Aryl Hydrocarbon Receptor-interacting Protein Gene Research Articles

Aryl Hydrocarbon Receptor-Interacting Protein (AIP) N-Terminus Gene Mutations Identified in Pituitary Adenoma Patients Alter Protein Stability and Function.

Mutations spanning the entire aryl hydrocarbon receptor-interacting protein (AIP) gene have been found in isolated familial cases of pituitary adenomas (PA). Missense mutations located in the N-terminus of the gene have been identified in several patients. However, the functional significance of these mutations remains a matter of controversy. In most studies, the N-terminus of AIP has been shown to regulate protein stability and subcellular localization of the AIP-AHR-HSP90 complex but not to be involved in protein-protein interactions. Other studies found that the N-terminal domain interacts directly with other proteins. The aim of this study was to analyze whether specific N-terminus AIP mutations identified in PA patients would be functionally different from wild-type (WT) AIP. In vitro analyses were used to assess the role of known N-terminus variants, a locally identified mutant, R9Q, and three other commonly genotyped N-terminus mutations R16H, V49M and K103R are found in PA patients. Given the functional effect of WT AIP on cAMP signalling alterations caused by N-terminus mutants on this pathway were also analyzed in GH3 cells. Results indicate that N-terminus mutations lead to de-regulation of the effect of WT AIP on cAMP signalling and increased cAMP thresholds in GH3 cells resulting in increased growth hormone (GH) secretion. Cycloheximide chase analysis identified a variation in protein degradation patterns between WT and N-terminus variants. Therefore, both functional and structural studies reveal that N-terminus mutations in the AIP gene alter protein behaviour significantly and hence can truly be pathogenic in nature.

Feline hypersomatotropism and acromegaly tumorigenesis: a potential role for the AIP gene

Acromegaly in humans is usually sporadic, however up to 20% of familial isolated pituitary adenomas are caused by germline sequence variants of the aryl-hydrocarbon-receptor interacting protein (AIP) gene. Feline acromegaly has similarities to human acromegalic families with AIP mutations. The aim of this study was to sequence the feline AIP gene, identify sequence variants and compare the AIP gene sequence between feline acromegalic and control cats, and in acromegalic siblings. The feline AIP gene was amplified through PCR using whole blood genomic DNA from 10 acromegalic and 10 control cats, and 3 sibling pairs affected by acromegaly. PCR products were sequenced and compared with the published predicted feline AIP gene. A single nonsynonymous SNP was identified in exon 1 (AIP:c.9T > G) of two acromegalic cats and none of the control cats, as well as both members of one sibling pair. The region of this SNP is considered essential for the interaction of the AIP protein with its receptor. This sequence variant has not previously been reported in humans. Two additional synonymous sequence variants were identified (AIP:c.481C > T and AIP:c.826C > T). This is the first molecular study to investigate a potential genetic cause of feline acromegaly and identified a nonsynonymous AIP single nucleotide polymorphism in 20% of the acromegalic cat population evaluated, as well as in one of the sibling pairs evaluated.

Analysis of GPR101 and AIP genes mutations in acromegaly: a multicentric study

This multicentric study aimed to investigate the prevalence of the G protein-coupled receptor 101 (GPR101) p.E308D variant and aryl hydrocarbon receptor interacting protein (AIP) gene mutations in a representative cohort of Italian patients with acromegaly. 215 patients with GH-secreting pituitary adenomas, referred to 4 Italian referral centres for pituitary diseases, have been included. Three cases of gigantism were present. Five cases were classified as FIPA. All the patients have been screened for germline AIP gene mutations and GPR101 gene p.E308D variant. Heterozygous AIP gene variants have been found in 7 patients (3.2%). Five patients carried an AIP mutation (2.3%; 4 females): 3 patients harboured the p.R3O4Q mutation, one had the p.R304* mutation and the last one the IVS3+1G>A mutation. The prevalence of AIP mutations was 3.3% and 2.8% when considering only the patients diagnosed when they were <30 or <40-year old, respectively. Furthermore, 2.0% of the patients with a pituitary macroadenoma and 4.2% of patients resistant to somatostatin analogues treatment were found to harbour an AIP gene mutation. None of the patients was found to carry the GPR101 p.E308D variant. The prevalence of AIP gene mutations among our sporadic and familial acromegaly cases was similar to that one reported in previous studies, but lower when considering only the cases diagnosed before 40years of age. The GPR101 p.E308D change is unlikely to have a role in somatotroph adenomas tumorigenesis, since none of our sporadic or familial patients tested positive for this variant.

