MAPK信号途径在一氧化氮抑制大鼠心肌肥大中的作用

实验观察了一氧化氮（NO）前体L－精氨酸对肾性高血压大鼠心肌组织eNOS蛋白表达及亚硝酸盐／硝酸盐含量、MKP－1蛋白表达及MAPK活性的影响,以及与心肌肥厚的关系,采用两肾一夹Goldblatt肾性高血压模型,随机分为5组：L－精氨酸高、中、低剂量组,分别于术后第5周给予L－精氨酸50、150及450mg/kg;L－NAME组,腹腔注射L－NAME 10mg/kg,同时给予L－精氨酸150mg/kg;高血压对照组,正常饮水,以及另设的一假手术对照组。用药8周后,用插管法测量大鼠动脉血压、左心室重与体重比值,用胶内原位磷酸化法测MFAPK活性、免疫印迹法检测心肌组织eNOS及MKP－1蛋白表达、酶还原法测定心肌组织亚硝酸盐／硝酸盐－硝酸盐含量。结果表明：（1）L－精氨酸可明显抑制肾动脉狭窄术后的血压升高、左心室重与体重比增加,增加心肌组织eNOS、MKP-1蛋白表达及亚硝酸盐－硝酸盐含量,降低心肌组织MAPK活性,其中以150mg/kg组作用最为明显;（2）NOS抑制剂L－NAME可明显抑制－精氨酸的以上作用,肾性高血压大鼠心肌组织eNOS蛋白表达下降。NO生成减少及MKP－1蛋白表达下降以及MAPK活性增强可能与高血压及心肌厚形成有关,L－精氨酸通过促进心肌组织eNOS蛋白表达、增加NO产生和MKP－1表达、减弱MAPK活性而发挥抗高血压及心肌肥厚的作用。     

Long-term activation of adenosine monophosphate-activated protein kinase attenuates pressure-overload-induced cardiac hypertrophy

Recent in vitro studies suggest that adenosine monophosphate (AMP)-activated protein kinase (AMPK) exerts inhibitory effects on cardiac hypertrophy. However, it is unclear whether long-term activation of AMPK will affect cardiac hypertrophy in vivo. In these reports, we investigate the in vivo effects of long-term AMPK activation on cardiac hypertrophy and the related molecular mechanisms. To examine the effects of AMPK activation in the development of pressure overload-induced cardiac hypertrophy, we administered 5-aminoimidazole 1 carboxamide ribonucleoside (AICAR, 0.5 mg/g body wt), a specific activator of AMPK, to rats with transaortic constriction (TAC) for 7 weeks. We found that long-term AMPK activation attenuated cardiac hypertrophy, and improved cardiac function in rats subjected to TAC. Furthermore, long-term AMPK activation attenuated protein synthesis, diminished calcineurin-nuclear factor of activated T cells (NFAT) and nuclear factor kappaB (NF-kappaB) signaling in pressure overload-induced hypertrophic hearts. Our in vitro experiments further proved that activation of AMPK by infection of AdAMPK blocked cardiac hypertrophy and NFAT, NF-kappaB, and MAPK signal pathways. The present study demonstrates for the first time that pharmacological activation of AMPK inhibits cardiac hypertrophy in through blocking signaling transduction pathways that are involved in cardiac growth. It presents a potential therapy strategy to inhibit pathological cardiac hypertrophy by increasing the activity of AMPK.     

自发性高血压大鼠心肌肥厚和心肌MAPK、AngⅡ的关系

放免法测定自发性高血压大鼠（ＳＨＲ）血浆及心肌血管紧张素Ⅱ（ＡｎｇⅡ）含量,凝胶内磷酸化法测定心肌丝裂素活化蛋白激酶活性（ＭＡＰＫ）,以心脏重／体重表示心肌肥厚程度。结果表明：与４个月的ＷＫＹ大鼠比较,４个月的ＳＨＲ血浆和心肌组织ＡｎｇⅡ及心肌ＭＡＰＫ活性分别增加了２１８．６％、１０１．２％和１０７．０％,心肌肥大程度严重,其中ＭＡＰＫ活性与心肌肥大程度呈明显正相关。提示４个月ＳＨＲ心肌肥厚可能是     

