Ubiquitin-conjugating Enzyme Ubc13 Research Articles

Proteome Profiling of S. cerevisiae Strains Lacking the Ubiquitin-Conjugating Enzymes Ubc4 and Ubc5 During Exponential Growth and After Heat Shock Treatment.

The Ubiquitin-Proteasome System (UPS) governs numerous cellular processes by modulating protein stability and activity via the conjugation of the small protein ubiquitin, either as a single molecule or as linkages with distinct functions. Dysregulation of the UPS has been associated with many diseases, including neurodegenerative and neurodevelopmental diseases, as well as cancer. Ubiquitin-conjugating enzymes (E2s) are important players of the UPS that work together with ubiquitin ligases (E3s) to promote substrate ubiquitylation. In this study, we conduct a comparative proteome-wide abundance profiling of S. cerevisiae cells during the exponential growth phase with and without heat shock treatment. We focus on cells with deletions of the two highly homologous E2s, UBC4 or UBC5, and use isobaric tag-based quantitative mass spectrometry to elucidate differences and similarities in their proteomic profiles. Our analysis revealed that the deletion of Ubc4 has a stronger effect on the proteome compared to the deletion of Ubc5, particularly in exponentially growing cells. In contrast, the effect on the proteome of deleting Ubc5 becomes evident only after heat shock, and even then, it remains minor compared to Ubc4. Furthermore, we identified proteins increasing in the absence of each enzyme, which may represent candidate substrates, potentially contributing to a better understanding of their cellular role.

Clr4SUV39H1 ubiquitination and non-coding RNA mediate transcriptional silencing of heterochromatin via Swi6 phase separation

Transcriptional silencing by RNAi paradoxically relies on transcription, but how the transition from transcription to silencing is achieved has remained unclear. The Cryptic Loci Regulator complex (CLRC) in Schizosaccharomyces pombe is a cullin-ring E3 ligase required for silencing that is recruited by RNAi. We found that the E2 ubiquitin conjugating enzyme Ubc4 interacts with CLRC and mono-ubiquitinates the histone H3K9 methyltransferase Clr4SUV39H1, promoting the transition from co-transcriptional gene silencing (H3K9me2) to transcriptional gene silencing (H3K9me3). Ubiquitination of Clr4 occurs in an intrinsically disordered region (Clr4IDR), which undergoes liquid droplet formation in vitro, along with Swi6HP1 the effector of transcriptional gene silencing. Our data suggests that phase separation is exquisitely sensitive to non-coding RNA (ncRNA) which promotes self-association of Clr4, chromatin association, and di-, but not tri- methylation instead. Ubc4-CLRC also targets the transcriptional co-activator Bdf2BRD4, down-regulating centromeric transcription and small RNA (sRNA) production. The deubiquitinase Ubp3 counteracts both activities.

Inhibition of K63 ubiquitination by G-Protein pathway suppressor 2 (GPS2) regulates mitochondria-associated translation

G-Protein Pathway Suppressor 2 (GPS2) is an inhibitor of non-proteolytic K63 ubiquitination mediated by the E2 ubiquitin-conjugating enzyme Ubc13. Previous studies have associated GPS2-mediated restriction of ubiquitination with the regulation of insulin signaling, inflammatory responses and mitochondria-nuclear communication across different tissues and cell types. However, a detailed understanding of the targets of GPS2/Ubc13 activity is lacking. Here, we have dissected the GPS2-regulated K63 ubiquitome in mouse embryonic fibroblasts and human breast cancer cells, unexpectedly finding an enrichment for proteins involved in RNA binding and translation on the outer mitochondrial membrane. Validation of selected targets of GPS2-mediated regulation, including the RNA-binding protein PABPC1 and translation factors RPS1, RACK1 and eIF3M, revealed a mitochondrial-specific strategy for regulating the translation of nuclear-encoded mitochondrial proteins via non-proteolytic ubiquitination. Removal of GPS2-mediated inhibition, either via genetic deletion or stress-induced nuclear translocation, promotes the import-coupled translation of selected mRNAs leading to the increased expression of an adaptive antioxidant program. In light of GPS2 role in nuclear-mitochondria communication, these findings reveal an exquisite regulatory network for modulating mitochondrial gene expression through spatially coordinated transcription and translation.

