Germline 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 (n=103), 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 (P=0.006). 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 (P=0.019). 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.

Human glioblastoma is the most frequent and aggressive form of brain tumour in the adult population. Proteolytic turnover of tumour suppressors by the ubiquitin-proteasome system is a mechanism that tumour cells can adopt to sustain their growth and invasiveness. However, the identity of ubiquitin-proteasome targets and regulators in glioblastoma are still unknown. Here we report that the RING ligase praja2 ubiquitylates and degrades Mob, a core component of NDR/LATS kinase and a positive regulator of the tumour-suppressor Hippo cascade. Degradation of Mob through the ubiquitin-proteasome system attenuates the Hippo cascade and sustains glioblastoma growth in vivo. Accordingly, accumulation of praja2 during the transition from low- to high-grade glioma is associated with significant downregulation of the Hippo pathway. These findings identify praja2 as a novel upstream regulator of the Hippo cascade, linking the ubiquitin proteasome system to deregulated glioblastoma growth.

The aim of this study was to investigate the expression and function of the transient receptor potential vanilloid 2 (TRPV2) in human glioma cells. By Real-Time–PCR and western blot analysis, we found that TRPV2 messenger RNA (mRNA) and protein were expressed in benign astrocyte tissues, and its expression progressively declined in high-grade glioma tissues as histological grade increased (n = 49 cases), and in U87MG cells and in MZC, FCL and FSL primary glioma cells. To investigate the function of TRPV2 in glioma, small RNA interfering was used to silence TRPV2 expression in U87MG cells. As evaluated by RT-Profiler PCR array, siTRPV2-U87MG transfected cells displayed a marked downregulation of Fas and procaspase-8 mRNA expression, associated with upregulation of cyclin E1, cyclin-dependent kinase 2, E2F1 transcriptor factor 1, V-raf-1 murine leukemia viral oncogene homolog 1 and Bcl-2-associated X protein (Bcl-X_L) mRNA expression. TRPV2 silencing increased U87MG cell proliferation as shown by the increased percentage of cells incorporating 5-bromo-2-deoxyuridine expressing β_III-tubulin and rescued glioma cells to Fas-induced apoptosis. These events were dependent on extracellular signal-regulated kinase (ERK) activation: indeed inhibition of ERK activation in siTRPV2-U87MG transfected cells by treatment with PD98059, a specific mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibitor, reduced Bcl-X_L protein levels, promoted Fas expression, and restored Akt/protein kinase B pathway activation leading to reduced U87MG cell survival and proliferation, and increased sensitivity to Fas-induced apoptosis. In addition, transfection of TRPV2 in MZC glioma cells, by inducing Fas overexpression, resulted in a reduced viability and an increased spontaneous and Fas-induced apoptosis. Overall, our findings indicate that TRPV2 negatively controls glioma cell survival and proliferation, as well as resistance to Fas-induced apoptotic cell death in an ERK-dependent manner.