NKX2-5 regulates the expression of beta-catenin and GATA4 in ventricular myocytes

Congenital heart defects in CTNNB1 syndrome: Raising clinical awareness

CTNNB1 [OMIM *116806] encodes β-catenin, an integral part of the cadherin/catenin complex, which functions as effector of Wnt signaling. CTNNB1 is highly expressed in brain as well as in other tissues, including heart. Heterozygous CTNNB1 pathogenic variations are associated with a neurodevelopmental disorder characterized by spastic diplegia and visual defects (NEDSDV) [OMIM #615075], featuring psychomotor delay, intellectual disability, behavioral disturbances, movement disorders, visual defects and subtle facial and somatic features. We report on a new series of 19 NEDSDV patients (mean age 10.3 years), nine of whom bearing novel CTNNB1 variants. Notably, five patients showed congenital heart anomalies including absent pulmonary valve with intact ventricular septum, atrioventricular canal with hypoplastic aortic arch, tetralogy of Fallot, and mitral valve prolapse. We focused on the cardiac phenotype characterizing such cases and reviewed the congenital heart defects in previously reported NEDSDV patients. While congenital heart defects had occasionally been reported so far, the present findings configure a higher rate of cardiac anomalies, suggesting dedicated heart examination to NEDSDV clinical management.

Induced pluripotent stem cell technology in bone biology

Technologies on the development and differentiation of human induced pluripotent stem cells (hiPSCs) are rapidly improving, and have been applied to create cell types relevant to the bone field. Differentiation protocols to form bona fide bone-forming cells from iPSCs are available, and can be used to probe details of differentiation and function in depth. When applied to iPSCs bearing disease-causing mutations, the pathogenetic mechanisms of diseases of the skeleton can be elucidated, along with the development of novel therapeutics. These cells can also be used for development of cell therapies for cell and tissue replacement.

Cardiac Transcription Regulators Differentiate Human Umbilical Cord Mesenchymal Stem Cells into Cardiac Cells

Stem cell-based therapy presents an attractive alternative to conventional therapies for degenerative diseases. Numerous studies have investigated the capability of human umbilical cord-derived mesenchymal stem cells (hUC-MSCs) to contribute to the regeneration of cardiomyocytes, and the results have encouraged further basic and clinical studies on the MSC-based treatment of cardiomyopathies. This study aimed to determine the potential of cardiomyogenic transcription factors in differentiating hUC-MSCs into cardiac-like cells in vitro. MSCs were isolated from umbilical cord tissue and were transduced with the transcription factor genes, GATA-4 and Nkx 2.5, via infection with lentiviruses, to promote differentiation into the cardiomyogenic lineage. Gene and protein expression were analysed with qPCR and immunocytochemical staining. After transduction, differentiated cardiac-like cells showed significant expression of cardiac genes and proteins, namely GATA-4, Nkx-2.5, cardiac troponin I (cTnI) and myosin heavy chain (MHC). The cardiomyogenic-induced group significantly overexpressed cardiac-specific genes (GATA-4, Nkx-2.5, cTnI, MHC, α-actinin and Wnt2). Expression of the calcium channel gene was also significantly increased, while the sodium channel gene was downregulated in the transduced hUC-MSCs, as compared to non-transduced cells. The results suggest that GATA-4 and Nkx-2.5 interact synergistically in the activation of downstream cardiac transcription factors, demonstrating the functional convergence of hUC-MSC differentiation into cardiac-like cells. These findings could potentially be utilised in the efficient production of cardiac-like cells from stem cells; these cardiac-like cells could then be used in various applications, such as for in vivo implantation in infarcted myocardium, and for drug screening in toxicity testing.

Identification and functional study of GATA4 gene regulatory variants in atrial septal defects

Background

Congenital heart disease (CHD) is the leading cause of mortality from birth defects. In adult CHD patients with successful surgical repair, cardiac complications including heart failure develop at late stage, likely due to genetic causes. To date, many mutations in cardiac developmental genes have been associated with CHD. Recently, regulatory variants in genes have been linked to many human diseases. Although mutations and splicing variants in GATA4 gene have been reported in CHD patients, few regulatory variants of GATA4 gene are identified in CHD patients.

Methods

GATA4 gene regulatory region was investigated in the patients with atrial septal defects (ASD) (n = 332) and ethnic-matched controls (n = 336).

Results

Five heterozygous regulatory variants including four SNPs [g.31360 T>C (rs372004083), g.31436G>A, g.31437C>A (rs769262495), g.31487C>G (rs1053351749) and g.31856C>T (rs1385460518)] were only identified in ASD patients. Functional analysis indicated that the regulatory variants significantly affected the transcriptional activity of GATA4 gene promoter. Furthermore, two of the five regulatory variants have evidently effected on transcription factor binding sites.

Conclusions

Our data suggested that GATA4 gene regulatory variants may confer ASD susceptibility by decreasing GATA4 levels.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12872-021-02136-w.

Tribbles Pseudokinase 3 Contributes to Cancer Stemness of Endometrial Cancer Cells by Regulating β-Catenin Expression

Simple Summary

Endometrial cancer (EC) is the second most common female malignancy worldwide, but the pathogenesis is not fully understood. Tribbles pseudokinase 3 (TRIB3) is a kind of scaffold protein that may regulate multiple cellular processes by organizing binding partner proteins involving signaling transduction pathways. The goal of this study is to investigate if TRIB3 is involved in the malignant features of EC. Our data demonstrate that TRIB3 positively regulates the cancer stem-cell activity and in vivo tumorigenicity of EC cells by modulating β-catenin signaling through directly interacting with the ELF4 transcription factor. Our results could lead to new insight for developing a novel therapeutic strategy for EC by targeting TRIB3.

Abstract

Endometrial cancer (EC) is the second most common gynecological malignancy worldwide. Tribbles pseudokinase 3 (TRIB3) is a scaffolding protein that regulates intracellular signal transduction, and its role in tumor development is controversial. Here, we investigated the biological function of TRIB3 in EC. We found that the messenger RNA (mRNA) expression level of TRIB3 was significantly and positively correlated with shorter overall survival of EC patients in The Cancer Genome Atlas database. The protein expression of TRIB3 was found to be significantly increased in EC cancer stem cells (CSCs) enriched by tumorsphere cultivation. Knockdown of TRIB3 in EC cells suppressed tumorsphere formation, the expression of cancer stemness genes, and the in vivo tumorigenesis. The expression of β-catenin at both the protein and the mRNA levels was downregulated upon TRIB3 silencing. TRIB3 was found to interact with E74 Like ETS transcription factor 4 (ELF4) in the nucleus and bound to ELF4 consensus sites within the catenin beta 1 (CTNNB1) promoter in EC cell lines. These data indicated that TRIB3 may regulate CTNNB1 transcription by enhancing the recruitment of ELF4 to the CTNNB1 promoter. In conclusion, our results suggest that TRIB3 plays an oncogenic role in EC and positively regulates the self-renewal and tumorigenicity of EC-CSCs. Targeting TRIB3 is considered as a potential therapeutic strategy in future EC therapy.