Regulation and function of Id2 in plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are specialized type I interferon (IFN-I) producing cells that promote anti-viral immune responses and contribute to autoimmunity. Development of pDCs requires the transcriptional regulator E2–2 and is opposed by inhibitor of DNA binding 2 (Id2). Prior work indicates Id2 is induced in pDCs upon maturation and may affect pDC IFN-I production via suppression of E2–2, suggesting an important yet uncharacterized role in this lineage. We found TLR7 agonists stimulate Id2 mRNA and protein expression in pDCs. We further show that transcriptional activation of Id2 is dependent on the E2 ubiquitin-conjugating enzyme Ubc13, but independent of IFN-I signaling in response to TLR7 agonist stimulation. Nonetheless, conditional Id2 depletion in pDCs indicates Id2 is dispensable for TLR7 agonist-induced maturation and inhibition of E2–2 expression. Thus, we identify new mechanisms of Id2 regulation by Ubc13, which may be relevant for understanding Id2 gene regulation in other contexts, while ruling out major roles for Id2 in pDC responses to TLR7 agonists.

Protein kinase 9 is not required for completion of the Plasmodium berghei life cycle

Protein kinases uniquely expressed in Plasmodium represent attractive drug targets. Previous studies have reported that Plasmodium falciparum Protein kinase 9 (Pk9) phosphorylates regulatory serine 106 of the ubiquitin-conjugating enzyme (Ubc13) thereby negatively regulating its activity. We investigated the effect of Pk9 depletion and Ubc13 mutation at S106 on the progression of rodent malaria model P. berghei life cycle. Our studies demonstrate that while phosphorylation of the regulatory serine 106 of Ubc13 is essential in blood stages, the lack of Pk9 expression neither altered Ubc13 phosphorylation nor parasite viability at all life cycle stages, though Ubc13 and Pk9 showed co-localization in the cytosol of erythrocytic and liver stages. Further, phosphorylation of Ubc13 in the absence of Pk9 reiterated the redundancy of its regulation in P. berghei. These results highlight the indispensable role of Ubc13 in P. berghei life cycle and redundancy in its phosphorylation by protein kinase and reiterate the need to validate novel gene function through genetic approaches for drug development strategies.

LEDGF/p75 Is Required for an Efficient DNA Damage Response.

Lens epithelium-derived growth factor splice variant of 75 kDa (LEDGF/p75) plays an important role in cancer, but its DNA-damage repair (DDR)-related implications are still not completely understood. Different LEDGF model cell lines were generated: a complete knock-out of LEDGF (KO) and re-expression of LEDGF/p75 or LEDGF/p52 using CRISPR/Cas9 technology. Their proliferation and migration capacity as well as their chemosensitivity were determined, which was followed by investigation of the DDR signaling pathways by Western blot and immunofluorescence. LEDGF-deficient cells exhibited a decreased proliferation and migration as well as an increased sensitivity toward etoposide. Moreover, LEDGF-depleted cells showed a significant reduction in the recruitment of downstream DDR-related proteins such as replication protein A 32 kDa subunit (RPA32) after exposure to etoposide. The re-expression of LEDGF/p75 rescued all knock-out effects. Surprisingly, untreated LEDGF KO cells showed an increased amount of DNA fragmentation combined with an increased formation of γH2AX and BRCA1. In contrast, the protein levels of ubiquitin-conjugating enzyme UBC13 and nuclear proteasome activator PA28γ were substantially reduced upon LEDGF KO. This study provides for the first time an insight that LEDGF is not only involved in the recruitment of CtIP but has also an effect on the ubiquitin-dependent regulation of DDR signaling molecules and highlights the role of LEDGF/p75 in homology-directed DNA repair.

Drosophila Uev1a is dually required for Ben-dependent DNA-damage response and fly mobility

K63-linked polyubiquitination requires the ubiquitin-conjugating enzyme Ubc13 and a Ubc/E2 variant Uev. Lower eukaryotic organisms contain one UEV gene required for DNA-damage tolerance, while vertebrates and higher plants contain multiple UEV genes with distinct functions. In contrast, Drosophila contains only one UEV gene designated dUev1a. Here we report that dUev1a forms a stable heterodimer with Ben, the Drosophila Ubc13 ortholog, that dUev1a-F15E completely abolishes the interaction, and that a conserved dUev1a-F15Y substitution severely reduces its interaction with Ben. dUev1a functionally rescues the corresponding yeast mms2 null mutant from killing by various DNA-damaging agents in a Ben-dependent manner, and the heterozygous dUev1a mutant flies are more sensitive to DNA-damaging agent, indicating that the function of UEV in DNA-damage response is conserved throughout eukaryotes. Meanwhile, dUev1a+/‐ mutant flies displayed reduced mobility characteristic of defects in the central nervous system and reminiscent of the bendless phenotypes, suggesting that dUev1a acts together with Ben in this process. Our observations collectively imply that dUev1a is dually required for DNA-damage response and neurological signaling in Drosophila, and that these processes are mediated by the Ben-dUev1a complex that promotes K63-linked polyubiquitination.

