The Ubiquitin-Proteasome System (UPS) is an important regulator of cell signaling and proteostasis, which are essential to a variety of cellular processes. The UPS is disrupted in many diseases including cancer, and targeting the UPS for cancer therapy is gaining wide interest. E3 ubiquitin ligases occupy a key position in the hierarchical UPS enzymatic cascade, largely responsible for determining substrate specificity and ubiquitin (Ub) chain topology. The E3 ligase UBR5 (aka EDD1) is emerging as a key regulator of the UPS in cancer and development. UBR5 expression is deregulated in many cancer types and UBR5 is frequently mutated in mantle cell lymphoma. UBR5 is highly conserved in metazoans, has unique structural features, and has been implicated in regulation of DNA damage response, metabolism, transcription, and apoptosis. Hence, UBR5 is a key regulator of cell signaling relevant to broad areas of cancer biology. However, the mechanism by which UBR5 may contribute to tumor initiation and progression remains poorly defined. This review synthesizes emerging insights from genetics, biochemistry, and cell biology to inform our understanding of UBR5 in cancer. These molecular insights indicate a role for UBR5 in integrating/coordinating various cellular signaling pathways. Finally, we discuss outstanding questions in UBR5 biology and highlight the need to systematically characterize substrates, and address limitations in current animal models, to better define the role of UBR5 in cancer. Mol Cancer Res; 13(12); 1523–32. ©2015 AACR.

Ubiquitination is one of the most widespread and frequent cellular posttranslational modifications (PTM) and is essential for normal cellular functions. Ubiquitination can regulate protein levels via degradation by the proteasome (1, 2), regulate protein–protein interactions, and modulating protein function and localization (3, 4). The small protein modifier Ubiquitin (Ub) forms an isopeptide bond with substrate proteins via acceptor lysine residues in a hierarchical enzymatic reaction catalyzed by an E3 Ub ligase (5). Much variety in Ub modification of substrate proteins arises from the ability of Ub to form either single conjugates (mono-ubiquitination) or chains (poly-ubiquitination) after repeated rounds of Ub attachment (6). Further complexity and diversity in Ub PTMs is generated by variation in Ub chain topology, depending on which Ub lysine residue is further ubiquitinated on the growing poly-Ub chain. Various poly-Ub chain topologies are known to effect different signaling outcomes via binding to specific adaptor proteins [reviewed elsewhere (4)]. Specificity of the Ubiquitin-Proteasome System (UPS) is largely determined by the approximately 617 (human) E3 Ub ligases (7), but significant pleiotropy and redundancy among E3 Ub ligases provides tissue specificity and fine-scale regulation of signaling outputs (6).

Correct functioning of the UPS is essential for many cellular processes such as cell-cycle progression and apoptosis. Consequently, the UPS is the subject of intense interest for its therapeutic potential in many diseases including cancer [reviewed elsewhere (8)]. Currently, only broad-acting proteasome inhibitors are in clinical use. Proteasome inhibitors bortezomib (Velcade) and carfilzomib (Kyprolis) have reached phase II clinical trials for use in mantle cell lymphoma (MCL) and multiple myeloma (9–12), although use is associated with peripheral neuropathy (12, 13). The E3 ligase modulator Lenalidomide (Revlimid, an analogue of Thalidomide), is also used in treatment of multiple myeloma but has associated resistance and toxicity (14).

The UPS targets a large range of proteins with important roles in cancer biology. Therapeutic benefit with reduced toxicity might be obtained by targeting more specific aspects of the UPS. For example, Ub-specific proteases, an extensive class of de-ubiquitinating enzymes, have promise as therapeutic targets (15). Of comparable interest and specificity are the E3 Ub ligases, especially as key proteins commonly associated with proliferation and cell-cycle arrest (such as p53, p27, Cyclins, and NF-κB) are specifically regulated by these enzymes (16).

One of the more intriguing members of the E3 ligase family is UBR5 [Ubiquitin protein ligase E3 component n-recognin 5, also known as EDD (E3 identified by Differential Display), EDD1, HHYD, KIAA0896, or DD5]. UBR5 is highly conserved (17) and is essential for mammalian development (18). UBR5 is rarely mutated in healthy somatic tissues, but is mutated and/or overexpressed in cancer (19, 20). UBR5 is known to modulate the DNA damage response (DDR) and transcription (see below for detailed discussion), and emerging roles for UBR5 in a number of biologic contexts have been identified using high-throughput, functional genomics screens. This review will summarize the characterized and emerging biologic roles of UBR5, its role in tumorigenesis, and its potential as a therapeutic target.

UBR5 is a homologue of hyperplastic discs (HYD), a Drosophila melanogaster tumor suppressor (21). Mammalian UBR5 is a HECT (homologous to E6-associated protein at the carboxy-terminus) E3 Ub ligase recognizing n-degrons (see Fig. 1; refs. 17, 22). The human UBR5 gene has 59 exons, encoding an approximately 10 kb mRNA and >300 kDa protein with widespread expression in various cell types. One splice variant (loss of nucleotides 884–901, removing amino-acid sequence VLLLPL) has been identified in 26/26 cancer cell lines investigated (19), although numerous other splice variants are predicted in genome databases. The structural/functional consequences of these variants are not known. UBR5 is highly conserved, but appears to be restricted to the metazoan lineage, and based on phylogenetic analysis is grouped in a distinct class of HECT ligases (Class IV; ref. 23). Class IV likely evolved from a common ancestral gene duplication and includes UBR5/EDD and three other families that are highly divergent at the sequence level.

Figure 1.

Functional domains and known posttranslational modification sites of UBR5. Arrow in HECT domain indicates position of highly conserved catalytic cysteine. Other domains shown are Ubiquitin activation (UBA), nuclear localization sequence (NLS), the Ubiquitin Recognin Box (UBR), and the homologous to the C-terminal region of Poly-Adenylation Binding Protein (PABC/MLLE) domain.

Figure 1.

Functional domains and known posttranslational modification sites of UBR5. Arrow in HECT domain indicates position of highly conserved catalytic cysteine. Other domains shown are Ubiquitin activation (UBA), nuclear localization sequence (NLS), the Ubiquitin Recognin Box (UBR), and the homologous to the C-terminal region of Poly-Adenylation Binding Protein (PABC/MLLE) domain.

Close modal

HECT E3 Ub ligases have a well characterized mechanism, forming a thio-ester linkage between Ub and the substrate protein, a reaction highly dependent on a conserved cysteine within the HECT domain (24, 25). The catalytically active HECT domain of UBR5 is made up of N- and C-lobes separated by a linker sequence as determined by high-resolution crystallography (26). However, the HECT domain of UBR5 has some unique structural features compared with other HECT ligases. The C-lobe of the UBR5 HECT domain does not have a surface for noncovalent binding of Ub, and it is unclear if this exists in the N-lobe (a feature seen in other HECT E3 Ub ligases such as NEDD4, and thought to keep Ub in close proximity for building poly-Ub chains; ref. 26). Instead, UBR5 interacts with Ub via the UBA domain (27). UBR5 also has a zinc finger Ubiquitin Recognin Box (UBR) domain, thought to be involved in N-rule substrate recognition (28), two nuclear localization sequences (29), and an MLLE/PABC domain [homologous to the C-terminal region of Poly-Adenylation Binding Protein (30); Fig. 1]. The MLLE/PABC domain is thought to be a protein–protein interaction motif (e.g., known to bind substrates such as PAIP2; refs. 31, 32) and may regulate ubiquitin transfer catalyzed by the HECT domain (33).

