Effects of fasudil, a Rho-kinase inhibitor, on myocardial preconditioning in anesthetized rats

Mechanism of H2S-mediated ROCK inhibition of total flavones of Rhododendra against myocardial ischemia injury

Our previous studies have indicated that pretreatment with total flavones of Rhododendra flower (TFR) may protect against myocardial ischemic injuries in rats and mice. The cystathionine γ-lyase/hydrogen sulfide (CSE/H₂S) pathway have been associated with several cardiovascular diseases, but the effect of TFR on the Rho-associated protein kinase (ROCK) and CSE/H₂S signaling pathways remains unknown. In the present study, the protective effects of TFR as a ROCK inhibitor in a mice model of myocardial infarction induced by isoproterenol (ISO) were investigated, and the hearts from the wild type and CSE knockout (KO) mice were examined. It was identified that the CSE KO mice exhibited decreased levels of ST segment elevation following anoxia/reoxygenation damage, increased LDH and CK-MB levels, aggravated pathological damage, and increased ROCK1, ROCK2 and MLC1 protein levels. In the CSE KO mice, there were no marked changes of the above experimental results between the TFR group and the model group. These results suggested that TFR-based inhibition of the RhoA/ROCK signal pathway may be mediated by the CSE-H₂S signalling pathway and may be a novel therapeutic target for myocardial ischemia injury.

Investigation of leukocyte RHO/ROCK gene expressions in patients with non-valvular atrial fibrillation

Atrial fibrillation (AF) is an arrhythmia caused by disorganized electrical activity in the atria, and it is an important cause of mortality and morbidity. There is a limited data about Rho/Rho-kinase (ROCK) pathway contribute to AF development. The aim of the present study was to elucidate leukocyte RHO/ROCK gene expressions in patients with non-valvular AF (NVAF). A total of 37 NVAF patients and 47 age and sex-matched controls were included in this study. mRNA was extracted from leukocytes, and real-time polymerase chain reaction was used for gene expression analysis. A marked increase in ROCK1 and ROCK2 gene expressions in patients with NVAF was observed (P<0.0001). The present study detected significant elevations in RHOBTB2, RND3 (RHOE), RHOC, RHOG, RHOH, RAC3, RHOB, RHOD, RHOV, RHOBTB1, RND2, RND1 and RHOJ gene expressions (P<0.01). However, there were marked decreases in CDC42, RAC2, and RHOQ gene expressions in patients with NVAF. No significant modifications were seen in the other Rho GTPase proteins RHOA, RAC1, RHOF, RHOU and RHOBTB3. To the best of our knowledge, the present study is the first to provide data that gene expression of leukocyte RHO/ROCK may contribute to the NVAF pathogenesis through activated leukocytes, which promotes the immune or inflammatory cascade.

An Update on the Association of Protein Kinases with Cardiovascular Diseases

Background:

Protein kinases are the enzymes involved in phosphorylation of different proteins which leads to functional changes in those proteins. They belong to serine-threonine kinases family and are classified into the AGC (Protein kinase A/ Protein kinase G/ Protein kinase C) families of protein and Rho-associated kinase protein (ROCK). The AGC family of kinases are involved in G-protein stimuli, muscle contraction, platelet biology and lipid signaling. On the other hand, ROCK regulates actin cytoskeleton which is involved in the development of stress fibres. Inflammation is the main signal in all ROCK-mediated disease. It triggers the cascade of a reaction involving various proinflammatory cytokine molecules.

Methods:

Two ROCK isoforms are found in mammals and invertebrates. The first isoforms are present mainly in the kidney, lung, spleen, liver, and testis. The second one is mainly distributed in the brain and heart.

Results:

ROCK proteins are ubiquitously present in all tissues and are involved in many ailments that include hypertension, stroke, atherosclerosis, pulmonary hypertension, vasospasm, ischemia-reperfusion injury and heart failure. Several ROCK inhibitors have shown positive results in the treatment of various disease including cardiovascular diseases.

Conclusion:

ROCK inhibitors, fasudil and Y27632, have been reported for significant efficiency in dropping vascular smooth muscle cell hyper-contraction, vascular inflammatory cell recruitment, cardiac remodelling and endothelial dysfunction which highlight ROCK role in cardiovascular diseases.

