Cardiovascular pathogenesis induced by angiotensin II (Ang-II) is a complex process often connected to oxidative stress. In the present study we show that, 4 h after addition, Ang-II induces a four- ...to fivefold increase in AP-1 activity in cultured neonatal rat cardiomyocytes and that the intracellular level of reactive oxygen species (ROS) correlates with the extent of AP-1 binding activity. Ang-II stimulated ROS generation in rat cardiomyocytes in a dose- and time-dependent manner. These effects of Ang-II were suppressed by the Ang-II receptor type I (AT
1) inhibitor CV-11974 as well as by the antioxidants diphenylene iodonium (DPI) and
N-acetyl-
l-cysteine (NAC), but not by AT
2 antagonist PD 122319. Furthermore, Ang-II induced a two- to threefold increase in protein synthesis and cell size during 12–24 h, which could be inhibited by CV-11974 as well as by DPI and NAC. Because the rat cardiomyocytes strongly expressed gp91
phox, this suggests that ROS generated in a gp91-containing NADPH oxidase are involved in signal transduction leading to AP-1 activation. Together, these findings indicate that Ang-II elicits the activation of the redox-sensitive AP-1 via ROS through AT
1, resulting in effects on cardiomyocyte function such as hypertrophy.
Tumor necrosis factor-α converting enzyme (TACE) is a membrane-anchored, Zn-dependent metalloprotease, which belongs to the ADAM (a disintegrin and metalloprotease) family. TACE functions as a ...membrane sheddase to release the ectodomain portions of many transmembrane proteins, including the precursors of TNFα, TGFα, several other cytokines, as well as the receptors for TNFα, and neuregulin (ErbB4). Mice with TACE
ΔZn/ΔZn null mutation die at birth with phenotypic changes, including failure of eyelid fusion, hair and skin defects, and abnormalities of lung development. Abnormal fetal heart development was not previously described. Herein, we report that TACE
ΔZn/ΔZn null mutant mice by late gestation exhibit markedly enlarged fetal hearts with increased myocardial trabeculation and reduced cell compaction, mimicking the pathological changes of noncompaction of ventricular myocardium. In addition, larger cardiomyocyte cell size and increased cell proliferation were observed in ventricles of TACE
ΔZn/ΔZn knockout mouse hearts. At the molecular level, reduced expression of epidermal growth factor receptor, attenuated protein cleavage of ErbB4, and changes in MAPK activation were also detected in TACE
ΔZn/ΔZn knockout heart tissues. The data suggest that TACE-mediated cell surface protein ectodomain shedding plays an essential and a novel regulatory role during cardiac development and modeling.
Activation of stress-activated mitogen-activated protein kinases (SAPKs), mainly c-Jun N-terminal kinase (JNK) and p38, have long been associated with different forms of cardiac pathology across a ...wide spectrum of species. However, their specific roles in the development of heart failure are still unclear. Previous studies in neonatal myocytes in culture suggest a critical role for both JNK and p38 in hypertrophy and apoptosis. A far more complex picture has been provided by recent observations from both cellular and transgenic models that have not only challenged their role in hypertrophy and cell death but have also pointed out novel functions of SAPKs in different aspects of cardiac pathology, including contractile function, extracellular matrix remodeling, intercellular communication, and metabolic regulation.
