A rho-associated protein kinase, ROKalpha, binds insulin receptor substrate-1 and modulates insulin signaling

Novel cardiovascular protective effects of RhoA signaling and its therapeutic implications

Ras homolog gene family member A (RhoA) belongs to the Rho GTPase superfamily, which was first studied in cancers as one of the essential regulators controlling cellular function. RhoA has long attracted attention as a key molecule involved in cell signaling and gene transcription, through which it affects cellular processes. A series of studies have demonstrated that RhoA plays crucial roles under both physiological states and pathological conditions in cardiovascular diseases. RhoA has been identified as an important regulator in cardiac remodeling by regulating actin stress fiber dynamics and cytoskeleton formation. However, its underlying mechanisms remain poorly understood, preventing definitive conclusions being drawn about its protective role in the cardiovascular system. In this review, we outline the characteristics of RhoA and its related signaling molecules, and present an overview of RhoA classical function and the corresponding cellular responses of RhoA under physiological and pathological conditions. Overall, we provide an update on the novel signaling under RhoA in the cardiovascular system and its potential clinical and therapeutic targets in cardiovascular medicine.

ROCK1 regulates insulin secretion from β-cells

OBJECTIVE

The endocrine pancreatic β-cells play a pivotal role in maintaining whole-body glucose homeostasis and its dysregulation is a consistent feature in all forms of diabetes. However, knowledge of intracellular regulators that modulate β-cell function remains incomplete. We investigated the physiological role of ROCK1 in the regulation of insulin secretion and glucose homeostasis.

METHODS

Mice lacking ROCK1 in pancreatic β-cells (RIP-Cre; ROCK1loxP/loxP, β-ROCK1-/-) were studied. Glucose and insulin tolerance tests as well as glucose-stimulated insulin secretion (GSIS) were measured. An insulin secretion response to a direct glucose or pyruvate or pyruvate kinase (PK) activator stimulation in isolated islets from β-ROCK1-/- mice or β-cell lines with knockdown of ROCK1 was also evaluated. A proximity ligation assay was performed to determine the physical interactions between PK and ROCK1.

RESULTS

Mice with a deficiency of ROCK1 in pancreatic β-cells exhibited significantly increased blood glucose levels and reduced serum insulin without changes in body weight. Interestingly, β-ROCK1-/- mice displayed a progressive impairment of glucose tolerance while maintaining insulin sensitivity mostly due to impaired GSIS. Consistently, GSIS markedly decreased in ROCK1-deficient islets and ROCK1 knockdown INS-1 cells. Concurrently, ROCK1 blockade led to a significant decrease in intracellular calcium and ATP levels and oxygen consumption rates in isolated islets and INS-1 cells. Treatment of ROCK1-deficient islets or ROCK1 knockdown β-cells either with pyruvate or a PK activator rescued the impaired GSIS. Mechanistically, we observed that glucose stimulation in β-cells greatly enhanced ROCK1 binding to PK.

CONCLUSIONS

Our findings demonstrate that β-cell ROCK1 is essential for glucose-stimulated insulin secretion and for glucose homeostasis and that ROCK1 acts as an upstream regulator of glycolytic pyruvate kinase signaling.

Effects of 12-week moderate aerobic exercise on ROCK2 activity, hs-CRP and glycemic index in obese patients with impaired glucose tolerance

BACKGROUND

Obesity is a chronic low-grade inflammatory state that is related to prediabetes, increased Rhoassociated kinase 2 (ROCK2) activity and concentration of high-sensitivity C-reactive protein (hs-CRP). Therefore, the study was conducted to investigate the effects of 12-week moderate aerobic exercise on ROCK2 activity, hs-CRP, glycosylated hemoglobin A1C (HbA1c), and glycemic index in obese patients with impaired glucose tolerance.

METHODS

In a quasi-experimental design with pre and post-test, 42 obese men with prediabetes [mean±SD, age: 44.73 ± 3.30 years, body mass index (BMI): 33.22 ± 2.05 kg/m², HbA1c: 6.29 % ± 0.75] were allocated into two randomized homogeneous groups: Aerobic training group (AT, n=22) or control group (C, n=20). Exercise group performed a moderate aerobic exercise program three sessions per week, 60 minutes per session for 12 weeks. Body mass, BMI, maximal oxygen consumption (VO₂max), serum levels of fasting blood glucose (FBG), insulin, insulin resistance (HOMA-IR), homeostasis model assessment of β-cell function (HOMA-B); HbA1c, hs-CRP, or ROCK2 activity were measured before and after the study period. The data were analyzed using repeated measures ANOVA 2×2 and paired sample t test at a significant level of p < 0.05.

RESULTS

AT caused a significant reduction in body mass (p≤ 0.001), BMI (p= 0.04), HOMA-B (p=0.003), serum levels of FBG (p= 0.002), HbA1c (p= 0.039), hs-CRP (p≤ 0.0001), and ROCK2 activity (p= 0.001). In contrast, in the same group, a significant increase was observed in VO₂max (p= 0.04).

CONCLUSION

The results of this study showed that moderate aerobic exercise was an effective and safe method to prevent type 2 diabetes and cardiovascular diseases in obese men with prediabetes by improving glucose metabolism, reduction of body mass, ROCK2 activity and serum levels of hs-CRP.

Insight Into Rho Kinase Isoforms in Obesity and Energy Homeostasis

Obesity and associated complications increasingly jeopardize global health and contribute to the rapidly rising prevalence of type 2 diabetes mellitus and obesity-related diseases. Developing novel methods for the prevention and treatment of excess body adipose tissue expansion can make a significant contribution to public health. Rho kinase is a Rho-associated coiled-coil-containing protein kinase (Rho kinase or ROCK). The ROCK family including ROCK1 and ROCK2 has recently emerged as a potential therapeutic target for the treatment of metabolic disorders. Up-regulated ROCK activity has been involved in the pathogenesis of all aspects of metabolic syndrome including obesity, insulin resistance, dyslipidemia and hypertension. The RhoA/ROCK-mediated actin cytoskeleton dynamics have been implicated in both white and beige adipogenesis. Studies using ROCK pan-inhibitors in animal models of obesity, diabetes, and associated complications have demonstrated beneficial outcomes. Studies via genetically modified animal models further established isoform-specific roles of ROCK in the pathogenesis of metabolic disorders including obesity. However, most reported studies have been focused on ROCK1 activity during the past decade. Due to the progress in developing ROCK2-selective inhibitors in recent years, a growing body of evidence indicates more attention should be devoted towards understanding ROCK2 isoform function in metabolism. Hence, studying individual ROCK isoforms to reveal their specific roles and principal mechanisms in white and beige adipogenesis, insulin sensitivity, energy balancing regulation, and obesity development will facilitate significant breakthroughs for systemic treatment with isoform-selective inhibitors. In this review, we give an overview of ROCK functions in the pathogenesis of obesity and insulin resistance with a particular focus on the current understanding of ROCK isoform signaling in white and beige adipogenesis, obesity and thermogenesis in adipose tissue and other major metabolic organs involved in energy homeostasis regulation.

Adherens junctions are involved in polarized contractile ring formation in dividing epithelial cells of Xenopus laevis embryos

Cells dividing in the plane of epithelial tissues proceed by polarized constriction of the actomyosin contractile ring, leading to asymmetric ingression of the plasma mem brane. Asymmetric cytokinesis results in the apical positioning of the actomyosin contractile ring and ultimately of the midbody. Studies have indicated that the contractile ring is associated with adherens junctions, whose role is to maintain epithelial tissue cohesion. However, it is yet unknown when the contractile ring becomes associated with adherens junctions in epithelial cells. Here, we examined contractile ring formation and activation in the epithelium of Xenopus embryos and explored the implication of adherens junctions in the contractile ring formation. We show that accumulation of proteins involved in contractile ring formation and activation is polarized, starting at apical cell-cell contacts at the presumptive division site and spreading within seconds towards the cell basal side. We also show that adherens junctions are involved in the kinetics of contractile ring formation. Our study reveals that the link between the adherens junctions and the contractile ring is established from the onset of cytokinesis.