Adenosine Receptors As Drug Targets for Treatment of Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a clinical condition characterized by pulmonary arterial remodeling and vasoconstriction, which promote chronic vessel obstruction and elevation of pulmonary vascular resistance. Long-term right ventricular (RV) overload leads to RV dysfunction and failure, which are the main determinants of life expectancy in PAH subjects. Therapeutic options for PAH remain limited, despite the introduction of prostacyclin analogs, endothelin receptor antagonists, phosphodiesterase type 5 inhibitors, and soluble guanylyl cyclase stimulators within the last 15 years. Through addressing the pulmonary endothelial and smooth muscle cell dysfunctions associated with PAH, these interventions delay disease progression but do not offer a cure. Emerging approaches to improve treatment efficacy have focused on beneficial actions to both the pulmonary vasculature and myocardium, and several new targets have been investigated and validated in experimental PAH models. Herein, we review the effects of adenosine and adenosine receptors (A₁, A_2A, A_2B, and A₃) on the cardiovascular system, focusing on the A_2A receptor as a pharmacological target. This receptor induces pulmonary vascular and heart protection in experimental models, specifically models of PAH. Targeting the A_2A receptor could potentially serve as a novel and efficient approach for treating PAH and concomitant RV failure. A_2A receptor activation induces pulmonary endothelial nitric oxide synthesis, smooth muscle cell hyperpolarization, and vasodilation, with important antiproliferative activities through the inhibition of collagen deposition and vessel wall remodeling in the pulmonary arterioles. The pleiotropic potential of A_2A receptor activation is highlighted by its additional expression in the heart tissue, where it participates in the regulation of intracellular calcium handling and maintenance of heart chamber structure and function. In this way, the activation of A_2A receptor could prevent the production of a hypertrophic and dysfunctional phenotype in animal models of cardiovascular diseases.

Mechanisms of favorable effects of Rho kinase inhibition on myocardial remodeling and systolic function after experimental myocardial infarction in the rat

OBJECTIVE

The objective of this study was to determine the molecular mechanisms by which cardiac Rho-associated coiled-coil containing protein kinase (ROCK) activation after myocardial infarction (MI) does intervene in cardiac systolic function decline and remodeling.

METHODS

Simultaneous measurement of different cardiac ROCK target proteins levels, in vivo left ventricular (LV) systolic function, myocardial fibrosis and hypertrophy in rats with MI under ROCK inhibition with fasudil.

RESULTS

Seven days after MI, the ventricular mass increased significantly by 5.6% in the MI group and was reduced with fasudil. LV systolic dysfunction improved significantly with fasudil whereas cardiac ROCK activation was reduced to sham levels. The ROCK inhibitor also reduced increased cardiac levels of both ROCK1 and ROCK2 isoforms, cardiomyocyte ROCK2 fluorescence levels and β-myosin heavy chain (MHC) levels in addition to myocardial collagen volume fraction decline. Compared with sham rats, troponin phosphorylation levels after MI were similar and ROCK inhibition reduced them. MI significantly increased phosphorylation levels of extracellular-signal-regulated kinase (ERK) 42 and ERK 44 by twofold and 63%, respectively, whereas in the fasudil-treated MI group these levels were similar to those in the sham group. MI significantly increased phosphorylated levels of the transcription factor GATA-4 and the ROCK inhibitor normalized them.

CONCLUSIONS

LV systolic dysfunction after MI was strongly associated with cardiac ROCK activation and subsequent phosphorylation of ROCK target proteins that promote ventricular remodeling such as β-MHC and the ERK/GATA-4 pathway. ROCK inhibition with fasudil significantly improved systolic function, diminished myocardial fibrosis and normalized β-MHC and ERK/GATA-4 phosphorylation levels.

Rho-associated kinase activity is an independent predictor of cardiovascular events in acute coronary syndrome

Rho-associated kinases play an important role in a variety of cellular functions. Although Rho-associated kinase activity has been shown to be an independent predictor for future cardiovascular events in a general population, there is no information on Rho-associated kinase activity in patients with acute coronary syndrome. We evaluated leukocyte Rho-associated kinase activity by Western blot analysis in 73 patients with acute coronary syndrome and 73 age- and gender-matched control subjects. Rho-associated kinase activity within 2 hours of acute coronary syndrome onset was higher in patients with acute coronary syndrome than in the control subjects (0.95±0.55 versus 0.69±0.31; P<0.001). Rho-associated kinase activity promptly increased from 0.95±0.55 to 1.11±0.81 after 3 hours and reached a peak of 1.21±0.76 after 1 day (P=0.03 and P=0.03, respectively) and then gradually decreased to 0.83±0.52 after 7 days, 0.78±0.42 after 14 days, and 0.72±0.30 after 6 months (P=0.22, P=0.29, and P=0.12, respectively). During a median follow-up period of 50.8 months, 31 first major cardiovascular events (death from cardiovascular causes, myocardial infarction, ischemic stroke, and coronary revascularization) occurred. After adjustment for age, sex, cardiovascular risk factors, and concomitant treatment with statins, increased Rho-associated kinase activity was associated with increasing risk of first major cardiovascular events (hazard ratio, 4.56; 95% confidence interval, 1.98–11.34; P<0.001). These findings suggest that Rho-associated kinase activity is dramatically changed after acute coronary syndrome and that Rho-associated kinase activity could be a useful biomarker to predict cardiovascular events in Japanese patients with acute coronary syndrome.

