Thesis presented April 13, 2021

Abstract:
My thesis focuses on the regulation of the endocytic pathway and the trafficking of plasma membrane receptors. Particular attention was paid to the study of the role of the ubiquitin- specific protease USP8 in the regulation of the receptor for the epithelial growth factor (EGF) and in Cushing's disease, a rare disease caused by a pituitary microadenoma leading to increased release of adrenocorticotropic hormone (ACTH) and major metabolic disturbances. I present here a high throughput screening campaign of a collection of 2,140 small molecules having been the subject of clinical or pre-clinical studies, which led to the selection of a chemical inhibitor of the catalytic activity USP8. I further showed that this inhibitor decreases the release of ACTH in murine corticotrophic cells. In addition to this, I investigated the regulation of CHMP1B, a known USP8 substrate playing a major role in EGF receptor trafficking and sorting. I identified, by a mass spectrometry approach, that the ubiquitin protease OTUB1 is another partner of CHMP1B and demonstrated the regulation of the ubiquitination and stability of CHMPIB by OTUBI. My thesis work brings both new fundamental knowledge to understand better the role of USP8 targets and partners in endocytosis, and a new inhibitor that may accelerate the discovery of therapeutic compounds for the treatment of Cushing's disease and cancers with increased USP8 activity.

Keywords:
Deubiquitinases, Endocytosis, Therapeutic molecules, Cell signaling, Ubiquitin system, Ubiquitin, Cushing's disease, USP8