Expression of UBR5 is responsive to progestin in human breast cancer cells, and shows varied expression in normal tissues (19). UBR5 is highly overexpressed in breast cancer at the mRNA level with increases in UBR5 protein also evident in many samples (19). This indicates that regulation of UBR5 is likely at the transcriptional level, though regulation of activity may also occur through PTM. Many phosphorylation sites have been identified in UBR5 (see Fig. 1; refs. 34–41), and UBR5 is known to be a phosphorylation target of ATM (42), CHK (43), and ERK kinases (44). However, this phosphorylation has not as yet been directly linked to UBR5 activity.

A number of studies have implicated UBR5 in various aspects of cancer biology and many of the molecular functions of UBR5 (e.g., DDR) are consistent with a role in cancer. Indeed, the Drosophila homologue Hyd was originally identified as a tumor suppressor gene (21). Human UBR5 was originally identified in a screen for progestin-regulated genes in breast cancer cells (17). Amplification of UBR5 has been reported in breast and ovarian cancer, mostly in the form of allelic imbalance resulting in increased UBR5 mRNA levels (19). UBR5 is located at genomic locus 8q22.3 (17), just downstream from MYC (8q22.4) but UBR5 amplification is independent of microsatellites examined in the more distal regions of the 8q arm (19). Provisional data from The Cancer Genome Atlas (TCGA) clearly show UBR5 amplification to be a common alteration in many cancer types (see Fig. 2A). UBR5 has been shown to mediate therapeutic resistance in ovarian cancer (20), likely through modulation of the DDR (see below). UBR5 was also identified in a transposon mutagenesis screen for cooperating mutations and pathways in pancreatic adenocarcinoma (45).

Figure 2.

UBR5 is commonly deregulated in many cancer types, with frequent amplification in breast cancer. A, UBR5 deregulation by cancer type [generated using cBioPortal analytical tool (97, 98) based upon data generated by the TCGA Research Network: http://cancergenome.nih.gov/, as of August 2014]. B, functional mutation spectrum of UBR5 by mutation type and location within UBR5 protein sequence, data from COSMIC (ref. 99; (cancer.sanger.ac.uk). Symbol size indicates relative mutation count. Note the tendency for frameshift and nonsense mutations toward carboxy-terminal region of UBR5 (associated with E3 Ub ligase function). C, survival analysis shows a strong survival disadvantage for patients with breast cancer with aberrations in UBR5 [generated using cBioPortal (97, 98) as above].

Figure 2.

UBR5 is commonly deregulated in many cancer types, with frequent amplification in breast cancer. A, UBR5 deregulation by cancer type [generated using cBioPortal analytical tool (97, 98) based upon data generated by the TCGA Research Network: http://cancergenome.nih.gov/, as of August 2014]. B, functional mutation spectrum of UBR5 by mutation type and location within UBR5 protein sequence, data from COSMIC (ref. 99; (cancer.sanger.ac.uk). Symbol size indicates relative mutation count. Note the tendency for frameshift and nonsense mutations toward carboxy-terminal region of UBR5 (associated with E3 Ub ligase function). C, survival analysis shows a strong survival disadvantage for patients with breast cancer with aberrations in UBR5 [generated using cBioPortal (97, 98) as above].

Close modal

Perhaps the most convincing evidence yet for an integral role for UBR5 in cancer comes from a recent study showing nonsynonymous mutations of UBR5 in 18% of MCL cases. Most of these mutations affected the conserved cysteine of the HECT domain, which would be expected to disrupt E3 ligase activity (46). Unfortunately, the embryonic lethality observed in Ubr5-null mice has precluded their use in cancer models but the development of conditional knockout models should make these studies more feasible.

Functional mutations in UBR5 may be more informative for inferring the biologic role of UBR5 in cancer. The COSMIC database contains details of published mutations throughout many cancer types (47). Point mutations occur frequently throughout the UBR5 open reading frame in cancer, and frameshift mutations tend to occur toward the PABC/HECT region, which would likely result in loss of E3 Ub ligase activity (see Fig. 2B). Loss of E3 Ub ligase activity in cancer suggests that UBR5-mediated ubiquitination has a tumor suppressive role. There is a clear overall survival advantage for breast cancer patients with normal UBR5 expression (provisional TCGA data; Fig. 2C).

UBR5 has been shown to directly interact with numerous proteins implicated in a wide variety of cellular processes, including the cell cycle, transcriptional and translational machinery, and the DDR. A list of currently known interacting proteins is shown in Table 1. Many of these are key to understanding the role of UBR5 in cancer development and progression.

Table 1.

UBR5 interacting proteins and substrates

UBR5 interacting proteins and substrates
UBR5 interacting proteins and substrates

Identification of E3 Ub ligase substrates is notoriously technically challenging and emerging systematic approaches hold great promise in this respect. Regardless, a subset of UBR5-interacting proteins have been validated as targets of UBR5 E3 Ub ligase activity, although many other interactions appear independent of E3 Ub ligase function, indicating that UBR5-mediated ubiquitination is tightly regulated and is likely context specific. Known targets of UBR5 ligase activity include the DDR proteins TopBP1 (48), RNF168 (49), and ATMIN (42), transcription factors β-catenin (50), pregnane X receptor (PXR; ref. 51), and E6-AP (52), translational machinery CDK9 (53) and PAIP2 (54), the KATNA1 subunit of the cell cycle–related protein KATANIN (55), and the rate limiting enzyme in gluconeogenesis PEPCK (56).

The first descriptions of a developmental role for UBR5 came from mutants of the UBR5 Drosophila homologue, hyperplastic discs [Hyd, otherwise known as I(3)c43]. These display a range of developmental phenotypes, including imaginal disc abnormalities (57), larval lethality, sterility (21), premature photoreceptor differentiation (58), failed oogenesis (59), defective spermatogenesis (60), and plasma membrane gap junction deficiency (61). The severity of these phenotypes appears dependent on the relative level of HYD protein in mutant animals (21). Functional studies identified that Hyd negatively regulates expression of Hedgehog (Hh) and Decapentaplegic (Dpp) in eye and wing discs. However the mechanism is complex and context specific (58). Recent studies suggest that Hyd regulates differential outputs of Hh signaling by directing selective association of Cubitis interruptus (Ci) with different promoters (62). Further, Hyd can coordinate Hh signaling by regulating Hh and Ci expression in concert with Shaggy (Sgg), the Drosophila orthologue of GSK3β (63).

