CAND1 controls in vivo dynamics of the Cullin 1-RING ubiquitin ligase repertoire

Signal Transduction Program, Sanford-Burnham Medical Research Institute, La Jolla, California 92037, USA.
Nature Communications (Impact Factor: 11.47). 03/2013; 4:1642. DOI: 10.1038/ncomms2636
Source: PubMed


The combinatorial architecture of cullin 1-RING ubiquitin ligases, in which multiple F-box containing substrate receptors compete for access to CUL1, poses special challenges to assembling cullin 1-RING ubiquitin ligase complexes through high affinity protein interactions while maintaining the flexibility to dynamically sample the entire F-box containing substrate receptor repertoire. Here, using highly quantitative mass spectrometry, we demonstrate that this problem is addressed by CAND1, a factor that controls the dynamics of the global cullin 1-RING ubiquitin ligase network by promoting the assembly of newly synthesized F-box containing substrate receptors with CUL1-RBX1 core complexes. Our studies of in vivo cullin 1-RING ubiquitin ligase dynamics and in vitro biochemical findings showing that CAND1 can displace F-box containing substrate receptors from Cul1p suggest that CAND1 functions in a cycle that serves to exchange F-box containing substrate receptors on CUL1 cores. We propose that this cycle assures comprehensive sampling of the entire F-box containing substrate receptor repertoire in order to maintain the cullin 1-RING ubiquitin ligase landscape, a function that we show to be critical for substrate degradation and normal physiology.

