MLL5, a homolog of Drosophila trithorax located within a segment of chromosome band 7q22 implicated in myeloid leukemia

KMT2E Haploinsufficiency Manifests Autism-Like Behaviors and Amygdala Neuronal Development Dysfunction in Mice

Autism spectrum disorders (ASD) are highly heterogeneous neurodevelopmental disorders characterized by impaired social interaction skills. Whole exome sequencing has identified loss-of-function mutations in lysine methyltransferase 2E (KMT2E, also named MLL5) in ASD patients and it is listed as an ASD high-risk gene in humans. However, experimental evidence of KMT2E in association with ASD-like manifestations or neuronal function is still missing. Relying on KMT2E^+/- mice, through animal behavior analyses, positron emission tomography (PET) imaging, and neuronal morphological analyses, we explored the role of KMT2E haploinsufficiency in ASD-like symptoms. Behavioral results revealed that KMT2E haploinsufficiency was sufficient to produce social deficit, accompanied by anxiety in mice. Whole-brain ¹⁸F-FDG-PET analysis identified that relative amygdala glycometabolism was selectively decreased in KMT2E^+/- mice compared to wild-type mice. The numbers and soma sizes of amygdala neurons in KMT2E^+/- mice were prominently increased. Additionally, KMT2E mRNA levels in human amygdala were significantly decreased after birth during brain development. Our findings support a causative role of KMT2E in ASD development and suggest that amygdala neuronal development abnormality is likely a major underlying mechanism.

An Alternative Splicing Variant of the Mixed-Lineage Leukemia 5 Protein Is a Cellular Adhesion Receptor for ScaA of Orientia tsutsugamushi

Scrub typhus is a mite-borne disease caused by the obligately intracellular bacterium Orientia tsutsugamushi. We previously demonstrated that ScaA, an autotransporter membrane protein of O. tsutsugamushi, is commonly shared in various genotypes and involved in adherence to host cells. Here, we identified a mixed-lineage leukemia 5 (MLL5) mammalian trithorax group protein as a host receptor that interacts with ScaA. MLL5, identified by yeast two-hybrid screening, is an alternative splicing variant of MLL5 (vMLL5) which contains 13 exons with additional intron sequences encoding a tentative transmembrane domain. Indeed, vMLL5 is expressed on the plasma membrane as well as in intracellular compartments in eukaryotic cells and colocalized with adherent O. tsutsugamushi. In addition, ScaA-expressing Escherichia coli showed significantly increased adherence to vMLL5-overexpressing cells compared with vector control cells. We mapped the C-terminal region of the passenger domain of ScaA as a ligand for vMLL5 and determined that the Su(var)3-9, Enhancer of zeste, Trithorax (SET) domain of MLL5 is an essential and sufficient motif for ScaA binding. We observed significant and specific inhibition of bacterial adhesion to host cells in competitive inhibition assays using the C-terminal fragment of ScaA or the SET domain of vMLL5. Moreover, immunization with the C-terminal fragment of ScaA provided neutralizing activity and protective immunity against lethal challenge with O. tsutsugamushi as efficiently as vaccination with the whole passenger domain of ScaA. These results indicate that vMLL5 is a novel cellular receptor for ScaA-mediated adhesion of O. tsutsugamushi and facilitates bacterial adhesion to host cells, thereby enhancing bacterial infection. IMPORTANCE O. tsutsugamushi is a mite-borne pathogen that causes scrub typhus. As an obligately intracellular pathogen, its adhesion to and invasion of host cells are critical steps for bacterial growth. However, the molecular basis of the bacterial ligand and host receptor interaction is poorly defined. Here, we identified a splicing variant of MLL5 (vMLL5) as a cellular adhesion receptor of ScaA, an outer membrane autotransporter protein of O. tsutsugamushi. We mapped the interacting domains in the bacterial ligand and host receptor and confirmed their functional interaction. In addition, immunization with the C-terminal region of ScaA, which involves an interaction with the SET domain of vMLL5, not only induces enhanced neutralizing antibodies but also provides protective immunity against lethal challenge with O. tsutsugamushi.

Epigenetic genes and epilepsy - emerging mechanisms and clinical applications

An increasing number of epilepsies are being attributed to variants in genes with epigenetic functions. The products of these genes include factors that regulate the structure and function of chromatin and the placing, reading and removal of epigenetic marks, as well as other epigenetic processes. In this Review, we provide an overview of the various epigenetic processes, structuring our discussion around five function-based categories: DNA methylation, histone modifications, histone-DNA crosstalk, non-coding RNAs and chromatin remodelling. We provide background information on each category, describing the general mechanism by which each process leads to altered gene expression. We also highlight key clinical and mechanistic aspects, providing examples of genes that strongly associate with epilepsy within each class. We consider the practical applications of these findings, including tissue-based and biofluid-based diagnostics and precision medicine-based treatments. We conclude that variants in epigenetic genes are increasingly found to be causally involved in the epilepsies, with implications for disease mechanisms, treatments and diagnostics.

MLL5 is involved in retinal photoreceptor maturation through facilitating CRX-mediated photoreceptor gene transactivation

Histone methylation, particularly at the H3K4 position, is thought to contribute to the specification of photoreceptor cell fate; however, the mechanisms linking histone methylation with transcription factor transactivation and photoreceptor gene expression have not yet been determined. Here, we demonstrate that MLL5 is abundantly expressed in the mouse retina. Mll5 deficiency impaired electroretinogram responses, alongside attenuated expression of a number of retina genes. Mechanistic studies revealed that MLL5 interacts with the retina-specific transcription factor, CRX, contributing to its binding to photoreceptor-specific gene promoters. Moreover, depletion of MLL5 impairs H3K4 methylation and H3K79 methylation, which subsequently compromises CRX-CBP assembly and H3 acetylation on photoreceptor promoters. Our data support a scenario in which recognition of H3K4 methylation by MLL5 is required for photoreceptor-specific gene transcription through maintaining a permissive chromatin state and proper CRX-CBP recruitment at promoter sites.

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MLL5 is essential for the expression of critical photoreceptor genes

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MLL5 depletion reduces H3K4/K79 methylation at photoreceptor gene promoters

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MLL5 interacts with CRX via its CD4 domain

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Recognition of H3K4me2/3 by MLL5 is a prerequisite for CRX recruitment to chromatin

Case Report: A Novel KMT2E Splice Site Variant as a Cause of O'Donnell-Luria-Rodan Syndrome in a Male Patient

BACKGROUND

O'Donnell-Luria-Rodan (ODLURO) syndrome is an autosomal dominant systemic disorder characterized by global developmental delay caused by mutations in the KMT2E gene. The aim of this study was to investigate the role of KMT2E mutations as a cause of ODLURO syndrome in a Chinese boy.

METHODS

We reported the clinical course of a Chinese boy who was diagnosed with ODLURO syndrome by the whole exome sequencing. We extracted genomic DNA of the proband and parents, gene variations were screened using whole-exome sequencing, followed by validation using direct Sanger sequencing. The effect of mRNA splicing variants were analyzed through a minigene splice assay and in vitro reverse transcription PCR (RT-PCR).

