During heart development the second heart field (SHF) provides progenitor cells for most cardiomyocytes and expresses the homeodomain factor Nkx2-5. We now show that feedback repression of Bmp2/Smad1 signaling by Nkx2-5 critically regulates SHF proliferation and outflow tract (OFT) morphology. In the cardiac fields of Nkx2-5 mutants, genes controlling cardiac specification (including Bmp2) and maintenance of the progenitor state were upregulated, leading initially to progenitor overspecification, but subsequently to failed SHF proliferation and OFT truncation. In Smad1 mutants, SHF proliferation and deployment to the OFT were increased, while Smad1 deletion in Nkx2-5 mutants rescued SHF proliferation and OFT development. In Nkx2-5 hypomorphic mice, which recapitulate human congenital heart disease (CHD), OFT anomalies were also rescued by Smad1 deletion. Our findings demonstrate that Nkx2-5 orchestrates the transition between periods of cardiac induction, progenitor proliferation, and OFT morphogenesis via a Smad1-dependent negative feedback loop, which may be a frequent molecular target in CHD.

The T-box family transcription factor gene TBX20 acts in a conserved regulatory network, guiding heart formation and patterning in diverse species. Mouse Tbx20 is expressed in cardiac progenitor cells, differentiating cardiomyocytes, and developing valvular tissue, and its deletion or RNA interference-mediated knockdown is catastrophic for heart development. TBX20 interacts physically, functionally, and genetically with other cardiac transcription factors, including NKX2-5, GATA4, and TBX5, mutations of which cause congenital heart disease (CHD). Here, we report nonsense (Q195X) and missense (I152M) germline mutations within the T-box DNA-binding domain of human TBX20 that were associated with a family history of CHD and a complex spectrum of developmental anomalies, including defects in septation, chamber growth, and valvulogenesis. Biophysical characterization of wild-type and mutant proteins indicated how the missense mutation disrupts the structure and function of the TBX20 T-box. Dilated cardiomyopathy was a feature of the TBX20 mutant phenotype in humans and mice, suggesting that mutations in developmental transcription factors can provide a sensitized template for adult-onset heart disease. Our findings are the first to link TBX20 mutations to human pathology. They provide insights into how mutation of different genes in an interactive regulatory circuit lead to diverse clinical phenotypes, with implications for diagnosis, genetic screening, and patient follow-up.

NF-B induces the expression of genes involved in immune response, apoptosis, inflammation, and the cell cycle. Certain NF-B-responsive genes are activated rapidly after the cell is stimulated by cytokines and other extracellular signals. However, the mechanism by which these genes are activated is not entirely understood. Here we report that even though NF-B interacts directly with TAF II s, induction of NF-B by tumor necrosis factor alpha (TNF-␣) does not enhance TFIID recruitment and preinitiation complex formation on some NF-B-responsive promoters. These promoters are bound by the transcription apparatus prior to TNF-␣ stimulus. Using the immediate-early TNF-␣-responsive gene A20 as a prototype promoter, we found that the constitutive association of the general transcription apparatus is mediated by Sp1 and that this is crucial for rapid transcriptional induction by NF-B. In vitro transcription assays confirmed that NF-B plays a postinitiation role since it enhances the transcription reinitiation rate whereas Sp1 is required for the initiation step. Thus, the consecutive effects of Sp1 and NF-B on the transcription process underlie the mechanism of their synergy and allow rapid transcriptional induction in response to cytokines.The family of NF-B transcription factors is a central component of the cellular response to a broad range of extracellular signals, many of them are related to immunological functions and stress. NF-B controls the expression of a large number of genes including inflammatory cytokines, chemokines, immunological factors, adhesion molecules, cell cycle regulators, and pro-and antiapoptotic factors (24). A major pathway regulating NF-B activity involves its nuclear transport. In unstimulated cells, NF-B is retained in the cytoplasm in an inactive form by IB proteins. Signals that activate NF-B trigger ubiquitination and degradation of IB by the proteosome, resulting in transport of NF-B into the nucleus and transcriptional activation of responsive genes. Since IB␣ is one of the NF-B target genes, the newly synthesized IB␣ negatively regulates NF-B, thus forming an autoregulatory loop.In the nucleus, transcriptional activation by NF-B involves its association with multiple coactivators. We reported previously that the substoichiometric TFIID subunit, TAF II 105, which is enriched in B cells, interacts directly with p65/Re1A, a member of the NF-B family, and is important for activation of a subset of NF-B-dependent antiapoptotic genes in vivo (30,36,37). Likewise, other TFIID subunits such as hTAF II 250, hTAF II 80, and hTAF II 28 were reported to bind to p65/Re1A (8), although the physiological importance of these interactions was not investigated. In addition to TFIID, the coactivator protein CREB-binding protein CBP and its homolog p300 were reported to be involved in transcription activation by the p65/Re1A subunit of NF-B (6, 25). p65 was also found to interact specifically with the composite coactivator ARC/DRIP, and this complex supports NF-B-dependent transcriptional activation in v...