Resveratrol prevents hypertension and cardiac hypertrophy in hypertensive rats and mice

Resveratrol (RESV) is a polyphenol with pleiotropic effects that include reduction of oxidative stress and increased vascular nitric oxide (NO) production. However, whether or not RESV can prevent rises in blood pressure (BP) is controversial and remains to be firmly established. The purpose of this study was to determine whether RESV attenuates elevated BP and subsequent adaptive cardiac hypertrophy and to better understand the mechanisms involved. The spontaneously hypertensive rat (SHR) and the angiotensin (Ang)-II infused mouse were used as hypertensive models. Compared to a standard control diet, consumption of diets containing RESV by SHRs and Ang-II hypertensive mice, markedly prevented rises in systolic BP. In addition, flow-mediated vasodilation was significantly improved by RESV in SHRs. RESV also reduced serum and cardiac levels of the lipid peroxidation by-product, 4-hydroxy-2-nonenal in the hypertensive rodents and inhibited the production of superoxide in human-derived endothelial cells. Analysis of mesenteric arteries from SHRs and Ang-II infused mice demonstrated that RESV increased endothelial NO synthase (eNOS) phosphorylation by enhancing the LKB1/adenosine monophosphate (AMP)-activated protein kinase (AMPK) signal transduction pathway. Moreover, RESV reduced hypertrophic growth of the myocardium through reduced hemodynamic load and inhibition of the p70 S6 kinase pro-hypertrophic signaling cascade. Overall, we show that high dose RESV reduces oxidative stress, improves vascular function, attenuates high BP and prevents cardiac hypertrophy through the preservation of the LKB1–AMPK–eNOS signaling axis.     

Sodium restriction prevents cardiac hypertrophy and oxidative stress in angiotensin II hypertension

The influence of a low-sodium (LS) diet was assessed on the cardiac and renal alterations and pro-oxidant effect associated with a 10-day infusion of angiotensin II (200 or 400 ng. kg(-1). min(-1), osmotic pumps). Tail-cuff pressure (TCP), albuminuria, and renal blood flow were determined at the end of the experiments. Heart weight index (HWI) and production of superoxide anion (O(2)(-).) by the left ventricle and H(2)O(2) by the aorta was measured with the use of bioluminescence. Although the final TCP was similar in LS and normal sodium (NS) rats infused with high and low doses of angiotensin II, respectively, the increase in HWI was prevented by the LS diet. Sodium restriction reduced the rise in albuminuria without a change in the renal effect of angiotensin II. The increased production of O(2)(-). and H(2)O(2) observed in NS rats was abrogated in LS rats. The beneficial influence of dietary sodium restriction on target organ damage induced by angiotensin II is independent of arterial pressure reduction and possibly related to attenuation of the prooxidant effect of the peptide.     

Pyruvate prevents cardiac dysfunction and AMP-activated protein kinase activation by hydrogen peroxide in isolated rat hearts

Ischemia-reperfusion injury in the heart results in enhanced production of H2O2 and activation of AMP-activated protein kinase (AMPK). Since mutations in AMPK result in cardiovascular dysfunction, we investigated whether the activation of AMPK mediates the H2O2-induced reduction in cardiac mechanical function. Isolated working rat hearts were perfused at 37 degrees C with Krebs-Henseleit solution. Following a 20-minute equilibration period, a single bolus of H2O2 (300 micromol/L) was added and the hearts were perfused for an additional 5 min. H2O2 induced a dramatic and progressive reduction in cardiac function. This was accompanied by rapid and significant activation of AMPK, an increase in Thr-172 phosphorylation of AMPK, and an increase in the creatine to phosphocreatine (Cr/PCr) ratio. Addition of pyruvate (5 mmol/L) to the perfusate prevented the H2O2-mediated reduction in cardiac mechanical dysfunction, activation of myocardial AMPK activity, increase in AMPK phosphorylation and the increase in the Cr/PCr ratio. Hearts challenged with H2O2 (300 micromol/L) in presence of either AMPK inhibitor Compound C (10 micromol/L) or its vehicle (dimethyl sulfoxide (DMSO), 0.1%) showed reduced impairment in cardiac mechanical function. Compound C but not its vehicle significantly inhibited myocardial AMPK activity. Thus, H2O2 induces cardiac dysfunction via both AMPK-dependent and independent mechanisms.     