In mice, homozygous deletion of Ubr5 causes embryonic lethality around E10.5 due to failed yolk sac and allantoic vascular development and failed chorioallantoic fusion (18). Although the molecular mechanism underlying this phenotype remains to be described, a cluster of UBR5-regulated genes was recently associated with vascular development. Specifically, vascular endothelial cell expression of UBR5 is necessary for normal vessel formation through a repressive effect on the angiogenic factor ACVRL (64).

The involvement of UBR5 in regulation of hedgehog signaling has not been investigated in mammalian models; however, depletion of Indian hedgehog disrupts murine vascular yolk sac development (65), and paracrine hedgehog signaling is involved in tumor angiogenesis via modulation of VEGF (66). Drosophila studies showing a role for Hyd in controlling Hh and Dpp signaling may also be relevant in this context, as both Hh (65) and BMP (67) signaling are key regulators of yolk sac vascular development. It remains to be determined if the role of UBR5 in vascular development has functional relevance to tumor angiogenesis.

The importance of UBR5 in development is further reinforced by results from a functional genomics screen identifying UBR5 as crucial for embryonic stem cells (ESC) growth (68). UBR5 was subsequently shown to regulate ESC self-renewal via maintenance of the pluripotency factor OCT4 (69). A key outstanding issue in understanding the role of UBR5 in regulating stem cell biology and development is to determine the role of E3 ligase activity in mediating these functions. Aside from its high conservation across species, perhaps the strongest indication for the importance of UBR5 in development comes from a systematic survey of loss-of-function (LoF) variants in human protein-coding genes by the Exome Aggregation Consortium (ExAC). UBR5 is one of the most highly conserved genes in this analysis, which identified just four LoF variants in UBR5 at very low allele frequencies [less than 1/10,000; ExAC, Cambridge, MA (http://exac.broadinstitute.org), June 2015]. A UBR5 missense mutation (c.5720G>A) was recently identified in affected individuals of a Japanese pedigree with familial adult myoclonic epilepsy, but not in any nonaffected family members or unrelated healthy residents of the pedigree's community (70). This mutation encodes a substitution at Arg1907 (Arg1907His), which is highly conserved across species but does not occur in any known functional domains.

The UPS is intimately involved at every stage of transcriptional control and it is now evident that transcriptional control is a key aspect of UBR5 function (see Fig. 3). These stages include: initiation of RNA transcription by transcription factors and their associated co-activators, which recruit the transcriptional machinery (RNA polymerase II/general transcription factors) to gene promoters [reviewed elsewhere (71)]; RNA elongation, which requires chromatin remodeling through the removal and re-deposition of histone proteins; and RNA processing and nuclear export [reviewed elsewhere (72)].

Figure 3.

Summary of well-characterized and emerging roles of UBR5. Arrows indicate upregulation or activation. Bars indicate downregulation or repression.

Figure 3.

Summary of well-characterized and emerging roles of UBR5. Arrows indicate upregulation or activation. Bars indicate downregulation or repression.

Close modal

UBR5 was first identified as a target gene of the progesterone receptor (PR), a member of the nuclear receptor family of ligand (e.g., steroid hormones, retinoic acid, thyroid hormone, etc.) induced DNA binding transcription factors (29). Interestingly, UBR5 enhanced the transcriptional activity of the PR itself (29). It is now evident that UBR5 has similar effects on several other nuclear receptors through a variety of mechanisms, which in some (but not all) cases involve the E3 ligase activity of UBR5, and which either directly target the receptor or alternatively other proteins in the receptor transcriptional complex.

A screen of potential transcriptional modulators found UBR5 was a negative regulator of estrogen receptor α (ERα) protein levels and activity. This action was dependent on ubiquitination and an intact UBR5 HECT domain, but ubiquitination of ER was independent of ligand occupancy. Depletion of UBR5 in MCF-7 breast cancer cells resulted in increased endogenous ER levels, an estradiol-induced increase in transcription of GREB1 and CCND1 (ER target genes), as well as increased cell proliferation (73). UBR5 is also a negative regulator of PXR (an orphan nuclear receptor) transcriptional activity. UBR5 together with dual-specificity tyrosine phosphorylation-regulated kinase 2 (DYRKK2) are found in a multiprotein complex with PXR. Phosphorylation of PXR by DYRKK2 facilitates its ubiquitination by UBR5, resulting in reduced PXR protein levels and activity (51).

In T-helper (TH17) cells, production of the pro-inflammatory cytokine IL17 is regulated by the transcription factor RORγt, an orphan nuclear receptor. Levels of RORγt are controlled by its proteasomal degradation, promoted by UBR5-mediated ubiquitination (74). Activity of UBR5 is regulated upstream by T-cell receptor signaling (deactivation) and TGF-B signaling (activating) through unknown mechanisms and by association between UBR5 and deubiquitin enzyme A (DUBA), which stabilizes the UBR5 protein possibly by inhibiting its auto-ubiquitlyation and consequent proteasomal destruction.

E6-associated protein (E6-AP) is a HECT domain ubiquitin ligase, which acts a co-activator for several nuclear receptors including ER, PR, AR, GR, and RARα [reviewed elsewhere (75)] as well as targeting the receptor co-activator SRC-1. As is the case for the UBR5 co-activation of PR (29), E6-AP's activity as a co-activator is not dependent on its HECT domain ubiquitin ligase activity. E6-AP itself is a ubiquitination substrate for UBR5 (52) and lowered UBR5 expression results in greatly increased levels and half-life of E6-AP. These results point to a possible role for UBR5 in regulating nuclear receptor transcriptional activity via its effects on E6-AP activity. Consequently, UBR5 affects the proteolytic activity of the E6-AP/E6 complex, which targets p53 and other substrates for ubiquitination. UBR5 knockdown in human papillomavirus (HPV) infected cells not only strongly reduced p53 levels but in line with UBR5's possible tumor suppressor function decreased apoptosis in response to etoposide-induced DNA damage and overcame S-phase arrest (52).

UBR5 also regulates other nonnuclear receptor transcription factors. β-catenin is ubiquitinated by UBR5, resulting in its stabilization, increased nuclear localization, and transcriptional co-activation of Wnt target genes (50). Ubiquitination is dependent upon phosphorylation of β-catenin by GSK-3B. Similarly, silencing of UBR5 decreases β-catenin levels and inhibits β-catenin/TCF transcription. This is in contrast to the previously well-defined role of GSK-3B, which is to phosphorylate β-catenin when Wnt signaling is absent, resulting in ubiquitination by the SCF ubiquitin ligase complex and subsequent β-catenin degradation (76). UBR5 also binds and stabilizes the transcriptional co-activator Myocardin, upregulating smooth muscle gene transcription independent of E3 ligase function (77).

These findings represent both positive and negative regulation of genes associated with lineage-specific gene expression. Given the requirement for UBR5 in maintenance of pluripotency, this indicates that UBR5 may act as a molecular switch involved with coordinating differentiation of multiple cell lineages.

A number of studies have implicated UBR5 in regulation of the cellular DDR (see Fig. 3), which is critical for maintenance of genomic integrity and suppression of tumorigenesis. These roles are likely partly responsible for the observed effects of UBR5 in mediating chemoresistance in ovarian cancer (see above).

