MKL1 is an epigenetic mediator of TNF-α-induced proinflammatory transcription in macrophages by interacting with ASH2

ASH2L, a COMPASS core subunit, is involved in the cell invasion and migration of triple-negative breast cancer cells through the epigenetic control of histone H3 lysine 4 methylation

ASH2L (Absent-Small-Homeotic-2-Like protein) is a core subunit of the COMPASS (COMplex of Proteins ASsociated with Set1) complex, the most notable writer of the methylation of histone H3 lysine 4 (H3K4). The COMPASS complex regulates active promoters or enhancers for gene expression, and its dysfunction is associated with aberrant development and disease. Here, we demonstrated that ASH2L mediated the cell invasion and migration activity of triple-negative breast cancer cells through the interaction with the COMPASS components and the target genomic regions. Transcriptome analysis indicated a potential correlation between ASH2L and the genes involved in inflammatory/immune responses. Among them, we found that the intrinsic expression of IL1B (interleukin 1 beta), an essential proinflammatory gene, was directly regulated by ASH2L. These results revealed a novel role of ASH2L on the maintenance of breast cancer malignancy possibly through H3K4 methylation of the target inflammatory/immune responsive genes.

Knockdown of MKL1 ameliorates oxidative stress-induced chondrocyte apoptosis and cartilage matrix degeneration by activating TWIST1-mediated PI3K/AKT signaling pathway in rats

Studies have reported that megakaryocytic leukemia 1 (MKL1) is closely related to the pathological process of a variety of inflammatory diseases, but its role in osteoarthritis (OA) needs to be clarified. This study aimed to investigate the regulatory role of MKL1 in oxidative stress-induced chondrocyte apoptosis and cartilage matrix degeneration. The expressions of target mRNAs and proteins were measured by using reverse transcription-quantitative polymerase chain reaction and western blotting. ELISA assay was used to measure the levels of IL-6, IL-8, and TNF-α in chondrocytes. And commercial kits based on different spectrophotometry or colorimetry methods were performed to validate oxidative stress. CCK-8 and apoptosis kits were used to determine cell viability and apoptosis. Rat OA model was established by anterior cruciate ligament transection (ACLT), and the expression of MKL1 was interfered by injecting sh-MKL1 lentiviral vector into caudal vein. The results showed that the expression of MKL1was induced by H₂O₂ in chondrocytes. Knockdown of MKL1 alleviated H₂O₂-induced inflammation and cell apoptosis, reduced H₂O₂-induced oxidative stress, and improved cartilage matrix degeneration of chondrocytes. Besides, inhibition of MKL1 regulated the activation of TWIST1-mediated PI3K/AKT signaling. Further studies have found that TWIST1-mediated PI3K/AKT signaling was involved in the regulation mechanism of MKL1 on chondrocyte apoptosis and cartilage matrix degeneration. Next, intervention with MKL1 inhibited the progression of OA in rats. These results demonstrated that MKL1 regulate the apoptosis and cartilage matrix degeneration of chondrocytes via TWIST1-mediated PI3K/AKT signaling.

Resident Fibroblast MKL1 Is Sufficient to Drive Pro-fibrogenic Response in Mice

Fibrosis is an evolutionarily conserved pathophysiological process serving bifurcated purposes. On the one hand, fibrosis is essential for wound healing and contributes to the preservation of organ function. On the other hand, aberrant fibrogenic response may lead to tissue remodeling and precipitate organ failure. Recently lineage tracing studies have shown that resident fibroblasts are the primary mediator of fibrosis taking place in key organs such as the heart, the lungs, and the kidneys. Megakaryocytic leukemia 1 (MKL1) is transcriptional regulator involved in tissue fibrosis. Here we generated resident fibroblast conditional MKL1 knockout (CKO) mice by crossing the Mkl1^f/f mice to the Col1a2-Cre^ERT2 mice. Models of cardiac fibrosis, pulmonary fibrosis, and renal fibrosis were reproduced in the CKO mice and wild type (WT) littermates. Compared to the WT mice, the CKO mice displayed across-the-board attenuation of fibrosis in different models. Our data cement the pivotal role MKL1 plays in tissue fibrosis but point to the cellular origin from which MKL1 exerts its pro-fibrogenic effects.

Myocardin-related transcription factor A (MRTF-A) regulates integrin beta 2 transcription to promote macrophage infiltration and cardiac hypertrophy in mice

AIMS

Macrophage-mediated inflammatory response represents a key pathophysiological process in a host of cardiovascular diseases including heart failure. Regardless of etiology, heart failure is invariably preceded by cardiac hypertrophy. In the present study we investigated the effect of macrophage-specific deletion of myocardin-related transcription factor A (MRTF-A) on cardiac hypertrophy and the underlying mechanism.

