Mixed Lineage Leukemia Protein-1 Research Articles

Developmental reprogramming of myometrial stem cells by endocrine disruptor linking to risk of uterine fibroids

BackgroundThe stage, when tissues and organs are growing, is very vulnerable to environmental influences, but it’s not clear how exposure during this time causes changes to the epigenome and increases the risk of hormone-related illnesses like uterine fibroids (UFs).MethodsDevelopmental reprogramming of myometrial stem cells (MMSCs), the putative origin from which UFs originate, was investigated in vitro and in the Eker rat model by RNA-seq, ChIP-seq, RRBS, gain/loss of function analysis, and luciferase activity assays.ResultsWhen exposed to the endocrine-disrupting chemical (EDC) diethylstilbestrol during Eker rat development, MMSCs undergo a reprogramming of their estrogen-responsive transcriptome. The reprogrammed genes in MMSCs are known as estrogen-responsive genes (ERGs) and are activated by mixed lineage leukemia protein-1 (MLL1) and DNA hypo-methylation mechanisms. Additionally, we observed a notable elevation in the expression of ERGs in MMSCs from Eker rats exposed to natural steroids after developmental exposure to EDC, thereby augmenting estrogen activity.ConclusionOur studies identify epigenetic mechanisms of MLL1/DNA hypo-methylation-mediated MMSC reprogramming. EDC exposure epigenetically targets MMSCs and leads to persistent changes in the expression of a subset of ERGs, imparting a hormonal imprint on the ERGs, resulting in a “hyper-estrogenic” phenotype, and increasing the hormone-dependent risk of UFs.

Epigenetic Modulation of Inflammatory Pathways in Myometrial Stem Cells and Risk of Uterine Fibroids.

The period during which tissue and organ development occurs is particularly vulnerable to the influence of environmental exposures. However, the specific mechanisms through which biological pathways are disrupted in response to developmental insults, consequently elevating the risk of hormone-dependent diseases, such as uterine fibroids (UFs), remain poorly understood. Here, we show that developmental exposure to the endocrine-disrupting chemical (EDC), diethylstilbestrol (DES), activates the inflammatory pathways in myometrial stem cells (MMSCs), which are the origin of UFs. Significantly, the secretome of reprogrammed MMSCs enhances the expression of critical inflammation-related genes in differentiated myometrial cells through the paracrine mechanism, which amplifies pro-inflammatory and immune suppression signaling in the myometrium. The expression of reprogrammed inflammatory responsive genes (IRGs) is driven by activated mixed-lineage leukemia protein-1 (MLL1) in MMSCs. The deactivation of MLL reverses the reprogramming of IRG expression. In addition, the inhibition of histone deacetylases (HDACs) also reversed the reprogrammed IRG expression induced by EDC exposure. This work identifies the epigenetic mechanisms of MLL1/HDAC-mediated MMSC reprogramming, and EDC exposure epigenetically targets MMSCs and imparts an IRG expression pattern, which may result in a "hyper-inflammatory phenotype" and an increased hormone-dependent risk of UFs later in life.

WDR5 drives the development of cervical squamous cell carcinoma by inducing epithelial-mesenchymal transition and cancer-associated fibroblasts formation

BackgroundWD repeat domain 5 (WDR5) has been indicated to be involved in tumor progression, however, its role in cervical cancer (CC) has not been investigated yet. MethodsA total of 350 pairs of CC tissues and para-carcinoma tissues (PCT) were collected. Primary human cervical epithelial cells (hCECs) and cancer-associated fibroblasts (CAFs) were isolated from cervical cancer tissues. MM102 was used to block the interaction between WDR5 and mixed lineage leukemia protein-1 (MLL1), and it was used in vivo to investigate its therapeutic value. ResultsWDR5 was up-regulated in cervical squamous cell carcinoma (CSCC) tissues compared to that in PCT. C-X-C motif chemokine ligand 8 (CXCL8) was indicated to be the target gene of WDR5. Highly expressed CXCL8 promoted epithelial-mesenchymal transition (EMT) to form CAFs, and enhanced the cytokine secretions in CAFs to promote CSCC progression. CXCL8 expression was regulated by the interaction between WDR5 and MLL1, and blocking the interaction between these two proteins using MM102 significantly suppressed tumor growth in mice models. ConclusionsWDR5 plays a key role in CSCC progression by inducing CXCL8 expression and promoting the transformation of CAFs from epithelial cells.