ATM signaling is required for efficient cell-cycle arrest following DNA damage (78) and proteomic screens have identified UBR5 as a phosphorylation substrate of ATM, CHK1, and CHK2 (43, 79, 80). The functional consequences of phosphorylation on UBR5 function are not clear but there are reciprocal effects on ATM and CHK2 activity. For example, upon DNA damage UBR5 relocates to the nucleus and is required for ATM-mediated phosphorylation of CHK2 (81). The interaction with CHK2 is mediated via phospho-dependent binding to its FHA domain and is required for the activation of downstream DDR checkpoints. UBR5 depletion compromises the maintenance of cell-cycle checkpoints, leading to polyploidy and cell death via mitotic catastrophe (82). UBR5 also regulates ATM signaling via ubiquitination of ATMIN following DNA damage (42) and mediates TOPBP1 ubiquitination (83) via an interaction with the BRCT domain of TOPBP1 (48). The BRCT domain is a common feature of DDR enzymes (84, 85), indicating UBR5 may interact with other DNA damage-related proteins (48).

UBR5 also acts to restrict recruitment of DNA repair machinery at the sites of double-stranded breaks (DSB) by indirectly regulating ubiquitination of phosphorylated H2AX (γ–H2AX). In concert with TRIP12, UBR5 is required to control the nuclear pool of RNF168 (49). RNF168 is a chromatin-associated E3 Ub ligase, which promotes genome stability by acting with RNF8 to ubiquitinate γ–H2AX at the site of DSBs, promoting recruitment of DNA repair machinery (86–88). In the absence of UBR5, excess RNF168 activity promotes ubiquitination of γ–H2AX beyond sites of damage, causing hyperaccumulation of ubiquitin-regulated genome caretakers such as 53BP1 and BRCA1.

Hence, UBR5 plays a key role in homeostasis of ubiquitin-mediated signaling after DNA damage, emphasizing the potential importance of dysregulated UBR5 expression and/or function in the evolution of cancer.

A number of large-scale functional genomics screens have identified putative novel roles for UBR5 in various biologic processes, including ciliogenesis, viral infection, apoptosis, and glucose homeostasis (see Fig. 3). Many of these remain to be validated but point to further roles for UBR5 and the UPS more generally in various aspects of cell biology and pathophysiology.

Primary cilia are microtubule-based organelles present on the apical surface of most vertebrate cell types (89), coordinating signaling pathways during development and in tissue homeostasis. Ciliopathy (defective cilia) is emerging as a major cause of various diseases and developmental disorders. UBR5 was identified in a whole-genome shRNA screen as a positive regulator of ciliogenesis (90), with UBR5 depletion causing decreased primary cilia formation. This screening hit was not further validated and the mechanism underlying this effect is yet to be determined, but the UPS is an established regulator of ciliogenesis (91).

A similar functional genomics approach was used to identify UBR5 (along with the transcription factor GRHL2) as a mediator of sensitivity to apoptosis. Depletion of UBR5 or GRHL2 increased sensitivity to Fas-ligand mediated apoptosis, and expression of both UBR5 and GRHL2 was slightly decreased in breast cancer cell lines less resistant to cell death (92). This indicates that UBR5 may play a role in suppressing apoptotic signaling.

The UPS is a well-established mediator of cellular response to viral infection and a number of studies have recently implicated UBR5 in regulation of viral infection. For example, UBR5 was identified in a siRNA screen for mediators of HIV replication (93). At the molecular level, UBR5 interacts with the HIV-1 VPR protein to regulate TERT activity (94) and also interacts with the HPV E6 protein and E6-AP (52).

Cross-talk between PTMs is emerging as an important regulatory mechanism in cell signaling (95, 96). An interesting example of this concept is demonstrated by the recent finding that acetylation of phosphoenolpyruvate caboxykinase (PEPCK) by P300 promotes its ubiquitination by UBR5, and subsequent proteasomal degradation (56). PEPCK catalyzes the conversion of oxaloacetate into phosphoenolpyruvate, a key step in gluconeogenesis. Phospho-dependent interactions involving UBR5 discussed above (e.g., CHK2 and DYRK2) are further examples of cross-talk between PTMs relevant to UBR5 function in cancer.

UBR5 is emerging as a key regulator of the UPS in cancer and development. However, it is unclear where UBR5 falls in the delineation between oncogene and tumor suppressor. In some cases, amplification and overexpression is clearly linked with chemoresistance and disease outcome (e.g., breast and ovarian cancer), whereas in other contexts, LoF mutations are clearly implicated in tumorigenesis (e.g., MCL). Development of better animal models allowing conditional modulation of UBR5 expression will be key to better understanding context-dependent roles of UBR5 in tumorigenesis and progression in various cancer types. These will be important not only in better understanding the biologic functions of UBR5 in cancer but in addressing the potential of UBR5 as therapeutic target. At this stage it is probably too early to define the potential utility of UBR5 as a therapeutic target in cancer.

UBR5 is a key regulator of cell signaling relevant to broad areas of cancer biology. However, despite insights from genetics, biochemistry, and cell biology, the precise mechanisms by which UBR5 contributes to tumor initiation and progression remain poorly defined. As an E3 ubiquitin ligase, many of the functions of UBR5 relevant to cancer are facilitated by its ubiquitylation of substrates. Many UBR5-interacting proteins have been identified and a number of these have been validated as substrates. However, there remains a clear need for systematic approaches to define the suite of UBR5 substrates in various contexts. This is a key knowledge gap in understanding the function of UBR5 and should be a priority for further research. It is also important to note that any development of UBR5 as a drug target will be heavily dependent on defining enzymatic substrates in a cancer context.

A clear outstanding question around UBR5 function in cancer is why the enzyme possesses many apparently divergent roles in multiple pathways in different tissue and disease contexts? Do these reflect discrete specific activities in different settings? An important consideration in this respect comes from the unique structure of UBR5, very high conservation of sequence, and restriction to the metazoan (i.e., multicellular) lineage. It is tempting to speculate that UBR5 evolved as a kind of signal integrator, coordinating extracellular signaling pathways (e.g., growth factor, hormonal, cilia) with regulation of cell-intrinsic pathways (e.g., proteostasis, DNA damage, etc.). The emergence of improved molecular tools, development of new model systems, and better definition of enzymatic substrates will provide a powerful platform for integrated approaches to define the function of UBR5 in normal cell biology and cancer pathology.

No potential conflicts of interest were disclosed.