Rho kinases in cardiovascular physiology and pathophysiology: the effect of fasudil

Rho kinase (ROCK) is a major downstream effector of the small GTPase RhoA. ROCK family, consisting of ROCK1 and ROCK2, plays central roles in the organization of actin cytoskeleton and is involved in a wide range of fundamental cellular functions, such as contraction, adhesion, migration, proliferation, and apoptosis. Due to the discovery of effective inhibitors, such as fasudil and Y27632, the biological roles of ROCK have been extensively explored with particular attention on the cardiovascular system. In many preclinical models of cardiovascular diseases, including vasospasm, arteriosclerosis, hypertension, pulmonary hypertension, stroke, ischemia-reperfusion injury, and heart failure, ROCK inhibitors have shown a remarkable efficacy in reducing vascular smooth muscle cell hypercontraction, endothelial dysfunction, inflammatory cell recruitment, vascular remodeling, and cardiac remodeling. Moreover, fasudil has been used in the clinical trials of several cardiovascular diseases. The continuing utilization of available pharmacological inhibitors and the development of more potent or isoform-selective inhibitors in ROCK signaling research and in treating human diseases are escalating. In this review, we discuss the recent molecular, cellular, animal, and clinical studies with a focus on the current understanding of ROCK signaling in cardiovascular physiology and diseases. We particularly note that emerging evidence suggests that selective targeting ROCK isoform based on the disease pathophysiology may represent a novel therapeutic approach for the disease treatment including cardiovascular diseases.

High‑dose fasudil preconditioning and postconditioning attenuate myocardial ischemia‑reperfusion injury in hypercholesterolemic rats

Fasudil may induce preconditioning and postconditioning against myocardial ischemia‑reperfusion injury in normal rats, however, their effectivenesses in hypercholesterolemia remains to be determined. The study aimed to investigate whether fasudil induces preconditioning and postconditioning in hypercholesterolemic rats and to determine the roles of the phosphoinositol 3‑kinase (PI3K)/Akt/endothelial nitric oxide synthase (eNOS) pathway and mitochondrial KATP (m‑KATP) channels in this process. Isolated rat hearts underwent 30 min global ischemia and 120 min reperfusion. Low‑ (1 mg/kg) or high‑dose (10 mg/kg) fasudil was administered 15 min prior to ischemia and at the initial onset of reperfusion. 5‑Hydroxydecanoic acid (5HD), an m‑KATP channel blocker, at 10 mg/kg was administered 5 min prior to reperfusion. Myocardial infarct size was estimated by 2,3,5‑triphenyltetrazolium chloride (TTC) staining and lactate dehydrogenase (LDH) and creatine kinase‑MB (CK‑MB) were analyzed from coronary effluents. Phosphorylation of Akt and eNOS was measured by immunoblotting. High‑dose fasudil‑induced preconditioning and postconditioning significantly reduced infarct size and the release of LDH and CK‑MB and increased the phosphorylation of Akt and eNOS compared with the control group, whereas low‑dose fasudil did not exert these beneficial effects. In addition, the cardioprotection of high‑dose fasudil‑induced preconditioning and postconditioning are blocked by 5HD. Low‑dose fasudil‑induced preconditioning and postconditioning are abrogated by hypercholesterolemia, while high‑dose fasudil restores the cardioprotection, which is involved in upregulation of the PI3K/Akt/eNOS pathway and inducing the opening of the m‑KATP channel.

Coptisine protects rat heart against myocardial ischemia/reperfusion injury by suppressing myocardial apoptosis and inflammation

OBJECTIVE

Protecting the heart from myocardial ischemia and reperfusion (I/R) damage is the focus of intense research. Coptisine is an isoquinoline alkaloid isolated from Coptidis Rhizoma. The present study investigated the potential effect of coptisine on myocardial I/R damage in rats and the underlying mechanisms.

