epidermal-growth-factor and Cardiomegaly

All ligands of the epidermal growth factor receptor (EGFR) which has important roles in development and disease, are shed from the plasma membrane by metalloproteases. The ectodomain shedding of EGFR ligands has emerged as a critical component in the functional activation of EGFR in the interreceptor cross-talk. Identification of the sheddases for EGFR ligands using mouse embryonic cells lacking candidate sheddases (a disintegrin and metalloprotease; ADAM) has revealed that ADAM10, -12 and -17 are the sheddases of the EGFR ligands in response to various shedding stimulants such as GPCR agonists, growth factors, cytokines, osmotic stress, wounding and phorbol ester. Among the EGFR ligands, heparin-binding EGF-like growth factor (HB-EGF) is a representative ligand to understand the pathophysiological roles of the ectodomain shedding in wound healing, cardiac diseases, etc. Here we focus on the ectodomain shedding of HB-EGF by ADAMs, which is not only a key event of receptor cross-talk but also a novel intercellular signaling by the carboxy-terminal fragment (CTF signal).

Topics: ADAM Proteins; ADAM12 Protein; ADAM17 Protein; Amyloid Precursor Protein Secretases; Animals; Aspartic Acid Endopeptidases; Cardiomegaly; Endopeptidases; Epidermal Growth Factor; ErbB Receptors; Heparin; Heparin-binding EGF-like Growth Factor; Humans; Intercellular Signaling Peptides and Proteins; Membrane Proteins; Metalloendopeptidases; Receptor Cross-Talk; Signal Transduction; Wound Healing

Heparin-binding EGF-like growth factor (HB-EGF), a member of the EGF family, is synthesized as a membrane-anchored precursor (proHB-EGF) that is cleaved to release a soluble HB-EGF by specific metalloproteases. Proteolytic cleavage of proHB-EGF yields amino- and carboxy-terminal fragments (HB-EGF and HB-EGF-C). Recent studies indicate that the processing of proHB-EGF is strictly regulated and involved in a variety of biological processes and that not only HB-EGF but also HB-EGF-C functions as a signaling molecule. ProHB-EGF generates dual intracellular signaling molecules by its proteolytic cleavage.

Topics: Animals; Cardiomegaly; Cell Membrane; Cytoplasm; Epidermal Growth Factor; Heparin; Heparin-binding EGF-like Growth Factor; Humans; Intercellular Signaling Peptides and Proteins; Models, Biological; Myocardium; Protein Structure, Tertiary; Signal Transduction; Submandibular Gland; Wound Healing

G-protein coupled receptor(GPCR) agonists are well-known inducers of cardiac hypertrophy. We found that the shedding of HB-EGF via metalloproteinase activation and subsequent transactivation of the epidermal growth factor receptor occurred when cardiomyocytes were stimulated by GPCR agonists, leading to cardiac hypertrophy. A new inhibitor of HB-EGF shedding, KB-R7785, blocked this signaling. We cloned a disintegrin and metalloprotease 12(ADAM12) as a specific enzyme to shed HB-EGF in the heart and found that dominant negative expression of ADAM12 abrogated this signaling. KB-R7785 bound directly to ADAM12, suggesting that inhibition of ADAM12 blocked the shedding of HB-EGF. In mice with cardiac hypertrophy, KB-R7785 inhibited the shedding of HB-EGF and attenuated hypertrophic changes. These data suggest that shedding of HB-EGF by ADAM12 plays an important role in cardiac hypertrophy, and that inhibition of HB-EGF shedding could be a potent therapeutic strategy for cardiac hypertrophy.

