Regulation of Cullin RING Ligases

Abstract

The ubiquitin/26S proteasome pathway largely mediates selective proteolysis in the nucleus and cytosol. This pathway catalyzes covalent attachment of ubiquitin (UBQ) to substrate proteins in an E1-E2-E3 cascade. Ubiquitin E3 ligases interact with substrates to catalyze UBQ transfer from E2 to substrate. Within the E3 ligase superfamily, cullin RING ligases (CRLs) are significant in plants because they are linked to hormonal signaling, developmental programs, and environmental responses. Thus, knowledge of CRL regulation is required for a complete understanding of these processes. A major mechanism modulating CRL activity is modification of the cullin subunit by RUB (RELATED TO UBIQUITIN), a ubiquitin-like protein, and demodification by the COP9 signalosome (CSN). CULLIN-ASSOCIATED NEDD8-DISSOCIATED 1 (CAND1) interacts with CRLs, affecting both rubylation and derubylation. Described here are the pathways, regulation, and biological function of rubylation and derubylation, as well as future directions and outstanding questions.

MLN4924 Is an Efficient Inhibitor of NEDD8 Conjugation in Plants

“…NEDD8 is conjugated to target proteins via an enzymatic cascade that is composed of an E1 NEDD8-activating enzyme (a heterodimer composed of NEDD8-ACTIVATING EN-ZYME1 [NAE1] and a UBA3 subunit), an E2 conjugating enzyme (Ubc12p), and an E3 ligase (RING BOX1 [RBX1] or DEFECTIVE IN CULLIN NEDDYLATION1; Gong and Yeh, 1999;Gray et al, 2002;Kurz et al, 2005). Neddylation is best studied as a posttranslational modification of the cullin (CUL) subunits of CUL-RING-type E3 ubiquitin ligases (CRLs; Hori et al, 1999), where it has been shown that neddylation is important for the proper enzymatic function of CRLs (Hotton and Callis, 2008). CRLs are evolutionarily conserved E3 ligase complexes that share the CUL and RBX1 subunits and that, depending on the identity of the CUL subunit, associate with different adaptor and degradation substrate receptor modules, such as S-PHASE KINASE-ASSOCIATED PROTEIN1 (SKP1) and F-box proteins to form CUL1-containing SCF-type E3 ligases or DNA DAMAGE-BINDING PROTEIN1 (DDB1) and DDB1-CUL4-ASSOCIATED FACTOR (DCAF) subunits to form CUL4-containing DCAF E3s (Hotton and Callis, 2008;Deshaies and Joazeiro, 2009).…”

“…Neddylation is best studied as a posttranslational modification of the cullin (CUL) subunits of CUL-RING-type E3 ubiquitin ligases (CRLs; Hori et al, 1999), where it has been shown that neddylation is important for the proper enzymatic function of CRLs (Hotton and Callis, 2008). CRLs are evolutionarily conserved E3 ligase complexes that share the CUL and RBX1 subunits and that, depending on the identity of the CUL subunit, associate with different adaptor and degradation substrate receptor modules, such as S-PHASE KINASE-ASSOCIATED PROTEIN1 (SKP1) and F-box proteins to form CUL1-containing SCF-type E3 ligases or DNA DAMAGE-BINDING PROTEIN1 (DDB1) and DDB1-CUL4-ASSOCIATED FACTOR (DCAF) subunits to form CUL4-containing DCAF E3s (Hotton and Callis, 2008;Deshaies and Joazeiro, 2009). NEDD8 is hydrolyzed from target proteins by CUL-deneddylating enzymes including subunit 5 of the CONSTITUTIVELY PHOTORMOPHOGENIC9 SIGNALOSOME Schwechheimer et al, 2001;Cope et al, 2002) or the deneddylase DEN1 Wu et al, 2003).…”

PEST sequences mediate heat shock factor 2 turnover by interacting with the Cul3 subunit of the Cul3-RING ubiquitin ligase

“…It has previously been shown that this can be mediated by interaction between substrate proteins and BTB domain-containing subunits of the ubiquitin ligase complexes (Bosu and Kipreos 2008;Hotton and Callis 2008;Petroski and Deshaies 2005;Sumara et al 2008). However, our results indicate that recruitment can also occur by interaction between PEST sequences in a substrate protein, in this case HSF2, and the Cul3 subunit of the Cul3-RING ligase complexes.…”

“…Cul3, a member of the Cullin family of proteins, is a subunit of a Cullin-RING ubiquitin E3 ligase complex that polyubiquitinates many important proteins, leading to their degradation by the proteasome (Bosu and Kipreos 2008;Hotton and Callis 2008;Petroski and Deshaies 2005;Sumara et al 2008). Cul3-containing ubiquitin ligases have been found to play important roles in the regulation of mitosis, development, cytoskeletal proteins, and transcription factors (Pintard et al 2004;Sumara et al 2008;.…”

E3 ubiquitin ligases and abscisic acid signaling

“…In Arabidopsis, five canonical cullin proteins (CUL1, CUL2, CUL3a, CUL3b and CUL4) have been shown to be components of E3 ligase complexes. 18 Based on the combination of cullin and substrate recognition subunit, CRLs are divided into three broad categories: SKP-Cullin-F-box (SCF), in which CUL1 or CUL2 interacts with the substrate recognition F-box protein via an adaptor, S-Phase-kinase-Associated Protein 1 (SKP1); BTB-CUL3-RBX1 (BCR), in which CUL3a or CUL3b interacts directly with substrate recognition proteins that contain a Broadcomplex, Tramtrack, Bric-a-Brac/Poxvirus and Zinc Finger (BTB/POZ) domain; CUL4-based ligases which utilize DNADamage Binding 1 (DDB1) as an adaptor to incorporate substrate recognition proteins DDB1-BINDING WD40 (DWD) or DDB1 and CUL4-ASSOCIATED Factor (DCAF) into the complex. 18 Although only two Arabidopsis RING domaincontaining proteins (RBX1a and RBX1b) have been discovered which serve as the E2 binding subunit of CRLs, the substrate recognition subunits are highly versatile, which greatly increases the number of potential CRLs.…”