The Expression of AIP-Related Molecules in Elucidation of Cellular Pathways in Pituitary Adenomas

Department of Medical Genetics, Genome-Scale Biology Research Program, University of Helsinki, Helsinki, Finland.
American Journal Of Pathology (Impact Factor: 4.59). 10/2009; 175(6):2501-7. DOI: 10.2353/ajpath.2009.081131
Source: PubMed


Germline mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene predispose to the development of pituitary adenomas. Here, we characterized AIP mutation positive (AIPmut+) and AIP mutation negative (AIPmut-) pituitary adenomas by immunohistochemistry. The expressions of the AIP-related proteins aryl hydrocarbon receptor (AHR), AHR nuclear translocator (ARNT), cyclin-dependent kinase inhibitor 1B encoding p27(Kip1), and hypoxia-inducible factor 1-alpha were examined in 14 AIPmut+ and 53 AIPmut- pituitary adenomas to detect possible expression differences. In addition, the expression of CD34, an endothelial and hematopoietic stem cell marker, was analyzed. We found ARNT to be less frequently expressed in AIPmut+ pituitary adenomas (P = 0.001), suggesting that AIP regulates the ARNT levels. AIP small interfering RNA-treated HeLa, HEK293, or Aip-null mouse embryonic fibroblast cells did not show lowered expression of ARNT. Instead, in the pituitary adenoma cell line GH3, Aip silencing caused a partial reduction of Arnt and a clear increase in cell proliferation. We also observed a trend for increased expression of nuclear AHR in AIPmut+ samples, although the difference was not statistically significant (P = 0.06). The expressions of p27(Kip1), hypoxia-inducible factor 1-alpha, or CD34 did not differ between tumor types. The present study shows that the expression of ARNT protein is significantly reduced in AIPmut+ tumors. We suggest that the down-regulation of ARNT may be connected to an imbalance in AHR/ARNT complex formation arising from aberrant cAMP signaling.