Rho Kinases in Health and Disease: From Basic Science to Translational Research

Rho-associated kinases ROCK1 and ROCK2 are key regulators of actin cytoskeleton dynamics downstream of Rho GTPases that participate in the control of important physiologic functions, S including cell contraction, migration, proliferation, adhesion, and inflammation. Several excellent review articles dealing with ROCK function and regulation have been published over the past few years. Although a brief overview of general molecular, biochemical, and functional properties of ROCKs is included, an effort has been made to produce an original work by collecting and synthesizing recent studies aimed at translating basic discoveries from cell and experimental models into knowledge of human physiology, pathophysiological mechanisms, and medical therapeutics. This review points out the specificity and distinct roles of ROCK1 and ROCK2 isoforms highlighted in the last few years. Results obtained from genetically modified mice and genetic analysis in humans are discussed. This review also addresses the involvement of ROCKs in human diseases and the potential use of ROCK activity as a biomarker or a pharmacological target for specific inhibitors.

Effects and mechanism of moderate aerobic exercise on impaired fasting glucose improvement

BACKGROUND

Exercise is beneficial for blood glucose metabolism. However, whether moderate aerobic exercise could improve impaired fasting glucose is unknown. And the mechanism is also needed to investigate.

METHODS

A cross-sectional research was performed and 120 participants with impaired fasting glucose (IFG) were randomly assigned into active and controlled groups. Briefly, participants in active group were required to take moderate aerobic exercise at least 30 min for five times per week, whereas in controlled group, participants were also advised to take exercise but not mandatorily required the same degree as that of active group. At baseline and 3 month's follow-up, laboratory and demographic variables were compared.

RESULTS

At baseline, no significant between-group differences were observed. Generally, leukocyte ROCK2 activity in the active and controlled groups were 58.7 ± 6.0 mg/mL and 60.2 ± 7.3 mg/mL, and daily average exercise time at baseline in both groups was extremely little, with 5.2 ± 3.8 min and 5.9 ± 3.5 min, respectively. After 3 months' follow-up, 52 and 56 participants in the active and controlled groups completed the whole program. Compared to baseline, leukocyte ROCK2 activity and daily average exercise time were improved in both groups. Nonetheless, compared to the controlled group, leukocyte ROCK2 activity was reduced more profoundly and the daily average exercise time was longer in the active group (37.5 ± 6.3 min versus 18.3 ± 7.2 min, p < 0.05). Moreover, the percentage of IFG in the active group was decreased more prominently than the controlled group (76.9% versus 82.1%, p < 0.05). Multivariate regression analyses revealed that exercise time and leukocyte ROCK2 activity was significantly associated with IFG, with OR of 0.836 (active group versus controlled group, 95% CI 0.825-0.852, p < 0.05) in exercise time, and 1.043 (controlled group versus active group, 95% CI 1.021-1.069, p < 0.05) in leukocyte ROCK2 activity. In addition, exercise time was significantly associated with leukocyte ROCK2 activity, with OR of 0.822 (active group versus controlled group, 95% CI 0.818-0.843, p < 0.05).

CONCLUSION

In subjects with IFG, increased daily average exercise time is beneficial for improving fasting blood glucose metabolism, and the mechanism may be associated with its effects on attenuating leukocyte ROCK2 activity.

Rho kinase is required to prevent retinal axons from entering the contralateral optic nerve

To grow out to contact target neurons an axon uses its distal tip, the growth cone, as a sensor of molecular cues that help the axon make appropriate guidance decisions at a series of choice points along the journey. In the developing visual system, the axons of the output cells of the retina, the retinal ganglion cells (RGCs), cross the brain midline at the optic chiasm. Shortly after, they grow past the brain entry point of the optic nerve arising from the contralateral eye, and extend dorso-caudally through the diencephalon towards their optic tectum target. Using the developing visual system of the experimentally amenable model Xenopus laevis, we find that RGC axons are normally prevented from entering the contralateral optic nerve. This mechanism requires the activity of a Rho-associated kinase, Rock, known to function downstream of a number of receptors that recognize cues that guide axons. Pharmacological inhibition of Rock in an in vivo brain preparation causes mis-entry of many RGC axons into the contralateral optic nerve, and this defect is partially phenocopied by selective disruption of Rock signaling in RGC axons. These data implicate Rock downstream of a molecular mechanism that is critical for RGC axons to be able to ignore a domain, the optic nerve, which they previously found attractive.

Lipid-induced Muscle Insulin Resistance Is Mediated by GGPPS via Modulation of the RhoA/Rho Kinase Signaling Pathway

Elevated circulating free fatty acid levels are important contributors to insulin resistance in the muscle and liver, but the underlying mechanisms require further elucidation. Here, we show that geranylgeranyl diphosphate synthase 1 (GGPPS), which is a branch point enzyme in the mevalonic acid pathway, promotes lipid-induced muscle insulin resistance through activation of the RhoA/Rho kinase signaling pathway. We have found that metabolic perturbation would increase GGPPS expression in the skeletal muscles of db/db mice and high fat diet-fed mice. To address the metabolic effects of GGPPS activity in skeletal muscle, we generated mice with specific GGPPS deletions in their skeletal muscle tissue. Heterozygous knock-out of GGPPS in the skeletal muscle improved systemic insulin sensitivity and glucose homeostasis in mice fed both normal chow and high fat diets. These metabolic alterations were accompanied by activated PI3K/Akt signaling and enhanced glucose uptake in the skeletal muscle. Further investigation showed that the free fatty acid-stimulated GGPPS expression in the skeletal muscle was able to enhance the geranylgeranylation of RhoA, which further induced the inhibitory phosphorylation of IRS-1 (Ser-307) by increasing Rho kinase activity. These results implicate a crucial role of the GGPPS/RhoA/Rho kinase/IRS-1 pathway in skeletal muscle, in which it mediates lipid-induced systemic insulin resistance in obese mice. Therefore, skeletal muscle GGPPS may represent a potential pharmacological target for the prevention and treatment of obesity-related type 2 diabetes.

Gene variations of ROCKs and risk of ischaemic stroke: the Women's Genome Health Study

Recent animal and human studies have demonstrated the importance of the ROCK (RhoA/Rho-associated kinase) pathway in IsST (ischaemic stroke). Whether the genetic variation within ROCK-associated genes modulates the risk of IsST remains elusive. The association between 66 tSNPs [tagging SNPs (single nucleotide polymorphisms)] of three ROCK-associated genes [ROCK1, ROCK2 and ARHGEF10 (Rho guanine-nucleotide-exchange factor 10)] and the incidence of IsST was investigated in 23294 Caucasian female participants of the prospective WGHS (Women's Genome Health Study). All were free of known cancer and cardiovascular disease at baseline. During a 15-year follow-up period, 323 participants developed their first ever IsST. Multivariable Cox regression analysis was performed to investigate the relationship between genotypes and risk of IsST assuming an additive genetic model. Haplotype-block analysis was also performed. A total of ten tSNPs were associated with the risk of IsST (three in ARHGEF10 and seven in ROCK1; P<0.050). Further investigation using the haplotype-block analysis revealed a similar significant association of pre-specified haplotypes of ROCK1 with the risk of IsST (P=0.005). If corroborated in other large prospective studies, the findings of the present study suggest that genetic variation within the ROCK-associated pathway gene loci examined, and in particular ROCK1 gene variation, may influence the risk of IsST.

