PP2A Controls Genome Integrity by Integrating Nutrient-Sensing and Metabolic Pathways with the DNA Damage Response.

Mec1ATR mediates the DNA damage response (DDR), integrating chromosomal signals and mechanical stimuli. We show that the PP2A phosphatases, ceramide-activated enzymes, couple cell metabolism with the DDR. Using genomic screens, metabolic analysis, and genetic and pharmacological studies, we found that PP2A attenuates the DDR and that three metabolic circuits influence the DDR by modulating PP2A activity. Irc21, a putative cytochrome b5 reductase that promotes the condensation reaction generating dihydroceramides (DHCs), and Ppm1, a PP2A methyltransferase, counteract the DDR by activating PP2A; conversely, the nutrient-sensing TORC1-Tap42 axis sustains DDR activation by inhibiting PP2A. Loss-of-function mutations in IRC21, PPM1, and PP2A and hyperactive tap42 alleles rescue mec1 mutants. Ceramides synergize with rapamycin, a TORC1 inhibitor, in counteracting the DDR. Hence, PP2A integrates nutrient-sensing and metabolic pathways to attenuate the Mec1ATR response. Our observations imply that metabolic changes affect genome integrity and may help with exploiting therapeutic options and repositioning known drugs.

E3-Independent Constitutive Monoubiquitination Complements Histone Methyltransferase Activity of SETDB1.

Ubiquitination typically occurs through the sequential action of three enzymes catalyzing ubiquitin activation (E1), conjugation (E2), and ligation (E3) and regulates diverse eukaryotic cellular processes. Although monoubiquitination commonly confers nondegradative activities, mechanisms underlying its temporal and spatial regulation and functional plasticity still remain largely unknown. Here we demonstrate that SETDB1, a major histone H3K9 methyltransferase is monoubiquitinated at the evolutionarily conserved lysine-867 in its SET-Insertion domain. This ubiquitination is directly catalyzed by UBE2E family of E2 enzymes in an E3-independent manner while the conjugated-ubiquitin (Ub) is protected from active deubiquitination. The resulting constitutive lysine-867 monoubiquitination is essential for SETDB1's enzymatic activity and endogenous retrovirus silencing in murine embryonic stem cells. Furthermore, the canonical hydrophobic patch on the conjugated-Ub is critical for Ub protection and function. Together, our findings highlight an E3-independent mechanism for monoubiquitination and reveal mechanistic details of SETDB1's enzymatic activity and the functional significance of its SET-Insertion.

Lysine methylation of the NF-κB subunit RelA by SETD6 couples activity of the histone methyltransferase GLP at chromatin to tonic repression of NF-κB signaling.

Signaling via the methylation of lysine residues in proteins has been linked to diverse biological and disease processes, yet the catalytic activity and substrate specificity of many human protein lysine methyltransferases (PKMTs) are unknown. We screened over 40 candidate PKMTs and identified SETD6 as a methyltransferase that monomethylated chromatin-associated transcription factor NF-κB subunit RelA at Lys310 (RelAK310me1). SETD6-mediated methylation rendered RelA inert and attenuated RelA-driven transcriptional programs, including inflammatory responses in primary immune cells. RelAK310me1 was recognized by the ankryin repeat of the histone methyltransferase GLP, which under basal conditions promoted a repressed chromatin state at RelA target genes through GLP-mediated methylation of histone H3 Lys9 (H3K9). NF-κB-activation-linked phosphorylation of RelA at Ser311 by protein kinase C-ζ (PKC-ζ) blocked the binding of GLP to RelAK310me1 and relieved repression of the target gene. Our findings establish a previously uncharacterized mechanism by which chromatin signaling regulates inflammation programs.

Investigating the functional role of SETD6 in lung adenocarcinoma.