METHODS AND RESULTS

Electrocardiogram examination showed that the administration of coptisine 10 min before ischemia significantly decreased I/R-induced arrhythmia after 30 min ischemia followed by 3 h reperfusion. The release of cardiac markers was also limited. Echocardiography was performed before ischemia and 24 h post-I/R, separately. The M-mode records showed that the reductions of ejection fraction (EF) and fractional shortening (FS) were attenuated in coptisine-treated rats compared with the I/R rats. Similar results were obtained with Evans Blue/triphenyl tetrazolium chloride (TTC) staining, in which coptisine notably reduced infarct size. Moreover, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay demonstrated coptisine suppressed myocardial apoptosis, which may be related to the upregulation of Bcl-2 protein and inhibition of caspase-3 activation. Coptisine treatment also attenuated the proinflammatory cytokines including interleukin (IL)-1β, IL-6, and tumor necrosis factor-α in heart tissue. Additionally, Western blot and immunohistochemical analysis showed that coptisine markedly reduced Rho, Rho-kinase 1 (ROCK1), and ROCK2 expression and attenuated the phosphorylation of myosin phosphatase targeting subunit-1, a downstream target of ROCK.

CONCLUSIONS

Coptisine exerts pronounced cardioprotection in rats subjected to myocardial I/R likely through suppressing myocardial apoptosis and inflammation by inhibiting the Rho/ROCK pathway.

Small G Proteins in the Cardiovascular System: Physiological and Pathological Aspects

Small G proteins exist in eukaryotes from yeast to human and constitute the Ras superfamily comprising more than 100 members. This superfamily is structurally classified into five families: the Ras, Rho, Rab, Arf, and Ran families that control a wide variety of cell and biological functions through highly coordinated regulation processes. Increasing evidence has accumulated to identify small G proteins and their regulators as key players of the cardiovascular physiology that control a large panel of cardiac (heart rhythm, contraction, hypertrophy) and vascular functions (angiogenesis, vascular permeability, vasoconstriction). Indeed, basal Ras protein activity is required for homeostatic functions in physiological conditions, but sustained overactivation of Ras proteins or spatiotemporal dysregulation of Ras signaling pathways has pathological consequences in the cardiovascular system. The primary object of this review is to provide a comprehensive overview of the current progress in our understanding of the role of small G proteins and their regulators in cardiovascular physiology and pathologies.

Rho kinase as a therapeutic target in cardiovascular disease

Rho kinase (ROCK) belongs to the AGC (PKA/PKG/PKC) family of serine/threonine kinases and is a major downstream effector of the small GTPase RhoA. ROCK plays central roles in the organization of the actin cytoskeleton and is involved in a wide range of fundamental cellular functions such as contraction, adhesion, migration, proliferation and gene expression. Two ROCK isoforms, ROCK1 and ROCK2, are assumed to be functionally redundant, based largely on the major common activators, the high degree of homology within the kinase domain and studies from overexpression with kinase constructs and chemical inhibitors (e.g., Y27632 and fasudil), which inhibit both ROCK1 and ROCK2. Extensive experimental and clinical studies support a critical role for the RhoA/ROCK pathway in the vascular bed in the pathogenesis of cardiovascular diseases, in which increased ROCK activity mediates vascular smooth muscle cell hypercontraction, endothelial dysfunction, inflammatory cell recruitment and vascular remodeling. Recent experimental studies, using ROCK inhibitors or genetic mouse models, indicate that the RhoA/ROCK pathway in myocardium contributes to cardiac remodeling induced by ischemic injury or persistent hypertrophic stress, thereby leading to cardiac decompensation and heart failure. This article, based on recent molecular, cellular and animal studies, focuses on the current understanding of ROCK signaling in cardiovascular diseases and in the pathogenesis of heart failure.

RhoA/Rho-kinase and vascular diseases: what is the link?

RhoA/Rho-kinase pathway plays an important role in many pathological conditions. RhoA participates in the regulation of smooth muscle tone and activates many downstream kinases. The best characterized are the serine/threonine kinase isoforms (Rho-kinase or ROCK), ROCKα/ROCK2 and ROCKβ/ROCK1. ROCK is necessary for diverse functions such as local blood flow, arterial/pulmonary blood pressure, airway resistance and intestinal peristalsis. ROCK activation permits actin/myosin interactions and smooth muscle cells contraction by maintaining the activity of myosin light-chain kinase, independently of the free cytosolic calcium level. The sensitization of smooth muscle myofilaments to calcium has been implicated in many pathological states, such as hypertension, diabetes, heart attack, stroke, pulmonary hypertension, erectile dysfunction, and cancer. The focus of this review is on the involvement of RhoA/Rho-kinase in diseases. We will briefly describe the ROCK isoforms and the role of RhoA/Rho-kinase in the vasculature, before exploring the most recent findings regarding this pathway and various diseases.