SNPs in the aryl hydrocarbon receptor-interacting protein gene associated with sporadic non-functioning pituitary adenoma.

Mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene have previously been associated with a predisposition to pituitary adenomas. However, to the best of our knowledge, mutations in AIP that relate specifically to sporadic non-functioning pituitary adenomas (NFPAs) have yet to be reported. Therefore, the present study aimed to identify single nucleotide polymorphisms (SNPs) in the AIP gene that may be associated with NFPAs. Peripheral blood samples and the entire coding sequence of the AIP gene from 56 patients with NFPAs and 56 controls were analyzed in triplicate. Of the 56 patients with NFPAs, 9 patients (16.1%) were identified as harboring five different SNPs, although no germline mutations in the AIP gene were detected in any of the patients. Three different SNPs (7051C>T, 8012G>C and 8020G>C) were identified in exons 4 and 6 in 3 different patients (each in 1 patient). Two different SNPs (7318C>A and 7886A>G) were identified in exons 5 and 6, respectively, in 6 different patients (each in 3 patients). No SNPs or germline mutations in the AIP gene were identified in the controls. The results of the present study suggested that mutations in the AIP gene might not have an important role in the tumorigenesis of NFPAs. However, further studies are required in order to investigate potential molecular and genetic mechanisms that may underlie the involvement of AIP in NFPA.

Do the aryl hydrocarbon receptor interacting protein variants (Q228K and Q307R) play a role in patients with familial and sporadic hormone-secreting pituitary adenomas?

The aim of this study was to examine mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene by sequence analysis of exons 1-6 using leukocyte genomic DNA obtained from a cohort of familial isolated pituitary adenoma (FIPA) and apparent sporadic functional pituitary adenoma Turkish patients. Fourteen FIPA and 90 sporadic pituitary adenoma (somatotrophinoma, prolactinoma, and corticotrophinoma) patients, 1 sporadic gigantism case, and 70 healthy controls were included in the study. We did not detect AIP mutations in patients with FIPAs or sporadic pituitary adenomas, including the gigantism case. Only two exonic homozygous missense single-nucleotide polymorphisms (rs641081 [Q228K] and rs4930195 [Q307R]) were identified in the AIP locus. Minor allele frequencies of the Q307R and Q228K variants were significantly higher in FIPA patients compared to controls. In addition, the minor allele frequency of the Q228K variant was significantly increased in patients with sporadic somatotrophinomas compared to controls, whereas the minor allele frequency of the Q307R variant was significantly increased in corticotrophinoma patients compared to controls. Conversely, the minor allele frequencies of Q228R and Q307R variants were similar between patients with prolactinomas and controls. No AIP gene mutation or variant was observed in the sporadic gigantism patient. These results suggest that Q228K and Q307R variants in the AIP gene might be involved in the genetic susceptibility to familial and sporadic pituitary adenomas (somatotrophinoma and corticotrophinoma) in the Turkish population.

