Zinc-induced Dnmt1 expression involves antagonism between MTF-1 and nuclear receptor SHP

HMGB2 is a potential diagnostic marker and therapeutic target for liver fibrosis and cirrhosis

BACKGROUND

High mobility group proteins 1 and 2 (HMGB1 and HMGB2) are 80% conserved in amino acid sequence. The function of HMGB1 in inflammation and fibrosis has been extensively characterized. However, an unaddressed central question is the role of HMGB2 on liver fibrosis. In this study, we provided convincing evidence that the HMGB2 expression was significantly upregulated in human liver fibrosis and cirrhosis, as well as in several mouse liver fibrosis models.

METHODS

The carbon tetrachloride (CCl4) induced liver fibrosis mouse model was used. AAV8-Hmgb2 was utilized to overexpress Hmgb2 in the liver, while Hmgb2-/- mice were used for loss of function experiments. The HMGB2 inhibitor inflachromene and liposome-shHMGB2 (lipo-shHMGB2) were employed for therapeutic intervention.

RESULTS

The serum HMGB2 levels were also markedly elevated in patients with liver fibrosis and cirrhosis. Deletion of Hmgb2 in Hmgb2-/- mice or inhibition of HMGB2 in mice using a small molecule ICM slowed the progression of CCl4-induced liver fibrosis despite constant HMGB1 expression. In contrast, AAV8-mediated overexpression of Hmgb2 enchanced CCl4-incuded liver fibrosis. Primary hepatic stellate cells (HSCs) isolated from Hmgb2-/- mice showed significantly impaired transdifferentiation and diminished activation of α-SMA, despite a modest induction of HMGB1 protein. RNA-seq analysis revealed the induction of top 45 CCl4-activated genes in multiple signaling pathways including integrin signaling and inflammation. The activation of these genes by CCl4 were abolished in Hmgb2-/- mice or in ICM-treated mice. These included C-X3-C motif chemokine receptor 1 (Cx3cr1) associated with inflammation, cyclin B (Ccnb) associated with cell cycle, DNA topoisomerase 2-alpha (Top2a) associated with intracellular component, and fibrillin (Fbn) and fibromodulin (Fmod) associated with extracellular matrix.

CONCLUSION

We conclude that HMGB2 is indispensable for stellate cell activation. Therefore, HMGB2 may serve as a potential therapeutic target to prevent HSC activation during chronic liver injury. The blood HMGB2 level may also serve as a potential diagnostic marker to detect early stage of liver fibrosis and cirrhosis in humans.

NUP98 and RAE1 sustain progenitor function through HDAC-dependent chromatin targeting to escape from nucleolar localization

Self-renewing somatic tissues rely on progenitors to support the continuous tissue regeneration. The gene regulatory network maintaining progenitor function remains incompletely understood. Here we show that NUP98 and RAE1 are highly expressed in epidermal progenitors, forming a separate complex in the nucleoplasm. Reduction of NUP98 or RAE1 abolishes progenitors' regenerative capacity, inhibiting proliferation and inducing premature terminal differentiation. Mechanistically, NUP98 binds on chromatin near the transcription start sites of key epigenetic regulators (such as DNMT1, UHRF1 and EZH2) and sustains their expression in progenitors. NUP98's chromatin binding sites are co-occupied by HDAC1. HDAC inhibition diminishes NUP98's chromatin binding and dysregulates NUP98 and RAE1's target gene expression. Interestingly, HDAC inhibition further induces NUP98 and RAE1 to localize interdependently to the nucleolus. These findings identified a pathway in progenitor maintenance, where HDAC activity directs the high levels of NUP98 and RAE1 to directly control key epigenetic regulators, escaping from nucleolar aggregation.

DNA methyltransferase 1 inhibits microRNA-497 and elevates GPRC5A expression to promote chemotherapy resistance and metastasis in breast cancer

Background

Abnormal DNA methylation of tumor suppressor gene promoter has been found in breast cancer. Therefore, the current study set out to explore how DNA methyltransferase 1 (DNMT1) affects breast cancer through mediating miR-497/GPRC5A axis.

Methods

After loss and gain-of-function approaches were conducted in MCF-7/ADR and MCF-7 cells, cell viability, IC50 value, invasion, migration and apoptosis were measured, respectively. In addition, drug resistance, metastasis and apoptosis-related protein expression were examined using immunoblotting. ChIP and dual-luciferase reporter gene assays were carried out to validate relationship among DNMT1, miR-497, and GPRC5RA. Subcutaneous xenograft tumor model in nude mice was established to detect effects of DNMT1 on growth and metastasis of breast cancer in vivo.