Arabidopsis Ubiquitin-Conjugating Enzymes UBC7, UBC13, and UBC14 Are Required in Plant Responses to Multiple Stress Conditions.

Protein ubiquitination plays important roles in plants, including stress responses. The ubiquitin (Ub) E2 enzymes are required in the transfer of Ub to a substrate and are also important in determining the Ub-chain linkage specificity. However, for many of the 37 E2 genes in Arabidopsis thaliana, there is currently little or no understanding of their functions. In this study, we investigated three members of an E2 subfamily. The single, double, and triple mutants of UBC7, UBC13, and UBC14 did not show any phenotypic changes under normal conditions, but were more sensitive than the wild-type (WT) plants to multiple stress conditions, suggesting that the three genes are not critical for normal growth, but required in plant stress responses. The severity of the phenotypes increased from single to triple mutants, suggesting that the functions of the three genes are not completely redundant. The three E2s are closely related to the yeast Ubc7 and its homologs in animals and human, which are an important component of the endoplasmic reticulum (ER)-associated degradation (ERAD) pathway. The stress sensitivity phenotypes of the mutants and shared evolutionary root with the Ubc7 homologs in yeast and metazoans suggest that UBC7, UBC13, and UBC14 may function in the plant ERAD pathway.

Deamidation disrupts native and transient contacts to weaken the interaction between UBC13 and RING-finger E3 ligases.

The deamidase OspI from enteric bacteria Shigella flexneri deamidates a glutamine residue in the host ubiquitin-conjugating enzyme UBC13 and converts it to glutamate (Q100E). Consequently, its polyubiquitination activity in complex with the RING-finger ubiquitin ligase TRAF6 and the downstream NF-κB inflammatory response is silenced. The precise role of deamidation in silencing the UBC13/TRAF6 complex is unknown. We report that deamidation inhibits the interaction between UBC13 and TRAF6 RING-domain (TRAF6RING) by perturbing both the native and transient interactions. Deamidation creates a new intramolecular salt-bridge in UBC13 that competes with a critical intermolecular salt-bridge at the native UBC13/TRAF6RING interface. Moreover, the salt-bridge competition prevents transient interactions necessary to form a typical UBC13/RING complex. Repulsion between E100 and the negatively charged surface of RING also prevents transient interactions in the UBC13/RING complex. Our findings highlight a mechanism wherein a post-translational modification perturbs the conformation and stability of transient complexes to inhibit protein-protein association.

A novel requirement for ubiquitin-conjugating enzyme UBC-13 in retrograde recycling of MIG-14/Wntless and Wnt signaling.

After endocytosis, transmembrane cargoes such as signaling receptors, channels, and transporters enter endosomes where they are sorted to different destinations. Retromer and ESCRT (endosomal sorting complex required for transport) are functionally distinct protein complexes on endosomes that direct cargo sorting into the recycling retrograde transport pathway and the degradative multivesicular endosome pathway (MVE), respectively. Cargoes destined for degradation in lysosomes are decorated with K63-linked ubiquitin chains, which serve as an efficient sorting signal for entry into the MVE pathway. Defects in K63-linked ubiquitination disrupt MVE sorting and degradation of membrane proteins. Here, we unexpectedly found that UBC-13, the E2 ubiquitin-conjugating enzyme that generates K63-linked ubiquitin chains, is essential for retrograde transport of multiple retromer-dependent cargoes including MIG-14/Wntless. Loss of ubc-13 disrupts MIG-14/Wntless trafficking from endosomes to the Golgi, causing missorting of MIG-14 to lysosomes and impairment of Wnt-dependent processes. We observed that retromer-associated SNX-1 and the ESCRT-0 subunit HGRS-1/Hrs localized to distinct regions on a common endosome in wild type but overlapped on ubc-13(lf) endosomes, indicating that UBC-13 is important for the separation of retromer and ESCRT microdomains on endosomes. Our data suggest that cargo ubiquitination mediated by UBC-13 plays an important role in maintaining the functionally distinct subdomains to ensure efficient cargo segregation on endosomes.