Topics: ADAM Proteins; ADAM12 Protein; Animals; Cardiomegaly; Depression, Chemical; Epidermal Growth Factor; ErbB Receptors; Glycine; Heparin-binding EGF-like Growth Factor; Humans; Hydroxamic Acids; Intercellular Signaling Peptides and Proteins; Membrane Proteins; Metalloendopeptidases; Mice; Protein Processing, Post-Translational; Signal Transduction; Transcriptional Activation

1. While the haemodynamic influences that cause cardiac hypertrophy are well known, the cellular and molecular mechanisms by which a mechanical stimulus is translated into a growth response by cardiac muscle have remained uncertain. 2. Current evidence suggests that a number of trophic factors may be released by cellular constituents of the heart, acting in an autocrine or paracrine manner to influence the growth response and phenotype of neighbouring cells. 3. Angiotensin II, acting via the AT1 receptor subtype, and both basic fibroblast growth factor and heparin-binding epidermal growth factor have been shown to exert hypertrophic actions in vivo and in vitro. Studies also indicate that cardiac myocytes themselves are capable of releasing all of these cytokines in response to increased mechanical load.

Topics: Angiotensin II; Animals; Cardiomegaly; Epidermal Growth Factor; Fibroblast Growth Factors; Heart; Heparin; Heparin-binding EGF-like Growth Factor; Intercellular Signaling Peptides and Proteins; Molecular Weight; Myocardium; Phenotype; Receptors, Angiotensin

Cardiac hypertrophy is an important risk factor for heart failure. Epidermal growth factor receptor (EGFR) has been found to play a role in the pathogenesis of various cardiovascular diseases. The aim of this current study was to examine the role of EGFR in angiotensin II (Ang II)-induced cardiac hypertrophy and identify the underlying molecular mechanisms. In this study, we observed that both Ang II and EGF could increase the phospohorylation of EGFR and protein kinase B (AKT)/extracellular signal-regulated kinase (ERK), and then induce cell hypertrophy in H9c2 cells. Both pharmacological inhibitors and genetic silencing significantly reduced Ang II-induced EGFR signalling pathway activation, hypertrophic marker overexpression, and cell hypertrophy. In addition, our results showed that Ang II-induced EGFR activation is mediated by c-Src phosphorylation. In vivo, Ang II treatment significantly led to cardiac remodelling including cardiac hypertrophy, disorganization and fibrosis, accompanied by the activation of EGFR signalling pathway in the heart tissues, while all these molecular and pathological alterations were attenuated by the oral administration with EGFR inhibitors. In conclusion, the c-Src-dependent EGFR activation may play an important role in Ang II-induced cardiac hypertrophy, and inhibition of EGFR by specific molecules may be an effective strategy for the treatment of Ang II-associated cardiac diseases.

Topics: Angiotensin II; Animals; Cardiomegaly; Cardiotonic Agents; Cell Line; Drug Evaluation, Preclinical; Epidermal Growth Factor; ErbB Receptors; Gene Knockdown Techniques; Mice, Inbred C57BL; Myocytes, Cardiac; Quinazolines; Rats; Tyrphostins

The tissue kallikrein-related peptidase family (KLK) is a group of trypsin- and chymotrypsin-like serine proteases that share a similar homology to parent tissue kallikrein (KLK1). KLK1 is identified in heart and has anti-hypertrophic effects. However, whether other KLK family members play a role in regulating cardiac function remains unknown. In the present study, we demonstrated for the first time that KLK8 was expressed in myocardium. KLK8 expression was upregulated in left ventricle of cardiac hypertrophy models. Both intra-cardiac adenovirus-mediated and transgenic-mediated KLK8 overexpression led to cardiac hypertrophy in vivo. In primary neonatal rat cardiomyocytes, KLK8 knockdown inhibited phenylephrine (PE)-induced cardiomyocyte hypertrophy, whereas KLK8 overexpression promoted cardiomyocyte hypertrophy via a serine protease activity-dependent but kinin receptor-independent pathway. KLK8 overexpression increased epidermal growth factor (EGF) production, which was blocked by the inhibitors of serine protease. EGF receptor (EGFR) antagonist and EGFR knockdown reversed the hypertrophy induced by KLK8 overexpression. KLK8-induced cardiomyocyte hypertrophy was also significantly decreased by blocking the protease-activated receptor 1 (PAR1) or PAR2 pathway. Our data suggest that KLK8 may promote cardiomyocyte hypertrophy through EGF signaling- and PARs-dependent but a kinin receptor-independent pathway. It is implied that different KLK family members can subtly regulate cardiac function and remodeling.

