The histone demethylase, Jmjd1a, interacts with the myocardin factors to regulate SMC differentiation marker gene expression

SWI/SNF Complex in Vascular Smooth Muscle Cells and Its Implications in Cardiovascular Pathologies

Mature vascular smooth muscle cells (VSMC) exhibit a remarkable degree of plasticity, a characteristic that has intrigued cardiovascular researchers for decades. Recently, it has become increasingly evident that the chromatin remodeler SWItch/Sucrose Non-Fermentable (SWI/SNF) complex plays a pivotal role in orchestrating chromatin conformation, which is critical for gene regulation. In this review, we provide a summary of research related to the involvement of the SWI/SNF complexes in VSMC and cardiovascular diseases (CVD), integrating these discoveries into the current landscape of epigenetic and transcriptional regulation in VSMC. These novel discoveries shed light on our understanding of VSMC biology and pave the way for developing innovative therapeutic strategies in CVD treatment.

Compact engineered human mechanosensitive transactivation modules enable potent and versatile synthetic transcriptional control

Engineered transactivation domains (TADs) combined with programmable DNA binding platforms have revolutionized synthetic transcriptional control. Despite recent progress in programmable CRISPR-Cas-based transactivation (CRISPRa) technologies, the TADs used in these systems often contain poorly tolerated elements and/or are prohibitively large for many applications. Here, we defined and optimized minimal TADs built from human mechanosensitive transcription factors. We used these components to construct potent and compact multipartite transactivation modules (MSN, NMS and eN3x9) and to build the CRISPR-dCas9 recruited enhanced activation module (CRISPR-DREAM) platform. We found that CRISPR-DREAM was specific and robust across mammalian cell types, and efficiently stimulated transcription from diverse regulatory loci. We also showed that MSN and NMS were portable across Type I, II and V CRISPR systems, transcription activator-like effectors and zinc finger proteins. Further, as proofs of concept, we used dCas9-NMS to efficiently reprogram human fibroblasts into induced pluripotent stem cells and demonstrated that mechanosensitive transcription factor TADs are efficacious and well tolerated in therapeutically important primary human cell types. Finally, we leveraged the compact and potent features of these engineered TADs to build dual and all-in-one CRISPRa AAV systems. Altogether, these compact human TADs, fusion modules and delivery architectures should be valuable for synthetic transcriptional control in biomedical applications.

SMYD2 regulates vascular smooth muscle cell phenotypic switching and intimal hyperplasia via interaction with myocardin

The SET and MYND domain-containing protein 2 (SMYD2) is a histone lysine methyltransferase that has been reported to regulate carcinogenesis and inflammation. However, its role in vascular smooth muscle cell (VSMC) homeostasis and vascular diseases has not been determined. Here, we investigated the role of SMYD2 in VSMC phenotypic modulation and vascular intimal hyperplasia and elucidated the underlying mechanism. We observed that SMYD2 expression was downregulated in injured carotid arteries in mice and phenotypically modulated VSMCs in vitro. Using an SMC-specific SMYD2 knockout mouse model, we found that SMYD2 ablation in VSMCs exacerbated neointima formation after vascular injury in vivo. Conversely, SMYD2 overexpression inhibited VSMC proliferation and migration in vitro and attenuated arterial narrowing in injured vessels in mice. SMYD2 downregulation promoted VSMC phenotypic switching accompanied with enhanced proliferation and migration. Mechanistically, genome-wide transcriptome analysis and loss/gain-of-function studies revealed that SMYD2 up-regulated VSMC contractile gene expression and suppressed VSMC proliferation and migration, in part, by promoting expression and transactivation of the master transcription cofactor myocardin. In addition, myocardin directly interacted with SMYD2, thereby facilitating SMYD2 recruitment to the CArG regions of SMC contractile gene promoters and leading to an open chromatin status around SMC contractile gene promoters via SMYD2-mediated H3K4 methylation. Hence, we conclude that SMYD2 is a novel regulator of VSMC contractile phenotype and intimal hyperplasia via a myocardin-dependent epigenetic regulatory mechanism.

Lysine 68 Methylation-Dependent SOX9 Stability Control Modulates Chondrogenic Differentiation in Dental Pulp Stem Cells

Dental pulp stem cells (DPSCs), characterized by easy availability, multi-lineage differentiation ability, and high proliferation ability, are ideal seed cells for cartilage tissue engineering. However, the epigenetic mechanism underlying chondrogenesis in DPSCs remains elusive. Herein, it is demonstrated that KDM3A and G9A, an antagonistic pair of histone-modifying enzymes, bidirectionally regulate the chondrogenic differentiation of DPSCs by controlling SOX9 (sex-determining region Y-type high-mobility group box protein 9) degradation through lysine methylation. Transcriptomics analysis reveals that KDM3A is significantly upregulated during the chondrogenic differentiation of DPSCs. In vitro and in vivo functional analyses further indicate that KDM3A promotes chondrogenesis in DPSCs by boosting the SOX9 protein level, while G9A hinders the chondrogenic differentiation of DPSCs by reducing the SOX9 protein level. Furthermore, mechanistic studies indicate that KDM3A attenuates the ubiquitination of SOX9 by demethylating lysine (K) 68 residue, which in turn enhances SOX9 stability. Reciprocally, G9A facilitates SOX9 degradation by methylating K68 residue to increase the ubiquitination of SOX9. Meanwhile, BIX-01294 as a highly specific G9A inhibitor significantly induces the chondrogenic differentiation of DPSCs. These findings provide a theoretical basis to ameliorate the clinical use of DPSCs in cartilage tissue-engineering therapies.

Prdm6 drives ductus arteriosus closure by promoting ductus arteriosus smooth muscle cell identity and contractility

Based upon our demonstration that the smooth muscle cell-selective (SMC-selective) putative methyltransferase, Prdm6, interacts with myocardin-related transcription factor-A, we examined Prdm6's role in SMCs in vivo using cell type-specific knockout mouse models. Although SMC-specific depletion of Prdm6 in adult mice was well tolerated, Prdm6 depletion in Wnt1-expressing cells during development resulted in perinatal lethality and a completely penetrant patent ductus arteriosus (DA) phenotype. Lineage tracing experiments in Wnt1Cre2 Prdm6fl/fl ROSA26LacZ mice revealed normal neural crest-derived SMC investment of the outflow tract. In contrast, myography measurements on DA segments isolated from E18.5 embryos indicated that Prdm6 depletion significantly reduced DA tone and contractility. RNA-Seq analyses on DA and ascending aorta samples at E18.5 identified a DA-enriched gene program that included many SMC-selective contractile associated proteins that was downregulated by Prdm6 depletion. Chromatin immunoprecipitation-sequencing experiments in outflow tract SMCs demonstrated that 50% of the genes Prdm6 depletion altered contained Prdm6 binding sites. Finally, using several genome-wide data sets, we identified an SMC-selective enhancer within the Prdm6 third intron that exhibited allele-specific activity, providing evidence that rs17149944 may be the causal SNP for a cardiovascular disease GWAS locus identified within the human PRDM6 gene.