1.
Hershko
A
,
Ciechanover
A
,
Rose
IA
. 
Identification of the active amino acid residue of the polypeptide of ATP-dependent protein breakdown
.
J Biol Chem
1981
;
256
:
1525
8
.
2.
Mitch
WE
,
Goldberg
AL
. 
Mechanisms of muscle wasting. The role of the ubiquitin-proteasome pathway
.
N Engl J Med
1996
;
335
:
1897
905
.
3.
Schnell
JD
,
Hicke
L
. 
Non-traditional functions of ubiquitin and ubiquitin-binding proteins
.
J Biol Chem
2003
;
278
:
35857
60
.
4.
Mukhopadhyay
D
,
Riezman
H
. 
Proteasome-independent functions of ubiquitin in endocytosis and signaling
.
Science
2007
;
315
:
201
5
.
5.
Passmore
LA
,
Barford
D
. 
Getting into position: the catalytic mechanisms of protein ubiquitylation
.
Biochem J
2004
;
379
:
513
25
.
6.
Kawabe
H
,
Brose
N
. 
The role of ubiquitylation in nerve cell development
.
Nat Rev Neurosci
2011
;
12
:
251
68
.
7.
Li
W
,
Bengtson
MH
,
Ulbrich
A
,
Matsuda
A
,
Reddy
VA
,
Orth
A
, et al
Genome-wide and functional annotation of human E3 ubiquitin ligases identifies MULAN, a mitochondrial E3 that regulates the organelle's dynamics and signaling
.
PLoS One
2008
;
3
:
e1487
.
8.
Popovic
D
,
Vucic
D
,
Dikic
I
. 
Ubiquitination in disease pathogenesis and treatment
.
Nat Med
2014
;
20
:
1242
53
.
9.
Fisher
RI
,
Bernstein
SH
,
Kahl
BS
,
Djulbegovic
B
,
Robertson
MJ
,
de Vos
S
, et al
Multicenter phase II study of bortezomib in patients with relapsed or refractory mantle cell lymphoma
.
J Clin Oncol
2006
;
24
:
4867
74
.
10.
Richardson
PG
,
Barlogie
B
,
Berenson
J
,
Singhal
S
,
Jagannath
S
,
Irwin
D
, et al
A phase 2 study of bortezomib in relapsed, refractory myeloma
.
N Engl J Med
2003
;
348
:
2609
17
.
11.
Vij
R
,
Siegel
DS
,
Jagannath
S
,
Jakubowiak
AJ
,
Stewart
AK
,
McDonagh
K
, et al
An open-label, single-arm, phase 2 study of single-agent carfilzomib in patients with relapsed and/or refractory multiple myeloma who have been previously treated with bortezomib
.
Br J Haematol
2012
;
158
:
739
48
.
12.
Vij
R
,
Wang
M
,
Kaufman
JL
,
Lonial
S
,
Jakubowiak
AJ
,
Stewart
AK
, et al
An open-label, single-arm, phase 2 (PX-171-004) study of single-agent carfilzomib in bortezomib-naive patients with relapsed and/or refractory multiple myeloma
.
Blood
2012
;
119
:
5661
70
.
13.
Argyriou
AA
,
Iconomou
G
,
Kalofonos
HP
. 
Bortezomib-induced peripheral neuropathy in multiple myeloma: a comprehensive review of the literature
.
Blood
2008
;
112
:
1593
9
.
14.
McCarthy
PL
,
Owzar
K
,
Hofmeister
CC
,
Hurd
DD
,
Hassoun
H
,
Richardson
PG
, et al
Lenalidomide after stem-cell transplantation for multiple myeloma
.
N Engl J Med
2012
;
366
:
1770
81
.
15.
Pal
A
,
Young
MA
,
Donato
NJ
. 
Emerging potential of therapeutic targeting of ubiquitin-specific proteases in the treatment of cancer
.
Cancer Res
2014
;
74
:
4955
66
.
16.
Johnson
D
. 
The ubiquitin-proteasome system: opportunities for therapeutic intervention in solid tumors
.
Endocr Relat Cancer
2015
;
22
:
T1
17
.
17.
Callaghan
MJ
,
Russell
AJ
,
Woollatt
E
,
Sutherland
GR
,
Sutherland
RL
,
Watts
CK
. 
Identification of a human HECT family protein with homology to the Drosophila tumor suppressor gene hyperplastic discs
.
Oncogene
1998
;
17
:
3479
91
.
18.
Saunders
DN
,
Hird
SL
,
Withington
SL
,
Dunwoodie
SL
,
Henderson
MJ
,
Biben
C
, et al
EDD, the murine hyperplastic disc gene, is essential for yolk sac vascularization and chorioallantoic fusion
.
Mol Cell Biol
2004
;
24
:
7225
34
.
19.
Clancy
JL
,
Henderson
MJ
,
Russell
AJ
,
Anderson
DW
,
Bova
RJ
,
Campbell
IG
, et al
EDD, the human orthologue of the hyperplastic discs tumour suppressor gene, is amplified and overexpressed in cancer
.
Oncogene
2003
;
22
:
5070
81
.
20.
O'Brien
PM
,
Davies
MJ
,
Scurry
JP
,
Smith
AN
,
Barton
CA
,
Henderson
MJ
, et al
The E3 ubiquitin ligase EDD is an adverse prognostic factor for serous epithelial ovarian cancer and modulates cisplatin resistance in vitro
.
Br J Cancer
2008
;
98
:
1085
93
.
21.
Mansfield
E
,
Hersperger
E
,
Biggs
J
,
Shearn
A
. 
Genetic and molecular analysis of hyperplastic discs, a gene whose product is required for regulation of cell proliferation in Drosophila melanogaster imaginal discs and germ cells
.
Dev Biol
1994
;
165
:
507
26
.
22.
Tasaki
T
,
Zakrzewska
A
,
Dudgeon
DD
,
Jiang
Y
,
Lazo
JS
,
Kwon
YT
. 
The substrate recognition domains of the N-end rule pathway
.
J Biol Chem
2009
;
284
:
1884
95
.
23.
Grau-Bove
X
,
Sebe-Pedros
A
,
Ruiz-Trillo
I
. 
A genomic survey of HECT ubiquitin ligases in eukaryotes reveals independent expansions of the HECT system in several lineages
.
Genome Biol Evol
2013
;
5
:
833
47
.
24.
Scheffner
M
,
Nuber
U
,
Huibregtse
JM
. 
Protein ubiquitination involving an E1-E2-E3 enzyme ubiquitin thioester cascade
.
Nature
1995
;
373
:
81
3
.
25.
Huibregtse
JM
,
Scheffner
M
,
Howley
PM
. 
E6-AP directs the HPV E6-dependent inactivation of p53 and is representative of a family of structurally and functionally related proteins
.
Cold Spring Harb Symp Quant Biol