Topics: Animals; Cardiomegaly; Epidermal Growth Factor; ErbB Receptors; Gene Expression Regulation; Heart Ventricles; Humans; Kallikreins; Myocardium; Myocytes, Cardiac; Rats; Receptor, PAR-1; Receptor, PAR-2; Serine Endopeptidases; Signal Transduction; Transcriptional Activation

Urotensin II (UTII) and its seven trans-membrane receptor (UTR) are up-regulated in the heart under pathological conditions. Previous in vitro studies have shown that UTII trans-activates the epidermal growth factor receptor (EGFR), however, the role of such novel signalling pathway stimulated by UTII is currently unknown. In this study, we hypothesized that EGFR trans-activation by UTII might exert a protective effect in the overloaded heart. To test this hypothesis, we induced cardiac hypertrophy by transverse aortic constriction (TAC) in wild-type mice, and tested the effects of the UTII antagonist Urantide (UR) on cardiac function, structure, and EGFR trans-activation. After 7 days of pressure overload, UR treatment induced a rapid and significant impairment of cardiac function compared to vehicle. In UR-treated TAC mice, cardiac dysfunction was associated with reduced phosphorylation levels of the EGFR and extracellular-regulated kinase (ERK), increased apoptotic cell death and fibrosis. In vitro UTR stimulation induced membrane translocation of β-arrestin 1/2, EGFR phosphorylation/internalization, and ERK activation in HEK293 cells. Furthermore, UTII administration lowered apoptotic cell death induced by serum deprivation, as shown by reduced TUNEL/Annexin V staining and caspase 3 activation. Interestingly, UTII-mediated EGFR trans-activation could be prevented by UR treatment or knockdown of β-arrestin 1/2. Our data show, for the first time in vivo, a new UTR signalling pathway which is mediated by EGFR trans-activation, dependent by β-arrestin 1/2, promoting cell survival and cardioprotection.

Topics: Animals; Apoptosis; Arrestins; beta-Arrestin 1; beta-Arrestins; Blood Pressure; Cardiomegaly; Cells, Cultured; Epidermal Growth Factor; ErbB Receptors; Humans; Male; Mice; Mice, Inbred C57BL; Receptors, G-Protein-Coupled; Transcriptional Activation; Urotensins

Submandibular salivary glands are the major source of epidermal growth factor (EGF) in mice. Acute secretion of EGF from these glands protects the heart against catecholamine-induced injury. Little is known about chronic adrenergic stimulation of salivary glands and the contribution of accumulated EGF to the adaptive hypertrophic response of the heart to such chronic adrenergic stimulation. Here we show that the EGF content of submandibular glands did not recover to normal values 24 h after a single phenylephrine injection or an aggressive encounter. Repeated (twice a day for 2 days) adrenergic stimulation resulted in an almost 90% decrease in EGF content in the submandibular glands. In these conditions, new adrenergic stimulation did not result in an increase in plasma EGF concentration, or in the activation of liver ErbB1 (the EGF receptor). Chronic isoproterenol or phenylephrine administration (7 days) induced atrial natriuretic factor expression in the heart and an increase in both ventricular weight and protein. The surgical removal of submandibular glands (sialoadenectomy) did not affect these adaptive responses of the heart. We conclude that EGF from submandibular glands does not contribute to heart hypertrophy, one of the adaptive responses induced by chronic adrenergic stimulation.

Topics: Adrenergic alpha-Agonists; Animals; Atrial Natriuretic Factor; Cardiomegaly; Epidermal Growth Factor; Heart; Isoproterenol; Male; Mice; Myocardium; Organ Size; Phenylephrine; Submandibular Gland

Epidermal growth factor (EGF) and ErbB family molecules play a role in heart development and function. To investigate the role of EGF family member, heparin-binding EGF-like growth factor (HB-EGF) in heart development, smooth muscle and endothelial cell lineage-specific HB-EGF knockout mice were generated using the Cre/loxP system in combination with the SM22alpha or TIE2 promoter. HB-EGF knockout mice displayed enlarged heart valves, and over half of these mice died during the first postnatal week, while survivors showed cardiac hypertrophy. These results suggest that expression of HB-EGF in smooth muscle and/or endothelial cell lineages is essential for proper heart development and function in mice.