Rho/Rho-associated coiled-coil forming kinase pathway as therapeutic targets for statins in atherosclerosis

SIGNIFICANCE

The 3-hydroxy-methylglutaryl coenzyme A reductase inhibitors or statins are important therapeutic agents for lowering serum cholesterol levels. However, recent studies suggest that statins may exert atheroprotective effects beyond cholesterol lowering. These so-called "pleiotropic effects" include effects of statins on vascular and inflammatory cells. Thus, it is important to understand whether other signaling pathways that are involved in atherosclerosis could be targets of statins, and if so, whether individuals with "overactivity" of these pathways could benefit from statin therapy, regardless of serum cholesterol level.

RECENT ADVANCES

Statins inhibit the synthesis of isoprenoids, which are important for the function of the Rho/Rho-associated coiled-coil containing kinase (ROCK) pathway. Indeed, recent studies suggest that inhibition of the Rho/ROCK pathway by statins could lead to improved endothelial function and decreased vascular inflammation and atherosclerosis. Thus, the Rho/ROCK pathway has emerged as an important target of statin therapy for reducing atherosclerosis and possibly cardiovascular disease.

CRITICAL ISSUES

Because atherosclerosis is both a lipid and an inflammatory disease, it is important to understand how inhibition of Rho/ROCK pathway could contribute to statins' antiatherosclerotic effects.

FUTURE DIRECTIONS

The role of ROCKs (ROCK1 and ROCK2) in endothelial, smooth muscle, and inflammatory cells needs to be determined in the context of atherogenesis. This could lead to the development of specific ROCK1 or ROCK2 inhibitors, which could have greater therapeutic benefits with less toxicity. Also, clinical trials will need to be performed to determine whether inhibition of ROCKs, with and without statins, could lead to further reduction in atherosclerosis and cardiovascular disease.

Calreticulin affects cell adhesiveness through differential phosphorylation of insulin receptor substrate-1

Cellular adhesion to the underlying substratum is regulated through numerous signaling pathways. It has been suggested that insulin receptor substrate 1 (IRS-1) is involved in some of these pathways, via association with and activation of transmembrane integrins. Calreticulin, as an important endoplasmic reticulum-resident, calcium-binding protein with a chaperone function, plays an obvious role in proteomic expression. Our previous work showed that calreticulin mediates cell adhesion not only by affecting protein expression but also by affecting the state of regulatory protein phosphorylation, such as that of c-src. Here, we demonstrate that calreticulin affects the abundance of IRS-1 such that the absence of calreticulin is paralleled by a decrease in IRS-1 levels and the unregulated overexpression of calreticulin is accompanied by an increase in IRS-1 levels. These changes in the abundance of calreticulin and IRS-1 are accompanied by changes in cell-substratum adhesiveness and phosphorylation, such that increases in the expression of calreticulin and IRS-1 are paralleled by an increase in focal contact-based cell-substratum adhesiveness, and a decrease in the expression of these proteins brings about a decrease in cell-substratum adhesiveness. Wild type and calreticulin-null mouse embryonic fibroblasts (MEFs) were cultured and the IRS-1 isoform profile was assessed. Differences in morphology and motility were also quantified. While no substantial differences in the speed of locomotion were found, the directionality of cell movement was greatly promoted by the presence of calreticulin. Calreticulin expression was also found to have a dramatic effect on the phosphorylation state of serine 636 of IRS-1, such that phosphorylation of IRS-1 on serine 636 increased radically in the absence of calreticulin. Most importantly, treatment of cells with the RhoA/ROCK inhibitor, Y-27632, which among its many effects also inhibited serine 636 phosphorylation of IRS-1, had profound effects on cell-substratum adhesion, in that it suppressed focal contacts, induced extensive close contacts, and increased the strength of adhesion. The latter effect, while counterintuitive, can be explained by the close contacts comprising labile bonds but in large numbers. In addition, the lability of bonds in close contacts would permit fast locomotion. An interesting and novel finding is that Y-27632 treatment of MEFs releases them from contact inhibition of locomotion, as evidenced by the invasion of a cell's underside by the thin lamellae and filopodia of a cell in close apposition.

Metabolic actions of Rho-kinase in periphery and brain

Obesity has increased at an alarming rate in recent years and is now a worldwide public health problem. Elucidating the mechanisms behind the metabolic dysfunctions associated with obesity is of high priority. The metabolic function of Rho-kinase (Rho-associated coiled-coil-containing kinase; ROCK) has been the subject of a great deal of investigation in metabolic-related diseases. It appears that inhibition of ROCK activity is beneficial for the treatment of a wide range of cardiovascular-related diseases. However, recent studies with genetic models of ROCK demonstrate that ROCK plays a positive role in insulin and leptin signaling. Here we discuss the newly identified functions of ROCK in regulating glucose and energy metabolism, with particular emphasis on metabolic actions of insulin and leptin.

A novel strategy to increase the proliferative potential of adult human β-cells while maintaining their differentiated phenotype

Our previous studies demonstrated that Wnt/GSK-3/β-catenin and mTOR signaling are necessary to stimulate proliferative processes in adult human β-cells. Direct inhibition of GSK-3, that engages Wnt signaling downstream of the Wnt receptor, increases β-catenin nuclear translocation and β-cell proliferation but results in lower insulin content. Our current goal was to engage canonical and non-canonical Wnt signaling at the receptor level to significantly increase human β-cell proliferation while maintaining a β-cell phenotype in intact islets. We adopted a system that utilized conditioned medium from L cells that expressed Wnt3a, R-spondin-3 and Noggin (L-WRN conditioned medium). In addition we used a ROCK inhibitor (Y-27632) and SB-431542 (that results in RhoA inhibition) in these cultures. Treatment of intact human islets with L-WRN conditioned medium plus inhibitors significantly increased DNA synthesis ∼6 fold in a rapamycin-sensitive manner. Moreover, this treatment strikingly increased human β-cell proliferation ∼20 fold above glucose alone. Only the combination of L-WRN conditioned medium with RhoA/ROCK inhibitors resulted in substantial proliferation. Transcriptome-wide gene expression profiling demonstrated that L-WRN medium provoked robust changes in several signaling families, including enhanced β-catenin-mediated and β-cell-specific gene expression. This treatment also increased expression of Nr4a2 and Irs2 and resulted in phosphorylation of Akt. Importantly, glucose-stimulated insulin secretion and content were not downregulated by L-WRN medium treatment. Our data demonstrate that engaging Wnt signaling at the receptor level by this method leads to necessary crosstalk between multiple signaling pathways including activation of Akt, mTOR, Wnt/β-catenin, PKA/CREB, and inhibition of RhoA/ROCK that substantially increase human β-cell proliferation while maintaining the β-cell phenotype.

