HIF-1α coordinates epigenetic activation of SIAH1 in hepatocytes in response to nutritional stress

E3 ubiquitin ligase Siah1 aggravates NAFLD through Scp2 ubiquitination

Nonalcoholic fatty liver disease (NAFLD) is one of the most common liver disorders and accompanied by multiple metabolic dysfunctions. Although excessive lipid accumulation in hepatocytes has been identified as a crucial mediator of NAFLD development, the underlying mechanisms are very complicated and remain largely unknown. In this study, we reported that upregulated expression of the seven in absentia homolog 1 (Siah1) in the liver exacerbated NAFLD progression. Conversely, Siah1 downregulation markedly alleviated the high fat diet-induced accumulation of hepatic fat and expression of genes related to lipid metabolism in vitro and in vivo. The mechanistic study revealed that Siah1 interacted with sterol carrier protein 2 (Scp2) and promotes its ubiquitination and degradation, suggesting that Siah1 is an important activator of Scp2 ubiquitination in the context of NAFLD. Our results demonstrated that Siah1 regulated the lipid accumulation in NAFLD by interacting with Scp2. Thus, this study presents Siah1 as a promising therapeutic target in the development of NAFLD.

Siah1 in cancer and nervous system diseases (Review)

The dysregulation of the ubiquitin‑proteasome system will result in the abnormal accumulation and dysfunction of proteins, thus leading to severe diseases. Seven in absentia homolog 1 (Siah1), an E3 ubiquitin ligase, has attracted wide attention due to its varied functions in physiological and pathological conditions, and the numerous newly discovered Siah1 substrates. In cancer and nervous system diseases, the functions of Siah1 as a promoter or a suppressor of diseases are related to the change in cellular microenvironment and subcellular localization. At the same time, complex upstream regulations make Siah1 different from other E3 ubiquitin ligases. Understanding the molecular mechanism of Siah1 will help the study of various signaling pathways and benefit the therapeutic strategy of human diseases (e.g., cancer and nervous system diseases). In the present review, the functions and regulations of Siah1 are described. Moreover, novel substrates of Siah1 discovered in recent studies will be highlighted in cancer and nervous system diseases, providing ideas for future research and clinical targeted therapies using Siah1.

Host cell factors stimulate HIV-1 transcription by antagonizing substrate-binding function of Siah1 ubiquitin ligase to stabilize transcription elongation factor ELL2

The Siah1 and Siah2 ubiquitin ligases are implicated in diverse biological processes ranging from cellular stress responses, signaling to transcriptional regulation. A key substrate of Siah1 is ELL2, which undergoes proteolysis upon polyubiquitination. ELL2 stimulates transcriptional elongation and is a subunit of the Super Elongation Complex (SEC) essential for HIV-1 transactivation. Previously, multiple transcriptional and post-translational mechanisms are reported to control Siah's expression and activity. Here we show that the activity of Siah1/2 can also be suppressed by host cell factor 1 (HCF1), and the hitherto poorly characterized HCF2, which themselves are not degraded but can bind and block the substrate-binding domain (SBD) of Siah1/2 to prevent their autoubiquitination and trans-ubiquitination of downstream targets including ELL2. This effect stabilizes ELL2 and enhances the ELL2-SEC formation for robust HIV-1 transactivation. Thus, our study not only identifies HCF1/2 as novel activators of HIV-1 transcription through inhibiting Siah1 to stabilize ELL2, but also reveals the SBD of Siah1/2 as a previously unrecognized new target for HCF1/2 to exert this inhibition.

An Interplay Between MRTF-A and the Histone Acetyltransferase TIP60 Mediates Hypoxia-Reoxygenation Induced iNOS Transcription in Macrophages