Results

It was found that DNMT1 was notably increased, while miR-497 was poorly-expressed in breast cancer. Highly-expressed DNMT1 could promote chemotherapy resistance and metastasis of breast cancer. Meanwhile, DNMT1 modified methylation of CpG island in miR-497 promoter region, thereby repressing miR-497 level. In addition, miR-497 targeted GPRC5A expression to curb chemotherapy resistance and metastasis of breast cancer cells. Lastly, in vivo experiments showed that knockdown of DNMT1 could suppress breast cancer growth and metastasis.

Conclusions

Collectively, our findings indicated that DNMT1 may inhibit miR-497 and boost the expression of GPRC5A through methylation, thus augmenting breast cancer chemotherapy resistance and metastasis, which provides novel mechanistic insight into the unrecognized roles of DNMT1 in breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02466-5.

Zinc affects nuclear factor kappa b and DNA methyltransferase activity in C3H cancer fibroblast cells induced by a 2100 MHz electromagnetic field

The use of mobile phones is becoming widespread with the development of technology, and as a result, its effects on human health are becoming more and more important every day. Studies have reported that the electromagnetic field (EMF) emitted by mobile phones may have adverse effects on the biological systems. In order to evaluate the effect of zinc (Zn) on C3H cancer fibroblast cells exposed to 2100 MHz EMF, we analyzed cell viability%, nuclear factor kappa b (NF-κB) and DNA methyltransferase (DNMT) activities. Cells were divided to following groups: Control, sham control, 2100 MHz EMF, 50 µM Zn + 2100 MHz EMF, 100 µM Zn + 2100 MHz EMF, and 200 µM Zn + 2100 MHz EMF for 2 h. We measurement cell viability, NF-κB and DNMT activities. There was increased cell viability % in the 2100 MHz EMF group compared to the control group, while the cell viability % was decreased in the 50, 100 and 200 µM Zn + 2100 MHz EMF groups compared to 2100 MHz EMF. NF-κB and DNMT activities were a significant increase in the 2100 MHz EMF group compared to the control group, although were statistically decreased in the 50, 100 and 200 µM Zn + 2100 MHz EMF groups compared to the 2100 MHz EMF group. Our results demonstrate that 2100 MHz EMF exposure in cancer fibroblast cells induce NF-κB and DNMT activities, whereas zinc supplementation reduce NF-κB and DNMT activities-induced 2100 MHz EMF.

Dietary Nano-ZnO Is Absorbed via Endocytosis and ZIP Pathways, Upregulates Lipogenesis, and Induces Lipotoxicity in the Intestine of Yellow Catfish

Nano-sized zinc oxide (nano-ZnO) affects lipid deposition, but its absorption patterns and mechanisms affecting lipid metabolism are still unclear. This study was undertaken to investigate the molecular mechanism of nano-ZnO absorption and its effects on lipid metabolism in the intestinal tissues of a widely distributed freshwater teleost yellow catfish Pelteobagrus fulvidraco. We found that 100 mg/kg dietary nano-ZnO (H-Zn group) significantly increased intestinal Zn contents. The zip6 and zip10 mRNA expression levels were higher in the H-Zn group than those in the control (0 mg/kg nano-ZnO), and zip4 mRNA abundances were higher in the control than those in the L-Zn (50 mg/kg nano-ZnO) and H-Zn groups. Eps15, dynamin1, dynamin2, caveolin1, and caveolin2 mRNA expression levels tended to reduce with dietary nano-ZnO addition. Dietary nano-ZnO increased triglyceride (TG) content and the activities of the lipogenic enzymes glucose 6-phosphate dehydrogenase (G6PD), 6-phosphogluconate dehydrogenase (6PGD), and isocitrate dehydrogenase (ICDH), upregulated the mRNA abundances of lipogenic genes 6pgd, fatty acid synthase (fas), and sterol regulatory element binding protein 1 (srebp1), and reduced the mRNA expression of farnesoid X receptor (fxr) and small heterodimer partner (shp). The SHP protein level in the H-Zn group was lower than that in the control and the L-Zn group markedly. Our in vitro study indicated that the intestinal epithelial cells (IECs) absorbed nano-ZnO via endocytosis, and nano-Zn-induced TG deposition and lipogenesis were partially attributable to the endocytosis of nano-ZnO in IECs. Mechanistically, nano-ZnO-induced TG deposition was closely related to the metal responsive transcription factor 1 (MTF-1)-SHP pathway. Thus, for the first time, we found that the lipogenesis effects of nano-ZnO probably depended on the key gene shp, which is potentially regulated by MTF1 and/or FXR. This novel signaling pathway of MTF-1 through SHP may be relevant to explain the toxic effects and lipotoxicity ascribed to dietary nano-ZnO addition.

