The many facets of MLL1 regulation

MLL1 inhibits the neurogenic potential of SCAPs by interacting with WDR5 and repressing HES1

Mesenchymal stem cell (MSC)-based therapy has emerged as a promising treatment for spinal cord injury (SCI), but improving the neurogenic potential of MSCs remains a challenge. Mixed lineage leukemia 1 (MLL1), an H3K4me3 methyltransferases, plays a critical role in regulating lineage-specific gene expression and influences neurogenesis. In this study, we investigated the role and mechanism of MLL1 in the neurogenesis of stem cells from apical papilla (SCAPs). We examined the expression of neural markers, and the nerve repair and regeneration ability of SCAPs using dynamic changes in neuron-like cells, immunofluorescence staining, and a SCI model. We employed a coimmunoprecipitation (Co-IP) assay, real-time RT-PCR, microarray analysis, and chromatin immunoprecipitation (ChIP) assay to investigate the molecular mechanism. The results showed that MLL1 knock-down increased the expression of neural markers, including neurogenic differentiation factor (NeuroD), neural cell adhesion molecule (NCAM), tyrosine hydroxylase (TH), βIII-tubulin and Nestin, and promoted neuron-like cell formation in SCAPs. In vivo, a transplantation experiment showed that depletion of MLL 1 in SCAPs can restore motor function in a rat SCI model. MLL1 can combine with WD repeat domain 5 (WDR5) and WDR5 inhibit the expression of neural markers in SCAPs. MLL1 regulates Hairy and enhancer of split 1 (HES1) expression by directly binds to HES1 promoters via regulating H3K4me3 methylation by interacting with WDR5. Additionally, HES1 enhances the expression of neural markers in SCAPs. Our findings demonstrate that MLL1 inhibits the neurogenic potential of SCAPs by interacting with WDR5 and repressing HES1. These results provide a potential therapeutic target for promoting the recovery of motor function in SCI patients.

The histone methyltransferase MLL1/KMT2A in monocytes drives coronavirus-associated coagulopathy and inflammation

Coronavirus-associated coagulopathy (CAC) is a morbid and lethal sequela of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. CAC results from a perturbed balance between coagulation and fibrinolysis and occurs in conjunction with exaggerated activation of monocytes/macrophages (MO/Mφs), and the mechanisms that collectively govern this phenotype seen in CAC remain unclear. Here, using experimental models that use the murine betacoronavirus MHVA59, a well-established model of SARS-CoV-2 infection, we identify that the histone methyltransferase mixed lineage leukemia 1 (MLL1/KMT2A) is an important regulator of MO/Mφ expression of procoagulant and profibrinolytic factors such as tissue factor (F3; TF), urokinase (PLAU), and urokinase receptor (PLAUR) (herein, "coagulopathy-related factors") in noninfected and infected cells. We show that MLL1 concurrently promotes the expression of the proinflammatory cytokines while suppressing the expression of interferon alfa (IFN-α), a well-known inducer of TF and PLAUR. Using in vitro models, we identify MLL1-dependent NF-κB/RelA-mediated transcription of these coagulation-related factors and identify a context-dependent, MLL1-independent role for RelA in the expression of these factors in vivo. As functional correlates for these findings, we demonstrate that the inflammatory, procoagulant, and profibrinolytic phenotypes seen in vivo after coronavirus infection were MLL1-dependent despite blunted Ifna induction in MO/Mφs. Finally, in an analysis of SARS-CoV-2 positive human samples, we identify differential upregulation of MLL1 and coagulopathy-related factor expression and activity in CD14+ MO/Mφs relative to noninfected and healthy controls. We also observed elevated plasma PLAU and TF activity in COVID-positive samples. Collectively, these findings highlight an important role for MO/Mφ MLL1 in promoting CAC and inflammation.

