3Fondazione 'Carlo Ferri' per la prevenzione e la cura dei tumori, via Edmondo Riva 42, 00015 Monterotondo, Italy AbstractGermline mutations of the aryl hydrocarbon receptor (AHR)-interacting protein (AIP) gene confer a predisposition to pituitary adenomas (PA), usually in the setting of familial isolated PA. To provide further insights into the possible role of AIP in pituitary tumour pathogenesis, the expression of AIP and AHR was determined by real-time RT-PCR and/or immunohistochemistry (IHC) in a large series of PA (nZ103), including 17 with AIP mutations (AIP mut ). Variable levels of AIP and AHR transcripts were detected in all PA, with a low AHR expression (P!0.0001 versus AIP). Cytoplasmic AIP and AHR were detected by IHC in 84.0 and 38.6% of PA respectively, and significantly correlated with each other (PZ0.006). Nuclear AHR was detected in a minority of PA (19.7%). The highest AIP expression was observed in somatotrophinomas and non-secreting (NS) PA, and multivariate analysis in somatotrophinomas showed a significantly lower AIP immunostaining in invasive versus non-invasive cases (PZ0.019). AIP expression was commonly low in other secreting PA. AIP immunostaining was abolished in a minority of AIP mut PA, with a frequent loss of cytoplasmic AHR and no evidence of nuclear AHR. In contrast, AIP overexpression in a subset of NS PA could be accompanied by nuclear AHR immunopositivity. We conclude that down-regulation of AIP and AHR may be involved in the aggressiveness of somatotrophinomas. Overall, IHC is a poorly sensitive tool for the screening of AIP mutations. Data obtained on AHR expression suggest that AHR signalling may be differentially affected according to PA phenotype.

Germline aryl hydrocarbon receptor interacting protein (AIP) gene mutations confer a predisposition to pituitary adenoma (PA), predominantly GH-secreting (GH-PA). As recent data suggest a role for AIP in the pathogenesis of sporadic GH-PA and their response to somatostatin analogues (SSA), the expression of AIP and its partner, aryl hydrocarbon receptor (AHR), was determined by semiquantitative immunohistochemistry scoring in 62 sporadic GH-PA (37 treated with SSA preoperatively). The influence of Gsp status was studied in a subset of tumours (nZ39, 14 Gsp C ) and six GH-PA were available for primary cultures. AIP and AHR were detected in most cases, with a positive correlation between AIP and cytoplasmic AHR (PZ0.012). Low AIP expression was significantly more frequent in untreated vs SSA-treated tumours (44.0 vs 20.5%, PZ0.016). AHR expression or localisation did not differ between the two groups. Similarly, in vitro octreotide induced a median twofold increase in AIP expression (range 1.2-13.9, PZ0.027) in GH-PA. In SSA-treated tumours, the AIP score was significantly higher in the presence of preoperative IGF1 decrease or tumour shrinkage (PZ0.008 and PZ0.014 respectively). In untreated tumours, low AIP expression was significantly associated with invasiveness (PZ0.028) and suprasellar extension (PZ0.019). The only effect of Gsp status was a significantly lower nuclear AHR score in Gsp C vs Gsp K tumours (PZ0.025), irrespective

ABSTRACT. Background: Mutations in the aryl hydrocarbon receptor interacting protein (AIP) gene have been described in about 15% of kindreds with familial isolated pituitary adenomas and in a minority of early onset sporadic pituitary adenomas (PA). Among the AIP mutations reported so far, the R304X (AIP R304X ) represents, together with the "Finnish mutation" Q14X, the most common one. Methods: Three AIP R304X Italian families, including a newly reported kindred, have been genotyped for 12 genetic markers surrounding the AIP gene in order to look for a potential founder effect in Italy. Disease penetrance and genotype-phenotype correlations were also addressed. Results: Analysis of chromosome 11' genetic markers revealed a common haplotype in 2 AIP R304X kindreds originating from central Italy. Overall, 17 mutations carriers were identified, including 7 patients and 10 unaffected subjects, respectively, arguing in this case for a disease penetrance of 41%. Mean age at diagnosis was 19.1±6.7 yr old, with females tending to be older than males. Though most PA were somatotropinomas (6/7), a great variability in disease severity was observed, even between subjects sharing the same at-risk haplotype. Conclusion: These data provide strong evidence for a new founder effect of the AIP R304X mutation in central Italy and the observed variations in disease severity point out the role of additional genetic or environmental factors in such kindreds. (J. Endocrinol. Invest. 33: 800-805, 2010)

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