BACKGROUND: SET domain containing 6 (SETD6) has been shown to be upregulated in multiple human cancers and can promote malignant cell survival. However, expression and function of SETD6 in lung adenocarcinoma (LUAD) remains unaddressed. This study aimed to demonstrate the expression pattern, biological roles and potential mechanisms by which SETD6 dysregulation is associated with LUAD. METHODS: The expression level of SETD6 was evaluated in LUAD clinical specimens and its correlation with clinical parameters were analyzed. In vitro, gain-of-function and loss-of-function experiments were performed to evaluate the effects of SETD6 on cell proliferation, apoptosis, migration, and colony formation of LUAD cell line A549. Western-blot was performed to investigate the involvement of nuclear factor-κB (NF-κB) and nuclear factor erythroid 2-related factor 2 (Nrf2) pathways as downstream signaling of SETD6 in LUAD cells. RESULTS: Compared with non-tumorous tissues, SETD6 was overexpressed in tumor tissues, and its overexpression significantly correlates with higher rates of regional lymph node metastasis and poor prognosis in patients with LUAD. In A549 cell line, SETD6 overexpression could promote cell proliferation, migration, colony formation and inhibit cell apoptosis, whereas SETD6 knockdown caused the opposite effects. Furthermore, we demonstrated that the mechanisms underlying the effect of SETD6 on LUAD biological behaviors may be through its interaction with NF-κB and Nrf2 signaling pathways. CONCLUSIONS: SETD6, which is highly expressed in LUAD tumor tissues, plays an important role in promoting the malignant behaviors of LUAD via likely the NF-κB and Nrf2 signaling pathways.

Cotranslational folding allows misfolding-prone proteins to circumvent deep kinetic traps.

Many large proteins suffer from slow or inefficient folding in vitro. It has long been known that this problem can be alleviated in vivo if proteins start folding cotranslationally. However, the molecular mechanisms underlying this improvement have not been well established. To address this question, we use an all-atom simulation-based algorithm to compute the folding properties of various large protein domains as a function of nascent chain length. We find that for certain proteins, there exists a narrow window of lengths that confers both thermodynamic stability and fast folding kinetics. Beyond these lengths, folding is drastically slowed by nonnative interactions involving C-terminal residues. Thus, cotranslational folding is predicted to be beneficial because it allows proteins to take advantage of this optimal window of lengths and thus avoid kinetic traps. Interestingly, many of these proteins' sequences contain conserved rare codons that may slow down synthesis at this optimal window, suggesting that synthesis rates may be evolutionarily tuned to optimize folding. Using kinetic modeling, we show that under certain conditions, such a slowdown indeed improves cotranslational folding efficiency by giving these nascent chains more time to fold. In contrast, other proteins are predicted not to benefit from cotranslational folding due to a lack of significant nonnative interactions, and indeed these proteins' sequences lack conserved C-terminal rare codons. Together, these results shed light on the factors that promote proper protein folding in the cell and how biomolecular self-assembly may be optimized evolutionarily.

A novel immune-related epigenetic signature based on the transcriptome for predicting the prognosis and therapeutic response of patients with diffuse large B-cell lymphoma.

Epigenetic modifications contribute to lymphomagenesis. Here, we performed an expression clustering analysis and identified two epigenetic-related clusters (EC1 and EC2). EC1 presented abundant TP53, MYD88, HIST1H1D, HIST1H1C, KMT2D and EZH2 mutations and an inferior prognosis. Pathways involved in the regulation of DNA methylation/demethylation, histone methyltransferase activity, and protein methyltransferase activity were significantly enriched in EC1. However, EC2 was frequently accompanied by B2M, CD70 and MEF2B mutations, which presented with enrichments in DNA damage repair, cytokine-mediated and B-cell activated immune signaling, increased levels of CD8+ T-, γδT- and T helper-cells, as well as immune scores and immunogenic cell death (ICD) modulators. According to the prediction, EC1 was more sensitive to vorinostat, serdemetan and navitoclax. However, ruxolitinib, cytarabine and CP466722 were more suitable treatments for EC2. The novel immune-related epigenetic signature exhibits promising clinical predictive value for diffuse large B-cell lymphoma (DLBCL), particularly for guiding epigenetic therapeutic regimens. R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisone) based combination treatment regimens are suggested.

Histone Methylation by SET Domain Proteins in Fungi.

Histone-modifying enzymes are responsible for regulating transcription, recombination, DNA repair, DNA replication, chromatid cohesion, and chromosome segregation. Fungi are ideally suited for comparative chromatin biology because sequencing of numerous genomes from many clades is coupled to existing rich methodology that allows truly holistic approaches, integrating evolutionary biology with mechanistic molecular biology and ecology, promising applications in medicine or plant pathology. While genome information is rich, mechanistic studies on histone modifications are largely restricted to two yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe, and one filamentous fungus, Neurospora crassa-three species that arguably are not representative of this diverse kingdom. Here, histone methylation serves as a paradigm to illustrate the roles chromatin modifications may play in more complex fungal life cycles. This review summarizes recent advances in our understanding of histone H3 methylation at two sites associated with active transcription, lysine 4 and lysine 36 (H3K4, H3K36); a site associated with the formation of constitutive heterochromatin, lysine 9 (H3K9); and a site associated with the formation of facultative heterochromatin, lysine 27 (H3K27). Special attention is paid to differences in how methylation marks interact in different taxa.

