Refine
Document Type
- Article (2)
- Doctoral Thesis (1)
Language
- English (3)
Has Fulltext
- yes (3)
Is part of the Bibliography
- no (3)
Keywords
- SUMO (3) (remove)
Institute
- Medizin (3)
The ubiquitin-related SUMO system represents a versatile post-translational modification pathway controlling a variety of cellular signalling networks. In mammalian cells, lysine residues of target proteins can be covalently modified with three SUMO isoforms (SUMO1, SUMO2 and SUMO3) resulting in conjugation of either single SUMO moieties or formation of poly-SUMO chains. Importantly, SUMO modification is a reversible process, where the deconjugation of SUMO from its substrates is mediated by SUMO proteases. In humans, the best-characterized subfamily is the SENP family of SUMO-specific isopeptidases comprised of SENP1-3 and SENP5-7. For undisturbed cellular signalling events, a proper balance of SUMO conjugation and deconjugation is crucial. SENPs fulfil the important function of counteracting SUMOylation. A key question is how the relatively low number of SENPs specifically controls the SUMOylation status of hundreds of cellular proteins.
The aim of this thesis was to uncover the regulation and substrate specificity of distinct SUMO isopeptidases in order to better understand their role in cellular signalling pathways.
In the first part of this work, we investigated the influence of hypoxia on SUMO signalling, in particular on the activity of SENPs. Importantly, we found that the catalytic activity of distinct SENPs (especially SENP1 and SENP3) is strongly but reversibly diminished under low oxygen. As a consequence, the SUMO modification of a specific subset of proteins is changed under hypoxia. We specifically identified proteins being hyperSUMOylated after 24 hours of hypoxia by SUMO1 immunoprecipitation followed by mass spectrometry. We further validated the transcriptional co-repressor BHLHE40 as hypoxic SUMO target and confirmed SENP1 as responsible isopeptidase for deconjugation of SUMOylated BHLHE40. We provide evidence that SUMO conjugation to BHLHE40 enhances its repressive functions on the expression of the metabolic master regulator PGC-1α. Therefore we propose a model where inactivation of SENP1 under hypoxia results in SUMOylated BHLHE40, possibly contributing to metabolic reprogramming under hypoxia.
To get insight into substrate selectivity of SENP family members, in particular SENP3 and SENP6, we choose a proteomic profiling strategy. For the identification of specific SUMO substrates controlled by SENP3, we applied a large-scale IP-MS approach in SENP3 KO and WT cells. The most strongly induced SUMO targets in the absence of SENP3 were key regulators of ribosome maturation. We identified factors involved in the remodelling of both 90S and 60S pre-ribosomes. SENP3 has already been described as being critically involved in maturation of the pre-60S subunit and 28S rRNA processing. Previously described SENP3-regulated master targets in this process are the ribosome maturation factors PELP1 and Las1L. Importantly, both were also identified as the most significantly regulated SENP3 targets in our unbiased proteomic approach. Importantly, however, enhanced SUMOylation was also detected on 90S-associated regulators, such as BMS1. Altogether, these data strengthen the functional link between SENP3 and ribosome biogenesis and point to a role of SENP3 beyond 60S maturation.
In addition to SENP3, we explored the substrate specificity of SENP6, which mainly acts on polymeric SUMO2/3 chains. Applying a proteomic profiling strategy, we were able to identify SENP6-controlled SUMO networks functioning in DNA damage response as well as chromatin organization. We demonstrated that SENP6 reverses polySUMOylation of several subunits of the cohesin complex, thereby regulating the SUMOylation status and chromatin association of this complex. Furthermore, we found a tight interaction of SENP6 with the hPSO4/PRP19 complex, involved in DNA damage response by activation of the ATR-CHK1 signalling cascade. In cells depleted of SENP6, we observe deficient recruitment of the co-activator ATRIP to chromatin which results in diminished CHK1 activation. We therefore illustrate a general role of SENP6 in the control of chromatin-associated protein networks involved in genome integrity and chromatin organization.
SUMO : glue or solvent for phase-separated ribonucleoprotein complexes and molecular condensates?
(2021)
Spatial organization of cellular processes in membranous or membrane-less organelles (MLOs, alias molecular condensates) is a key concept for compartmentalizing biochemical pathways. Prime examples of MLOs are the nucleolus, PML nuclear bodies, nuclear splicing speckles or cytosolic stress granules. They all represent distinct sub- cellular structures typically enriched in intrinsically disordered proteins and/or RNA and are formed in a process driven by liquid-liquid phase separation. Several MLOs are critically involved in proteostasis and their formation, disassembly and composition are highly sensitive to proteotoxic insults. Changes in the dynamics of MLOs are a major driver of cell dysfunction and disease. There is growing evidence that post-translational modifications are critically involved in controlling the dynamics and composition of MLOs and recent evidence supports an important role of the ubiquitin-like SUMO system in regulating both the assembly and disassembly of these structures. Here we will review our current understanding of SUMO function in MLO dynamics under both normal and pathological conditions.
SUMOylation is a reversible posttranslational modification pathway catalyzing the conjugation of small ubiquitin-related modifier (SUMO) proteins to lysine residues of distinct target proteins. SUMOylation modifies a wide variety of cellular regulators thereby affecting a multitude of key processes in a highly dynamic manner. The SUMOylation pathway displays a hallmark in cellular stress-adaption, such as heat or redox stress. It has been proposed that enhanced cellular SUMOylation protects the brain during ischemia, however, little is known about the specific regulation of the SUMO system and the potential target proteins during cardiac ischemia and reperfusion injury (I/R). By applying left anterior descending (LAD) coronary artery ligation and reperfusion in mice, we detect dynamic changes in the overall cellular SUMOylation pattern correlating with decreased SUMO deconjugase activity during I/R injury. Further, unbiased system-wide quantitative SUMO-proteomics identified a sub-group of SUMO targets exhibiting significant alterations in response to cardiac I/R. Notably, transcription factors that control hypoxia- and angiogenesis-related gene expression programs, exhibit altered SUMOylation during ischemic stress adaptation. Moreover, several components of the ubiquitin proteasome system undergo dynamic changes in SUMO conjugation during cardiac I/R suggesting an involvement of SUMO signaling in protein quality control and proteostasis in the ischemic heart. Altogether, our study reveals regulated candidate SUMO target proteins in the mouse heart, which might be important in coping with hypoxic/proteotoxic stress during cardiac I/R injury.