Ferroptotic stress facilitates smooth muscle cell dedifferentiation in arterial remodelling by disrupting mitochondrial homeostasis

Smooth muscle cell (SMC) phenotypic switch from a quiescent 'contractile' phenotype to a dedifferentiated and proliferative state underlies the development of cardiovascular diseases (CVDs); however, our understanding of the mechanism is still incomplete. In the present study, we explored the potential role of ferroptosis, a novel nonapoptotic form of cell death, in SMC phenotypic switch and related neointimal formation. We found that ferroptotic stress was triggered in cultured dedifferentiated SMCs and arterial neointimal tissue of wire-injured mice. Moreover, pro-ferroptosis stress was activated in arterial neointimal tissue of clinical patients who underwent carotid endarterectomy. Blockade of ferroptotic stress via administration of a pharmacological inhibitor or by global genetic overexpression of glutathione peroxidase-4 (GPX4), a well-established anti-ferroptosis molecule, delayed SMC phenotype switch and arterial remodelling. Conditional SMC-specific gene delivery of GPX4 using adreno-associated virus in the carotid artery inhibited ferroptosis and prevented neointimal formation. Conversely, ferroptosis stress directly triggered dedifferentiation of SMCs. Transcriptomics analysis demonstrated that inhibition of ferroptotic stress mainly targets the mitochondrial respiratory chain and oxidative phosphorylation. Mechanistically, ferroptosis inhibition corrected the disrupted mitochondrial homeostasis in dedifferentiated SMCs, including enhanced mitochondrial ROS production, dysregulated mitochondrial dynamics, and mitochondrial hyperpolarization, and ultimately inhibited SMC phenotypic switch and growth. Copper-diacetyl-bisN4-methylthiosemicarbazone (CuATSM), an agent used for clinical molecular imaging and that potently inhibits ferroptosis, prevented SMC phenotypic switch, neointimal formation and arterial inflammation in mice. These results indicate that pro-ferroptosis stress is likely to promote SMC phenotypic switch during neointimal formation and imply that inhibition of ferroptotic stress may be a promising translational approach to treat CVDs with SMC phenotype switch.

Smooth muscle cell FTO regulates contractile function

The fat mass and obesity gene (FTO) is a N6-methyladenosine RNA demethylase that was initially linked by Genome-wide association studies to increased rates of obesity. Subsequent studies have revealed multiple mass-independent effects of the gene, including cardiac myocyte contractility. We created a mouse with a conditional and inducible smooth muscle cell deletion of Fto (Myh11 Cre+ Ftofl/fl) and did not observe any changes in mouse body mass or mitochondrial metabolism. However, the mice had significantly decreased blood pressure (hypotensive), despite increased heart rate and sodium, and significantly increased plasma renin. Remarkably, the third-order mesenteric arteries from these mice had almost no myogenic tone or capacity to constrict to smooth muscle depolarization or phenylephrine. Microarray analysis from Fto-/--isolated smooth muscle cells demonstrated a significant decrease in serum response factor (Srf) and the downstream effectors Acta2, Myocd, and Tagln; this was confirmed in cultured human coronary arteries with FTO siRNA. We conclude Fto is an important component to the contractility of smooth muscle cells.NEW & NOTEWORTHY We show a key role for the fat mass obesity (FTO) gene in regulating smooth muscle contractility, possibly by methylation of serum response factor (Srf).

The Jumonji Domain-Containing Histone Demethylase Homolog 1D/lysine Demethylase 7A (JHDM1D/KDM7A) Is an Epigenetic Activator of RHOJ Transcription in Breast Cancer Cells

The small GTPase RHOJ is a key regulator of breast cancer metastasis by promoting cell migration and invasion. The prometastatic stimulus TGF-β activates RHOJ transcription via megakaryocytic leukemia 1 (MKL1). The underlying epigenetic mechanism is not clear. Here, we report that MKL1 deficiency led to disrupted assembly of the RNA polymerase II preinitiation complex on the RHOJ promoter in breast cancer cells. This could be partially explained by histone H3K9/H3K27 methylation status. Further analysis confirmed that the H3K9/H3K27 dual demethylase JHDM1D/KDM7A was essential for TGF-β-induced RHOJ transcription in breast cancer cells. MKL1 interacted with and recruited KDM7A to the RHOJ promoter to cooperatively activate RHOJ transcription. KDM7A knockdown attenuated migration and invasion of breast cancer cells in vitro and mitigated the growth and metastasis of breast cancer cells in nude mice. KDM7A expression level, either singularly or in combination with that of RHOJ, could be used to predict prognosis in breast cancer patients. Of interest, KDM7A appeared to be a direct transcriptional target of TGF-β signaling. A SMAD2/SMAD4 complex bound to the KDM7A promoter and mediated TGF-β-induced KDM7A transcription. In conclusion, our data unveil a novel epigenetic mechanism whereby TGF-β regulates the transcription of the prometastatic small GTPase RHOJ. Screening for small-molecule inhibitors of KDM7A may yield effective therapeutic solutions to treat malignant breast cancers.

Myocardin-Related Transcription Factor A Mediates LPS-Induced iNOS Transactivation

Macrophage-dependent inflammation plays a critical role in atherogenesis. Inducible nitric oxide synthase (iNOS) is one of key pro-inflammatory mediators produced in macrophages and its levels can be upregulated by lipopolysaccharide (LPS). The epigenetic mechanism whereby LPS induces iNOS transcription is incompletely understood. We show here myocardin-related transcription factor A (MRTF-A) potentiated iNOS promoter activity in macrophages. There was a decrease in LPS-induced iNOS expression in several cell models due to the lack of MRTF-A. LPS treatment promoted nuclear accumulation of MRTF-A and its interaction with NF-κB/p65 on the iNOS promoter. The absence of MRTF-A prevented the accumulation of active histone marks on the iNOS promoter in response to LPS treatment. Mechanistically, MRTF-A recruited ASH2, a key component of the mammalian histone H3K4 methyltransferase complex, to the iNOS promoter. Silencing of ASH2 attenuated iNOS expression following LPS treatment. Together, our data highlight a role for MRTF-A-dependent recruitment of H3K4 methyltransferase in iNOS induction and as such provide a novel target in the intervention of atherosclerosis.

MRTF: Basic Biology and Role in Kidney Disease

A lesser known but crucially important downstream effect of Rho family GTPases is the regulation of gene expression. This major role is mediated via the cytoskeleton, the organization of which dictates the nucleocytoplasmic shuttling of a set of transcription factors. Central among these is myocardin-related transcription factor (MRTF), which upon actin polymerization translocates to the nucleus and binds to its cognate partner, serum response factor (SRF). The MRTF/SRF complex then drives a large cohort of genes involved in cytoskeleton remodeling, contractility, extracellular matrix organization and many other processes. Accordingly, MRTF, activated by a variety of mechanical and chemical stimuli, affects a plethora of functions with physiological and pathological relevance. These include cell motility, development, metabolism and thus metastasis formation, inflammatory responses and—predominantly-organ fibrosis. The aim of this review is twofold: to provide an up-to-date summary about the basic biology and regulation of this versatile transcriptional coactivator; and to highlight its principal involvement in the pathobiology of kidney disease. Acting through both direct transcriptional and epigenetic mechanisms, MRTF plays a key (yet not fully appreciated) role in the induction of a profibrotic epithelial phenotype (PEP) as well as in fibroblast-myofibroblast transition, prime pathomechanisms in chronic kidney disease and renal fibrosis.