Relationship between aryl hydrocarbon receptor interacting protein gene expression and clinical characteristics in human pituitary somatotrophinomas

Objective To investigate the expression of aryl Hydrocarbon Receptor Interacting protein (AIP)gene mutations and relationship with clinical biochemical characteristics in human somatotropinomas. Methods From October 2009 to September 2012, 96 acromegaly or gigantism patients were diagnosed in a single pituitary center, with consistent treatment and follow-up. Genomic DNA from tumor tissues was extracted and sequenced. Clinical data were retrospectively analyzed. Results Overall,55 patients(57.3%)had one or more single base substitutions in AIP gene from their tumor tissues. Thirteen point mutations were detected in total, and 5 novel ones(c. 609C> G, c. 646- 38C> T, c. 646- 35C> T, c. 646- 34A> T and c. 692C> T)were firstly reported according to the National Center for Biotechnology Information(NCBI)single nucleotide polymorphism(SNP)database. Somatic AIPmut group showed characteristics as younger onset age(P<0.05), larger tumor diameter(P<0.05), higher invasiveness and aggressiveness(P< 0.05), and more prevalence in recurrent tumors(P<0.05),than the negative group. Conclusion Somatic AIP gene mutation screen may be clinically crucial for the substantial treatment and outcome prejudgement, as well as the follow- up duration and frequency. The treatment strategy for AIPmut patients remains stressful; in the meanwhile, the role of AIP gene in the pathogenesis of somatotropinomas await more investigation. Key words: Somatotrophinoma; Growth hormone; Aryl hydrocarbon receptor interacting protein gene; Mutation

An unusual case of an ACTH-secreting macroadenoma with a germline variant in the aryl hydrocarbon receptor-interacting protein (AIP) gene.

SummaryA patient of Cushing's disease (CD) characterized by a large tumor and only subtle symptoms of hormonal hypersecretion was examined. The patient had a germline variant in the aryl hydrocarbon receptor-interacting protein (AIP) gene. A 50-year-old male presenting with headache was diagnosed with a large pituitary tumor by magnetic resonance imaging (MRI). His visual fields were intact and he exhibited no features of CD. Owing to an exuberant response to synacthen, an overnight dexamethasone suppression test was performed revealing inadequate suppression of plasma cortisol (419 nmol/l). Owing to tumor growth and visual field impairment, he underwent transsphenoidal surgery and developed hypocortisolemia. The pathology specimen revealed a sparsely granulated corticotrope adenoma. Postoperative MRI showed a large tumor remnant. The patient developed skin hyperpigmentation and a synacthen test demonstrated high basal and stimulated cortisol levels; an overnight dexamethasone suppression test showed no suppression (791 nmol/l) and elevated plasma ACTH levels (135 ng/l). A transcranial operation was performed followed by radiotherapy. Two months after radiotherapy, he developed secondary adrenocortical failure. Genetic testing revealed an AIP variant of unknown significance (p.R16H) without loss of the normal AIP allele in the tumor. A literature review showed ten CD patients with AIP gene variants, of whom five (including our case) were p.R16H. CD is occasionally dominated by pituitary tumor growth rather than symptoms of hypersecretion. The particular AIP gene variant identified in our patient is shared by four other reported cases of CD. Future studies are needed to assess whether the reported AIP gene variant is more than just coincidental.Learning points CD is occasionally dominated by pituitary tumor growth rather than symptoms of hypersecretion.Resolution of both tumor remnant and hormonal hypersecretion may occur within 2 months after postoperative radiotherapy.The particular AIP gene variant identified in our patient is shared by four other reported cases of CD.

Frequency of AIP gene mutations in young patients with acromegaly: a registry-based study.

Familial and sporadic GH-secreting pituitary adenomas are associated with mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene. Patients with an AIP mutation (AIPmut) tend to have more aggressive tumors occurring at a younger age. The objective of the study was to investigate the frequency of AIPmut in patients diagnosed at 30 years of age or younger. The German Acromegaly Registry database (1795 patients in 58 centers) was screened for patients diagnosed with acromegaly at 30 years of age or younger (329 patients). Sixteen centers participated and 91 patients consented to AIPmut analysis. DNA was analyzed by direct sequencing and multiplex ligation dependent probe amplification Main outcome Measures: The number of patients with AIPmut was measured. Five patients had either a mutation (c.490C>T, c.844C>T, and c.911G>A, three males) or gross deletions of exons 1 and 2 of the AIP gene (n = 2, one female). The overall frequency of an AIPmut was 5.5%, and 2.3% or 2.4% in patients with an apparently sporadic adenoma or macroadenoma, respectively. By contrast, three of four patients (75%) with a positive family history were tested positive for an AIPmut. Except for a positive family history, there were no significant differences between patients with and without an AIPmut. The frequency of AIPmut in this registry-based cohort of young patients with acromegaly is lower than previously reported. Patients with a positive family history should be tested for an AIPmut, whereas young patients without an apparent family history should be screened, depending on the individual cost to benefit ratio.

