Tumor microenvironment defines the invasive phenotype of AIP -mutation-positive pituitary tumors

The molecular mechanisms leading to aryl hydrocarbon receptor interacting protein ( AIP ) mutation-induced aggressive, young-onset growth hormone-secreting pituitary tumors are not fully understood. In this study, we have identified that AIP -mutation-positive tumors are infiltrated by a large number of macrophages compared to sporadic tumors. Tissue from pituitary-specific Aip -knockout ( Aip Flox/Flox ;Hesx1 Cre/+ ) mice recapitulated this phenotype. Our human pituitary tumor transcriptome data revealed the “epithelial-to-mesenchymal transition (EMT) pathway” as one of the most significantly altered pathways in AIP pos tumors. Our in vitro data suggest that bone marrow-derived macrophage-conditioned media induces more prominent EMT-like phenotype and enhanced migratory and invasive properties in Aip -knockdown somatomammotroph cells compared to non-targeting controls. We identified that tumor-derived cytokine CCL5 is upregulated in AIP -mutation-positive human adenomas. Aip -knockdown GH3 cell-conditioned media increases macrophage migration, which is inhibited by the CCL5/CCR5 antagonist maraviroc. Our results suggest that a crosstalk between the tumor and its microenvironment plays a key role in the invasive nature of AIP -mutation-positive tumors and the CCL5/CCR5 pathway is a novel potential therapeutic target.