Cardiac ischemia-reperfusion injury (IRI) represents a major pathophysiological event associated with permanent loss of heart function. Several inter-dependent processes contribute to cardiac IRI that include accumulation of reactive oxygen species (ROS), aberrant inflammatory response, and depletion of energy supply. Inducible nitric oxide synthase (iNOS) is a pro-inflammatory mediator and a major catalyst of ROS generation. In the present study we investigated the epigenetic mechanism whereby iNOS transcription is up-regulated in macrophages in the context of cardiac IRI. We report that germline deletion or systemic inhibition of myocardin-related transcription factor A (MRTF-A) in mice attenuated up-regulation of iNOS following cardiac IRI in the heart. In cultured macrophages, depletion or inhibition of MRTF-A suppressed iNOS induction by hypoxia-reoxygenation (HR). In contrast, MRTF-A over-expression potentiated activation of the iNOS promoter by HR. MRTF-A directly binds to the iNOS promoter in response to HR stimulation. MRTF-A binding to the iNOS promoter was synonymous with active histone modifications including trimethylated H3K4, acetylated H3K9, H3K27, and H4K16. Further analysis revealed that MRTF-A interacted with H4K16 acetyltransferase TIP60 to synergistically activate iNOS transcription. TIP60 depletion or inhibition achieved equivalent effects as MRTF-A depletion/inhibition in terms of iNOS repression. Of interest, TIP60 appeared to form a crosstalk with the H3K4 trimethyltransferase complex to promote iNOS trans-activation. In conclusion, we data suggest that the MRTF-A-TIP60 axis may play a critical role in iNOS transcription in macrophages and as such be considered as a potential target for the intervention of cardiac IRI.

Brahma Related Gene 1 (Brg1) Regulates Cellular Cholesterol Synthesis by Acting as a Co-factor for SREBP2

Hepatocyte is a hub for cholesterol metabolism. Augmented synthesis of cholesterol in the liver is associated with hypercholesterolemia and contributes to the pathogenesis of a host of cardiovascular and metabolic diseases. Sterol response element binding protein 2 (SREBP2) regulates hepatic cholesterol metabolism by activating the transcription of rate-limiting enzymes in the cholesterol biosynthesis pathway. The underlying epigenetic mechanism is not well understood. We report here that mice with hepatocyte-specific knockout (CKO) of Brg1, a chromatin remodeling protein, exhibit reduced levels of hepatic cholesterol compared to the wild type (WT) littermates when placed on a high-fact diet (HFD) or a methionine-and-choline-deficient diet (MCD). Down-regulation of cholesterol levels as a result of BRG1 deficiency was accompanied by attenuation of cholesterogenic gene transcription. Likewise, BRG1 knockdown in hepatocytes markedly suppressed the induction of cholesterogenic genes by lipid depletion formulas. Brg1 interacted with SREBP2 and was recruited by SREBP2 to the cholesterogenic gene promoters. Reciprocally, Brg1 deficiency dampened the occupancies of SREBP2 on target promoters likely through modulating H3K9 methylation on the cholesterogenic gene promoters. Mechanistically, Brg1 recruited the H3K9 methyltransferase KDM3A to co-regulate pro-cholesterogenic transcription. KDM3A silencing dampened the cholesterogenic response in hepatocytes equivalent to Brg1 deficiency. In conclusion, our data demonstrate a novel epigenetic pathway that contributes to SREBP2-dependent cholesterol synthesis in hepatocytes.

Histone Deacetylase 11 Contributes to Renal Fibrosis by Repressing KLF15 Transcription

Renal fibrosis represents a key pathophysiological process in patients with chronic kidney diseases (CKD) and is typically associated with a poor prognosis. Renal tubular epithelial cells (RTECs), in response to a host of pro-fibrogenic stimuli, can trans-differentiate into myofibroblast-like cells and produce extracellular matrix proteins to promote renal fibrosis. In the present study we investigated the role of histone deacetylase 11 (HDAC11) in this process and the underlying mechanism. We report that expression levels of HDAC11 were up-regulated in the kidneys in several different animal models of renal fibrosis. HDAC11 was also up-regulated by treatment of Angiotensin II (Ang II) in cultured RTECs. Consistently, pharmaceutical inhibition with a small-molecule inhibitor of HDAC11 (quisinostat) attenuated unilateral ureteral obstruction (UUO) induced renal fibrosis in mice. Similarly, HDAC11 inhibition by quisinostat or HDAC11 depletion by siRNA blocked Ang II induced pro-fibrogenic response in cultured RTECs. Mechanistically, HDAC11 interacted with activator protein 2 (AP-2α) to repress the transcription of Kruppel-like factor 15 (KLF15). In accordance, KLF15 knockdown antagonized the effect of HDAC11 inhibition or depletion and enabled Ang II to promote fibrogenesis in RTECs. Therefore, we data unveil a novel AP-2α-HDAC11-KLF15 axis that contributes to renal fibrosis.