SUV39H2 controls trophoblast stem cell fate

BACKGROUND

The placenta is formed by the coordinated expansion and differentiation of trophoblast stem (TS) cells along a multi-lineage pathway. Dynamic regulation of histone 3 lysine 9 (H3K9) methylation is pivotal to cell differentiation for many cell lineages, but little is known about its involvement in trophoblast cell development.

METHODS

Expression of H3K9 methyltransferases was surveyed in rat TS cells maintained in the stem state and following differentiation. The role of suppressor of variegation 3-9 homolog 2 (SUV39H2) in the regulation of trophoblast cell lineage development was investigated using a loss-of-function approach in rat TS cells and ex vivo cultured rat blastocysts.

RESULTS

Among the twelve-known H3K9 methyltransferases, only SUV39H2 exhibited robust differential expression in stem versus differentiated TS cells. SUV39H2 transcript and protein expression were high in the stem state and declined as TS cells differentiated. Disruption of SUV39H2 expression in TS cells led to an arrest in TS cell proliferation and activation of trophoblast cell differentiation. SUV39H2 regulated H3K9 methylation status at loci exhibiting differentiation-dependent gene expression. Analyses of SUV39H2 on ex vivo rat blastocyst development supported its role in regulating TS cell expansion and differentiation. We further identified SUV39H2 as a downstream target of caudal type homeobox 2, a master regulator of trophoblast lineage development.

CONCLUSIONS

Our findings indicate that SUV39H2 contributes to the maintenance of TS cells and restrains trophoblast cell differentiation.

GENERAL SIGNIFICANCE

SUV39H2 serves as a contributor to the epigenetic regulation of hemochorial placental development.

NG2/CSPG4, CD146/MCAM and VAP1/AOC3 are regulated by myocardin-related transcription factors in smooth muscle cells

The present work addressed the hypothesis that NG2/CSPG4, CD146/MCAM, and VAP1/AOC3 are target genes of myocardin-related transcription factors (MRTFs: myocardin/MYOCD, MRTF-A/MKL1, MRTF-B/MKL2) and serum response factor (SRF). Using a bioinformatics approach, we found that CSPG4, MCAM, and AOC3 correlate with MYOCD, MRTF-A/MKL1, and SRF across human tissues. No other transcription factor correlated as strongly with these transcripts as SRF. Overexpression of MRTFs increased both mRNA and protein levels of CSPG4, MCAM, and AOC3 in cultured human smooth muscle cells (SMCs). Imaging confirmed increased staining for CSPG4, MCAM, and AOC3 in MRTF-A/MKL1-transduced cells. MRTFs exert their effects through SRF, and the MCAM and AOC3 gene loci contained binding sites for SRF. SRF silencing reduced the transcript levels of these genes, and time-courses of induction paralleled the direct target ACTA2. MRTF-A/MKL1 increased the activity of promoter reporters for MCAM and AOC3, and transcriptional activation further depended on the chromatin remodeling enzyme KDM3A. CSPG4, MCAM, and AOC3 responded to the MRTF-SRF inhibitor CCG-1423, to actin dynamics, and to ternary complex factors. Coincidental detection of these proteins should reflect MRTF-SRF activity, and beyond SMCs, we observed co-expression of CD146/MCAM, NG2/CSPG4, and VAP1/AOC3 in pericytes and endothelial cells in the human brain. This work identifies highly responsive vascular target genes of MRTF-SRF signaling that are regulated via a mechanism involving KDM3A.

Serum response factor-cofactor interactions and their implications in disease

Serum response factor (SRF), a member of the Mcm1, Agamous, Deficiens, and SRF (MADS) box transcription factor, is widely expressed in all cell types and plays a crucial role in the physiological function and development of diseases. SRF regulates its downstream genes by binding to their CArG DNA box by interacting with various cofactors. However, the underlying mechanisms are not fully understood, therefore attracting increasing research attention due to the importance of this topic. This review's objective is to discuss the new progress in the studies of the molecular mechanisms involved in the activation of SRF and its impacts in physiological and pathological conditions. Notably, we summarized the recent studies on the interaction of SRF with its two main types of cofactors belonging to the myocardin families of transcription factors and the members of the ternary complex factors. The knowledge of these mechanisms will create new opportunities for understanding the dynamics of many traits and disease pathogenesis especially, cardiovascular diseases and cancer that could serve as targets for pharmacological control and treatment of these diseases.

Histone demethylase Jumonji domain-containing 1A inhibits proliferation and progression of gastric cancer by upregulating runt-related transcription factor 3

The histone demethylase Jumonji domain‐containing 1A (JMJD1A) is overexpressed in multiple cancers and promotes cancer progression. However, the role and mechanism of JMJD1A in gastric cancer (GC) remains poorly understood. Here, we found that JMJD1A could suppress GC cell proliferation and xenograft tumor growth. Using RNA sequencing, we identified runt‐related transcription factor 3 (RUNX3) as a novel target gene of JMJD1A. Mechanistically, we identified that JMJD1A upregulated RUNX3 through co–activating Ets‐1 and reducing the H3K9me1/2 levels at the RUNX3 promoter in GC cells. Functionally, JMJD1A inhibits the growth of GC cells in vivo, which is partially dependent on RUNX3. Moreover, JMJD1A expression was decreased in GC and low expression of JMJD1A was correlated with an aggressive phenotype and a poor prognosis in patients with GC. Importantly, JMJD1A expression was positively associated with RUNX3 expression in GC samples. These studies indicated that JMJD1A upregulates RUNX3 expression via co–activation of transcription factor Ets‐1 to inhibit proliferation of GC cells. Our findings provide new insight into the mechanism by which JMJD1A regulates RUNX3 transcription and suggest that JMJD1A and/or RUNX3 may be used as a therapeutic intervention for GC.

JMJD1A Represses the Development of Cardiomyocyte Hypertrophy by Regulating the Expression of Catalase

The histone demethylase JMJD family is involved in various physiological and pathological functions. However, the roles of JMJD1A in the cardiovascular system remain unknown. Here, we studied the function of JMJD1A in cardiac hypertrophy. The mRNA and protein levels of JMJD1A were significantly downregulated in the hearts of human patients with hypertrophic cardiomyopathy and the hearts of C57BL/6 mice underwent cardiac hypertrophy induced by transverse aortic constriction (TAC) surgery or isoproterenol (ISO) infusion. In neonatal rat cardiomyocytes (NRCMs), siRNA-mediated JMJD1A knockdown facilitated ISO or angiotensin II-induced increase in cardiomyocyte size, protein synthesis, and expression of hypertrophic fetal genes, including atrial natriuretic peptide (Anp), brain natriuretic peptide (Bnp), and Myh7. By contrast, overexpression of JMJD1A with adenovirus repressed the development of ISO-induced cardiomyocyte hypertrophy. We observed that JMJD1A reduced the production of total cellular and mitochondrial levels of reactive oxygen species (ROS), which was critically involved in the effects of JMJD1A because either N-acetylcysteine or MitoTEMPO treatment blocked the effects of JMJD1A deficiency on cardiomyocyte hypertrophy. Mechanism study demonstrated that JMJD1A promoted the expression and activity of Catalase under basal condition or oxidative stress. siRNA-mediated loss of Catalase blocked the protection of JMJD1A overexpression against ISO-induced cardiomyocyte hypertrophy. These findings demonstrated that JMJD1A loss promoted cardiomyocyte hypertrophy in a Catalase and ROS-dependent manner.

