SILAC-based phosphoproteomics reveals an inhibitory role of KSR1 in p53 transcriptional activity via modulation of DBC1

BACKGROUND We have previously identified kinase suppressor of ras-1 (KSR1) as a potential regulatory gene in breast cancer. KSR1, originally described as a novel protein kinase, has a role in activation of mitogen-activated protein kinases. Emerging evidence has shown that KSR1 may have dual functions as an active kinase as well as a scaffold facilitating multiprotein complex assembly. Although efforts have been made to study the role of KSR1 in certain tumour types, its involvement in breast cancer remains unknown. METHODS A quantitative mass spectrometry analysis using stable isotope labelling of amino acids in cell culture (SILAC) was implemented to identify KSR1-regulated phosphoproteins in breast cancer. In vitro luciferase assays, co-immunoprecipitation as well as western blotting experiments were performed to further study the function of KSR1 in breast cancer. RESULTS Of significance, proteomic analysis reveals that KSR1 overexpression decreases deleted in breast cancer-1 (DBC1) phosphorylation. Furthermore, we show that KSR1 decreases the transcriptional activity of p53 by reducing the phosphorylation of DBC1, which leads to a reduced interaction of DBC1 with sirtuin-1 (SIRT1); this in turn enables SIRT1 to deacetylate p53. CONCLUSION Our findings integrate KSR1 into a network involving DBC1 and SIRT1, which results in the regulation of p53 acetylation and its transcriptional activity

The NEDD8 inhibitor MLN4924 increases the size of the nucleolus and activates p53 through the ribosomal-Mdm2 pathway

International audienceThe ubiquitin-like molecule NEDD8 is essential for viability, growth and development, and is a potential target for therapeutic intervention. We found that the small molecule inhibitor of NEDDylation, MLN4924, alters the morphology and increases the surface size of the nucleolus in human and germline cells of Caenorhabditis elegans in the absence of nucleolar fragmentation. SILAC proteomics and monitoring of rRNA production, processing and ribosome profiling shows that MLN4924 changes the composition of the nucleolar proteome but does not inhibit RNA Pol I transcription. Further analysis demonstrates that MLN4924 activates the p53 tumour suppressor through the RPL11/RPL5-Mdm2 pathway, with characteristics of nucleolar stress. The study identifies the nucleolus as a target of inhibitors of NEDDylation and provides a mechanism for p53 activation upon NEDD8 inhibition. It also indicates that targeting the nucleolar proteome without affecting nucleolar transcription initiates the required signalling events for the control of cell cycle regulators

Influenza A viruses alter the stability and antiviral contribution of host E3-ubiquitin ligase Mdm2 during the time-course of infection

International audienceThe interplay between influenza A viruses (IAV) and the p53 pathway has been reported in several studies, highlighting the antiviral contribution of p53. Here, we investigated the impact of IAV on the E3-ubiquitin ligase Mdm2, a major regulator of p53, and observed that IAV targets Mdm2, notably via its non-structural protein (NS1), therefore altering Mdm2 stability, p53/Mdm2 interaction and regulatory loop during the time-course of infection. This study also highlights a new antiviral facet of Mdm2 possibly increasing the list of its many p53-independent functions. Altogether, our work contributes to better understand the mechanisms underlining the complex interactions between IAV and the p53 pathway, for which both NS1 and Mdm2 arise as key players

MAGE-A cancer/testis antigens inhibit MDM2 ubiquitylation function and promote increased levels of MDM4

Melanoma antigen A (MAGE-A) proteins comprise a structurally and biochemically similar sub-family of Cancer/Testis antigens that are expressed in many cancer types and are thought to contribute actively to malignancy. MAGE-A proteins are established regulators of certain cancer-associated transcription factors, including p53, and are activators of several RING finger-dependent ubiquitin E3 ligases. Here, we show that MAGE-A2 associates with MDM2, a ubiquitin E3 ligase that mediates ubiquitylation of more than 20 substrates including mainly p53, MDM2 itself, and MDM4, a potent p53 inhibitor and MDM2 partner that is structurally related to MDM2. We find that MAGE-A2 interacts with MDM2 via the N-terminal p53-binding pocket and the RING finger domain of MDM2 that is required for homo/hetero-dimerization and for E2 ligase interaction. Consistent with these data, we show that MAGE-A2 is a potent inhibitor of the E3 ubiquitin ligase activity of MDM2, yet it does not have any significant effect on p53 turnover mediated by MDM2. Strikingly, however, increased MAGE-A2 expression leads to reduced ubiquitylation and increased levels of MDM4. Similarly, silencing of endogenous MAGE-A expression diminishes MDM4 levels in a manner that can be rescued by the proteasomal inhibitor, bortezomid, and permits increased MDM2/MDM4 association. These data suggest that MAGE-A proteins can: (i) uncouple the ubiquitin ligase and degradation functions of MDM2; (ii) act as potent inhibitors of E3 ligase function; and (iii) regulate the turnover of MDM4. We also find an association between the presence of MAGE-A and increased MDM4 levels in primary breast cancer, suggesting that MAGE-A-dependent control of MDM4 levels has relevance to cancer clinically