Topics: Animals; Cardiomegaly; Cell Lineage; Endothelial Cells; Epidermal Growth Factor; Genes, Lethal; Heart; Heart Valves; Heparin-binding EGF-like Growth Factor; Intercellular Signaling Peptides and Proteins; Mice; Mice, Knockout; Muscle, Smooth; Myocardium

Cardiac hypertrophy is a complex and nonhomogenous response to various stimuli. In this study, we used high-density oligonucleotide microarray to examine gene expression profiles during physiological hypertrophy, pathological hypertrophy, and heart failure in Dahl salt-sensitive rats. There were changes in 404/3,160 and 874/3,160 genes between physiological and pathological hypertrophy and the transition from hypertrophy to heart failure, respectively. There were increases in stress response genes (e.g., heat shock proteins) and inflammation-related genes (e.g., pancreatitis-associated protein and arachidonate 12-lipoxygenase) in pathological processes but not in physiological hypertrophy. Furthermore, atrial natriuretic factor and brain natriuretic protein showed distinctive changes that are very specific to different conditions. In addition, we used a resampling-based gene score-calculating method to define significantly altered gene clusters, based on Gene Ontology classification. It revealed significant alterations in genes involved in the apoptosis pathway during pathological hypertrophy, suggesting that the apoptosis pathway may play a role during the transition to heart failure. In addition, there were significant changes in glucose/insulin signaling, protein biosynthesis, and epidermal growth factor signaling during physiological hypertrophy but not during pathological hypertrophy.

Topics: Animals; Apoptosis; Atrial Natriuretic Factor; Blotting, Northern; Cardiomegaly; Echocardiography; Epidermal Growth Factor; Gene Expression Profiling; Gene Expression Regulation; Heart Failure; Hypertrophy; Inflammation; Insulin; Natriuretic Peptide, Brain; Oligonucleotide Array Sequence Analysis; Pancreatitis-Associated Proteins; Physical Conditioning, Animal; Rats; Rats, Inbred Dahl; RNA; Signal Transduction

The effects of long-acting calcium channel blockers on pressure overload-induced cardiac hypertrophy have been little studied in experimental animals and the underlying mechanisms are not fully understood. We previously reported that cardiomyocyte hypertrophy could be induced via phosphorylation of the epidermal growth factor receptor (EGFR). In this study, we investigated whether amlodipine attenuates cardiac hypertrophy by inhibiting EGFR phosphorylation. We found that amlodipine dose-dependently inhibited epinephrine-induced protein synthesis and EGFR phosphorylation in cultured neonatal rat cardiomyocytes. Our in vivo study revealed that amlodipine could ameliorate myocardial hypertrophy induced by transverse aortic constriction (TAC) in C57/B6 mice. One week after TAC, amlodipine treatment (3 mg/kg/day) significantly reduced the heart-to-body weight ratio (6.04 +/- 0.16 mg/g vs. 6.90 +/- 0.45 mg/g in untreated TAC mice, P < 0.01). These results indicate that amlodipine ameliorates cardiomyocyte hypertrophy via inhibition of EGFR phosphorylation.

