Endocrine Abstracts

Pituitary tumours (PTs) constitute approximately 15% of all brain tumours, affecting up to 5% of the general population. The majority of PTs are hormonally active tumours (approximately 70%), resulting in significant comorbidities associated with hormone release. Furthermore, clinically non-functioning PTs (NFPTs, around 30%) exhibit mass effect-related comorbidities due to delayed diagnosis, despite lacking a link to hormone excess. Recent studies indicate that aberrant alternative splicing is a prevalent characteristic observed in various endocrine and tumour pathologies, including PTs. In this context, other machineries involved in mRNA metabolism, such as RNA-Exosome and Nonsense-Mediated-Decay (NMD), have also been associated with several endocrine-related cancers. Therefore, our objective was to characterize the presence of components belonging to the RNA-Exosome and NMD machineries, and to determine their putative pathophysiological role in PTs. Specifically, we evaluated the expression levels of 28 and 24 genes involved in RNA-Exosome and NMD machineries, respectively, using 73 NFPTs, 50 somatotropinomas and 10 normal-pituitaries (as control-tissues) and a microfluidic-array based on qPCR-technology. The main results were consistently validated across various human external cohorts. Additionally, diverse functional and molecular approaches were performed in GH3 cell-line and primary patient-derived tumour cells using available pharmacological inhibitors of the RNA-Exosome (isoginkgetin) and NMD (NMDi) machineries, and specific candidate-genes siRNAs. Bioinformatic analysis revealed a heterogeneous dysregulation in both cellular machineries in PTs, highlighting the overexpression of EXOSC5 and CBP80 (from RNA-Exosome and NMD, respectively), as the most discriminating factors between tumour and non-tumour samples. Moreover, expression levels of these two genes were associated with different aggressiveness parameters, suggesting a potential oncogenic role in both GHomas and NFPTs. Additionally, in vitro silencing of CBP80 and EXOSC5 expression through specific siRNAs reduced several endocrine and tumour parameters (i.e., proliferation, colony-formation, secretion) in GH3 cells, as well as NFPT and GHoma primary patient-derived cells. We also observed a modulation of several molecular markers related to the cell-cycle and other key pro-oncogenic features in response to CBP80 and/or EXOSC5 silencing. Finally, pharmacological inhibition of the NMD but not of the RNA-Exosome resulted in a significant dose-response alteration of several functional parameters, including a reduction in the proliferation rate and other aggressiveness features. Altogether, we provide solid evidence indicating a drastic alteration of mRNA metabolism machineries (such as RNA-Exosome and NMD) in PTs, wherein CBP80 and EXOSC5 could represent novel diagnostic/prognostic biomarkers and therapeutic targets in GHomas and NFPTs.