Abstract The cardiac renin–angiotensin system (RAS) has been implicated in mediating myocyte hypertrophy, remodeling, and fibroblast proliferation in the hemodynamically overloaded heart. However, ...the intracellular signaling mechanisms responsible for regulation of angiotensinogen (Ao), a substrate of the RAS system, are largely unknown. Here we report the identification of JNK1/2 as a negative, and p38α as a major positive regulator of Ao gene expression. Isolated neonatal rat ventricular myocytes (NRVM) and fibroblasts (NRFB) plated on deformable membranes coated with collagen IV, were exposed to 20% equiaxial static-stretch (0–24 h). Mechanical stretch initially depressed Ao gene expression (4 h), whereas after 8 h, Ao gene expression increased in a time-dependent manner. Blockade of JNK1/2 with SP600125 increased basal Ao gene expression in NRVM (10.52 ± 1.98 fold, P < 0.001) and NRFB (13.32 ± 2.07 fold, P < 0.001). Adenovirus-mediated expression of wild-type JNK1 significantly inhibited, whereas expression of dominant-negative JNK1 and JNK2 increased basal and stretch-mediated (24 h) Ao gene expression, showing both JNK1 and JNK2 to be negative regulators of Ao gene expression in NRVM and NRFB. Blockade of p38α/β by SB202190 or p38α by SB203580 significantly inhibited stretch-induced (24 h) Ao gene expression, whereas expression of wild-type p38α increased stretch-induced Ao gene expression in both NRVM (8.41 ± 1.50 fold, P < 0.001) and NRFB (3.39 ± 0.74 fold, P < 0.001). Conversely, expression of dominant-negative p38α significantly inhibited stretch response. Moreover, expression of constitutively active MKK6b (E) significantly stimulated Ao gene expression in the absence of stretch, indicating that p38 activation alone is sufficient to induce Ao gene expression. Taken together p38α was demonstrated to be a positive regulator, whereas JNK1/2 was found to be a negative regulator of Ao gene expression. Prolonged stretch diminished JNK1/2 activation, which was accompanied by a reciprocal increase in p38 activation and Ao gene expression. This suggests that a balance in JNK1/2 and p38α activation determines the level of Ao gene expression in myocardial cells.
Cardiac stress consistently activates c-Jun NH2-terminal kinase (JNK) pathways, however the role of different members of the JNK family is unclear. In this study, we applied pressure overload (TAC) ...in mice with selective deletion of the three JNK genes (Jnk1−/−, Jnk2−/−, and Jnk3−/−). Following TAC, all three JNK knockout mouse lines developed cardiac hypertrophy similar to wild-type mice (WT), but only JNK1−/− mice displayed a significant reduction in fractional shortening after 3 and 7 days of pressure overload, associated with a significant increase in terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling staining and marked inflammatory infiltrate. After the acute deterioration stage, JNK1−/− mice underwent a slow recovery followed by a steady progression of cardiac dysfunction, becoming indistinguishable from WT after 12 weeks of TAC. These data suggest that JNK1 plays a protective role in response to pressure overload, preventing the early deterioration in cardiac function following an acute increase in afterload.
Cell protection from stresses by the major heat shock protein Hsp72 was previously attributed to its ability to prevent aggregation and to accelerate refolding of damaged proteins. This repair ...function of Hsp72 may play an important role in cell survival after extremely harsh protein damaging treatments leading to necrotic cell death. On the other hand, protein repair function of Hsp72 cannot explain how it protects cells from stresses which do not cause direct protein damage, e.g. some genotoxic agents. These stresses kill cells through activation of apoptosis, and Hsp72 increases cell survival by interfering with the apoptotic program. Recently it has been found that Hsp72 mediates suppression of a stress-activated protein kinase, JNK, an early component of stress-induced apoptotic signalling pathway. This finding provides the basis for the anti-apoptotic activity of Hsp72. These observations can explain increased stress sensitivity of aged cells in which compromised inducibility of Hsp72 leads to a loss of control of JNK activation by stresses and subsequently to a higher rate of apoptotic death.
Cardiac hypertrophy is formed in response to hemodynamic overload. Although a variety of factors such as catecholamines, angiotensin II (AngII), and endothelin-1 (ET-1) have been reported to induce ...cardiac hypertrophy, little is known regarding the factors that inhibit the development of cardiac hypertrophy. Production of atrial natriuretic peptide (ANP) is increased in the hypertrophied heart and ANP has recently been reported to inhibit the growth of various cell types. We therefore examined whether ANP inhibits the development of cardiac hypertrophy. Pretreatment of cultured cardiomyocytes with ANP inhibited the AngII- or ET-1-induced increase in the cell size and the protein synthesis. ANP also inhibited the AngII- or ET-1-induced hypertrophic responses such as activation of mitogen-activated protein kinase (MAPK) and induction of immediate early response genes and fetal type genes. To determine how ANP inhibits cardiomyocyte hypertrophy, we examined the mechanism of ANP-induced suppression of the MAPK activation. ANP strongly induced expression of MAPK phosphatase-1 (MKP-1) and overexpression of
MKP-1 inhibited AngII- or ET-1-induced hypertrophic responses. These growth-inhibitory actions of ANP were mimicked by a cyclic GMP analog 8-bromo-cyclic GMP. Taken together, ANP directly inhibits the growth factor-induced cardiomyocyte hypertrophy at least partly via induction of MKP-1. Our present study suggests that the formation of cardiac hypertrophy is regulated not only by positive but by negative factors in response to hemodynamic load.