Zn Supplement-Antagonized Cadmium-Induced Cytotoxicity in Macrophages In Vitro: Involvement of Cadmium Bioaccumulation and Metallothioneins Regulation

Cadmium (Cd) is a toxic metal leading to multiple forms of organ damage. Zinc (Zn) was reported as a potential antagonist against Cd toxicity. The present study investigates the antagonistic effect of Zn (20 μM) on Cd (20 or 50 μM) cytotoxicity in macrophages in vitro. The results shows that Cd exposure caused dose-dependent morphologic and ultrastructural alterations in RAW 264.7 macrophages. Zn supplement significantly inhibited Cd cytotoxicity in RAW 264.7 or HD-11 macrophages by mitigating cell apoptosis, excessive ROS output, and mitochondrial membrane depolarization. Notably, Zn supplement for 12 h remarkably prevented intracellular Cd2+ accumulation in 20 μM (95.99 ± 9.93 vs 29.64 ± 5.08 ng/106 cells; P = 0.0008) or 50 μM Cd (179.78 ± 28.66 vs 141.62 ± 22.15 ng/106 cells; P = 0.003) exposed RAW 264.7 cells. Further investigation found that Cd promoted metallothioneins (MTs) and metal regulatory transcription factor 1 (MTF-1) expression in RAW 264.7 macrophages. Twenty μM Zn supplement dramatically enhanced MTs and MTF-1 levels in Cd-exposed RAW 264.7 macrophages. Intracellular Zn2+ chelation or MTF-1 gene silencing inhibited MTs synthesis in Cd-exposed RAW 264.7 macrophages, which was accompanied by the declined expression of MTF-1, indicating that regulation of Zn on MTs was partially achieved by MTF-1 mobilization. In conclusion, this study demonstrates the antagonism of Zn against Cd cytotoxicity in macrophages and reveals its antagonistic mechanism by preventing Cd2+ bioaccumulation and promoting MTs expression.

H19 potentiates let-7 family expression through reducing PTBP1 binding to their precursors in cholestasis

Cholestasis induces the hepatic long non-coding RNA H19, which promotes the progression of cholestatic liver fibrosis. However, microRNAs that are dysregulated by H19 during cholestasis remain elusive. Using miRNA-sequencing analysis followed by qPCR validation, we identified marked upregulation of eight members of the let-7 family in cholestatic livers by bile duct ligation (BDL) and H19 overexpression. In particular, the expression of let-7a-1/7d/7f-1 was highly induced in H19-BDL livers but decreased in H19KO-BDL livers. Interestingly, H19 decreased the nuclear let-7 precursors as well as the primary transcripts of let-7a-1/7d/7f-1 levels in BDL mouse livers. Bioinformatics, RNA pull-down, and RNA immunoprecipitation (RIP) assays revealed that the crucial RNA-binding protein polypyrimidine tract-binding protein 1 (PTBP1), an H19 interaction partner, interacted with the precursors of let-7a-1 and let-7d and suppressed their maturation. Both PTBP1 and let-7 expression was differentially regulated by different bile acid species in hepatocyte and cholangiocyte cells. Further, H19 negatively regulated PTBP1's mRNA and protein levels but did not affect its subcellular distribution in BDL mouse livers. Moreover, we found that H19 restrained but PTBP1 facilitated the bioavailability of let-7 miRNAs to their targets. Taken together, this study revealed for the first time that H19 promoted let-7 expression by decreasing PTBP1's expression level and its binding to the let-7 precursors in cholestasis.

Deficiency of pyruvate dehydrogenase kinase 4 sensitizes mouse liver to diethylnitrosamine and arsenic toxicity through inducing apoptosis

BACKGROUND AND AIM

Pyruvate dehydrogenase kinase 4 (PDK4) is a metabolism switch that regulates glucose oxidation and the tricarboxylic acid cycle (TCA cycle) in the mitochondria. Liver detoxifies xenobiotics and is constantly challenged by various injuries. This study aims at understanding how the loss of the metabolism regulator PDK4 contributes to liver injuries.

METHODS

Wild-type (WT) and Pdk4 knockout (Pdk4 ^-/-) mice of different ages were examined for spontaneous hepatic apoptosis. Juvenile or adult mice of two genotypes were insulted by diethylnitrosamine (DEN), arsenic, galactosamine (GalN)/lipopolysaccharide (LPS), anti-CD95 (Jo2) antibody or carbon tetrachloride (CCl4). Liver injury was monitored by blood biochemistry test. Apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, poly (ADP-ribose) polymerase (PARP) cleavage, and caspase activity assay. Inflammatory response was determined by nuclear factor (NF)-κB activation and the activation of NF-κB target genes. Primary hepatocytes were isolated and cell viability was evaluated by MTS assay.

RESULTS

We showed that systematic Pdk4 ^-/- in mice resulted in age-dependent spontaneous hepatic apoptosis. PDK4-deficiency increased the toxicity of DEN in juvenile mice, which correlated with a lethal consequence and massive hepatic apoptosis. Similarly, chronic arsenic administration induced more severe hepatic apoptosis in Pdk4 ^-/- mice compared to WT control mice. An aggravated hepatic NF-κB mediated-inflammatory response was observed in Pdk4 ^-/- mice livers. In vitro, Pdk4-deficient primary hepatocytes were more vulnerable to DEN and arsenic challenges and displayed higher caspase activity than wild type cells. Notably, hepatic PDK4 mRNA level was remarkably reduced during acute liver failure induced by GalN/LPS or Jo2 antibody. The diminished PDK4 expression was also observed in CCl4-induced acute liver injury.

