitary adenomas remains a subject of interest. Recently, mutations in the aryl hydrocarbon receptor-interacting protein (AIP) were identified as germline events leading to pituitary tumor predisposition in Finnish and Italian families with familial growth hormone-secreting pituitary adenomas and acromegaly. We examined the frequency of AIP mutations in pituitary tumors and blood of Canadian patients with sporadic pituitary somatotroph adenomas and sporadic pituitary adenomas of other types. Genomic DNA was extracted from pituitary tumors and white blood cells obtained from peripheral blood. Three PCR reactions were carried out to amplify the sites of known mutation, and amplified products were sequenced. AIP mutations were not detected as germline events in blood or as somatic alterations in tumors of 66 patients with pituitary adenomas. These included 50 acromegalics and 16 patients with other types of pituitary tumor. No mutations were detected in the blood of 22 controls and 10 patients with other endocrinopathies. Our results indicate that mutations in AIP are not identified in sporadic pituitary adenomas of Canadian patients. This rare mechanism of pituitary tumorigenesis appears to be unique to the initial Finnish and Italian families described.

A growth hormone receptor mutation impairs growth hormone autofeedback signaling in pituitary tumors.

Pituitary tumors are a diverse group of neoplasms that are classified based on clinical manifestations, hormone excess, and histomorphologic features. Those that cause growth hormone (GH) excess and acromegaly are subdivided into morphologic variants that have not yet been shown to have pathogenetic significance or predictive value for therapy and outcome. Here, we identify a selective somatic histidine-to-leucine substitution in codon 49 of the extracellular domain of the GH receptor (GHR) in a morphologic subtype of human GH-producing pituitary tumors that is characterized by the presence of cytoskeletal aggresomes. This GHR mutation significantly impairs glycosylation-mediated receptor processing, maturation, ligand binding, and signaling. Pharmacologic GH antagonism recapitulates the morphologic phenotype of pituitary tumors from which this mutation was identified, inducing the formation of cytoskeletal keratin aggresomes. This novel GHR mutation provides evidence for impaired hormone autofeedback in the pathogenesis of these pituitary tumors. It explains the lack of responsiveness to somatostatin analogue therapy of this tumor type, in contrast to the exquisite sensitivity of tumors that lack aggresomes, and has therapeutic implications for the safety of GH antagonism as a therapeutic modality in acromegaly.