CDKN2a/p16 Antagonizes Hepatic Stellate Cell Activation and Liver Fibrosis by Modulating ROS Levels

The lipid-storage hepatic stellate cells (HSC) play as pivotal role in liver fibrosis being able to trans-differentiate into myofibroblasts in response to various pro-fibrogenic stimuli. In the present study we investigated the role of CDKN2a/p16, a negative regulator of cell cycling, in HSC activation and the underlying mechanism. Levels of p16 were significantly down-regulated in activated HSCs isolated from mice induced to develop liver fibrosis compared to quiescent HSCs isolated from the control mice ex vivo. There was a similar decrease in p16 expression in cultured HSCs undergoing spontaneous activation or exposed to TGF-β treatment in vitro. More important, p16 down-regulation was observed to correlate with cirrhosis in humans. In a classic model of carbon tetrachloride (CCl₄) induced liver fibrosis, fibrogenesis was far more extensive in mice with p16 deficiency (KO) than the wild type (WT) littermates. Depletion of p16 in cultured HSCs promoted the synthesis of extracellular matrix (ECM) proteins. Mechanistically, p16 deficiency accelerated reactive oxygen species (ROS) generation in HSCs likely through the p38 MAPK signaling. P38 inhibition or ROS cleansing attenuated ECM production in p16 deficient HSCs. Taken together, our data unveil a previously unappreciated role for p16 in the regulation of HSC activation. Screening for small-molecule compounds that can boost p16 activity may yield novel therapeutic strategies against liver fibrosis.

Deacetylation of MRTF-A by SIRT1 defies senescence induced down-regulation of collagen type I in fibroblast cells

Aging provokes both morphological and functional changes in cells, which are accompanied by a fundamental shift in gene expression patterns. One of the characteristic alterations associated with senescence in fibroblast cells is the down-regulation of collagen type I genes. In the present study, we investigated the contribution of myocardin-related transcription factor A, or MRTF-A, in this process. In mouse embryonic fibroblast (MEF) cells and human foreskin fibroblast (HFF) cells, senescence, induced by either progressive passage or treatment with hydrogen peroxide (H₂O₂), led to augmented lysine acetylation of MRTF-A paralleling down-regulation of collagen type I and SIRT1, a lysine deacetylase. SIRT1 interacted with MRTF-A to promote MRTF-A deacetylation. SIRT1 over-expression or activation by selective agonists enhanced trans-activation of the collagen promoters by MRTF-A. On the contrary, SIRT1 depletion or inhibition by specific antagonists suppressed trans-activation of the collagen promoters by MRTF-A. Likewise, mutation of four lysine residues within MRTF-A rendered it more potent in terms of activating the collagen promoters but unresponsive to SIRT1. Importantly, SIRT1 activation in senescent fibroblasts mitigated repression of collagen type I expression whereas SIRT1 inhibition promoted the loss of collagen type I expression prematurely in young fibroblasts. Mechanistically, SIRT1 enhanced the affinity of MRTF-A for the collagen type I promoters. In conclusion, our data unveil a novel mechanism that underscores aging-associated loss of collagen type I in fibroblasts via SIRT1-mediated post-translational modification of MRTF-A.

MKL1 promotes endothelial-to-mesenchymal transition and liver fibrosis by activating TWIST1 transcription

Excessive fibrogenic response in the liver disrupts normal hepatic anatomy and function heralding such end-stage liver diseases as hepatocellular carcinoma and cirrhosis. Sinusoidal endothelial cells contribute to myofibroblast activation and liver fibrosis by undergoing endothelial-mesenchymal transition (EndMT). The underlying mechanism remains poorly defined. Here we report that inhibition or endothelial-specific deletion of MKL1, a transcriptional modulator, attenuated liver fibrosis in mice. MKL1 inhibition or deletion suppressed EndMT induced by TGF-β. Mechanistically, MKL1 was recruited to the promoter region of TWIST1, a master regulator of EndMT, and activated TWIST1 transcription in a STAT3-dependent manner. A small-molecule STAT3 inhibitor (C188-9) alleviated EndMT in cultured cells and bile duct ligation (BDL) induced liver fibrosis in mice. Finally, direct inhibition of TWIST1 by a small-molecule compound harmine was paralleled by blockade of EndMT in cultured cells and liver fibrosis in mice. In conclusion, our data unveil a novel mechanism underlying EndMT and liver fibrosis and highlight the possibility of targeting the STAT3-MKL1-TWIST1 axis in the intervention of aberrant liver fibrogenesis.