CONCLUSIONS

PDK4 may contribute to the protection from apoptotic injury in mouse liver.

Nuclear Receptor SHP: A Critical Regulator of miRNA and lncRNA Expression and Function

Small heterodimer partner (SHP, NR0B2) is identified as a unique orphan nuclear receptor that acts as a transcriptional repressor. SHP plays a crucial role in the control of various physiological processes and in several diseases by regulating the expression of disease-specific genes. Non-coding RNAs (ncRNAs), including long noncoding RNAs (lncRNAs) and microRNAs (miRNAs), are encoded of RNAs that are transcribed but not translated into proteins, which are involved in diverse developmental and cellular processes in eukaryotic organisms. Research during the past decade has identified factors participating in the regulation of ncRNAs biogenesis and function. In this review, we summarize recent findings demonstrating a critical role of SHP as a transcriptional regulator of ncRNAs expression and function.

H19 promotes cholestatic liver fibrosis by preventing ZEB1-mediated inhibition of epithelial cell adhesion molecule

Based on our recent finding that disruption of bile acid (BA) homeostasis in mice results in the induction of hepatic long noncoding RNA H19 expression, we sought to elucidate the role of H19 in cholestatic liver fibrosis. Hepatic overexpression of H19RNA augmented bile duct ligation (BDL)-induced liver fibrosis, which was accompanied by the elevation of serum alanine aminotransferase, aspartate aminotransferase, bilirubin, and BA levels. Multiple genes related to liver fibrosis, inflammation, and biliary hyperplasia were increased in H19-BDL versus null-BDL mice, whereas genes in BA synthesis were decreased. Livers and spleens of H19-BDL mice showed significant enrichment of CD3+γδ+, interleukin-4, and interleukin-17 producing CD4+ and CD8+ immune cell populations. H19 down-regulated hepatic zinc finger E-box-binding homeobox 1 (ZEB1) but up-regulated epithelial cell adhesion molecule (EpCAM) and SRY (sex determining region Y)-box 9 expression. Mechanistically, ZEB1 repressed EpCAM promoter activity and gene transcription. H19RNA impeded ZEB1's inhibitory action by interacting with ZEB1 protein to prevent its binding to the EpCAM promoter. Hepatic overexpression of ZEB1 or knockdown of EpCAM diminished H19-induced fibrosis; the latter was also prevented in H19^-/- mice. H19RNA was markedly induced by bile acids in mouse small cholangiocytes and to a lesser extent in mouse large cholangiocytes. The up-regulation of H19RNA and EpCAM correlated positively with the down-regulation of ZEB1 in primary sclerosing cholangitis and primary biliary cirrhosis liver specimens.

CONCLUSION

The activation of hepatic H19RNA promoted cholestatic liver fibrosis in mice through the ZEB1/EpCAM signaling pathway. (Hepatology 2017;66:1183-1196).

Pyruvate Dehydrogenase Kinase 4 Deficiency Results in Expedited Cellular Proliferation through E2F1-Mediated Increase of Cyclins

Hepatocellular carcinoma (HCC) is a common form of cancer with prevalence worldwide. There are many factors that lead to the development and progression of HCC. This study aimed to identify potential new tumor suppressors, examine their function as cell cycle modulators, and investigate their impact on the cyclin family of proteins and cyclin-dependent kinases (CDKs). In this study, the pyruvate dehydrogenase kinase (PDK)4 gene was shown to have potential tumor suppressor characteristics. PDK4 expression was significantly downregulated in human HCC. Pdk4-/- mouse liver exhibited a consistent increase in cell cycle regulator proteins, including cyclin D1, cyclin E1, cyclin A2, some associated CDKs, and transcription factor E2F1. PDK4-knockdown HCC cells also progressed faster through the cell cycle, which concurrently expressed high levels of cyclins and E2F1 as seen in the Pdk4-/- mice. Interestingly, the induced cyclin E1 and cyclin A2 caused by Pdk4 deficiency was repressed by arsenic treatment in mouse liver and in HCC cells. E2f1 deficiency in E2f1-/- mouse liver or knockdown E2F1 using small hairpin RNAs in HCC cells significantly decreased cyclin E1, cyclin A2, and E2F1 proteins. In contrast, inhibition of PDK4 activity in HCC cells increased cyclin E1, cyclin A2, and E2F1 proteins. These findings demonstrate that PDK4 is a critical regulator of hepatocyte proliferation via E2F1-mediated regulation of cyclins.