Rationale:The cardiac gene regulatory network (GRN) is controlled by transcription factors and signaling inputs, but network logic in development and it unraveling in disease is poorly understood. In development, the membrane-tethered signaling ligand Neuregulin (Nrg)1, expressed in endocardium, is essential for ventricular morphogenesis. In adults, Nrg1 protects against heart failure and can induce cardiomyocytes to divide.Objective: To understand the role of Nrg1 in heart development through analysis of null and hypomorphic Nrg1 mutant mice. Methods and Results:Chamber domains were correctly specified in Nrg1 mutants, although chamber-restricted genes Hand1 and Cited1 failed to be activated. The chamber GRN subsequently decayed with individual genes exhibiting decay patterns unrelated to known patterning boundaries. Both trabecular and nontrabecular myocardium were affected. Network demise was spatiotemporally dynamic, the most sensitive region being the central part of the left ventricle, in which the GRN underwent complete collapse. Other regions were partially affected with graded sensitivity. In vitro, Nrg1 promoted phospho-Erk1/2-dependent transcription factor expression, cardiomyocyte maturation and cell cycle inhibition. We monitored cardiac pErk1/2 in embryos and found that expression was Nrg1-dependent and levels correlated with cardiac GRN sensitivity in mutants. Conclusions:The chamber GRN is fundamentally labile and dependent on signaling from extracardiac sources.Nrg1-ErbB1/4 -Erk1/2 signaling critically sustains elements of the GRN in trabecular and nontrabecular myocardium, challenging our understanding of Nrg1 function. Transcriptional decay patterns induced by reduced Nrg1 suggest a novel mechanism for cardiac transcriptional regulation and dysfunction in disease, potentially linking biomechanical feedback to molecular pathways for growth and differentiation. (Circ Res. 2010;107:715-727.) Key Words: neuregulin 1 Ⅲ cardiac gene regulation Ⅲ heart development Ⅲ cardiac gene regulatory network A n early patterning event in vertebrate heart development is the specification of myocardium of the atrial and ventricular chambers, a specialized muscle adapted to pumping blood through a closed circulatory system at high pressure. 1 Luminal myocytes of the cardiac chambers develop sponge-like convolutions termed trabeculae, which in development serve as a morphological marker for chamber specification. The trabecular zone is also marked by a unique set of genes. Chamber muscle is an electric syncytium through which action potentials spread via gap junctions, guided by caudal pacemaker myocytes and their conduction and Purkinje fiber tracts.Nontrabecular myocardium of the atrium, inner curvature, atrioventricular (AV) canal and outflow tract (OFT) is less specialized for contraction and gives rise to the myogenic layers of the outflow and inflow vessels, and cells of the proximal conduction system including the sinoatrial (SA) and AV nodes. 1 Nontrabecular myocardium also plays a critical role in induct...