CircRNA hsa_circ_0018289 exerts an oncogenic role in cervical cancer progression through miR-1294/ICMT axis.

BACKGROUND: circRNA hsa_circ_0018289-mediated growth and metastasis of CC cells were investigated, as well as the mechanistic pathway. METHODS: Quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR) was carried out to examine the expression of hsa_circ_0018289, microRNA (miR)-1294, and isoprenylcysteine carboxyl methyltransferase (ICMT). CC cell proliferation, migration, and invasion were evaluated by 5-ethynyl-2'-deoxyuridine (EdU) incorporation, colony formation, transwell assays, Western blot analysis of ICMT, and glycolysis-associated proteins. Dual-luciferase reporter or RNA pull-down analysis of the target interaction between miR-1294 and hsa_hsa_circ_0018289 or ICMT. Xenograft model assay was implemented to assess the role of hsa_circ_0018289 in vivo. Immunofluorescence (IHC) was employed to detect the level of Ki-67. RESULTS: Hsa_circ_0018289 was elevated in CC tissues and cells, its deficiency could repress growth, metastasis, and glycolysis of CC cells in vitro, as well as hamper tumor growth in vivo. Hsa_circ_0018289 sponged miR-1294 while miR-1294 bound with ICMT, and the inhibition of miR-1294 or addition of ICMT could partially relieve the effect caused by hsa_circ_0018289 depletion. CONCLUSION: Hsa_circ_0018289 contributes to malignant development by regulating the miR-1294/ICMT axis, affording novel insight into CC therapy.

Cockayne syndrome group B deficiency reduces H3K9me3 chromatin remodeler SETDB1 and exacerbates cellular aging.

Cockayne syndrome is an accelerated aging disorder, caused by mutations in the CSA or CSB genes. In CSB-deficient cells, poly (ADP ribose) polymerase (PARP) is persistently activated by unrepaired DNA damage and consumes and depletes cellular nicotinamide adenine dinucleotide, which leads to mitochondrial dysfunction. Here, the distribution of poly (ADP ribose) (PAR) was determined in CSB-deficient cells using ADPr-ChAP (ADP ribose-chromatin affinity purification), and the results show striking enrichment of PAR at transcription start sites, depletion of heterochromatin and downregulation of H3K9me3-specific methyltransferases SUV39H1 and SETDB1. Induced-expression of SETDB1 in CSB-deficient cells downregulated PAR and normalized mitochondrial function. The results suggest that defects in CSB are strongly associated with loss of heterochromatin, downregulation of SETDB1, increased PAR in highly-transcribed regions, and mitochondrial dysfunction.

Regulation of constitutive and alternative splicing by PRMT5 reveals a role for Mdm4 pre-mRNA in sensing defects in the spliceosomal machinery.

The tight control of gene expression at the level of both transcription and post-transcriptional RNA processing is essential for mammalian development. We here investigate the role of protein arginine methyltransferase 5 (PRMT5), a putative splicing regulator and transcriptional cofactor, in mammalian development. We demonstrate that selective deletion of PRMT5 in neural stem/progenitor cells (NPCs) leads to postnatal death in mice. At the molecular level, the absence of PRMT5 results in reduced methylation of Sm proteins, aberrant constitutive splicing, and the alternative splicing of specific mRNAs with weak 5' donor sites. Intriguingly, the products of these mRNAs are, among others, several proteins regulating cell cycle progression. We identify Mdm4 as one of these key mRNAs that senses the defects in the spliceosomal machinery and transduces the signal to activate the p53 response, providing a mechanistic explanation of the phenotype observed in vivo. Our data demonstrate that PRMT5 is a master regulator of splicing in mammals and uncover a new role for the Mdm4 pre-mRNA, which could be exploited for anti-cancer therapy.

Photoregulation of PRMT-1 Using a Photolabile Non-Canonical Amino Acid.