GRAF3 serves as a blood volume-sensitive rheostat to control smooth muscle contractility and blood pressure

Vascular resistance is a major determinant of BP and is controlled, in large part, by RhoA-dependent smooth muscle cell (SMC) contraction within small peripheral arterioles and previous studies from our lab indicate that GRAF3 is a critical regulator of RhoA in vascular SMC. The elevated contractile responses we observed in GRAF3 deficient vessels coupled with the hypertensive phenotype provided a mechanistic link for the hypertensive locus recently identified within the GRAF3 gene. On the basis of our previous findings that the RhoA signaling axis also controls SMC contractile gene expression and that GRAF3 expression was itself controlled by this pathway, we postulated that GRAF3 serves as an important counter-regulator of SMC phenotype. Indeed, our new findings presented herein indicate that GRAF3 expression acts as a pressure-sensitive rheostat to control vessel tone by both reducing calcium sensitivity and restraining expression of the SMC-specific contractile proteins that support this function. Collectively, these studies highlight the potential therapeutic value of GRAF3 in the control of human hypertension.

Histone methylation and vascular biology

The vasculature not only transports oxygenated blood, metabolites, and waste products but also serves as a conduit for hormonal communication between distant tissues. Therefore, it is important to maintain homeostasis within the vasculature. Recent studies have greatly expanded our understanding of the regulation of vasculature development and vascular-related diseases at the epigenetic level, including by protein posttranslational modifications, DNA methylation, and noncoding RNAs. Integrating epigenetic mechanisms into the pathophysiologic conceptualization of complex and multifactorial vascular-related diseases may provide promising therapeutic approaches. Several reviews have presented detailed discussions of epigenetic mechanisms not including histone methylation in vascular biology. In this review, we primarily discuss histone methylation in vascular development and maturity, and in vascular diseases.

Megakaryocytic Leukemia 1 Bridges Epigenetic Activation of NADPH Oxidase in Macrophages to Cardiac Ischemia-Reperfusion Injury

BACKGROUND

Excessive accumulation of reactive oxygen species (ROS), catalyzed by the NADPH oxidases (NOX), is involved in the pathogenesis of ischemia-reperfusion (IR) injury. The underlying epigenetic mechanism remains elusive.

METHODS

We evaluated the potential role of megakaryocytic leukemia 1 (MKL1), as a bridge linking epigenetic activation of NOX to ROS production and cardiac ischemia-reperfusion injury.

RESULTS

Following IR injury, MKL1-deficient (knockout) mice exhibited smaller myocardial infarction along with improved heart function compared with wild-type littermates. Similarly, pharmaceutical inhibition of MKL1 with CCG-1423 also attenuated myocardial infarction and improved heart function in mice. Amelioration of IR injury as a result of MKL1 deletion or inhibition was accompanied by reduced ROS in vivo and in vitro. In response to IR, MKL1 levels were specifically elevated in macrophages, but not in cardiomyocytes, in the heart. Of note, macrophage-specific deletion (MϕcKO), instead of cardiomyocyte-restricted ablation (CMcKO), of MKL1 in mice led to similar improvements of infarct size, heart function, and myocardial ROS generation. Reporter assay and chromatin immunoprecipitation assay revealed that MKL1 directly bound to the promoters of NOX genes to activate NOX transcription. Mechanistically, MKL1 recruited the histone acetyltransferase MOF (male absent on the first) to modify the chromatin structure surrounding the NOX promoters. Knockdown of MOF in macrophages blocked hypoxia/reoxygenation-induced NOX transactivation and ROS accumulation. Of importance, pharmaceutical inhibition of MOF with MG149 significantly downregulated NOX1/NOX4 expression, dampened ROS production, and normalized myocardial function in mice exposed to IR injury. Finally, administration of a specific NOX1/4 inhibitor GKT137831 dampened ROS generation and rescued heart function after IR in mice.

CONCLUSIONS

Our data delineate an MKL1-MOF-NOX axis in macrophages that contributes to IR injury, and as such we have provided novel therapeutic targets in the treatment of ischemic heart disease.

Ablation of serum response factor in hepatic stellate cells attenuates liver fibrosis

Trans-differentiation, or activation, of hepatic stellate cells (HSCs) is a hallmark event in liver fibrosis although the underlying mechanism is not fully appreciated. Serum response factor (SRF) is a pleiotropic sequence-specific transcription factor with a ubiquitous expression pattern. In the present study, we investigated the effect of HSC-specific ablation of SRF on liver fibrosis in vivo and the underlying mechanism. We report that SRF bound to the promoter regions of pro-fibrogenic genes, including collagen type I (Col1a1/Col1a2) and alpha smooth muscle actin (Acta2), with greater affinity in activated HSCs compared to quiescent HSCs. Ablation of SRF in HSCs in vitro downregulated the expression of fibrogenic genes by dampening the accumulation of active histone marks. SRF also interacted with MRTF-A, a well-documented co-factor involved in liver fibrosis, on the pro-fibrogenic gene promoters during HSC activation. In addition, SRF directly regulated MRTF-A transcription in activated HSCs. More importantly, HSC conditional SRF knockout (CKO) mice developed a less robust pro-fibrogenic response in the liver in response to CCl₄ injection and BDL compared to wild-type littermates. In conclusion, our data demonstrate that SRF may play an essential role in HSC activation and liver fibrosis. KEY MESSAGES: • SRF deficiency decelerates activation of hepatic stellate cells (HSCs) in vitro. • SRF epigenetically activates pro-fibrogenic transcription to promote HSC maturation. • SRF interacts with MRTF-A and contributes to MRTF-A transcription. • Conditional SRF deletion in HSCs attenuates BDL-induced liver fibrosis in mice. • Conditional SRF ablation in HSCs attenuates CCl₄-induced liver fibrosis in mice.

HDAC6 is associated with the formation of aortic dissection in human

BACKGROUND

The pathological features of aortic dissection (AD) include vascular smooth muscle cell (VSMC) loss, elastic fiber fraction, and inflammatory responses in the aorta. However, little is known about the post-translational modification mechanisms responsible for these biological processes.

METHODS

A total of 72 aorta samples, used for protein detection, were collected from 36 coronary artery disease (CAD, served as the control) patients and 36 type A AD (TAAD) patients. Chromatin immunoprecipitation (ChIP)-PCR was used to identify the genes regulated by H3K23ac, and tubastatin A, an inhibitor of HDAC6, was utilized to clarify the downstream mechanisms regulated by HDAC6.