ERK-MAPK signaling opposes rho-kinase to reduce cardiomyocyte apoptosis in heart ischemic preconditioning

We and others have reported that Rho-kinase plays an important role in the pathogenesis of heart ischemia/reperfusion (I/R) injury. Studies have also demonstrated that the activation of Rho-kinase is reversed in ischemic preconditioning (IPC). However, the mechanisms by which Rho-kinase is increased in I/R and reversed in IPC are not thoroughly understood. In female Wistar rats, we created I/R by ligating the left anterior-descending branch of the coronary artery (LAD) for 30 min and releasing the ligature for 180 min. IPC rats underwent IPC (two cycles of 5-min ligation of the LAD and 5-min reflow) before I/R. IPC caused a significant increase in extracellular signal-regulated kinase (ERK)1/2 activity and reduced Rho-kinase activity and cardiomyocyte apoptosis (P<0.05 versus I/R). Administration of PD98059, an inhibitor of ERK-mitogen-activated protein kinase (MAPK), increased cardiomyocyte apoptosis, Caspase-3 activity and myocardial infarction size (P<0.05 versus IPC). Western-blot analysis showed that administration of PD98059 increased Rho-kinase activity. Treatment with fasudil, an inhibitor of Rho-kinase, reversed cell apoptosis caused by treatment with PD98059 in IPC. In addition, ROCK1 (Rho-kinase 1) may be the major Rho-kinase isoform that is opposed by ERK-MAPK signaling in IPC. These results indicate that ERK-MAPK signaling is required in IPC to oppose Rho-kinase activity in cardiomyocyte apoptosis in vivo.

Inhibition of the activity of Rho-kinase reduces cardiomyocyte apoptosis in heart ischemia/reperfusion via suppressing JNK-mediated AIF translocation

BACKGROUND

Recent studies have demonstrated that Rho-kinase has been proposed to play an important role in the pathogenesis of heart ischemia/reperfusion (I/R) injury. However, the mechanism of Rho-kinase mediated cardiomyocyte apoptosis in I/R is still not thoroughly understood.

METHOD

Studies were performed with female Wistar rats.

RESULTS

Ischemia followed by reperfusion caused a significant increase in Rho-kinase, c-Jun NH2-terminal kinase (JNK) and apoptosis-inducing factor (AIF) activity. Administration of fasudil, an inhibitor of Rho-kinase, decreased myocardial infarction size from 59.89+/-3.83% to 38.62+/-2.66% (P<0.05) and cell apoptosis from 32.78+/-5.1% to 17.05+/-4.2% (P<0.05). Western blot analysis showed that administration of fasudil reduced the activation of JNK and attenuated mitochondrial-nuclear translocation of AIF. Additionally, administration of SP600125, an inhibitor of JNK, attenuated mitochondrial-nuclear translocation of AIF.

CONCLUSION

The inhibition of Rho-kinase reduced cell apoptosis in I/R in vivo via suppression of JNK-mediated AIF translocation.

Administration of the Rho-kinase inhibitor fasudil before ischemia or just after reperfusion, but not 30 min after reperfusion, protects the stunned myocardium in swine

OBJECTIVES

We assessed the effect of administration time for fasudil treatment of the stunned myocardium in 40 anesthetized open chest swine.

MATERIALS AND METHODS

All swine were subjected to 12 min ischemia followed by reperfusion to generate stunned myocardium. Group A (n = 11) received saline in place of fasudil both before ischemia and after reperfusion. Group B (n = 10) received 30 min intravenous fasudil at a rate of 13 mug/kg/min starting 45 min before ischemia and received saline after reperfusion. Groups C (n = 10) and D (n = 9) received saline before ischemia, and received fasudil at a rate of 13 microg kg(-1) min(-1) starting just before reperfusion in group C and 30 min after reperfusion in group D. In both groups, treatment lasted 30 min. Myocardial contractility was assessed by percent segment shortening (%SS).

