The role of the mammalian GET pathway in the mouse liver
von Lena Musiol
Datum der mündl. Prüfung:2016-11-15
Betreuer:Prof. Dr. Blanche Schwappach-Pignataro
Gutachter:Prof. Dr. Blanche Schwappach-Pignataro
Gutachter:Prof. Dr. Reinhard Jahn
EnglischThe correct insertion of membrane proteins is essential for the normal functioning of a eukaryotic cell, and different classes of membrane proteins employ different mechanisms of insertion into their target membrane. One of these pathways is the GET pathway, which promotes the insertion of tail-anchored proteins into the ER membrane. Tail-anchored protein substrates of this pathway are then involved in trafficking, metabolism, or protein translocation in the cell. The key players of the pathway in mammals are the cytosolic ATPase TRC40 and the heterodimeric receptor at the ER membrane consisting of CAML and WRB. Recent studies showed a second function for the yeast homologue of TRC40, Get3, to not only work in tail-anchored protein targeting, but also as an ATP-independent chaperone under oxidative stress conditions. While the pathway is not essential in yeast, loss of some of its main components results in early embryonic lethality in mice, but the reason for this is so far not fully understood. In this study, a mouse model was established to further elucidate the role of the mammalian GET pathway in vivo. The model allows a deletion of the middle exons of WRB in a hepatocyte-specific manner by using the Cre- Lox system, leading to an impairment of the pathway in the liver, a tissue that is high in secretion, protein biosynthesis and trafficking. The results obtained show that this deletion leads to severe liver damage in mice, which was evident in situ, as well is in liver enzyme levels in the blood and increasing fibrosis in the organs, shown by histological analysis. The liver damage changed from an acute state to a more chronic damage with increasing age of the animals. Furthermore, the massive damage and loss of hepatocytes led to subsequent liver regeneration. At the stage of acute liver damage, some of the substrates of the mammalian GET pathway were shown to be affected by the disturbance of the pathway. The protein levels of Syntaxin5 and Syntaxin6, two SNAREs, were decreased in hepatocytes, and Stx5 displayed a clear loss of targeting to the Golgi membrane in hepatocytes. In conclusion, the study shows that a targeted disruption of WRB in hepatocytes severely impairs liver function and integrity, and some substrates of the mammalian GET pathway show a higher susceptibility to this impairment than others.
Keywords: Tail-anchored proteins; membrane proteins; liver; GET pathway; TRC40; WRB; CAML; endoplasmic reticulum