MLL regulates the actin cytoskeleton and cell migration by stabilising Rho GTPases via the expression of RhoGDI1

Attainment of proper cell shape and the regulation of cell migration are essential processes in the development of an organism. The mixed lineage leukemia (MLL or KMT2A) protein, a histone 3 lysine 4 (H3K4) methyltransferase, plays a critical role in cell-fate decisions during skeletal development and haematopoiesis in higher vertebrates. Rho GTPases - RhoA, Rac1 and CDC42 - are small G proteins that regulate various key cellular processes, such as actin cytoskeleton formation, the maintenance of cell shape and cell migration. Here, we report that MLL regulates the homeostasis of these small Rho GTPases. Loss of MLL resulted in an abnormal cell shape and a disrupted actin cytoskeleton, which lead to diminished cell spreading and migration. MLL depletion affected the stability and activity of Rho GTPases in a SET domain-dependent manner, but these Rho GTPases were not direct transcriptional targets of MLL. Instead, MLL regulated the transcript levels of their chaperone protein RhoGDI1 (also known as ARHGDIA). Using MDA-MB-231, a triple-negative breast cancer cell line with high RhoGDI1 expression, we show that MLL depletion or inhibition by small molecules reduces tumour progression in nude mice. Our studies highlight the central regulatory role of MLL in Rho/Rac/CDC42 signalling pathways. This article has an associated First Person interview with the first author of the paper.

Prenatal Δ9-Tetrahydrocannabinol Exposure in Males Leads to Motivational Disturbances Related to Striatal Epigenetic Dysregulation

BACKGROUND

Cannabis remains one of the most widely abused drugs during pregnancy. In utero exposure to its principal psychoactive component, Δ⁹-tetrahydrocannabinol (THC), can result in long-term neuropsychiatric risk for the progeny. This study investigated epigenetic signatures underlying these enduring consequences.

METHODS

Rat dams were exposed daily to THC (0.15 mg/kg) during pregnancy, and adult male offspring were examined for reward and depressive-like behavioral endophenotypes. Using unbiased sequencing approaches, we explored transcriptional and epigenetic profiles in the nucleus accumbens (NAc), a brain area central to reward and emotional processing. An in vitro CRISPR (clustered regularly interspaced short palindromic repeats) activation model coupled with RNA sequencing was also applied to study specific consequences of epigenetic dysregulation, and altered molecular signatures were compared with human major depressive disorder transcriptome datasets.

RESULTS

Prenatal THC exposure induced increased motivation for food, heightened learned helplessness and anhedonia, and altered stress sensitivity. We identified a robust increase specific to males in the expression of Kmt2a (histone-lysine N-methyltransferase 2A) that targets H3K4 (lysine 4 on histone H3) in cellular chromatin. Normalizing Kmt2a in the NAc rescued the motivational phenotype of prenatally THC-exposed animals. Comparison of RNA- and H3K4me3-sequencing datasets from the NAc of rat offspring with the in vitro model of Kmt2a upregulation revealed overlapping, significant disturbances in pathways that mediate synaptic plasticity. Similar transcriptional alterations were detected in human major depressive disorder.

CONCLUSIONS

These studies provide direct evidence for the persistent effects of prenatal cannabis exposure on transcriptional and epigenetic deviations in the NAc via Kmt2a dysregulation and associated psychiatric vulnerability.

Clinical Utility of a Unique Genome-Wide DNA Methylation Signature for KMT2A-Related Syndrome

Wiedemann–Steiner syndrome (WDSTS) is a Mendelian syndromic intellectual disability (ID) condition associated with hypertrichosis cubiti, short stature, and characteristic facies caused by pathogenic variants in the KMT2A gene. Clinical features can be inconclusive in mild and unusual WDSTS presentations with variable ID (mild to severe), facies (typical or not) and other associated malformations (bone, cerebral, renal, cardiac and ophthalmological anomalies). Interpretation and classification of rare KMT2A variants can be challenging. A genome-wide DNA methylation episignature for KMT2A-related syndrome could allow functional classification of variants and provide insights into the pathophysiology of WDSTS. Therefore, we assessed genome-wide DNA methylation profiles in a cohort of 60 patients with clinical diagnosis for WDSTS or Kabuki and identified a unique highly sensitive and specific DNA methylation episignature as a molecular biomarker of WDSTS. WDSTS episignature enabled classification of variants of uncertain significance in the KMT2A gene as well as confirmation of diagnosis in patients with clinical presentation of WDSTS without known genetic variants. The changes in the methylation profile resulting from KMT2A mutations involve global reduction in methylation in various genes, including homeobox gene promoters. These findings provide novel insights into the molecular etiology of WDSTS and explain the broad phenotypic spectrum of the disease.