RESULTS

The proband presented with recurrent seizures and developmental delay. Using genetic analysis, we identified that the proband carried a de novo heterozygous splicing variant (c.1248+1G>T) in the KMT2E gene. In vivo transcript analysis showed that the proband did not carry any KMT2E mRNA transcript, while a specific exon11-exon13 (440 bp) transcript was detected in the unaffected parents. The in vitro minigene splice assay conducted in HEK293 cells confirmed that the c.1248+1G>T variant resulted in exon 12 skipping, which in turn caused an alteration in KMT2E mRNA splicing. The mutant transcript created a premature stop codon at the 378 amino acid position that could have been caused nonsense-mediated mRNA decay (NMD).

CONCLUSION

We verified the pathogenic effect of the KMT2E c.1248+1G>T splicing variant, which disturbed normal mRNA splicing and caused mRNA decay. Our findings suggest that splice variants play an important role in the molecular basis of ODLURO, and that careful molecular profiling of these patients could play an essential role in tailoring of personalized treatment options soon.

MLL5 improves ATRA driven differentiation and promotes xenotransplant engraftment in acute promyelocytic leukemia model

Although the mixed lineage leukemia 5 (MLL5) gene has prognostic implications in acute promyelocyte leukemia (APL), the underlying mechanism remains to be elucidated. Here, we demonstrate the critical role exerted by MLL5 in APL regarding cell proliferation and resistance to drug-induced apoptosis, through mtROS regulation. Additionally, MLL5 overexpression increased the responsiveness of APL leukemic cells to all-trans retinoic acid (ATRA)-induced differentiation, via regulation of the epigenetic modifiers SETD7 and LSD1. In silico analysis indicated that APL blasts with MLL5^high transcript levels were associated with retinoic acid binding and downstream signaling, while MLL5^low blasts displayed decreased expression of epigenetic modifiers (such as KMT2C, PHF8 and ARID4A). Finally, APL xenograft transplants demonstrated improved engraftment of MLL5-expressing cells and increased myeloid differentiation over time. Concordantly, evaluation of engrafted blasts revealed increased responsiveness of MLL5-expressing cells to ATRA-induced granulocytic differentiation. Together, we describe the epigenetic changes triggered by the interaction of MLL5 and ATRA resulting in enhanced granulocytic differentiation.

Effects of MLL5 and HOXA regulated by NRP1 on radioresistance in A549

Radiotherapy is widely used in the management of lung cancer, and physicians are aware that the effect of radiotherapy is dependent on radiosensitivity. Although a series of blockers and activators targeting molecules related to radioresistance have been developed as radiation sensitizers, compensatory mechanisms or drug resistance limits their clinical efficacy. The identification of a key molecule related to lung cancer cell radioresistance or an effective molecular target is a challenging but important problem in radiation oncology. A previous study found that neuropilin 1 (NRP1) is related to radioresistance in A549 cells and is associated with VEGF, PI3K-Akt, MAPK-ERK, P38, NF-κβ and TGF-β. Inhibition of NRP1 can increase the radiosensitivity of A549 cells. Therefore, NRP1 may be a molecular target for radiotherapy-sensitizing drugs in lung cancer. The present study investigated the key downstream genes of NRP1, verified their regulation and clarified their roles in regulating lung cancer radioresistance. NRP1 positively regulated the downstream homeobox genes (HOXs) HOXA6, HOXA9 and mixed lineage leukaemia 5 (MLL5) in addition to MLL5-regulated HOXA6 and HOXA9, but these genes did not regulate NRP1. MLL5, HOXA6 and HOXA9 levels were decreased in tumour tissues and positively correlated with NRP1. All of these genes were induced by ionizing radiation in vivo and in vitro. NRP1 expression was significantly lower in squamous cell carcinoma compared with that in adenocarcinoma, and lymph node metastasis occurred more often in patients with lung cancer with high MLL5 and NRP1 expression compared with patients with low MLL5 and NRP1 expression. Collectively, these data confirmed that NRP1 is associated with MLL5 and regulates radioresistance through HOXA6 and HOXA9.

A chromatin perspective on metabolic and genotoxic impacts on hematopoietic stem and progenitor cells

Fate determination in self-renewal and differentiation of hematopoietic stem and progenitor cells (HSCs and HPCs) is ultimately controlled by gene expression, which is profoundly influenced by the global and local chromatin state. Cellular metabolism directly influences the chromatin state through the dynamic regulation of the enzymatic activities that modify DNA and histones, but also generates genotoxic metabolites that can damage DNA and thus pose threat to the genome integrity. On the other hand, mechanisms modulating the chromatin state impact metabolism by regulating the expression and activities of key metabolic enzymes. Moreover, through regulating either DNA damage response directly or expression of genes involved in this process, chromatin modulators play active and crucial roles in guarding the genome integrity, breaching of which results in defective HSPC function. Therefore, HSPC function is regulated by the dynamic and two-way interactions between metabolism and chromatin. Here, we review recent advances that provide a chromatin perspective on the major impacts the metabolic and genotoxic factors can have on HSPC function and fate determination.

Why are so many MLL lysine methyltransferases required for normal mammalian development?

The mixed lineage leukemia (MLL) family of proteins became known initially for the leukemia link of its founding member. Over the decades, the MLL family has been recognized as an important class of histone H3 lysine 4 (H3K4) methyltransferases that control key aspects of normal cell physiology and development. Here, we provide a brief history of the discovery and study of this family of proteins. We address two main questions: why are there so many H3K4 methyltransferases in mammals; and is H3K4 methylation their key function?

Set3 Is Required for Asexual Development, Aflatoxin Biosynthesis, and Fungal Virulence in Aspergillus flavus

Aspergillus flavus is an opportunistic pathogenic fungus for both plant and animal that produces carcinogenic toxins termed aflatoxins (AFs). To identify possible genetic targets to reduce AF contamination, in this study, we have characterized a novel A. flavus Set3, and it shares sequence homology with the yeast protein Set3. The set3 deletion mutants present no difference in growth rate but alterations in asexual development and secondary metabolite production when compared to the A. flavus wild type. Specifically, deletion of set3 gene decreases conidiophore formation and conidial production through downregulating expression of brlA and abaA genes. In addition, normal levels of set3 are required for sclerotial development and expression of sclerotia-related genes nsdC and sclR. Further analyses demonstrated that Set3 negatively regulates AF production as well as the concomitant expression of genes in the AF gene cluster. Importantly, our results also display that A. flavus Set3 is involved in crop kernel colonization. Taking together, these results reveal that a novel Set3 plays crucial roles in morphological development, secondary metabolism, and fungal virulence in A. flavus.

Planarian flatworms as a new model system for understanding the epigenetic regulation of stem cell pluripotency and differentiation

Planarian flatworms possess pluripotent stem cells (neoblasts) that are able to differentiate into all cell types that constitute the adult body plan. Consequently, planarians possess remarkable regenerative capabilities. Transcriptomic studies have revealed that gene expression is coordinated to maintain neoblast pluripotency, and ensure correct lineage specification during differentiation. But as yet they have not revealed how this regulation of expression is controlled. In this review, we propose that planarians represent a unique and effective system to study the epigenetic regulation of these processes in an in vivo context. We consolidate evidence suggesting that although DNA methylation is likely present in some flatworm lineages, it does not regulate neoblast function in Schmidtea mediterranea. A number of phenotypic studies have documented the role of histone modification and chromatin remodelling complexes in regulating distinct neoblast processes, and we focus on four important examples of planarian epigenetic regulators: Nucleosome Remodeling Deacetylase (NuRD) complex, Polycomb Repressive Complex (PRC), the SET1/MLL methyltransferases, and the nuclear PIWI/piRNA complex. Given the recent advent of ChIP-seq in planarians, we propose future avenues of research that will identify the genomic targets of these complexes allowing for a clearer picture of how neoblast processes are coordinated at the epigenetic level. These insights into neoblast biology may be directly relevant to mammalian stem cells and disease. The unique biology of planarians will also allow us to investigate how extracellular signals feed into epigenetic regulatory networks to govern concerted neoblast responses during regenerative polarity, tissue patterning, and remodelling.

