Structural and functional characterization of the transmembrane protein 45A (TMEM45A) in triple negative breast cancers

Promoter

Prof. Johan WOUTERS, UNamur, Laboratory of Structural Biological Chemistry - CBS (promoter)

Prof. Carine MICHIELS, UNamur, Laboratory of Cellular and Molecular Biology - URBC (co-promoter)

Jury

MICHAUX Catherine (UNamur), Présidente; WOUTERS Johan (UNamur), Promoteur et Secrétaire; DE LAUNOIT Yvan (Université de Lille); GOORMAGHTIGH Erik (ULB); LE CALVE Benjamin (UNamur); MICHIELS Carine (UNamur), Co-promoteur

Summary

Cancer is the second cause of death over the world. Despite recent advances in new therapies, too many cancer patients still die. A better knowledge of the emergence, development and outcome of this disease is thus required for a better patient outcome. TMEM45A protein was studied for the first time by the team of Professor Carine Michiels in the context of drug resistance to chemotherapeutic agents in hypoxia. Besides this first role, TMEM45A invalidation was shown to affect cell proliferation and migration of ovarian cancer and glioma cells in vitro. This work focus on the study of TMEM45A in triple-negative breast cancer. In order to gain insights into the structure and the functions of TMEM45A, a strategy based on several steps was established. The first part of this work was dedicated to the structural characterization of the protein TMEM45A. Structural evidence was obtained thanks to the screening of induction conditions for TMEM45A production by bacteria, homology modelling and the topology-based strategy. Despite technical limitations, secondary structure elements have been highlighted. The second part focuses on TMEM45A invalidation-associated phenotype in cell lines derived from triple-negative breast cancer. TMEM45A depletion was performed using shRNA technology. TMEM45A knockdown inhibited cell growth and cell migration in MDA-MB-231, MDA-MB-453 and Hs 578T cells. Since the function and the mechanism of action of this protein as well as cellular pathways triggered by TMEM45A were still unknown, we investigated its partners through co-immunoprecipitation and mass spectrometry approaches. This study evidenced that TMEM45A regulated the ubiquitin-proteasome system by controlling the protein expression level of one regulator of this system, CAND1. In consequence, the protein abundance of a tumor suppressor protein was modified, which directly impacts the cell migratory capacities. This work thus unraveled a new pathway regulated by TMEM45A that may explain how this protein modulates cancer cell aggressiveness.