Protein methyltransferases are vital to the epigenetic modification of gene expression. Thus, obtaining a better understanding of and control over the regulation of these crucial proteins has significant implications for the study and treatment of numerous diseases. One ideal mechanism of protein regulation is the specific installation of a photolabile-protecting group through the use of photocaged non-canonical amino acids. Consequently, PRMT1 was caged at a key tyrosine residue with a nitrobenzyl-protected Schultz amino acid to modulate protein function. Subsequent irradiation with UV light removes the caging group and restores normal methyltransferase activity, facilitating the spatial and temporal control of PRMT1 activity. Ultimately, this caged PRMT1 affords the ability to better understand the protein's mechanism of action and potentially regulate the epigenetic impacts of this vital protein.

Isoprenylcysteine carboxy methyltransferase (ICMT) is associated with tumor aggressiveness and its expression is controlled by the p53 tumor suppressor.

Isoprenyl cysteine carboxyl methyltransferase (ICMT) plays a key role in post-translational regulation of prenylated proteins. On the basis of previous results, we hypothesized that the p53 pathway and ICMT expression may be linked in cancer cells. Here, we studied whether WT p53 and cancer-associated p53 point mutants regulate ICMT levels and whether ICMT overexpression affects tumor progression. Studying the effect of p53 variants on ICMT mRNA and protein levels in cancer cells, we found that WT p53 and p53 mutants differentially affect ICMT expression, indicating that p53 status influences ICMT levels in tumors. To investigate the underlying mechanisms, we constructed ICMT-luciferase reporters and found that WT p53 represses ICMT transcription. In contrast, p53 mutants showed a positive effect on ICMT expression. Promoter truncation analyses pinpointed the repressive effect of WT p53 to the -209 and -14 region on the ICMT promoter, and ChIP assays indicated that WT p53 is recruited to this region. Instead, a different promoter region was identified as responsible for the mutant p53 effect. Studying the effect of ICMT overexpression on tumor-associated phenotypes in vitro and in vivo, and analyzing breast and lung cancer databases, we identified a correlation between p53 status and ICMT expression in breast and lung cancers. Moreover, we observed that ICMT overexpression is correlated with negative clinical outcomes. Our work unveils a link between postprenylation protein processing and the p53 pathway, indicating that the functional interplay between WT and mutant p53 alters ICMT levels, thereby affecting tumor aggressiveness.

Human FAM173A is a mitochondrial lysine-specific methyltransferase that targets adenine nucleotide translocase and affects mitochondrial respiration.

Lysine methylation is a common posttranslational modification of nuclear and cytoplasmic proteins but is also present in mitochondria. The human protein denoted "family with sequence similarity 173 member B" (FAM173B) was recently uncovered as a mitochondrial lysine (K)-specific methyltransferase (KMT) targeting the c-subunit of mitochondrial ATP synthase (ATPSc), and was therefore renamed ATPSc-KMT. We here set out to investigate the biochemical function of its yet uncharacterized paralogue FAM173A. We demonstrate that FAM173A localizes to mitochondria, mediated by a noncanonical targeting sequence that is partially retained in the mature protein. Immunoblotting analysis using methyllysine-specific antibodies revealed that FAM173A knock-out (KO) abrogates lysine methylation of a single mitochondrial protein in human cells. Mass spectrometry analysis identified this protein as adenine nucleotide translocase (ANT), represented by two highly similar isoforms ANT2 and ANT3. We found that methylation occurs at Lys-52 of ANT, which was previously reported to be trimethylated. Complementation of KO cells with WT or enzyme-dead FAM173A indicated that the enzymatic activity of FAM173A is required for ANT methylation at Lys-52 to occur. Both in human cells and in rat organs, Lys-52 was exclusively trimethylated, indicating that this modification is constitutive, rather than regulatory and dynamic. Moreover, FAM173A-deficient cells displayed increased mitochondrial respiration compared with FAM173A-proficient cells. In summary, we demonstrate that FAM173A is the long-sought KMT responsible for ANT methylation at Lys-52, and point out the functional significance of Lys-52 methylation in ANT. Based on the established naming nomenclature for KMTs, we propose to rename FAM173A to ANT-KMT (gene name ANTKMT).

Mechanism suppressing H3K9 trimethylation in pluripotent stem cells and its demise by polyQ-expanded huntingtin mutations.

