The cardiac-muscle specific enhancer-promoter of slow/cardiac troponin C binds HMG-2

Identification of teleost tnnc1a enhancers for specific pan-cardiac transcription

Troponin C regulates muscle contraction by forming the troponin complex with troponin I and troponin T. Different muscle types express different troponin C genes. The mechanisms of such differential transcription are not fully understood. The Zebrafish tnnc1a gene is restrictively expressed in cardiac muscles. We here identify the enhancers and promoters of the zebrafish and medaka tnnc1a genes, including intronic enhancers in zebrafish and medaka and an upstream enhancer in the medaka. The intronic and upstream enhancers are likely functionally redundant. The GFP transgenic reporter driven by these enhancers is expressed more strongly in the ventricle than in the atrium, recapitulating the expression pattern of the endogenous zebrafish tnnc1a gene. Our study identifies a new set of enhancers for cardiac-specific transgenic expression in zebrafish. These enhancers can serve as tools for future identification of transcription factor networks that drive cardiac-specific gene transcription.

MiR-21, MiR-29a, GATA4, and MEF2c Expression Changes in Endothelin-1 and Angiotensin II Cardiac Hypertrophy Stimulated Isl-1+Sca-1+c-kit+ Porcine Cardiac Progenitor Cells In Vitro

Cost- and time-intensive porcine translational disease models offer great opportunities to test drugs and therapies for pathological cardiac hypertrophy and can be supported by porcine cell culture models that provide further insights into basic disease mechanisms. Cardiac progenitor cells (CPCs) residing in the adult heart have been shown to differentiate in vitro into cardiomyocytes and could contribute to cardiac regeneration. Therefore, it is important to evaluate their changes on the cellular level caused by disease. We successfully isolated Isl1⁺Sca1⁺cKit⁺ porcine CPCs (pCPCs) from pig hearts and stimulated them with endothelin-1 (ET-1) and angiotensin II (Ang II) in vitro. We also performed a cardiac reprogramming transfection and tested the same conditions. Our results show that undifferentiated Isl1⁺Sca1⁺cKit⁺ pCPCs were significantly upregulated in GATA4, MEF2c, and miR-29a gene expressions and in BNP and MCP-1 protein expressions with Ang II stimulation, but they showed no significant changes in miR-29a and MCP-1 when stimulated with ET-1. Differentiated Isl1⁺Sca1⁺cKit⁺ pCPCs exhibited significantly higher levels of MEF2c, GATA4, miR-29a, and miR-21 as well as Cx43 and BNP with Ang II stimulation. pMx-MGT-transfected Isl1⁺Sca1⁺cKit⁺ pCPCs showed significant elevations in MEF2c, GATA4, and BNP expressions when stimulated with ET-1. Our model demonstrates that in vitro stimulation leads to successful Isl1⁺Sca1⁺cKit⁺ pCPC hypertrophy with upregulation of cardiac remodeling associated genes and profibrotic miRNAs and offers great possibilities for further investigations of disease mechanisms and treatment.

Cell signaling pathways for the regulation of GATA4 transcription factor: Implications for cell growth and apoptosis

GATA4 is a member of the GATA family of zinc finger transcription factor, which regulates gene transcription by binding to GATA elements. GATA4 was originally discovered as a regulator of cardiac development and subsequently identified as a major regulator of adult cardiac hypertrophy. GATA4 regulates gene expression of various genes, which are involved in cardiac development and cardiac hypertrophy and heart failure. In addition to the heart, GATA4 plays important roles in the reproductive system, gastrointestinal system, respiratory system and cancer. Positive and negative regulations of GATA4 therefore are important components of biologic functions. The activation of GATA4 occurs via various cell signaling events. Earlier studies have identified protein-protein interactions of GATA4 with other factors. The discovery of interactions of GATA4 with nuclear factor for activated T cells (NFAT) revealed the importance of calcium signaling in the activation of GATA4. GATA4 can also be phosphorylated by mitogen activated protein kinases and protein kinase A. Lysine modifications also occur on the GATA4 molecule including acetylation and sumoylation. Both reactive oxygen-dependent and -independent antioxidant-sensitive pathways for GATA4 activation have also been demonstrated. The GATA4 activity is also regulated by modulating the level of GATA4 expression via transcriptional as well as translational mechanisms. This work summarizes the current understanding of regulatory mechanisms for modulating GATA4 activity.

GATA-4 regulates cardiac morphogenesis through transactivation of the N-cadherin gene

Cardia bifida is known to occur in animal models lacking the cardiogenic transcriptional factor GATA-4. The downstream target genes responsible for this cardiac deformity remain unknown, however. Treatment with small interfering RNAs (siRNA) specifically targeting GATA-4 into cardiac mesodermal cells led to the development of cardia bifida in chick embryos. RT-PCR using mRNAs extracted from cardiac tubes revealed that the GATA-4-specific siRNA selectively suppresses expression of N-cadherin mRNA, one of the genes essential for the single heart formation, without affecting other cardiac marker mRNAs. Analysis of the N-cadherin gene promoter activity using a luciferase reporter gene system and electrophoretic mobility shift assays revealed that GATA-4 binds directly to the N-cadherin gene promoter region, thereby transactivating its expression. We therefore concluded that the cardia bifida observed in the GATA-4-deleted model is caused by the transcriptional down-regulation of N-cadherin expression.

Nuclear protein binding at the beta-myosin heavy chain A/T-rich element is enriched following increased skeletal muscle activity

In adult mouse skeletal muscle, beta-myosin heavy chain (betaMyHC) gene expression is primarily restricted to slow-type I fibers but can be induced in fast-type II fibers by mechanical overload (MOV). Our previous transgenic analyses have delimited an 89-base pair (bp) MOV-responsive region (-293 to -205), and shown that mutation of the MCAT and C-rich elements within this region did not abolish betaMyHC transgene induction by MOV. In this study we describe an A/T-rich element (betaA/T-rich; -269 5'-GGAGATATTTTT-3' -258) located within this 89-bp region that, only under MOV conditions, revealed enriched binding as characterized by electrophoretic mobility shift assays and dimethyl sulfate and diethyl pyrocarbonate interference footprinting. Direct, competition, and supershift electrophoretic mobility shift assays revealed highly enriched specific binding activity at the betaA/T-rich element that was antigenically distinct from GATA-4, MEF2A-D, SRF, and Oct-1, nuclear proteins that were previously shown to bind A/T-rich elements. In vitro translated GATA-4, MEF2C, SRF, and Oct-1 bound to consensus GATA, MEF2, SRE, and Oct-1 elements, respectively, but not to the betaA/T-rich element. Two-dimensional UV cross-linking of the bromodeoxyuridine-substituted betaA/T-rich element with mechanically overloaded plantaris (MOV-P) nuclear extract detected two proteins (44 and 48 kDa). Our results indicate that the betaA/T-rich element may function in vivo as a betaMyHC MOV-inducible element during hypertrophy of adult skeletal muscle by binding two distinct proteins identified only in MOV-P nuclear extract.