Interferon kappa (IFNk) in keratinocytes is critical for normal wound repair and is decreased in diabetic wounds

Abstract Wound repair following acute injury requires a coordinated inflammatory response. Type I interferon (IFN) signaling is important for regulating the inflammatory response post- skin injury. IFN kappa (IFNk), a type I IFN, has recently been found to drive skin inflammation in lupus and psoriasis; however, the role of IFNk in the context of normal or dysregulated wound healing is unclear. Thus, this project explores the role of IFNk in wound repair. Here, we found that IFNk expression is upregulated in keratinocytes early post-injury and is essential for normal tissue repair. Under diabetic conditions, IFNk was decreased in wound keratinocytes, and early inflammation was impaired. Further, we found that the histone methyltransferase mixed lineage leukemia protein-1(MLL1) regulates IFNk expression in diabetic wound keratinocytes via an H3K4me3 mediated mechanism. Using a series of in vivo studies with a genetically engineered mouse model(Mll1fl/flK14cre−) and human wound tissues from patients with T2D, we demonstrate that MLL1 controls wound keratinocyte-mediated IFNk and MLL1 is decreased in T2D keratinocytes. Importantly, we find the administration of IFNk early following injury improves diabetic tissue repair. These findings have significant implications for understanding the complex role type I interferons play in keratinocytes in normal and diabetic wound healing. Additionally, they suggest IFNk may be a viable therapeutic target to improve diabetic wound repair. Supported by MNORC P30-DK089503

CD40L/CD40 Regulates Adipokines and Cytokines by H3K4me3 Modification in Epicardial Adipocytes.

Epicardial adipose tissue (EAT) dysfunction mediates chronic inflammation by regulating inflammation-related adipokines and cytokines, and it further promotes coronary artery disease (CAD) development. CD40L/CD40 is involved in multiple inflammatory pathways that contribute to various pathophysiological processes. However, the function of CD40L/CD40 in the expression and production of adipokines and cytokines in epicardial adipocytes remains unclear. The purpose of the present study was to explore the role and underlying mechanisms of CD40L/CD40 in adipokine and cytokine expression and production. We isolated adipocytes from EAT tissues of CAD and non-CAD patients. We noticed that CD40 was dramatically increased in EAT tissues of CAD patients. Loss-of-function and gain-of-function studies were performed. The results showed that CD40 silencing reduced recombinant CD40 ligand (rCD40L)-induced upregulation of plasminogen activator inhibitor-1, leptin, interleukin-6, and monocyte chemotactic protein-1 messenger RNA levels and secretion. Overexpression of CD40 displayed the opposite results. In addition, rCD40L triggered mixed lineage leukemia protein-1 (MLL1) expression both in messenger RNA and protein levels. CD40 depletion apparently blocked MLL1 expression, whereas gain of function of CD40 resulted in augmentation of MLL1 levels. Interestingly, chromatin immunoprecipitation-quantitative real-time polymerase chain reaction analysis revealed that CD40 elimination dampened histone H3 lysine 4 trimethylation enrichment at plasminogen activator inhibitor-1, leptin, interleukin-6, and monocyte chemotactic protein-1 promoter regions in the presence of rCD40L. The reverse pattern was observed upon ectopic expression of CD40. Most important, MLL1 silencing effectively reversed the promotive effects of CD40 on adipokine and cytokine secretion. Taken together, our findings suggest that CD40L/CD40 regulates adipokine and cytokine expression by H3 lysine 4 trimethylation modification in adipocytes.

The internal interaction in RBBP5 regulates assembly and activity of MLL1 methyltransferase complex.

The Mixed Lineage Leukemia protein 1 (MLL1) plays an essential role in the maintenance of the histone H3 lysine 4 (H3K4) methylation status for gene expression during differentiation and development. The methyltransferase activity of MLL1 is regulated by three conserved core subunits, WDR5, RBBP5 and ASH2L. Here, we determined the structure of human RBBP5 and demonstrated its role in the assembly and regulation of the MLL1 complex. We identified an internal interaction between the WD40 propeller and the C-terminal distal region in RBBP5, which assisted the maintenance of the compact conformation of the MLL1 complex. We also discovered a vertebrate-specific motif in the C-terminal distal region of RBBP5 that contributed to nucleosome recognition and methylation of nucleosomes by the MLL1 complex. Our results provide new insights into functional conservation and evolutionary plasticity of the scaffold protein RBBP5 in the regulation of KMT2-family methyltransferase complexes.