Low rate of germline AIP mutations in patients with apparently sporadic pituitary adenomas before the age of 40: a single-centre adult cohort.

To study the prevalence of germline mutations of the aryl-hydrocarbon receptor interacting protein (AIP) gene in a large cohort of patients seen in the Oxford Centre for Diabetes Endocrinology and Metabolism (OCDEM), UK, with apparently sporadic pituitary adenomas, who were either diagnosed or had relevant clinical manifestations by the age of 40 years. We prospectively investigated all patients who were seen at Oxford University Hospital, OCDEM, and a tertiary referral centre, between 2012 and 2013, and presented with pituitary tumours under the age of 40 years and with no family history: a total of 127 patients were enrolled in the study. Leukocyte-origin genomic DNA underwent sequence analysis of exons 1-6 and the flanking intronic regions of the AIP gene (NM_003977.2), with dosage analysis by multiplex ligation-dependent probe amplification. AIP variants were detected in 3% of the 127 patients, comprising four of 48 patients with acromegaly (8%), 0 of 43 with prolactinomas, 0 of the 20 patients with non-functioning adenomas, 0 of 15 with corticotroph adenomas and 0 of one with a thyrotroph adenomas. Definite pathogenetic mutations were seen in 2/4 variants, comprising 4.2% of patients with acromegaly. This prospective cohort study suggests a relatively low prevalence of AIP gene mutations in young patients with apparently sporadic pituitary adenomas presenting to a tertiary pituitary UK centre. Those with somatotroph macroadenomas have a higher rate of AIP mutation. These findings should inform discussion of genetic testing guidelines.

AHR over-expression in papillary thyroid carcinoma: clinical and molecular assessments in a series of Italian acromegalic patients with a long-term follow-up.

AimAcromegaly reportedly carries an increased risk of malignant and benign thyroid tumors, with a prevalence of thyroid cancer of around 3–7%. Germline mutations in the aryl-hydrocarbon receptor (AHR) interacting protein (AIP) have been identified in familial forms of acromegaly. The molecular and endocrine relationships between follicular thyroid growth and GH-secreting pituitary adenoma have yet to be fully established. Our aim was to study the prevalence of differentiated thyroid cancer (DTC) in acromegaly, focusing on the role of genetic events responsible for the onset of thyroid cancer.MethodsGermline mutations in the AIP gene were assessed in all patients; BRAF and H-N-K RAS status was analyzed by direct sequencing in thyroid specimens, while immunohistochemistry was used to analyze the protein expression of AIP and AHR. A set of PTCs unrelated to acromegaly was also studied.Results12 DTCs (10 papillary and 2 follicular carcinomas) were identified in a cohort of 113 acromegalic patients. No differences in GH/IGF-1 levels or disease activity emerged between patients with and without DTC, but the former were older and more often female. BRAF V600E was found in 70% of the papillary thyroid cancers; there were no RAS mutations. AIP protein expression was similar in neoplastic and normal cells, while AHR protein was expressed more in PTCs carrying BRAF mutations than in normal tissue, irrespective of acromegaly status.ConclusionsThe prevalence of DTC in acromegaly is around 11% and endocrinologists should bear this in mind, especially when examining elderly female patients with uninodular goiter. The DTC risk does not seem to correlate with GH/IGF-1 levels, while it may be associated with BRAF mutations and AHR over-expression. Genetic or epigenetic events probably play a part in promoting thyroid carcinoma.