Kinetics of the multitasking high-affinity Win binding site of WDR5 in restricted and unrestricted conditions

Recent advances in quantitative proteomics show that WD40 proteins play a pivotal role in numerous cellular networks. Yet, they have been fairly unexplored and their physical associations with other proteins are ambiguous. A quantitative understanding of these interactions has wide-ranging significance. WD40 repeat protein 5 (WDR5) interacts with all members of human SET1/MLL methyltransferases, which regulate methylation of the histone 3 lysine 4 (H3K4). Here, using real-time binding measurements in a high-throughput setting, we identified the kinetic fingerprint of transient associations between WDR5 and 14-residue WDR5 interaction (Win) motif peptides of each SET1 protein (SET1Win). Our results reveal that the high-affinity WDR5-SET1Win interactions feature slow association kinetics. This finding is likely due to the requirement of SET1Win to insert into the narrow WDR5 cavity, also named the Win binding site. Furthermore, our explorations indicate fairly slow dissociation kinetics. This conclusion is in accordance with the primary role of WDR5 in maintaining the functional integrity of a large multisubunit complex, which regulates the histone methylation. Because the Win binding site is considered a key therapeutic target, the immediate outcomes of this study could form the basis for accelerated developments in medical biotechnology.

Comprehensive Analysis of MEN1 Mutations and Their Role in Cancer

Simple Summary

Cancers are characterized by accumulation of genetic mutations in key cell cycle regulators that alter or disable the function of these genes. Such mutations can be inherited or arise spontaneously during the life of the individual. The MEN1 gene prevents uncontrolled cell division and it is considered a tumor suppressor. Inherited MEN1 mutations are associated with certain parathyroid and pancreatic syndromes while spontaneous mutations have been detected in cancer cells. We investigated whether inherited mutations appear in cancer cells which would suggest that patients with parathyroid and pancreatic syndromes have a predisposition to develop cancer. We find a weak correlation between the spectrum of inherited mutations and those appearing spontaneously. Thus, inherited MEN1 mutations may not be a good predictor of tumorigenesis.

Abstract

MENIN is a scaffold protein encoded by the MEN1 gene that functions in multiple biological processes, including cell proliferation, migration, gene expression, and DNA damage repair. MEN1 is a tumor suppressor gene, and mutations that disrupts MEN1 function are common to many tumor types. Mutations within MEN1 may also be inherited (germline). Many of these inherited mutations are associated with a number of pathogenic syndromes of the parathyroid and pancreas, and some also predispose patients to hyperplasia. In this study, we cataloged the reported germline mutations from the ClinVar database and compared them with the somatic mutations detected in cancers from the Catalogue of Somatic Mutations in Cancer (COSMIC) database. We then used statistical software to determine the probability of mutations being pathogenic or driver. Our data show that many confirmed germline mutations do not appear in tumor samples. Thus, most mutations that disable MEN1 function in tumors are somatic in nature. Furthermore, of the germline mutations that do appear in tumors, only a fraction has the potential to be pathogenic or driver mutations.