Regulation of glucose transport by ROCK1 differs from that of ROCK2 and is controlled by actin polymerization

A role of Rho-associated coiled-coil-containing protein kinase (ROCK)1 in regulating whole-body glucose homeostasis has been reported. However, cell-autonomous effects of ROCK1 on insulin-dependent glucose transport in adipocytes and muscle cells have not been elucidated. To determine the specific role of ROCK1 in glucose transport directly, ROCK1 expression in 3T3-L1 adipocytes and L6 myoblasts was biologically modulated. Here, we show that small interfering RNA-mediated ROCK1 depletion decreased insulin-induced glucose transport in adipocytes and myoblasts, whereas adenovirus-mediated ROCK1 expression increased this in a dose-dependent manner, indicating that ROCK1 is permissive for glucose transport. Inhibition of ROCK1 also impaired glucose transporter 4 translocation in 3T3-L1 adipocytes. Importantly, the ED₅₀ of insulin for adipocyte glucose transport was reduced when ROCK1 was expressed, leading to hypersensitivity to insulin. These effects are dependent on actin cytoskeleton remodeling, because inhibitors of actin polymerization significantly decreased ROCK1's effect to promote insulin-stimulated glucose transport. Unlike ROCK2, ROCK1 binding to insulin receptor substrate (IRS)-1 was not detected by immunoprecipitation, although cell fractionation demonstrated both ROCK isoforms localize with IRS-1 in low-density microsomes. Moreover, insulin's ability to increase IRS-1 tyrosine 612 and serine 632/635 phosphorylation was attenuated by ROCK1 suppression. Replacing IRS-1 serine 632/635 with alanine reduced insulin-stimulated phosphatidylinositol 3-kinase activation and glucose transport in 3T3-L1 adipocytes, indicating that phosphorylation of these serine residues of IRS-1, which are substrates of the ROCK2 isoform in vitro, are crucial for maximal stimulation of glucose transport by insulin. Our studies identify ROCK1 as an important positive regulator of insulin action on glucose transport in adipocytes and muscle cells.

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.

Cholesterol-independent neuroprotective and neurotoxic activities of statins: perspectives for statin use in Alzheimer disease and other age-related neurodegenerative disorders

Statins, long known to be beneficial in conditions where dyslipidemia occurs by lowering serum cholesterol levels, also have been proposed for use in neurodegenerative conditions, including Alzheimer disease. However, it is not clear that the purported effectiveness of statins in neurodegenerative disorders is directly related to cholesterol-lowering effects of these agents; rather, the pleiotropic functions of statins likely play critical roles. Moreover, it is becoming more apparent with additional studies that statins can have deleterious effects in preclinical studies and lack effectiveness in various recent clinical trials. This perspective paper outlines pros and cons of the use of statins in neurodegenerative disorders, with particular emphasis on Alzheimer disease.

In vivo activation of ROCK1 by insulin is impaired in skeletal muscle of humans with type 2 diabetes

To determine whether serine/threonine ROCK1 is activated by insulin in vivo in humans and whether impaired activation of ROCK1 could play a role in the pathogenesis of insulin resistance, we measured the activity of ROCK1 and the protein content of the Rho family in vastus lateralis muscle of lean, obese nondiabetic, and obese type 2 diabetic subjects. Biopsies were taken after an overnight fast and after a 3-h hyperinsulinemic euglycemic clamp. Insulin-stimulated GDR was reduced 38% in obese nondiabetic subjects compared with lean, 62% in obese diabetic subjects compared with lean, and 39% in obese diabetic compared with obese nondiabetic subjects (all comparisons P < 0.001). Insulin-stimulated IRS-1 tyrosine phosphorylation is impaired 41-48% in diabetic subjects compared with lean or obese subjects. Basal activity of ROCK1 was similar in all groups. Insulin increased ROCK1 activity 2.1-fold in lean and 1.7-fold in obese nondiabetic subjects in muscle. However, ROCK1 activity did not increase in response to insulin in muscle of obese type 2 diabetic subjects without change in ROCK1 protein levels. Importantly, insulin-stimulated ROCK1 activity was positively correlated with insulin-mediated GDR in lean subjects (P < 0.01) but not in obese or type 2 diabetic subjects. Moreover, RhoE GTPase that inhibits the catalytic activity of ROCK1 by binding to the kinase domain of the enzyme is notably increased in obese type 2 diabetic subjects, accounting for defective ROCK1 activity. Thus, these data suggest that ROCK1 may play an important role in the pathogenesis of resistance to insulin action on glucose disposal in muscle of obese type 2 diabetic subjects.

Molecular mechanism of insulin resistance in obesity and type 2 diabetes

Insulin resistance is a major risk factor for developing type 2 diabetes caused by the inability of insulin-target tissues to respond properly to insulin, and contributes to the morbidity of obesity. Insulin action involves a series of signaling cascades initiated by insulin binding to its receptor, eliciting receptor autophosphorylation and activation of the receptor tyrosine kinase, resulting in tyrosine phosphorylation of insulin receptor substrates (IRSs). Phosphorylation of IRSs leads to activation of phosphatidylinositol 3-kinase (PI3K) and, subsequently, to activation of Akt and its downstream mediator AS160, all of which are important steps for stimulating glucose transport induced by insulin. Although the mechanisms underlying insulin resistance are not completely understood in skeletal muscle, it is thought to result, at least in part, from impaired insulin-dependent PI3K activation and downstream signaling. This review focuses on the molecular basis of skeletal muscle insulin resistance in obesity and type 2 diabetes. In addition, the effects of insulin-sensitizing agent treatment and lifestyle intervention of human insulin-resistant subjects on insulin signaling cascade are discussed. Furthermore, the role of Rho-kinase, a newly identified regulator of insulin action in insulin control of metabolism, is addressed.

Identification of ROCK1 as an upstream activator of the JIP-3 to JNK signaling axis in response to UVB damage

Although apoptosis triggered by ultraviolet B (UVB)-mediated activation of the c-Jun N-terminal kinase (JNK) pathway is mediated by both intrinsic and extrinsic pathways, the mechanism of initiation of JNK activation remains obscure. Here, we report the characterization of the JNK-interacting protein 3 (JIP-3) scaffolding protein as an interacting partner of Rho-associated kinase 1 (ROCK1), as determined by tandem affinity protein purification. Upon UVB-induced stress in keratinocytes, ROCK1 was activated, bound to JIP-3, and activated the JNK pathway. Moreover, phosphorylation of JIP-3 by ROCK1 was crucial for the recruitment of JNK. Inhibition of the activity of ROCK1 in keratinocytes resulted in decreased activation of the JNK pathway and thus a reduction in apoptosis. ROCK1(+/-) mice exhibited decreased UVB-mediated activation of JNK and apoptosis relative to wild-type mice. Our findings present a new molecular mechanism by which ROCK1 functions as a UVB sensor that regulates apoptosis, an important event in the prevention of skin cancer.

Superoxide from NADPH oxidase upregulates type 5 phosphodiesterase in human vascular smooth muscle cells: inhibition with iloprost and NONOate

BACKGROUND AND PURPOSE

To determine whether there is an association between vascular NADPH oxidase (NOX), superoxide, the small GTPase Rac(1) and PDE type 5 (PDE5) in human vascular smooth muscle cell (hVSMCs).

EXPERIMENTAL APPROACH

hVSMCs were incubated with xanthine-xanthine oxidase (X-XO; a superoxide generating system) or the thromboxane A(2) analogue, U46619 (+/-superoxide dismutase (SOD) or apocynin) for 16 h. The expression of PDE5 and NOX-1 was assessed using Western blotting and superoxide measured. The role of Rac(1) in superoxide generation was assessed by overexpressing either the dominant-negative or constitutively active Rac isoforms. The effects of iloprost, DETA-NONOate and the Rho-kinase inhibitor, Y27632, on PDE5 and NOX-1 expression were also studied.

KEY RESULTS

Following 16 h incubation, U46619 and X-XO promoted the expression of PDE5 and NOX-1, an effect blocked by SOD or apocynin when co-incubated over the same time course. X-XO and U46619 both promoted the formation of superoxide. Overexpression of dominant-negative Rac(1) or addition of iloprost, DETA-NONOate or Y27632 completely blocked both superoxide release and PDE5 protein expression and activity.

CONCLUSIONS AND IMPLICATIONS

These data demonstrate that superoxide derived from NOX upregulates the expression of PDE5 in human VSMCs. As PDE5 hydrolyses cyclic GMP, this effect may blunt the vasculoprotective actions of NO.