Immune genes are primed for robust transcription by proximal long noncoding RNAs located in nuclear compartments.

Accumulation of trimethylation of histone H3 at lysine 4 (H3K4me3) on immune-related gene promoters underlies robust transcription during trained immunity. However, the molecular basis for this remains unknown. Here we show three-dimensional chromatin topology enables immune genes to engage in chromosomal contacts with a subset of long noncoding RNAs (lncRNAs) we have defined as immune gene-priming lncRNAs (IPLs). We show that the prototypical IPL, UMLILO, acts in cis to direct the WD repeat-containing protein 5 (WDR5)-mixed lineage leukemia protein 1 (MLL1) complex across the chemokine promoters, facilitating their H3K4me3 epigenetic priming. This mechanism is shared amongst several trained immune genes. Training mediated by β-glucan epigenetically reprograms immune genes by upregulating IPLs in manner dependent on nuclear factor of activated T cells. The murine chemokine topologically associating domain lacks an IPL, and the Cxcl genes are not trained. Strikingly, the insertion of UMLILO into the chemokine topologically associating domain in mouse macrophages resulted in training of Cxcl genes. This provides strong evidence that lncRNA-mediated regulation is central to the establishment of trained immunity.

Biochemical Reconstitution and Phylogenetic Comparison of Human SET1 Family Core Complexes Involved in Histone Methylation

Mixed lineage leukemia protein-1 (MLL1) is a member of the SET1 family of histone H3 lysine 4 (H3K4) methyltransferases that are required for metazoan development. MLL1 is the best characterized human SET1 family member, which includes MLL1-4 and SETd1A/B. MLL1 assembles with WDR5, RBBP5, ASH2L, DPY-30 (WRAD) to form the MLL1 core complex, which is required for H3K4 dimethylation and transcriptional activation. Because all SET1 family proteins interact with WRAD in vivo, it is hypothesized they are regulated by similar mechanisms. However, recent evidence suggests differences among family members that may reflect unique regulatory inputs in the cell. Missing is an understanding of the intrinsic enzymatic activities of different SET1 family complexes under standard conditions. In this investigation, we reconstituted each human SET1 family core complex and compared subunit assembly and enzymatic activities. We found that in the absence of WRAD, all but one SET domain catalyzes at least weak H3K4 monomethylation. In the presence of WRAD, all SET1 family members showed stimulated monomethyltransferase activity but differed in their di- and trimethylation activities. We found that these differences are correlated with evolutionary lineage, suggesting these enzyme complexes have evolved to accomplish unique tasks within metazoan genomes. To understand the structural basis for these differences, we employed a "phylogenetic scanning mutagenesis" assay and identified a cluster of amino acid substitutions that confer a WRAD-dependent gain-of-function dimethylation activity on complexes assembled with the MLL3 or Drosophila trithorax proteins. These results form the basis for understanding how WRAD differentially regulates SET1 family complexes in vivo.

A Novel Non-SET Domain Multi-subunit Methyltransferase Required for Sequential Nucleosomal Histone H3 Methylation by the Mixed Lineage Leukemia Protein-1 (MLL1) Core Complex

Gene expression within the context of eukaryotic chromatin is regulated by enzymes that catalyze histone lysine methylation. Histone lysine methyltransferases that have been identified to date possess the evolutionarily conserved SET or Dot1-like domains. We previously reported the identification of a new multi-subunit histone H3 lysine 4 methyltransferase lacking homology to the SET or Dot1 family of histone lysine methyltransferases. This enzymatic activity requires a complex that includes WRAD (WDR5, RbBP5, Ash2L, and DPY-30), a complex that is part of the MLL1 (mixed lineage leukemia protein-1) core complex but that also exists independently of MLL1 in the cell. Here, we report that the minimal complex required for WRAD enzymatic activity includes WDR5, RbBP5, and Ash2L and that DPY-30, although not required for enzymatic activity, increases the histone substrate specificity of the WRAD complex. We also show that WRAD requires zinc for catalytic activity, displays Michaelis-Menten kinetics, and is inhibited by S-adenosyl-homocysteine. In addition, we demonstrate that WRAD preferentially methylates lysine 4 of histone H3 within the context of the H3/H4 tetramer but does not methylate nucleosomal histone H3 on its own. In contrast, we find that MLL1 and WRAD are required for nucleosomal histone H3 methylation, and we provide evidence suggesting that each plays distinct structural and catalytic roles in the recognition and methylation of a nucleosome substrate. Our results indicate that WRAD is a new H3K4 methyltransferase with functions that include regulating the substrate and product specificities of the MLL1 core complex.