KMT2A regulates cervical cancer cell growth through targeting VDAC1

Cervical cancer is an aggressive cutaneous malignancy, illuminating the molecular mechanisms of tumorigenesis and discovering novel therapeutic targets are urgently needed. KMT2A is a transcriptional co-activator regulating gene expression during early development and hematopoiesis, but the role of KMT2A in cervical cancer remains unknown. Here, we demonstrated that KMT2A regulated cervical cancer growth via targeting VADC1. Knockdown of KMT2A significantly suppressed cell proliferation and migration and induced apoptosis in cervical cancer cells, accompanying with activation of PARP/caspase pathway and inhibition of VADC1. Overexpression of VDAC1 reversed the KMT2A knockdown-mediated regulation of cell proliferation, migration and apoptosis. The in vivo results from a cervical cancer xenograft mouse model also validated that KMT2A knockdown suppressed tumor growth by inhibiting VDAC1, whereas KMT2A overexpression promoted cervical cancer growth. Moreover, analyses of Biewenga cervix database and clinical samples showed that both KMT2A and VDAC1 were upregulated in cervix squamous cell carcinoma compared with cervix uteri tissues, and their expression was negatively correlated with the differentiation grade of cervical cancer. Our results therefore indicated that the KMT2A/VDAC1 signaling axis may be a potential new mechanism of cervical carcinogenesis.

t(11;16)(q23;p13)/KMT2A-CREBBP in hematologic malignancies: presumptive evidence of myelodysplasia or therapy-related neoplasm?

Fusion partners of KMT2A affect disease phenotype and influence the current World Health Organization classification of hematologic neoplasms. The t(11;16)(q23;p13)/KMT2A-CREBBP is considered presumptive evidence of a myelodysplastic syndrome (MDS) and a MDS-related cytogenetic abnormality in the classification of acute myeloid leukemia (AML). Here, we report 18 cases of hematologic neoplasms with t(11;16). There were 8 males and 10 females with a median age of 51.9 years at time of detection of t(11;16). Of 17 patients with enough clinical information and pathological materials for review, 16 had a history of cytotoxic therapies for various malignancies including 12/15 patients who received topoisomerase II inhibitors, and 15 were classified as having therapy-related neoplasms. The median interval from the diagnosis of primary malignancy to the detection of t(11;16) was 23.2 months. Dysplasia, usually mild, was observed in 7/17 patients. Blasts demonstrated monocytic differentiation in 8/8 patients who developed AML at the time or following detection of t(11;16). t(11;16) was observed as the sole chromosomal abnormality in 10/18 patients. KMT2A rearrangement was confirmed in 11/11 patients. The median survival from the detection of t(11;16) was 15.4 months. In summary, t(11;16)(q23;p13) is rare and overwhelmingly associated with prior exposure of cytotoxic therapy. Instead of being considered presumptive evidence of myelodysplasia, we suggest that the detection of t(11;16) should automatically prompt a search for a history of malignancy and cytotoxic therapy so that proper risk stratification and clinical management are made accordingly. The dismal outcome of patients with t(11;16) is in keeping with that of therapy-related neoplasms.

miR-193a targets MLL1 mRNA and drastically decreases MLL1 protein production: Ectopic expression of the miRNA aberrantly lowers H3K4me3 content of the chromatin and hampers cell proliferation and viability

Mixed-lineage leukaemia 1 (MLL1) enzyme plays major role in regulating genes associated with vertebrate development. Cell physiology and homeostasis is regulated by microRNAs in diverse microenvironment. In this investigation we have identified conserved miR-193a target sites within the 3'-UTR of MLL1 gene transcript. Utilizing wild type and mutated 3'-UTR constructs and luciferase reporter assays we have clearly demonstrated that miR-193a directly targets the 3'-UTR region of the MLL1 mRNA. Ectopic expression of miR-193a modulated global H3K4 mono-, di- and tri-methylation levels and affects the expression of CAV1, a gene which is specifically modulated by H3K4me3. To determine the implications of this in vitro finding in aberrant physiological conditions we analyzed prostate cancer tissue samples. In this context miR-193a RNA was undetectable and MLL1 was highly expressed with concomitantly high levels of H3K4me, H3K4me2, and H3K4me3 enrichment in the promoters of MLL1 responsive genes. Finally, we showed that prolonged ectopic expression of miR-193a inhibits growth and cell migration, and induces apoptosis. Thus, while our study unveils amplitude of the epigenome, including miRnome it establishes that; (i) miR-193a directly target MLL1 mRNA, (ii) miR-193a impair MLL1 protein production, (iii) miR-193a reduces the overall methylation marks of the genome.