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Available from: Dieter A. Wolf, Aug 13, 2014
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    • "As its name already reveals, CAND1 was identified as an interactor of non-neddylated cullins (Liu et al., 2002; Zheng et al., 2002; Oshikawa et al., 2003). Through a series of elegant experiments from at least three independent laboratories it was recently shown that CAND1 functions as a novel type of exchange factor for CRLs (Pierce et al., 2013; Wu et al., 2013; Zemla et al., 2013). In a highly quantitative and not only therefore remarkable analysis of the diverse protein–protein interactions that can take place between the subunits of SCF-type CRL complexes and CAND1, it could be shown that CAND1 can promote the disassembly of SCF complexes and that FBPs can remove CAND1 from CULLIN1 (Pierce et al., 2013; Figure 4). "
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    ABSTRACT: NEDD8, in plants and yeasts also known as RELATED TO UBIQUITIN (RUB), is an evolutionarily conserved 76 amino acid protein highly related to ubiquitin. Like ubiquitin, NEDD8 can be conjugated to and deconjugated from target proteins, but unlike ubiquitin, NEDD8 has not been reported to form chains similar to the different polymeric ubiquitin chains that have a role in a diverse set of cellular processes. NEDD8-modification is best known as a post-translational modification of the cullin subunits of cullin-RING E3 ubiquitin ligases. In this context, structural analyses have revealed that neddylation induces a conformation change of the cullin that brings the ubiquitylation substrates into proximity of the interacting E2 conjugating enzyme. In turn, NEDD8 deconjugation destabilizes the cullin RING ligase complex allowing for the exchange of substrate recognition subunits via the exchange factor CAND1. In plants, components of the neddylation and deneddylation pathway were identified based on mutants with defects in auxin and light responses and the characterization of these mutants has been instrumental for the elucidation of the neddylation pathway. More recently, there has been evidence from animal and plant systems that NEDD8 conjugation may also regulate the behavior or fate of non-cullin substrates in a number of ways. Here, the current knowledge on NEDD8 processing, conjugation and deconjugation is presented, where applicable, in the context of specific signaling pathways from plants.
    Frontiers in Plant Science 03/2014; 5:103. DOI:10.3389/fpls.2014.00103 · 3.95 Impact Factor
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    • "The variety of these mechanisms provides the means to upregulate required FBPs in response to intrinsic and extrinsic signals, while continually clearing those that are no longer required, ensuring that the available pool addresses the needs of the cell at any given time. The mechanism by which one FBP is ‘switched-out’ and replaced by another has recently been reported and is controlled by the ‘exchange factor’ Cand1 [27,28]. By increasing the dissociation rate of Skp1 : FBP complexes from the cullin scaffold, without affecting the kinetics of its reassembly, Cand1 keeps the spectrum of SCF activity within the cell dynamic and capable of responding to a changing cellular environment. "
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    ABSTRACT: F-box proteins (FBPs) are substrate-recruiting subunits of Skp1-cullin1-FBP (SCF)-type E3 ubiquitin ligases. To date, 69 FBPs have been identified in humans, but ubiquitinated substrates have only been identified for a few, with the majority of FBPs remaining 'orphans'. In recent years, a growing body of work has identified non-canonical, SCF-independent roles for about 12% of the human FBPs. These atypical FBPs affect processes as diverse as transcription, cell cycle regulation, mitochondrial dynamics and intracellular trafficking. Here, we provide a general review of FBPs, with a particular emphasis on these expanded functions. We review Fbxo7 as an exemplar of this special group as it has well-defined roles in both SCF and non-SCF complexes. We review its function as a cell cycle regulator, via its ability to stabilize p27 protein and Cdk6 complexes, and as a proteasome regulator, owing to its high affinity binding to PI31. We also highlight recent advances in our understanding of Fbxo7 function in Parkinson's disease, where it functions in the regulation of mitophagy with PINK1 and Parkin. We postulate that a few extraordinary FBPs act as platforms that seamlessly segue their canonical and non-canonical functions to integrate different cellular pathways and link their regulation.
    Open Biology 10/2013; 3(10):130131. DOI:10.1098/rsob.130131 · 5.78 Impact Factor
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    • "It has become increasingly clear that NEDD8 plays numerous roles in altering the activities of CRLs. Aside from its well-established role as a multimodal activator of CRL complex activity (Saha and Deshaies, 2008; Duda et al, 2011), NEDD8 also plays a pivotal role in governing the exchange of F-box protein containing substrate receptors via its antagonism of CAND1 binding (Pierce et al, 2013; Wu et al, 2013; Zemla et al, 2013; and additional references therein), as well as interacting with additional protein partners to direct CRLs to other machineries involved in substrate degradation, such as the p97 segregase (Bandau et al, 2012; den Besten et al, 2012). Here, we show that NEDD8 is also important for targeting specific CRLs to members of the Ariadne subfamily of RBR E3 ligases. "
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    ABSTRACT: RING (Really Interesting New Gene)-in-between-RING (RBR) enzymes are a distinct class of E3 ubiquitin ligases possessing a cluster of three zinc-binding domains that cooperate to catalyse ubiquitin transfer. The regulation and biological function for most members of the RBR ligases is not known, and all RBR E3s characterized to date are auto-inhibited for in vitro ubiquitylation. Here, we show that TRIAD1 and HHARI, two members of the Ariadne subfamily ligases, associate with distinct neddylated Cullin-RING ligase (CRL) complexes. In comparison to the modest E3 ligase activity displayed by isolated TRIAD1 or HHARI, binding of the cognate neddylated CRL to TRIAD1 or HHARI greatly stimulates RBR ligase activity in vitro, as determined by auto-ubiquitylation, their ability to stimulate dissociation of a thioester-linked UBCH7∼ubiquitin intermediate, and reactivity with ubiquitin-vinyl methyl ester. Moreover, genetic evidence shows that RBR ligase activity impacts both the levels and activities of neddylated CRLs in vivo. Cumulatively, our work proposes a conserved mechanism of CRL-induced Ariadne RBR ligase activation and further suggests a reciprocal role of this special class of RBRs as regulators of distinct CRLs.
    The EMBO Journal 09/2013; 32(21). DOI:10.1038/emboj.2013.209 · 10.43 Impact Factor
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