NEDD8 | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Aliases | NEDD8 , NEDD-8, neural precursor cell expressed, developmentally down-regulated 8, NEDD8 ubiquitin like modifier | ||||||||||||||||||||||||||||||||||||||||||||||||||
External IDs | OMIM: 603171 MGI: 97301 HomoloGene: 4485 GeneCards: NEDD8 | ||||||||||||||||||||||||||||||||||||||||||||||||||
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NEDD8 is a protein that in humans is encoded by the NEDD8 gene. [5] [6] (in Saccharomyces cerevisiae this protein is known as Rub1) This ubiquitin-like (UBL) protein becomes covalently conjugated to a limited number of cellular proteins, in a process called NEDDylation similar to ubiquitination. Human NEDD8 shares 60% amino acid sequence identity to ubiquitin. The primary known substrates of NEDD8 modification are the cullin subunits of cullin-based E3 ubiquitin ligases, which are active only when NEDDylated. Their NEDDylation is critical for the recruitment of E2 to the ligase complex, thus facilitating ubiquitin conjugation. NEDD8 modification has therefore been implicated in cell cycle progression and cytoskeletal regulation.
As with ubiquitin and SUMO, NEDD8 is conjugated to cellular proteins after its C-terminal tail is processed. The NEDD8 activating E1 enzyme is a heterodimer composed of APPBP1 and UBA3 subunits. [7] The APPBP1/UBA3 enzyme has homology to the N- and C-terminal halves of the ubiquitin E1 enzyme, respectively. The UBA3 subunit contains the catalytic center and activates NEDD8 in an ATP-dependent reaction by forming a high-energy thiolester intermediate. The activated NEDD8 is subsequently transferred to the UbcH12 E2 enzyme, and is then conjugated to specific substrates in the presence of the appropriate E3 ligases.
As reviewed by Brown et al., [8] the best-characterized activated-NEDD8 substrates are the cullins (CUL1, 2, 3, 4A, 4B, 5, and 7 and PARC in human cells), that serve as molecular scaffolds for cullin-RING ubiquitin ligases (CRLs). Neddylation results in covalent conjugation of a NEDD8 moiety onto a conserved cullin lysine residue. [9] Cullin neddylation increases CRL ubiquitylation activity via conformational changes that optimize ubiquitin transfer to target proteins
There are several different proteases which can remove NEDD8 from protein conjugates. UCHL1, UCHL3 and USP21 proteases have dual specificity for NEDD8 and ubiquitin. Proteases specific for NEDD8 removal are the COP9 signalosome which removes NEDD8 from the CUL1 subunit of SCF ubiquitin ligases, and NEDP1 (or DEN1, SENP8). [10]
As shown by Brown et al., [8] NEDD8 accumulation at DNA-damage sites is a highly dynamic process. Neddylation is needed during a short period of the global genome repair (GGR) sub-pathway of DNA nucleotide excision repair (NER). In GGR of NER, after DNA damage is caused by UV irradiation, Cul4A in the DNA damage binding protein 2 (DDB2) complex is activated by NEDD8, and this allows GGR-NER to proceed to remove the damage. [11]
Neddylation also has a role in repair of double-strand breaks. [8] Non-homologous end joining(NHEJ) is a DNA repair pathway frequently used to repair DNA double-strand breaks. The first step in this pathway depends on the Ku70/Ku80 heterodimer that forms a highly stable ring structure encircling DNA ends. [12] But the Ku heterodimer needs to be removed when NHEJ is completed, or it blocks transcription or replication. The Ku heterodimer is ubiquitylated in a DNA-damage and neddylation-dependent manner to promote the release of Ku and other NHEJ factors from the site of repair after the process is completed. [8]
As discussed by Jin and Roberston in their review, [13] silencing of a DNA repair gene by hypermethylation of its promoter may be a very early step in progression to cancer. Gene silencing of a DNA repair gene at the transcription level is proposed to act similarly to a germ-line mutation in a DNA repair gene. Loss of DNA repair capability by either mechanism introduces genome instability and predisposes the cell and its descendants to progression to cancer. Epigenetically silenced DNA repair genes occur frequently in the 17 most common cancers (see e.g. Frequency of hypermethylation of DNA repair genes in cancer). [13]
As discussed above, activated-NEDD8 is needed in two DNA repair pathways: NER and NHEJ. If activation of NEDD8 is inhibited, cells with induced deficiency of NER or NHEJ may then die because of deficient DNA repair leading to accumulation of DNA damages. The effect of NEDD8 inhibition may be greater for cancer cells than for normal cells if the cancer cells are independently deficient in DNA repair due to prior epigenetic silencing of DNA repair genes active in alternative pathways (see synthetic lethality).