1994
;
59
:
237
45
.
26.
Matta-Camacho
E
,
Kozlov
G
,
Menade
M
,
Gehring
K
. 
Structure of the HECT C-lobe of the UBR5 E3 ubiquitin ligase
.
Acta Crystallogr Sect F Struct Biol Cryst Commun
2012
;
68
:
1158
63
.
27.
Kozlov
G
,
Nguyen
L
,
Lin
T
,
De Crescenzo
G
,
Park
M
,
Gehring
K
. 
Structural basis of ubiquitin recognition by the ubiquitin-associated (UBA) domain of the ubiquitin ligase EDD
.
J Biol Chem
2007
;
282
:
35787
95
.
28.
Tasaki
T
,
Mulder
LC
,
Iwamatsu
A
,
Lee
MJ
,
Davydov
IV
,
Varshavsky
A
, et al
A family of mammalian E3 ubiquitin ligases that contain the UBR box motif and recognize N-degrons
.
Mol Cell Biol
2005
;
25
:
7120
36
.
29.
Henderson
MJ
,
Russell
AJ
,
Hird
S
,
Muñoz
M
,
Clancy
JL
,
Lehrbach
GM
, et al
EDD, the human hyperplastic discs protein, has a role in progesterone receptor coactivation and potential involvement in DNA damage response
.
J Biol Chem
2002
;
277
:
26468
78
.
30.
Deo
RC
,
Sonenberg
N
,
Burley
SK
. 
X-ray structure of the human hyperplastic discs protein: an ortholog of the C-terminal domain of poly(A)-binding protein
.
Proc Natl Acad Sci U S A
2001
;
98
:
4414
9
.
31.
Kozlov
G
,
De Crescenzo
G
,
Lim
NS
,
Siddiqui
N
,
Fantus
D
,
Kahvejian
A
, et al
Structural basis of ligand recognition by PABC, a highly specific peptide-binding domain found in poly(A)-binding protein and a HECT ubiquitin ligase
.
EMBO J
2004
;
23
:
272
81
.
32.
Lim
NS
,
Kozlov
G
,
Chang
TC
,
Groover
O
,
Siddiqui
N
,
Volpon
L
, et al
Comparative peptide binding studies of the PABC domains from the ubiquitin-protein isopeptide ligase HYD and poly(A)-binding protein. Implications for HYD function
.
J Biol Chem
2006
;
281
:
14376
82
.
33.
Munoz-Escobar
J
,
Matta-Camacho
E
,
Kozlov
G
,
Gehring
K
. 
The MLLE domain of the ubiquitin ligase UBR5 binds to its catalytic domain to regulate substrate binding
.
J Biol Chem
2015
;
290
:
22841
50
.
34.
Dephoure
N
,
Zhou
C
,
Villén
J
,
Beausoleil
SA
,
Bakalarski
CE
,
Elledge
SJ
, et al
A quantitative atlas of mitotic phosphorylation
.
Proc Natl Acad Sci U S A
2008
;
105
:
10762
7
.
35.
Mayya
V
,
Lundgren
DH
,
Hwang
SI
,
Rezaul
K
,
Wu
L
,
Eng
JK
, et al
Quantitative phosphoproteomic analysis of T cell receptor signaling reveals system-wide modulation of protein-protein interactions
.
Sci Signal
2009
;
2
:
ra46
.
36.
Olsen
JV
,
Vermeulen
M
,
Santamaria
A
,
Kumar
C
,
Miller
ML
,
Jensen
LJ
, et al
Quantitative phosphoproteomics reveals widespread full phosphorylation site occupancy during mitosis
.
Sci Signal
2010
;
3
:
ra3
.
37.
Bethard
JR
,
Zheng
H
,
Roberts
L
,
Eblen
ST
. 
Identification of phosphorylation sites on the E3 ubiquitin ligase UBR5/EDD
.
J Proteomics
2011
;
75
:
603
9
.
38.
Rigbolt
KT
,
Prokhorova
TA
,
Akimov
V
,
Henningsen
J
,
Johansen
PT
,
Kratchmarova
I
, et al
System-wide temporal characterization of the proteome and phosphoproteome of human embryonic stem cell differentiation
.
Sci Signal
2011
;
4
:
rs3
.
39.
Daub
H
,
Olsen
JV
,
Bairlein
M
,
Gnad
F
,
Oppermann
FS
,
Körner
R
, et al
Kinase-selective enrichment enables quantitative phosphoproteomics of the kinome across the cell cycle
.
Mol Cell
2008
;
31
:
438
48
.
40.
Gauci
S
,
Helbig
AO
,
Slijper
M
,
Krijgsveld
J
,
Heck
AJ
,
Mohammed
S
. 
Lys-N and trypsin cover complementary parts of the phosphoproteome in a refined SCX-based approach
.
Anal Chem
2009
;
81
:
4493
501
.
41.
Rush
J
,
Moritz
A
,
Lee
KA
,
Guo
A
,
Goss
VL
,
Spek
EJ
, et al
Immunoaffinity profiling of tyrosine phosphorylation in cancer cells
.
Nat Biotechnol
2005
;
23
:
94
101
.
42.
Zhang
T
,
Cronshaw
J
,
Kanu
N
,
Snijders
AP
,
Behrens
A
. 
UBR5-mediated ubiquitination of ATMIN is required for ionizing radiation-induced ATM signaling and function
.
Proc Natl Acad Sci U S A
2014
;
111
:
12091
6
.
43.
Kim
MA
,
Kim
HJ
,
Brown
AL
,
Lee
MY
,
Bae
YS
,
Park
JI
, et al
Identification of novel substrates for human checkpoint kinase Chk1 and Chk2 through genome-wide screening using a consensus Chk phosphorylation motif
.
Exp Mol Med
2007
;
39
:
205
12
.
44.
Eblen
ST
,
Kumar
NV
,
Shah
K
,
Henderson
MJ
,
Watts
CK
,
Shokat
KM
, et al
Identification of novel ERK2 substrates through use of an engineered kinase and ATP analogs
.
J Biol Chem
2003
;
278
:
14926
35
.
45.
Mann
KM
,
Ward
JM
,
Yew
CC
,
Kovochich
A
,
Dawson
DW
,
Black
MA
, et al
Sleeping Beauty mutagenesis reveals cooperating mutations and pathways in pancreatic adenocarcinoma
.
Proc Natl Acad Sci U S A
2012
;
109
:
5934
41
.
46.
Meissner
B
,
Kridel
R
,
Lim
RS
,
Rogic
S
,
Tse
K
,
Scott
DW
, et al
The E3 ubiquitin ligase UBR5 is recurrently mutated in mantle cell lymphoma
.
Blood
2013
;
121
:
3161
4
.
47.
Forbes
SA
,
Bhamra
G
,
Bamford
S
,
Dawson
E
,
Kok
C
,
Clements
J
, et al
The catalogue of somatic mutations in cancer (COSMIC)
.
Curr Protoc Hum Genet
2008
;
Chapter 10, Unit 10 11, doi:10.1002/0471142905.hg1011s57
.
48.
Honda
Y
,
Tojo
M
,
Matsuzaki
K
,
Anan
T
,
Matsumoto
M
,
Ando
M
, et al