Mitogen-activated protein kinase kinase 7 (MKK7) induces cardiac hypertrophy by activating the c-Juns NH2-terminal kinases (JNK). It has been reported that growth arrest and DNA-damage-inducible beta ...(GADD45Β) binds to MKK7 directly and blocks its catalytic activity, mediates the inhibition of JNK signaling. However, the potential role of GADD45Β on cardiac hypertrophy has not been investigated. In this study, we found co-infection of cardiomyocytes with adenoviral vectors expressing MKK7 and GADD45B could counteract the characteristic hypertropic responses, including an increase in cell size and elevated atrial natriuretic factor (ANP) expression which induced by overexpression of MKK7. Furthermore, siRNA-mediated knockdown of GADD45B could also cause cardiomyocytes hypertrophy. GeneChip data showed that GADD45B mRNA decreased significantly in patients with hypertrophy cardiomyopathy (HCM) compared with healthy subjects. Association study indicated that haplotype (rs2024144–rs3783501) of GADD45B affected the thickness of inter-ventricular septum in patients with HCM. Dual-luciferase assay showed that C–A haplotype displayed significantly increased transcription activity compared to T–G haplotype.
LDL is the most abundant cholesterol transport vehicle in plasma and a major prognostic indicator of atherosclerosis. Hepatic LDL receptors limit circulating LDL levels, since cholesterol ...internalized by the liver can be excreted. As such, mechanisms regulating LDL receptor expression in liver cells are appealing targets for cholesterol-lowering therapeutic strategies. Activation of HepG2 cells with phorbol esters enhances LDL receptor mRNA levels through transcriptional and posttranscriptional mechanisms. Here, we show that 12-O-tetradecanoyl-phorbol-13-acetate (TPA)-induced stabilization of receptor mRNA requires the activity of protein kinase C and is accompanied by activation of the major mitogen activated protein kinase pathways. Inhibitor studies demonstrated that receptor mRNA stabilization is independent of the extracellular signal-regulated kinase or p38MAPK, but requires activation of the c-Jun N-terminal kinase (JNK). An essential role for JNK in stabilizing receptor mRNA was further confirmed through small interfering RNA (siRNA) experiments and by activating JNK through two protein kinase C-independent mechanisms. Finally, prolonged JNK activation increased steady-state levels of receptor mRNA and protein, and significantly enhanced cellular LDL-binding activity. These data suggest that JNK may play an important role in posttranscriptional control of LDL receptor expression, thus constituting a novel mechanism to enhance plasma LDL clearance by liver cells.
Background: The c-Jun N-terminal kinases (JNKs) are members of the mitogen-activated protein (MAP) kinase family, and regulate signal transduction in response to environmental stress. Activation and ...nuclear localization of JNK3, a neuronal-specific isoform of JNK, has been associated with hypoxic and ischemic damage of CA1 neurons in the hippocampus. Knockout mice lacking JNK3 showed reduced apoptosis of hippocampal neurons and reduced seizure induced by kainic acid, a glutamate-receptor agonist. Thus, JNK3 may be important in the pathology of neurological disorders and is of significant medical interest.
Results: We report here the structure of unphosphorylated JNK3 in complex with adenylyl imidodiphosphate, an ATP analog. JNK3 has a typical kinase fold, with the ATP-binding site situated within a cleft between the N- and C-terminal domains. In contrast to other known MAP kinase structures, the ATP-binding site of JNK3 is well ordered; the glycine-rich nucleotide-binding sequence forms a
β-strand–turn–
β-strand structure over the nucleotide. Unphosphorylated JNK3 assumes an open conformation, in which the N- and C-terminal domains are twisted apart relative to their positions in cAMP-dependent protein kinase. The rotation leads to the misalignment of some of the catalytic residues. The phosphorylation lip of JNK3 partially blocks the substrate-binding site.
Conclusions: This is the first JNK structure to be determined, providing a unique opportunity to compare structures from the three MAP kinase subfamilies. The structure reveals atomic-level details of the shape of JNK3 and the interactions between the kinase and the nucleotide. The misalignment of catalytic residues and occlusion of the active site by the phosphorylation lip may account for the low activity of unphosphorylated JNK3. The structure provides a framework for understanding the substrate specificity of different JNK isoforms, and should aid the design of selective JNK3 inhibitors.