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Gene transfer has therapeutic potential for treating HIV-1 infection by generating cells that are resistant to the virus. We have engineered a novel self-inactivating lentiviral vector, LVsh5/C46, using two viral-entry inhibitors to block early steps of HIV-1 cycle. The LVsh5/C46 vector encodes a short hairpin RNA (shRNA) for downregulation of CCR5, in combination with the HIV-1 fusion inhibitor, C46. We demonstrate here the effective delivery of LVsh5/C46 to human T cell lines, peripheral blood mononuclear cells, primary CD4+ T lymphocytes, and CD34+ hematopoietic stem/progenitor cells (HSPC). CCR5-targeted shRNA (sh5) and C46 peptide were stably expressed in the target cells and were able to effectively protect gene-modified cells against infection with CCR5- and CXCR4-tropic strains of HIV-1. LVsh5/C46 treatment was nontoxic as assessed by cell growth and viability, was noninflammatory, and had no adverse effect on HSPC differentiation. LVsh5/C46 could be produced at a scale sufficient for clinical development and resulted in active viral particles with very low mutagenic potential and the absence of replication-competent lentivirus. Based on these in vitro results, plus additional in vivo safety and efficacy data, LVsh5/C46 is now being tested in a phase 1/2 clinical trial for the treatment of HIV-1 disease.

Background The transcription factor NKX2-5 is crucial for heart development and mutations in this gene have been implicated in diverse congenital heart diseases (CHD) and conduction defects (CD) in mouse models and humans. Whether NKX2-5 mutations have a role in adult-onset heart disease is unknown. Methods and Results Mutation screening was performed in 220 probands with adult-onset dilated cardiomypathy (DCM). Six NKX2-5 coding sequence variants were identified, including 3 non-synonymous variants. A novel heterozygous mutation, I184M, located within the NKX2-5 homeodomain (HD), was identified in one family. A subset of family members had CHD, but there was an unexpectedly high prevalence of DCM. Functional analysis of I184M in vitro demonstrated a striking increase in protein expression when transfected into COS-7 cells or HL-1 cardiomyocytes, due to reduced degradation by the ubiquitin-proteasome system (UPS). In functional assays, DNA binding activity of I184M was reduced, resulting in impaired activation of target genes, despite increased expression levels of mutant protein. Conclusions Certain NKX2-5 HD mutations show abnormal protein degradation via the UPS and partially impaired transcriptional activity. We propose that this class of mutation can impair heart development and mature heart function, and contribute to NKX2-5-related cardiomyopathies with graded severity.

The left/right (LR) axial pathway establishes asymmetry in the patterning and morphogenesis of multiple internal organs, including the heart. In mammals, this pathway involves the breaking of molecular symmetry in or around the node, transfer of asymmetry information to the lateral plate mesoderm (LPM), propagation of molecular asymmetries throughout the LPM, and interpretation of these signals for proper organ morphogenesis (Nonaka et al. 2002). Recent experiments have demonstrated that the breaking of bilateral symmetry in the mouse node occurs via a process termed "nodal flow," in which motile cilia in the node generate leftward movement of molecular determinants via lipoprotein vesicles (Hirokawa et al. 2006;. NODAL, a transforming growth factor ␤ (TGF␤) superfamily member, is a key molecule in the LR cascade. NODAL acts first in mesoderm specification and anterior-posterior axis formation, signaling through a membrane complex containing type I and II TGF␤ serine/ threonine kinase receptors, as well as GPI-anchored members of the EGF-CFC family. This complex phosphorylates intracellular SMAD2 and SMAD3, which associate with the common TGF␤/NODAL/BMP (bone morphogenetic protein) pathway SMAD, SMAD4, and forkhead transcription factor FOXH1, to regulate downstream target genes (Shen 2007). In the LR pathway,