Caractérisation de la fusion PDGFRA::USP8 associée aux tumeurs des tissus mous

Details

Supervisors

Demoulin, Jean-Baptiste

Faculty

Faculté de pharmacie et des sciences biomédicales

Degree label

Master [120] en sciences biomédicales, à finalité approfondie

Abstract

enThe PDGFRA::USP8 fusion, recently identified in sixteen patients with soft tissue tumors, has not yet been functionally characterized. PDGFRα (Platelet-Derived Growth Factor Receptor α) is a receptor tyrosine kinase involved in the regulation of cell proliferation, survival, differentiation, and migration. USP8 is a deubiquitinase that finely regulates endosomal trafficking. The aim of this project is to characterize this fusion in order to better understand its potential role in tumorigenesis and to evaluate its effects on key cellular processes such as ubiquitination, proliferation, and differentiation. A luciferase reporter assay demonstrated that the fusion displays constitutive activity requiring both the kinase domain of PDGFRα and the deubiquitinase activity of USP8. Western blot analyses revealed ligand-independent activation of several signaling pathways, including the MAPK pathway, phosphatidylinositol-3-kinase, the phospholipase C-γ pathway, and STAT3. This constitutive activity can be inhibited by imatinib. Confocal microscopy showed that endothelial cells expressing the fusion display numerous filopodia, structures associated with cell migration and invasion, indicating a potentially pro-migratory phenotype. A mutation that inactivates USP8 (C786A) leads to reduced expression of the fusion protein, suggesting that the deubiquitinase activity of USP8 is essential for maintaining its stability. Furthermore, PDGFRα immunoprecipitation shows an absence of ubiquitination for the PDGFRA::USP8 fusion, whereas this ubiquitination signal is restored in the presence of the inactivating C786A mutation. These findings support the hypothesis that USP8 may deubiquitinate the fusion, thereby promoting its recycling and retention at the plasma membrane. In the absence of USP8 activity, the fusion would instead be targeted to lysosomal degradation. In conclusion, this work aims to characterize the PDGFRA::USP8 fusion identified in soft tissue tumors by investigating its expression, associated signaling activation, cellular effects, and the mechanisms involved in its oncogenic potential.