Pevonedistat (MLN4924), a drug inhibiting activation of NEDD8, has shown a significant therapeutic effect in four Phase I clinical cancer trials in 2015-2016. These include pevonedistat trials against acute myeloid leukemia and myelodysplastic syndromes, [14] relapsed/refractory multiple myeloma or lymphoma, [15] metastatic melanoma, [16] and advanced solid tumors. [17]
PPARγ has a crucial role in adipogenesis and lipid accumulation within adipocytes (fat cells). [18] Activated NEDD8 stabilizes PPARγ, allowing increased adipogenesis. In experiments with mice, Pevonedistat, a drug inhibiting activation of NEDD8, prevented high-fat diet-induced obesity and glucose intolerance. [18]
The transcriptional activity of NF-κB is primarily regulated by physical interaction with inhibitory IκB proteins (IκBα and IκBβ), which prevents its nuclear translocation. [19] Degradation of the IκBα subunit of IκB is mediated by ubiquitination, and this ubiquitination depends on neddylation. [20] Pevonedistat (MLN4924) inhibits activation of NEDD8, that then inhibits ubiquitination of IκBα, and this inhibits NF-κB translocation to the nucleus. [19]
Pevonedistat, through its effects on NF-κB and a target of NF-κB (microRNA-155), prolonged the survival of mice engrafted with leukemic cells. [19]
Inhibition of NEDD8 activation by pevonedistat was found to induce growth arrest and apoptosis in 16/122 (13%) colorectal cancer (CRC) cell lines. Further analyses in patient-derived tumor xenografts revealed that pevonedistat is effective on poorly differentiated, high-grade mucinous CRC. [21]
NEDD8 has been shown to interact with:
Ubiquitin is a small regulatory protein found in most tissues of eukaryotic organisms, i.e., it is found ubiquitously. It was discovered in 1975 by Gideon Goldstein and further characterized throughout the late 1970s and 1980s. Four genes in the human genome code for ubiquitin: UBB, UBC, UBA52 and RPS27A.
Ubiquitin-like modifier activating enzyme 1 (UBA1) is an enzyme which in humans is encoded by the UBA1 gene. UBA1 participates in ubiquitination and the NEDD8 pathway for protein folding and degradation, among many other biological processes. This protein has been linked to X-linked spinal muscular atrophy type 2, neurodegenerative diseases, and cancers.
Cullin 1, also known as CUL1, is a human protein and gene from cullin family. This protein plays an important role in protein degradation and protein ubiquitination.
RING-box protein 1 is a protein that in humans is encoded by the RBX1 gene.
Cullin-4A is a protein that in humans is encoded by the CUL4A gene. CUL4A belongs to the cullin family of ubiquitin ligase proteins and is highly homologous to the CUL4B protein. CUL4A regulates numerous key processes such as DNA repair, chromatin remodeling, spermatogenesis, haematopoiesis and the mitotic cell cycle. As a result, CUL4A has been implicated in several cancers and the pathogenesis of certain viruses including HIV. A component of a CUL4A complex, Cereblon, was discovered to be a major target of the teratogenic agent thalidomide.
Cullin-5 is a protein that in humans is encoded by the CUL5 gene.
Cullin-2 is a protein that in humans is encoded by the CUL2 gene.
Ubiquitin-conjugating enzyme E2 D1 is a protein that in humans is encoded by the UBE2D1 gene.
Cullin-4B is a protein that in humans is encoded by the CUL4B gene which is located on the X chromosome. CUL4B has high sequence similarity with CUL4A, with which it shares certain E3 ubiquitin ligase functions. CUL4B is largely expressed in the nucleus and regulates several key functions including: cell cycle progression, chromatin remodeling and neurological and placental development in mice. In humans, CUL4B has been implicated in X-linked intellectual disability and is frequently mutated in pancreatic adenocarcinomas and a small percentage of various lung cancers. Viruses such as HIV can also co-opt CUL4B-based complexes to promote viral pathogenesis. CUL4B complexes containing Cereblon are also targeted by the teratogenic drug thalidomide.
Cullin 3 is a protein that in humans is encoded by the CUL3 gene.
Ubiquitin-conjugating enzyme E2 D3 is a protein that in humans is encoded by the UBE2D3 gene.
NEDD8-activating enzyme E1 regulatory subunit is a protein that in humans is encoded by the NAE1 gene.
NEDD8-activating enzyme E1 catalytic subunit is a protein that in humans is encoded by the UBA3 gene.
NEDD8 ultimate buster 1 is a protein that in humans is encoded by the NUB1 gene.
Ubiquitin-conjugating enzyme E2 C is a protein that in humans is encoded by the UBE2C gene.
E3 ubiquitin-protein ligase RNF8 is an enzyme that in humans is encoded by the RNF8 gene. RNF8 has activity both in immune system functions and in DNA repair.
NEDD8-conjugating enzyme Ubc12 is a protein that in humans is encoded by the UBE2M gene.
Sentrin-specific protease 8 is an enzyme that in humans is encoded by the SENP8 gene.
Cullins are a family of hydrophobic scaffold proteins which provide support for ubiquitin ligases (E3). All eukaryotes appear to have cullins. They combine with RING proteins to form Cullin-RING ubiquitin ligases (CRLs) that are highly diverse and play a role in myriad cellular processes, most notably protein degradation by ubiquitination.
Ubiquitin-like proteins (UBLs) are a family of small proteins involved in post-translational modification of other proteins in a cell, usually with a regulatory function. The UBL protein family derives its name from the first member of the class to be discovered, ubiquitin (Ub), best known for its role in regulating protein degradation through covalent modification of other proteins. Following the discovery of ubiquitin, many additional evolutionarily related members of the group were described, involving parallel regulatory processes and similar chemistry. UBLs are involved in a widely varying array of cellular functions including autophagy, protein trafficking, inflammation and immune responses, transcription, DNA repair, RNA splicing, and cellular differentiation.