Endocrine Abstracts

Pituitary adenomas (PAs) are benign neoplasms that comprise 10–20% of all intracranial tumors. Mutations in the aryl hydrocarbon receptor interacting protein (AIP) have been identified to cause a small subset of hereditary PAs. To study the mechanisms of tumor formation in patients with AIP-mutated PAs we conducted a miRNA array analysis comparing AIP-mutated PAs with AIP-wild type PAs. We found a novel and specific set of miRNAs differentially expressed between the two groups of PAs. We selected several candidate miRNAs and validated them in the patient tissues. To characterize the candidate miRNAs in vitro and clarify their role in AIP dependent tumorigenesis we performed functional studies using mouse embryonic fibroblasts (MEFs) derived from Aip knockout (AIP-KO) mice and a rat somatotroph tumor cell line (GH3). In the AIP-KO MEFs we saw that transfection of mutant AIP altered the expression of two of the candidate miRNAs according to the changes observed in the miRNA array. Additionally, cell viability and cell migration were increased after transfection of mutant AIP. Since deregulation of cAMP levels is a common feature of PAs we also checked cAMP levels upon transfection of mutant AIP. We could observe that mutant AIP increased cAMP levels in AIP-KO MEFs. Overexpression of the candidate miRNAs in GH3 cells increased cell migration and cAMP levels while apoptosis was decreased. To further clarify the role of the selected miRNAs in tumor development we identified their predicted targets and focused on those involved in cAMP signalling. We plan to validate the role of these predicted targets in PAs in the future. In conclusion, we identified novel miRNAs in AIP-mutated PAs and were able to show that these miRNAs promote a tumor-like behaviour in several functional assays in AIP-KO MEFs and GH3 somatotroph cells.