Lineage-specific differentiation of osteogenic progenitors from pluripotent stem cells reveals the FGF1-RUNX2 association in neural crest-derived osteoprogenitors

Human pluripotent stem cells (hPSCs) can provide a platform to model bone organogenesis and disease. To reflect the developmental process of the human skeleton, hPSC differentiation methods should include osteogenic progenitors (OPs) arising from three distinct embryonic lineages: the paraxial mesoderm, lateral plate mesoderm, and neural crest. Although OP differentiation protocols have been developed, the lineage from which they are derived, as well as characterization of their genetic and molecular differences, has not been well reported. Therefore, to generate lineage-specific OPs from human embryonic stem cells and human induced pluripotent stem cells, we employed stepwise differentiation of paraxial mesoderm-like cells, lateral plate mesoderm-like cells, and neural crest-like cells toward their respective OP subpopulation. Successful differentiation, confirmed through gene expression and in vivo assays, permitted the identification of transcriptomic signatures of all three cell populations. We also report, for the first time, high FGF1 levels in neural crest-derived OPs-a notable finding given the critical role of fibroblast growth factors (FGFs) in osteogenesis and mineral homeostasis. Our results indicate that FGF1 influences RUNX2 levels, with concomitant changes in ERK1/2 signaling. Overall, our study further validates hPSCs' power to model bone development and disease and reveals new, potentially important pathways influencing these processes.

TGF-β1 combined with Sal-B promotes cardiomyocyte differentiation of rat mesenchymal stem cells

Transforming growth factor β1 (TGF-β1) and salvianolic acid B (Sal-B) are key signaling factors for stem cell differentiation into cardiomyocytes (CMs). The present study compared the biological effect of TGF-β1 and Sal-B, alone or in combination, on bone marrow mesenchymal stromal cells (BMSCs) that differentiate into myocardial-like cells in a simulated myocardial microenvironment in vitro. BMSCs were isolated from bones of limbs of 10 male Sprague Dawley rats and cultured. The 2nd-generation BMSCs were co-incubated with TGF-β1 and Sal-B, alone or in combination, for 72 h. The control group was BMSCs cultured without any inductive substance. The levels GATA binding protein 4 (GATA4) and homeobox protein NKx2.5 were determined by reverse-transcription quantitative polymerase chain reaction and immunofluorescence staining was used to evaluate α-sarcomeric actin and cardiac troponin I (cTNI) as cardiomyogenic differentiation markers. The ultrastructure of BMSCs in each group was also observed. BMSCs were initially spindle-shaped with irregular processes. The cells gradually increased in number 24 h post-inoculation and proliferated 7 days later. Compared with the control group, BMSCs in the treatment groups had fusiform shapes, orientating with one accord and were connected with adjoining cells forming myotube-like structures on day 28. The morphology and architecture/myotubes of BMSCs was similar among the treatment groups, but the amount of cells in the combined group was comparatively higher. The results of immunofluorescence staining revealed the expression of the CM-specific proteins α-sarcomeric actin and cTNI in these cells. The expression of these cardiac-specific markers in the combined group was significantly higher than that in the other groups (P<0.01 or P<0.05). In addition, the transcriptional expression of GATA4 and NKx2.5 in the treatment groups was stable and significantly higher than that in the control group on day 7. Transmission electron microscopy showed that BMSCs in the treatment groups all had myofilaments, rough endoplasmic reticulum and mitochondria in the cytoplasm when compared with the control group. Taken together, these results indicated that the combination of TGF-β1 and Sal-B effectively promotes cardiomyogenic differentiation of BMSCs in vitro and their application may represent a therapeutic strategy for the treatment of ischemic heart disease.

The optimization of cell therapy by combinational application with apicidin-treated mesenchymal stem cells after myocardial infarction

Although mesenchymal stem cells (MSC) have been shown to be safe in preclinical studies of cardiovascular disease, multiple meta-analyses have debated whether functional improvement is significant or not. The cardiac differentiation from MSC is achievable using cardiogenic factors, however, the high cost and long culture period may limit the applications. Here, we developed a novel method to optimize the therapeutic outcome for myocardial infarction (MI). Treatment of MSC with apicidin, a histone deacetylase inhibitor, dramatically increased the expressions of cardiac markers such as GATA4, Nkx2.5, and cardiac troponin I (cTnI). In AC/MSC, stemness-related genes and yes-associated protein (YAP), a potent oncogene that drives cell proliferation, were significantly suppressed. Furthermore apicidin treatment or YAP knockdown downregulated miR-130a expression followed by induction of cardiac markers in MSC. In the comparison study, we found that both cardiac gene induction and angiogenesis were most prominent in the mixture of non-treated MSC and AC/MSC (Mix). Using mouse MI model, we show that application of Mix was strongly associated with cardiac differentiation of injected MSC and improved cardiac performance. Our results suggest that suppression of YAP/miR-130a shifts MSC cell fate toward cardiac lineage and identify apicidin as a potential pharmacological target for therapeutic development.

Bioinspired onion epithelium-like structure promotes the maturation of cardiomyocytes derived from human pluripotent stem cells

Organized cardiomyocyte alignment is critical to maintain the mechanical properties of the heart. In this study, we present a new and simple strategy to fabricate a biomimetic microchip designed with an onion epithelium-like structure and investigate the guided behavior of human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CMs) on the substrate. The hiPSC-CMs were observed to be confined by the three dimensional surficial features morphologically, analogous to the in vivo microenvironment, and exhibited an organized anisotropic alignment on the onion epithelium-like structure with good beating function. The calcium imaging of hiPSC-CMs demonstrated a more mature Ca²⁺ spark pattern as well. Furthermore, the expression of sarcomere genes (TNNI3, MYH6 and MYH7), potassium channel genes (KCNE1 and KCNH2), and calcium channel genes (RYR2) was significantly up-regulated on the substrate with an onion epithelium-like structure instead of the surface without the structure, indicating a more matured status of cardiomyocytes induced by this structure. It appears that the biomimetic micropatterned structure, analogous to in vivo cellular organization, is an important factor that might promote the maturation of hiPSC-CMs, providing new biological insights to guide hiPSC-CM maturation by biophysical factors. The established approach may offer an effective in vitro model for investigating cardiomyocyte differentiation, maturation and tissue engineering applications.