RESULTS

We found that the protein level of histone deacetylase HDAC6 was reduced in the aortas of patients suffering from TAAD and that the protein levels of H4K12ac, and H3K23ac significantly increased, while H3K18ac, H4K8ac, and H4K5ac dramatically decreased when compared with CAD patients. Although H3K23ac, H3K18ac, and H4K8ac increased in the human VSMCs after treatment with the HDAC6 inhibitor tubastatin A, only H3K23ac showed the same results in human tissues. Notably, the results of ChIP-PCR demonstrated that H3K23ac was enriched in extracellular matrix (ECM)-related genes, including Col1A2, Col3A1, CTGF, POSTN, MMP2, TIMP2, and ACTA2, in the aortic samples of TAAD patients. In addition, our results showed that HDAC6 regulates H4K20me2 and p-MEK1/2 in the pathological process of TAAD.

CONCLUSIONS

These results indicate that HDAC6 is involved in human TAAD formation by regulating H3K23ac, H4K20me2 and p-MEK1/2, thus, providing a strategy for the treatment of TAAD by targeting protein post-translational modifications (PTMs), chiefly histone PTMs.

A potential common role of the Jumonji C domain-containing 1A histone demethylase and chromatin remodeler ATRX in promoting colon cancer

Jumonji C domain-containing 1A (JMJD1A) is a histone demethylase and epigenetic regulator that has been implicated in cancer development. In the current study, its mRNA and protein expression was analyzed in human colorectal tumors. It was demonstrated that JMJD1A levels were increased and correlated with a more aggressive phenotype. Downregulation of JMJD1A in human HCT116 colorectal cancer cells caused negligible growth defects, but robustly decreased clonogenic activity. Transcriptome analysis revealed that JMJD1A downregulation led to multiple changes in HCT116 cells, including inhibition of MYC- and MYCN-regulated pathways and stimulation of the TP53 tumor suppressor response. One gene identified to be stimulated by JMJD1A was α-thalassemia/mental retardation syndrome X-linked (ATRX), which encodes for a chromatin remodeler. The JMJD1A protein, but not a catalytically inactive mutant, activated the ATRX gene promoter and JMJD1A also affected levels of dimethylation on lysine 9 of histone H3. Similar to JMJD1A, ATRX was significantly overexpressed in human colorectal tumors and correlated with increased disease recurrence and lethality. Furthermore, ATRX downregulation in HCT116 cells reduced their growth and clonogenic activity. Accordingly, upregulation of ATRX may represent one mechanism by which JMJD1A promotes colorectal cancer. In addition, the data presented in this study suggest that the current notion of ATRX as a tumor suppressor is incomplete and that ATRX might context dependently also function as a tumor promoter.

KDM3A inhibition attenuates high concentration insulin‑induced vascular smooth muscle cell injury by suppressing MAPK/NF‑κB pathways

Previous studies have indicated that lysine (K)-specific demethylase 3A (KDM3A) is associated with diverse diabetes-associated cardiovascular complications in response to high glucose levels. However, the effects of KDM3A on the pathological progression of cardiovascular injuries in response to high insulin levels remain unknown. The present study aimed to explore whether KDM3A knockdown may attenuate high insulin-induced vascular smooth muscle cell (VSMC) dysfunction, and to further investigate the underlying mechanisms. Primary VSMCs were isolated from the thoracic aorta of Sprague-Dawley rats. Lentiviral vectors encoding control-small interfering (si)RNA or KDM3A-siRNA were transduced into VSMCs for 72 h, and cells were subsequently incubated in medium containing 100 nM insulin for a further 5 days. Cellular proli feration, migration and apoptosis were measured by Cell Counting kit-8, Transwell chamber assay and flow cytometry, respectively. Reactive oxygen species (ROS) were detected using the dihydroethidium fluorescent probe. The mRNA expression levels of interleukin-6 and monocyte chemotactic protein-1 were measured by reverse transcription-quantitative polymerase chain reaction. Furthermore, the protein expression levels of KDM3A, mitogen-activated protein kinases (MAPKs), nuclear factor (NF)-κB/p65, B-cell lymphoma 2 (Bcl-2)-associated X protein and Bcl-2 were evaluated by western blotting. Lentivirus transduction with KDM3A-siRNA markedly reduced the elevated expression of KDM3A induced by high insulin stimulation in VSMCs. In addition, inhibition of KDM3A significantly ameliorated insulin-induced VSMC proliferation and migration, which was accompanied by decreased ROS levels, cell apoptosis and inflammatory cytokine levels. Furthermore, KDM3A gene silencing mitigated phosphorylation of MAPKs and NF-κB/p65 activation. In conclusion, KDM3A inhibition may exert numerous protective effects on high insulin-stimulated VSMCs, and the underlying mechanisms may be partly associated with inactivation of MAPK/NF-κB signaling pathways.

Possible Muscle Repair in the Human Cardiovascular System

The regenerative potential of tissues and organs could promote survival, extended lifespan and healthy life in multicellular organisms. Niches of adult stemness are widely distributed and lead to the anatomical and functional regeneration of the damaged organ. Conversely, muscular regeneration in mammals, and humans in particular, is very limited and not a single piece of muscle can fully regrow after a severe injury. Therefore, muscle repair after myocardial infarction is still a chimera. Recently, it has been recognized that epigenetics could play a role in tissue regrowth since it guarantees the maintenance of cellular identity in differentiated cells and, therefore, the stability of organs and tissues. The removal of these locks can shift a specific cell identity back to the stem-like one. Given the gradual loss of tissue renewal potential in the course of evolution, in the last few years many different attempts to retrieve such potential by means of cell therapy approaches have been performed in experimental models. Here we review pathways and mechanisms involved in the in vivo repair of cardiovascular muscle tissues in humans. Moreover, we address the ongoing research on mammalian cardiac muscle repair based on adult stem cell transplantation and pro-regenerative factor delivery. This latter issue, involving genetic manipulations of adult cells, paves the way for developing possible therapeutic strategies in the field of cardiovascular muscle repair.

Intrahepatic upregulation of MRTF-A signaling contributes to increased hepatic vascular resistance in cirrhotic rats with portal hypertension

BACKGROUND

Portal hypertension in cirrhosis is mediated, in part, by increased intrahepatic resistance, reflecting massive structural changes associated with fibrosis and intrahepatic vasoconstriction. Activation of the Rho/MRTF/SRF signaling pathway is essential for the cellular regulatory network of fibrogenesis. The aim of this study was to investigate MRTF-A-mediated regulation of intrahepatic fibrogenesis in cirrhotic rats.

METHODS

Portal hypertension was induced in rats via an injection of CCl₄ oil. Hemodynamic measurements were obtained using a polyethylene PE-50 catheter and pressure transducers. Expression of hepatic fibrogenesis was measured using histological staining. Expression of protein was measured using western blotting.

RESULTS

Upregulation of MRTF-A protein expression in the livers of rats with CCl₄-induced cirrhosis was relevant to intrahepatic resistance and hepatic fibrogenesis in portal hypertensive rats with increased modeling time. Inhibition of MRTF-A by CCG-1423 decelerated hepatic fibrosis, decreased intrahepatic resistance and portal pressure, and alleviated portal hypertension.