Interplay between SUMOylation and NEDDylation regulates RPL11 localization and function

The ribosomal protein L11 (RPL11) integrates different types of stress into a p53-mediated response. Here, we analyzed the impact of the ubiquitin-like protein SUMO on the RPL11-mouse double-minute 2 homolog-p53 signaling. We show that small ubiquitin-related modifier (SUMO)1 and SUMO2 covalently modify RPL11. We find that SUMO negatively modulates the conjugation of the ubiquitin-like protein neural precursor cell-expressed developmentally downregulated 8 (NEDD8) to RPL11 and promotes the translocation of the RP outside of the nucleoli. Moreover, the SUMO-conjugating enzyme, Ubc9, is required for RPL11-mediated activation of p53. SUMOylation of RPL11 is triggered by ribosomal stress, as well as by alternate reading frame protein upregulation. Collectively, our data identify SUMO protein conjugation to RPL11 as a new regulator of the p53-mediated cellular response to different types of stress and reveal a previously unknown SUMO-NEDD8 interplay.-El Motiam, A., Vidal, S., de la Cruz-Herrera, C. F., Da Silva-Alvarez, S., Baz-Martinez, M., Seoane, R., Vidal, A., Rodriguez, M. S., Xirodimas, D. P., Carvalho, A. S., Beck, H. C., Matthiesen, R., Collado, M., Rivas, C. Interplay between SUMOylation and NEDDylation regulates RPL11 localization and function

Reconstitution of Mdm2-Dependent Post-Translational Modifications of p53 in Yeast

p53 mediates cell cycle arrest or apoptosis in response to DNA damage. Its activity is subject to a tight regulation involving a multitude of post-translational modifications. The plethora of functional protein interactions of p53 at present precludes a clear understanding of regulatory principles in the p53 signaling network. To circumvent this complexity, we studied here the minimal requirements for functionally relevant p53 post-translational modifications by expressing human p53 together with its best characterized modifier Mdm2 in budding yeast. We find that expression of the human p53-Mdm2 module in yeast is sufficient to faithfully recapitulate key aspects of p53 regulation in higher eukaryotes, such as Mdm2-dependent targeting of p53 for degradation, sumoylation at lysine 386 and further regulation of this process by p14ARF. Interestingly, sumoylation is necessary for the recruitment of p53-Mdm2 complexes to yeast nuclear bodies morphologically akin to human PML bodies. These results suggest a novel role for Mdm2 as well as for p53 sumoylation in the recruitment of p53 to nuclear bodies. The reductionist yeast model that was established and validated in this study will now allow to incrementally study simplified parts of the intricate p53 network, thus helping elucidate the core mechanisms of p53 regulation as well as test novel strategies to counteract p53 malfunctions

ARF-BP1 as a potential therapeutic target

In this review, we discuss the recent identification of ARF-BP1 (also known as Mule, UREB1, E3histone, LASU1, and HectH9). ARF-BP1, a HECT domain-containing E3 ubiquitin ligase, interacts with ARF and p53. Its ubiquitin ligase activity is inhibited by ARF. Inactivation of ARF-BP1 stabilised p53 and induced apoptosis. Notably, inactivation of ARF-BP1 also caused cell growth repression in p53-null cells and breast cancer cells with mutant p53. Thus, ARF-BP1 emerges as a novel therapeutic target against cancer regardless of p53 status

Neddylation inhibition prevents acetaminophen-induced liver damage by enhancing the anabolic cardiolipin pathway

\ua9 2024 The AuthorsDrug-induced liver injury (DILI) is a significant cause of acute liver failure (ALF) and liver transplantation in the Western world. Acetaminophen (APAP) overdose is a main contributor of DILI, leading to hepatocyte cell death through necrosis. Here, we identified that neddylation, an essential post-translational modification involved in the mitochondria function, was upregulated in liver biopsies from patients with APAP-induced liver injury (AILI) and in mice treated with an APAP overdose. MLN4924, an inhibitor of the neuronal precursor cell-expressed developmentally downregulated protein 8 (NEDD8)-activating enzyme (NAE-1), ameliorated necrosis and boosted liver regeneration in AILI. To understand how neddylation interferes in AILI, whole-body biotinylated NEDD8 (bioNEDD8) and ubiquitin (bioUB) transgenic mice were investigated under APAP overdose with and without MLN4924. The cytidine diphosphate diacylglycerol (CDP-DAG) synthase TAM41, responsible for producing cardiolipin essential for mitochondrial activity, was found modulated under AILI and restored its levels by inhibiting neddylation. Understanding this ubiquitin-like crosstalk in AILI is essential for developing promising targeted inhibitors for DILI treatment