Activation of Galectin-3 (LGALS3) Transcription by Injurious Stimuli in the Liver Is Commonly Mediated by BRG1

Galectin-3 (encoded by LGALS3) is a glycan-binding protein that regulates a diverse range of pathophysiological processes contributing to the pathogenesis of human diseases. Previous studies have found that galectin-3 levels are up-regulated in the liver by a host of different injurious stimuli. The underlying epigenetic mechanism, however, is unclear. Here we report that conditional knockout of Brahma related gene (BRG1), a chromatin remodeling protein, in hepatocytes attenuated induction of galectin-3 expression in several different animal models of liver injury. Similarly, BRG1 depletion or pharmaceutical inhibition in cultured hepatocytes suppressed the induction of galectin-3 expression by treatment with LPS plus free fatty acid (palmitate). Further analysis revealed that BRG1 interacted with AP-1 to bind to the proximal galectin-3 promoter and activate transcription. Mechanistically, DNA demethylation surrounding the galectin-3 promoter appeared to be a rate-limiting step in BRG1-mediated activation of galectin-3 transcription. BRG1 recruited the DNA 5-methylcytosine dioxygenase TET1 to the galectin-3 to promote active DNA demethylation thereby activating galectin-3 transcription. Finally, TET1 silencing abrogated induction of galectin-3 expression by LPS plus palmitate in cultured hepatocytes. In conclusion, our data unveil a novel epigenetic pathway that contributes to injury-associated activation of galectin-3 transcription in hepatocytes.

Epigenetic regulation of lung cancer cell proliferation and migration by the chromatin remodeling protein BRG1

Malignant lung cancer cells are characterized by uncontrolled proliferation and migration. Aberrant lung cancer cell proliferation and migration are programmed by altered cancer transcriptome. The underlying epigenetic mechanism is unclear. Here we report that expression levels of BRG1, a chromatin remodeling protein, were significantly up-regulated in human lung cancer biopsy specimens of higher malignancy grades compared to those of lower grades. Small interfering RNA mediated depletion or pharmaceutical inhibition of BRG1 suppressed proliferation and migration of lung cancer cells. BRG1 depletion or inhibition was paralleled by down-regulation of cyclin B1 (CCNB1) and latent TGF-β binding protein 2 (LTBP2) in lung cancer cells. Further analysis revealed that BRG1 directly bound to the CCNB1 promoter to activate transcription in response to hypoxia stimulation by interacting with E2F1. On the other hand, BRG1 interacted with Sp1 to activate LTBP2 transcription. Mechanistically, BRG1 regulated CCNB1 and LTBP2 transcription by altering histone modifications on target promoters. Specifically, BRG1 recruited KDM3A, a histone H3K9 demethylase, to remove dimethyl H3K9 from target gene promoters thereby activating transcription. KDM3A knockdown achieved equivalent effects as BRG1 silencing by diminishing lung cancer proliferation and migration. Of interest, BRG1 directly activated KDM3A transcription by forming a complex with HIF-1α. In conclusion, our data unveil a novel epigenetic mechanism whereby malignant lung cancer cells acquired heightened ability to proliferate and migrate. Targeting BRG1 may yield effective interventional strategies against malignant lung cancers.

MKL1 mediates TGF-β-induced CTGF transcription to promote renal fibrosis

Aberrant fibrogenesis impairs the architectural and functional homeostasis of the kidneys. It also predicts poor diagnosis in patients with end-stage renal disease (ESRD). Renal tubular epithelial cells (RTEC) can trans-differentiate into myofibroblasts to produce extracellular matrix proteins and contribute to renal fibrosis. Connective tissue growth factor (CTGF) is a cytokine upregulated in RTECs during renal fibrosis. In the present study, we investigated the regulation of CTGF transcription by megakaryocytic leukemia 1 (MKL1). Genetic deletion or pharmaceutical inhibition of MKL1 in mice mitigated renal fibrosis following the unilateral ureteral obstruction procedure. Notably, MKL1 deficiency in mice downregulated CTGF expression in the kidneys. Likewise, MKL1 knockdown or inhibition in RTEs blunted TGF-β induced CTGF expression. Further, it was discovered that MKL1 bound directly to the CTGF promoter by interacting with SMAD3 to activate CTGF transcription. In addition, MKL1 mediated the interplay between p300 and WDR5 to regulate CTGF transcription. CTGF knockdown dampened TGF-β induced pro-fibrogenic response in RTEs. MKL1 activity was reciprocally regulated by CTGF. In conclusion, we propose that targeting the MKL1-CTGF axis may generate novel therapeutic solutions against aberrant renal fibrogenesis.

