The RAS pathway is among the most frequently activated signaling nodes in cancer. However, the mechanisms that alter RAS activity in human pathologies are not entirely understood. The most prevalent post-translational modification within the GTPase core domain of NRAS and KRAS is ubiquitination at lysine 128 (K128), which is significantly decreased in cancer samples compared to normal tissue. Here, we found that K128 ubiquitination creates an additional binding interface for RAS GTPase-activating proteins (GAPs), NF1 and RASA1, thus increasing RAS binding to GAP proteins and promoting GAP-mediated GTP hydrolysis. Stimulation of cultured cancer cells with growth factors or cytokines transiently induces K128 ubiquitination and restricts the extent of wild-type RAS activation in a GAP-dependent manner. In KRAS mutant cells, K128 ubiquitination limits tumor growth by restricting RAL/ TBK1 signaling and negatively regulating the autocrine circuit induced by mutant KRAS. Reduction of K128 ubiquitination activates both wild-type and mutant RAS signaling and elicits a senescence-associated secretory phenotype, promoting RAS-driven pancreatic tumorigenesis.
- MeSH
- GTP Phosphohydrolases metabolism genetics MeSH
- Humans MeSH
- Lysine metabolism MeSH
- Membrane Proteins metabolism genetics MeSH
- Mice MeSH
- Cell Line, Tumor MeSH
- Neurofibromin 1 MeSH
- p120 GTPase Activating Protein metabolism genetics MeSH
- Protein Serine-Threonine Kinases metabolism genetics MeSH
- Proto-Oncogene Proteins p21(ras) * metabolism genetics MeSH
- ras Proteins metabolism genetics MeSH
- Signal Transduction MeSH
- Ubiquitination * MeSH
- Protein Binding * MeSH
- Animals MeSH
- Check Tag
- Humans MeSH
- Mice MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
Split reporter protein-based genetic section systems are widely used to identify and characterize protein-protein interactions (PPI). The assembly of split markers that antagonize toxins, rather than required for synthesis of missing metabolites, facilitates the seeding of high density of cells and selective growth. Here we present a newly developed split chloramphenicol acetyltransferase (split-CAT) -based genetic selection system. The N terminus fragment of CAT is fused downstream of the protein of interest and the C terminus fragment is tethered upstream to its postulated partner. We demonstrate the system's advantages for the study of PPIs. Moreover, we show that co-expression of a functional ubiquitylation cascade where the target and ubiquitin are tethered to the split-CAT fragments results in ubiquitylation-dependent selective growth. Since proteins do not have to be purified from the bacteria and due to the high sensitivity of the split-CAT reporter, detection of challenging protein cascades and post-translation modifications is enabled. In addition, we demonstrate that the split-CAT system responds to small molecule inhibitors and molecular glues (GLUTACs). The absence of ubiquitylation-dependent degradation and deubiquitylation in E. coli significantly simplify the interpretation of the results. We harnessed the developed system to demonstrate that like NEDD4, UBE3B also undergoes self-ubiquitylation-dependent inactivation. We show that self-ubiquitylation of UBE3B on K665 induces oligomerization and inactivation in yeast and mammalian cells respectively. Finally, we showcase the advantages of split-CAT in the study of human diseases by demonstrating that mutations in UBE3B that cause Kaufman oculocerebrofacial syndrome exhibit clear E. coli growth phenotypes.
- MeSH
- Enzyme Activation MeSH
- Biological Assay methods MeSH
- Chloramphenicol O-Acetyltransferase genetics metabolism MeSH
- Escherichia coli genetics metabolism MeSH
- Gene Expression * MeSH
- Protein Processing, Post-Translational MeSH
- Proteolysis MeSH
- Genes, Reporter * MeSH
- Ubiquitination * MeSH
- Ubiquitin-Protein Ligases metabolism MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Ubiquitylation and deubiquitylation play a pivotal role in protein homeostasis (proteostasis). Proteostasis shapes the proteome landscape in the human brain and its impairment is linked to neurodevelopmental and neurodegenerative disorders. Here we discuss the emerging roles of deubiquitylating enzymes in neuronal function and survival. We provide an updated perspective on the genetics, physiology, structure, and function of deubiquitylases in neuronal health and disease.
