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CIC-DUX4 sarcoma (CDS) is a highly aggressive and metastatic small round type of predominantly pediatric sarcoma driven by a fusion oncoprotein comprising the transcriptional repressor Capicua (CIC) fused to the C-terminal transcriptional activation domain of DUX4. CDS rapidly develops resistance to chemotherapy, thus novel specific therapies are greatly needed. We demonstrate that CIC-DUX4 requires P300/CBP to induce histone H3 acetylation, activate its targets, and drive oncogenesis. We describe the synthetic route to a selective and highly potent P300/CBP inhibitor named iP300w and related stereoisomers, and find that iP300w efficiently suppresses CIC-DUX4 transcriptional activity and reverses CIC-DUX4 induced acetylation. iP300w is active at 100-fold lower concentrations than related stereoisomers or A-485. At low doses, iP300w shows specificity to CDS cancer cell lines, rapidly inducing cell cycle arrest and preventing growth of established CDS xenograft tumors when delivered in vivo. The effectiveness of iP300w to inactivate CIC-DUX4 highlights a promising therapeutic opportunity for CDS.

Summary: Double homeobox (DUX) transcription factors are unique to eutherian mammals. DUX4 regulates expression of repetitive elements during early embryogenesis, but misexpression of DUX4 causes facioscapulohumeral muscular dystrophy (FSHD) and translocations overexpressing the DUX4 double homeodomain cause B cell leukemia. Here, we report the crystal structure of the tandem homeodomains of DUX4 bound to DNA. The homeodomains bind DNA in a head-to-head fashion, with the linker making anchoring DNA minor-groove interactions and unique protein contacts. Remarkably, despite being tandem duplicates, the DUX4 homeodomains recognize different core sequences. This results from an arginine-to-glutamate mutation, unique to primates, causing alternative positioning of a key arginine side chain in the recognition helix. Mutational studies demonstrate that this primate-specific change is responsible for the divergence in sequence recognition that likely drove coevolution of embryonically regulated repeats in primates. Our work provides a framework for understanding the endogenous function of DUX4 and its role in FSHD and cancer. : Lee et al. determine the crystal structure of the facioscapulohumeral muscular dystrophy and cancer-associated transcription factor DUX4, bound to DNA. The structure gives insight into how the double homeodomain of DUX4, which is related by duplication of an ancestral homeodomain, has evolved different sequence specificities, uniquely in the primate lineage. Keywords: double homeobox, DUX, tandem homeodomains, facioscapulohumeral muscular dystrophy, FSHD, B cell leukemia, retrovirus-like elements, cleavage stage development, DNA sequence readout, crystal structure

ULK1 (unc51-like autophagy activating kinase 1) is a serine/threonine kinase that plays a key role in regulating macroautophagy/autophagy induction in response to amino acid starvation. Despite the recent progress in understanding ULK1 functions, the molecular mechanism by which ULK1 regulates the induction of autophagy remains elusive. In this study, we determined that ULK1 phosphorylates Ser30 of BECN1 (Beclin 1) in association with ATG14 (autophagy-related 14) but not with UVRAG (UV radiation resistance associated). The Ser30 phosphorylation was induced by deprivation of amino acids or treatments with Torin 1 or rapamycin, the conditions that inhibit MTORC1 (mechanistic target of rapamycin complex 1), and requires ATG13 and RB1CC1 (RB1 inducible coiled-coil 1), proteins that interact with ULK1. Hypoxia or glutamine deprivation, which inhibit MTORC1, was also able to increase the phosphorylation in a manner dependent upon ULK1 and ULK2. Blocking the BECN1 phosphorylation by replacing Ser30 with alanine suppressed the amino acid starvation-induced activation of the ATG14-containing PIK3C3/VPS34 (phosphatidylinositol 3-kinase catalytic subunit type 3) kinase, and reduced autophagy flux and the formation of phagophores and autophagosomes. The Ser30-to-Ala mutation did not affect the ULK1-mediated phosphorylations of BECN1 Ser15 or ATG14 Ser29, indicating that the BECN1 Ser30 phosphorylation might regulate autophagy independently of those 2 sites. Taken together, these results demonstrate that BECN1 Ser30 is a ULK1 target site whose phosphorylation activates the ATG14-containing PIK3C3 complex and stimulates autophagosome formation in response to amino acid starvation, hypoxia, and MTORC1 inhibition.