MLL5 (KMT2E): structure, function, and clinical relevance

The mixed lineage leukemia (MLL) family of genes, also known as the lysine N-methyltransferase 2 (KMT2) family, are homologous to the evolutionarily conserved trithorax group that plays critical roles in the regulation of homeotic gene (HOX) expression and embryonic development. MLL5, assigned as KMT2E on the basis of its SET domain homology, was initially categorized under MLL (KMT2) family together with other six SET methyltransferase domain proteins (KMT2A-2D and 2F-2G). However, emerging evidence suggests that MLL5 is distinct from the other MLL (KMT2) family members, and the protein it encodes appears to lack intrinsic histone methyltransferase (HMT) activity towards histone substrates. MLL5 has been reported to play key roles in diverse biological processes, including cell cycle progression, genomic stability maintenance, adult hematopoiesis, and spermatogenesis. Recent studies of MLL5 variants and isoforms and putative MLL5 homologs in other species have enriched our understanding of the role of MLL5 in gene expression regulation, although the mechanism of action and physiological function of MLL5 remains poorly understood. In this review, we summarize recent research characterizing the structural features and biological roles of MLL5, and we highlight the potential implications of MLL5 dysfunction in human disease.

upSET, the Drosophila homologue of SET3, Is Required for Viability and the Proper Balance of Active and Repressive Chromatin Marks

Chromatin plays a critical role in faithful implementation of gene expression programs. Different post-translational modifications (PTMs) of histone proteins reflect the underlying state of gene activity, and many chromatin proteins write, erase, bind, or are repelled by, these histone marks. One such protein is UpSET, the Drosophila homolog of yeast Set3 and mammalian KMT2E (MLL5). Here, we show that UpSET is necessary for the proper balance between active and repressed states. Using CRISPR/Cas-9 editing, we generated S2 cells that are mutant for upSET We found that loss of UpSET is tolerated in S2 cells, but that heterochromatin is misregulated, as evidenced by a strong decrease in H3K9me2 levels assessed by bulk histone PTM quantification. To test whether this finding was consistent in the whole organism, we deleted the upSET coding sequence using CRISPR/Cas-9, which we found to be lethal in both sexes in flies. We were able to rescue this lethality using a tagged upSET transgene, and found that UpSET protein localizes to transcriptional start sites (TSS) of active genes throughout the genome. Misregulated heterochromatin is apparent by suppressed position effect variegation of the wm4 allele in heterozygous upSET-deleted flies. Using nascent-RNA sequencing in the upSET-mutant S2 lines, we show that this result applies to heterochromatin genes generally. Our findings support a critical role for UpSET in maintaining heterochromatin, perhaps by delimiting the active chromatin environment.

The Human Mixed Lineage Leukemia 5 (MLL5), a Sequentially and Structurally Divergent SET Domain-Containing Protein with No Intrinsic Catalytic Activity

Mixed Lineage Leukemia 5 (MLL5) plays a key role in hematopoiesis, spermatogenesis and cell cycle progression. Chromatin binding is ensured by its plant homeodomain (PHD) through a direct interaction with the N-terminus of histone H3 (H3). In addition, MLL5 contains a Su(var)3-9, Enhancer of zeste, Trithorax (SET) domain, a protein module that usually displays histone lysine methyltransferase activity. We report here the crystal structure of the unliganded SET domain of human MLL5 at 2.1 Å resolution. Although it shows most of the canonical features of other SET domains, both the lack of key residues and the presence in the SET-I subdomain of an unusually large loop preclude the interaction of MLL5 SET with its cofactor and substrate. Accordingly, we show that MLL5 is devoid of any in vitro methyltransferase activity on full-length histones and histone H3 peptides. Hence, the three dimensional structure of MLL5 SET domain unveils the structural basis for its lack of methyltransferase activity and suggests a new regulatory mechanism.

Structural Insight into Recognition of Methylated Histone H3K4 by Set3

The plant homeodomain (PHD) finger of Set3 binds methylated lysine 4 of histone H3 in vitro and in vivo; however, precise selectivity of this domain has not been fully characterized. Here, we explore the determinants of methyllysine recognition by the PHD fingers of Set3 and its orthologs. We use X-ray crystallographic and spectroscopic approaches to show that the Set3 PHD finger binds di- and trimethylated states of H3K4 with comparable affinities and employs similar molecular mechanisms to form complexes with either mark. Composition of the methyllysine-binding pocket plays an essential role in determining the selectivity of the PHD fingers. The finding that the histone-binding activity is not conserved in the PHD finger of Set4 suggests different functions for the Set3 and Set4 paralogs.

DNA Damage-Induced HSPC Malfunction Depends on ROS Accumulation Downstream of IFN-1 Signaling and Bid Mobilization

Mouse mutants with an impaired DNA damage response frequently exhibit a set of remarkably similar defects in the HSPC compartment that are of largely unknown molecular basis. Using Mixed-Lineage-Leukemia-5 (Mll5)-deficient mice as prototypical examples, we have identified a mechanistic pathway linking DNA damage and HSPC malfunction. We show that Mll5 deficiency results in accumulation of DNA damage and reactive oxygen species (ROS) in HSPCs. Reduction of ROS efficiently reverses hematopoietic defects, establishing ROS as a major cause of impaired HSPC function. The Ink4a/Arf locus also contributes to HSPC phenotypes, at least in part via promotion of ROS. Strikingly, toxic ROS levels in Mll5^-/- mice are critically dependent on type 1 interferon (IFN-1) signaling, which triggers mitochondrial accumulation of full-length Bid. Genetic inactivation of Bid diminishes ROS levels and reverses HSPC defects in Mll5^-/- mice. Overall, therefore, our findings highlight an unexpected IFN-1 > Bid > ROS pathway underlying DNA damage-associated HSPC malfunction.

MLL5 maintains spindle bipolarity by preventing aberrant cytosolic aggregation of PLK1

Faithful chromosome segregation with bipolar spindle formation is critical for the maintenance of genomic stability. Perturbation of this process often leads to severe mitotic failure, contributing to tumorigenesis. MLL5 has been demonstrated to play vital roles in cell cycle progression and the maintenance of genomic stability. Here, we identify a novel interaction between MLL5 and PLK1 in the cytosol that is crucial for sustaining spindle bipolarity during mitosis. Knockdown of MLL5 caused aberrant PLK1 aggregation that led to acentrosomal microtubule-organizing center (aMTOC) formation and subsequent spindle multipolarity. Further molecular studies revealed that the polo-box domain (PBD) of PLK1 interacted with a binding motif on MLL5 (Thr887-Ser888-Thr889), and this interaction was essential for spindle bipolarity. Overexpression of wild-type MLL5 was able to rescue PLK1 mislocalization and aMTOC formation in MLL5-KD cells, whereas MLL5 mutants incapable of interacting with the PBD failed to do so. We thus propose that MLL5 preserves spindle bipolarity through maintaining cytosolic PLK1 in a nonaggregated form.