Cooperation of HECT-domain ubiquitin ligase hHYD and DNA topoisomerase II-binding protein for DNA damage response
.
J Biol Chem
2002
;
277
:
3599
605
.
49.
Gudjonsson
T
,
Altmeyer
M
,
Savic
V
,
Toledo
L
,
Dinant
C
,
Grøfte
M
, et al
TRIP12 and UBR5 suppress spreading of chromatin ubiquitylation at damaged chromosomes
.
Cell
2012
;
150
:
697
709
.
50.
Hay-Koren
A
,
Caspi
M
,
Zilberberg
A
,
Rosin-Arbesfeld
R
. 
The EDD E3 ubiquitin ligase ubiquitinates and up-regulates beta-catenin
.
Mol Biol Cell
2011
;
22
:
399
411
.
51.
Ong
SS
,
Goktug
AN
,
Elias
A
,
Wu
J
,
Saunders
D
,
Chen
T
, et al
Stability of the human pregnane X receptor is regulated by E3 ligase UBR5 and serine/threonine kinase DYRK2
.
Biochem J
2014
;
459
:
193
203
.
52.
Tomaic
V
,
Pim
D
,
Thomas
M
,
Massimi
P
,
Myers
MP
,
Banks
L
. 
Regulation of the human papillomavirus type 18 E6/E6AP ubiquitin ligase complex by the HECT domain-containing protein EDD
.
J Virol
2011
;
85
:
3120
7
.
53.
Cojocaru
M
,
Bouchard
A
,
Cloutier
P
,
Cooper
JJ
,
Varzavand
K
,
Price
DH
, et al
Transcription factor IIS cooperates with the E3 ligase UBR5 to ubiquitinate the CDK9 subunit of the positive transcription elongation factor B
.
J Biol Chem
2011
;
286
:
5012
22
.
54.
Yoshida
M
,
Yoshida
K
,
Kozlov
G
,
Lim
NS
,
De Crescenzo
G
,
Pang
Z
, et al
Poly(A) binding protein (PABP) homeostasis is mediated by the stability of its inhibitor, Paip2
.
EMBO J
2006
;
25
:
1934
44
.
55.
Maddika
S
,
Chen
J
. 
Protein kinase DYRK2 is a scaffold that facilitates assembly of an E3 ligase
.
Nat Cell Biol
2009
;
11
:
409
19
.
56.
Jiang
W
,
Wang
S
,
Xiao
M
,
Lin
Y
,
Zhou
L
,
Lei
Q
, et al
Acetylation regulates gluconeogenesis by promoting PEPCK1 degradation via recruiting the UBR5 ubiquitin ligase
.
Mol Cell
2011
;
43
:
33
44
.
57.
Martin
P
,
Martin
A
,
Shearn
A
. 
Studies of l(3)c43hs1 a polyphasic, temperature-sensitive mutant of Drosophila melanogaster with a variety of imaginal disc defects
.
Dev Biol
1977
;
55
:
213
32
.
58.
Lee
JD
,
Amanai
K
,
Shearn
A
,
Treisman
JE
. 
The ubiquitin ligase Hyperplastic discs negatively regulates hedgehog and decapentaplegic expression by independent mechanisms
.
Development
2002
;
129
:
5697
706
.
59.
Szabad
J
,
Jursnich
VA
,
Bryant
PJ
. 
Requirement for cell-proliferation control genes in Drosophila oogenesis
.
Genetics
1991
;
127
:
525
33
.
60.
Pertceva
JA
,
Dorogova
NV
,
Bolobolova
EU
,
Nerusheva
OO
,
Fedorova
SA
,
Omelyanchuk
LV
. 
The role of Drosophila hyperplastic discs gene in spermatogenesis
.
Cell Biol Int
2010
;
34
:
991
6
.
61.
Ryerse
JS
,
Nagel
BA
. 
Gap junction distribution in the Drosophila wing disc mutants vg, l(2)gd, l(3)c43hs1, and l(2)gl4
.
Dev Biol
1984
;
105
:
396
403
.
62.
Wang
G
,
Tang
X
,
Chen
Y
,
Cao
J
,
Huang
Q
,
Ling
X
, et al
Hyperplastic discs differentially regulates the transcriptional outputs of hedgehog signaling
.
Mech Dev
2014
;
133
:
117
25
.
63.
Moncrieff
S
,
Moncan
M
,
Scialpi
F
,
Ditzel
M
. 
Regulation of hedgehog ligand expression by the N-End rule ubiquitin-protein ligase hyperplastic discs and the drosophila GSK3beta homologue, shaggy
.
PLoS One
2015
;
10
:
e0136760
.
64.
Chen
HW
,
Yang
CC
,
Hsieh
CL
,
Liu
H
,
Lee
SC
,
Tan
BC
. 
A functional genomic approach reveals the transcriptional role of EDD in the expression and function of angiogenesis regulator ACVRL1
.
Biochim Biophys Acta
2013
;
1829
:
1309
19
.
65.
Byrd
N
,
Becker
S
,
Maye
P
,
Narasimhaiah
R
,
St-Jacques
B
,
Zhang
X
, et al
Hedgehog is required for murine yolk sac angiogenesis
.
Development
2002
;
129
:
361
72
.
66.
Chen
W
,
Tang
T
,
Eastham-Anderson
J
,
Dunlap
D
,
Alicke
B
,
Nannini
M
, et al
Canonical hedgehog signaling augments tumor angiogenesis by induction of VEGF-A in stromal perivascular cells
.
Proc Natl Acad Sci U S A
2011
;
108
:
9589
94
.
67.
Winnier
G
,
Blessing
M
,
Labosky
PA
,
Hogan
BL
. 
Bone morphogenetic protein-4 is required for mesoderm formation and patterning in the mouse
.
Genes Dev
1995
;
9
:
2105
16
.
68.
Plank
M
,
Hu
G
,
Silva
AS
,
Wood
SH
,
Hesketh
EE
,
Janssens
G
, et al
An analysis and validation pipeline for large-scale RNAi-based screens
.
Sci Rep
2013
;
3
:
1076
.
69.
Buckley
SM
,
Aranda-Orgilles
B
,
Strikoudis
A
,
Apostolou
E
,
Loizou
E
,
Moran-Crusio
K
, et al
Regulation of pluripotency and cellular reprogramming by the ubiquitin-proteasome system
.
Cell Stem Cell
2012
;
11
:
783
98
.
70.
Kato
T
,
Tamiya
G
,
Koyama
S
,
Nakamura
T
,
Makino
S
,
Arawaka
S
, et al
UBR5 gene mutation is associated with familial adult myoclonic epilepsy in a Japanese Family
.
ISRN Neurol
2012
;
2012
:
508308
.
71.
Kwak
J
,
Workman
JL
,
Lee
D
. 
The proteasome and its regulatory roles in gene expression
.
Biochim Biophys Acta
2011
;
1809
:
88
96
.
72.
Weake
VM
,
Workman
JL
. 
Histone ubiquitination: triggering gene activity
.
Mol Cell
2008
;
29
:
653
63
.
73.
Bolt
MJ
,
Stossi
F
,
Callison
AM
,
Mancini
MG
,
Dandekar
R
,
Mancini
MA
. 