Pluripotent stem cells are invaluable resources to study development and disease, holding a great promise for regenerative medicine. Here we use human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) from patients with Huntington's disease (HD-iPSCs) to shed light into the normal function of huntingtin (HTT) and its demise in disease. We find that HTT binds ATF7IP, a regulator of the histone H3 methyltransferase SETDB1. HTT inhibits the interaction of the ATF7IP-SETDB1 complex with other heterochromatin regulators and transcriptional repressors, maintaining low levels of H3K9 trimethylation (H3K9me3) in hESCs. Loss of HTT promotes global increased H3K9me3 levels and enrichment of H3K9me3 marks at distinct genes, including transcriptional regulators of neuronal differentiation. Although these genes are normally expressed at low amounts in hESCs, HTT knockdown (KD) reduces their induction during neural differentiation. Notably, mutant expanded polyglutamine repeats in HTT diminish its interaction with ATF7IP-SETDB1 complex and trigger H3K9me3 in HD-iPSCs. Conversely, KD of ATF7IP in HD-iPSCs reduces H3K9me3 alterations and ameliorates gene expression changes in their neural counterparts. Taken together, our results indicate ATF7IP as a potential target to correct aberrant H3K9me3 levels induced by mutant HTT.

Antibacterial activity and mode of action of potassium tetraborate tetrahydrate against soft-rot bacterial plant pathogens.

Bacterial soft rot caused by the bacteria Dickeya and Pectobacterium is a destructive disease of vegetables, as well as ornamental plants. Several management options exist to help control these pathogens. Because of the limited success of these approaches, there is a need for the development of alternative methods to reduce losses. In this study, we evaluated the effect of potassium tetraborate tetrahydrate (PTB) on the growth of six Dickeya and Pectobacterium spp. Disc diffusion assays showed that Dickeya spp. and Pectobacterium spp. differ in their sensitivity to PTB. Spontaneous PTB-resistant mutants of Pectobacterium were identified and further investigation of the mechanism of PTB resistance was conducted by full genome sequencing. Point mutations in genes cpdB and supK were found in a single Pectobacterium atrosepticum PTB-resistant mutant. Additionally, point mutations in genes prfB (synonym supK) and prmC were found in two independent Pectobacterium brasiliense PTB-resistant mutants. prfB and prmC encode peptide chain release factor 2 and its methyltransferase, respectively. We propose the disruption of translation activity due to PTB leads to Pectobacterium growth inhibition. The P. atrosepticum PTB-resistant mutant showed altered swimming motility. Disease severity was reduced for P. atrosepticum-inoculated potato stems sprayed with PTB. We discuss the potential risk of selecting for bacterial resistance to this chemical.

Protein Methyltransferase Inhibition Decreases Endocrine Specification Through the Upregulation of Aldh1b1 Expression.

Understanding the mechanisms that promote the specification of pancreas progenitors and regulate their self-renewal and differentiation will help to maintain and expand pancreas progenitor cells derived from human pluripotent stem (hPS) cells. This will improve the efficiency of current differentiation protocols of hPS cells into ß-cells and bring such cells closer to clinical applications for the therapy of diabetes. Aldehyde dehydrogenase 1b1 (Aldh1b1) is a mitochondrial enzyme expressed specifically in progenitor cells during mouse pancreas development, and we have shown that its functional inactivation leads to accelerated differentiation and deficient ß-cells. In this report, we aimed to identify small molecule inducers of Aldh1b1 expression taking advantage of a mouse embryonic stem (mES) cell Aldh1b1 lacZ reporter line and a pancreas differentiation protocol directing mES cells into pancreatic progenitors. We identified AMI-5, a protein methyltransferase inhibitor, as an Aldh1b1 inducer and showed that it can maintain Aldh1b1 expression in embryonic pancreas explants. This led to a selective reduction in endocrine specification. This effect was due to a downregulation of Ngn3, and it was mediated through Aldh1b1 since the effect was abolished in Aldh1b1 null pancreata. The findings implicated methyltransferase activity in the regulation of endocrine differentiation and showed that methyltransferases can act through specific regulators during pancreas differentiation. Stem Cells 2019;37:640-651.

Smad3-mediated recruitment of the methyltransferase SETDB1/ESET controls Snail1 expression and epithelial-mesenchymal transition.

During epithelial-mesenchymal transition (EMT), reprogramming of gene expression is accompanied by histone modifications. Whether EMT-promoting signaling directs functional changes in histone methylation has not been established. We show here that the histone lysine methyltransferase SETDB1 represses EMT and that, during TGF-ß-induced EMT, cells attenuate SETDB1 expression to relieve this inhibition. SETDB1 also controls stem cell generation, cancer cell motility, invasion, metastatic dissemination, as well as sensitivity to certain cancer drugs. These functions may explain the correlation of breast cancer patient survival with SETDB1 expression. At the molecular level, TGF-ß induces SETDB1 recruitment by Smad3, to repress Smad3/4-activated transcription of SNAI1, encoding the EMT "master" transcription factor SNAIL1. Suppression of SNAIL1-mediated gene reprogramming by SETDB1 occurs through H3K9 methylation at the SNAI1 gene that represses its H3K9 acetylation imposed by activated Smad3/4 complexes. SETDB1 therefore defines a TGF-ß-regulated balance between histone methylation and acetylation that controls EMT.