Mixed Lineage Leukemia 5 (MLL5) Protein Stability Is Cooperatively Regulated by O-GlcNac Transferase (OGT) and Ubiquitin Specific Protease 7 (USP7)

Mixed lineage leukemia 5 (MLL5) protein is a trithorax family histone 3 lysine 4 (H3K4) methyltransferase that regulates diverse biological processes, including cell cycle progression, hematopoiesis and cancer. The mechanisms by which MLL5 protein stability is regulated have remained unclear to date. Here, we showed that MLL5 protein stability is cooperatively regulated by O-GlcNAc transferase (OGT) and ubiquitin-specific protease 7 (USP7). Depletion of OGT in cells led to a decrease in the MLL5 protein level through ubiquitin/proteasome-dependent proteolytic degradation, whereas ectopic expression of OGT protein suppressed MLL5 ubiquitylation. We further identified deubiquitinase USP7 as a novel MLL5-associated protein using mass spectrometry. USP7 stabilized the MLL5 protein through direct binding and deubiquitylation. Loss of USP7 induced degradation of MLL5 protein. Conversely, overexpression of USP7, but not a catalytically inactive USP7 mutant, led to decreased ubiquitylation and increased MLL5 stability. Co-immunoprecipitation and co-immunostaining assays revealed that MLL5, OGT and USP7 interact with each other to form a stable ternary complex that is predominantly located in the nucleus. In addition, upregulation of MLL5 expression was correlated with increased expression of OGT and USP7 in human primary cervical adenocarcinomas. Our results collectively reveal a novel molecular mechanism underlying regulation of MLL5 protein stability and provide new insights into the functional interplay among O-GlcNAc transferase, deubiquitinase and histone methyltransferase.

MLL5 Orchestrates a Cancer Self-Renewal State by Repressing the Histone Variant H3.3 and Globally Reorganizing Chromatin

Mutations in the histone 3 variant H3.3 have been identified in one-third of pediatric glioblastomas (GBMs), but not in adult tumors. Here we show that H3.3 is a dynamic determinant of functional properties in adult GBM. H3.3 is repressed by mixed lineage leukemia 5 (MLL5) in self-renewing GBM cells. MLL5 is a global epigenetic repressor that orchestrates reorganization of chromatin structure by punctuating chromosomes with foci of compacted chromatin, favoring tumorigenic and self-renewing properties. Conversely, H3.3 antagonizes self-renewal and promotes differentiation. We exploited these epigenetic states to rationally identify two small molecules that effectively curb cancer stem cell properties in a preclinical model. Our work uncovers a role for MLL5 and H3.3 in maintaining self-renewal hierarchies in adult GBM.

Assessment of MLL methyltransferase gene expression in larynx carcinoma

Larynx cancer is the second most common type of cancer among all head and neck cancers. Deregulation of epigenetic effectors, including altered expression of histone methyltransferases from the MLL (mixed lineage leukemia) family, have been reported in many cancer types, yet little is known concerning their involvement in larynx cancer. Our objective was to determine the expression profile of MLL genes in larynx carcinoma and normal adjacent tissues and correlate this profile to tumor characteristics. We analyzed the expression profile of 5 MLL genes in 13 cases of larynx carcinoma and their adjacent non-tumor tissues using quantitative real-time PCR. MLL3 was significantly downregulated in tumor samples compared to their normal counterparts, and all MLL genes showed decreased expression in advanced tumors compared to tumors in the initial stage. Altered expression in a single MLL gene was associated with a similar alteration in the other MLL genes, revealing a strong correlation of expression in each individual patient. In conclusion, MLL genes may have similar transcriptional control, and decreased expression of these genes may contribute to larynx cancer progression.

Association of the histone-lysine N-methyltransferase MLL5 gene with coronary artery disease in Chinese Han people

BACKGROUND

MLL5, a member of the histone-lysine N-methyltransferase family, has been implicated in the control of the cell cycle progression and survival. The aim of this study was to explore the relationship between the interaction of histone-lysine N-methyltransferase MLL5 gene polymorphism and CAD in a Chinese Han population.

METHODS

Using a case-control study of Chinese CAD patients (n = 565) and healthy controls (n = 694), we investigated the MLL5 gene polymorphism by the use of polymerase chain reaction fragment length polymorphism (PCR-RFLP) analysis.

RESULTS

For total, the distribution of SNP1 (rs12671368) and SNP2 (rs2192932) genotypes showed a significant difference between CAD and control participants (P1 = 0.03, P2 = 0.02). For total the distribution of SNP1 (rs12671368) and SNP2 (rs2192932) alleles in the dominant model (GG vs. AA + AG) and the recessive model (AA vs. AG + GG) showed a significant difference between CAD and control participants (for allele: P1 < 0.01 and P2 = 0.05, for dominant model: P1 > 0.05 and P2 = 0.02, for recessive model: P1 = 0.03 and P2 = 0.78, respectively). For total the significant difference of the distribution of SNP1 and SNP2 in the dominant model and recessive model was retained after adjusting for covariates (for dominant model: SNP1 OR: 1.68, 95% confidence interval [CI]: 1.08-2.64, P = 0.02; SNP2 OR: 0.51, 95% CI: 0.36-0.72, P = 0.01; for recessive model: SNP1 OR: 1.84, 95% confidence interval [CI]: 1.28-2.64, P < 0.01; SNP2 OR: 0.65, 95% CI: 0.35-1.22, P = 0.18).

CONCLUSIONS

The GG genotype of rs12671368 and the AA genotype of rs2192932 in the MLL5 gene could be protective genetic markers of CAD.

-7/7q- syndrome in myeloid-lineage hematopoietic malignancies: attempts to understand this complex disease entity

The recurrence of chromosomal abnormalities in a specific subtype of cancer strongly suggests that dysregulated gene expression in the corresponding region has a critical role in disease pathogenesis. -7/7q-, defined as the entire loss of chromosome 7 and partial deletion of its long arm, is among the most frequently observed chromosomal aberrations in myeloid-lineage hematopoietic malignancies such as myelodysplastic syndrome and acute myeloid leukemia, particularly in patients treated with cytotoxic agents and/or irradiation. Tremendous efforts have been made to clarify the molecular mechanisms underlying the disease development, and several possible candidate genes have been cloned. However, the study is still underway, and the entire nature of this syndrome is not completely understood. In this review, we focus on the attempts to identify commonly deleted regions in patients with -7/7q-; isolate the candidate genes responsible for disease development, cooperative genes and the factors affecting disease prognosis; and determine effective and potent therapeutic approaches. We also refer to the possibility that the accumulation of multiple gene haploinsufficiency, rather than the loss of a single tumor suppressor gene, may contribute to the development of diseases with large chromosomal deletions such as -7/7q-.

Impact of MLL5 expression on decitabine efficacy and DNA methylation in acute myeloid leukemia

Hypomethylating agents are widely used in patients with myelodysplastic syndromes and unfit patients with acute myeloid leukemia. However, it is not well understood why only some patients respond to hypomethylating agents. We found previously that the effect of decitabine on hematopoietic stem cell viability differed between Mll5 wild-type and null cells. We, therefore, investigated the role of MLL5 expression levels on outcome of acute myeloid leukemia patients who were treated with decitabine. MLL5 above the median expression level predicted longer overall survival independent of DNMT3A mutation status in bivariate analysis (median overall survival for high vs. low MLL5 expression 292 vs. 167 days; P=0.026). In patients who received three or more courses decitabine, high MLL5 expression and wild-type DNMT3A independently predicted improved overall survival (median overall survival for high vs. low MLL5 expression 468 vs. 243 days; P=0.012). In transformed murine cells, loss of Mll5 was associated with resistance to low-dose decitabine, less global DNA methylation in promoter regions, and reduced DNA demethylation upon decitabine treatment. Together, these data support our clinical observation of improved outcome in decitabine-treated patients who express MLL5 at high levels, and suggest a mechanistic role of MLL5 in the regulation of DNA methylation.