Characterization of a Novel WDR5-binding Site That Recruits RbBP5 through a Conserved Motif to Enhance Methylation of Histone H3 Lysine 4 by Mixed Lineage Leukemia Protein-1*

Histone modification is well established as a fundamental mechanism driving the regulation of transcription, replication, and DNA repair through the control of chromatin structure. Likewise, it is apparent that incorrect targeting of histone modifications contributes to misregulated gene expression and hence to developmental disorders and diseases of genomic instability such as cancer. The KMT2 family of SET domain methyltransferases, typified by mixed lineage leukemia protein-1 (MLL1), is responsible for histone H3 lysine 4 methylation, a marker of active genes. To ensure that this modification is correctly targeted, a multiprotein complex associates with the methyltransferase and directs activity. We have identified a novel interaction site on the core complex protein WD repeat protein-5 (WDR5), and we mapped the complementary site on its partner retinoblastoma-binding protein-5 (RbBP5). We have characterized this interaction by x-ray crystallography and show how it is fundamental to the assembly of the complex and to the regulation of methyltransferase activity. We show which region of RbBP5 contributes directly to mixed lineage leukemia activation, and we combine our structural and biochemical data to produce a model to show how WDR5 and RbBP5 act cooperatively to stimulate activity.

Structural basis for the recognition of Set1 family Win motifs by WDR5

The Mixed Lineage Leukemia protein‐1 (MLL1) associates with WDR5, RbBP5 and Ash2L to form the MLL1 core complex that catalyzes mono‐ and dimethylation of histone H3 Lysine 4 (H3K4). We have recently established that WDR5 interacts with MLL1 through a highly conserved WDR5 interaction (Win) motif in MLL1 and a peptide derived from the Win motif in MLL1 has been shown to disrupt this interaction and specifically inhibit the H3K4 dimethylation activity of the MLL1 core complex. The Win motif is highly conserved among the metazoan Set1 family members, however, little is known about how the different Set1 family Win motifs are recognized by WDR5. To understand the molecular details of these interactions, here we compare 3‐dimensional structures and thermodynamic binding properties of different human Set1 family Win motif based peptides bound to WDR5. We show that Win motif peptides derived from human Set1 family members (MLL2, MLL3, MLL4, SET1a and SET1b) interact with WDR5 with dissociation constants (Kd) ranging from 50–470 nM. These binding affinities are 4 to 30‐fold tighter than the interaction between MLL1 Win motif and WDR5. The crystal structure of WDR5 bound to the human SET1a Win motif peptide reveals more favorable interactions outside the Arginine binding pocket in WDR5 that contributes to the increased affinity as compared to that of MLL1 Win motif peptide. We also demonstrate that the human SET1a Win motif peptide is a four‐fold better inhibitor of the H3K4 dimethylation activity of the MLL1 core complex with an IC50 value of 70 μM. These studies establish the structural basis for the differential interaction affinities between WDR5 and Set1 family Win motifs and suggest a framework for the design of Win motif based peptide inhibitors of Set1 family complexes.

Mixed lineage leukemia: a structure–function perspective of the MLL1 protein

Several acute lymphoblastic and myelogenous leukemias are correlated with alterations in the human mixed lineage leukemia protein-1 (MLL1) gene. MLL1 is a member of the evolutionarily conserved SET1 family of histone H3 lysine 4 (H3K4) methyltransferases, which are required for the regulation of distinct groups of developmentally regulated genes in metazoans. Despite the important biological role of SET1 family enzymes and their involvement in human leukemias, relatively little is understood about how these enzymes work. Here we review several recent structural and biochemical studies that are beginning to shed light on the molecular mechanisms for the regulation of H3K4 methylation by the human MLL1 enzyme.