Topics: Amlodipine; Animals; Cardiomegaly; Cells, Cultured; Epidermal Growth Factor; Epinephrine; ErbB Receptors; Heparin; Male; Mice; Myocardium; Phosphorylation; Phosphotyrosine; Protein Biosynthesis; Rats

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a potent mitogen for smooth muscle cells and has been implicated in atherosclerosis, tissue regeneration after ischemia, vascular development, and tumor angiogenesis. We examined the hypothesis that HB-EGF participates in angiogenesis and collateral growth in ischemia.. During 3 weeks after femoral artery ligation, no attenuation occurred in recovery of hindlimb perfusion or distal saphenous artery flow in HB-EGF-null (HB-EGF(-/-)) versus wild-type mice. Lumen diameters of remodeled collaterals in gracilis muscle were similar by morphometry (87+/-8 versus 94+/-6 microm) and angiography, although medial thickening was reduced. Gastrocnemius muscle underwent comparable angiogenesis (41% and 33% increase in capillary-to-muscle fiber ratio). Renal renin mRNA, arterial pressure, and heart rate during anesthesia or conscious unrestrained conditions were similar between groups. These latter findings validate comparisons of perfusion data and also suggest that differences in arterial pressure and/or renin-angiotensin activity are not masking an otherwise inhibitory effect of HB-EGF absence. Four days after ligation, EGF receptor phosphorylation increased in muscle by 104% in wild-type but by only 30% in HB-EGF(-/-) mice. This argues against compensation by other EGF receptor ligands.. Our results suggest that HB-EGF is not required for arteriogenesis or angiogenesis in hindlimb ischemia.

Topics: Animals; Cardiomegaly; Epidermal Growth Factor; ErbB Receptors; Femoral Artery; Heparin-binding EGF-like Growth Factor; Hindlimb; Intercellular Signaling Peptides and Proteins; Ischemia; Ligation; Mice; Mice, Mutant Strains; Muscle, Skeletal; Neovascularization, Physiologic; Phenotype; Phosphorylation

The epidermal growth factor receptor (EGFR) and ectoshedding of heparin-binding epidermal growth factor (HBEGF), an EGFR ligand, have been linked to the development of cardiac myocyte hypertrophy. However, the precise role that the liganded EGFR plays in the transcriptional activation of the gene program that accompanies hypertrophy remains undefined. Utilizing the human (h) BNP gene as a model of hypertrophy-dependent gene activation, we show that activation of the EGFR plays an important role in mediating mechanical strain-dependent stimulation of the hBNP promoter. Strain promotes endothelin (ET) generation through NAD(P)H oxidase-dependent production of reactive oxygen species. ET in turn induces metalloproteinase-mediated cleavage of pro-HBEGF and ectoshedding of HBEGF, which activates the EGFR and stimulates hBNP promoter activity. HBEGF also stimulates other phenotypic markers of hypertrophy including protein synthesis and sarcomeric assembly. The antioxidant N-acetylcysteine or the NAD(P)H oxidase inhibitor, apocynin, inhibited strain-dependent activation of the ET-1 promoter, HBEGF shedding, and hBNP promoter activation. The metalloproteinase inhibitor, GM-6001, prevented the induction of HBEGF ectoshedding and the hBNP promoter response to strain, suggesting a critical role for the metalloproteinase-dependent cleavage event in signaling the strain response. These findings suggest that metalloproteinase activity as an essential step in this pathway may prove to be a relevant therapeutic target in the management of cardiac hypertrophy.

Topics: Animals; Cardiomegaly; Epidermal Growth Factor; ErbB Receptors; Gene Expression Regulation; MAP Kinase Signaling System; Mitogen-Activated Protein Kinases; Natriuretic Peptide, Brain; Rats; Signal Transduction; Stress, Mechanical; Transcriptional Activation