Genetic rescue of lineage-balanced blood cell production reveals a crucial role for STAT3 antiinflammatory activity in hematopoiesis

Blood cell formation must be appropriately maintained throughout life to provide robust immune function, hemostasis, and oxygen delivery to tissues, and to prevent disorders that result from over- or underproduction of critical lineages. Persistent inflammation deregulates hematopoiesis by damaging hematopoietic stem and progenitor cells (HSPCs), leading to elevated myeloid cell output and eventual bone marrow failure. Nonetheless, antiinflammatory mechanisms that protect the hematopoietic system are understudied. The transcriptional regulator STAT3 has myriad roles in HSPC-derived populations and nonhematopoietic tissues, including a potent antiinflammatory function in differentiated myeloid cells. STAT3 antiinflammatory activity is facilitated by STAT3-mediated transcriptional repression of Ube2n, which encodes the E2 ubiquitin-conjugating enzyme Ubc13 involved in proinflammatory signaling. Here we demonstrate a crucial role for STAT3 antiinflammatory activity in preservation of HSPCs and lineage-balanced hematopoiesis. Conditional Stat3 removal from the hematopoietic system led to depletion of the bone marrow lineage- Sca-1+ c-Kit+ CD150+ CD48- HSPC subset (LSK CD150+ CD48- cells), myeloid-skewed hematopoiesis, and accrual of DNA damage in HSPCs. These responses were accompanied by intrinsic transcriptional alterations in HSPCs, including deregulation of inflammatory, survival and developmental pathways. Concomitant Ube2n/Ubc13 deletion from Stat3-deficient hematopoietic cells enabled lineage-balanced hematopoiesis, mitigated depletion of bone marrow LSK CD150+ CD48- cells, alleviated HSPC DNA damage, and corrected a majority of aberrant transcriptional responses. These results indicate an intrinsic protective role for STAT3 in the hematopoietic system, and suggest that this is mediated by STAT3-dependent restraint of excessive proinflammatory signaling via Ubc13 modulation.

RNF8/UBC13 ubiquitin signaling suppresses synapse formation in the mammalian brain

Although ubiquitin ligases have been implicated in autism, their roles and mechanisms in brain development remain incompletely understood. Here, we report that in vivo knockdown or conditional knockout of the autism-linked ubiquitin ligase RNF8 or associated ubiquitin-conjugating enzyme UBC13 in rodent cerebellar granule neurons robustly increases the number of parallel fiber presynaptic boutons and functional parallel fiber/Purkinje cell synapses. In contrast to the role of nuclear RNF8 in proliferating cells, RNF8 operates in the cytoplasm in neurons to suppress synapse differentiation in vivo. Proteomics analyses reveal that neuronal RNF8 interacts with the HECT domain protein HERC2 and scaffold protein NEURL4, and knockdown of HERC2 or NEURL4 phenocopies the inhibition of RNF8/UBC13 signaling on synapse differentiation. In behavior analyses, granule neuron-specific knockout of RNF8 or UBC13 impairs cerebellar-dependent learning. Our study defines RNF8 and UBC13 as components of a novel cytoplasmic ubiquitin-signaling network that suppresses synapse formation in the brain.

XIAP upregulates expression of HIF target genes by targeting HIF1α for Lys63-linked polyubiquitination.

The cellular response to hypoxia is characterised by a switch in the transcriptional program, mediated predominantly by the hypoxia inducible factor family of transcription factors (HIF). Regulation of HIF1 is primarily controlled by post-translational modification of the HIF1α subunit, which can alter its stability and/or activity. This study identifies an unanticipated role for the X-linked inhibitor of apoptosis (XIAP) protein as a regulator of Lys63-linked polyubiquitination of HIF1α. Lys63-linked ubiquitination of HIF1α by XIAP is dependent on the activity of E2 ubiquitin conjugating enzyme Ubc13. We find that XIAP and Ubc13 dependent Lys63-linked polyubiquitination promotes HIF1α nuclear retention leading to an increase in the expression of HIF1 responsive genes. Inhibition of the Lys63-linked polyubiquitination pathway leads to reduced levels of nuclear HIF1α, promoter occupancy, HIF-dependent gene expression and cell viability. Our data reveals an additional and significant level of control of the HIF1 by XIAP, with important implications in understanding the role of HIF1 and XIAP in human disease.