BRG1 deficiency in endothelial cells alleviates thioacetamide induced liver fibrosis in mice

Liver sinusoidal endothelial cells play a key role maintaining the hepatic homeostasis, the disruption of which is associated with such end-stage liver diseases as hepatocellular carcinoma and cirrhosis. In the present study we investigated the role of brahma-related gene 1 (BRG1), a chromatin remodeling protein, in regulating endothelial transcription and the implication in liver fibrosis. We report that endothelial-specific deletion of BRG1 in mice attenuated liver fibrosis induced by injection with thioacetamide (TAA). Coincidently, alleviation of liver fibrosis as a result of endothelial BRG1 deletion was accompanied by an up-regulation of eNOS activity and NO bioavailability. In cultured endothelial cells, exposure to lipopolysaccharide (LPS) suppressed eNOS activity whereas BRG1 depletion with small interfering RNA restored eNOS-dependent NO production. Further analysis revealed that BRG1 was recruited to the caveolin-1 (CAV1) promoter by Sp1 and activated transcription of CAV1, which in turn inhibited eNOS activity. Mechanistically, BRG1 interacted with the H3K4 trimethyltransferase MLL1 to modulate H3K4 trimethylation surrounding the CAV1 promoter thereby contributing to LPS-induced CAV1 activation. In conclusion, our data unveil a novel role for BRG1 in the regulation of endothelial function and liver fibrosis.

Forkhead transcription factor FOXO3a mediates interferon-γ-induced MHC II transcription in macrophages

Macrophages are professional antigen-presenting cells relying on the expression of class II major histocompatibility complex (MHC II) genes. Interferon-γ (IFN-γ) activates MHC II transcription via the assembly of an enhanceosome centred on class II trans-activator (CIITA). In the present study, we investigated the role of the forkhead transcription factor FOXO3a in IFN- γ-induced MHC II transcription in macrophages. Knockdown of FOXO3a, but not FOXO1 or FOXO4, diminished IFN-γ-induced MHC II expression in RAW cells. On the contrary, over-expression of FOXO3a, but neither FOXO1 nor FOXO4, enhanced CIITA-mediated trans-activation of the MHC II promoter. IFN-γ treatment promoted the recruitment of FOXO3a to the MHC II promoter. Co-immunoprecipitation and RE-ChIP assays showed that FOXO3a was a component of the MHC II enhanceosome forming interactions with CIITA, RFX5, RFXB and RFXAP. FOXO3a contributed to MHC II transcription by altering histone modifications surrounding the MHC II promoter. Of interest, FOXO3a was recruited to the type IV CIITA promoter and directly activated CIITA transcription by interacting with signal transducer of activation and transcription 1 in response to IFN-γ stimulation. In conclusion, our data unveil a novel role for FOXO3a in the regulation of MHC II transcription in macrophages.

Ageing and epigenetics: linking neurodevelopmental and neurodegenerative disorders

Epigenetics has classically been recognized as crucial to neurodevelopment and neurodevelopmental disorders. More recently its role in ageing processes, including neurodegenerative disorders has emerged, although far more research is required in this area, particularly in humans. Epigenetic processes that regulate gene expression comprise strata of DNA modification (e.g. methylation), histone modification (e.g. histone acetylation), and mRNA translation (e.g. by microRNAs). These strata are progressively more fluid whereby changes in DNA methylation may persist for many years whilst expression of microRNAs fluctuates over short periods. There is considerable 'cross-talk' between these epigenetic strata. Epigenetic mechanisms are open to parental imprinting and thus they are candidates for linking diseases, not just over the life course, but also intergenerationally. There is a genetic overlap between intellectual disability and cognitive ageing. Epigenetic pathways may strengthen the links between neurodevelopmental disorders and neurodegenerative diseases. WHAT THIS PAPER ADDS: DNA methylation has relevance to both neurological development and neurodegeneration. Links between epigenetics, genotype and phenotype are emerging.