DUX4 drives global histone H3 hyperacetylation; and a new P300 inhibitor, iP300w, blocks DUX4-mediated transcription and toxicity., Facioscapulohumeral muscular dystrophy (FSHD) results from mutations causing overexpression of the transcription factor, DUX4, which interacts with the histone acetyltransferases, EP300 and CBP. We describe the activity of a new spirocyclic EP300/CBP inhibitor, iP300w, which inhibits the cytotoxicity of the DUX4 protein and reverses the overexpression of most DUX4 target genes, in engineered cell lines and FSHD myoblasts, as well as in an FSHD animal model. In evaluating the effect of iP300w on global histone H3 acetylation, we discovered that DUX4 overexpression leads to a dramatic global increase in the total amount of acetylated histone H3. This unexpected effect requires the C-terminus of DUX4, is conserved with mouse Dux, and may facilitate zygotic genome activation. This global increase in histone H3 acetylation is reversed by iP300w, highlighting the central role of EP300 and CBP in the transcriptional mechanism underlying DUX4 cytotoxicity and the translational potential of blocking this interaction.

Loss of silencing of the DUX4 gene on chromosome 4 causes facioscapulohumeral muscular dystrophy. While high level DUX4 expression induces apoptosis, the effects of low level DUX4 expression on human myogenic cells are not well understood. Low levels and sporadic expression of DUX4 have been reported in FSHD biopsy samples and myoblast cultures. Here, we show that a large set of human myogenic genes is rapidly deregulated by DUX4, including MYOD1 and MYF5, which are efficiently repressed even by low, non-toxic levels of DUX4. Human myoblasts modified to express low nontoxic levels of DUX4 were significantly impaired from differentiating into myotubes in vitro. Surprisingly, inhibition of differentiation does not require the transcriptional activation domain, thus is likely a feature of all mammalian DUX genes. DUX4 does not bind near the MYF5 gene, but has a prominent ChIP-seq peak within the MYF5 −118 kb enhancer. We find that when DUX4 binds at this site, it directs enhancer activity towards a nearby transcriptional start site for a noncoding nonfunctional RNA we name DIME (DUX4-induced MYF5 enhancer) transcript. These data highlight the anti-myogenic properties of DUX4 in human myogenic progenitor cells, and provide an example of enhancer disruption in the downregulation of MYF5.

Facioscapulohumeral muscular dystrophy (FSHD) is caused by inappropriate expression of the double homeodomain protein DUX4. DUX4 has bimodal effects, inhibiting myogenic differentiation and blocking MyoD at low levels of expression, and killing myoblasts at high levels. Pax3 and Pax7, which contain related homeodomains, antagonize the cell death phenotype of DUX4 in C2C12 cells, suggesting some type of competitive interaction. Here, we show that the effects of DUX4 on differentiation and MyoD expression require the homeodomains but do not require the C-terminal activation domain of DUX4. We tested the set of equally related homeodomain proteins (Pax6, Pitx2c, OTX1, Rax, Hesx1, MIXL1 and Tbx1) and found that only Pax3 and Pax7 display phenotypic competition. Domain analysis on Pax3 revealed that the Pax3 homeodomain is necessary for phenotypic competition, but is not sufficient, as competition also requires the paired and transcriptional activation domains of Pax3. Remarkably, substitution mutants in which DUX4 homeodomains are replaced by Pax7 homeodomains retain the ability to inhibit differentiation and to induce cytotoxicity.

sFSHD is a genetically dominant myopathy caused by mutations that cause expression of the normally silent DUX4 gene. This transcription factor has been shown to interfere with myogenesis when misexpressed at very low levels in myoblasts, and to cause cell death when overexpressed at high levels. A previous report using adeno-associated virus to deliver high levels of DUX4 to mouse skeletal muscle demonstrated severe pathology that was suppressed on a p53 knockout background, implying that DUX4 acted through the p53 pathway. Here, we investigate the p53-dependence of DUX4 using both in vitro cellular and the transgenic iDUX4[2.7] mouse models. We find that inhibiting p53 has no effect on the cytoxicity of DUX4 in vitro. When crossed onto the p53 null background, we find no suppression of the male-specific lethality or skin phenotypes of the DUX4 transgene, and find that primary myoblasts from this mouse are still killed by DUX4 expression. These data challenge the notion that the p53 pathway is central to the pathogenicity of DUX4.Summary StatementDUX4 is thought to mediate cytopathology through p53. Here, DUX4 is shown to kill primary myoblasts and promote pathological phenotypes in the iDUX4[2.7] mouse model on the p53-null background, calling into question this notion.