The AIP (aryl hydrocarbon receptor-interacting protein) gene and its relation to the pathogenesis of pituitary adenomas

Pituitary adenomas are monoclonal neoplasms that may secrete excessive quantities of their endogenous hormones, or may not be associated with any obvious syndrome, in which case they are known as non-functioning pituitary adenomas. Around 2 % have been said to occur in a familial setting, in the absence of any other tumor, now described as familial isolated pituitary adenomas (FIPA). Some 15-30 % of such families harbor inactivating germ-line mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene, along with 20 % of pediatric seemingly sporadic cases. AIP mutants are referred to as having pituitary adenoma predisposition, and present with early onset, aggressive macroadenomas, most of which secrete somatotropin. Evidence from transfection studies implies that AIP acts as a tumor suppressor; although whether this is mediated through an interaction with the aryl hydrocarbon receptor, phosphodiesterases, or with cell cycle regulators such as survivin or RET remains controversial. However, at present an interaction with the cyclic AMP pathway seems most plausible. Recently, evidence has shown that AIP may act at the cell surface, causing changes in integrin function. The presence of AIP mutations in a significant proportion of FIPA families as well as in apparently sporadic cases, particularly in young patients, suggests a need to screen such patients for AIP mutations to enable better clinical management. However, the absence of AIP mutations in over half of such cases highlights the need to search for further gene mutations.

Familial acromegaly due to aryl hydrocarbon receptor-interacting protein (AIP) gene mutation in a Turkish cohort

Aryl hydrocarbon receptor-interacting protein (AIP) is associated with 15-20% of familial isolated pituitary adenomas and 50-80% of cases with AIP mutation exhibit a somatotropinoma. Herein we report clinical characteristics of a large family where AIP R304X variants have been identified. AIP mutation analysis was performed on a large (n = 52) Turkish family across six generations. Sella MRIs of 30 family members were obtained. Basal pituitary hormone levels were evaluated in 13 family members harboring an AIP mutation. Thirteen of 52 family members (25%) were found to have a heterozygous nonsense germline R304X mutation in the AIP gene. Seven of the 13 mutation carriers (53.8%) had current or previous history of pituitary adenoma. Of these 7 mutation carriers, all but one had somatotropinoma/somatolactotropinoma (85.7% of the pituitary adenomas). Of the 6 acromegaly patients with AIP mutation (F/M: 3/3) the mean age at diagnosis of acromegaly was 32 ± 10.3 years while the mean age of symptom onset was 24.8 ± 9.9 years. Three of the six (50%) acromegaly cases with AIP mutation within the family presented with a macroadenoma and none presented with gigantism. Biochemical disease control was achieved in 66.6% (4/6) of the mutation carriers with acromegaly after a mean follow-up period of 18.6 ± 17.6 years. Common phenotypic characteristics of familial pituitary adenoma or somatotropinoma due to AIP mutation vary between families or even between individuals within a family.

Aryl Hydrocarbon Receptor Interacting Protein (AIP) Mutations Occur Rarely in Sporadic Parathyroid Adenomas

The molecular pathogenesis of primary hyperparathyroidism is still largely unknown. The aryl hydrocarbon receptor interacting protein (AIP) gene has a major role in the pathogenesis of familial isolated pituitary adenoma. We evaluated the involvement of the AIP gene in sporadic parathyroid adenomas. We performed direct sequencing and multiplex ligation-dependent probe amplification analyses of the AIP gene in a large series of sporadic parathyroid adenomas. Loss of heterozygosity (LOH) at the AIP locus was studied, and aryl hydrocarbon receptor interacting protein immunostaining was also performed. In addition, alterations in the MEN1 gene were studied. A somatic AIP mutation, substitution of arginine with glutamine at codon 304 (R304Q), was identified in 2 of 132 tumors. The mutation was germline in both cases despite the nonfamilial presentation. Heterozygous AIP large deletions were detected in 29 cases including 1 of the 2 mutated tumors, confirming a biallelic inactivation of the AIP gene. The AIP-mutated tumor with LOH showed decreased AIP immunostaining compared with normal parathyroid. LOH at the MEN1 locus, which often shared LOH at the AIP locus, was found in one third of tumors. Somatic MEN1 mutations were found in the 1 of the 2 AIP-mutated tumors and in 22 parathyroid adenomas. In addition, multiplex ligation-dependent probe amplification analysis revealed 1 large deletion of the MEN1 gene in 1 patient. The AIP gene is rarely involved in parathyroid adenomas, but the germline nature of the mutations suggests that it might predispose to primary hyperparathyroidism. MEN1 gene alterations occur in a substantial proportion of sporadic parathyroid adenomas.