Serum response factor (SRF) promotes ROS generation and hepatic stellate cell activation by epigenetically stimulating NCF1/2 transcription

Activation of hepatic stellate cells (HSC) is a hallmark event in liver fibrosis. Accumulation of reactive oxygen species (ROS) serves as a driving force for HSC activation. The regulatory subunits of the NOX complex, NCF1 (p47^phox) and NCF2 (p67^phox), are up-regulated during HSC activation contributing to ROS production and liver fibrosis. The transcriptional mechanism underlying NCF1/2 up-regulation is not clear. In the present study we investigated the role of serum response factor (SRF) in HSC activation focusing on the transcriptional regulation of NCF1/2. We report that compared to wild type littermates HSC-conditional SRF knockout (CKO) mice exhibited a mortified phenotype of liver fibrosis induced by thioacetamide (TAA) injection or feeding with a methionine-and-choline deficient diet (MCD). More importantly, SRF deletion attenuated ROS levels in HSCs in vivo. Similarly, SRF knockdown in cultured HSCs suppressed ROS production in vitro. Further analysis revealed that SRF deficiency resulted in repression of NCF1/NCF2 expression. Mechanistically, SRF regulated epigenetic transcriptional activation of NCF1/NCF2 by interacting with and recruiting the histone acetyltransferase KAT8 during HSC activation. In conclusion, we propose that SRF integrates transcriptional activation of NCF1/NCF2 and ROS production to promote liver fibrosis.

An interaction between MKL1, BRG1, and C/EBPβ mediates palmitate induced CRP transcription in hepatocytes

Non-alcoholic steatohepatitis (NASH) is one of the most predominant disorders in metabolic syndrome. Induction of pro-inflammatory mediators in hepatocytes exposed to free fatty acids represents a hallmark event during NASH pathogenesis. C-reactive protein (CRP) is a prototypical pro-inflammatory mediator. In the present study, we investigated the mechanism by which megakaryocytic leukemia 1 (MKL1) mediates palmitate (PA) induced CRP transcription in hepatocytes. We report that over-expression of MKL1, but not MKL2, activated the CRP promoter whereas depletion or inhibition of MKL1 repressed the CRP promoter. MKL1 potentiated the induction of the CRP promoter activity by PA treatment. Importantly, MKL1 knockdown by siRNA or pharmaceutical inhibition by CCG-1423 attenuated the induction of endogenous CRP expression in hepatocytes. Similarly, primary hepatocytes isolated from wild type (WT) mice produced more CRP than those isolated from MKL1 deficient (KO) mice when stimulated with PA. Mechanistically, the sequence-specific transcription factor CCAAT-enhancer-binding protein (C/EBPβ) interacted with MKL1 and recruited MKL1 to activate CRP transcription. Reciprocally, MKL1 modulated C/EBPβ activity by recruiting the chromatin remodeling protein BRG1 to the CRP promoter to alter histone modifications. In conclusion, our data delineate a novel epigenetic mechanism underlying augmented hepatic inflammation during NASH pathogenesis.

Endothelial-specific deletion of Brahma-related gene 1 (BRG1) assuages unilateral ureteral obstruction induced renal injury in mice

Renal homeostasis is regulated by the interplay among different cell types in the kidneys including endothelial cells. In the present study we investigated the phenotypic regulation of endothelial cells by BRG1, a chromatin remodeling protein, in a mouse model of obstructive nephropathy (ON). We report that endothelial-specific deletion of BRG1 attenuated renal inflammation induced by unilateral ureteral tract obstruction (UUO) in mice, as evidenced by down-regulation of pro-inflammatory cytokines and diminished infiltration of immune cells. Moreover, endothelial BRG1 deficiency suppressed UUO-induced renal fibrosis in mice as measured by expression of pro-fibrogenic genes, picrosirius red staining of collagenous tissues, and quantification of hydroxylproline levels. Mechanistically, BRG1 activated the transcription of adhesion molecules and chemokines in endothelial cells by recruiting histone modifying enzymes leading to macrophage adhesion and chemotaxis. In conclusion, we propose that epigenetic regulation of endothelial function by BRG1 may play an active role in ON pathogenesis.