Neddylation inhibition ameliorates steatosis in NAFLD by boosting hepatic fatty acid oxidation via the DEPTOR-mTOR axis

Objective: Neddylation is a druggable and reversible ubiquitin-like post-translational modification upregulated in many diseases, including liver fibrosis, hepatocellular carcinoma, and more recently, non-alcoholic fatty liver disease (NAFLD). Herein, we propose to address the effects of neddylation inhibition and the underlying mechanisms in pre-clinical models of NAFLD. Methods: Hepatic neddylation measured by immunohistochemical analysis and NEDD8 serum levels measured by ELISA assay were evaluated in NAFLD clinical and pre-clinical samples. The effects of neddylation inhibition by using a pharmacological small inhibitor, MLN4924, or molecular approaches were assessed in isolated mouse hepatocytes and pre-clinical mouse models of diet-induced NAFLD, male adult C57BL/6 mice, and the AlfpCre transgenic mice infected with AAV-DIO-shNedd8. Results: Neddylation inhibition reduced lipid accumulation in oleic acid-stimulated mouse primary hepatocytes and ameliorated liver steatosis, preventing lipid peroxidation and inflammation in the mouse models of diet-induced NAFLD. Under these conditions, increased Deptor levels and the concomitant repression of mTOR signaling were associated with augmented fatty acid oxidation and reduced lipid content. Moreover, Deptor silencing in isolated mouse hepatocytes abolished the anti-steatotic effects mediated by neddylation inhibition. Finally, serum NEDD8 levels correlated with hepatic neddylation during the disease progression in the clinical and pre-clinical models. Conclusions: Overall, the upregulation of Deptor, driven by neddylation inhibition, is proposed as a novel effective target and therapeutic approach to tackle NAFLDThis work was supported by grants from Gobierno Vasco-Departamento de Salud 2013111114 (to M.L.M.-C), ELKARTEK 2016, Departamento de Industria del Gobierno Vasco (to M.L.M−C), Ministerio de Ciencia, Innovación y Universidades MICINN: SAF2017-87301-R, and RTI2018-096759-A-100 integrado en el Plan Estatal de Investigación Científica y Técnica y Innovación, cofinanciado con Fondos FEDER (to M.L.M− T.C.D respectively); MCIU/AEI/FEDER, UE (RTI2018-095134-B-100) (to P.A.), AECC Bizkaia (M.S-M); Asociación Española contra el Cáncer (T.C.D), Fundación Científica de la Asociación Española Contra el Cáncer (AECC Scientific Foundation) Rare Tumor Calls 2017 (to M.L.M, J.M.B., M.A.A., J.J.G.M.), La Caixa Foundation Program (to M.L.M and J.M.B.), 2018 BBVA Foundation Grants for Scientific Research Teams (to M.L.M.-C.), Ayudas para apoyar grupos de investigación del sistema Universitario Vasco IT971-16 (P.A.). MyFirst Grant AIRC n.16888, Ricerca Finalizzata Ministero della Salute RF-2016-02364358, Ricerca corrente Fondazione IRCCS Ca’ Granda Ospedale Maggiore Policlinico (to LV), the European Union (EU) Programme Horizon 2020 (under grant agreement No. 777377) for the project LITMUS- “Liver Investigation: Testing Marker Utility in Steatohepatitis” (to LV), Fondazione IRCCS Ca’ Granda “Liver BIBLE” PR-0391, Fondazione IRCCS Ca’ Granda core COVID-19 Biobank (RC100017A) (to LV). This research was funded by the CIBERehd (EHD15PI05/2016) and “Fondo de Investigaciones Sanitarias, Instituto de Salud Carlos III”, Spain (PI16/00598 and PI19/00819, co-funded by European Regional Development Fund/European Social Fund, “Investing in your future”); Spanish Ministry of Economy, Industry and Competitiveness (SAF2016-75197-R); “Junta de Castilla y Leon” (SA063P17); AECC Scientific Foundation (2017/2020), Spain; “Centro Internacional sobre el Envejecimiento” (OLD-HEPAMARKER, 0348_CIE_6_E), Spain; University of Salamanca Foundation, Spain (PC-TCUE18-20_051), and Fundació Marato TV3 (Ref. 201916–31), Spain. RB acknowledges BFU2017-84653-P (MINECO/FEDER, EU), SEV-2016-0644 (Severo Ochoa Excellence Program), 765445-EU (UbiCODE Program), SAF2017-90900-REDT (UBIRed Program), and IT1165-19 (Basque Country Government). Ciberehd_ISCIII_MINECO is funded by the Instituto de Salud Carlos III. We thank MINECO for the Severo Ochoa Excellence Accreditation to CIC bioGUNE (SEV-2016-0644)S