RESULTS AND DISCUSSION

Three swine in group A, 2 swine in each of groups B and C, and one swine in group D had ventricular fibrillation or tachycardia after reperfusion and were excluded from further analysis. The changes of %SS from baseline at 90 min after reperfusion in groups B and C were 68 +/- 8% and 75 +/- 8%, respectively, which were significantly higher than in group A or D (47 +/- 10% or 43 +/- 8%).

CONCLUSION

We conclude that fasudil administered before ischemia or just after reperfusion, but not 30 min after reperfusion, protects the stunned myocardium.

Cardioprotective effect of rosuvastatin in vivo is dependent on inhibition of geranylgeranyl pyrophosphate and altered RhoA membrane translocation

Hydroxymethyl glutaryl (HMG)-coenzyme A (CoA) reductase inhibitors (statins) protect the myocardium against ischemia-reperfusion injury via a mechanism unrelated to cholesterol lowering. Statins may inhibit isoprenylation and thereby prevent activation of proteins such as RhoA. We hypothesized that statins protect the myocardium against ischemia-reperfusion injury via a mechanism involving inhibition of geranylgeranyl pyrophosphate synthesis and translocation of RhoA to the plasma membrane. Sprague-Dawley rats were given either the HMG-CoA reductase inhibitor rosuvastatin, geranylgeranyl pyrophosphate dissolved in methanol, the combination of rosuvastatin and geranylgeranyl pyrophosphate, rosuvastatin and methanol, or distilled water (control) by intraperitoneal injection for 48 h before ischemia-reperfusion. Animals were anesthetized and either subjected to 30 min of coronary artery occlusion followed by 2 h of reperfusion where at infarct size was determined, or the expression of RhoA protein was determined in cytosolic and membrane fractions of nonischemic myocardium. There were no significant differences in hemodynamics between the control group and the other groups before ischemia or during ischemia and reperfusion. The infarct size was 80 +/- 3% of the area at risk in the control group. Rosuvastatin reduced infarct size to 64 +/- 2% (P<0.001 vs. control). Addition of geranylgeranyl pyrophosphate (77 +/- 2%, P<0.01 vs. rosuvastatin) but not methanol (65 +/- 2%, not significant vs. rosuvastatin) abolished the cardioprotective effect of rosuvastatin. Geranylgeranyl pyrophosphate alone did not affect infarct size per se (84 +/- 2%). Rosuvastatin increased the cytosol-to-membrane ratio of RhoA protein in the myocardium (P<0.05 vs. control). These changes were abolished by addition of geranylgeranyl pyrophosphate. We conclude that the cardioprotection and the increase of the RhoA cytosol-to-membrane ratio induced by rosuvastatin in vivo are blocked by geranylgeranyl pyrophosphate. The inhibition of geranylgeranyl pyrophosphate formation and subsequent modulation of cytosol/membrane-bound RhoA are of importance for the protective effect of statins against myocardial ischemia-reperfusion injury.

Neural Differentiation of Human Neuroblastoma GOTO Cells via a Rho-Rho Kinase-Phosphorylation Signal Transduction and Continuous Observation of a Single GOTO Cell during Differentiation

Nerve growth factor, retinoic acid, dibutyryl cAMP, ganglioside G(Q1b), and botulinum C3 exoenzyme were evaluated for their neural differentiating potential on human neuroblastoma GOTO cells. C3 exoenzyme is an ADP-ribosyltransferase inactivating Rho protein (a small GTP-binding protein). C3 exoenzyme caused the fastest differentiation of GOTO cells into neural cells and induced the strongest network of the cells. Fasudil, an inhibitor of Rho-kinase, induced outgrowth of the neurites in the GOTO cells. Calyculin A, an inhibitor of phosphatases including myosin phosphatase, counteracted C3 exoenzyme-induced neurite outgrowth of the cells. These findings suggest that differentiation of GOTO cells triggered by C3 exoenzyme is attained via inactivation of Rho protein, inhibition of Rho-kinase, and activation of myosin phosphatase. Because of the strong differentiating potential of C3 exoenzyme, the transduction pathway consisting of Rho protein, Rho-kinase, and myosin phosphatase seems to be main stream in the neural differentiation of GOTO cells. A single GOTO cell was observed continuously after treatment with C3 exoenzyme. The cell started to change shape from its original morphology only 15 min after treatment with C3 exoenzyme, and it was completely spherical within 60 min. Neurites appeared on the membrane of the cell 2 hr after the treatment and then gradual outgrowth began. These observations are fundamental information in elucidating the mechanism of neural differentiation, especially at an early stage.