Long noncoding RNA MEG3 induces cholestatic liver injury by interaction with PTBP1 to facilitate shp mRNA decay

Bile acids (BAs) play critical physiological functions in cholesterol homeostasis, and deregulation of BA metabolism causes cholestatic liver injury. The long noncoding RNA maternally expressed gene 3 (MEG3) was recently shown as a potential tumor suppressor; however, its basic hepatic function remains elusive. Using RNA pull-down with biotin-labeled sense or anti-sense MEG 3RNA followed by mass spectrometry, we identified RNA-binding protein polypyrimidine tract-binding protein 1 (PTBP1) as a MEG3 interacting protein and validated their interaction by RNA immunoprecipitation (RIP). Bioinformatics analysis revealed putative binding sites for PTBP1 within the coding region (CDS) of small heterodimer partner (SHP), a key repressor of BA biosynthesis. Forced expression of MEG3 in hepatocellular carcinoma cells guided and facilitated PTBP1 binding to the Shp CDS, resulting in Shp mRNA decay. Transient overexpression of MEG3 RNA in vivo in mouse liver caused rapid Shp mRNA degradation and cholestatic liver injury, which was accompanied by the disruption of BA homeostasis, elevation of liver enzymes, as well as dysregulation of BA synthetic enzymes and metabolic genes. Interestingly, RNA sequencing coupled with quantitative PCR (qPCR) revealed a drastic induction of MEG3 RNA in Shp^-/- liver. SHP inhibited MEG3 gene transcription by repressing cAMP response element-binding protein (CREB) transactivation of the MEG3 promoter. In addition, the expression of MEG3 and PTBP1 was activated in human fibrotic and cirrhotic livers.

CONCLUSION

MEG3 causes cholestasis by serving as a guide RNA scaffold to recruit PTBP1 to destabilize Shp mRNA. SHP in turn represses CREB-mediated activation of MEG3 expression in a feedback-regulatory fashion. (Hepatology 2017;65:604-615).

Metabolomics Analysis Revealed Distinct Cyclic Changes of Metabolites Altered by Chronic Ethanol-Plus-Binge and Shp Deficiency

BACKGROUND

Chronic ethanol (EtOH) consumption causes alcoholic liver disease (ALD), and disruption of the circadian system facilitates the development of ALD. Small heterodimer partner (SHP) is a nuclear receptor and critical regulator of hepatic lipid metabolism. This study aimed at depicting circadian metabolomes altered by chronic EtOH-plus-binge and Shp deficiency using high-throughput metabolomics.

METHODS

Wild-type (WT) C57BL/6 and Shp^-/- mice were fed the control diet (CD) or Lieber-DeCarli EtOH liquid diet (ED) for 10 days followed by a single bout of maltose (CD + M) or EtOH (ED + E) binge on the 11th day. Serum and liver were collected over a 24-hour light/dark (LD) cycle at Zeitgeber time ZT12, ZT18, ZT0, and ZT6, and metabolomics was performed using gas chromatography-mass spectrometry.

RESULTS

A total of 110 metabolites were identified in liver and of those 80 were also present in serum from pathways of carbohydrates, lipids, pentose phosphate, amino acids, nucleotides, and tricarboxylic acid cycle. In the liver, 91% of metabolites displayed rhythmicity with ED + E, whereas in the serum, only 87% were rhythmic. Bioinformatics analysis identified unique metabolome patterns altered in WT CD + M, WT ED + E, Shp^-/- CD + M, and Shp^-/- ED + E groups. Specifically, metabolites from the nucleotide and amino acid pathway (ribose, glucose-6-phosphate, glutamic acid, aspartic acid, and sedoheptulose-7-P) were elevated in Shp^-/- CD + M mice during the dark cycle, whereas metabolites including N-methylalanine, 2-hydroxybutyric acid, and 2-hydroxyglutarate were elevated in WT ED + E mice during the light cycle. The rhythmicity and abundance of other individual metabolites were also significantly altered by both control and EtOH diets.

CONCLUSIONS

Metabolomics provides a useful means to identify unique metabolites altered by chronic EtOH-plus-binge.

Nuclear Receptors as Therapeutic Targets in Liver Disease: Are We There Yet?

Nuclear receptors (NR) are ligand-modulated transcription factors that play diverse roles in cell differentiation, development, proliferation, and metabolism and are associated with numerous liver pathologies such as cancer, steatosis, inflammation, fibrosis, cholestasis, and xenobiotic/drug-induced liver injury. The network of target proteins associated with NRs is extremely complex, comprising coregulators, small noncoding microRNAs, and long noncoding RNAs. The importance of NRs as targets of liver disease is exemplified by the number of NR ligands that are currently used in the clinics or in clinical trials with promising results. Understanding the regulation by NR during pathophysiological conditions, and identifying ligands for orphan NR, points to a potential therapeutic approach for patients with liver diseases. An overview of complex NR metabolic networks and their pharmacological implications in liver disease is presented here.

