Endocrine Abstracts

Background: Heterozygote germline mutations in the aryl-hydrocarbon receptor interacting protein (AIP) gene play a role in the pathogenesis of pituitary adenoma development in familial isolated pituitary adenoma as well as simplex pituitary adenoma cases. AIP mutation positive patients develop often aggressively growing tumours in early teenage years.

Aims: The aim of this study was to perform comparative gene expression analysis of AIP mutation-positive (AIPpos) pituitary adenomas to discover the genes/pathways responsible for the aggressive clinical phenotype of these tumours.

Methods: Gene expression analysis on normal pituitary, AIP mutation positive, familial AIPneg as well as sporadic somatotrophinomas (n=25) using the Affymetrix Gene-Chip array. Differential expression of selected genes was validated by RT-qPCR and immunohistochemistry. In vitro stimulation of epithelial-to-mesenchymal transition (EMT) was performed on stable AIP-knockdown cells using forskolin, as well as TGFbeta1 and assessed using the EMT markers by Western blotting. In vitro invasion assay was performed on AIP siRNA-knocked down BxPC3 cells using BioCoat-Matrigel invasion chambers.

Results: One of the top altered pathways in AIPpos adenomas was the ‘EMT’. Validation by RT-qPCR and immunohistochemistry showed significant decrease for EMT markers E-cadherin, beta-catenin, PERP, ESRP1 and increase for ZEB1 (P ranging <0.05 to <0.0001). In vitro EMT stimulation lead to induction of EMT as indicated by down-regulation of epithelial marker (E-cadherin, 17±0.4 and 24±0.7, respectively, P=0.001) and up-regulation of mesenchymal marker (ZEB1, 3±0.28 and 2±0.10, respectively, P=0.02) as well as an increase in actin stress fibres formation. Invasion assay revealed that AIP silencing led to ~45% increase in invasion compared to non-targeting siRNA (627±99 and 294±46, respectively, P=0.02).

Conclusions: This study revealed a unique molecular signature related to increased invasiveness in AIPpos pituitary adenomas and therefore provides a potential molecular mechanism to explain how these tumours acquire more aggressive behaviour.