METHODS AND RESULTS

We report that when subjected to transverse aortic constriction (TAC), macrophage MRTF-A conditional knockout (CKO) mice developed a less severe phenotype of cardiac hypertrophy compared to wild type (WT) littermates and were partially protected from the loss of heart function. In addition, there was less extensive cardiac fibrosis in the CKO mice than WT mice following the TAC procedure. Further analysis revealed that cardiac inflammation, as assessed by levels of pro-inflammatory cytokines and chemokines, was dampened in CKO mice paralleling reduced infiltration of macrophages in the heart. Mechanistically, MRTF-A deficiency attenuated the expression of integrin beta 2 (ITGB2/CD18) in macrophage thereby disrupting adhesion of macrophages to vascular endothelial cells. MRTF-A was recruited by Sp1 to the ITGB2 promoter and cooperated with Sp1 to activate ITGB2 transcription in macrophages. Administration of a CD18 blocking antibody attenuated TAC induced cardiac hypertrophy in mice. Interaction between MRTF-A and the histone demethylase KDM3A likely contributed to IGTB2 transcription and consequently adhesion of macrophages to endothelial cells.

CONCLUSIONS

Our data suggest that MRTF-A may regulate macrophage trafficking and contribute to the pathogenesis of cardiac hypertrophy by activating ITGB2 transcription.

MKL1-induced lncRNA SNHG18 drives the growth and metastasis of non-small cell lung cancer via the miR-211-5p/BRD4 axis

Megakaryocytic leukemia 1 (MKL1) is a key transcription factor involved in non-small cell lung cancer (NSCLC) growth and metastasis. Yet, its downstream target genes, especially long non-coding RNA (lncRNA) targets, are poorly investigated. In this study, we employed lncRNA array technology to identify differentially expressed lncRNAs in NSCLC cells with or without overexpression of MKL1. Candidate lncRNAs were further explored for their clinical significance and function in NSCLC. The results showed that MKL1 promoted the expression of lncRNA SNHG18 in NSCLC cells. SNHG18 upregulation in NSCLC specimens correlated with lymph node metastasis and reduced overall survival of NSCLC patients. SNHG18 expression served as an independent prognostic factor for NSCLC. Knockdown of SNHG18 blocked MKL1-induced growth and invasion of NSCLC cells in vitro. Animal studies validated the requirement for SNHG18 in NSCLC growth and metastasis. Moreover, overexpression of SNHG18 promoted NSCLC cell proliferation and invasion. Mechanically, SNHG18 exerted its prometastatic effects on NSCLC cells through repression of miR-211-5p and induction of BRD4. Clinical evidence indicated that SNHG18 expression was negatively correlated with miR-211-5p expression in NSCLC tissues. Altogether, SNHG18 acts as a lncRNA mediator of MKL1 in NSCLC. SNHG18 facilitates NSCLC growth and metastasis by modulating the miR-211-5p/BRD4 axis. Therefore, SNHG18 may be a potential therapeutic target for the treatment of NSCLC.

BAY11-7082 inhibits the expression of tissue factor and plasminogen activator inhibitor-1 in type-II alveolar epithelial cells following TNF-α stimulation via the NF-κB pathway

Pulmonary inflammation strongly promotes alveolar hypercoagulation and fibrinolytic inhibition. NF-κB signaling regulates the expression of molecules associated with coagulation and fibrinolytic inhibition in type-II alveolar epithelial cells (AECII) stimulated by lipopolysaccharide. However, whether TNF-α-induced alveolar hypercoagulation and fibrinolysis inhibition is also associated with the NF-κB pathway remains to be determined. The aim of the present study was to determine whether BAY11-7082, an inhibitor of the NF-κB pathway, inhibits the expressions of tissue factor (TF) and plasminogen activator inhibitor-1 (PAI-1) in AECⅡ in response to TNF-α. Rat AECII were treated with BAY11-7082 for 24 h and stimulated with TNF-α for 1 h. The expression of TF and PAI-1 were determined using western blotting and reverse transcription-quantitative PCR. The concentrations of TF and PAI-1 in culture supernatant were also measured by ELISA. Moreover, levels of NF-κB p65 (p65), phosphorylated (p)-p65 (p-p65), inhibitor of NF-κB α (IκBα) and p-IκBα were also evaluated. Immunofluorescence was used to detect p65 levels in cell nuclei. TNF-α significantly promoted TF and PAI-1 expression either at the mRNA or protein level in AECII cells. Concentrations of TF and PAI-1 in supernatant also significantly increased upon TNF-α stimulation. Furthermore, TNF-α upregulated the levels of p-IκBα, p65, and p-p65 in the cytoplasm. Immunofluorescence analysis indicated that TNF-α increased p65 translocation from the cytoplasm to the nucleus. However, AECII pre-treated with BAY11-7082 expressed lower levels of TF and PAI-1 following TNF-α treatment. Levels of p-IκBα, p65 and p-p65 in the cytoplasm also decreased, and translocation of p65 from cytoplasm into the nucleus was inhibited by BAY11-7082 pretreatment. These findings suggest that BAY11-7082 improves the hypercoagulation and fibrinolytic inhibition induced by TNF-α in alveolar epithelial cells via the NF-κB signaling pathway. BAY11-7082 might represent a therapeutic option for alveolar hypercoagulation and fibrinolytic inhibition in acute respiratory distress syndrome.