A Novel Small Molecule Activator of Nuclear Receptor SHP Inhibits HCC Cell Migration via Suppressing Ccl2

Small heterodimer partner (SHP, NR0B2) is a nuclear orphan receptor without endogenous ligands. Due to its crucial inhibitory role in liver cancer, it is of importance to identify small molecule agonists of SHP. As such, we initiated a probe discovery effort to identify compounds capable of modulating SHP function. First, we performed binding assays using small molecule microarrays (SMM) and discovered 5-(diethylsulfamoyl)-3-hydroxynaphthalene-2-carboxylic acid (DSHN) as a novel activator of SHP. DSHN transcriptionally activated Shp mRNA, but also stabilized the SHP protein by preventing its ubiquitination and degradation. Second, we identified Ccl2 as a new SHP target gene by RNA-seq. We showed that activation of SHP by DSHN repressed Ccl2 expression and secretion by inhibiting p65 activation of CCL2 promoter activity, as demonstrated in vivo in Shp^-/- mice and in vitro in HCC cells with SHP overexpression and knockdown. Third, we elucidated a strong inhibitory effect of SHP and DSHN on HCC cell migration and invasion by antagonizing the effect of CCL2. Lastly, by interrogating a publicly available database to retrieve SHP expression profiles from multiple types of human cancers, we established a negative association of SHP expression with human cancer metastasis and patient survival. In summary, the discovery of a novel small molecule activator of SHP provides a therapeutic perspective for future translational and preclinical studies to inhibit HCC metastasis by blocking Ccl2 signaling. Mol Cancer Ther; 15(10); 2294-301. ©2016 AACR.

Arsenic silences hepatic PDK4 expression through activation of histone H3K9 methylatransferase G9a

It is well established that increased liver cancer incidence is strongly associated with epigenetic silencing of tumor suppressor genes; the latter is contributed by the environmental exposure to arsenic. Pyruvate dehydrogenase kinase 4 (PDK4) is a mitochondrial protein that regulates the TCA cycle. However, the epigenetic mechanisms mediated by arsenic to control PDK4 expression remain elusive. In the present study, we showed that histone methyltransferase G9a- and Suv39H-mediated histone H3 lysine 9 (H3K9) methylations contributed to PDK4 silencing in hepatic cells. The PDK4 expression was induced by G9a inhibitor BRD4770 (BRD) and Suv39H inhibitor Chaetocin (CHA). In contrast, arsenic exposure decreased PDK4 expression by inducing G9a and increasing H3K9 di- and tri-methylations levels (H3K9me2/3). In addition, arsenic exposure antagonizes the effect of BRD by enhancing the enrichment of H3K9me2/3 in the PKD4 promoter. Moreover, knockdown of G9a using siRNA induced PDK4 expression in HCC cells. Furthermore, arsenic decreased hepatic PDK4 expression as well as diminished the induction of PDK4 by BRD in mouse liver and hepatocytes. Overall, the results suggest that arsenic causes aberrant repressive histone modification to silence PDK4 in both HCC cells and in mouse liver.

New Insights into Orphan Nuclear Receptor SHP in Liver Cancer

Small heterodimer partner (SHP; NR0B2) is a unique orphan nuclear receptor (NR) that contains a putative ligand-binding domain but lacks a DNA-binding domain. SHP is a transcriptional corepressor affecting diverse metabolic processes including bile acid synthesis, cholesterol and lipid metabolism, glucose and energy homeostasis, and reproductive biology via interaction with multiple NRs and transcriptional factors (TFs). Hepatocellular carcinoma (HCC) is one of the most deadly human cancers worldwide with few therapeutic options and poor prognosis. Recently, it is becoming clear that SHP plays an antitumor role in the development of liver cancer. In this review, we summarize the most recent findings regarding the new SHP interaction partners, new structural insights into SHP’s gene repressing activity, and SHP protein posttranslational modifications by bile acids. We also discuss the pleiotropic role of SHP in regulating cell proliferation, apoptosis, DNA methylation, and inflammation that are related to antitumor role of SHP in HCC. Improving our understanding of SHP’s antitumor role in the development of liver cancer will provide new insights into developing novel treatments or prevention strategies. Future research will focus on developing more efficacious and specific synthetic SHP ligands for pharmaceutical applications in liver cancer and several metabolic diseases such as hypercholesterolemia, obesity, diabetes, and fatty liver disease.

