SUMO-1 modification of IkappaBalpha inhibits NF-kappaB activation

School of Biomedical Science, University of St. Andrews, Fife, United Kingdom.
Molecular Cell (Impact Factor: 14.02). 09/1998; 2(2):233-9.
Source: PubMed


Activation of NF-kappaB is achieved by ubiquitination and proteasome-mediated degradation of IkappaBalpha. We have detected modified IkappaBalpha, conjugated to the small ubiquitin-like protein SUMO-1, which is resistant to signal-induced degradation. In the presence of an E1 SUMO-1-activating enzyme, Ubch9 conjugated SUMO-1 to IkappaBalpha primarily on K21, which is also utilized for ubiquitin modification. Thus, SUMO-1-modified IkappaBalpha cannot be ubiquitinated and is resistant to proteasome-mediated degradation. As a result, overexpression of SUMO-1 inhibits signal-induced activation of NF-kappaB-dependent transcription. Unlike ubiquitin modification, which requires phosphorylation of S32 and S36, SUMO-1 modification of IkappaBalpha is inhibited by phosphorylation. Thus, while ubiquitination targets proteins for rapid degradation, SUMO-1 modification acts antagonistically to generate proteins resistant to degradation.

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Available from: Manuel S. Rodriguez, Aug 22, 2014
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    • "Like other PTMs, SUMOylation is reversible and the conjugation/deconjugation mechanisms are reminiscent of the ubiquitin pathway (Muller et al., 2001). In contrast to ubiquitination though, SUMOylation does not directly target proteins for degradation but rather regulates other functions such as nuclear localization, protein–protein interactions, transcriptional activity and, interestingly, ubiquitination itself (Desterro et al., 1998; Buschmann et al., 2000). SUMOylation was first implicated in the clock following the discovery of a SUMOylation consensus motif in BMAL1 (Cardone et al., 2005). "
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    ABSTRACT: Circadian rhythms, endogenous cycles of about 24 h in physiology, are generated by a master clock located in the suprachiasmatic nucleus of the hypothalamus and other clocks located in the brain and peripheral tissues. Circadian disruption is known to increase the incidence of various illnesses, such as mental disorders, metabolic syndrome, and cancer. At the molecular level, periodicity is established by a set of clock genes via autoregulatory translation-transcription feedback loops. This clock mechanism is regulated by post-translational modifications such as phosphorylation and ubiquitination, which set the pace of the clock. Ubiquitination in particular has been found to regulate the stability of core clock components but also other clock protein functions. Mutation of genes encoding ubiquitin ligases can cause either elongation or shortening of the endogenous circadian period. Recent research has also started to uncover roles for deubiquitination in the molecular clockwork. Here, we review the role of the ubiquitin pathway in regulating the circadian clock and we propose that ubiquitination is a key element in a clock protein modification code that orchestrates clock mechanisms and circadian behavior over the daily cycle.
    Frontiers in Molecular Neuroscience 08/2014; 7:69. DOI:10.3389/fnmol.2014.00069 · 4.08 Impact Factor
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    • "Several studies have implicated sumoylation in regulation of stability of its target proteins [28], [29]. In order to test whether sumoylation may impact on Ago2 stability, we first compared the half-lives of wild-type Ago2, Ago2-K402R and Ago2-4KR by performing cycloheximide (CHX) time-course experiments upon transfection into HeLa cells. "
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    ABSTRACT: Gene silencing by small RNAs has emerged as a powerful post-transcriptional regulator of gene expression, however processes underlying regulation of the small RNA pathway in vivo are still largely elusive. Here, we identified sumoylation as a novel post-translational modification acting on Ago2, the main effector of small RNA-mediated gene silencing. We demonstrate that Ago2 can be modified by SUMO1 and SUMO2/3 and identified Lys402 as the major Ago2 sumoylation site in vivo. Ago2 physically interacts with the SUMO E2 conjugating enzyme Ubc9 and the E3 ligase RanBP2 facilitates Ago2 sumoylation in vitro. Mutation of Lys402 enhances the stability of Ago2 protein and impairment of cellular sumoylation by siRNA- or shRNA-mediated extinction of Ubc9 or in Ubc9 knockout mouse tissues results in increased steady-state levels and enhanced stability of Ago2. Similarly, knockdown of RanBP2 or of the SAE2 E1 enzyme enhances Ago2 protein levels. Lys402 is located in the L2g1 loop linking the PAZ and PIWI domains of Ago2, in the immediate vicinity of Tyr393 which can be phosphorylated, implying that the L2g1 linker represents an easily accessible hot spot for post-translational modifications. Altogether, our results show that sumoylation of Ago2 at Lys402 negatively regulates its stability, thereby establishing a first link between SUMO and the small RNA machinery.
    PLoS ONE 07/2014; 9(7):e102957. DOI:10.1371/journal.pone.0102957 · 3.23 Impact Factor
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    • "This could occur via three mechanisms: i) Stabilisation of BET-1 expression levels; ii) increase in BET-1’s affinity to acetylated histones; or iii) increase in BET-1’s capacity to access acetylated histones. i) As a small ubiquitine like modifier, SUMO can compete with ubiquitination and can protect against degradation [56]. ii) Addition of a SUMO peptide to a protein can cause conformational changes enhancing affinity for its target [57]. "
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    ABSTRACT: Attenuation of RAS/RAF/MAPK signalling is essential to prevent hyperactivation of this oncogenic pathway. In C. elegans, the sumoylation pathway and a combination of histone tail modifications regulate gene expression to attenuate the LET-60 (RAS) signalling pathway. We hypothesised that a number of chromatin regulators are likely to depend on sumoylation to attenuate the pathway. To reveal these, we designed an RNAi-based dimorphic genetic screen that selects candidates based on their ability to act as enhancers of a sumo mutant phenotype, such interactions would suggest that the candidates may be physically associated with sumoylation. We found 16 enhancers, one of which BET-1, is a conserved double bromodomain containing protein. We further characterised BET-1 and showed that it can physically associate with SMO-1 and UBC-9, and that it can be sumoylated in vitro within the second bromodomain at lysine 252. Previous work has shown that BET-1 can bind acetyl-lysines on histone tails to influence gene expression. In conclusion, our screening approach has identified BET-1 as a Sumo-dependent attenuator of LET-60-mediated signalling and our characterisation suggests that BET-1 can be sumoylated.
    PLoS ONE 12/2013; 8(12):e83659. DOI:10.1371/journal.pone.0083659 · 3.23 Impact Factor
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