Synergistic role of 5-azacytidine and ascorbic acid in directing cardiosphere derived cells to cardiomyocytes in vitro by downregulating Wnt signaling pathway via phosphorylation of β-catenin

Background

Cardiosphere derived cells (CDCs) represent a valuable source in stem cell based therapy for cardiovascular diseases, yet poor differentiation rate hinders the transplantation efficiency. The aim of this study is to check the ability of 5-Azacytidine (Aza) alone and in combination with ascorbic acid (Aza+AA) in delineating CDCs to cardiomyogenesis and the underlying Wnt signaling mechanism in induced differentiation.

Methods

CDCs were treated with Aza and Aza+AA for a period of 14 days to examine the expression of cardiac specific markers and Wnt downstream regulators by immunofluorescence, real time PCR and western blot.

Results

Results revealed that Aza+AA induced efficient commitment of CDCs to cardiomyogenic lineage. Immunofluorescence analysis showed significant augment for Nkx 2.5, GATA 4 and α-Sarcomeric actinin markers in Aza+AA group than control group (p = 0.0118, p = 0.009 and p = 0.0091, respectively). Relative upregulation of cardiac markers, Nkx 2.5 (p = 0.0156), GATA 4 (p = 0.0087) and down regulation of Wnt markers, β-catenin (p = 0.0107) and Cyclin D1 (p = 0. 0116) in Aza+AA group was revealed by RNA expression analysis. Moreover, the Aza+AA induced prominent expression of GATA 4, α-Sarcomeric actinin and phospho β-catenin while non phospho β-catenin and Cyclin D1 expression was significantly suppressed as displayed in protein expression analysis. Generation of spontaneous beating in Aza+AA treated CDCs further reinforced that Aza+AA accelerates the cardiomyogenic potential of CDCs.

Conclusion

Combined treatment of Aza along with AA implicit in inducing cardiomyogenic potential of CDCs and is associated with down regulating Wnt signaling pathway. Altogether, CDCs represent a valuable tool for the treatment of cardiovascular disorders.

Gallic Acid Reduces Blood Pressure and Attenuates Oxidative Stress and Cardiac Hypertrophy in Spontaneously Hypertensive Rats

Gallic acid (GA) has been reported to have beneficial effects on cancer, vascular calcification, and diabetes-induced myocardial dysfunction. We hypothesized that GA controls hypertension via oxidative stress response regulation in an animal model for essential hypertension. Spontaneously hypertensive rats (SHRs) were administered GA for 16 weeks. GA treatment lowered elevated systolic blood pressure in SHRs through the inhibition of vascular contractility and components of the renin-angiotensin II system. In addition, GA administration reduced aortic wall thickness and body weight in SHRs. In SHRs, GA attenuated left ventricular hypertrophy and reduced the expression of cardiac-specific transcription factors. NADPH oxidase 2 (Nox2) and GATA4 mRNA expression was induced in SHR hearts and angiotensin II-treated H9c2 cells; this expression was downregulated by GA treatment. Nox2 promoter activity was increased by the synergistic action of GATA4 and Nkx2-5. GA seems to regulate oxidative stress by inhibiting the DNA binding activity of GATA4 in the rat Nox2 promoter. GA reduced the GATA4-induced Nox activity in SHRs and angiotensin II-treated H9c2 cells. GA administration reduced the elevation of malondialdehyde levels in heart tissue obtained from SHRs. These findings suggest that GA is a potential therapeutic agent for treating cardiac hypertrophy and oxidative stress in SHRs.

BMP-2 combined with salvianolic acid B promotes cardiomyocyte differentiation of rat bone marrow mesenchymal stem cells

The present study tested the hypotheses that bone morphogenetic protein 2(BMP-2) combined with salvianolic acid B(Sal-B) enhance the differentiation of rat bone marrow mesenchymal stem cells (BMSCs) towards cardiomyocytes in vitro. BMSCs were treated with BMP-2 and Sal-B, alone or in combination, for 72 h, then added new media (excluding inductive substance) and cultured for 4 weeks. The morphologic characteristics, surface antigens and mRNA expression of several transcription factors were also assessed. We found that they could all be identified by the positive staining for cardiomyocyte-specific proteins, desmin and cardiac troponin T, in these cells. Furthermore, the mRNA expression of GATA-4 and Nkx2.5 genes was slightly increased on day 7, enhanced on day 14 and decreased on day 28 while α-MHC gene was not expressed on day 7, but expressed slightly on day 14 and enhanced on day 28. The expression of these cardiac-specific markers in treatment groups were all significantly higher than those in the control group, respectively (P < 0.05). Transmission electron microscopy showed that BMSCs in treatment groups all had myofilaments, z line-like substances and mitochondria. Taken together, these results indicate that BMP-2 combined with Sal-B promotes myocardial differentiation of BMSCs, which may represent a potential therapeutic strategy for the treatment of ischemic heart disease.

Point mutations in murine Nkx2-5 phenocopy human congenital heart disease and induce pathogenic Wnt signaling

Mutations in the Nkx2-5 gene are a main cause of congenital heart disease. Several studies have addressed the phenotypic consequences of disrupting the Nkx2-5 gene locus, although animal models to date failed to recapitulate the full spectrum of the human disease. Here, we describe a new Nkx2-5 point mutation murine model, akin to its human counterpart disease-generating mutation. Our model fully reproduces the morphological and physiological clinical presentations of the disease and reveals an understudied aspect of Nkx2-5-driven pathology, a primary right ventricular dysfunction. We further describe the molecular consequences of disrupting the transcriptional network regulated by Nkx2-5 in the heart and show that Nkx2-5-dependent perturbation of the Wnt signaling pathway promotes heart dysfunction through alteration of cardiomyocyte metabolism. Our data provide mechanistic insights on how Nkx2-5 regulates heart function and metabolism, a link in the study of congenital heart disease, and confirms that our models are the first murine genetic models to our knowledge to present all spectra of clinically relevant adult congenital heart disease phenotypes generated by NKX2-5 mutations in patients.