On the Mechanism of Multiple Lysine Methylation by the Human Mixed Lineage Leukemia Protein-1 (MLL1) Core Complex

Transcription in eukaryotic genomes depends on enzymes that regulate the degree of histone H3 lysine 4 (H3K4) methylation. The mixed lineage leukemia protein-1 (MLL1) is a member of the SET1 family of H3K4 methyltransferases and is frequently rearranged in acute leukemias. Despite sequence comparisons that predict that SET1 family enzymes should only monomethylate their substrates, mono-, di-, and trimethylation of H3K4 has been attributed to SET1 family complexes in vivo and in vitro. To better understand this paradox, we have biochemically reconstituted and characterized a five-component 200-kDa MLL1 core complex containing human MLL1, WDR5, RbBP5, Ash2L, and DPY-30. We demonstrate that the isolated MLL1 SET domain is a slow monomethyltransferase and that tyrosine 3942 of MLL1 prevents di- and trimethylation of H3K4. In contrast, a complex containing the MLL1 SET domain, WDR5, RbBP5, Ash2L, and DPY-30, displays a marked approximately 600-fold increase in enzymatic activity but only to the dimethyl form of H3K4. Single turnover kinetic experiments reveal that the reaction leading to H3K4 dimethylation involves the transient accumulation of a monomethylated species, suggesting that the MLL1 core complex uses a non-processive mechanism to catalyze multiple lysine methylation. We have also discovered that the non-SET domain components of the MLL1 core complex possess a previously unrecognized methyltransferase activity that catalyzes H3K4 dimethylation within the MLL1 core complex. Our results suggest that the mechanism of multiple lysine methylation by the MLL1 core complex involves the sequential addition of two methyl groups at two distinct active sites within the complex.

Structure of WDR5 Bound to Mixed Lineage Leukemia Protein-1 Peptide

The mixed lineage leukemia protein-1 (MLL1) catalyzes histone H3 lysine 4 methylation and is regulated by interaction with WDR5 (WD-repeat protein-5), RbBP5 (retinoblastoma-binding protein-5), and the Ash2L (absent, small, homeotic discs-2-like) oncoprotein. In the accompanying investigation, we describe the identification of a conserved arginine containing motif, called the "Win" or WDR5 interaction motif, that is essential for the assembly and H3K4 dimethylation activity of the MLL1 core complex. Here we present a 1.7-A crystal structure of WDR5 bound to a peptide derived from the MLL1 Win motif. Our results show that Arg-3765 of MLL1 is bound in the same arginine binding pocket on WDR5 that was previously suggested to bind histone H3. Thermodynamic binding experiments show that the MLL1 Win peptide is preferentially recognized by WDR5. These results are consistent with a model in which WDR5 recognizes Arg-3765 of MLL1, which is essential for the assembly and enzymatic activity of the MLL1 core complex.

A Conserved Arginine-containing Motif Crucial for the Assembly and Enzymatic Activity of the Mixed Lineage Leukemia Protein-1 Core Complex

The mixed lineage leukemia protein-1 (MLL1) belongs to the SET1 family of histone H3 lysine 4 methyltransferases. Recent studies indicate that the catalytic subunits of SET1 family members are regulated by interaction with a conserved core group of proteins that include the WD repeat protein-5 (WDR5), retinoblastoma-binding protein-5 (RbBP5), and the absent small homeotic-2-like protein (Ash2L). It has been suggested that WDR5 functions to bridge the interactions between the catalytic and regulatory subunits of SET1 family complexes. However, the molecular details of these interactions are unknown. To gain insight into the interactions among these proteins, we have determined the biophysical basis for the interaction between the human WDR5 and MLL1. Our studies reveal that WDR5 preferentially recognizes a previously unidentified and conserved arginine-containing motif, called the "Win" or WDR5 interaction motif, which is located in the N-SET region of MLL1 and other SET1 family members. Surprisingly, our structural and functional studies show that WDR5 recognizes arginine 3765 of the MLL1 Win motif using the same arginine binding pocket on WDR5 that was previously shown to bind histone H3. We demonstrate that WDR5's recognition of arginine 3765 of MLL1 is essential for the assembly and enzymatic activity of the MLL1 core complex in vitro.

Regulation of MLL1 H3K4 methyltransferase activity by its core components

Histone H3 Lys4 (H3K4) methylation is a prevalent mark associated with transcription activation. A common feature of several H3K4 methyltransferase complexes is the presence of three structural components (RbBP5, Ash2L and WDR5) and a catalytic subunit containing a SET domain. Here we report the first biochemical reconstitution of a functional four-component mixed-lineage leukemia protein-1 (MLL1) core complex. This reconstitution, combined with in vivo assays, allows direct analysis of the contribution of each component to MLL1 enzymatic activity and their roles in transcriptional regulation. Moreover, taking clues from a crystal structure analysis, we demonstrate that WDR5 mediates interactions of the MLL1 catalytic unit both with the common structural platform and with the histone substrate. Mechanistic insights gained from this study can be generalized to the whole family of SET1-like histone methyltransferases in mammals.