ASH2L is involved in promotion of endometrial cancer progression via upregulation of PAX2 transcription

Absent, small or homeotic 2‐like protein (ASH2L) is a core component of a multimeric histone methyltransferase complex that is involved in the maintenance of active transcription, participating in several cancers, however the biological function and molecular mechanism of ASH2L in endometrial cancer (ECa) are largely unknown. Endometrial cancer is a common malignant tumor in women and the incidence of this cancer is on the rise. Estrogen‐ERα signaling, as an oncogenic pathway, plays a crucial role in endometrial carcinogenesis. Therefore, further exploration of the molecular mechanisms around ERα‐mediated gene transcription in ECa would be helpful to the understanding of tumor development and to finding a new therapeutic target for ECa. Here, our study demonstrated that ASH2L was highly expressed in ECa samples, and higher expression of ASH2L was positively correlated with a poor prognosis. Moreover, we identified that ASH2L associated with ERα and that knockdown of ASH2L resulted in decreased expression of a subset of the estrogen‐induced target genes, including paired box 2 (PAX2), an oncogenic gene in ECa. ASH2L was recruited to cis‐regulatory elements in PAX2, thereby altering histone H3K4me3 and H3K27me3 levels, to enhance ERα‐mediated transactivation. Finally, depletion of ASH2L suppressed endometrial cancer cell proliferation and migration. Our findings suggest that ASH2L participates in the promotion of ECa progression, if not totally at least partially, via upregulation of PAX2 transcription.

The complex activities of the SET1/MLL complex core subunits in development and disease

In mammalian cells, the SET1/MLL complexes are the main writers of the H3K4 methyl mark that is associated with active gene expression. The activities of these complexes are critically dependent on the association of the catalytic subunit with their shared core subunits, WDR5, RBBP5, ASH2L, and DPY30, collectively referred as WRAD. In addition, some of these core subunits can bind to proteins other than the SET1/MLL complex components. This review starts with discussion of the molecular activities of these core subunits, with an emphasis on DPY30 in organizing the assembly of the SET1/MLL complexes with other associated factors. This review then focuses on the roles of the core subunits in stem cells and development, as well as in diseased cell states, mainly cancer, and ends with discussion on dissecting the responsible activities of the core subunits and how we may target them for potential disease treatment. This article is part of a Special Issue entitled: The MLL family of proteins in normal development and disease edited by Thomas A Milne.

PRMT6 mediates inflammation via activation of the NF-κB/p65 pathway on a cigarette smoke extract-induced murine emphysema model

INTRODUCTION

Smoke-driven lung inflammation is considered to be the major pathophysiology mechanism of Chronic Obstructive Pulmonary Disease (COPD)/emphysema. Protein arginine methyltransferase 6 (PRMT6) is a key epigenetic enzyme, which is related to protecting the tri-methylation of H3K4 (H3K4me3). We hypothesized that PTMT6 protects lung inflammation through the nuclear factor kappa B (NF-κB) pathway.

METHODS

Mice were injected with cigarette smoke extract (CSE) or PBS to establish a mice model, intratracheally instilled with overexpressed PRMT6 or negative control vector. Morphometry of lung slides and lung function were measured. We determined the protein expression of PRMT6 and its related histone targets, the activation of NF-κB pathway, the level of tumor necrosis factor α (TNFα) and interleukin-1β (IL-1β).

RESULTS

After PRMT6 overexpression, the morphometry indexes and lung function were improved. Also, the expression of H3K4me3 was decreased. Overexpressed PRMT6 could suppress CSE-induced NF-κB activation and pro-inflammation genes expression.

CONCLUSIONS

The overexpressed PRMT6 could serve as an inflammation inhibitor, potentially through blocking the NF-κB/p65 pathway in the murine emphysema model.