Intramyocardial implantation of differentiated rat bone marrow mesenchymal stem cells enhanced by TGF-β1 improves cardiac function in heart failure rats

The present study tested the hypotheses that i) transforming growth factor beta 1 (TGF-β1) enhances differentiation of rat bone marrow mesenchymal stem cells (MSCs) towards the cardiomyogenic phenotype and ii) intramyocardial implantation of the TGF-β1-treated MSCs improves cardiac function in heart failure rats. MSCs were treated with different concentrations of TGF-β1 for 72 h, and then morphological characteristics, surface antigens and mRNA expression of several transcription factors were assessed. Intramyocardial implantation of these TGF-β1-treated MSCs to infarcted heart was also investigated. MSCs were initially spindle-shaped with irregular processes. On day 28 after TGF-β1 treatment, MSCs showed fusiform shape, orientating parallel with one another, and were connected with adjoining cells forming myotube-like structures. Immunofluorescence revealed the expression of cardiomyocyte-specific proteins, α-sarcomeric actin and troponin T, in these cells. The mRNA expression of GATA4 and Nkx2.5 genes was slightly increased on day 7, enhanced on day 14 and decreased on day 28 while α-MHC gene was not expressed on day 7, but expressed slightly on day 14 and enhanced on day 28. Transmission electron microscopy showed that the induced cells had myofilaments, z line-like substances, desmosomes, and gap junctions, in contrast with control cells. Furthermore, intramyocardial implantation of TGF-β1-treated MSCs to infarcted heart reduced scar area and increased the number of muscle cells. This structure regeneration was concomitant with the improvement of cardiac function, evidenced by decreased left ventricular end-diastolic pressure, increased left ventricular systolic pressure and increased maximal positive pressure development rate. Taken together, these results indicate that intramyocardial implantation of differentiated MSCs enhanced by TGF-β1 improved cardiac function in heart failure rats.

HOXB5 induces invasion and migration through direct transcriptional up-regulation of β-catenin in human gastric carcinoma

HOX (homeobox) genes encode a family of transcriptional regulators, which have an important role in morphogenesis and differentiation during embryonic development. Their deregulated expression is involved in the carcinogenesis of many human solid tumours. In the present study, we show that HOXB5 mRNA was significantly overexpressed in gastric cancer tissues compared with adjacent normal tissues. HOXB5-up-regulated cancer cells showed increased invasion and migration activity, but no change in proliferation activity, whereas HOXB5-down-regulated cells showed decreased invasion and migration activity. Up-regulation of HOXB5 resulted in up-regulation of β-catenin, whereas inhibition of HOXB5 expression by siRNA led to the down-regulation of β-catenin. Moreover, a significant correlation between HOXB5 and CTNNB1 (β-catenin) mRNA expression was detected in gastric cancer tissues. Furthermore, we found that HOXB5 binds directly to the CTNNB1 promoter region and activates the transcriptional expression of β-catenin, as well as its downstream target genes, encoding cyclin D1 and c-Myc, leading to an increase in the invasion and migration activity of human gastric cancer cells. Thus HOXB5 may be an important regulator of the Wnt/β-catenin signalling pathway, thereby contributing to gastric cancer progression and metastasis.

Arsenic trioxide alters the differentiation of mouse embryonic stem cell into cardiomyocytes

Chronic arsenic exposure is associated with increased morbidity and mortality for cardiovascular diseases. Arsenic increases myocardial infarction mortality in young adulthood, suggesting that exposure during foetal life correlates with cardiac alterations emerging later. Here, we investigated the mechanisms of arsenic trioxide (ATO) cardiomyocytes disruption during their differentiation from mouse embryonic stem cells. Throughout 15 days of differentiation in the presence of ATO (0.1, 0.5, 1.0 μM) we analysed: the expression of i) marker genes of mesoderm (day 4), myofibrillogenic commitment (day 7) and post-natal-like cardiomyocytes (day 15); ii) sarcomeric proteins and their organisation; iii) Connexin 43 and iv) the kinematics contractile properties of syncytia. The higher the dose used, the earlier the stage of differentiation affected (mesoderm commitment, 1.0 μM). At 0.5 or 1.0 μM the expression of cardiomyocyte marker genes is altered. Even at 0.1 μM, ATO leads to reduction and skewed ratio of sarcomeric proteins and to a rarefied distribution of Connexin 43 cardiac junctions. These alterations contribute to the dysruption of the sarcomere and syncytium organisation and to the impairment of kinematic parameters of cardiomyocyte function. This study contributes insights into the mechanistic comprehension of cardiac diseases caused by in utero arsenic exposure.

NKX2-5 mutations causative for congenital heart disease retain functionality and are directed to hundreds of targets

We take a functional genomics approach to congenital heart disease mechanism. We used DamID to establish a robust set of target genes for NKX2-5 wild type and disease associated NKX2-5 mutations to model loss-of-function in gene regulatory networks. NKX2-5 mutants, including those with a crippled homeodomain, bound hundreds of targets including NKX2-5 wild type targets and a unique set of "off-targets", and retained partial functionality. NKXΔHD, which lacks the homeodomain completely, could heterodimerize with NKX2-5 wild type and its cofactors, including E26 transformation-specific (ETS) family members, through a tyrosine-rich homophilic interaction domain (YRD). Off-targets of NKX2-5 mutants, but not those of an NKX2-5 YRD mutant, showed overrepresentation of ETS binding sites and were occupied by ETS proteins, as determined by DamID. Analysis of kernel transcription factor and ETS targets show that ETS proteins are highly embedded within the cardiac gene regulatory network. Our study reveals binding and activities of NKX2-5 mutations on WT target and off-targets, guided by interactions with their normal cardiac and general cofactors, and suggest a novel type of gain-of-function in congenital heart disease.

PROX1 promotes hepatocellular carcinoma proliferation and sorafenib resistance by enhancing β-catenin expression and nuclear translocation

Aberrant activation of the Wnt/β-catenin pathway is frequent in hepatocellular carcinoma (HCC) and contributes to HCC initiation and progression. This abnormal activation may result from somatic mutations in the genes of the Wnt/β-catenin pathway and/or dysregulation of the Wnt/β-catenin pathway. The mechanism for the latter remains poorly understood. Prospero-related homeobox 1 (PROX1) is a downstream target of the Wnt/β-catenin pathway in human colorectal cancer and elevated PROX1 expression promotes malignant progression. However, the Wnt/β-catenin pathway does not regulate PROX1 expression in the liver and HCC cells. Here we report that PROX1 promotes HCC cell proliferation in vitro and tumor growth in HCC xenograft mice. PROX1 and β-catenin levels are positively correlated in tumor tissues as well as in cultured HCC cells. PROX1 can upregulate β-catenin transcription by stimulating the β-catenin promoter and enhance the nuclear translocation of β-catenin in HCC cells, which leads to the activation of the Wnt/β-catenin pathway. Moreover, we show that increase in PROX1 expression renders HCC cells more resistant to sorafenib treatment, which is the standard therapy for advanced HCC. Overall, we have pinpointed PROX1 as a critical factor activating the Wnt/β-catenin pathway in HCC, which promotes HCC proliferation and sorafenib resistance.