- MeSH
- Humans MeSH
- Neurodegenerative Diseases genetics MeSH
- Ubiquitination genetics MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Review MeSH
Ubiquitin (Ub) receptors respond to ubiquitylation signals. They bind ubiquitylated substrates and exert their activity in situ. Intriguingly, Ub receptors themselves undergo rapid ubiquitylation and deubiquitylation. Here we asked what is the function of ubiquitylation of Ub receptors? We focused on yeast epsin, a Ub receptor that decodes the ubiquitylation signal of plasma membrane proteins into an endocytosis response. Using mass spectrometry, we identified lysine-3 as the major ubiquitylation site in the epsin plasma membrane binding domain. By projecting this ubiquitylation site onto our crystal structure, we hypothesized that this modification would compete with phosphatidylinositol-4,5-bisphosphate (PIP2) binding and dissociate epsin from the membrane. Using an E. coli-based expression of an authentic ubiquitylation apparatus, we purified ubiquitylated epsin. We demonstrated in vitro that in contrast to apo epsin, the ubiquitylated epsin does not bind to either immobilized PIPs or PIP2-enriched liposomes. To test this hypothesis in vivo, we mimicked ubiquitylation by the fusion of Ub at the ubiquitylation site. Live cell imaging demonstrated that the mimicked ubiquitylated epsin dissociates from the membrane. Our findings suggest that ubiquitylation of the Ub receptors dissociates them from their products to allow binding to a new ubiquitylated substrates, consequently promoting cyclic activity of the Ub receptors.
- MeSH
- Cell Membrane metabolism MeSH
- Models, Molecular MeSH
- Protein Domains MeSH
- Saccharomyces cerevisiae Proteins chemistry metabolism MeSH
- Ubiquitination * MeSH
- Protein Binding MeSH
- Vesicular Transport Proteins chemistry metabolism MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Mutant protein aggregation and misfolding is often correlated with toxicity in neurodegenerative diseases. Aggregate-prone proteins are tagged by ubiquitin that signals them for destruction by the proteasome or autophagy, two key pathways for protein degradation and proteostasis. Here, we review recent studies showing that the regulation of aggregate-prone proteins by ubiquitin signaling is more complex than initially postulated. We discuss how the ubiquitin code of aggregate-prone proteins is written by specific E3 ubiquitin ligases and edited by deubiquitylating enzymes (DUBs) in cells and in brain tissues, as well as how this affects protein degradation. These studies have advanced our understanding of the specificity of the ubiquitin system and provide new information about its relevance to neurodegenerative diseases and therapy.
- MeSH
- Humans MeSH
- Models, Molecular MeSH
- Protein Aggregates MeSH
- Proteins chemistry genetics metabolism MeSH
- Proteolysis MeSH
- Signal Transduction MeSH
- Ubiquitin chemistry metabolism MeSH
- Animals MeSH
- Check Tag
- Humans MeSH
- Animals MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
- Review MeSH
Ubiquitylation is an eukaryotic signal that regulates most cellular pathways. However, four major hurdles pose challenges to study ubiquitylation: (1) high redundancy between ubiquitin (Ub) cascades, (2) ubiquitylation is tightly regulated in the cell, (3) the transient nature of the Ub signal, and (4) difficulties to purify functional ubiquitylation apparatus for in vitro assay. Here, we present systems that express functional Ub cascades in E. coli, which lacks deubiquitylases, Ub-dependent degradations, and control mechanisms for ubiquitylation. Therefore, expression of an ubiquitylation cascade results in the accumulation of stable ubiquitylated protein that can be genetically selected or purified, thus circumventing the above challenges. Co-expression of split antibiotic resistance protein fragments tethered to Ub and ubiquitylation targets along with ubiquitylation enzymes (E1, E2, and E3) gives rise to bacterial growth on selective media. We show that ubiquitylation rate is highly correlated with growth efficiency. Hence, genetic libraries and simple manipulations in the selection system facilitate the identification and characterization of components and interfaces along Ub cascades. The bacterial expression system also facilitates the detection of ubiquitylated proteins. Furthermore, the expression system allows affinity chromatography-based purification of milligram quantities of ubiquitylated proteins for downstream biochemical, biophysical, and structural studies.