Calcineurin promotes protein kinase C and c-Jun NH2-terminal kinase activation in the heart. Cross-talk between cardiac hypertrophic signaling pathways

Multiple intracellular signaling pathways have been shown to regulate the hypertrophic growth of cardiomyocytes. Both necessary and sufficient roles have been described for the mitogen activated protein kinase(1) (MAPK) signaling pathway, specific protein kinase C (PKC) isoforms, and calcineurin. Here we investigate the interdependence between calcineurin, MAPK, and PKC isoforms in regulating cardiomyocyte hypertrophy using three separate approaches. Hearts from hypertrophic calcineurin transgenic mice were characterized for PKC and MAPK activation. Transgenic hearts demonstrated activation of c-Jun NH(2)-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK1/2), but not p38 MAPK factors. Calcineurin transgenic hearts demonstrated increased activation of PKCalpha, beta(1), and theta, but not of epsilon, beta(2), or lambda. In a second approach, cultured cardiomyocytes were infected with a calcineurin adenovirus to induce hypertrophy and the effects of pharmacologic inhibitors or co-infection with a dominant negative adenovirus were examined. Calcineurin-mediated hypertrophy was prevented with PKC inhibitors, Ca(2+) chelation, and attenuated with a dominant negative SEK-1 (MKK4) adenovirus, but inhibitors of ERK or p38 activation had no effect. In a third approach, we examined the activation of MAPK factors and PKC isoforms during the progression of load-induced hypertrophy in aortic banded rats with or without cyclosporine. We determined that inhibition of calcineurin activity with cyclosporine prevented PKCalpha, theta, and JNK activation, but did not affect PKCepsilon, beta, lambda, ERK1/2, or p38 activation. Collectively, these data indicate that calcineurin hypertrophic signaling is interconnected with PKCalpha, theta, and JNK in the heart, while PKCepsilon, beta, lambda, p38, and ERK1/2 are not involved in calcineurin-mediated hypertrophy.     

Muscarinic activation of mitogen-activated protein kinase in PC12 cells

Muscarinic acetylcholine receptors (mAChRs) activate many downstream signaling pathways, some of which can lead to mitogen-activated protein kinase (MAPK) phosphorylation and activation. MAPKs play roles in regulating cell growth, differentiation, and synaptic plasticity. Here, the activation of MAPK was examined in PC12 cells endogenously expressing mAChRs. Western blot analysis using a phosphospecific MAPK antibody revealed a dose-dependent and atropine-sensitive increase in MAPK phosphorylation in cells stimulated with carbachol (CCh). The maximal response occurred after 5 min and was rapidly reduced to baseline. To investigate the receptors responsible for CCh activation of MAPK in PC12 cells, the mAChR subtypes present were determined using RT-PCR and immunoprecipitation. RT-PCR was used to amplify fragments of the appropriate sizes for m1, m4, and m5, and the identities of the bands were confirmed with restriction digests. Immunoprecipitation using subtype-specific antibodies showed that approximately 95% of the expressed receptors were m4, whereas the remaining approximately 5% were m1 and m5. A highly specific m1 toxin completely blocked MAPK phosphorylation in response to CCh stimulation. The mAChR-induced MAPK activation was abolished by protein kinase C down-regulation and partially inhibited by pertussis toxin. Although m1 represents a small proportion of the total mAChR population, pharmacological evidence suggests that m1 is responsible for MAPK activation in PC12 cells.     