The regulation of troponins I, C and ANP by GATA4 and Nkx2-5 in heart of hibernating thirteen-lined ground squirrels, Ictidomys tridecemlineatus

Hibernation is an adaptive strategy used by various mammals to survive the winter under situations of low ambient temperatures and limited or no food availability. The heart of hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus) has the remarkable ability to descend to low, near 0°C temperatures without falling into cardiac arrest. We hypothesized that the transcription factors GATA4 and Nkx2-5 may play a role in cardioprotection by facilitating the expression of key downstream targets such as troponin I, troponin C, and ANP (atrial natriuretic peptide). This study measured relative changes in transcript levels, protein levels, protein post-translational modifications, and transcription factor binding over six stages: euthermic control (EC), entrance into torpor (EN), early torpor (ET), late torpor (LT), early arousal (EA), and interbout arousal (IA). We found differential regulation of GATA4 whereby transcript/protein expression, post-translational modification (phosphorylation of serine 261), and DNA binding were enhanced during the transitory phases (entrance and arousal) of hibernation. Activation of GATA4 was paired with increases in cardiac troponin I, troponin C and ANP protein levels during entrance, while increases in p-GATA4 DNA binding during early arousal was paired with decreases in troponin I and no changes in troponin C and ANP protein levels. Unlike its binding partner, the relative mRNA/protein expression and DNA binding of Nkx2-5 did not change during hibernation. This suggests that either Nkx2-5 does not play a substantial role or other regulatory mechanisms not presently studied (e.g. posttranslational modifications) are important during hibernation. The data suggest a significant role for GATA4-mediated gene transcription in the differential regulation of genes which aid cardiac-specific challenges associated with torpor-arousal.

Myocyte enhancer factor 2C regulation of hepatocellular carcinoma via vascular endothelial growth factor and Wnt/β-catenin signaling

Hepatocellular carcinoma (HCC) is one of the leading malignancies worldwide. Myocyte enhancer factor 2C (MEF2C) was traditionally regarded as a development-associated factor and was recently reported to be an oncogene candidate. We have previously reported overexpression of MEF2C in HCC; however, the roles of MEF2C in HCC remain to be clarified. In this study, HCC cell lines and a xenograft mouse model were used to determine the functions of MEF2C in vitro and in vivo, respectively. Specific plasmids and small interfering RNA were used to upregulate and downregulate MEF2C expression, respectively. Functional assays were performed to assess the influence of MEF2C on cell proliferation, and VEGF-induced vasculogenic mimicry, migration/invasion as well as angiogenesis. Co-immunoprecipitation was conducted to identify the interaction of MEF2C and β-catenin. Human HCC tissue microarrays were used to investigate correlations among MEF2C, β-catenin and involved biomarkers. MEF2C was found to mediate VEGF-induced vasculogenic mimicry, angiogenesis and migration/invasion, with involvement of the p38 MAPK and PKC signaling pathways. However, MEF2C itself inhibited tumor growth in vitro and in vivo. MEF2C was upregulated by and directly interacted with β-catenin. The nuclear translocation of β-catenin blocked by MEF2C was responsible for MEF2C-mediated growth inhibition. The nuclear translocation of MEF2C was associated with intracellular calcium signaling induced by β-catenin. HCC microarrays showed correlations of nuclear MEF2C with the angiogenesis-associated biomarker, CD31, and cytosolic MEF2C with the proliferation-associated biomarker, Ki-67. MEF2C showed double-edged activities in HCC, namely mediating VEGF-induced malignancy enhancement while inhibiting cancer proliferation via blockade of Wnt/β-catenin signaling. The overall effect of MEF2C in HCC progression regulation was dictated by its subcellular distribution. This should be determined prior to any MEF2C-associated intervention in HCC.

The inferred cardiogenic gene regulatory network in the mammalian heart

Cardiac development is a complex, multiscale process encompassing cell fate adoption, differentiation and morphogenesis. To elucidate pathways underlying this process, a recently developed algorithm to reverse engineer gene regulatory networks was applied to time-course microarray data obtained from the developing mouse heart. Approximately 200 genes of interest were input into the algorithm to generate putative network topologies that are capable of explaining the experimental data via model simulation. To cull specious network interactions, thousands of putative networks are merged and filtered to generate scale-free, hierarchical networks that are statistically significant and biologically relevant. The networks are validated with known gene interactions and used to predict regulatory pathways important for the developing mammalian heart. Area under the precision-recall curve and receiver operator characteristic curve are 9% and 58%, respectively. Of the top 10 ranked predicted interactions, 4 have already been validated. The algorithm is further tested using a network enriched with known interactions and another depleted of them. The inferred networks contained more interactions for the enriched network versus the depleted network. In all test cases, maximum performance of the algorithm was achieved when the purely data-driven method of network inference was combined with a data-independent, functional-based association method. Lastly, the network generated from the list of approximately 200 genes of interest was expanded using gene-profile uniqueness metrics to include approximately 900 additional known mouse genes and to form the most likely cardiogenic gene regulatory network. The resultant network supports known regulatory interactions and contains several novel cardiogenic regulatory interactions. The method outlined herein provides an informative approach to network inference and leads to clear testable hypotheses related to gene regulation.

The functional diversity of essential genes required for mammalian cardiac development

Genes required for an organism to develop to maturity (for which no other gene can compensate) are considered essential. The continuing functional annotation of the mouse genome has enabled the identification of many essential genes required for specific developmental processes including cardiac development. Patterns are now emerging regarding the functional nature of genes required at specific points throughout gestation. Essential genes required for development beyond cardiac progenitor cell migration and induction include a small and functionally homogenous group encoding transcription factors, ligands and receptors. Actions of core cardiogenic transcription factors from the Gata, Nkx, Mef, Hand, and Tbx families trigger a marked expansion in the functional diversity of essential genes from midgestation onwards. As the embryo grows in size and complexity, genes required to maintain a functional heartbeat and to provide muscular strength and regulate blood flow are well represented. These essential genes regulate further specialization and polarization of cell types along with proliferative, migratory, adhesive, contractile, and structural processes. The identification of patterns regarding the functional nature of essential genes across numerous developmental systems may aid prediction of further essential genes and those important to development and/or progression of disease. genesis 52:713–737, 2014.

Activation of GATA4 gene expression at the early stage of cardiac specification

Currently, there are no effective treatments to directly repair damaged heart tissue after cardiac injury since existing therapies focus on rescuing or preserving reversibly damaged tissue. Cell-based therapies using cardiomyocytes generated from stem cells present a promising therapeutic approach to directly replace damaged myocardium with new healthy tissue. However, the molecular mechanisms underlying the commitment of stem cells into cardiomyocytes are not fully understood and will be critical to guide this new technology into the clinic. Since GATA4 is a critical regulator of cardiac differentiation, we examined the molecular basis underlying the early activation of GATA4 gene expression during cardiac differentiation of pluripotent stem cells. Our studies demonstrate the direct involvement of histone acetylation and transcriptional coactivator p300 in the regulation of GATA4 gene expression. More importantly, we show that histone acetyltransferase (HAT) activity is important for GATA4 gene expression with the use of curcumin, a HAT inhibitor. In addition, the widely used histone deacetylase inhibitor valproic acid enhances both histone acetylation and cardiac specification.