Smooth muscle cells (SMC) of the bladder undergo hypertrophy and hyperplasia following exposure to sustained mechanical overload. Although superficial similarities in the response of the heart and bladder to hypertrophic stimuli suggest that similar molecular mechanisms may be involved, this remains to be demonstrated. In this study we compared signal transduction pathway activation in primary culture bladder SMC and cardiac myofibroblasts in response to cyclic stretch. The effects of growth factor stimulation on pathway activation in bladder SMC were also investigated.. Primary culture rodent bladder SMC or cardiac myofibroblasts were subjected to cyclic stretch-relaxation in the absence or presence of pharmacologic inhibitors of the phosphoinositide-3-kinase, (PI3K)/Akt, extracellular signal-regulated kinase-mitogen activated protein kinase (Erk-MAPK) or the p38 stress-activated protein kinase-2 (SAPK2) pathways. In parallel experiments human bladder SMC were treated with platelet-derived growth factor-BB (PDGF-BB), heparin-binding EGF-like growth factor (HB-EGF) or fibroblast growth factor-2 (FGF-2). In each case the extent of DNA synthesis was determined by uptake of tritiated thymidine, and activation of specific signaling intermediates was determined by immunoblot analysis using antibodies to the non-phosphorylated and phosphorylated (activated) forms of Akt, p38 and Erk1/2.. Akt and p38 were rapidly phosphorylated in stretched bladder SMC and cardiac myofibroblasts, and stretch-induced DNA synthesis in these cells was ablated with inhibitors of PI3K or p38 but not Erk-MAPK. Similarly, PDGF-BB up-regulated DNA synthesis in bladder SMC in a p38 and Akt-dependent manner.. We conclude that distinct stimuli, such as mechanical stretch and PDGF-BB, promote DNA synthesis in bladder SMC through shared downstream signaling pathways. Furthermore, phenotypically similar cells from the bladder and heart show comparable pathway activation in response to stretch. These findings suggest that similar molecular mechanisms underlie the altered growth responses of the bladder and heart to mechanical overload. This study also provides the first report of Akt activation in bladder SMC and suggests that Akt, consistent with its pivotal role in cardiac hypertrophy, may also be a key regulator of remodeling in the SMC compartment of the bladder exposed to hypertrophic/hyperplastic stimuli in vivo.

Topics: Animals; Becaplermin; Cardiomegaly; Cells, Cultured; DNA; Enzyme Activation; Enzyme Inhibitors; Epidermal Growth Factor; Fibroblast Growth Factor 2; Heparin-binding EGF-like Growth Factor; Hypertrophy; Intercellular Signaling Peptides and Proteins; Mitogen-Activated Protein Kinases; Muscle, Smooth; Myocardium; p38 Mitogen-Activated Protein Kinases; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Platelet-Derived Growth Factor; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; Proto-Oncogene Proteins c-sis; Rats; Signal Transduction; Stress, Mechanical; Up-Regulation; Urinary Bladder

Topics: ADAM Proteins; ADAM12 Protein; Cardiomegaly; Disintegrins; Epidermal Growth Factor; GTP-Binding Proteins; Heparin-binding EGF-like Growth Factor; Intercellular Signaling Peptides and Proteins; Membrane Proteins; Metalloendopeptidases; Receptors, Cell Surface; Signal Transduction

G-protein-coupled receptor (GPCR) agonists are well-known inducers of cardiac hypertrophy. We found that the shedding of heparin-binding epidermal growth factor (HB-EGF) resulting from metalloproteinase activation and subsequent transactivation of the epidermal growth factor receptor occurred when cardiomyocytes were stimulated by GPCR agonists, leading to cardiac hypertrophy. A new inhibitor of HB-EGF shedding, KB-R7785, blocked this signaling. We cloned a disintegrin and metalloprotease 12 (ADAM12) as a specific enzyme to shed HB-EGF in the heart and found that dominant-negative expression of ADAM12 abrogated this signaling. KB-R7785 bound directly to ADAM12, suggesting that inhibition of ADAM12 blocked the shedding of HB-EGF. In mice with cardiac hypertrophy, KB-R7785 inhibited the shedding of HB-EGF and attenuated hypertrophic changes. These data suggest that shedding of HB-EGF by ADAM12 plays an important role in cardiac hypertrophy, and that inhibition of HB-EGF shedding could be a potent therapeutic strategy for cardiac hypertrophy.