SETD6 dominant negative mutation in familial colorectal cancer type X.

Familiar colorectal cancer type X (FCCTX) comprises families that fulfill the Amsterdam criteria for hereditary non-polyposis colorectal cancer, but that lack the mismatch repair deficiency that defines the Lynch syndrome. Thus, the genetic cause that increases the predisposition to colorectal and other related cancers in families with FCCTX remains to be elucidated. Using whole-exome sequencing, we have identified a truncating mutation in the SETD6 gene (c.791_792insA, p.Met264IlefsTer3) in all the affected members of a FCCTX family. SETD6 is a mono-methyltransferase previously shown to modulate the NF-κB and Wnt signaling pathways, among other. In the present study, we characterized the truncated version of SETD6, providing evidence that this SETD6 mutation may play a role in the cancer inheritance in this family. Here we demonstrate that the truncated SETD6 lacks its enzymatic activity as a methyltransferase, while maintaining other properties such as its expression, localization and substrate-binding ability. In addition, we show that the mutant allele is expressed and that the resulting protein competes with the wild type for their substrates, pointing to a dominant negative nature. These findings suggest that the identified mutation impairs the normal function of SETD6, which may result in the deregulation of the different pathways in which it is involved, contributing to the increased susceptibility to cancer in this FCCTX family.

Isoprenylcysteine carboxylmethyltransferase is associated with nasopharyngeal carcinoma chemoresistance and Ras activation.

Development of chemo-resistance in nasopharyngeal carcinoma (NPC) poses the therapeutic challenge and its mechanisms are still poorly understood. In this work, we demonstrate that targeting isoprenylcysteine carboxylmethyltransferase (Icmt) is a therapeutic strategy to overcome NPC chemo-resistance. We found that Icmt mRNA and protein levels were increased in NPC cells after prolonged exposure to chemotherapy. Using pharmacological inhibitor cysmethynil or genetic siRNA approaches, we showed that Icmt inhibition was more effective against chemoresistant compared to chemosensitive NPC cells, suggesting that chemoresistant NPC cells is more dependent on Icmt function. The combination of Icmt inhibition with 5-FU or cisplatin resulted in greater efficacy than single chemotherapeutic agent alone in NPC. Notably, we demonstrated that the in vitro observations were translatable to in vivo NPC cancer xenograft mouse model. Mechanism analysis indicated that Icmt inhibition decreased Ras and RhoA activities, leading to the suppression of Ras and RhoA-mediated downstream signaling in NPC cells. The reverse of the inhibitory effects of cysmethynil by constitutively active Ras suggests that Ras is the critical effector of Icmt in NPC cells. Our work is the first to show that Icmt plays an important role in the development of NPC chemoresistance. Our findings also suggest that targeting Icmt represents a promising strategy to inhibit Ras function.

The c-MYC-BMI1 axis is essential for SETDB1-mediated breast tumourigenesis.

Characterising the activated oncogenic signalling that leads to advanced breast cancer is of clinical importance. Here, we showed that SET domain, bifurcated 1 (SETDB1), a histone H3 lysine 9 methyltransferase, is aberrantly expressed and behaves as an oncogenic driver in breast cancer. SETDB1 enhances c-MYC and cyclin D1 expression by promoting the internal ribosome entry site (IRES)-mediated translation of MYC/CCND1 mRNA, resulting in prominent signalling of c-MYC to promote cell cycle progression, and provides a growth/self-renewal advantage to breast cancer cells. The activated c-MYC-BMI1 axis is essential for SETDB1-mediated breast tumourigenesis, because silencing of either c-MYC or BMI1 profoundly impairs the enhanced growth/colony formation conferred by SETDB1. Furthermore, c-MYC directly binds to the SETDB1 promoter region and enhances its transcription, suggesting a positive regulatory interplay between SETDB1 and c-MYC. In this study, we identified SETDB1 as a prominent oncogene and characterised the underlying mechanism whereby SETDB1 drives breast cancer, providing a therapeutic rationale for targeting SETDB1-BMI1 signalling in breast cancer. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.