CONCLUSION

Increased intrahepatic resistance in rats with CCl₄-induced portal hypertension is associated with an upregulation of MRTF-A signaling. Inhibition of this pathway in the liver can decrease hepatic fibrosis and intrahepatic resistance, as well as reduce portal pressure in cirrhotic rats with CCl₄-induced portal hypertension.

KDM3A coordinates actin dynamics with intraflagellar transport to regulate cilia stability

Cilia assembly and disassembly are coupled to actin dynamics, ensuring a coherent cellular response during environmental change. How these processes are integrated remains undefined. The histone lysine demethylase KDM3A plays important roles in organismal homeostasis. Loss-of-function mouse models of Kdm3a phenocopy features associated with human ciliopathies, whereas human somatic mutations correlate with poor cancer prognosis. We demonstrate that absence of KDM3A facilitates ciliogenesis, but these resulting cilia have an abnormally wide range of axonemal lengths, delaying disassembly and accumulating intraflagellar transport (IFT) proteins. KDM3A plays a dual role by regulating actin gene expression and binding to the actin cytoskeleton, creating a responsive "actin gate" that involves ARP2/3 activity and IFT. Promoting actin filament formation rescues KDM3A mutant ciliary defects. Conversely, the simultaneous depolymerization of actin networks and IFT overexpression mimics the abnormal ciliary traits of KDM3A mutants. KDM3A is thus a negative regulator of ciliogenesis required for the controlled recruitment of IFT proteins into cilia through the modulation of actin dynamics.

MKL1 defines the H3K4Me3 landscape for NF-κB dependent inflammatory response

Macrophage-dependent inflammatory response is considered a pivotal biological process that contributes to a host of diseases when aberrantly activated. The underlying epigenetic mechanism is not completely understood. We report here that MKL1 was both sufficient and necessary for p65-dependent pro-inflammatory transcriptional program in immortalized macrophages, in primary human and mouse macrophages, and in an animal model of systemic inflammation (endotoxic shock). Extensive chromatin immunoprecipitation (ChIP) profiling and ChIP-seq analyses revealed that MKL1 deficiency erased key histone modifications synonymous with transactivation on p65 target promoters. Specifically, MKL1 defined histone H3K4 trimethylation landscape for NF-κB dependent transcription. MKL1 recruited an H3K4 trimethyltransferase SET1 to the promoter regions of p65 target genes. There, our work has identified a novel modifier of p65-dependent pro-inflammatory transcription, which may serve as potential therapeutic targets in treating inflammation related diseases.

Blood pressure-associated polymorphism controls ARHGAP42 expression via serum response factor DNA binding

We recently demonstrated that selective expression of the Rho GTPase-activating protein ARHGAP42 in smooth muscle cells (SMCs) controls blood pressure by inhibiting RhoA-dependent contractility, providing a mechanism for the blood pressure-associated locus within the ARHGAP42 gene. The goals of the current study were to identify polymorphisms that affect ARHGAP42 expression and to better assess ARHGAP42's role in the development of hypertension. Using DNase I hypersensitivity methods and ENCODE data, we have identified a regulatory element encompassing the ARHGAP42 SNP rs604723 that exhibits strong SMC-selective, allele-specific activity. Importantly, CRISPR/Cas9-mediated deletion of this element in cultured human SMCs markedly reduced endogenous ARHGAP42 expression. DNA binding and transcription assays demonstrated that the minor T allele variation at rs604723 increased the activity of this fragment by promoting serum response transcription factor binding to a cryptic cis-element. ARHGAP42 expression was increased by cell stretch and sphingosine 1-phosphate in a RhoA-dependent manner, and deletion of ARHGAP42 enhanced the progression of hypertension in mice treated with DOCA-salt. Our analysis of a well-characterized cohort of untreated borderline hypertensive patients suggested that ARHGAP42 genotype has important implications in regard to hypertension risk. Taken together, our data add insight into the genetic mechanisms that control blood pressure and provide a potential target for individualized antihypertensive therapies.

MRTF potentiates TEAD-YAP transcriptional activity causing metastasis

Yes-associated protein (YAP) and myocardin-related transcription factor (MRTF) play similar roles and exhibit significant crosstalk in directing transcriptional responses to chemical and physical extracellular cues. The mechanism underlying this crosstalk, however, remains unclear. Here, we show MRTF family proteins bind YAP via a conserved PPXY motif that interacts with the YAP WW domain. This interaction allows MRTF to recruit NcoA3 to the TEAD-YAP transcriptional complex and potentiate its transcriptional activity. We show this interaction of MRTF and YAP is critical for LPA-induced cancer cell invasion in vitro and breast cancer metastasis to the lung in vivo We also demonstrate the significance of MRTF-YAP binding in regulation of YAP activity upon acute actin cytoskeletal damage. Acute actin disruption induces nucleo-cytoplasmic shuttling of MRTF, and this process underlies the LATS-independent regulation of YAP activity. Our results provide clear evidence of crosstalk between MRTF and YAP independent of the LATS kinases that normally act upstream of YAP signaling. Our results also suggest a mechanism by which extracellular stimuli can coordinate physiological events downstream of YAP.

Histone demethylase KDM3a, a novel regulator of vascular smooth muscle cells, controls vascular neointimal hyperplasia in diabetic rats

BACKGROUND AND AIMS

Deregulation of histone demethylase KDM3a, an important regulator for H3K9 methylation, is correlated with obesity and abnormal metabolism in rodent models. However, the function of KDM3a in vascular remodeling under diabetic condition is unknown.

METHODS

Adenoviruses expressing KDM3a and lentiviruses expressing KDM3a-targeting siRNA were generated to study the role of KDM3a both in vivo and in vitro. The carotid artery balloon injury model was established in diabetic SD rats to evaluate the significance of KDM3a in vascular injury.

RESULTS

Diabetic vessels were associated with sustained loss of histone H3 lysine 9 di-methylation (H3K9me2) and elevation of KDM3a. This phenomenon was induced by high glucose (HG) and was persistently present even after removal from diabetic condition and high glucose in vascular smooth muscle cells (VSMCs). After 28-day balloon injury, KDM3a overexpression accelerated while KDM3a knockdown reduced neointima formation, following vascular injury in diabetic rats without glucose control. Microarray analysis revealed KDM3a altered the expression of vascular remodeling genes; particularly, it mediated the Rho/ROCK and AngII/AGTR1 pathways. In the in vivo study, HG and Ang II-stimulated proliferation and migration of VSMCs were enhanced by KDM3a overexpression, whereas markedly prevented by KDM3a knockdown. KDM3a regulated the transcription of AGTR1 and ROCK2 via controlling H3K9me2 in the proximal promoter regions.

CONCLUSIONS

Histone demethylase KDM3a promotes vascular neointimal hyperplasia in diabetic rats via AGTR1 and ROCK2 signaling pathways. Targeting KDM3a might represent a promising therapeutic approach for the prevention of coronary artery disease with diabetes.