Disruption of aryl hydrocarbon receptor homeostatic levels during embryonic stem cell differentiation alters expression of homeobox transcription factors that control cardiomyogenesis

BACKGROUND

The aryl hydrocarbon receptor (AHR) is a ligand-activated transcription factor that regulates the expression of xenobiotic detoxification genes and is a critical mediator of gene-environment interactions. Many AHR target genes identified by genome-wide gene expression profiling have morphogenetic functions, suggesting that AHR may play a role in embryonic development.

OBJECTIVES

To characterize the developmental functions of the AHR, we studied the consequences of AHR activation by the agonist 2,3,7,8-tetrachlorodibenzo-p-doxin (TCDD), and the result of its repression by the antagonists 6,2,4-trimethoxyflavone and CH 223191 or by short-hairpin RNA (shRNA)-mediated Ahr knockdown during spontaneous differentiation of embryonic stem (ES) cells into cardiomyocytes.

METHODS

We generated an AHR-positive cardiomyocyte lineage differentiated from mouse ES cells that expresses puromycin resistance and enhanced green fluorescent protein (eGFP) under the control of the Cyp1a1 (cytochrome P450 1a1) promoter. We used RNA sequencing (RNA.Seq) to analyze temporal trajectories of TCDD-dependent global gene expression in these cells during differentiation.

RESULTS

Activation, inhibition, and knockdown of Ahr significantly inhibited the formation of contractile cardiomyocyte nodes. Global expression analysis of AHR-positive cells showed that activation of the AHR/TCDD axis disrupted the concerted expression of genes that regulate multiple signaling pathways involved in cardiac and neural morphogenesis and differentiation, including dozens of genes encoding homeobox transcription factors and Polycomb and trithorax group proteins.

CONCLUSIONS

Disruption of AHR expression levels resulted in gene expression changes that perturbed cardiomyocyte differentiation. The main function of the AHR during development appears to be the coordination of a complex regulatory network responsible for attainment and maintenance of cardiovascular homeostasis.

Lrrc10 is a novel cardiac-specific target gene of Nkx2-5 and GATA4

Cardiac gene expression is precisely regulated and its perturbation causes developmental defects and heart disease. Leucine-rich repeat containing 10 (Lrrc10) is a cardiac-specific factor that is crucial for proper cardiac development and deletion of Lrrc10 in mice results in dilated cardiomyopathy. However, the mechanisms regulating Lrrc10 expression in cardiomyocytes remain unknown. Therefore, we set out to determine trans-acting factors and cis-elements critical for mediating Lrrc10 expression. We identify Lrrc10 as a transcriptional target of Nkx2-5 and GATA4. The Lrrc10 promoter region contains two highly conserved cardiac regulatory elements, which are functional in cardiomyocytes but not in fibroblasts. In vivo, Nkx2-5 and GATA4 endogenously occupy the proximal and distal cardiac regulatory elements of Lrrc10 in the heart. Moreover, embryonic hearts of Nkx2-5 knockout mice have dramatically reduced expression of Lrrc10. These data demonstrate the importance of Nkx2-5 and GATA4 in regulation of Lrrc10 expression in vivo. The proximal cardiac regulatory element located at around -200bp is synergistically activated by Nkx2-5 and GATA4 while the distal cardiac regulatory element present around -3kb requires SRF in addition to Nkx2-5 and GATA4 for synergistic activation. Mutational analyses identify a pair of adjacent Nkx2-5 and GATA binding sites within the proximal cardiac regulatory element that are necessary to induce expression of Lrrc10. In contrast, only the GATA site is functional in the distal regulatory element. Taken together, our data demonstrate that the transcription factors Nkx2-5 and GATA4 cooperatively regulate cardiac-specific expression of Lrrc10.

Mouse embryonic stem cells irradiated with γ-rays differentiate into cardiomyocytes but with altered contractile properties

Embryonic stem cells (ESCs) for their derivation from the inner cell mass of a blastocyst represent a valuable in vitro model to investigate the effects of ionizing radiation on early embryonic cellular response. Following irradiation, both human and mouse ESCs (mESCs) maintain their pluripotent status and the capacity to differentiate into embryoid bodies and to form teratomas. Although informative of the maintenance of a pluripotent status, these studies never investigated the capability of irradiated ESCs to form specific differentiated phenotypes. Here, for the first time, 5Gy-irradiated mESCs were differentiated into cardiomyocytes, thus allowing the analysis of the long-term effects of ionizing radiations on the differentiation potential of a pluripotent stem cell population. On treated mESCs, 96h after irradiation, a genome-wide expression analysis was first performed in order to determine whether the treatment influenced gene expression of the surviving mESCs. Microarrays analysis showed that only 186 genes were differentially expressed in treated mESCs compared to control cells; a quarter of these genes were involved in cellular differentiation, with three main gene networks emerging, including cardiogenesis. Based on these results, we differentiated irradiated mESCs into cardiomyocytes. On day 5, 8 and 12 of differentiation, treated cells showed a significant alteration (qRT-PCR) of the expression of marker genes (Gata-4, Nkx-2.5, Tnnc1 and Alpk3) when compared to control cells. At day 15 of differentiation, although the organization of sarcomeric α-actinin and troponin T proteins appeared similar in cardiomyocytes differentiated from either mock or treated cells, the video evaluation of the kinematics and dynamics of the beating cardiac syncytium evidenced altered contractile properties of cardiomyocytes derived from irradiated mESCs. This alteration correlated with significant reduction of Connexin 43 foci. Our results indicate that mESCs populations that survive an ionizing irradiation treatment are capable to differentiate into cardiomyocytes, but they have altered contractile properties.

Temporal modulation of β-catenin signaling by multicellular aggregation kinetics impacts embryonic stem cell cardiomyogenesis

Pluripotent stem cell differentiation recapitulates aspects of embryonic development, including the regulation of morphogenesis and cell specification via precise spatiotemporal signaling. The assembly and reorganization of cadherins within multicellular aggregates may similarly influence β-catenin signaling dynamics and the associated cardiomyogenic differentiation of pluripotent embryonic stem cells (ESCs). In this study, dynamic changes in β-catenin expression and transcriptional activity were analyzed in response to altered cell adhesion kinetics during embryoid body (EB) formation and differentiation. Modulation of intercellular adhesion kinetics by rotary orbital mixing conditions led to temporal modulation of T-cell factor/lymphoid enhancer-binding factor activity, as well as changes in the spatial localization and phosphorylation state of β-catenin expression. Slower rotary speeds, which promoted accelerated ESC aggregation, resulted in the early accumulation of nuclear dephosphorylated β-catenin, which was followed by a decrease in β-catenin transcriptional activity and an increase in the gene expression of Wnt inhibitors such as Dkk-1. In addition, EBs that exhibited increased β-catenin transcriptional activity at early stages of differentiation subsequently demonstrated increased expression of genes related to cardiomyogenic phenotypes, and inhibition of the Wnt pathway during the initial 4 days of differentiation significantly decreased cardiomyogenic gene expression. Together, the results of this study indicate that the expression and transcriptional activity of β-catenin are temporally regulated by multicellular aggregation kinetics of pluripotent ESCs and influence mesoderm and cardiomyocyte differentiation.