Prognostic impact of KMT2E transcript levels on outcome of patients with acute promyelocytic leukaemia treated with all-trans retinoic acid and anthracycline-based chemotherapy: an International Consortium on Acute Promyelocytic Leukaemia study

The KMT2E (MLL5) gene encodes a histone methyltransferase implicated in the positive control of genes related to haematopoiesis. Its close relationship with retinoic acid-induced granulopoiesis suggests that the deregulated expression of KMT2E might lead acute promyelocytic leukaemia (APL) blasts to become less susceptible to the conventional treatment protocols. Here, we assessed the impact of KMT2E expression on the prognosis of 121 APL patients treated with ATRA and anthracycline-based chemotherapy. Univariate analysis showed that complete remission (P = 0·006), 2-year overall survival (OS) (P = 0·005) and 2-year disease-free survival (DFS) rates (P = 0·037) were significantly lower in patients with low KMT2E expression; additionally, the 2-year cumulative incidence of relapse was higher in patients with low KMT2E expression (P = 0·04). Multivariate analysis revealed that low KMT2E expression was independently associated with lower remission rate (odds ratio [OR]: 7·18, 95% confidence interval [CI]: 1·71-30·1; P = 0·007) and shorter OS (hazard ratio [HR]: 0·27, 95% CI: 0·08-0·87; P = 0·029). Evaluated as a continuous variable, KMT2E expression retained association with poor remission rate (OR: 10·3, 95% CI: 2·49-43·2; P = 0·001) and shorter survival (HR: 0·17, 95% IC: 0·05-0·53; P = 0·002), while the association with DFS was of marginal significance (HR: 1·01; 95% CI: 0·99-1·02; P = 0·06). In summary, low KMT2E expression may predict poor outcome in APL patients.

NKp44L: A new tool for fighting cancer

We have recently identified that the ligand of natural cytotoxicity triggering receptor 2 (NCR2, best known as NKp44) is expressed on a large panel of malignant cells. This ligand provides a new tool to investigate how stressed cells are recognized and eliminated by natural killer (NK) cells, and to develop novel immunotherapeutic paradigms against cancer.

The genetics of the myelodysplastic syndromes: Classical cytogenetics and recent molecular insights

Myelodysplastic syndromes (MDS) are a complex group of clonal hematopoietic disorders with an attendant diverse array of associated genetic changes. Conventional cytogenetics plays a prominent and well-established role in determining the contemporary diagnosis and prognosis of these disorders. More recently, molecular approaches have been useful in further characterizing this group of diseases, albeit in a largely experimental context, with the detection of changes at the single gene level including mutations, amplification and epigenetic phenomena. Nevertheless, we remain largely ignorant of the genetic underpinnings of MDS. Here we briefly review the established role of cytogenetics in MDS, and emphasize recent advances in unraveling the genetics of MDS, with a view towards how such findings might facilitate our ability to understand, diagnose and treat these disorders in a more rational manner.

Identification of a cellular ligand for the natural cytotoxicity receptor NKp44

With an array of activating and inhibitory receptors, natural killer (NK) cells are involved in the eradication of infected, transformed, and tumor cells. NKp44 is a member of the natural cytotoxicity receptor family, which is exclusively expressed on activated NK cells. Here, we identify natural cytotoxicity receptor NKp44 (NKp44L), a novel isoform of the mixed-lineage leukemia-5 protein, as a cellular ligand for NKp44. Unlike the other MLL family members, NKp44L is excluded from the nucleus, but expressed at the cell-surface level; its subcellular localization is being associated with the presence of a specific C-terminal motif. Strikingly, NKp44L has not been detected on circulating cells isolated from healthy individuals, but it is expressed on a large panel of the tumor and transformed cells. The sharply decreased NK lysis activity induced by anti-NKp44L antibodies directly demonstrates the role of NKp44L in cytotoxicity. Taken together, these results show that NKp44L could be critical for NK cell-mediated innate immunity. The identification and cellular distribution of NKp44L highlight the role of this self-molecule as a danger signal to alert the NK cell network.

The role of maintenance proteins in the preservation of epithelial cell identity during mammary gland remodeling and breast cancer initiation

During normal postnatal mammary gland development and adult remodeling related to the menstrual cycle, pregnancy, and lactation, ovarian hormones and peptide growth factors contribute to the delineation of a definite epithelial cell identity. This identity is maintained during cell replication in a heritable but DNA-independent manner. The preservation of cell identity is fundamental, especially when cells must undergo changes in response to intrinsic and extrinsic signals. The maintenance proteins, which are required for cell identity preservation, act epigenetically by regulating gene expression through DNA methylation, histone modification, and chromatin remodeling. Among the maintenance proteins, the Trithorax (TrxG) and Polycomb (PcG) group proteins are the best characterized. In this review, we summarize the structures and activities of the TrxG and PcG complexes and describe their pivotal roles in nuclear estrogen receptor activity. In addition, we provide evidence that perturbations in these epigenetic regulators are involved in disrupting epithelial cell identity, mammary gland remodeling, and breast cancer initiation.

Molecular basis for chromatin binding and regulation of MLL5

The human mixed-lineage leukemia 5 (MLL5) protein mediates hematopoietic cell homeostasis, cell cycle, and survival; however, the molecular basis underlying MLL5 activities remains unknown. Here, we show that MLL5 is recruited to gene-rich euchromatic regions via the interaction of its plant homeodomain finger with the histone mark H3K4me3. The 1.48-Å resolution crystal structure of MLL5 plant homeodomain in complex with the H3K4me3 peptide reveals a noncanonical binding mechanism, whereby K4me3 is recognized through a single aromatic residue and an aspartate. The binding induces a unique His-Asp swapping rearrangement mediated by a C-terminal α-helix. Phosphorylation of H3T3 and H3T6 abrogates the association with H3K4me3 in vitro and in vivo, releasing MLL5 from chromatin in mitosis. This regulatory switch is conserved in the Drosophila ortholog of MLL5, UpSET, and suggests the developmental control for targeting of H3K4me3. Together, our findings provide first insights into the molecular basis for the recruitment, exclusion, and regulation of MLL5 at chromatin.

UpSET-ting the balance: modulating open chromatin features in metazoan genomes

Appropriate gene expression relies on the sophisticated interplay between genetic and epigenetic factors. Histone acetylation and an open chromatin configuration are key features of transcribed regions and are mainly present around active promoters. Our recent identification of the SET-domain containing protein UpSET established a new functional link between the modulation of open chromatin features and active recruitment of well-known co-repressors in metazoans. Structurally, the SET domain of UpSET resembles H3K4 and H3K36 methyltransferases; however, it is does not confer histone methyltransferase activity. Rather than methylating histones to regulate gene expression like other SET domain-containing proteins, UpSET fine-tunes transcription by modulating the chromatin structure around active promoters resulting in suppression of expression of off-target genes or nearby repetitive elements. Chromatin modulation by UpSET occurs in part through its interaction with histone deacetylases. Here, we discuss the different scenarios in which UpSET could play key roles in modulating gene expression.