Effects of atorvastatin and pravastatin on signal transduction related to glucose uptake in 3T3L1 adipocytes

A number of patients with hyperlipidemia are prescribed 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors that are concomitantly used along with the treatment of diabetes mellitus. The effects of atorvastatin and pravastatin on insulin-induced glucose uptake and the related signal transduction in 3T3L1 adipocytes were studied. 3T3L1 fibroblasts were differentiated into adipocytes, pretreated with atorvastatin or pravastatin, and then exposed to insulin. Glucose uptake and the amount of insulin signal proteins were measured. Atorvastatin significantly decreased insulin-stimulated 2-deoxyglucose uptake in 3T3L1 adipocytes associated with the prevention of translocation of GLUT4 into the plasma membrane. The amounts of Rab4 and RhoA that required lipid modification with farnesyl or geranylgeranyl pyrophosphate, in the membrane fraction were decreased by atorvastatin. Insulin-induced tyrosine phosphorylation of IRS-1 and serine/threonine phosphorylation of Akt were reduced by atorvastatin. Pravastatin did not modify these insulin-induced changes in the signal transduction. Inhibitors of the RhoA/Rho kinase system, C3 and Y27632, as well as atorvastatin reduced insulin-induced changes in signal transduction. Atorvastatin and pravastatin did not affect messenger RNA expression, protein level, and tyrosine phosphorylation of insulin receptors. In conclusion, hydrophobic atorvastatin decreases the glucose uptake by 3T3L1 adipocytes since it can enter the cell and prevents lipid modification of some proteins that are involved in the insulin signal transduction process.

Inhibition of ROCK activity allows InlF-mediated invasion and increased virulence of Listeria monocytogenes

Listeria monocytogenes is an intracellular bacterial pathogen that causes life-threatening disease. The mechanisms used by L. monocytogenes to invade non-professional phagocytic cells are not fully understood. In addition to the requirement of bacterial determinants, host cell conditions profoundly influence infection. Here, we have shown that inhibition of the RhoA/ROCK pathway by pharmacological inhibitors or RNA interference results in increased L. monocytogenes invasion of murine fibroblasts and hepatocytes. InlF, a member of the internalin multigene family with no known function, was identified as a L. monocytogenes-specific factor mediating increased host cell binding and entry. Conversely, activation of RhoA/ROCK activity resulted in decreased L. monocytogenes adhesion and invasion. Furthermore, virulence of wild-type bacteria during infection of mice was significantly increased upon inhibition of ROCK activity, whereas colonization and virulence of an inlF deletion mutant was not affected, thus supporting a role for InlF as a functional virulence determinant in vivo under specific conditions. In addition, inhibition of ROCK activity in human-derived cells enhanced either bacterial adhesion or adhesion and entry in an InlF-independent manner, further suggesting a host species or cell type-specific role for InlF and that additional bacterial determinants are involved in mediating ROCK-regulated invasion of human cells.

Pleiotropic effects of statin therapy: molecular mechanisms and clinical results

Statins inhibit the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, which is required for cholesterol biosynthesis, and are beneficial in the primary and secondary prevention of cardiovascular disease. Most of the benefits of statin therapy are owing to the lowering of serum cholesterol levels. However, by inhibiting HMG-CoA reductase, statins can also inhibit the synthesis of isoprenoids, which are important lipid attachments for intracellular signaling molecules, such as Rho, Rac and Cdc42. Therefore, it is possible that statins might exert cholesterol-independent or 'pleiotropic' effects through direct inhibition of these small GTP-binding proteins. Recent studies have shown that statins might have important roles in diseases that are not mediated by cholesterol. Here, we review data from recent clinical trials that support the concept of statin pleiotropy and provide a rationale for their clinical importance.

Rho kinase (ROCK) inhibitors

The Rho kinase (ROCK) isoforms, ROCK1 and ROCK2, were initially discovered as downstream targets of the small GTP-binding protein Rho. Because ROCKs mediate various important cellular functions such as cell shape, motility, secretion, proliferation, and gene expression, it is likely that this pathway will intersect with other signaling pathways known to contribute to cardiovascular disease. Indeed, ROCKs have already been implicated in the regulation of vascular tone, proliferation, inflammation, and oxidative stress. However, it is not entirely clear how ROCKs are regulated, what some of their downstream targets are, and whether ROCK1 and ROCK2 mediate different cellular functions. Clinically, inhibition of ROCK pathway is believed to contribute to some of the cardiovascular benefits of statin therapy that are independent of lipid lowering (ie, pleiotropic effects). To what extent ROCK activity is inhibited in patients on statin therapy is not known, but it may have important clinical implications. Indeed, several pharmaceutical companies are already actively engaged in the development of ROCK inhibitors as the next generation of therapeutic agents for cardiovascular disease because evidence from animal studies suggests the potential involvement of ROCK in hypertension and atherosclerosis.

ROCK and Rho: biochemistry and neuronal functions of Rho-associated protein kinases

Rho-associated protein kinases (ROCKs) play key roles in mediating the control of the actin cytoskeleton by Rho family GTPases in response to extracellular signals. Such signaling pathways contribute to diverse neuronal functions from cell migration to axonal guidance to dendritic spine morphology to axonal regeneration to cell survival. In this review, the authors summarize biochemical knowledge of ROCK function and categorize neuronal ROCK-dependent signaling pathways. Further study of ROCK signal transduction mechanisms and specificities will enhance our understanding of brain development, plasticity, and repair. The ROCK pathway also provides a potential site for therapeutic intervention to promote neuronal regeneration and to limit degeneration.

Genetic and pharmacological inhibition of Rho-associated kinase II enhances adipogenesis

Rho-associated kinase (ROCK) regulates reorganization of actin cytoskeleton. During adipogenesis, the structure of filamentous actin is converted from long stress fibers to cortical actin, suggesting that the ROCK is involved in adipogenesis. Two ROCK isoforms have been identified: ROCK-I and ROCK-II. However, pharmacological inhibitors of ROCK cannot distinguish two ROCK isoforms. In the present study, we examined the role of ROCK in adipogenesis and actin cytoskeleton using genetic and pharmacological approaches. Y-27632, which inhibits the activity of both ROCK isoforms, enhanced adipogenesis through the up-regulation of adipogenic transcription factors in 3T3-L1 cells. Furthermore, Y-27632 restored inhibition of adipogenesis by lysophosphatidic acid, which activates Rho. Regarding actin cytoskeleton, Y-27632 disrupted stress fibers in 3T3-L1 preadipocytes. Next, we analyzed adipogenesis of mouse embryonic fibroblasts (MEFs) derived from ROCK-I and ROCK-II knock-out mice, respectively. Adipogenesis of ROCK-II (-/-) MEFs was markedly enhanced compared with wild-type MEFs while that of ROCK-I (-/-) MEFs was not. In contrast to pharmacological approaches, no obvious alteration was found in actin cytoskeleton of ROCK-II (-/-) MEFs compared with wild-type MEFs. In 3T3-L1 cells, knockdown of ROCK-II by RNA interference enhanced the expression of adipogenic transcription factors while that of ROCK-I did not. Moreover, Y-27632 inhibited IRS-1 serine phosphorylation and enhanced Akt phosphorylation in 3T3-L1 preadipocytes. Similarly, Akt phosphorylation in ROCK-II (-/-) MEFs was augmented compared with wild-type MEFs. In conclusion, inhibition of ROCK-II, not ROCK-I, enhances adipogenesis accompanied by the up-regulation of adipogenic transcription factors. Augmentation of insulin signaling may contribute to the enhancement of adipogenesis.