Altered subcellular localization of heat shock protein 90 is associated with impaired expression of the aryl hydrocarbon receptor pathway in dogs.

The aryl hydrocarbon receptor (AHR) mediates biological responses to toxic chemicals. An unexpected role for AHR in vascularization was suggested when mice lacking AHR displayed impaired closure of the ductus venosus after birth, as did knockout mice for aryl hydrocarbon receptor interacting protein (AIP) and aryl hydrocarbon receptor nuclear translocator (ARNT). The resulting intrahepatic portosystemic shunts (IHPSS) are frequently diagnosed in specific dog breeds, such as the Irish wolfhound. We compared the expression of components of the AHR pathway in healthy Irish wolfhounds and dogs with IHPSS. To this end, we analyzed the mRNA expression in the liver of AHR,AIP, ARNT, and other genes involved in this pathway, namely, those for aryl hydrocarbon receptor nuclear translocator 2 (ARNT2), hypoxia inducible factor 1alpha (HIF1A), heat shock protein 90AA1 (HSP90AA1), cytochromes P450 (CYP1A1, CYP1A2, and CYP1B1), vascular endothelial growth factor A (VEGFA), nitric oxide synthesase 3 (NOS3), and endothelin (EDN1). The observed low expression of AHR mRNA in the Irish wolfhounds is in associated with a LINE-1 insertion in intron 2, for which these dogs were homozygous. Down regulation in Irish wolfhounds was observed for AIP, ARNT2, CYP1A2, CYP1B1 and HSP90AA1 expression, whereas the expression of HIF1A was increased. Immunohistochemistry revealed lower levels of AHR, HIF1A, and VEGFA protein in the nucleus and lower levels of ARNT and HSP90AA1 protein in the cytoplasm of the liver cells of Irish wolfhounds. The impaired expression of HSP90AA1 could trigger the observed differences in mRNA and protein levels and therefore explain the link between two very different functions of AHR: regulation of the closure of the ductus venosus and the response to toxins.

Prevalence of familial isolated pituitary adenomas

• Clinically relevant pituitary adenomas have a prevalence of approximately 1:1000 • While pituitary adenomas usually occur as sporadic disease, an increasing number of patients are being recognised with a family member also suffering from a pituitary adenoma • If no other syndromic features are present, these families are categorised as familial isolated pituitary adenoma (FIPA) • Germline mutations of the AIP (aryl-hydrocarbon receptor interacting protein) gene are associated with a predisposition to pituitary adenomas • In published studies, 20% of the FIPA families, 20% of sporadic childhood and 13% of sporadic young-onset (≤30y) acromegaly patients carry a germline AIP mutation

Familial pituitary adenomas – who should be tested for AIP mutations?

Familial Isolated Pituitary Adenomas (FIPA), an autosomal dominant disease with low penetrance is being increasingly recognized. FIPA families can be divided into two distinct groups based on genetic and phenotypic features. Patients with mutations in the aryl hydrocarbon receptor-interacting protein (AIP) gene are characterized by young-onset somatotroph or lactotroph macroadenomas, while in the other, larger group of FIPA patients with typically adult-onset disease and more varied adenoma types, no causative gene(s) has been identified. Young-onset macroadenoma patients can also be identified with germline AIP mutation without an apparent family history. Further data and longer follow-up are necessary to establish formal guidelines, but the current data suggest genetic screening of the AIP gene in patients with a pituitary adenoma and no other associated features who have (i) a family history of pituitary adenoma, (ii) childhood-onset pituitary adenoma or (iii) a pituitary somatotroph or lactotroph macroadenoma diagnosed before the age of 30 years.