The chromatin remodeling protein BRG1 links ELOVL3 trans-activation to prostate cancer metastasis

Prostate cancer malignancies are intimately correlated with deregulated fatty acid metabolism. The underlying epigenetic mechanism is not fully understood. In the present study we investigated the mechanism whereby the chromatin remodeling protein BRG1 regulates the transcription of long-chain fatty acid elongase 3 (Elovl3) in prostate cancer cells. We report that in response to pro-metastatic cues (androgen and TGF-β) BRG1 expression was up-regulated along with Elvol3 in prostate cancer cells. BRG1 over-expression potentiated whereas BRG1 knockdown attenuated prostate cancer cell migration and invasion. Coincidently, Elovl3 was up-regulated following BRG1 over-expression and down-regulated after BRG1 knockdown in prostate cancer cells. Further analysis revealed that BRG1 interacted with and was recruited by retinoic acid receptor-related orphan receptor (RORγ) to the Elovl3 promoter to activate transcription. Chromatin immunoprecipitation (ChIP) profiling demonstrated that BRG1 interacted with histone acetyltransferase p300 to activate Elovl3 transcription. Depletion of p300 by siRNA or inhibition of p300 by curcumin attenuated Elovl3 trans-activation in prostate cancer cells. Together, our data identify a novel epigenetic pathway that links Elovl3 transcription to prostate cancer cell migration and invasion.

The histone demethylase Kdm4 suppresses activation of hepatic stellate cell by inducing MiR-29 transcription

One of the hallmark events during liver fibrosis is the transition of quiescent hepatic stellate cells (HSC) into activated myofibroblasts, which are responsible for the production and deposition of pro-fibrogenic proteins. The epigenetic mechanism underlying HSC trans-differentiation is not fully understood. In the present study we investigated the contribution of histone H3K9 demethylase KDM4 in this process. We report that expression levels of KDM4 were down-regulated during HSC activation paralleling the up-regulation of alpha smooth muscle cell actin (Acta2), a marker of mature myofibroblast. Furthermore, HSCs isolated from mice induced to develop liver fibrosis exhibit lowered KDM4 expression compared to the control mice. In accordance, KDM4 depletion with siRNA accelerated HSC activation. Of interest, the loss of KDM4 was mirrored by the repression of miR-29, an antagonist of liver fibrosis, during HSC activation both in vitro and in vivo. KDM4 knockdown resulted in the down-regulation of miR-29 expression. Mechanistically, the sequence-specific transcription factor SREBP2 interacted with KDM4 to activate miR-29 transcription. In conclusion, our data delineate a novel epigenetic mechanism underlying HSC activation. Targeting this axis may yield potential therapeutics against liver fibrosis.

The RNA-Protein Interactome of Differentiated Kidney Tubular Epithelial Cells

BACKGROUND

RNA-binding proteins (RBPs) are fundamental regulators of cellular biology that affect all steps in the generation and processing of RNA molecules. Recent evidence suggests that regulation of RBPs that modulate both RNA stability and translation may have a profound effect on the proteome. However, regulation of RBPs in clinically relevant experimental conditions has not been studied systematically.

METHODS

We used RNA interactome capture, a method for the global identification of RBPs to characterize the global RNA-binding proteome (RBPome) associated with polyA-tailed RNA species in murine ciliated epithelial cells of the inner medullary collecting duct. To study regulation of RBPs in a clinically relevant condition, we analyzed hypoxia-associated changes of the RBPome.

RESULTS

We identified >1000 RBPs that had been previously found using other systems. In addition, we found a number of novel RBPs not identified by previous screens using mouse or human cells, suggesting that these proteins may be specific RBPs in differentiated kidney epithelial cells. We also found quantitative differences in RBP-binding to mRNA that were associated with hypoxia versus normoxia.

CONCLUSIONS

These findings demonstrate the regulation of RBPs through environmental stimuli and provide insight into the biology of hypoxia-response signaling in epithelial cells in the kidney. A repository of the RBPome and proteome in kidney tubular epithelial cells, derived from our findings, is freely accessible online, and may contribute to a better understanding of the role of RNA-protein interactions in kidney tubular epithelial cells, including the response of these cells to hypoxia.