Endocrine Abstracts

Introduction: Aryl hydrocarbon receptor interacting protein (AIP) is a multifunctional co-chaperone protein: it behaves as a tumour suppressor in the pituitary, but may have other roles including oncogenic function in other tissues. Protein phosphorylation is an important posttranslational modification that regulates protein activity, which is crucial for understanding protein function. To understand the molecular pathways altered in AIP deficient cells, we have performed global phosphoproteomics analysis of Aip-knockout mouse embryonic fibroblasts (Aip-KO MEFs) cells.

Aim: The aim of this study was to discover altered protein phosphorylation-related signalling pathways in Aip-KO MEFs.

Method: Phosphoproteomics analysis was performed by mass spectrometry (MS). Lysates were collected in four replicates from WT and Aip-KO cells. Phosphopeptides were enriched using titanium dioxide and subsequently analysed by LC-MS/MS. Ingenuity pathway analysis (IPA) was used for pathway analysis.

Results: We have identified 352 significantly altered phosphopeptides (200 hyper- and 152-hypophosphorylated) in Aip-KO MEFs compared to wild type cells. Among the hyperphosphorylated peptides, 10 were kinases and five were phosphatases. IPA analysis revealed two significantly activated pathways. The “Endocannabinoid cancer inhibition pathway’ (Camkk2, Map2k7, Prkab2, Smpd3, Tcf4 and Twist1) was not previously suggested to be involved with AIP. The “Epithelial adherens junction signalling’ (Arhgef17, Ctnna1, Nectin-1, Prkab2, Tcf4, and Vcl) pathway we have previously identified in gene expression and protein data of AIPpos human and mouse pituitary tumours. Functional enrichment analysis showed adherens junction, tight junction and actin cytoskeleton are the top significantly enriched pathways. Protein-protein interaction networks also showed the tight junction and signalling by Rho GTPases. Multiple kinase-mediated signalling pathways are altered in Aip-KO MEFs. The exact mechanism for the differential phosphorylation for these kinases needs to be validated by functional assays and explored further.

Conclusions: This study revealed novel insights into AIP-mediated signalling events and can be used as a valuable resource for further understanding of its function in invasive pituitary tumour development. It appears that adherens junction and tight junction pathways are of the most enriched pathways de-regulated in Aip-KO MEFs, suggesting a critical role of AIP in these pathways. Therefore, new treatments targeting these pathways may have potential to the management of patients with aggressive AIPpos pituitary tumours.