Epigenetic Modification in Macrophages: A Promising Target for Tumor and Inflammation-associated Disease Therapy

Macrophages are essential for supporting tissue homeostasis, regulating immune response, and promoting tumor progression. Due to its heterogeneity, macrophages have different phenotypes and functions in various tissues and diseases. It is becoming clear that epigenetic modification playing an essential role in determining the biological behavior of cells. In particular, changes of DNA methylation, histone methylation and acetylation regulated by the corresponding epigenetic enzymes, can directly control macrophages differentiation and change their functions under different conditions. In addition, epigenetic enzymes also have become anti-tumor targets, such as HDAC, LSD1, DNMT, and so on. In this review, we presented an overview of the latest progress in the study of macrophages phenotype and function regulated by epigenetic modifications, including DNA methylation and histone modifications, to better understand how epigenetic modification controls macrophages phenotype and function in inflammation-associated diseases, and the application prospect in anti-tumor.

Hematopoietic stem and progenitor cell proliferation and differentiation requires the trithorax protein Ash2l

Post-translational modifications of core histones participate in controlling the expression of genes. Methylation of lysine 4 of histone H3 (H3K4), together with acetylation of H3K27, is closely associated with open chromatin and gene transcription. H3K4 methylation is catalyzed by KMT2 lysine methyltransferases that include the mixed-lineage leukemia 1–4 (MLL1-4) and SET1A and B enzymes. For efficient catalysis, all six require a core complex of four proteins, WDR5, RBBP5, ASH2L, and DPY30. We report that targeted disruption of Ash2l in the murine hematopoietic system results in the death of the mice due to a rapid loss of mature hematopoietic cells. However, lin⁻Sca1⁺Kit⁺ (LSK) cells, which are highly enriched in hematopoietic stem and multi-potent progenitor cells, accumulated in the bone marrow. The loss of Ash2l resulted in global reduction of H3K4 methylation and deregulated gene expression, including down-regulation of many mitosis-associated genes. As a consequence, LSK cells accumulated in the G2-phase of the cell cycle and were unable to proliferate and differentiate. In conclusion, Ash2l is essential for balanced gene expression and for hematopoietic stem and multi-potent progenitor cell physiology.

Epigenetic activation of PERP transcription by MKL1 contributes to ROS-induced apoptosis in skeletal muscle cells

Excessive reactive oxygen species (ROS) causes irreparable damages to cells and commit cells to programmed cell death or apoptosis. A panel of well-documented pro-apoptotic genes, including p53 apoptosis effector related to PMP-22 (PERP), are up-regulated and collectively mediate ROS induced apoptosis. The epigenetic mechanism whereby ROS stimulates PERP transcription, however, lacks in-depth characterization. Here we report that the transcriptional modulator megakaryocytic leukemia 1 (MKL1) is activated by H2O2 treatment in skeletal muscle cells (C2C12). Small interfering RNA (siRNA) mediated silencing or small-molecule compound (CCG-1423) mediated inhibition of MKL1 attenuated H2O2 induced apoptosis of C2C12 cells. Over-expression of MKL1 potentiated trans-activation of PERP whereas MKL1 ablation/inhibition abrogated the induction of PERP by H2O2 in C2C12 cells. Mechanistically, MKL1 interacted with and was recruited to the PERP promoter by the transcription factor E2F1. Once bound to the PERP promoter, MKL1 engaged the histone demethylase KDM3A to modulate the chromatin structure surrounding the PERP promoter thereby leading to PERP trans-activation. Depletion of either E2F1 or KDM3A blocked the induction of PERP by H2O2. In conclusion, our data illustrate a novel epigenetic pathway that links PERP transcription to ROS-induced apoptosis in skeletal muscle cells.

Myocardin-related transcription factor A (MRTF-A) contributes to acute kidney injury by regulating macrophage ROS production

A host of pathogenic factors induce acute kidney injury (AKI) leading to insufficiencies of renal function. In the present study we evaluated the role of myocardin-related transcription factor A (MRTF-A) in the pathogenesis of AKI. We report that systemic deletion of MRTF-A or inhibition of MRTF-A activity with CCG-1423 significantly attenuated AKI in mice induced by either ischemia-reperfusion or LPS injection. Of note, MRTF-A deficiency or suppression resulted in diminished renal ROS production in AKI models with down-regulation of NAPDH oxdiase 1 (NOX1) and NOX4 expression. In cultured macrophages, MRTF-A promoted NOX1 transcription in response to either hypoxia-reoxygenation or LPS treatment. Interestingly, macrophage-specific MRTF-A deletion ameliorated AKI in mice. Mechanistic analyses revealed that MRTF-A played a role in regulating histone H4K16 acetylation surrounding the NOX gene promoters by interacting with the acetyltransferase MYST1. MYST1 depletion repressed NOX transcription in macrophages. Finally, administration of a MYST1 inhibitor MG149 alleviated AKI in mice. Therefore, we data illustrate a novel epigenetic pathway that controls ROS production in macrophages contributing to AKI. Targeting the MRTF-A-MYST1-NOX axis may yield novel therapeutic strategies to combat AKI.