Regulation of MLL/COMPASS stability through its proteolytic cleavage by taspase1 as a possible approach for clinical therapy of leukemia

In this study, Zhao et al. investigated the biological significance of MLL1 cleavage by the endopeptidase taspase1. They demonstrate that taspase1-dependent cleavage of MLL1 results in the destabilization of MLL, and thus their findings provide insights into the direct regulation of the stability of MLL1 through its cleavage by taspase1.

Chromosomal translocations of the Mixed-lineage leukemia 1 (MLL1) gene generate MLL chimeras that drive the pathogenesis of acute myeloid and lymphoid leukemia. The untranslocated MLL1 is a substrate for proteolytic cleavage by the endopeptidase threonine aspartase 1 (taspase1); however, the biological significance of MLL1 cleavage by this endopeptidase remains unclear. Here, we demonstrate that taspase1-dependent cleavage of MLL1 results in the destabilization of MLL. Upon loss of taspase1, MLL1 association with chromatin is markedly increased due to the stabilization of its unprocessed version, and this stabilization of the uncleaved MLL1 can result in the displacement of MLL chimeras from chromatin in leukemic cells. Casein kinase II (CKII) phosphorylates MLL1 proximal to the taspase1 cleavage site, facilitating its cleavage, and pharmacological inhibition of CKII blocks taspase1-dependent MLL1 processing, increases MLL1 stability, and results in the displacement of the MLL chimeras from chromatin. Accordingly, inhibition of CKII in a MLL-AF9 mouse model of leukemia delayed leukemic progression in vivo. This study provides insights into the direct regulation of the stability of MLL1 through its cleavage by taspase1, which can be harnessed for targeted therapeutic approaches for the treatment of aggressive leukemia as the result of MLL translocations.

RNA Sequencing and Pathway Analysis Identify Important Pathways Involved in Hypertrichosis and Intellectual Disability in Patients with Wiedemann-Steiner Syndrome

A growing number of histone modifiers are involved in human neurodevelopmental disorders, suggesting that proper regulation of chromatin state is essential for the development of the central nervous system. Among them, heterozygous de novo variants in KMT2A, a gene coding for histone methyltransferase, have been associated with Wiedemann-Steiner syndrome (WSS), a rare developmental disorder mainly characterized by intellectual disability (ID) and hypertrichosis. As KMT2A is known to regulate the expression of multiple target genes through methylation of lysine 4 of histone 3 (H3K4me), we sought to investigate the transcriptomic consequences of KMT2A variants involved in WSS. Using fibroblasts from four WSS patients harboring loss-of-function KMT2A variants, we performed RNA sequencing and identified a number of genes for which transcription was altered in KMT2A-mutated cells compared to the control ones. Strikingly, analysis of the pathways and biological functions significantly deregulated between patients with WSS and healthy individuals revealed a number of processes predicted to be altered that are relevant for hypertrichosis and intellectual disability, the cardinal signs of this disease.

Molecular and cellular issues of KMT2A variants involved in Wiedemann-Steiner syndrome

Variants in KMT2A, encoding the histone methyltransferase KMT2A, are a growing cause of intellectual disability (ID). Up to now, the majority of KMT2A variants are non-sense and frameshift variants causing a typical form of Wiedemann-Steiner syndrome. We studied KMT2A gene in a cohort of 200 patients with unexplained syndromic and non-syndromic ID and identified four novel variants, one splice and three missense variants, possibly deleterious. We used primary cells from the patients and molecular approaches to determine the deleterious effects of those variants on KMT2A expression and function. For the putative splice variant c.11322-1G>A, we showed that it led to only one nucleotide deletion and loss of the C-terminal part of the protein. For two studied KMT2A missense variants, c.3460C>T (p.(Arg1154Trp)) and c.8558T>G (p.(Met2853Arg)), located at the cysteine-rich CXXC domain and the transactivation domain of the protein, respectively, we found altered KMT2A target genes expression in patient's fibroblasts compared to controls. Furthermore, we found a disturbed subcellular distribution of KMT2A for the c.3460C>T mutant. Taken together, our results demonstrated the deleterious impact of the splice variant and of the missense variants located at two different functional domains and suggested reduction of KMT2A function as the disease-causing mechanism.