RNF8 E3 Ubiquitin Ligase Stimulates Ubc13 E2 Conjugating Activity That Is Essential for DNA Double Strand Break Signaling and BRCA1 Tumor Suppressor Recruitment

DNA double strand break (DSB) responses depend on the sequential actions of the E3 ubiquitin ligases RNF8 and RNF168 plus E2 ubiquitin-conjugating enzyme Ubc13 to specifically generate histone Lys-63-linked ubiquitin chains in DSB signaling. Here, we defined the activated RNF8-Ubc13∼ubiquitin complex by x-ray crystallography and its functional solution conformations by x-ray scattering, as tested by separation-of-function mutations imaged in cells by immunofluorescence. The collective results show that the RING E3 RNF8 targets E2 Ubc13 to DSB sites and plays a critical role in damage signaling by stimulating polyubiquitination through modulating conformations of ubiquitin covalently linked to the Ubc13 active site. Structure-guided separation-of-function mutations show that the RNF8 E2 stimulating activity is essential for DSB signaling in mammalian cells and is necessary for downstream recruitment of 53BP1 and BRCA1. Chromatin-targeted RNF168 rescues 53BP1 recruitment involved in non-homologous end joining but not BRCA1 recruitment for homologous recombination. These findings suggest an allosteric approach to targeting the ubiquitin-docking cleft at the E2-E3 interface for possible interventions in cancer and chronic inflammation, and moreover, they establish an independent RNF8 role in BRCA1 recruitment.

N-Glycosylation process in both ER and Golgi plays pivotal role in plant immunity

N-glycosylation of proteins in the endoplasmic reticulum (ER) and Golgi apparatus is essential for protein posttranslational modification in plant cells. Although the Nglycosylation in the ER and Golgi apparatus has been known to regulate protein quality control, salt stress and cellulose biosynthesis, few evidences related to the roles of Nglycosylation in plant immunity have been reported. Arabidopsis thaliana mutants defective in N-glycosylation, namely, staurosporin and temperature sensitive 3a and 3b (stt3a and stt3b) of oligosaccharyltransferase subunit and complex glycan 1 (cgl1) in Golgi apparatus were used in this study. Results showed that Arabidopsis mutant stt3a was more susceptible against Pseudomonas syringae pv. tomato DC3000 (Pst) and Erwinia carotovora subsp. carotovora (ECC). In addition, stt3a was less resistant against Pst harboring effector protein AvrRpm1 compared to the wild type plant. However stt3b showed less significant changes in susceptibility against these three bacterial strains. These results infer the functions of STT3B in N-glycosylation that STT3B is likely supplementary to the main STT3A. Flg22-induced PR1 accumulation and callose deposition were blocked in Nglycosylation mutants, implying that N-glycosylation is involved in the PAMP-triggered immunity. However, Nglycosylation was not absolutely required for AvrRpm1- and AvrRpt2-triggered immunity. STT3A-binding proteins were searched in order to understand the role of STT3A in plant immunity. Ubiquitin-conjugating enzyme E2s, UBC7 and UBC13, were found to be binding proteins of STT3A by yeast two-hybrid assay.

Endoplasmic Reticulum Exit of Golgi-resident Defective for SREBP Cleavage (Dsc) E3 Ligase Complex Requires Its Activity

Layers of quality control ensure proper protein folding and complex formation prior to exit from the endoplasmic reticulum. The fission yeast Dsc E3 ligase is a Golgi-localized complex required for sterol regulatory element-binding protein (SREBP) transcription factor activation that shows architectural similarity to endoplasmic reticulum-associated degradation E3 ligases. The Dsc E3 ligase consists of five integral membrane proteins (Dsc1-Dsc5) and functionally interacts with the conserved AAA-ATPase Cdc48. Utilizing an in vitro ubiquitination assay, we demonstrated that Dsc1 has ubiquitin E3 ligase activity that requires the E2 ubiquitin-conjugating enzyme Ubc4. Mutations that specifically block Dsc1-Ubc4 interaction prevent SREBP cleavage, indicating that SREBP activation requires Dsc E3 ligase activity. Surprisingly, Golgi localization of the Dsc E3 ligase complex also requires Dsc1 E3 ligase activity. Analysis of Dsc E3 ligase complex formation, glycosylation, and localization indicated that Dsc1 E3 ligase activity is specifically required for endoplasmic reticulum exit of the complex. These results define enzyme activity-dependent sorting as an autoregulatory mechanism for protein trafficking.