E2F1 is a novel fibrogenic gene that regulates cholestatic liver fibrosis through the Egr-1/SHP/EID1 network

E2F transcription factor 1 (E2F1) is an important regulator of metabolic diseases; however, its role in liver function remains elusive. This study unraveled a regulatory cascade involving E2F1, early growth response-1 (Egr-1), nuclear receptor small heterodimer partner (SHP, NR0B2), and EIA-like inhibitor of differentiation 1 (EID1) in cholestatic liver fibrosis. Liver E2F1 messenger RNA (mRNA) and protein expression was strongly up-regulated in human nonalcoholic steatohepatitis (NASH) and alcohol cirrhosis; the latter was inversely correlated with diminished SHP expression. E2F1 was also highly induced by 3,5-diethoxycarbonyl-1, 4-dihydrocollidine (DDC) feeding and bile-duct ligation (BDL) in mice. E2F1-/- mice exhibited reduced biliary fibrosis by DDC as determined by Masson Trichrome and Picro Sirius red staining, and decreased serum bile acid (BA), BA pool size, and fecal BA excretion. In addition, cholestatic liver fibrosis induced by BDL, as determined by immunohistochemistry analysis of a1 collagen expression, was increased in SHP-/- mice but attenuated in hepatocyte SHP-overexpressed transgenic (STG) mice. Egr-1 exhibited marked induction in livers of SHP-/- mice compared to the wild-type mice in both sham and BDL groups, and reduction in STG livers. Egr-1 promoter was activated by E2F1, and the activation was abrogated by expression of SHP and its co-repressor EID1 in hepatoma cells Huh7, Hepa1, and stellate cells LX2. Chromatin immunoprecipitation assays further confirmed the association of E2F1, SHP, and EID1 proteins with the Egr-1 promoter, and their direct protein interactions were determined by glutathione S-transferase pull-down assays. Interestingly, E2F1 activated Egr-1 expression in a biphasic fashion as described in both human and mouse hepatocytes.

CONCLUSION

E2F1 is a fibrogenic gene and could serve as a potential new diagnostic marker for nonalcoholic and alcoholic liver fibrosis/cirrhosis.

Genome-wide transcriptome analysis identifies novel gene signatures implicated in human chronic liver disease

The molecular mechanisms behind human liver disease progression to cirrhosis remain elusive. Nuclear receptor small heterodimer partner (SHP/Nr0b2) is a hepatic tumor suppressor and a critical regulator of liver function. SHP expression is diminished in human cirrhotic livers, suggesting a regulatory role in human liver diseases. The goal of this study was to identify novel SHP-regulated genes that are involved in the development and progression of chronic liver disease. To achieve this, we conducted the first comprehensive RNA sequencing (RNA-seq) analysis of Shp(-/-) mice, compared the results with human hepatitis C cirrhosis RNA-seq and nonalcoholic steatohepatitis (NASH) microarray datasets, and verified novel results in human liver biospecimens. This approach revealed new gene signatures associated with chronic liver disease and regulated by SHP. Several genes were selected for validation of physiological relevance based on their marked upregulation, novelty with regard to liver function, and involvement in gene pathways related to liver disease. These genes include peptidoglycan recognition protein 2, dual specific phosphatase-4, tetraspanin 4, thrombospondin 1, and SPARC-related modular calcium binding protein-2, which were validated by qPCR analysis of 126 human liver specimens, including steatosis, fibrosis, and NASH, alcohol and hepatitis C cirrhosis, and in mouse models of liver inflammation and injury. This RNA-seq analysis identifies new genes that are regulated by the nuclear receptor SHP and implicated in the molecular pathogenesis of human chronic liver diseases. The results provide valuable transcriptome information for characterizing mechanisms of these diseases.

Characterization of the mitochondrial localization of the nuclear receptor SHP and regulation of its subcellular distribution by interaction with Bcl2 and HNF4α

The nuclear receptor small heterodimer partner SHP was shown recently to translocate to the mitochondria, interact with Bcl2, and induce apoptosis in liver cancer cells. However, the exact mitochondrial localization of SHP remains to be determined. In addition, the detailed interaction domains between SHP and Bcl2 have not been characterized. Using biochemistry and molecular biology approaches, we demonstrate that SHP is localized to the mitochondrial outer membrane. Interestingly, compared with the full-length SHP, the N-terminal deleted protein exhibits increased expression in the mitochondria and decreased expression in the nucleus. GST pull-down assays demonstrate that the interaction domain of SHP shows the strongest interaction with Bcl2. Furthermore, the interaction of Bcl2 with SHP is completely abolished by deletion of the Bcl2 transmembrane domain (TM), whereas deletion of the Bcl2 BH1 domain enhances the interaction. As expected, AHPN, a synthetic SHP ligand, markedly augments the direct protein-protein interaction between Bcl2 and SHP. Ectopic expression of hepatocyte nuclear factor 4 alpha (HNF4α) results in exclusive nuclear translocation of SHP proteins that contain either the full-length or the N-terminal domain, but has a minimal effect on the subcellular distribution of SHP protein containing only the interaction domain or repression domain. These results indicate that the N-terminal domain of SHP is important for itsnuclear translocation via HNF4α. Overall, this study provides novel insights into the domains of SHP that are critical for its shutting between different subcellular compartments.

