An important event in the pathogenesis of heart failure is the development of pathological cardiac hypertrophy. In cultured cardiomyocytes, the transcription factor Gata4 is required for agonist-induced hypertrophy. We hypothesized that, in the intact organism, Gata4 is an important regulator of postnatal heart function and of the hypertrophic response of the heart to pathological stress. To test this hypothesis, we studied mice heterozygous for deletion of the second exon of Gata4 (G4D). At baseline, G4D mice had mild systolic and diastolic dysfunction associated with reduced heart weight and decreased cardiomyocyte number. After transverse aortic constriction (TAC), G4D mice developed overt heart failure and eccentric cardiac hypertrophy, associated with significantly increased fibrosis and cardiomyocyte apoptosis. Inhibition of apoptosis by overexpression of the insulin-like growth factor 1 receptor prevented TAC-induced heart failure in G4D mice. Unlike WT-TAC controls, G4D-TAC cardiomyocytes hypertrophied by increasing in length more than width. Gene expression profiling revealed up-regulation of genes associated with apoptosis and fibrosis, including members of the TGF-␤ pathway. Our data demonstrate that Gata4 is essential for cardiac function in the postnatal heart. After pressure overload, Gata4 regulates the pattern of cardiomyocyte hypertrophy and protects the heart from load-induced failure.apoptosis ͉ hypertrophy ͉ fibrosis ͉ gene expression ͉ Igf-1 H eart failure is one of the leading causes of morbidity and mortality in industrialized countries (1). An important event in the pathogenesis of heart failure is the development of pathological cardiac hypertrophy (2). This is characterized by increased cardiomyocyte size, increased protein synthesis, and altered gene expression. Over time, the changes in gene expression can be maladaptive and contribute to progression of heart failure (3).A large body of evidence suggests that the transcription factor Gata4 is an important regulator of cardiomyocyte hypertrophy (4, 5). Gata4 has been implicated in the regulation of an array of cardiac genes in response to hypertrophic agonists, including atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), skeletal ␣-actin, ␣-myosin heavy chain (␣-MHC), and ␤-myosin heavy chain (␤-MHC) (4, 5). Gata4 overexpression is sufficient to induce the hypertrophic response in cultured neonatal cardiomyocytes and transgenic mice (6). Moreover, the hypertrophic response of cultured neonatal rat cardiomyocytes requires Gata4 (6, 7).We sought to investigate the in vivo role of Gata4 in regulating postnatal heart function and the response to hypertrophic stress. Traditional loss-of-function approaches have been complicated by early embryonic lethality in Gata4 null embryos (8, 9). In our hands, embryos with embryonic cardiac-restricted Gata4 inactivation also suffered from fetal demise (10). These embryos died from heart failure, and the mutant hearts were characterized by marked myocardial hypoplasia due to decreased ca...

No abstract

Using the plasminogen activator inhibitor (PAI) promoter to drive the expression of a reporter gene (mouse CD2), we devised a system to clone negative regulators of the transforming growth factor-␤ (TGF-␤) signaling pathway. We infected a TGF-␤-responsive cell line (MvLu1) with a retroviral cDNA library, selecting by fluorescence-activated cell sorter single cells displaying low PAI promoter activity in response to TGF-␤. Using this strategy we cloned the proto-oncogene brain factor-1 (BF-1). BF-1 represses the PAI promoter in part by associating with both unphosphorylated Smad3 (in the cytoplasm) and phosphorylated Smad3 (in the nucleus), thus preventing its binding to DNA. BF-1 also associates with Smad1, -2, and -4; the Smad MH2 domain binds to BF-1, and the C-terminal segment of BF-1 is uniquely and solely required for binding to Smads. Further, BF-1 represses another TGF-␤-induced promoter (p15), it upregulates a TGF-␤-repressed promoter (Cyclin A), and it reverses the growth arrest caused by TGF-␤. Our results suggest that BF-1 is a general inhibitor of TGF-␤ signaling and as such may play a key role during brain development. Transforming growth factor-␤ (TGF-␤)1 signals through a series of events that includes transphosphorylation and activation of the TGF-␤ type I receptor (T␤-RI) by the TGF-␤ type II receptor (T␤-RII) and phosphorylation of Smad3 by the T␤-RI, followed by the assembly and nuclear translocation of a Smad3/ Smad4 complex (1, 2-7). This process results in the transcriptional regulation of genes required in development and extracellular matrix production (i.e. up-regulation of extracellular matrix genes) as well as of genes involved in cell cycle regulation (i.e. up-regulation of the cell cycle inhibitor p15) (8 -12).The importance of TGF-␤ in tumorigenesis is underscored by the finding in a variety of cancers of inactivating mutations and a loss of heterozygosity affecting genes involved in the TGF-␤ signaling cascade (13-17). More recently, several laboratories have reported a group of known oncoproteins that repress Smad3-dependent transcription (18, 19 -22). Here we report the use of a novel retroviral functional cloning system to clone the brain factor 1 (BF-1) cDNA as a functional antagonist of TGF-␤ signaling.Recently, Dou et al. (23) also showed that BF-1 expression inhibits TGF-␤ signaling. Although several of their results are similar to ours (BF-1 expression causes resistance to TGF-␤-mediated growth inhibition and reverses TGF-␤-induced transcriptional activation), we differ on one crucial point. Dou et al. could not detect interactions between any Smad proteins and BF-1, and they claim that BF-1 exerts its inhibitory effects by binding with the transcriptional coactivator FAST-2. In contrast, we show that BF-1 inhibits TGF-␤-induced gene activation in part by associating with unphosphorylated Smad3 in the cytoplasm. BF-1 does not affect Smad phosphorylation induced by TGF-␤ binding to its receptor, but it does prevent Smad binding to DNA by associating with phosphorylated Smad...

Transperineal US has increased in use in the last decade. It is helpful in the evaluation of distal genitourinary structures, the rectum and overlying soft tissues. When used in conjunction with transabdominal US, transperineal US can further delineate anatomy and assess abnormalities that affect the lower pelvis. This paper describes optimal technique and common indications for transperineal US in children with examples of congenital and acquired lesions in pediatric patients.