Convergence of Parkin, PINK1, and α-Synuclein on Stress-induced Mitochondrial Morphological Remodeling

Mutations in PARKIN (PARK2), an ubiquitin ligase, cause early onset Parkinson disease. Parkin was shown to bind, ubiquitinate, and target depolarized mitochondria for destruction by autophagy. This process, mitophagy, is considered crucial for maintaining mitochondrial integrity and suppressing Parkinsonism. Here, we report that under moderate mitochondrial stress, parkin does not translocate to mitochondria to induce mitophagy; rather, it stimulates mitochondrial connectivity. Mitochondrial stress-induced fusion requires PINK1 (PARK6), mitofusins, and parkin ubiquitin ligase activity. Upon exposure to mitochondrial toxins, parkin binds α-synuclein (PARK1), and in conjunction with the ubiquitin-conjugating enzyme Ubc13, stimulates K63-linked ubiquitination. Importantly, α-synuclein inactivation phenocopies parkin overexpression and suppresses stress-induced mitochondria fission, whereas Ubc13 inactivation abrogates parkin-dependent mitochondrial fusion. The convergence of parkin, PINK1, and α-synuclein on mitochondrial dynamics uncovers a common function of these PARK genes in the mitochondrial stress response and provides a potential physiological basis for the prevalence of α-synuclein pathology in Parkinson disease.

Nuclear localization and stabilization of GPS2 depend on arginine methylation and interaction with the cofactor TBL1

G‐protein pathway suppressor 2 (GPS2) is a multifunctional protein involved in the regulation of different metabolic organs. First identified as part of the N‐CoR corepressor complex, GPS2 has been shown to be an important cofactor in the nucleus for mediating transcriptional regulation and meiotic recombination. In addition, we recently reported that GPS2 plays a key non‐transcriptional role in the cytosol where it regulates the pro‐inflammatory tumor necrosis factor alpha (TNFα) pathway by directly interacting with the ubiquitin conjugating enzyme Ubc13 and inhibiting its enzymatic activity. While these observations suggest that GPS2 localization is an important determinant of its molecular function, a clear understanding of GPS2 differential targeting to specific cellular locations is still missing.Here we show that GPS2 nuclear localization is tightly regulated by a fine balance between stabilization and protein degradation, with the interaction between GPS2 and the exchange cofactor TBL1 being required to protect GPS2 from proteasomal degradation and to mediate its nuclear localization. Moreover, our data data indicate that arginine methylation on R323 by PRMT6 plays a critical role in regulating GPS2 stability. Thus, our findings together further support the idea that posttranslational modifications, including ubiquitination and arginine methylation, are necessary to regulate GPS2 molecular function in vivo.

Rad25 Protein Is Targeted for Degradation by the Ubc4-Ufd4 Pathway

Proteasome-mediated proteolysis provides dynamic spatial and temporal modulation of protein concentration in response to various intrinsic and extrinsic challenges. To gain a better understanding of the role of the proteasome in DNA repair, we systematically monitored the stability of 26 proteins involved in nucleotide excision repair (NER) under normal growth conditions. Among six NER factors found to be regulated by the proteasome, we further delineated the specific pathway involved in the degradation of Rad25, a subunit of TFIIH. We demonstrate that Rad25 turnover requires the ubiquitin-conjugating enzyme Ubc4 and the ubiquitin ligase Ufd4. Interestingly, the deletion of UFD4 specifically suppresses the rad25 mutant defective in transcription. Our results reveal a novel function of the Ufd4 pathway and another tie between the proteasome and NER regulators.

MiR-205 acts as a tumour radiosensitizer by targeting ZEB1 and Ubc13.

Tumor cells associated with therapy resistance (radioresistance and drug resistance) are likely to give rise to local recurrence and distant metastatic relapse. Recent studies revealed microRNA (miRNA)-mediated regulation of metastasis and epithelial-mesenchymal transition; however, whether specific miRNAs regulate tumor radioresistance and can be exploited as radiosensitizing agents remains unclear. Here we find that miR-205 promotes radiosensitivity and is downregulated in radioresistant subpopulations of breast cancer cells, and that loss of miR-205 is highly associated with poor distant relapse-free survival in breast cancer patients. Notably, therapeutic delivery of miR-205 mimics via nanoliposomes can sensitize the tumor to radiation in a xenograft model. Mechanistically, radiation suppresses miR-205 expression through ataxia telangiectasia mutated (ATM) and zinc finger E-box binding homeobox 1 (ZEB1). Moreover, miR-205 inhibits DNA damage repair by targeting ZEB1 and the ubiquitin-conjugating enzyme Ubc13. These findings identify miR-205 as a radiosensitizing miRNA and reveal a new therapeutic strategy for radioresistant tumors.