HIF-KDM3A-MMP12 regulatory circuit ensures trophoblast plasticity and placental adaptations to hypoxia

The hemochorial placenta develops from the coordinated multilineage differentiation of trophoblast stem (TS) cells. An invasive trophoblast cell lineage remodels uterine spiral arteries, facilitating nutrient flow, failure of which is associated with pathological conditions such as preeclampsia, intrauterine growth restriction, and preterm birth. Hypoxia plays an instructive role in influencing trophoblast cell differentiation and regulating placental organization. Key downstream hypoxia-activated events were delineated using rat TS cells and tested in vivo, using trophoblast-specific lentiviral gene delivery and genome editing. DNA microarray analyses performed on rat TS cells exposed to ambient or low oxygen and pregnant rats exposed to ambient or hypoxic conditions showed up-regulation of genes characteristic of an invasive/vascular remodeling/inflammatory phenotype. Among the shared up-regulated genes was matrix metallopeptidase 12 (MMP12). To explore the functional importance of MMP12 in trophoblast cell-directed spiral artery remodeling, we generated an Mmp12 mutant rat model using transcription activator-like nucleases-mediated genome editing. Homozygous mutant placentation sites showed decreased hypoxia-dependent endovascular trophoblast invasion and impaired trophoblast-directed spiral artery remodeling. A link was established between hypoxia/HIF and MMP12; however, evidence did not support Mmp12 as a direct target of HIF action. Lysine demethylase 3A (KDM3A) was identified as mediator of hypoxia/HIF regulation of Mmp12 Knockdown of KDM3A in rat TS cells inhibited the expression of a subset of the hypoxia-hypoxia inducible factor (HIF)-dependent transcripts, including Mmp12, altered H3K9 methylation status, and decreased hypoxia-induced trophoblast cell invasion in vitro and in vivo. The hypoxia-HIF-KDM3A-MMP12 regulatory circuit is conserved and facilitates placental adaptations to environmental challenges.

IOX1, a JMJD2A inhibitor, suppresses the proliferation and migration of vascular smooth muscle cells induced by angiotensin II by regulating the expression of cell cycle-related proteins

The epigenetic modification of vascular smooth muscle cell (VSMC) phenotypic switching, proliferation, migration, apoptosis and extracellular matrix synthesis is known to occur in atherosclerosis. The aim of the present study was to investigate the effects of IOX1, a Jumonji domain-containing 2A (JMJD2A) inhibitor, on regulation of the cell cycle in angiotensin II (Ang II)-stimulated VSMCs and to elucidate the possible mechanisms involved. The proliferation and migration of the Ang II-stimulated VSMCs in the presence or absence of IOX1 were evaluated in vitro. Flow cytometric analysis was used to determine the effects of IOX1 on cell cycle progression. RT-qPCR and western blot analysis were carried out to measure the expression levels of cell cycle-related genes. The trimethylation of histone H3 lysine 9 (H3K9me3) at the promoters of these genes was detected by chromatin immunoprecipitation (ChIP) assay. We confirmed that the JMJD2A levels were increased, whereas the H3K9me3 levels were decreased in the Ang II-stimulated VSMCs. The inhibition of JMJD2A by IOX1 suppressed the Ang II-induced cell proliferation, migration and cell cycle progression by inhibiting cyclin D1 expression and increasing p21 expression. The underlying mechanisms were related to the restoration of the H3K9me3 levels at the promoters of these genes. In conclusion, the findings of our study indicate that IOX1 exerts its anti-proliferative and anti-migratory effects by regulating the expression of the cell cycle-related proteins, cyclin D1 and p21.

Identification of a novel actin-dependent signal transducing module allows for the targeted degradation of GLI1

The Down syndrome-associated DYRK1A kinase has been reported as a stimulator of the developmentally important Hedgehog (Hh) pathway, but cells from Down syndrome patients paradoxically display reduced Hh signalling activity. Here we find that DYRK1A stimulates GLI transcription factor activity through phosphorylation of general nuclear localization clusters. In contrast, in vivo and in vitro experiments reveal that DYRK1A kinase can also function as an inhibitor of endogenous Hh signalling by negatively regulating ABLIM proteins, the actin cytoskeleton and the transcriptional co-activator MKL1 (MAL). As a final effector of the DYRK1A-ABLIM-actin-MKL1 sequence, we identify the MKL1 interactor Jumonji domain demethylase 1A (JMJD1A) as a novel Hh pathway component stabilizing the GLI1 protein in a demethylase-independent manner. Furthermore, a Jumonji-specific small-molecule antagonist represents a novel and powerful inhibitor of Hh signal transduction by inducing GLI1 protein degradation in vitro and in vivo.

MKL1 is an epigenetic modulator of TGF-β induced fibrogenesis

Transforming growth factor (TGF-β) induced activation of portal fibroblast cells serves as a primary cause for liver fibrosis following cholestatic injury. The underlying epigenetic mechanism is not clear. We studied the role of a transcriptional modulator, megakaryoblastic leukemia 1 (MKL1) in this process. We report here that MKL1 deficiency ameliorated BDL-induced liver fibrosis in mice as assessed by histological stainings and expression levels of pro-fibrogenic genes. MKL1 silencing by small interfering RNA (siRNA) abrogated TGF-β induced transactivation of pro-fibrogenic genes in portal fibroblast cells. TGF-β stimulated the binding of MKL1 on the promoters of pro-fibrogenic genes and promoted the interaction between MKL1 and SMAD3. While SMAD3 was necessary for MKL1 occupancy on the gene promoters, MKL1 depletion impaired SMAD3 binding reciprocally. TGF-β treatment induced the accumulation of trimethylated histone H3K4 on the gene promoters by recruiting a methyltransferase complex. Knockdown of individual members of this complex significantly weakened the binding of SMAD3 and down-regulated the activation of portal fibroblast cells. In conclusion, we have identified an epigenetic pathway that dictates TGF-β induced pro-fibrogenic transcription in portal fibroblast thereby providing novel insights for the development of therapeutic solutions to treat liver fibrosis.

MKL1 potentiates lung cancer cell migration and invasion by epigenetically activating MMP9 transcription

Malignant tumors are exemplified by excessive proliferation and aggressive migration/invasion contributing to increased mortality of cancer patients. Matrix metalloproteinase 9 (MMP9) expression is positively correlated with lung cancer malignancy. The mechanism underlying an elevated MMP9 expression is not clearly defined. We demonstrate here that the transcriptional modulator megakaryocytic leukemia 1 (MKL1) was activated by hypoxia and transforming growth factor (TGF-β), two prominent pro-malignancy factors, in cultured lung cancer cells. MKL1 levels were also increased in more invasive types of lung cancer in humans. Depletion of MKL1 in lung cancer cells attenuated migration and invasion both in vitro and in vivo. Overexpression of MKL1 potentiated the induction of MMP9 transcription by hypoxia and TGF-β, whereas MKL1 silencing diminished MMP9 expression. Of interest, MKL1 knockdown eliminated histone H3K4 methylation surrounding the MMP9 promoter. Further analyses revealed that MKL1 recruited ASH2, a component of the H3K4 methyltransferase complex, to activate MMP9 transcription. Depletion of ASH2 ameliorated cancer cell migration and invasion in an MMP9-dependent manner. Together our data indicate that MKL1 potentiates lung cancer cell migration and invasion by epigenetically activating MMP9 transcription.

