Endocrine Abstracts

Background: Familial isolated pituitary adenoma (FIPA) is an autosomal dominant condition with incomplete penetrance. Heterozygote mutations have been identified in the aryl-hydrocarbon receptor interacting protein (AIP) gene in 20% of FIPA families causing young-onset aggressive tumours.

Aims: The aim of this study was to perform comparative gene expression microarray analysis of familial AIP positive and AIP negative adenomas and compare them to sporadic tumours and normal pituitary to discover novel genes and pathways responsible for familial pituitary tumorigenesis.

Methods: We have performed gene expression analysis on normal pituitary, sporadic GH-secreting adenomas, AIP positive and AIP negative familial somatotroph adenomas (five samples of each category) using the Affymetrix human Gene Chip HG-U133 Plus 2.0 array. Data analysis was carried out in the statistical ‘R’ environment. Ingenuity Pathway Analysis (IPA) tool was used for pathway analysis. Expression of the ten selected genes from microarray analysis was validated by quantitative reverse transcriptase PCR. Functional assays were performed using BioCoat-Matrigel invasion chambers.

Results: We have identified differentially expressed genes in AIPpos (451 up; 1249 down) and AIPneg (234 up; 1609 down) pituitary adenomas compared to normal pituitary. A smaller number of genes differ in their expression levels between familial AIP positive and sporadic adenomas (10 up; 22 down) and 45 genes (20 up; 25 down) in AIPpos compared to AIPneg tumours. IPA of these genes revealed one of the significantly altered functional modules: ‘cellular invasion signature’. Several genes of the invasion signature have been validated by RT-qPCR. Functional studies on invasion characteristic with AIP knockdown cells support these data.

Conclusion: The observed transcriptional changes probably reflect the more aggressive clinical phenotype in AIP positive patients. The identified genes may predict the invasive potential of these tumours.

Declaration of funding