Facioscapulohumeral muscular dystrophy (FSHD) is a genetically dominant myopathy caused by mutations that disrupt repression of the normally silent DUX4 gene, which encodes a transcription factor that has been shown to interfere with myogenesis when misexpressed at very low levels in myoblasts and to cause cell death when overexpressed at high levels. A previous report using adeno-associated virus to deliver high levels of DUX4 to mouse skeletal muscle demonstrated severe pathology that was suppressed on a p53-knockout background, implying that DUX4 acted through the p53 pathway. Here, we investigate the p53 dependence of DUX4 using various in vitro and in vivo models. We find that inhibiting p53 has no effect on the cytoxicity of DUX4 on C2C12 myoblasts, and that expression of DUX4 does not lead to activation of the p53 pathway. DUX4 does lead to expression of the classic p53 target gene Cdkn1a (p21) but in a p53-independent manner. Meta-analysis of 5 publicly available data sets of DUX4 transcriptional profiles in both human and mouse cells shows no evidence of p53 activation, and further reveals that Cdkn1a is a mouse-specific target of DUX4. When the inducible DUX4 mouse model is crossed onto the p53-null background, we find no suppression of the male-specific lethality or skin phenotypes that are characteristic of the DUX4 transgene, and find that primary myoblasts from this mouse are still killed by DUX4 expression. These data challenge the notion that the p53 pathway is central to the pathogenicity of DUX4.

Objective: Facioscapulohumeral muscular dystrophy (FSHD) is a neuromuscular disease with an unclear genetic mechanism. Most patients have a contraction of the D4Z4 macrosatellite repeat array at 4qter, which is thought to cause partial demethylation (FSHD1) of the contracted allele. Demethylation has been surveyed at 3 restriction enzyme sites in the first repeat and only a single site across the entire array, and current models postulate that a generalized D4Z4 chromatin alteration causes FSHD. The background of normal alleles has confounded the study of epigenetic alterations; however, rare patients (FSHD2) have a form of the disease in which demethylation is global, i.e., on all D4Z4 elements throughout the genome. Our objective was to take advantage of the global nature of FSHD2 to identify where disease-relevant methylation changes occur within D4Z4. Methods: Using bisulfite sequencing of DNA from blood and myoblast cells, methylation levels at 74 CpG sites across 3 disparate regions within D4Z4 were measured in FSHD2 patients and controls. Results: We found that rates of demethylation caused by FSHD2 are not consistent across D4Z4. We identified a focal region of extreme demethylation within a 5′ domain, which we named DR1. Other D4Z4 regions, including the DUX4 ORF, were hypomethylated but to a much lesser extent. Conclusions: These data challenge the simple view that FSHD is caused by a broad “opening” of D4Z4 and lead us to postulate that the region of focal demethylation is the site of action of the key D4Z4 chromatin regulatory factors that go awry in FSHD.

Facioscapulohumeral muscular dystrophy is a genetically dominant, currently untreatable muscular dystrophy. It is caused by mutations that enable expression of the normally silent DUX4 gene, which encodes a pathogenic transcription factor. A screen based on Tet-on DUX4-induced mouse myoblast death previously uncovered compounds from a 44,000-compound library that protect against DUX4 toxicity. Many of those compounds acted downstream of DUX4 in an oxidative stress pathway. Here, we extend this screen to an additional 160,000 compounds and, using greater stringency, identify a new set of DUX4-protective compounds. From 640 hits, we performed secondary screens, repurchased 46 of the most desirable, confirmed activity, and tested each for activity against other cell death-inducing insults. The majority of these compounds also protected against oxidative stress. Of the 100 repurchased compounds identified through both screens, only SHC40, 75, and 98 inhibited DUX4 target genes, but they also inhibited dox-mediated DUX4 expression. Using a target gene readout on the 640-compound hit set, we discovered three overlooked compounds, SHC351, 540, and 572, that inhibit DUX4 target gene upregulation without nonspecific effects on the Tet-on system. These novel inhibitors of DUX4 transcriptional activity may thus act on pathways or cofactors needed by DUX4 for transcriptional activation in these cells.