Mixed lineage leukemia 5 (MLL5) protein regulates cell cycle progression and E2F1-responsive gene expression via association with host cell factor-1 (HCF-1)

Trithorax group proteins methylate lysine 4 of histone 3 (H3K4) at active gene promoters. MLL5 protein, a member of the Trithorax protein family, has been implicated in the control of the cell cycle progression; however, the underlying molecular mechanism(s) have not been fully determined. In this study, we found that the MLL5 protein can associate with the cell cycle regulator "host cell factor" (HCF-1). The interaction between MLL5 and HCF-1 is mediated by the "HCF-1 binding motif" (HBM) of the MLL5 protein and the Kelch domain of the HCF-1 protein. Confocal microscopy showed that the MLL5 protein largely colocalized with HCF-1 in the nucleus. Knockdown of MLL5 resulted in reduced cell proliferation and cell cycle arrest in the G1 phase. Moreover, down-regulation of E2F1 target gene expression and decreased H3K4me3 levels at E2F1-responsive promoters were observed in MLL5 knockdown cells. Additionally, the core subunits, including ASH2L, RBBP5, and WDR5, that are necessary for effective H3K4 methyltransferase activities of the Trithorax protein complexes, were absent in the MLL5 complex, suggesting that a distinct mechanism may be used by MLL5 for exerting its H3K4 methyltransferase activity. Together, our findings demonstrate that MLL5 could associate with HCF-1 and then be recruited to E2F1-responsive promoters to stimulate H3K4 trimethylation and transcriptional activation, thereby facilitating the cell cycle G1 to S phase transition.

Epigenetic regulation of planarian stem cells by the SET1/MLL family of histone methyltransferases

Chromatin regulation is a fundamental mechanism underlying stem cell pluripotency, differentiation, and the establishment of cell type-specific gene expression profiles. To examine the role of chromatin regulation in stem cells in vivo, we study regeneration in the freshwater planarian Schmidtea mediterranea. These animals possess a high concentration of pluripotent stem cells, which are capable of restoring any damaged or lost tissues after injury or amputation. Here, we identify the S. mediterranea homologs of the SET1/MLL family of histone methyltransferases and COMPASS and COMPASS-like complex proteins and investigate their role in stem cell function during regeneration. We identified six S. mediterranea homologs of the SET1/MLL family (set1, mll1/2, trr-1, trr-2, mll5–1 and mll5–2), characterized their patterns of expression in the animal, and examined their function by RNAi. All members of this family are expressed in the stem cell population and differentiated tissues. We show that set1, mll1/2, trr-1, and mll5–2 are required for regeneration and that set1, trr-1 and mll5–2 play roles in the regulation of mitosis. Most notably, knockdown of the planarian set1 homolog leads to stem cell depletion. A subset of planarian homologs of COMPASS and COMPASS-like complex proteins are also expressed in stem cells and implicated in regeneration, but the knockdown phenotypes suggest that some complex members also function in other aspects of planarian biology. This work characterizes the function of the SET1/MLL family in the context of planarian regeneration and provides insight into the role of these enzymes in adult stem cell regulation in vivo.

UpSET recruits HDAC complexes and restricts chromatin accessibility and acetylation at promoter regions

Developmental gene expression results from the orchestrated interplay between genetic and epigenetic mechanisms. Here, we describe upSET, a transcriptional regulator encoding a SET domain-containing protein recruited to active and inducible genes in Drosophila. However, unlike other Drosophila SET proteins associated with gene transcription, UpSET is part of an Rpd3/Sin3-containing complex that restricts chromatin accessibility and histone acetylation to promoter regions. In the absence of UpSET, active chromatin marks and chromatin accessibility increase and spread to genic and flanking regions due to destabilization of the histone deacetylase complex. Consistent with this, transcriptional noise increases, as manifest by activation of repetitive elements and off-target genes. Interestingly, upSET mutant flies are female sterile due to upregulation of key components of Notch signaling during oogenesis. Thus UpSET defines a class of metazoan transcriptional regulators required to fine tune transcription by preventing the spread of active chromatin.

Molecular and Epigenetic Mechanisms of MLL in Human Leukemogenesis

Epigenetics is often defined as the study of heritable changes in gene expression or chromosome stability that don’t alter the underlying DNA sequence. Epigenetic changes are established through multiple mechanisms that include DNA methylation, non-coding RNAs and the covalent modification of specific residues on histone proteins. It is becoming clear not only that aberrant epigenetic changes are common in many human diseases such as leukemia, but that these changes by their very nature are malleable, and thus are amenable to treatment. Epigenetic based therapies have so far focused on the use of histone deacetylase (HDAC) inhibitors and DNA methyltransferase inhibitors, which tend to have more general and widespread effects on gene regulation in the cell. However, if a unique molecular pathway can be identified, diseases caused by epigenetic mechanisms are excellent candidates for the development of more targeted therapies that focus on specific gene targets, individual binding domains, or specific enzymatic activities. Designing effective targeted therapies depends on a clear understanding of the role of epigenetic mutations during disease progression. The Mixed Lineage Leukemia (MLL) protein is an example of a developmentally important protein that controls the epigenetic activation of gene targets in part by methylating histone 3 on lysine 4. MLL is required for normal development, but is also mutated in a subset of aggressive human leukemias and thus provides a useful model for studying the link between epigenetic cell memory and human disease. The most common MLL mutations are chromosome translocations that fuse the MLL gene in frame with partner genes creating novel fusion proteins. In this review, we summarize recent work that argues MLL fusion proteins could function through a single molecular pathway, but we also highlight important data that suggests instead that multiple independent mechanisms underlie MLL mediated leukemogenesis.

MLL5 maintains genomic integrity by regulating the stability of the chromosomal passenger complex through a functional interaction with Borealin

Mixed lineage leukemia 5 (MLL5) is a versatile nuclear protein associated with many cellular events. We have shown previously that phosphorylation of MLL5 by Cdk1 is required for mitotic entry. In this paper, the function of MLL5 in mitotic regulation is further explored. SiRNA-mediated downregulation of MLL5 caused improper chromosome alignment at metaphase and resulted in failure of DNA segregation and cytokinesis. Mechanistic studies revealed that the chromosomal passenger complex (CPC), which plays a key role in chromosomal bi-orientation, was delocalized from the inner centromere region because of proteasome-mediated degradation in MLL5-depleted cells. Biochemical analyses further demonstrated that the central domain of MLL5 interacted with the C-terminus of Borealin, and the interaction is essential to maintain the stability of Borealin. Moreover, the mitotic defects in MLL5-depleted cells were rescued by overexpression of FLAG-MLL5, but not by a FLAG-MLL5 mutant that did not contain the central domain. Collectively, our results suggest that MLL5 functionally interacts with Borealin, facilitates the expression of CPC, and hence contributes to mitotic fidelity and genomic integrity.