- MeSH
- Escherichia coli genetics metabolism MeSH
- Gene Expression * MeSH
- Genetic Vectors genetics MeSH
- Protein Conformation MeSH
- Models, Molecular MeSH
- Gene Order MeSH
- Proteins chemistry genetics isolation & purification metabolism MeSH
- Ubiquitin-Activating Enzymes metabolism MeSH
- Ubiquitin-Conjugating Enzymes metabolism MeSH
- Ubiquitin metabolism MeSH
- Ubiquitination MeSH
- Ubiquitin-Protein Ligases metabolism MeSH
- Publication type
- Journal Article MeSH
- Research Support, Non-U.S. Gov't MeSH
Ubiquitylation controls protein function and degradation. Therefore, ubiquitin ligases need to be tightly controlled. We discovered an evolutionarily conserved allosteric restraint mechanism for Nedd4 ligases and demonstrated its function with diverse substrates: the yeast soluble proteins Rpn10 and Rvs167, and the human receptor tyrosine kinase FGFR1 and cardiac IKS potassium channel. We found that a potential trimerization interface is structurally blocked by the HECT domain α1-helix, which further undergoes ubiquitylation on a conserved lysine residue. Genetic, bioinformatics, biochemical and biophysical data show that attraction between this α1-conjugated ubiquitin and the HECT ubiquitin-binding patch pulls the α1-helix out of the interface, thereby promoting trimerization. Strikingly, trimerization renders the ligase inactive. Arginine substitution of the ubiquitylated lysine impairs this inactivation mechanism and results in unrestrained FGFR1 ubiquitylation in cells. Similarly, electrophysiological data and TIRF microscopy show that NEDD4 unrestrained mutant constitutively downregulates the IKS channel, thus confirming the functional importance of E3-ligase autoinhibition.
- MeSH
- Potassium Channels, Voltage-Gated chemistry metabolism MeSH
- Endosomal Sorting Complexes Required for Transport metabolism MeSH
- Humans MeSH
- Microfilament Proteins chemistry metabolism MeSH
- Protein Multimerization * MeSH
- Proteasome Endopeptidase Complex chemistry metabolism MeSH
- Receptor, Fibroblast Growth Factor, Type 1 chemistry metabolism MeSH
- Saccharomyces cerevisiae Proteins chemistry metabolism MeSH
- Ubiquitination * MeSH
- Ubiquitin-Protein Ligases metabolism MeSH
- Check Tag
- Humans MeSH
- Publication type
- Journal Article MeSH
Analytical ultracentrifugation (AUC) is a first principles based method to determine absolute sedimentation coefficients and buoyant molar masses of macromolecules and their complexes, reporting on their size and shape in free solution. The purpose of this multi-laboratory study was to establish the precision and accuracy of basic data dimensions in AUC and validate previously proposed calibration techniques. Three kits of AUC cell assemblies containing radial and temperature calibration tools and a bovine serum albumin (BSA) reference sample were shared among 67 laboratories, generating 129 comprehensive data sets. These allowed for an assessment of many parameters of instrument performance, including accuracy of the reported scan time after the start of centrifugation, the accuracy of the temperature calibration, and the accuracy of the radial magnification. The range of sedimentation coefficients obtained for BSA monomer in different instruments and using different optical systems was from 3.655 S to 4.949 S, with a mean and standard deviation of (4.304 ± 0.188) S (4.4%). After the combined application of correction factors derived from the external calibration references for elapsed time, scan velocity, temperature, and radial magnification, the range of s-values was reduced 7-fold with a mean of 4.325 S and a 6-fold reduced standard deviation of ± 0.030 S (0.7%). In addition, the large data set provided an opportunity to determine the instrument-to-instrument variation of the absolute radial positions reported in the scan files, the precision of photometric or refractometric signal magnitudes, and the precision of the calculated apparent molar mass of BSA monomer and the fraction of BSA dimers. These results highlight the necessity and effectiveness of independent calibration of basic AUC data dimensions for reliable quantitative studies.