Effect of cyclic AMP and estrogen/progesterone on the transcription of DNA methyltransferases during the decidualization of human endometrial stromal cells

Progesterone, estrogen and cyclic adenosine monophosphate (cAMP) together regulate the decidualization of human endometrial stromal cells in a time-dependent manner. The role of DNA methylation and the three active DNA methyltransferases (DNMTs) in the regulation of decidualization is gaining interest but the exact role of this epigenetic mechanism during decidualization is largely unknown. We aimed to understand the effect of the main regulators of decidualization on the expression of the DNMTs and in turn on the expression of steroid hormone receptors during the decidualization. We conducted a time-course analysis from 6 h to 10 days to examine the change in gene expression of the DNMTs and the steroid hormone receptors over time in response to estradiol, medroxy-progesterone acetate (MPA) and dibutyryl-cAMP (db-cAMP) in a human endometrial stromal cells (HESC) cell line. Only the combination treatment with MPA-mix (estradiol + MPA + db-cAMP) up-regulated ERα, PGR, progesterone receptor B (PRB) and androgen receptor at 24 h. Both decidualization pathways of db-cAMP and estradiol/MPA, independently and combined, consistently down-regulated DNMT3B mRNA expression from 6 h till 10 days, whereas DNMT1 and DNMT3A mRNA expression were down-regulated transiently. Forced expression of DNMT3B in HESC for 10 days attenuated IGFBP1 mRNA and protein expression; and forced expression of DNMT3B combined with MPA-mix treatment synergistically increased the expression of PRB at 24 h. The HESC morphology and proliferation remained unchanged in response to forced expression of DNMT3B. In conclusion, mRNA expression of the DNMTs during decidualization is dynamic, so that expression varies according to the cAMP or estradiol/MPA pathway treatments that regulate them in a time-dependent manner. Although forced expression of DNMT3B by itself is insufficient to inhibit decidualization, forced expression of DNMT3B in combination with MPA-mix synergistically up-regulated PRB, as well as attenuated the expression of IGFBP1, the decidualization marker.

Cell and molecular biology of DNA methyltransferase 1

The DNA cytosine methyltransferase 1 (DNMT1) is a ubiquitous nuclear enzyme that catalyzes the well-established reaction of placing methyl groups on the unmethylated cytosines in methyl-CpG:CpG base pairs in the hemimethylated DNA formed by methylated parent and unmethylated daughter strands. This activity regenerates fully methylated methyl-CpG:methyl-CpG pairs. Despite the straightforward nature of its catalytic activity, detailed biochemical, genetic, and developmental studies revealed intricate details of the central regulatory role of DNMT1 in governing the epigenetic makeup of the nuclear genome. DNMT1 mediates demethylation and also participates in seemingly wide cellular functions unrelated to maintenance DNA methylation. This review brings together mechanistic details of maintenance methylation by DNMT1, its regulation at transcriptional and posttranscriptional levels, and the seemingly unexpected functions of DNMT1 in the context of DNA methylation which is central to epigenetic changes that occur during development and the process of cell differentiation.

Cross-regulation of protein stability by p53 and nuclear receptor SHP

We report here a novel interplay between tumor suppressor p53 and nuclear receptor SHP that controls p53 and SHP stability. Overexpression of p53 causes rapid SHP protein degradation, which does not require the presence of Mdm2 and is mediated by the proteosome pathway. Overexpressing SHP alone does not affect p53 stability. However, SHP destabilizes p53 by augmentation of Mdm2 ubiquitin ligase activity toward p53. The single amino acid substitution in the SHP protein SHPK170R increases SHP binding to p53 relative to SHP wild-type, whereas SHPG171A variant shows a diminished p53 binding. As a result of the cross-regulation, the tumor suppressor function of p53 and SHP in inhibition of colon cancer growth is compromised. Our findings reveal a unique scenario for a cross-inhibition between two tumor suppressors to keep their expression and function in check.

An autoregulatory feedback loop between Mdm2 and SHP that fine tunes Mdm2 and SHP stability

Mdm2 is a crucial negative regulator of the tumor suppressor function of p53. However, little is known about Mdm2 protein stability regulation by other tumor suppressors. Nuclear receptor small heterodimer partner (SHP, NROB2) functions as a tumor suppressor in liver cancer. We show here a surprising finding of a feedback regulatory loop between SHP and Mdm2. SHP stabilizes Mdm2 protein by abrogating Mdm2 self-ubiquitination, and Mdm2 in turn attenuates SHP protein levels under p53-deficient conditions. Such cross-regulation critically depends on the physical interaction of SHP with Mdm2 through the SHP K170 residue. The Mdm2-SHP interplay represents a novel component of Mdm2 signaling that is likely to dictate Mdm2 activity and function.