Photoperiod influences growth and mll (mixed-lineage leukaemia) expression in Atlantic cod

Photoperiod is associated to phenotypic plasticity of somatic growth in several teleost species. However, the molecular mechanisms underlying this phenomenon are currently unknown but it is likely that epigenetic regulation by methyltransferases is involved. The MLL (mixed-lineage leukaemia) family comprises histone methyltransferases that play a critical role in regulating gene expression during early development in mammals. So far, these genes have received scant attention in teleost fish. In the present study, the mean weight of Atlantic cod juveniles reared under continuous illumination was found to be 13% greater than those kept under natural photoperiod conditions for 120 days. We newly determined cDNA sequences of five mll (mll1, mll2, mll3a, mll4b and mll5) and two setd1 (setd1a and setd1ba) paralogues from Atlantic cod. Phylogenetic analysis revealed that the cod genes clustered within the appropriate mll clade and comparative mapping of mll paralogues showed that these genes lie within a region of conserved synteny among teleosts. All mll and setd1 genes were highly expressed in gonads and fast muscle of adult cod, albeit at different levels, and they were differentially regulated with photoperiod in muscle of juvenile fish. Following only one day of exposure to constant light, mll1, mll4b and setd1a were up to 57% lower in these fish compared to the natural photoperiod group. In addition, mRNA expression of myogenic regulatory factors (myog and myf-5) and pax7 in fast muscle was also affected by different photoperiod conditions. Notably, myog was significantly elevated in the continuous illumination group throughout the time course of the experiment. The absence of a day/night cycle is associated with a generalised decrease in mll expression concomitant with an increase in myog transcript levels in fast muscle of Atlantic cod, which may be involved in the observed epigenetic regulation of growth by photoperiod in this species.

The SET domain protein, Set3p, promotes the reliable execution of cytokinesis in Schizosaccharomyces pombe

In response to perturbation of the cell division machinery fission yeast cells activate regulatory networks that ensure the faithful completion of cytokinesis. For instance, when cells are treated with drugs that impede constriction of the actomyosin ring (low doses of Latrunculin A, for example) these networks ensure that cytokinesis is complete before progression into the subsequent mitosis. Here, we identify three previously uncharacterized genes, hif2, set3, and snt1, whose deletion results in hyper-sensitivity to LatA treatment and in increased rates of cytokinesis failure. Interestingly, these genes are orthologous to TBL1X, MLL5, and NCOR2, human genes that encode components of a histone deacetylase complex with a known role in cytokinesis. Through co-immunoprecipitation experiments, localization studies, and phenotypic analysis of gene deletion mutants, we provide evidence for an orthologous complex in fission yeast. Furthermore, in light of the putative role of the complex in chromatin modification, together with our results demonstrating an increase in Set3p levels upon Latrunculin A treatment, global gene expression profiles were generated. While this analysis demonstrated that the expression of cytokinesis genes was not significantly affected in set3Δ backgrounds, it did reveal defects in the ability of the mutant to regulate genes with roles in the cellular response to stress. Taken together, these findings support the existence of a conserved, multi-protein complex with a role in promoting the successful completion of cytokinesis.

GlcNAcylation of histone H2B facilitates its monoubiquitination

Chromatin reorganization is governed by multiple post-translational modifications of chromosomal proteins and DNA. These histone modifications are reversible, dynamic events that can regulate DNA-driven cellular processes. However, the molecular mechanisms that coordinate histone modification patterns remain largely unknown. In metazoans, reversible protein modification by O-linked N-acetylglucosamine (GlcNAc) is catalysed by two enzymes, O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA). However, the significance of GlcNAcylation in chromatin reorganization remains elusive. Here we report that histone H2B is GlcNAcylated at residue S112 by OGT in vitro and in living cells. Histone GlcNAcylation fluctuated in response to extracellular glucose through the hexosamine biosynthesis pathway (HBP). H2B S112 GlcNAcylation promotes K120 monoubiquitination, in which the GlcNAc moiety can serve as an anchor for a histone H2B ubiquitin ligase. H2B S112 GlcNAc was localized to euchromatic areas on fly polytene chromosomes. In a genome-wide analysis, H2B S112 GlcNAcylation sites were observed widely distributed over chromosomes including transcribed gene loci, with some sites co-localizing with H2B K120 monoubiquitination. These findings suggest that H2B S112 GlcNAcylation is a histone modification that facilitates H2BK120 monoubiquitination, presumably for transcriptional activation.

Trithorax group proteins: switching genes on and keeping them active

Cellular memory is provided by two counteracting groups of chromatin proteins termed Trithorax group (TrxG) and Polycomb group (PcG) proteins. TrxG proteins activate transcription and are perhaps best known because of the involvement of the TrxG protein MLL in leukaemia. However, in terms of molecular analysis, they have lived in the shadow of their more famous counterparts, the PcG proteins. Recent advances have improved our understanding of TrxG protein function and demonstrated that the heterogeneous group of TrxG proteins is of critical importance in the epigenetic regulation of the cell cycle, senescence, DNA damage and stem cell biology.

Update on cytogenetic and molecular changes in myelodysplastic syndromes

Myelodysplastic syndromes (MDS) are characterized by ineffective hematopoiesis and a high propensity to transform to acute myeloid leukemia (AML). In the pathogenesis of the disease, both gene mutations and cytogenetic changes play an important role. The latter have been integrated into prognostic scoring systems including the IPSS (International Prognostic Scoring System) and WPSS (World Health Organization [WHO] classification-based Prognostic Scoring System). In these systems and in multivariate analyses comparing clinical and genetic data, complex karyotypes are associated with a particularly poor prognosis. del(5q) plays a distinct role by classifying the only genetically defined WHO subtype. Also, due to advancement in technology such as whole genome sequencing, the number of known mutations occurring in MDS is steadily increasing. Important recent discoveries include mutations in EZH2, DNMT3A, ASXL1 and IDH1/2. Like TET2, the most commonly mutated gene in MDS, all are involved in epigenetic regulation. Mutations such as ASXL1, RUNX1, EZH2, ETV6/TEL and TP53 have an adverse impact on patient overall survival. Early evidence suggests that some mutations might influence treatment response, necessitating reassessment of the prognostic effect of genetic alterations in the light of every new treatment. This review discusses clinical and biological effects of the most common cytogenetic and molecular aberrations in patients with MDS.

A New Three-Way Translocation t(4;11;7)(q21;q23;q22) in a Mixed-Phenotype Acute Leukemia

A 68-year-old man was admitted to our hospital in September 2008 because of a left-sided chest pain. Bone marrow examination showed that 85.5% of leukemic cells were positive for myeloperoxidase (MPO) and were negative for esterase stain. Flow cytometric analysis (FCM) revealed the expression of CD19, CD79a, CD13, CD33, CD34, and HLA-DR on the blasts. Cytogenetic analysis of bone marrow cells using the G-banding technique demonstrated 47, XY, +X, t(4;11;7)(q21;q23;q22) in five of the 20 analyzed cells. The patient was diagnosed as having mixed biphenotypic acute leukemia according to the European Group for Immunologic Classification of Leukemia criteria. Mixed-phenotype acute leukemia is a rare, difficult to diagnose entity. Whether patients with mixed-phenotype acute leukemia should be treated with regimens designed for acute myeloid leukemia, acute lymphoblastic leukemia, or both remains unclear.

Mll5 is required for normal spermatogenesis

Background

Mll5 is currently a member of the Mll family of SET domain histone methyltransferase proteins but studies have also showed that it could be part of the SET3 branch of proteins. Recently, constitutive knock out animal studies have shown that Mll5 is required for proper haematopoietic stem cell differentiation, and loss of Mll5 results in synthetic lethality for genome de-methylation. Mll5 deficient male mice are infertile and here we analyse the consequences of Mll5 deficiency for spermatogenesis.