RhoA/Rho kinase blocks muscle differentiation via serine phosphorylation of insulin receptor substrate-1 and -2

Although the RhoA/Rho kinase (RhoA/ROK) pathway has been extensively investigated, its roles and downstream signaling pathways are still not well understood in myogenic processes. Therefore, we examined the effects of RhoA/ROK on myogenic processes and their signaling molecules using H9c2 and C2C12 cells. Increases in RhoA/ROK activities and serine phosphorylation levels of insulin receptor substrate (IRS)-1 (Ser307 and Ser636/639) and IRS-2 were found in proliferating myoblasts, whereas IRS-1/2 tyrosine phosphorylation and phosphatidylinositol (PI) 3-kinase activity increased during the differentiation process. ROK strongly bound to IRS-1/2 in proliferation medium but dissociated from them in differentiation medium (DM). ROK inactivation by a ROK inhibitor, Y27632, or a dominant-negative ROK, decreased IRS-1/2 serine phosphorylation with increases in IRS-1/2 tyrosine phosphorylation and PI 3-kinase activity, which led to muscle differentiation even in proliferation medium. Inhibition of ROK also enhanced differentiation in DM. ROK activation by a constitutive active ROK blocked muscle differentiation with the increased IRS-1/2 serine phosphorylation, followed by decreases in IRS-1/2 tyrosine phosphorylation and PI 3-kinase activity in DM. Interestingly, fibroblast growth factor-2 added to DM also blocked muscle differentiation through RhoA/ROK activation. Fibroblast growth factor-2 blockage of muscle differentiation was reversed by Y27632. Collectively, these results suggest that the RhoA/ROK pathway blocks muscle differentiation by phosphorylating IRS proteins at serine residues, resulting in the decreased IRS-1/2 tyrosine phosphorylation and PI 3-kinase activity. The absence of the inhibitory effects of RhoA/ROK in DM due to low concentrations of myogenic inhibitory growth factors seems to allow IRS-1/2 tyrosine phosphorylation, which stimulates muscle differentiation via transducing normal myogenic signaling.

Cross-species microarray analysis with the OSCAR system suggests an INSR->Pax6->NQO1 neuro-protective pathway in aging and Alzheimer's disease

OSCAR is a web platform for cluster and cross-species analysis of microarray data. It provides a comprehensive but friendly environment to both users and algorithm developers. For users, OSCAR provides cluster tools for both single and multiple species data, together with interactive analysis features. For single species data, OSCAR currently provides Hierarchical Clustering, K-means, partition around medoids (PAM), Self-Organizing Map (SOM), Tight Clustering and a novel algorithm called ‘Consensus Tight-clustering’. The new Consensus Tight-clustering algorithm delivers robust gene clusters and its result is more resistant to false positives than other state-of-the-art algorithms. For cross-species data analysis, OSCAR provides two novel computational tools: ‘coherentCluster’, ‘coherentSubset’ and a novel visualization tool: ‘comparative heatmap’. Applying the coherentCluster algorithm to human and fly aging data, we identified several coherent clusters of genes, which share co-regulation patterns that are highly correlated with the aging process in both of the two species. One coherent cluster suggests insulin receptor (INSR) may regulate Pax6 in both species and across different tissues. Further analysis with human brain expression and pathological data suggests an INSR->Pax6->quinone oxidoreductase (NQO1)->detoxification neuro-protective pathway might be present in aging or diseased brain. For algorithm developers, OSCAR is a plug-and-play platform. With little effort, developers can plug their own algorithms into the OSCAR server without revealing the source codes, which will equip their command line executables with user-friendly interface and interactive analysis capability. In summary, OSCAR initiates an open platform for development and application of clustering and cross-species analysis programs. OSCAR stands for an open system for cluster analysis of microarray data. It is available at: http://biocomp.bioen.uiuc.edu/oscar

Marked increase of insulin gene transcription by suppression of the Rho/Rho-kinase pathway

The hallmarks of type 2 diabetes are pancreatic beta-cell dysfunction and insulin resistance. It has been suggested that Rho/Rho-kinase is a mediator of insulin signaling, and thereby involved in the development of insulin resistance, regulation of insulin action, and glucose homeostasis, but the role of Rho/Rho-kinase in beta-cells remained unknown. The aim of this study was to examine the possible role of Rho/Rho-kinase in beta-cell function. Immunostaining showed that RhoA was expressed in mature beta-cells, with higher expression observed in beta-cells of diabetic C57BL/KsJ-db/db mice compared to non-diabetic mice. In addition, to examine the functional role of Rho/Rho-kinase in beta-cells, we evaluated the effect of Rho-kinase inhibitors on insulin biosynthesis. Northern blot analysis showed that insulin mRNA levels were markedly increased by Rho-kinase inhibitors, Y-27632 and fasudil, in beta-cell-derived HIT-T15 cells. Furthermore, using the luciferase reporter gene assay, insulin promoter activity was also dramatically increased by Y-27632, which was associated with an increase in the insulin mRNA level. These results suggest that suppression of Rho/Rho-kinase increases insulin promoter activity, which leads to an increase in insulin mRNA level. Taken together, Rho/Rho-kinase is activated in beta-cells under diabetic conditions and suppression of the Rho/Rho-kinase pathway increases insulin gene transcription. These results imply that Rho/Rho-kinase activation is involved in the suppression of insulin expression found in diabetes and that suppression of the Rho/Rho-kinase pathway could be a useful tool to augment insulin gene transcription.

ROCKs as therapeutic targets in cardiovascular diseases

There is growing evidence that Rho-kinases (ROCKs), the immediate downstream targets of the small guanosine triphosphate-binding protein Rho, may contribute to cardiovascular disease. ROCKs play a central role in diverse cellular functions such as smooth muscle contraction, stress fiber formation and cell migration and proliferation. Overactivity of ROCKs is observed in cerebral ischemia, coronary vasospasm, hypertension, vascular inflammation, arteriosclerosis and atherosclerosis. ROCKs, therefore, may be an important and still relatively unexplored therapeutic target in cardiovascular disease. Recent experimental and clinical studies using ROCK inhibitors such as Y-27632 and fasudil have revealed a critical role of ROCKs in embryonic development, inflammation and oncogenesis. This review will focus on the potential role of ROCKs in cellular functions and discuss the prospects of ROCK inhibitors as emerging therapy for cardiovascular diseases.

Physiological role of ROCKs in the cardiovascular system

Rho-associated kinases (ROCKs), the immediate downstream targets of RhoA, are ubiquitously expressed serine-threonine protein kinases that are involved in diverse cellular functions, including smooth muscle contraction, actin cytoskeleton organization, cell adhesion and motility, and gene expression. Recent studies have shown that ROCKs may play a pivotal role in cardiovascular diseases such as vasospastic angina, ischemic stroke, and heart failure. Indeed, inhibition of ROCKs by statins or other selective inhibitors leads to the upregulation and activation of endothelial nitric oxide synthase (eNOS) and reduction of vascular inflammation and atherosclerosis. Thus inhibition of ROCKs may contribute to some of the cholesterol-independent beneficial effects of statin therapy. Currently, two ROCK isoforms have been identified, ROCK1 and ROCK2. Because ROCK inhibitors are nonselective with respect to ROCK1 and ROCK2 and also, in some cases, may be nonspecific with respect to other ROCK-related kinases such as myristolated alanine-rich C kinase substrate (MARCKS), protein kinase A, and protein kinase C, the precise role of ROCKs in cardiovascular disease remains unknown. However, with the recent development of ROCK1- and ROCK2-knockout mice, further dissection of ROCK signaling pathways is now possible. Herein we review what is known about the physiological role of ROCKs in the cardiovascular system and speculate about how inhibition of ROCKs could provide cardiovascular benefits.

