Identification and characterization of phosphatases, master regulators of cellular stress signalling pathways

点击翻译按钮获取中文摘要

The reversible phosphorylation of proteins is a post-translational modification controlling a wide range of signalling events involved in virtually all cellular processes. Almost one third of cellular proteins become phosphorylated, underlining the immense importance of this tightly regulated signalling network. To control the modification of that many targets, cells encode around 400 kinases with differing specificities. In contrast, protein phosphatases, which reverse the phosphorylation of proteins, were long thought to be unspecific enzymes due to the rather small number of genes encoding for these enzymes. Furthermore, the purified catalytic entities display a fairly non-discriminating activity towards their substrates in in vitro assays. However, research from recent years demonstrated that many phosphatases are obligatory oligomeric enzymes, forming a large number of holoenzymes with distinct substrate specificities. Protein phosphatase 1 (PP1) accounts for the majority of serine/threonine dephosphorylation events in eukaryotic cells. To date, approximately 200 regulatory subunits of PP1 are identified, which determine its specificity and subcellular localization. Despite their tremendous importance in controlling cellular signalling, little is known about the biology of specific PP1 holoenzymes. During my stay in the Bertolotti lab, I plan to identify and characterize new phosphatase holoenzymes, playing a major role in the regulation and termination of cellular stress signalling. For this purpose, I aim to investigate the PP1 interactome during endoplasmic reticulum (ER) and cytosolic stress conditions to identify regulatory subunits, which are involved in the regulation and signal termination of these pathways. Additionally, I aim to elucidate the signalling events involved in the dephosphorylation of the ubiquitin conjugating enzyme UBE2J1, which is a key player in protein homeostasis at the ER. UBE2J1 is phosphorylated upon different stresses and this modification appears to be essential for cellular survival. In a third project, I will focus on the characterization of a specific PP1 regulatory subunit potentially involved in cytosolic stress signalling. Altogether, the identification and characterization of new PP1 holoenzymes will deepen our understanding of stress response pathways and related diseases.