Myocardin related transcription factor A programs epigenetic activation of hepatic stellate cells

BACKGROUND & AIMS

Activation of hepatic stellate cells (HSCs) represents a key process in liver injury and, in the absence of intervention, leads to irreversible cirrhosis contributing significantly to the mortality of patients with liver disease. A missing link in the current understanding of HSC activation is the involvement of the epigenetic machinery. We investigated the role of the myocardin related transcription factor A (MRTF-A) in HSC activation.

METHODS

Liver fibrosis was induced in wild type (WT) and MRTF-A deficient (KO) mice by CCl4 injection. Expression of mRNA and protein was measured by real-time PCR, Western blotting, and immunohistochemistry. Protein binding to DNA was assayed by chromatin immunoprecipitation (ChIP). Knockdown of endogenous proteins was mediated by either small interfering RNA (siRNA) or short hairpin RNA (shRNA), carried by lentiviral particles.

RESULTS

KO mice exhibited resistance to CCl4-induced liver fibrosis compared to WT littermates. The expression of activated HSC signature genes was suppressed in the absence of MRTF-A. ChIP assays revealed that MRTF-A deficiency led to the erasure of key histone modifications, associated with transcriptional activation, such as H3K4 di- and tri-methylation, on the promoter regions of fibrogenic genes. Mechanistically, MRTF-A recruited a histone methyltransferase complex (COMPASS) to the promoters of fibrogenic genes to activate transcription. Silencing of individual COMPASS components dampened transactivation of fibrogenic genes in vitro and blocked liver fibrosis in mice. Oestradiol suppressed HSC activation by dampening the expression and binding activity of COMPASS.

CONCLUSIONS

Our data illustrate a novel mechanism that connects MRTF-A dependent histone H3K4 methylation to HSC activation.

Myocardin in biology and disease

Myocardin (MYOCD) is a potent transcriptional coactivator that functions primarily in cardiac muscle and smooth muscle through direct contacts with serum response factor (SRF) over cis elements known as CArG boxes found near a number of genes encoding for contractile, ion channel, cytoskeletal, and calcium handling proteins. Since its discovery more than 10 years ago, new insights have been obtained regarding the diverse isoforms of MYOCD expressed in cells as well as the regulation of MYOCD expression and activity through transcriptional, post-transcriptional, and post-translational processes. Curiously, there are a number of functions associated with MYOCD that appear to be independent of contractile gene expression and the CArG-SRF nucleoprotein complex. Further, perturbations in MYOCD gene expression are associated with an increasing number of diseases including heart failure, cancer, acute vessel disease, and diabetes. This review summarizes the various biological and pathological processes associated with MYOCD and offers perspectives to several challenges and future directions for further study of this formidable transcriptional coactivator.

Specific phosphorylation of histone demethylase KDM3A determines target gene expression in response to heat shock

Phosphorylation of histone demethylase KDM3A in response to thermal stress enables its specific recruitment to target genes by Stat1.

Histone lysine (K) residues, which are modified by methyl- and acetyl-transferases, diversely regulate RNA synthesis. Unlike the ubiquitously activating effect of histone K acetylation, the effects of histone K methylation vary with the number of methyl groups added and with the position of these groups in the histone tails. Histone K demethylases (KDMs) counteract the activity of methyl-transferases and remove methyl group(s) from specific K residues in histones. KDM3A (also known as JHDM2A or JMJD1A) is an H3K9me2/1 demethylase. KDM3A performs diverse functions via the regulation of its associated genes, which are involved in spermatogenesis, metabolism, and cell differentiation. However, the mechanism by which the activity of KDM3A is regulated is largely unknown. Here, we demonstrated that mitogen- and stress-activated protein kinase 1 (MSK1) specifically phosphorylates KDM3A at Ser264 (p-KDM3A), which is enriched in the regulatory regions of gene loci in the human genome. p-KDM3A directly interacts with and is recruited by the transcription factor Stat1 to activate p-KDM3A target genes under heat shock conditions. The demethylation of H3K9me2 at the Stat1 binding site specifically depends on the co-expression of p-KDM3A in the heat-shocked cells. In contrast to heat shock, IFN-γ treatment does not phosphorylate KDM3A via MSK1, thereby abrogating its downstream effects. To our knowledge, this is the first evidence that a KDM can be modified via phosphorylation to determine its specific binding to target genes in response to thermal stress.

Histone methylation regulates gene expression and can have drastic consequences for health if the process is defective. Histone lysine demethylases (KDMs) counteract the activity of methyl-transferases and remove methyl group(s) from histones. KDM3A is a H3K9me2/1 demethylase that performs diverse functions via the regulation of its target genes, which are involved in spermatogenesis, metabolism, and cell differentiation. However, the mechanisms underlying KDM3A regulation of specific genes at specific times are largely unknown. Here we found that a physiological stress—elevated temperature—induces KDM3A phosphorylation in human cells via the MSK1 kinase. This phosphorylated form of KDM3A directly interacts with the transcription factor Stat1, which enables Stat1 to recruit KDM3A to Stat1-binding sequences at the promoters of specific target genes. KDM3A then acts to demethylate H3K9me2/1 at these targets, thereby causing specific gene expression in response to the thermal stress. We conclude that heat shock can affect the expression of many genes in human cells via a novel activation mechanism that is centered around the phosphorylation of KDM3A.

DNA methylation of a GC repressor element in the smooth muscle myosin heavy chain promoter facilitates binding of the Notch-associated transcription factor, RBPJ/CSL1

OBJECTIVE

The goal of the present study was to identify novel mechanisms that regulate smooth muscle cell (SMC) differentiation marker gene expression.

APPROACH AND RESULTS

We demonstrate that the CArG-containing regions of many SMC-specific promoters are imbedded within CpG islands. A previously identified GC repressor element in the SM myosin heavy chain (MHC) promoter was highly methylated in cultured aortic SMC but not in the aorta, and this difference was inversely correlated with SM MHC expression. Using an affinity chromatography/mass spectroscopy-based approach, we identified the multifunctional Notch transcription factor, recombination signal binding protein for immunoglobulin κ J region (RBPJ), as a methylated GC repressor-binding protein. RBPJ protein levels and binding to the endogenous SM MHC GC repressor were enhanced by platelet-derived growth factor-BB treatment. A methylation mimetic mutation to the GC repressor that facilitated RBPJ binding inhibited SM MHC promoter activity as did overexpression of RBPJ. Consistent with this, knockdown of RBPJ in phenotypically modulated human aortic SMC enhanced endogenous SMC marker gene expression, an effect likely mediated by increased recruitment of serum response factor and Pol II to the SMC-specific promoters. In contrast, the depletion of RBPJ in differentiated transforming growth factor-β-treated SMC inhibited SMC-specific gene activation, supporting the idea that the effects of RBPJ/Notch signaling are context dependent.

CONCLUSIONS

Our results indicate that methylation-dependent binding of RBPJ to a GC repressor element can negatively regulate SM MHC promoter activity and that RBPJ can inhibit SMC marker gene expression in phenotypically modulated SMC. These results will have important implications on the regulation of SMC phenotype and on Notch-dependent transcription.