Systems level-based RNAi screening by high content analysis identifies UBR5 as a regulator of estrogen receptor-alpha protein levels and activity
.
Oncogene
2015
;
34
:
154
64
.
74.
Rutz
S
,
Kayagaki
N
,
Phung
QT
,
Eidenschenk
C
,
Noubade
R
,
Wang
X
, et al
Deubiquitinase DUBA is a post-translational brake on interleukin-17 production in T cells
.
Nature
2015
;
518
:
417
21
.
75.
Ramamoorthy
S
,
Nawaz
Z
. 
E6-associated protein (E6-AP) is a dual function coactivator of steroid hormone receptors
.
Nucl Recept Signal
2008
;
6
:
e006
.
76.
Su
Y
,
Fu
C
,
Ishikawa
S
,
Stella
A
,
Kojima
M
,
Shitoh
K
, et al
APC is essential for targeting phosphorylated beta-catenin to the SCFbeta-TrCP ubiquitin ligase
.
Mol Cell
2008
;
32
:
652
61
.
77.
Hu
G
,
Wang
X
,
Saunders
DN
,
Henderson
M
,
Russell
AJ
,
Herring
BP
, et al
Modulation of myocardin function by the ubiquitin E3 ligase UBR5
.
J Biol Chem
2010
;
285
:
11800
9
.
78.
Bartek
J
,
Lukas
J
. 
DNA damage checkpoints: from initiation to recovery or adaptation
.
Curr Opin Cell Biol
2007
;
19
:
238
45
.
79.
Matsuoka
S
,
Ballif
BA
,
Smogorzewska
A
,
McDonald
ER
 3rd
,
Hurov
KE
,
Luo
J
, et al
ATM and ATR substrate analysis reveals extensive protein networks responsive to DNA damage
.
Science
2007
;
316
:
1160
6
.
80.
Mu
JJ
,
Wang
Y
,
Luo
H
,
Leng
M
,
Zhang
J
,
Yang
T
, et al
A proteomic analysis of ataxia telangiectasia-mutated (ATM)/ATM-Rad3-related (ATR) substrates identifies the ubiquitin-proteasome system as a regulator for DNA damage checkpoints
.
J Biol Chem
2007
;
282
:
17330
4
.
81.
Henderson
MJ
,
Munoz
MA
,
Saunders
DN
,
Clancy
JL
,
Russell
AJ
,
Williams
B
, et al
EDD mediates DNA damage-induced activation of CHK2
.
J Biol Chem
2006
;
281
:
39990
40000
.
82.
Munoz
MA
,
Saunders
DN
,
Henderson
MJ
,
Clancy
JL
,
Russell
AJ
,
Lehrbach
G
, et al
The E3 ubiquitin ligase EDD regulates S-phase and G(2)/M DNA damage checkpoints
.
Cell Cycle
2007
;
6
:
3070
7
.
83.
Yamane
K
,
Tsuruo
T
. 
Conserved BRCT regions of TopBP1 and of the tumor suppressor BRCA1 bind strand breaks and termini of DNA
.
Oncogene
1999
;
18
:
5194
203
.
84.
Bork
P
,
Hofmann
K
,
Bucher
P
,
Neuwald
AF
,
Altschul
SF
,
Koonin
EV
. 
A superfamily of conserved domains in DNA damage-responsive cell cycle checkpoint proteins
.
FASEB J
1997
;
11
:
68
76
.
85.
Callebaut
I
,
Mornon
JP
. 
From BRCA1 to RAP1: a widespread BRCT module closely associated with DNA repair
.
FEBS Lett
1997
;
400
:
25
30
.
86.
Doil
C
,
Mailand
N
,
Bekker-Jensen
S
,
Menard
P
,
Larsen
DH
,
Pepperkok
R
, et al
RNF168 binds and amplifies ubiquitin conjugates on damaged chromosomes to allow accumulation of repair proteins
.
Cell
2009
;
136
:
435
46
.
87.
Mailand
N
,
Bekker-Jensen
S
,
Faustrup
H
,
Melander
F
,
Bartek
J
,
Lukas
C
, et al
RNF8 ubiquitylates histones at DNA double-strand breaks and promotes assembly of repair proteins
.
Cell
2007
;
131
:
887
900
.
88.
Kuo
LJ
,
Yang
LX
. 
Gamma-H2AX - a novel biomarker for DNA double-strand breaks
.
In Vivo
2008
;
22
:
305
9
.
89.
Oh
EC
,
Katsanis
N
. 
Cilia in vertebrate development and disease
.
Development
2012
;
139
:
443
8
.
90.
Kim
J
,
Lee
JE
,
Heynen-Genel
S
,
Suyama
E
,
Ono
K
,
Lee
K
, et al
Functional genomic screen for modulators of ciliogenesis and cilium length
.
Nature
2010
;
464
:
1048
51
.
91.
Kasahara
K
,
Kawakami
Y
,
Kiyono
T
,
Yonemura
S
,
Kawamura
Y
,
Era
S
, et al
Ubiquitin-proteasome system controls ciliogenesis at the initial step of axoneme extension
.
Nat Commun
2014
;
5
:
5081
.
92.
Dompe
N
,
Rivers
CS
,
Li
L
,
Cordes
S
,
Schwickart
M
,
Punnoose
EA
, et al
A whole-genome RNAi screen identifies an 8q22 gene cluster that inhibits death receptor-mediated apoptosis
.
Proc Natl Acad Sci U S A
2011
;
108
:
E943
51
.
93.
Zhou
H
,
Xu
M
,
Huang
Q
,
Gates
AT
,
Zhang
XD
,
Castle
JC
, et al
Genome-scale RNAi screen for host factors required for HIV replication
.
Cell Host Microbe
2008
;
4
:
495
504
.
94.
Wang
X
,
Singh
S
,
Jung
HY
,
Yang
G
,
Jun
S
,
Sastry
KJ
, et al
HIV-1 Vpr protein inhibits telomerase activity via the EDD-DDB1-VPRBP E3 ligase complex
.
J Biol Chem
2013
;
288
:
15474
80
.
95.
Xiong
Y
,
Lei
QY
,
Zhao
S
,
Guan
KL
. 
Regulation of glycolysis and gluconeogenesis by acetylation of PKM and PEPCK
.
Cold Spring Harb Symp Quant Biol
2011
;
76
:
285
9
.
96.
Webb
K
,
Bennett
EJ
. 
Eavesdropping on PTM cross-talk through serial enrichment
.
Nat Methods
2013
;
10
:
620
1
.
97.
Cerami
E
,
Gao
J
,
Dogrusoz
U
,
Gross
BE
,
Sumer
SO
,
Aksoy
BA
, et al
The cBio cancer genomics portal: an open platform for exploring multidimensional cancer genomics data
.
Cancer Discov
2012
;
2
:
401
4
.
98.
Gao
J
,
Aksoy
BA
,
Dogrusoz
U
,
Dresdner
G
,
Gross
B
,
Sumer
SO
, et al
Integrative analysis of complex cancer genomics and clinical profiles using the cBioPortal
.
Sci Signal
2013
;
6
:
pl1
.
99.
Forbes
SA
,
Beare
D
,
Gunasekaran
P
,
Leung
K
,
Bindal
N
,
Boutselakis
H
, et al
COSMIC: exploring the world's knowledge of somatic mutations in human cancer
.
Nucleic Acids Res
2015
;
43
:
D805
11
.