KMT2A promotes melanoma cell growth by targeting hTERT signaling pathway

Melanoma is an aggressive cutaneous malignancy, illuminating the exact mechanisms and finding novel therapeutic targets are urgently needed. In this study, we identified KMT2A as a potential target, which promoted the growth of human melanoma cells. KMT2A knockdown significantly inhibited cell viability and cell migration and induced apoptosis, whereas KMT2A overexpression effectively promoted cell proliferation in various melanoma cell lines. Further study showed that KMT2A regulated melanoma cell growth by targeting the hTERT-dependent signal pathway. Knockdown of KMT2A markedly inhibited the promoter activity and expression of hTERT, and hTERT overexpression rescued the viability inhibition caused by KMT2A knockdown. Moreover, KMT2A knockdown suppressed tumorsphere formation and the expression of cancer stem cell markers, which was also reversed by hTERT overexpression. In addition, the results from a xenograft mouse model confirmed that KMT2A promoted melanoma growth via hTERT signaling. Finally, analyses of clinical samples demonstrated that the expression of KMT2A and hTERT were positively correlated in melanoma tumor tissues, and KMT2A high expression predicted poor prognosis in melanoma patients. Collectively, our results indicate that KMT2A promotes melanoma growth by activating the hTERT signaling, suggesting that the KMT2A/hTERT signaling pathway may be a potential therapeutic target for melanoma.

Somatic cancer mutations in the MLL1 histone methyltransferase modulate its enzymatic activity and dependence on the WDR5/RBBP5/ASH2L complex

Somatic missense mutations in the mixed lineage leukemia 1 (MLL1) histone H3K4 methyltransferase are often observed in cancers. MLL1 forms a complex with WDR5, RBBP5, and ASH2L (WRA) which stimulates its activity. The MM‐102 compound prevents the interaction between MLL1 and WDR5 and functions as an MLL1 inhibitor. We have studied the effects of four cancer mutations in the catalytic SET domain of MLL1 on the enzymatic activity of MLL1 and MLL1–WRA complexes. In addition, we studied the interaction of the MLL1 mutants with the WRA proteins and inhibition of MLL1–WRA complexes by MM‐102. All four investigated mutations had strong effects on the activity of MLL1. R3903H was inactive and S3865F showed reduced activity both alone and in complex with WRA, but its activity was stimulated by the WRA complex. By contrast, R3864C and R3841W were both more active than wild‐type MLL1, but still less active than the wild‐type MLL1–WRA complex. Both mutants were not stimulated by complex formation with WRA, although no differences in the interaction with the complex proteins were observed. These results indicate that both mutants are in an active conformation even in the absence of the WRA complex and their normal control of activity by the WRA complex is altered. In agreement with this observation, the activity of R3864C and R3841W was not reduced by addition of the MM‐102 inhibitor. We show that different cancer mutations in MLL1 lead to a loss or increase in activity, illustrating the complex and tumor‐specific role of MLL1 in carcinogenesis. Our data exemplify that biochemical investigations of somatic tumor mutations are required to decipher their pathological role. Moreover, our data indicate that MM‐102 may not be used as an MLL1 inhibitor if the R3864C and R3841W mutations are present. More generally, the efficacy of any enzyme inhibitor must be experimentally confirmed for mutant enzymes before an application can be considered.

Targeting human SET1/MLL family of proteins

The SET1 family of proteins, and in particular MLL1, are essential regulators of transcription and key mediators of normal development and disease. Here, we summarize the detailed characterization of the methyltransferase activity of SET1 complexes and the role of the key subunits, WDR5, RbBP5, ASH2L, and DPY30. We present new data on full kinetic characterization of human MLL1, MLL3, SET1A, and SET1B trimeric, tetrameric, and pentameric complexes to elaborate on substrate specificities and compare our findings with what has been reported before. We also review exciting recent work identifying potent inhibitors of oncogenic MLL1 function through disruption of protein–protein interactions within the MLL1 complex.

