9049

AIP

ARA9|FKBP16|FKBP37|SMTPHN|XAP-2|XAP2;aryl hydrocarbon receptor interacting protein;AIP;aryl hydrocarbon receptor interacting protein

AH receptor-interacting protein|HBV X-associated protein 2|immunophilin homolog ARA9

11q13.3

protein-coding

CONTEXT: mutations have been identified in the aryl hydrocarbon receptor-interacting protein (AIP) gene in familial isolated pituitary adenomas (FIPA). It is not clear, however, how this molecular chaperone is involved in tumorigenesis. OBJECTIVE: AIP sequence changes and expression were studied in FIPA and sporadic adenomas. The function of normal and mutated AIP molecules was studied on cell proliferation and protein-protein interaction. Cellular and ultrastructural AIP localization was determined in pituitary cells. PATIENTS: Twenty-six FIPA kindreds and 85 sporadic pituitary adenoma patients were included in the study. RESULTS: Nine families harbored AIP mutations. Overexpression of wild-type AIP in TIG3 and HEK293 human fibroblast and GH3 pituitary cell lines dramatically reduced cell proliferation, whereas mutant AIP lost this ability. All the mutations led to a disruption of the protein-protein interaction between AIP and phosphodiesterase-4A5. In normal pituitary, AIP colocalizes exclusively with GH and prolactin, and it is found in association with the secretory vesicle, as shown by double-immunofluorescence and electron microscopy staining. In sporadic pituitary adenomas, however, AIP is expressed in all tumor types. In addition, whereas AIP is expressed in the secretory vesicle in GH-secreting tumors, similar to normal GH-secreting cells, in lactotroph, corticotroph, and nonfunctioning adenomas, it is localized to the cytoplasm and not in the secretory vesicles. CONCLUSIONS: Our functional evaluation of AIP mutations is consistent with a tumor-suppressor role for AIP and its involvement in familial acromegaly. The abnormal expression and subcellular localization of AIP in sporadic pituitary adenomas indicate deranged regulation of this protein during tumorigenesis.

Hibernomas are benign tumors with morphological features resembling brown fat. They consistently display cytogenetic rearrangements, typically translocations, involving chromosome band 11q13. Here we demonstrate that these aberrations are associated with concomitant deletions of AIP and MEN1, tumor suppressor genes that are located 3 Mb apart and that underlie the hereditary syndromes pituitary adenoma predisposition and multiple endocrine neoplasia type I. MEN1 and AIP displayed a low expression in hibernomas whereas the expression of genes up-regulated in brown fat--PPARA, PPARG, PPARGC1A, and UCP1--was high. Thus, loss of MEN1 and AIP is likely to be pathogenetically essential for hibernoma development. Simultaneous loss of two tumor suppressor genes has not previously been shown to result from a neoplasia-associated translocation. Furthermore, in contrast to the prevailing assumption that benign tumors harbor relatively few genetic aberrations, the present analyses demonstrate that a considerable number of chromosome breaks are involved in the pathogenesis of hibernoma.