Genetic analysis in a patient presenting with meningioma and familial isolated pituitary adenoma (FIPA) reveals selective involvement of the R81X mutation of the AIP gene in the pathogenesis of the pituitary tumor

Familial isolated pituitary adenoma (FIPA), defined as the occurrence of at least two cases of pituitary adenoma in a family that does not exhibit features of syndromic diseases, such as Carney complex or Multiple Endocrine Neoplasia type 1 or 4, is a rare autosomal dominant disease with low penetrance. About 20 % of the families with FIPA harbor inactivating mutation in aryl hydrocarbon receptor-interacting protein gene (AIP) associated with loss of heterozygosity of the same genetic locus (11q13) in the tumor. Rarely different types of extra-pituitary tumors have been described in the setting of AIP mutation-positive FIPA. We present the case of a patient who was diagnosed with acromegaly due to the AIP mutation c.241C>T (p.R81X) at the age of 34 years, and treated by transsphenoidal surgery. At the age of 43 years she was diagnosed with a meningioma, and at age 46 had recurrence of the somatotropinoma. Genetic studies demonstrated loss of the normal allele (by sequencing and microsatellite analysis) in DNA from the pituitary adenoma but not from the meningioma, suggesting a selective involvement of AIP mutation in the pathogenesis of the pituitary adenoma, and a casual association with the meningioma. Further investigations are required to define the exact role of AIP in non-pituitary tumorigenesis.

Germline AIP Mutations in Apparently Sporadic Pituitary Adenomas: Prevalence in a Prospective Single-Center Cohort of 443 Patients

Germline mutations of the AIP (aryl-hydrocarbon receptor interacting protein) gene are associated with a predisposition to pituitary adenomas. Such mutations are found in about half of patients with familial acromegaly, but penetrance is incomplete. We studied the prevalence of germline AIP mutations in a large cohort of patients with apparently sporadic pituitary adenomas. A total of 443 patients with pituitary adenomas of all histotypes, who had no familial history of pituitary adenomas or multiple endocrine neoplasia and who were examined at Bicêtre University Hospital, a tertiary referral center, between 2007 and 2010, were enrolled in this prospective study. The entire coding sequence of the AIP gene was screened for germline mutations. A subgroup of patients were screened for large deletions or duplications of the AIP and MEN1 genes by multiplex ligation-dependent probe amplification. AIP mutations were detected in 16 (3.6%) of the 443 patients, comprising six of 148 patients with acromegaly (4.1%), six of 132 patients with prolactinomas (4.5%), one of 113 patients with nonfunctioning adenomas (0.9%), three of 44 patients with corticotropic adenomas (6.8%), and none of the six patients with thyrotropic adenomas. This is the first report of an AIP mutation leading to a truncated protein in a patient with Cushing's disease. Patients with AIP mutation were younger at diagnosis (24.1 vs. 42.8 yr) and had predominantly macroadenoma (12 of 16). No mutations were found in patients diagnosed after age 40 yr, whereas the prevalence before this age was 7.2% (16 of 222). Studies of seven of the AIP-mutated patients' families showed that one asymptomatic parent carried the same mutation in each case. This large prospective cohort study confirms the very low prevalence of germline AIP mutations in patients with apparently sporadic pituitary adenomas. We propose to limit AIP testing to patients diagnosed before age 40 yr with apparently sporadic large pituitary adenomas, especially GH- or PRL-secreting adenomas.

AIP and its interacting partners

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.

Hyperplasia–adenoma sequence in pituitary tumorigenesis related to aryl hydrocarbon receptor interacting protein gene mutation

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.