Genetic Modifiers of the Breast Tumor Microenvironment

Multiple nonmalignant cell types in the tumor microenvironment (TME) impact breast cancer risk, metastasis, and response to therapy, yet most heritable mechanisms that influence TME cell function and breast cancer outcomes are largely unknown. Breast cancer risk is ∼30% heritable and >170 genetic loci have been associated with breast cancer traits. However, the majority of candidate genes have poorly defined mechanistic roles in breast cancer biology. Research indicates that breast cancer risk modifiers directly impact cancer cells, yet it is equally plausible that some modifier alleles impact the nonmalignant TME. The objective of this review is to examine the list of current breast cancer candidate genes that may modify breast cancer risk and outcome through the TME.

HADC5 deacetylates MKL1 to dampen TNF-α induced pro-inflammatory gene transcription in macrophages

Macrophage-dependent inflammatory response on the one hand functions as a key line of defense in host immunity but on the other hand underlies the pathogenesis of a host of human pathologies when aberrantly activated. Our previous investigations have led to the identification of megakaryocytic leukemia 1 (MKL1) as a key co-factor of NF-κB/p65 participating in TNF-α induced pro-inflammatory transcription in macrophages. How post-translational modifications contribute to the modulation of MKL1 activity remains an underexplored subject matter. Here we report that the lysine deacetylase HDAC5 interacts with and deacetylates MKL1 in cells. TNF-α treatment down-regulates HDAC5 expression and expels HDAC5 from the promoters of pro-inflammatory genes in macrophages. In contrast, over-expression of HDAC5 attenuates TNF-α induced pro-inflammatory transcription. Mechanistically, HDAC5-mediated MKL1 deacetylation disrupts the interaction between MKL1 and p65. In addition, deacetylation of MKL1 by HDAC5 blocks its nuclear translocation in response to TNF-α treatment. In conclusion, our work has identified an important pathway that contributes to the regulation of pro-inflammatory response in macrophages.

Pediatric Acute Megakaryoblastic Leukemia: Multitasking Fusion Proteins and Oncogenic Cooperations

Pediatric leukemia presents specific clinical and genetic features from adult leukemia but the underpinning mechanisms of transformation are still unclear. Acute megakaryoblastic leukemia (AMKL) is the malignant accumulation of progenitors of the megakaryocyte lineage that normally produce blood platelets. AMKL is diagnosed de novo, in patients showing a poor prognosis, or in Down syndrome (DS) patients with a better prognosis. Recent data show that de novo AMKL is primarily associated with chromosomal alterations leading to the expression of fusions between transcriptional regulators. This review highlights the most recurrent genetic events found in de novo pediatric AMKL patients and, based on recent functional analyses, proposes a mechanism of leukemogenesis common to de novo and DS-AMKL.

MKL1 links epigenetic activation of MMP2 to ovarian cancer cell migration and invasion

Responding to pro-metastatic cues such as low oxygen tension, cancer cells develop several different strategies to facilitate migration and invasion. During this process, expression levels of matrix metalloproteinases (MMPs) are up-regulated so that cancer cells can more easily enter or exit the circulation. In this report we show that message levels of the transcriptional modulator MKL1 were elevated in malignant forms of ovarian cancer tissues in humans when compared to more benign forms accompanying a similar change in MMP2 expression. MKL1 silencing blocked hypoxia-induced migration and invasion of ovarian cancer cells (SKOV-3) in vitro. Over-expression of MKL1 activated while MKL1 depletion repressed MMP2 transcription in SKOV-3 cells. MKL1 was recruited to the MMP2 promoter by NF-κB in response to hypoxia. Mechanistically, MKL1 recruited a histone methyltransferase, SET1, and a chromatin remodeling protein, BRG1, and coordinated their interaction to alter the chromatin structure surrounding the MMP2 promoter leading to transcriptional activation. Both BRG1 and SET1 were essential for hypoxia-induced MMP2 trans-activation. Finally, expression levels of SET1 and BRG1 were positively correlated with ovarian cancer malignancies in humans. Together, our data suggest that MKL1 promotes ovarian cancer cell migration and invasion by epigenetically activating MMP2 transcription.