Zinc finger transcription factor 191, directly binding to β-catenin promoter, promotes cell proliferation of hepatocellular carcinoma

Activation of β-catenin, the central effector of the canonical wingless-type (Wnt) pathway, has been implicated in hepatocellular carcinoma (HCC). However, the transcription regulation mechanism of the β-catenin gene in HCC remains unknown. Here we report that human zinc finger protein 191 (ZNF191) is a potential regulator of β-catenin transcription. ZNF191, a Krüppel-like protein, specifically interacts with the TCAT motif, which constitutes the HUMTH01 microsatellite in the tyrosine hydroxylase (TH) gene ex vivo. We demonstrate that ZNF191 is significantly overexpressed in human HCC specimens and is associated with growth of human HCC cells. Global profiling of gene expression in ZNF191 knockdown human hepatic L02 cells revealed that the important Wnt signal pathway genes β-catenin and cyclin D1 messenger RNAs (mRNAs) are significantly down-regulated. In agreement with transcription level, β-catenin and cyclin D1 proteins are also down-regulated in transient and stable ZNF191 knockdown L02 and hepatoma Hep3B cell lines. Moreover, significant correlation between ZNF191 and β-catenin mRNA expression was detected in human HCCs. Promoter luciferase assay indicated that ZNF191 can increase transcription activity of the full-length β-catenin (CTNNB1) promoter, and nucleotide (nt)-1407/-907 of the CTNNB1 promoter exhibited the maximum transcriptional activity. Electrophoretic mobility shift assay showed that purified ZNF191 protein can directly bind to the CTNNB1 promoter, and the binding region is located at nt-1254/-1224. Finally, we demonstrate that the key binding sequence of ZNF191 in vivo is ATTAATT.

CONCLUSION

ZNF191 can directly bind to the CTNNB1 promoter and activate the expression of β-catenin and its downstream target genes such as cyclin D1 in hepatoma cell lines. This study uncovers a new molecular mechanism of transcription regulation of the β-catenin gene in HCC.

Transcription factor binding site polymorphism in the motilin gene associated with left-sided displacement of the abomasum in German Holstein cattle

Left-sided displacement of the abomasum (LDA) is a common disease in many dairy cattle breeds. A genome-wide screen for QTL for LDA in German Holstein (GH) cows indicated motilin (MLN) as a candidate gene on bovine chromosome 23. Genomic DNA sequence analysis of MLN revealed a total of 32 polymorphisms. All informative polymorphisms used for association analyses in a random sample of 1,136 GH cows confirmed MLN as a candidate for LDA. A single nucleotide polymorphism (FN298674:g.90T>C) located within the first non-coding exon of bovine MLN affects a NKX2-5 transcription factor binding site and showed significant associations (OR_allele = 0.64; −log₁₀P_allele = 6.8, −log₁₀P_genotype = 7.0) with LDA. An expression study gave evidence of a significantly decreased MLN expression in cows carrying the mutant allele (C). In individuals heterozygous or homozygous for the mutation, MLN expression was decreased by 89% relative to the wildtype. FN298674:g.90T>C may therefore play a role in bovine LDA via the motility of the abomasum. This MLN SNP appears useful to reduce the incidence of LDA in German Holstein cattle and provides a first step towards a deeper understanding of the genetics of LDA.

ISL1 directly regulates FGF10 transcription during human cardiac outflow formation

The LIM homeodomain gene Islet-1 (ISL1) encodes a transcription factor that has been associated with the multipotency of human cardiac progenitors, and in mice enables the correct deployment of second heart field (SHF) cells to become the myocardium of atria, right ventricle and outflow tract. Other markers have been identified that characterize subdomains of the SHF, such as the fibroblast growth factor Fgf10 in its anterior region. While functional evidence of its essential contribution has been demonstrated in many vertebrate species, SHF expression of Isl1 has been shown in only some models. We examined the relationship between human ISL1 and FGF10 within the embryonic time window during which the linear heart tube remodels into four chambers. ISL1 transcription demarcated an anatomical region supporting the conserved existence of a SHF in humans, and transcription factors of the GATA family were co-expressed therein. In conjunction, we identified a novel enhancer containing a highly conserved ISL1 consensus binding site within the FGF10 first intron. ChIP and EMSA demonstrated its direct occupation by ISL1. Transcription mediated by ISL1 from this FGF10 intronic element was enhanced by the presence of GATA4 and TBX20 cardiac transcription factors. Finally, transgenic mice confirmed that endogenous factors bound the human FGF10 intronic enhancer to drive reporter expression in the developing cardiac outflow tract. These findings highlight the interest of examining developmental regulatory networks directly in human tissues, when possible, to assess candidate non-coding regions that may be responsible for congenital malformations.

Mechanisms of cardiogenesis in cardiovascular progenitor cells

Self-renewing cells of the vertebrate heart have become a major subject of interest in the past decade. However, many researchers had a hard time to argue against the orthodox textbook view that defines the heart as a postmitotic organ. Once the scientific community agreed on the existence of self-renewing cells in the vertebrate heart, their origin was again put on trial when transdifferentiation, dedifferentiation, and reprogramming could no longer be excluded as potential sources of self-renewal in the adult organ. Additionally, the presence of self-renewing pluripotent cells in the peripheral blood challenges the concept of tissue-specific stem and progenitor cells. Leaving these unsolved problems aside, it seems very desirable to learn about the basic biology of this unique cell type. Thus, we shall here paint a picture of cardiovascular progenitor cells including the current knowledge about their origin, basic nature, and the molecular mechanisms guiding proliferation and differentiation into somatic cells of the heart.

Transactivation in Drosophila of human enhancers by human transcription factors involved in congenital heart diseases

BACKGROUND

The human transcription factors (TFs) GATA4, NKX2.5 and TBX5 form part of the core network necessary to build a human heart and are involved in Congenital Heart Diseases (CHDs). The human natriuretic peptide precursor A (NPPA) and α-myosin heavy chain 6 (MYH6) genes are downstream effectors involved in cardiogenesis that have been demonstrated to be in vitro targets of such TFs.