Topics: ADAM Proteins; ADAM12 Protein; Angiotensin II; Animals; Aorta, Thoracic; Cardiomegaly; Disease Models, Animal; Disintegrins; Epidermal Growth Factor; ErbB Receptors; Glycine; GTP-Binding Proteins; Heart Ventricles; Heparin-binding EGF-like Growth Factor; Hydroxamic Acids; Hypertension; Intercellular Signaling Peptides and Proteins; Male; Membrane Proteins; Metalloendopeptidases; Phenylephrine; Protease Inhibitors; Protein Processing, Post-Translational; Rats; Signal Transduction; Systole; Transcriptional Activation

Epidermal growth factor (EGF) was tested for its ability to promote hypertrophic responses in neonatal rat ventricular cardiomyocytes. Exposure of these cells to 100 n m EGF for 2-18 h resulted in a time-dependent increase in protein synthesis reaching 174+/-18% of control values at 18 h. After 30 min stimulation, the mRNA levels of c-jun and c-fos were also increased 20- and 36-fold, respectively. We also investigated EGF-induced activation of Stat (signal transducers and activators of transcription) proteins as well as the possible interactions of this signaling pathway with the p38 and p42/44 MAP kinases cascades. EGF did not activate Stat1 and Stat3, but did induce a rapid and transient activation of Stat5, which corresponded mainly to Stat5b DNA-binding. The EGF-promoted Stat5 DNA-binding was decreased in a concentration-dependent manner by the p38 MAPK inhibitor SB 203580 (IC(50)=1.2 microm), whereas it was tripled by 50 micro m PD 98059, an inhibitor of the p42/44 MAPK cascade. This is the first demonstration that EGF increases protein synthesis and early response gene expression in cardiomyocytes, responses considered as markers of hypertrophy in these cells. The results further show that EGF activates Stat5, that this response requires p38 MAPK stimulation, and it is negatively modulated by p42/44 MAPK.

Topics: Animals; Cardiomegaly; Cells, Cultured; DNA-Binding Proteins; Epidermal Growth Factor; ErbB Receptors; Heart Ventricles; Milk Proteins; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; p38 Mitogen-Activated Protein Kinases; Phosphorylation; Protein Biosynthesis; Proto-Oncogene Proteins c-fos; Proto-Oncogene Proteins c-jun; Rats; Rats, Wistar; STAT1 Transcription Factor; STAT3 Transcription Factor; STAT5 Transcription Factor; Trans-Activators

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a recently characterized member of the EGF family of peptide signaling factors that acts as an early response gene to growth stimuli in vascular smooth muscle cells, as well as being a potent mitogen for these cells. As many of these growth stimuli also induce a hypertrophic response in heart muscle, we examined the regulation of HB-EGF mRNA abundance and function in primary cultures of neonatal rat ventricular myocytes and adult rat ventricular myocytes (ARVM). HB-EGF mRNA levels increased 40- and 6-fold in neonatal rat ventricular myocytes and ARVM, respectively, following a 2-4-h exposure to the alpha-adrenergic agonist phenylephrine, a known hypertrophic stimulus for these cells. Phenylephrine had no effect on HB-EGF mRNA stability, and induction of HB-EGF could be blocked completely by actinomycin D. HB-EGF mRNA abundance was also increased 15-fold in ARVM maintained in defined medium that had been induced to contract at 3 Hz by continual uniform electric field stimulation, a mechanical stimulus that we have shown preserves contractile function and induces cell growth in vitro. To determine whether cardiac myocytes would respond to exogenous HB-EGF, quiescent ARVM were exposed to defined medium conditioned by transfected COS MT cells overexpressing HB-EGF. These myocytes exhibited nearly a 2-fold increase in protein content at 24 h compared with unstimulated control ARVM exposed to medium conditioned by COS cells transfected with the plasmid vector alone. Thus, neonatal and adult cardiac muscle cells respond to both neurohumoral and mechanical growth stimuli with a marked increase in HB-EGF mRNA, which may act as an early response gene to facilitate hypertrophic growth in these cells.

Topics: Age Factors; Animals; Animals, Newborn; Cardiomegaly; Cells, Cultured; Dactinomycin; Epidermal Growth Factor; Heart; Heart Ventricles; Heparin-binding EGF-like Growth Factor; Intercellular Signaling Peptides and Proteins; Male; Myocardium; Phenylephrine; Physical Stimulation; Rats; Rats, Sprague-Dawley; RNA, Messenger