Encephalomyocarditis virus induces PKR-independent mitogen-activated protein kinase activation in macrophages

In this study, we provide evidence that the double-stranded RNA-dependent protein kinase (PKR) is not required for virus-induced expression of inducible nitric oxide synthase (iNOS) or the activation of specific signaling pathways in macrophages. The infection of RAW264.7 cells with encephalomyocarditis virus (EMCV) induces iNOS expression and nitric oxide production, which are unaffected by a dominant-negative mutant of PKR. EMCV infection also activates the mitogen-activated protein kinase, cyclic AMP response element binding protein, and nuclear factor kappaB (NF-kappaB) signaling cascades at 15 to 30 min postinfection in PKR+/+ and PKR-/- macrophages. Activation of these signaling cascades does not temporally correlate with PKR activity or the accumulation of EMCV RNA, suggesting that an interaction between a structural component of the virion and the cell surface may activate macrophages. Consistent with this hypothesis, empty EMCV capsids induced comparable levels of iNOS expression, nitrite production, and activation of these signaling cascades to those induced by intact virions. These findings support the hypothesis that virion-host cell interactions are primary mediators of the PKR-independent activation of signaling pathways that participate in the macrophage antiviral response of inflammatory gene expression.     

Stretch-dependent activation and desensitization of mitogen-activated protein kinase in carotid arteries

Arterial smooth muscle stretch is an important physiologicalmodulator of vascular function. To identify intracellular processes altered during muscle stretch, we found previously that extracellular signal-regulated kinase-mitogen-activated protein kinase (MAPK) activity increased in response to the application of mechanical loads.In the present study, stretch-dependent activation of MAPK in porcinecarotid arteries was investigated as was the phosphorylation of thethin filament-binding protein caldesmon, which is known to be asubstrate for the kinase in fully differentiated smooth muscle. MAPKactivity was 67 pmol · min¹ · mgprotein¹ in unloaded musclestrips immediately after attachment to force transducers and 139 pmol · min¹ · mgprotein¹ within 30 s ofmuscle stretch. When muscle strips were continually stretched, MAPKactivity remained elevated for ~2 h and then decreased over 16 h to16 pmol · min¹ · mgprotein¹. When musclestrips were stretched and then unloaded, MAPK activity decreased within1 h to the level present in the muscle before the stretch. Theseeffects of muscle stretch on MAPK activity were additive to the effectsof KCl or phorbol ester stimulation and were partially inhibited byreducing extracellular Ca²⁺.Eliminating extracellular Ca²⁺ hadno effect on phorbol 12,13-dibutyrate (PDBu)-dependent contractions orMAPK activity; however, KCl-dependent contractions and MAPK activitywere completely abolished by this procedure. An antibody specific fordetecting caldesmon phosphorylated by MAPK, vs. protein kinase C (PKC),was developed and used to assess relative caldesmon phosphorylation inunstimulated and PDBu-stimulated muscle strips. In all casesinvestigated, the level of MAPK activity correlated withphosphocaldesmon immunoreactivity. Because arterial MAPK activity isregulated by PKC- and stretch-dependent mechanisms, these data areconsistent with a role for MAPK and the subsequent phosphorylation ofcaldesmon as mediators in the stretch activation of vascular smoothmuscle.

     

Phosphorylation-dependent activation of TAK1 mitogen-activated protein kinase kinase kinase by TAB1

TAK1 is a mitogen-activated protein kinase kinase kinase (MAP3K) that is involved in the c-Jun N-terminal kinase/p38 MAPKs and NF-kappaB signaling pathways. Here, we characterized the molecular mechanisms of TAK1 activation by its specific activator TAB1. Autophosphorylation of two threonine residues in the activation loop of TAK1 was necessary for TAK1 activation. Association with TAK1 and induction of TAK1 autophosphorylation required the C-terminal 24 amino acids of TAB1, but full TAK1 activation required additional C-terminal Ser/Thr rich sequences. These results demonstrated that the association between the kinase domain of TAK1 and the C-terminal TAB1 triggered the phosphorylation-dependent TAK1 activation mechanism.     