JNK and ROKalpha function in the noncanonical Wnt/RhoA signaling pathway to regulate Xenopus convergent extension movements

The Wnt/planar cell polarity (PCP) pathway plays a critical role in wing, eye, and sensory bristle development of Drosophila and in convergent extension (CE) movements during vertebrate gastrulation. In Drosophila, Jun N-terminal kinase (JNK) and Rho-associated kinase (ROK) participate in RhoA-mediated PCP pathway during eye and wing development. In mammalian cells, Rac1 and Cdc42 but not RhoA are required for JNK activation by Wnt/PCP signals. However, there has been no evidence that Rho GTPases regulate JNK activation in Wnt/PCP pathway during Xenopus CE movements. Here, we report that Xenopus RhoA (XRhoA), but not Xenopus Cdc42 (XCdc42), is essential for JNK activation downstream of the Wnt/PCP pathway during Xenopus CE movements, and the phenotypic effect of loss of XRhoA function was rescued by Xenopus JNK1 (XeJNK1). In addition, XRhoA rescues the inhibition of CE movements by the DEP domain deletion mutant of Xenopus Dsh (Xdsh-DeltaDEP), which has dominant negative (DN) effects on JNK activation, and the PDZ domain deletion mutant of Xdsh (Xdsh-DeltaPDZ). Moreover, we demonstrate that Xenopus Rho-associated kinase alpha (xROKalpha), which is expressed mainly in mesoderm and ectoderm that undergo extensive cell rearrangements, regulates CE movements without affecting gene expression, and injection of xROKalpha rescued the inhibition of CE movements caused by DN XRhoA. Finally, we show that ROKalpha and JNK synergistically rescued embryos overexpressing DN XRhoA, which exhibit gastrulation defects, although ROKalpha is not required for JNK activation. Together, these data suggest that JNK and ROKalpha function in the noncanonical Wnt/RhoA pathway to regulate Xenopus CE movements.

Transcription-dependent and transcription-independent functions of the classical progesterone receptor in Xenopus ovaries

Two forms of the classical progesterone receptors (PR), XPR-1 and XPR-2, have been cloned in Xenopus laevis. Their relative roles in mediating progesterone action in the ovaries are not clear. Using antibodies generated against the cloned XPR-2, we demonstrated here that the somatic follicle cells expressed an 80-kDa PR protein, termed XPR-1. Treatment of follicle cells with progesterone resulted in disappearance of this protein, consistent with proteosome-mediated XPR-1 protein degradation. A smaller (approximately 70 kDa) PR protein, termed XPR-2, was expressed in the oocytes, but not in follicle cells. XPR-2 underwent progesterone-induced phosphorylation but not protein degradation. Treating isolated ovarian fragments with progesterone caused oocyte maturation and the release of the mature oocytes from the ovarian tissues ("ovulation"). Inhibition of transcription, with actinomycin D, did not interfere with progesterone-induced oocyte maturation but blocked "ovulation" so that mature oocytes were trapped in the follicles. These results suggest that the dual functions of progesterone, transcription-dependent follicle rupture and transcription-independent oocyte maturation, are mediated by the two forms of PR proteins differentially expressed in the follicle cells and the oocytes, respectively.

Role of Rho-kinase in regulation of insulin action and glucose homeostasis

Accumulating evidence indicates an important role for serine phosphorylation of IRS-1 in the regulation of insulin action. Recent studies suggest that Rho-kinase (ROK) is a mediator of insulin signaling, via interaction with IRS-1. Here we show that insulin stimulation of glucose transport is impaired when ROK is chemically or biologically inhibited in cultured adipocytes and myotubes and in isolated soleus muscle ex vivo. Inactivation of ROK also reduces insulin-stimulated IRS-1 tyrosine phosphorylation and PI3K activity. Moreover, inhibition of ROK activity in mice causes insulin resistance by reducing insulin-stimulated glucose uptake in skeletal muscle in vivo. Mass spectrometry analysis identifies IRS-1 Ser632/635 as substrates of ROK in vitro, and mutation of these sites inhibits insulin signaling. These results strongly suggest that ROK regulates insulin-stimulated glucose transport in vitro and in vivo. Thus, ROK is an important regulator of insulin signaling and glucose metabolism.

Inhibition of Rho-kinase leads to rapid activation of phosphatidylinositol 3-kinase/protein kinase Akt and cardiovascular protection

OBJECTIVE

Rho-kinase activity is increased in cardiovascular diseases and in patients with cardiovascular risk factors. However, it is not known whether inhibition of Rho-kinase could lead to cardiovascular protection and, if so, by what mechanism.

METHODS AND RESULTS

In human endothelial cells, the Rho-kinase inhibitor, hydroxyfasudil (HF) (1 to 100 micromol/L), increased Akt serine-473 phosphorylation within 15 minutes, leading to a 2.2-fold and 4.0-fold increase in Akt kinase activity and nitric oxide (NO) release, respectively. Activation of Akt and eNOS by HF was completely blocked by the phosphatidylinositol 3-kinase (PI3-kinase) inhibitor, LY294002 (10 micromol/L). To determine the physiological relevance of this pathway, we used 2 models of ischemia-reperfusion (I/R) injury. Acute administration of fasudil (10 mg/kg, intraperitoneal, 1 hour before ischemia) decreased leukocyte recruitment and adhesion to the mesenteric endothelium after I/R injury in wild-type but not eNOS-/- mice. Similarly, treatment with fasudil decreased myocardial infarct size by 38% in rats subjected to transient coronary artery occlusion. Cotreatment with 2 PI3-kinase inhibitors, wortmannin and LY294002, or the eNOS inhibitor, L-NAME, blocked the cardiovascular protective effects of fasudil.

CONCLUSIONS

Inhibition of Rho-kinase leads to the activation of the PI3-kinase/Akt/eNOS pathway and cardiovascular protection. These findings suggest that Rho-kinase may play an important role in mediating the inflammatory response to I/R injury.

Modulation of insulin action

Insulin is a key hormone regulating the control of metabolism and the maintenance of normoglycaemia and normolipidaemia. Insulin acts by binding to its cell surface receptor, thus activating the receptor's intrinsic tyrosine kinase activity, resulting in receptor autophosphorylation and phosphorylation of several substrates. Tyrosine phosphorylated residues on the receptor itself and on subsequently bound receptor substrates provide docking sites for downstream signalling molecules, including adapters, protein serine/threonine kinases, phosphoinositide kinases and exchange factors. Collectively, those molecules orchestrate the numerous insulin-mediated physiological responses. A clear picture is emerging of the way in which insulin elicits several intracellular signalling pathways to mediate its physiologic functions. A further challenge, being pursued by several laboratories, is to understand the molecular mechanisms that underlie insulin action at the peripheral level, deregulation of which ultimately leads to hyperglycaemia and Type 2 diabetes. We review how circulating factors such as insulin itself, TNF-alpha, interleukins, fatty acids and glycation products influence insulin action through insulin signalling molecules themselves or through other pathways ultimately impinging on the insulin-signalling pathway. Understanding how the mechanism by which molecular insulin action is modulated by these factors will potentially provide new targets for pharmacological agents, to enable the control of altered glucose and lipid metabolism and diabetes.

Rocks: multifunctional kinases in cell behaviour

ROCKs, or Rho kinases, are serine/threonine kinases that are involved in many aspects of cell motility, from smooth-muscle contraction to cell migration and neurite outgrowth. Recent experiments have defined new functions of ROCKs in cells, including centrosome positioning and cell-size regulation, which might contribute to various physiological and pathological states.