RESULTS

To study the interactions between these human TFs and their target enhancers in vivo, we overexpressed them in the whole Drosophila cardiac tube using the UAS/GAL4 system. We observed that all three TFs up-regulate their natural target enhancers in Drosophila and cause developmental defects when overexpressed in eyes and wings.

CONCLUSIONS

A strong potential of the present model might be the development of combinatorial and mutational assays to study the interactions between human TFs and their natural target promoters, which are not easily undertaken in tissue culture cells because of the variability in transfection efficiency, especially when multiple constructs are used. Thus, this novel system could be used to determine in vivo the genetic nature of the human mutant forms of these TFs, setting up a powerful tool to unravel the molecular genetic mechanisms that lead to CHDs.

Comparative analysis of the ATRX promoter and 5' regulatory region reveals conserved regulatory elements which are linked to roles in neurodevelopment, alpha-globin regulation and testicular function

Background

ATRX is a tightly-regulated multifunctional protein with crucial roles in mammalian development. Mutations in the ATRX gene cause ATR-X syndrome, an X-linked recessive developmental disorder resulting in severe mental retardation and mild alpha-thalassemia with facial, skeletal and genital abnormalities. Although ubiquitously expressed the clinical features of the syndrome indicate that ATRX is not likely to be a global regulator of gene expression but involved in regulating specific target genes. The regulation of ATRX expression is not well understood and this is reflected by the current lack of identified upstream regulators. The availability of genomic data from a range of species and the very highly conserved 5' regulatory regions of the ATRX gene has allowed us to investigate putative transcription factor binding sites (TFBSs) in evolutionarily conserved regions of the mammalian ATRX promoter.

Results

We identified 12 highly conserved TFBSs of key gene regulators involved in biologically relevant processes such as neural and testis development and alpha-globin regulation.

Conclusions

Our results reveal potentially important regulatory elements in the ATRX gene which may lead to the identification of upstream regulators of ATRX and aid in the understanding of the molecular mechanisms that underlie ATR-X syndrome.

Lentivirus-mediated Wnt11 gene transfer enhances Cardiomyogenic differentiation of skeletal muscle-derived stem cells

Wnt signaling plays a crucial role in regulating cell proliferation, differentiation and inducing cardiomyogenesis. Skeletal muscle-derived stem cells (MDSCs) have been shown to be multipotent; however, their potential to aid in the healing of the heart after myocardial infarction appears to be due to the paracrine effects they impart on the host environment. The goal of this study was to investigate whether Wnt11 could promote the differentiation of MDSCs into cardiomyocytes and enhance the repair of infarcted myocardium. MDSCs transduced with a lentivirus encoding for Wnt11 increased mRNA and protein expression of the early cardiac markers NK2 transcription factor related 5 (NKx2.5) and Connexin43 (Cx43) and also led to an increased expression of late-stage cardiac markers including: α, β-myosin heavy chain (MHC) and brain natriuretic protein (BNP) at the mRNA level, and MHC and Troponin I (TnI) at the protein level. We also observed that Wnt11 expression significantly enhanced c-jun N-terminal kinase activity in transduced MDSCs, and that some of the cells beat spontaneously but are not fully differentiated cardiomyocytes. Finally, lentivirus-Wnt11-transduced MDSCs showed greater survival and cardiac differentiation after being transplanted into acutely infarct-injured myocardium. These findings could one day lead to strategies that could be utilized in cardiomyoplasty treatments of myocardial infarction.

A de novo mutation in NKX2.5 associated with atrial septal defects, ventricular noncompaction, syncope and sudden death

BACKGROUND

Mutations in transcription factor NKX2.5 cause congenital heart disease (CHD). We identified a CHD family with atrial septal defects (ASDs), atrioventricular block, ventricular noncompaction, syncope and sudden death. Our objective is to identify the disease-causing mutation in the CHD family.

METHODS

Direct DNA sequence analysis was used to identify the CHD mutation. The functional effects of the mutation were characterized by a luciferase reporter assay and immunostaining.

RESULTS

A novel, de novo 2-bp insertion (c.512insGC) was identified in exon 2 of NKX2.5. Mutation c.512insGC co-segregates with CHD in the family, and is not present in 200 controls. Functional studies indicate that the c.512insGC mutation impedes nuclear localization of NKX2.5 and causes a total loss of transactivation activity of NKX2.5. Furthermore, no NKX2.5 mutation was identified in 125 sporadic Chinese CHD patients.

CONCLUSIONS

(1) NKX2.5 mutation c.512insGC is associated with ASDs, syncope and sudden death. It is the second de novo mutation identified in NKX2.5. (2) NKX2.5 mutations are rare in sporadic CHD patients. (3) This study for the first time identifies association between a NKX2.5 mutation and ventricular noncompaction. Our results significantly expand the phenotypic spectrum of NKX2.5 mutations.

Stat3 directly controls the expression of Tbx5, Nkx2.5, and GATA4 and is essential for cardiomyocyte differentiation of P19CL6 cells

The transcription factor Stat3 (signal transducer and activator of transcription 3) mediates many physiological processes, including embryogenesis, stem cell self-renewal, and postnatal survival. In response to gp130 receptor activation, Stat3 becomes phosphorylated by the receptor-associated Janus kinase, forms dimers, and enters the nucleus where it binds to Stat3 target genes and regulates their expression. In this report, we demonstrate that Stat3 binds directly to the promoters and regulates the expression of three genes that are essential for cardiac differentiation: Tbx5, Nkx2.5, and GATA4. We further demonstrate that Tbx5, Nkx2.5, and GATA4 expression is dependent on Stat3 in response to ligand treatment and during ligand-independent differentiation of P19CL6 cells into cardiomyocytes. Finally, we show that Stat3 is necessary for the differentiation of P19CL6 cells into beating cardiomyocytes. All together, these results demonstrate that Stat3 is required for the differentiation of cardiomyocytes through direct transcriptional regulation of Tbx5, Nkx2.5, and GATA4.

Examining the cardiac NK-2 genes in early heart development

The cardiac NK-2 transcription factors are the vertebrate relatives of the Drosophila tinman gene. Without the Drosophila tinman gene, fruit flies fail to form their heart ("dorsal vessel"), and mutations or altered expression of cardiac NK-2 genes may lead to abnormal heart formation in vertebrates. Although the cardiac NK-2 gene NKX2-5 is recognized as an important factor in cases of human congenital heart disease and heart development in vertebrates, the roles of the other cardiac NK-2 genes are less clear. This report reviews what is known about the cardiac NK-2 genes in cardiac development, comparing studies in several different model systems.