Inhibitor-2 prevents protein phosphatase 1-induced cardiac hypertrophy and mortality

Cardiac-specific overexpression of the catalytic subunit of protein phosphatase type 1 (PP1) in mice results in hypertrophy, depressed contractility, propensity to heart failure, and premature death. To further address the role of PP1 in heart function, PP1 mice were crossed with mice that overexpress a functional COOH-terminally truncated form of PP1 inhibitor-2 (I-2(140)). Protein phosphatase activity was increased in PP1 mice but was normalized in double transgenic (DT) mice. The maximal rates of contraction (+dP/dt) and of relaxation (-dP/dt) were reduced in catheterized PP1 mice but normalized in DT mice. Similar contractile abnormalities were observed in isolated, perfused work-performing hearts and in whole animals by means of echocardiography. The increased absolute and relative heart weights observed in PP1 mice were normalized in DT mice. Histological analyses indicated that PP1 mice had significant cardiac fibrosis, which was absent in DT mice. Furthermore, PP1 mice exhibited an age-dependent increase in mortality, which was abrogated in DT mice. These results indicate that I-2 overexpression prevents the detrimental effects of PP1 overexpression in the heart and further underscore the fundamental role of PP1 in cardiac function. Therefore, PP1 inhibitors such as I-2 could offer new therapeutic options to ameliorate the deleterious effects of heart failure.     

Urotensin II promotes hypertrophy of cardiac myocytes via mitogen-activated protein kinases

Urotensin II and its receptor are coexpressed in the heart and up-regulated during cardiac dysfunction. In cultured neonatal cardiomyocytes, we mimicked this up-regulation using an adenovirus to increase expression of the urotensin receptor. In this model system, urotensin II promoted strong hypertrophic growth and phenotypic changes, including cell enlargement and sarcomere reorganization. Urotensin II potently activated the MAPKs, ERK1/2 and p38, and blocking these kinases with PD098059 and SB230580, respectively, significantly inhibited urotensin II-mediated hypertrophy. In contrast, urotensin II did not activate JNK. The activation of ERK1/2 and p38 as well as cellular hypertrophy was independent of protein kinase C, and calcium and phosphoinositide 3-kinase, yet dependent on the capacity of the urotensin receptor to trans-activate the epidermal growth factor receptor. Urotensin II promoted the tyrosine phosphorylation of epidermal growth factor receptors, which was inhibited by the selective epidermal growth factor receptor kinase inhibitor, AG1478. These data indicate that perturbations in cardiac homeostasis, which lead to up-regulation of urotensin II receptors, promote urotensin II-mediated cardiomyocyte hypertrophy via ERK1/2 and p38 signaling pathways in an epidermal growth factor receptor-dependent manner.     

Nuclear mitogen-activated protein kinase activation by protein kinase czeta during reoxygenation after ischemic hypoxia

We examined the upstream kinases for mitogen-activated protein kinase (MAPK) activation during ischemic hypoxia and reoxygenation using H9c2 cells derived from rat cardiomyocytes. Protein kinase C (PKC)zeta, an atypical PKC isoform mainly expressed in rat heart, has been shown to act as an upstream kinase of MAPK during ischemic hypoxia and reoxygenation by analyses with PKC inhibitors, antisense DNA, a dominant negative kinase defective mutant, and constitutively active mutants of PKCzeta. Immunocytochemical observations show PKCzeta staining in the nucleus during ischemic hypoxia and reoxygenation when phosphorylated MAPK is also detected in the nucleus. This nuclear localization of PKCzeta is inhibited by treatment with wortmannin, a phosphoinositide 3-kinase inhibitor that also inhibits MAPK activation in a dose-dependent manner. This is supported by the inhibition of MAPK phosphorylation by another blocker of phosphoinositide 3-kinase, LY294002. An upstream kinase of MAPK, MEK1/2, is significantly phosphorylated 15 min after reoxygenation and observed mainly in the nucleus, whereas it is present in the cytoplasm in serum stimulation. The phosphorylation of MEK is blocked by PKC inhibitors and phosphoinositide 3-kinase inhibitors, as observed in the case of MAPK phosphorylation. These observations indicate that PKCzeta, which is activated by phosphoinositide 3-kinase, induces MAPK activation through MEK in the nucleus during reoxygenation after ischemic hypoxia.     