DeSUMOylation: An Important Therapeutic Target and Protein Regulatory Event

The discovery of the process of small ubiquitin-like modifier (SUMO)-mediated post-translational modification of targets (SUMOylation) in early 1990s proved to be a significant step ahead in understanding mechanistic regulation of proteins and their functions in diverse life processes at the cellular level. The critical step in reversing the SUMOylation pathway is its ability to be dynamically deSUMOylated by SUMO/sentrin-specific protease (SENP). This review is intended to give a brief introduction about the process of SUMOylation, different mammalian deSUMOylating enzymes with special emphasis on their regulation of ribosome biogenesis at the molecular level, and its emerging roles in mitochondrial dynamics that might reveal usefulness of SENPs for therapeutic applications.

Analysis of Mll1 deficiency identifies neurogenic transcriptional modules and Brn4 as a factor for direct astrocyte-to-neuron reprogramming

BACKGROUND

Mixed lineage leukemia-1 (Mll1) epigenetically regulates gene expression patterns that specify cellular identity in both embryonic development and adult stem cell populations. In the adult mouse brain, multipotent neural stem cells (NSCs) in the subventricular zone generate new neurons throughout life, and Mll1 is required for this postnatal neurogenesis but not for glial cell differentiation. Analysis of Mll1-dependent transcription may identify neurogenic genes useful for the direct reprogramming of astrocytes into neurons.

OBJECTIVE

To identify Mll1-dependent transcriptional modules and to determine whether genes in the neurogenic modules can be used to directly reprogram astrocytes into neurons.

METHODS

We performed gene coexpression module analysis on microarray data from differentiating wild-type and Mll1-deleted subventricular zone NSCs. Key developmental regulators belonging to the neurogenic modules were overexpressed in Mll1-deleted cells and cultured cortical astrocytes, and cell phenotypes were analyzed by immunocytochemistry and electrophysiology.

RESULTS

Transcriptional modules that correspond to neurogenesis were identified in wild-type NSCs. Modules related to astrocytes and oligodendrocytes were enriched in Mll1-deleted NSCs, consistent with their gliogenic potential. Overexpression of genes selected from the neurogenic modules enhanced the production of neurons from Mll1-deleted cells, and overexpression of Brn4 (Pou3f4) in nonneurogenic cortical astroglia induced their transdifferentiation into electrophysiologically active neurons.

CONCLUSION

Our results demonstrate that Mll1 is required for the expression of neurogenic but not gliogenic transcriptional modules in a multipotent NSC population and further indicate that specific Mll1-dependent genes may be useful for direct reprogramming strategies.

ARTD1 Suppresses Interleukin 6 Expression by Repressing MLL1-Dependent Histone H3 Trimethylation

ADP-ribosyltransferase diphtheria-toxin like 1/poly(ADP-ribose) polymerase 1 (ARTD1/PARP1) is a chromatin-associated protein in the nucleus and plays an important role in different cellular processes such as regulation of gene transcription. ARTD1 has been shown to coregulate the inflammatory response by modulating the activity of the transcription factor nuclear factor κB (NF-κB), the principal regulator of interleukin 6 (IL-6), an important inflammatory cytokine implicated in a variety of diseases such as cancer. However, to what extent and how ARTD1 regulates IL-6 transcription has not been clear. Here, we show that ARTD1 suppresses lipopolysaccharide (LPS)-induced IL-6 expression in macrophages, without affecting the recruitment of the NF-κB subunit RelA to the IL-6 promoter and independent of its enzymatic activity. Interestingly, knockdown of ARTD1 did not alter H3 occupancy but increased LPS-induced trimethylation of histone 3 at lysine 4 (H3K4me3), a hallmark of transcriptionally active genes. We found that ARTD1 mediates its effect through the methyltransferase MLL1, by catalyzing H3K4me3 at the IL-6 promoter and forming a complex with NF-κB. These results demonstrate that ARTD1 modulates IL-6 expression by regulating the function of an NF-κB enhanceosome complex, which involves MLL1 and does not require ADP-ribosylation.