Methodology/Principal Findings

Mll5 deficient male mice, but not female mice, are infertile. Here we show using RNA in-situ hybridization that Mll5 is expressed in the germ cells of the testes of wild type mice. Consistent with the expression of Mll5, we demonstrate by electron microscopy, video microscopy and in vitro fertilisation techniques that Mll5 deficient mice have defects in terminal maturation and packaging of sperm. The defects seen include detachment of the acrosomal cap and impaired excess cytoplasm removal. Functional tests of sperm motility show a lack of progressive motility of spermatozoa from Mll5 deficient animals. None of these defects could be rescued by in vitro fertilization. Using microarray analysis we show that transcripts implicated in spermatogenesis are dysregulated.

Conclusions/Significance

Our data demonstrate a clear role of Mll5 in mammalian spermatogenesis at the level of terminal differentiation providing further support for its classification in the SET3 branch of proteins. Moreover, this study identifies Tlk2, Utx, Gpr64, Sult4a1, Rap2ip, Vstm2 and HoxA10 as possible Mll5 targets that together may account for the observed spermatozoa maturation defects.

A novel MLL5 isoform that is essential to activate E6 and E7 transcription in HPV16/18-associated cervical cancers

Human papillomavirus (HPV) is the primary cause of human cervical cancer. The viral proteins E6 and E7 are essential to transform noncancerous epithelial cells into cancerous carcinomas by targeting key tumor suppressors p53 and retinoblastoma (Rb) proteins, respectively, but the cellular factors involved in E6 and E7 transcription themselves are incompletely understood. In this study, we defined a novel isoform of the mixed lineage leukemia 5 gene (MLL5β) as a specific and critical regulator of E6 and E7 transcription in cervical carcinoma cells. MLL5β is present in HPV16/18-positive cells including human primary cervical carcinoma specimens. Interaction of MLL5β with the AP-1-binding site at the distal region of the HPV18 long control region led to activation of E6/E7 transcription. Conversely, RNA interference-mediated knockdown of MLL5β downregulated both E6 and E7 expression. MLL5β downregulation was sufficient to restore p53 protein levels and reduce Rb phosphorylation, thereby reactivating apoptosis and cell-cycle checkpoints. By defining this novel MLL5β isoform and its specific critical role in activating E6/E7 gene transcription in HPV16/18-induced cervical cancers, our work highlights the potential of MLL5β as a biomarker and new therapeutic target in primary HPV-induced cervical cancers.

Camptothecin-induced downregulation of MLL5 contributes to the activation of tumor suppressor p53

Mixed lineage leukemia 5 (MLL5) has been implicated in multiple aspects of cell physiology, such as hematopoiesis, cell cycle control and chromatin regulatory network. In this study, we present evidence that MLL5 is involved in the camptothecin (CPT)-induced p53 activation. CPT promoted the degradation of MLL5 protein in a time- and dose-dependent manner in actively replicating cells. The downregulation of MLL5 led to phosphorylation of p53 at Ser392, which was abrogated by exogenous overexpression of MLL5. In MLL5-knockdown cells, p53 protein was stabilized and bound to DNA with higher affinity, leading to activation of downstream genes. Co-immunoprecipitation showed that MLL5 preferentially interacted with the tetramerized form of p53, and knockdown of MLL5 promoted chromatin accumulation of p53 tetramers, suggesting that the association of MLL5 with p53 may prevent the p53 tetramers from binding to the chromatin target sites. The role of MLL5 in CPT-induced p53 activation was conserved in developing zebrafish, where CPT downregulated zebrafish Mll5 protein, and the microinjection of zebrafish mll5 mRNA substantially blocked the CPT-induced apoptosis. In summary, our study proposed MLL5 as a novel component in the regulation of p53 homeostasis and a new cellular determinant of CPT.

Prognostic importance of histone methyltransferase MLL5 expression in acute myeloid leukemia

PURPOSE

To assess the prognostic importance of mixed lineage leukemia 5 (MLL5) expression in acute myeloid leukemia (AML).

PATIENTS AND METHODS

MLL5 transcript levels from 509 patients with AML who were treated in multicenter trials AML SHG 0199 and AML SHG 0295 and 48 healthy volunteers were analyzed by real-time reverse-transcription polymerase chain reaction in the context of other molecular markers (NPM1, FLT3, CEBPA, IDH1/IDH2, NRAS, KIT, MN1, BAALC, ERG, and WT1).

RESULTS

Patients with high (n = 127) compared with low (n = 382) MLL5 expression had a higher complete response rate in multivariate analysis (odds ratio, 1.87; 95% CI, 1.08 to 3.24; P = .026). In multivariate analysis, high MLL5 expression was a favorable prognostic marker for overall survival (OS; hazard ratio [HR], 0.66; 95% CI, 0.49 to 0.89; P = .007) and relapse-free survival (RFS; HR, 0.72; 95% CI, 0.52 to 1.01; P = .057). Patient characteristics, cytogenetic aberrations, and gene mutations were similarly distributed between patients with high and low MLL5 expression except for a higher platelet count in those with high MLL5 expression. MLL5 expression independently predicted prognosis in cytogenetically normal AML patients (n = 268; OS: HR, 0.53; 95% CI, 0.33 to 086; P = .011; RFS: HR, 0.61; 95% CI, 0.38 to 0.99; P = .05) and in patients with core-binding factor leukemias (n = 81; OS: HR, 0.12; 95% CI, 0.02 to 0.91; P = .04; RFS: HR, 0.18; 95% CI, 0.04 to 0.77; P = .02). The prognostic importance of high MLL5 expression was independently validated in 167 patients treated in the AMLSG 07/04 trial (OS: HR, 0.5; 95% CI, 0.27 to 0.92; P = .023; RFS: HR, 0.49; 95% CI, 0.25 to 0.96; P = .033).

CONCLUSION

High MLL5 expression levels are associated with a favorable outcome and may improve risk and treatment stratification in AML.

Phosphorylation of mixed lineage leukemia 5 by CDC2 affects its cellular distribution and is required for mitotic entry

The human mixed lineage leukemia-5 (MLL5) gene is frequently deleted in myeloid malignancies. Emerging evidence suggests that MLL5 has important functions in adult hematopoiesis and the chromatin regulatory network, and it participates in regulating the cell cycle machinery. Here, we demonstrate that MLL5 is tightly regulated through phosphorylation on its central domain at the G(2)/M phase of the cell cycle. Upon entry into mitosis, the phosphorylated MLL5 delocalizes from condensed chromosomes, whereas after mitotic exit, MLL5 becomes dephosphorylated and re-associates with the relaxed chromatin. We further identify that the mitotic phosphorylation and subcellular localization of MLL5 are dependent on Cdc2 kinase activity, and Thr-912 is the Cdc2-targeting site. Overexpression of the Cdc2-targeting MLL5 fragment obstructs mitotic entry by competitive inhibition of the phosphorylation of endogenous MLL5. In addition, G(2) phase arrest caused by depletion of endogenous MLL5 can be compensated by exogenously overexpressed full-length MLL5 but not the phosphodomain deletion or MLL5-T912A mutant. Our data provide evidence that MLL5 is a novel cellular target of Cdc2, and the phosphorylation of MLL5 may have an indispensable role in the mitotic progression.