Bcl-xL prevents staurosporine-induced hepatocyte apoptosis by restoring protein kinase B/mitogen-activated protein kinase activity and mitochondria integrity

Our study reports that staurosporine induces apoptosis in cultured rat hepatocytes in a dose- and time-dependent fashion. Staurosporine induced apparent cleavage of caspase-8, caspase-9, and caspase-3. The release of cytochrome c from mitochondria, and Bid activation were also detected in staurosporine-treated primary hepatocytes. These results suggest that mitochondria-mediated cell death signaling may be involved in staurosporine-induced hepatocyte apoptosis. Bcl-x(L) overexpression protected from "loss of" mitochondrial transmembrane potential and prevented staurosporine-induced caspase-3 and caspase-8 cleavage. Overexpression of constitutively active ERK and PKB inhibited staurosporine-induced caspase-3 activation and hepatocyte death. PI3K inhibitor (LY294002) and ERK inhibitor (PD98059) significantly reversed the protective effects of Bcl-x(L) on staurosporine-induced hepatocyte death. Our data suggest that Bcl-x(L) prevents staurosporine-induced hepatocyte apoptosis by modulating protein kinase B and p44/42 mitogen-activated protein kinase activity and disrupts mitochondria death signaling.     

Megakaryocytic differentiation induced by constitutive activation of mitogen-activated protein kinase kinase.

The K562 erythroleukemia cell line was used to study the molecular mechanisms regulating lineage commitment of hematopoietic stem cells. Phorbol esters, which initiate megakaryocyte differentiation in this cell line, caused a rapid increase in extracellular-signal-regulated kinase (ERK), which remained elevated for 2 h and returned to near-basal levels by 24 h. In the absence of extracellular stimuli, ERK could be activated by expression of constitutively active mutants of mitogen-activated protein (MAP) kinase kinase (MKK), resulting in cell adhesion and spreading, increased cell size, inhibition of cell growth, and induction of the platelet-specific integrin alphaIIb beta3, all hallmarks of megakaryocytic differentiation. In contrast, expression of wild-type MKK had little effect. In addition, constitutively active MKK suppressed the expression of an erythroid marker, alpha-globin, indicating the ability to suppress cellular responses necessary for alternative cell lineages. The MKK inhibitor PD98059 blocked MKK/ERK activation and cellular responses to phorbol ester, demonstrating that activation of MKK is necessary and sufficient to induce a differentiation program along the megakaryocyte lineage. Thus, the MAP kinase cascade, which promotes cell growth and proliferation in many cell types, instead inhibits cell proliferation and initiates lineage-specific differentiation in K562 cells, establishing a model system to investigate the mechanisms by which this signal transduction pathway specifies cell fate and developmental processes.     

Galphaq-dependent activation of mitogen-activated protein kinase kinase 4/c-Jun N-terminal kinase cascade.

G-protein-coupled receptors (GPCRs) typically activate c-Jun N-terminal kinase (JNK) through the G protein betagamma subunit (Gbetagamma), in a manner dependent on Rho family small GTPases, in mammalian cells. Here we show that JNK activation by the prototypic Gq-coupled alpha1B-adrenergic receptor is mediated by the alpha subunit of Gq (Galphaq), not by Gbetagamma, using a transient transfection system in human embryonic kidney cells. JNK activation by the alpha1B-adrenergic receptor/Galphaq was selectively mediated by mitogen-activated protein kinase kinase 4 (MKK4), but not MKK7. Also, MKK4 activation by the alpha1B-adrenergic receptor/Galphaq required c-Src and Rho family small GTPases. Furthermore, activation of the alpha1B-adrenergic receptor stimulated JNK activity through Src family tyrosine kinases and Rho family small GTPases in hamster smooth muscle cells that natively express the alpha1B-adrenergic receptor. Together, these results suggest that the alpha1B-adrenergic receptor/Galphaq may up-regulate JNK activity through a MKK4 pathway dependent on c-Src and Rho family small GTPases in mammalian cells.     

Atrial natriuretic peptide inhibits cardiomyocyte hypertrophy through mitogen-activated protein kinase phosphatase-1

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.