The carboxy-terminal pleckstrin homology domain of ROCK interacts with filamin-A

The small GTPase Rho and its effector ROCK/Rho-kinase regulate actin cytoskeletal reorganization through phosphorylation of the regulatory light chain of myosin II. We previously reported that ROCK co-purified with the actin-binding protein filamin-A from HeLa cells. Here, we show that the pleckstrin homology (PH) domain of ROCK, but not the kinase or coiled-coil domain, interacts with filamin-A. We also determined that the PH domain of ROCK binds to the carboxy-terminal region of filamin-A containing the last 24th repeat. ROCK co-localized with filamin-A at the protrusive cell membranes of HeLa cells.

Insulin receptor substrate 4 associates with the protein IRAS

The insulin receptor substrates (IRSs) are key components in signaling from the insulin receptor, and consequently any proteins that interact with them are expected to participate in insulin signaling. In this study we have searched for proteins that interact with IRS-4 by identifying the proteins that coimmunoprecipitated with IRS-4 from human embryonic kidney 293 cells by microsequencing through mass spectrometry. A group of proteins was found. These included phosphatidylinositol 3-kinase, a protein previously identified as an IRS-4 interactor, and several proteins for which there was no previous evidence of IRS-4 association. One of these proteins, named IRAS, that had been found earlier in another context was examined in detail. The results from the overexpression of IRAS, where its amount was about the same as that of IRS-4, indicated that IRAS associated directly with IRS-4 and showed that the increased complexation of IRS-4 with IRAS did not alter the insulin-stimulated tyrosine phosphorylation of IRS-4 or the association of IRS-4 with phosphatidylinositol 3-kinase or Grb2. On the other hand, overexpression of IRAS enhanced IRS-4-dependent insulin stimulation of the extracellularly regulated kinase. The domains of IRAS and IRS-4 responsible for the association of these two proteins were identified, and it was shown that IRAS also associates with IRS-1, IRS-2, and IRS-3.

Modulation of CREB activity by the Rho GTPase regulates cell and organism size during mouse embryonic development

Rho GTPases regulate several aspects of tissue morphogenesis during animal development. We found that mice lacking the Rho-inhibitory protein, p190-B RhoGAP, are 30% reduced in size and exhibit developmental defects strikingly similar to those seen in mice lacking the CREB transcription factor. In p190-B RhoGAP-deficient mice, CREB phosphorylation is substantially reduced in embryonic tissues. Embryo-derived cells contain abnormally high levels of active Rho protein, are reduced in size, and exhibit defects in CREB activation upon exposure to insulin or IGF-1. The cell size defect is rescued by expression of constitutively activated CREB, and in wild-type cells, expression of activated Rho or dominant-negative CREB results in reduced cell size. Together, these results suggest that activity of the Rho GTPase modulates a signal from insulin/IGFs to CREB that determines cell size and animal size during embryogenesis.

RhoGAP: the next big thing for small mice?

The size of an organism is determined by the number and size of its constituent cells. The insulin/IGF-1 signaling systems have been long recognized to play a critical role in the determination of body size. Now the generation of mice deficient for a RhoGAP suggests that this small G protein might also regulate the growth of animals.

Regulated cationic channel function in Xenopus oocytes expressing Drosophila big brain

Big brain (bib) is a neurogenic gene that when mutated causes defects in cell fate determination during Drosophila neurogenesis through an unknown mechanism. The protein Big Brain (BIB) has sequence identity with the major intrinsic protein family that includes the water- and ion-conducting aquaporin channels. We show here that BIB expressed heterologously in Xenopus oocytes provides a voltage-insensitive, nonselective cation channel function with permeability to K+ > Na+ >> tetraethylammonium. The conductance, activated in response to endogenous signaling pathways in BIB-expressing oocytes, is decreased after treatment with 20 microm insulin and is enhanced with 10 microm lavendustin A, a tyrosine kinase inhibitor. Western blot analysis confirms that BIB is tyrosine-phosphorylated. Both tyrosine phosphorylation and the potentiating effect of lavendustin A are removed by partial deletion of the C terminus (amino acids 317-700). Current activation is not observed in control oocytes or in oocytes expressing a nonfunctional mutant (BIB E71N) that appears to be expressed on the plasma membrane by confocal microscopy and Western blotting. These results indicate that BIB can participate in tyrosine kinase-regulated transmembrane signaling and may suggest a role for membrane depolarization in the neurogenic function of BIB in early development.

Active Rho kinase (ROK-alpha ) associates with insulin receptor substrate-1 and inhibits insulin signaling in vascular smooth muscle cells

Recent studies from our laboratory have shown that insulin stimulates myosin-bound phosphatase (MBP) in vascular smooth muscle cells (VSMCs) by decreasing site-specific phosphorylation of the myosin-bound subunit (MBS) of MBP via nitric oxide/cGMP-mediated Rho/Rho kinase inactivation. Here we tested potential interactions between Rho kinase and insulin signaling pathways. In control VSMCs, insulin inactivates ROK-alpha, the major Rho kinase isoform in VSMCs, and inhibits thrombin-induced increase in ROK-alpha association with the insulin receptor substrate-1 (IRS-1). Hypertension (in spontaneous hypertensive rats) or expression of an active RhoA(V14) up-regulates Rho kinase activity and increases ROK-alpha/IRS-1 association resulting in IRS-1 serine phosphorylation that leads to inhibition of both insulin-induced IRS-1 tyrosine phosphorylation and phosphatidylinositol 3-kinase (PI3-kinase) activation. In contrast, expression of dominant negative RhoA or cGMP-dependent protein kinase type I alpha inactivates Rho kinase, abolishes ROK-alpha/IRS-1 association, and potentiates insulin-induced tyrosine phosphorylation and PI3-kinase activation leading to decreased MBS(T695) phosphorylation and decreased MBP inhibition. Collectively, these results suggest a novel function for ROK-alpha in insulin signal transduction at the level of IRS-1 and potential cross-talk between cGMP-dependent protein kinase type I alpha, Rho/Rho kinase signaling, and insulin signaling at the level of IRS-1/PI3-kinase.

GIPC participates in G protein signaling downstream of insulin-like growth factor 1 receptor

Several recent studies have demonstrated that insulin-like growth factor (IGF)-1-induced mitogen-activated protein kinase (MAP kinase) activation is abolished by pertussis toxin, suggesting that trimeric G proteins of the G(i) class are novel cellular targets of the IGF-1 signaling pathway. We report here that the intracellular domain of the Xenopus IGF-1 receptor is capable of binding to the Xenopus homolog of mammalian GIPC, a PDZ domain-containing protein previously identified as a binding partner of G(i)-specific GAP (RGS-GAIP). Binding of xGIPC to xIGF-1 receptor is independent of the kinase activity of the receptor and appears to require the PDZ domain of xGIPC. Injection of two C-terminal truncation mutants that retained the PDZ domain blocked IGF-1-induced Xenopus MAP kinase activation and oocyte maturation. While full-length xGIPC injection did not significantly alter insulin response, it greatly enhanced human RGS-GAIP in stimulating the insulin response in frog oocytes. This represents the first demonstration that GIPC x RGS-GAIP complex acts positively in IGF-1 receptor signal transduction.

Signalling through the insulin receptor

The insulin receptor substrates function at the heart of the insulin signalling network. It has recently become apparent that the intracellular localisation of these molecules is regulated in a precise manner that is critical for both the generation and the termination of the insulin signal. Some insulin receptor substrate isoforms appear to be associated with an insoluble matrix that resembles the cytoskeleton. When inappropriately dissociated from this matrix the signalling network collapses concomitant with loss of insulin sensitivity.