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Available from: Karoliina Stefanius
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    • "Already characterized protein partners of AIP include: (1) the Aryl Hydrocarbon Receptor (AhR, also known as the " dioxin receptor " ) itself, a member of the bHLH/PAS (basic Helix-Loop-Helix/Per-Arnt-Sim) family of transcription factors involved in cell response to polycyclic aromatic hydrocarbons but also in developmental processes and the regulation of cell cycle and differentiation, which unliganded form is stabilized in the cytoplasm in a multimeric AIP/AhR/Hsp90 complex; (2) the phosphodiesterases PDE4A5 and PDE2A, which are implicated in the cAMP signaling pathway; (3) the anti-apoptotic factor survivin and Ret, which prevents the formation of the AIP/survivin complex; (4) members of the steroid receptor superfamily such as PPAR-a , the b -thyroid hormone receptor 1 (TR b 1) and the glucocorticoid receptor; (5) additional proteins among which viral proteins and proteins involved in mitochondrial import (Oz fi rat and Korbonits 2010 and Jaffrain-Rea et al. 2010a ) . The molecular pathways involved in AIPrelated pathogenesis have not been elucidated yet, but in vitro experiments on the rat lactosomatotroph cell line GH 3 have clearly shown that overexpression of the wild-type AIP gene reduces its proliferation rate, whereas the transfection of some AIP mut genes inhibits this effect (Leontiou et al. 2008 ) and AIP gene silencing had a proproliferative effect (Heliövaara et al. 2009 ) . This is in agreement with the proliferative index observed in the AIP +/− mice model cited hitherto (Raitila et al. 2010 ) . "
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    ABSTRACT: Pituitary adenomas (PA) are common endo-crine neoplasia, generally presenting as sporadic diseases, with a multifactorial pathogenesis including somatic mutational events in cancer-related genes. However, genetic predisposition can currently be recognized in >5% of affected patients, mostly involving the Multiple Endocrine Neoplasia type 1 (MEN1) gene and the more recently identi fi ed Aryl hydrocarbon receptor Interacting Protein (AIP) gene, both being tumor-suppressor genes. Germline mutations in the AIP gene can be observed in a FIPA (Familial Isolated Pituitary Adenoma) context, but also in a minority of young patients with an apparently sporadic disease. Although the role of AIP in the pathogenesis of PA remains largely unknown, it is known to be mainly expressed by somatototrophs, with a frequent loss of expression in most AIP-mutated PA and in invasive somatotro-pinomas. The best characterized function of AIP is to stabilize the Aryl hydrocarbon Receptor, also known as the dioxin receptor, in the cytoplasm, but multiple interactions of AIP with other proteins involved in endo-crine signalling and the regulation of cell cycle and apoptosis have been reported. In this chapter, current knowledge about the possible role of AhR and additional AIP-related proteins in pituitary tumorigenesis will be analysed.
    Full-text · Chapter · Jan 2013
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    • "AIP may act as a tumor suppressor gene, as loss of heterozygosity (LOH) occurs in pituitary tumor tissue (Vierimaa et al. 2006), although AIP immunostaining is abolished in only a minority of tumors from AIP mutation-bearing patients (Jaffrain-Rea et al. 2009). AIP overexpression in vitro decreases cell proliferation (Leontiou et al. 2008), AIP gene silencing results in cell proliferation (Heliovaara et al. 2009), and recent results from an Aip knockout mouse match the human phenotype (Raitila et al. 2010). We describe the detailed morphological and pathological features of pituitary tumors in a new FIPA family with a novel AIP mutation, paying particular attention to somatic genetic status of AIP in surgical samples that revealed features of pituitary hyperplasia, which is a novel pathological topic that has not previously been well described in this genetic background. "
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    ABSTRACT: Mutations of the aryl hydrocarbon receptor interacting protein (AIP) gene are associated with pituitary adenomas that usually occur as familial isolated pituitary adenomas (FIPA). Detailed pathological and tumor genetic data on AIP mutation-related pituitary adenomas are not sufficient. Non-identical twin females presented as adolescents to the emergency department with severe progressive headache caused by large pituitary macroadenomas require emergency neurosurgery; one patient had incipient pituitary apoplexy. Post-surgically, the patients were found to have silent somatotrope adenomas on pathological examination. Furthermore, the light microscopic, immunohistochemical, and electron microscopic studies demonstrated tumors of virtually identical characteristics. The adenomas were accompanied by multiple areas of pituitary hyperplasia, which stained positively for GH, indicating somatotrope hyperplasia. Genetic analyses of the FIPA kindred revealed a novel E216X mutation of the AIP gene, which was present in both the affected patients and the unaffected father. Molecular analysis of surgical specimens revealed loss of heterozygosity (LOH) in the adenoma but showed that LOH was not present in the hyperplastic pituitary tissue from either patient. AIP immunostaining confirmed normal staining in the hyperplastic tissue and decreased staining in the adenoma in the tumors from both patients. These results demonstrate that patients with AIP germline mutation can present with silent somatotrope pituitary adenomas. The finding of somatotrope hyperplasia unaccompanied by AIP LOH suggests that LOH at the AIP locus might be a late event in a potential progression from hyperplastic to adenomatous tissue.
    Full-text · Article · Mar 2011 · Endocrine Related Cancer
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    • "These findings agree with the AhR mapping data because AIP and ARNT have been shown to contact, at least in part, the same or an adjacent binding site on the AhR (Meyer & Perdew 1999). Even if AIP does not interact with ARNT, two recent studies showed that the expression of ARNT protein is significantly reduced in AIP-mutated pituitary tumours, suggesting that loss of AIP leads to an imbalance in the AhR–ARNT complex formation (Heliovaara et al. 2009, Raitila et al. 2010). p23 was then demonstrated to contact AIP in co-immunoprecipitation (co-IP) experiments (Hollingshead et al. 2004), but only indirectly via hsp90, as previously demonstrated for AhR (Nair et al. 1996). "
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    ABSTRACT: Germline mutations in the aryl hydrocarbon receptor-interacting protein gene (AIP) predispose to young-onset pituitary tumours, most often to GH- or prolactin-secreting adenomas, and most of these patients belong to familial isolated pituitary adenoma families. The molecular pathway initiated by the loss-of-function AIP mutations leading to pituitary tumour formation is unknown. AIP, a co-chaperone of heat-shock protein 90 and various nuclear receptors, belongs to the family of tetratricopeptide repeat (TPR)-containing proteins. It has three antiparallel α-helix motifs (TPR domains) that mediate the interaction of AIP with most of its partners. In this review, we summarise the known interactions of AIP described so far. The identification of AIP partners and the understanding of how AIP interacts with these proteins might help to explain the specific phenotype of the families with heterozygous AIP mutations, to gain deeper insight into the pathological process of pituitary tumour formation and to identify novel drug targets.
    Full-text · Article · Mar 2011 · Journal of Endocrinology
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