BACKGROUND: Facioscapulohumeral muscular dystrophy (FSHD) is caused by epigenetic alterations at the D4Z4 macrosatellite repeat locus on chromosome 4, resulting in inappropriate expression of the DUX4 protein. The DUX4 protein is therefore the primary molecular target for therapeutic intervention. METHODS: We have developed a high-throughput screen based on the toxicity of DUX4 when overexpressed in C2C12 myoblasts, and identified inhibitors of DUX4-induced toxicity from within a diverse set of 44,000 small, drug-like molecules. A total of 1,280 hits were then subjected to secondary screening for activity against DUX4 expressed by 3T3 fibroblasts, for absence of activity against the tet-on system used to conditionally express DUX4, and for potential effects on cellular proliferation rate. RESULTS: This allowed us to define a panel of 52 compounds to use as probes to identify essential pathways of DUX4 activity. We tested these compounds for their ability to protect wild-type cells from other types of cell death-inducing insults. Remarkably, we found that 60% of the DUX4 toxicity inhibitors that we identified also protected cells from tert-butyl hydrogen peroxide, an oxidative stress-inducing compound. Compounds did not protect against death induced by caspase activation, DNA damage, protein misfolding, or ER stress. Encouragingly, many of these compounds are also protective against DUX4 expression in human cells. CONCLUSION: These data suggest that oxidative stress is a dominant pathway through which DUX4-provoked toxicity is mediated in this system, and we speculate that enhancing the oxidative stress response pathway might be clinically beneficial in FSHD.

Background Satellite cells (SCs) are indispensable for muscle regeneration and repair; however, due to low frequency in primary muscle and loss of engraftment potential after ex vivo expansion, their use in cell therapy is currently unfeasible. To date, an alternative to this limitation has been the transplantation of SC-derived myogenic progenitor cells (MPCs), although these do not hold the same attractive properties of stem cells, such as self-renewal and long-term regenerative potential. Methods We develop a method to expand wild-type and dystrophic fresh isolated satellite cells using transient expression of Pax3. This approach can be combined with genetic correction of dystrophic satellite cells and utilized to promote muscle regeneration when transplanted into dystrophic mice. Results Here, we show that SCs from wild-type and dystrophic mice can be expanded in culture through transient expression of Pax3, and these expanded activated SCs can regenerate the muscle. We test this approach in a gene therapy model by correcting dystrophic SCs from a mouse lacking dystrophin using a Sleeping Beauty transposon carrying the human μDYSTROPHIN gene. Transplantation of these expanded corrected cells into immune-deficient, dystrophin-deficient mice generated large numbers of dystrophin-expressing myofibers and improved contractile strength. Importantly, in vitro expanded SCs engrafted the SC compartment and could regenerate muscle after secondary injury. Conclusion These results demonstrate that Pax3 is able to promote the ex vivo expansion of SCs while maintaining their stem cell regenerative properties. Electronic supplementary material The online version of this article (doi:10.1186/s13395-015-0061-7) contains supplementary material, which is available to authorized users.

Background Misexpression of the double homeodomain transcription factor DUX4 results in facioscapulohumeral muscular dystrophy (FSHD). A DNA-binding consensus with two tandem TAAT motifs based on chromatin IP peaks has been discovered; however, the consensus has multiple variations (flavors) of unknown relative activity. In addition, not all peaks have this consensus, and the Pitx1 promoter, the first DUX4 target sequence mooted, has a different TAAT-rich sequence. Furthermore, it is not known whether and to what extent deviations from the consensus affect DNA-binding affinity and transcriptional activation potential. Results Here, we take both unbiased and consensus sequence-driven approaches to determine the DNA-binding specificity of DUX4 and its tolerance to mismatches at each site within its consensus sequence. We discover that the best binding and the greatest transcriptional activation are observed when the two TAAT motifs are separated by a C residue. The second TAAT motif in the consensus sequence is actually (T/C)AAT. We find that a T is preferred here. DUX4 has no transcriptional activity on “half-sites”, i.e., those bearing only a single TAAT motif. We further find that DUX4 does not bind to the TAATTA motif in the Pitx1 promoter, that Pitx1 sequences have no competitive band shift activity, and that the Pitx1 sequence is transcriptionally inactive, calling into question PITX1 as a DUX4 target gene. Finally, by multimerizing binding sites, we find that DUX4 transcriptional activation demonstrates tremendous synergy and that at low DNA concentrations, at least two motifs are necessary to detect a transcriptional response. Conclusions These studies illuminate the DNA-binding sequence preferences of DUX4. Electronic supplementary material The online version of this article (doi:10.1186/s13395-016-0080-z) contains supplementary material, which is available to authorized users.