Rho GTPase signaling in inflammation and transformation

S-Nitrosylation of Septin2 Exacerbates Aortic Aneurysm and Dissection by Coupling the TIAM1-RAC1 Axis in Macrophages

BACKGROUND

S-Nitrosylation (SNO), a prototypic redox-based posttranslational modification, is involved in cardiovascular disease. Aortic aneurysm and dissection are high-risk cardiovascular diseases without an effective cure. The aim of this study was to determine the role of SNO of Septin2 in macrophages in aortic aneurysm and dissection.

METHODS

Biotin-switch assay combined with liquid chromatography-tandem mass spectrometry was performed to identify the S-nitrosylated proteins in aortic tissue from both patients undergoing surgery for aortic dissection and Apoe-/- mice infused with angiotensin II. Angiotensin II-induced aortic aneurysm model and β-aminopropionitrile-induced aortic aneurysm and dissection model were used to determine the role of SNO of Septin2 (SNO-Septin2) in aortic aneurysm and dissection development. RNA-sequencing analysis was performed to recapitulate possible changes in the transcriptome profile of SNO-Septin2 in macrophages in aortic aneurysm and dissection. Liquid chromatography-tandem mass spectrometry and coimmunoprecipitation were used to uncover the TIAM1-RAC1 (Ras-related C3 botulinum toxin substrate 1) axis as the downstream target of SNO-Septin2. Both R-Ketorolac and NSC23766 treatments were used to inhibit the TIAM1-RAC1 axis.

RESULTS

Septin2 was identified S-nitrosylated at cysteine 111 (Cys111) in both aortic tissue from patients undergoing surgery for aortic dissection and Apoe-/- mice infused with Angiotensin II. SNO-Septin2 was demonstrated driving the development of aortic aneurysm and dissection. By RNA-sequencing, SNO-Septin2 in macrophages was demonstrated to exacerbate vascular inflammation and extracellular matrix degradation in aortic aneurysm. Next, TIAM1 (T lymphoma invasion and metastasis-inducing protein 1) was identified as a SNO-Septin2 target protein. Mechanistically, compared with unmodified Septin2, SNO-Septin2 reduced its interaction with TIAM1 and activated the TIAM1-RAC1 axis and consequent nuclear factor-κB signaling pathway, resulting in stronger inflammation and extracellular matrix degradation mediated by macrophages. Consistently, both R-Ketorolac and NSC23766 treatments protected against aortic aneurysm and dissection by inhibiting the TIAM1-RAC1 axis.

CONCLUSIONS

SNO-Septin2 drives aortic aneurysm and dissection through coupling the TIAM1-RAC1 axis in macrophages and activating the nuclear factor-κB signaling pathway-dependent inflammation and extracellular matrix degradation. Pharmacological blockade of RAC1 by R-Ketorolac or NSC23766 may therefore represent a potential treatment against aortic aneurysm and dissection.

The Immunomodulatory Effects of Statins on Macrophages

Statins are 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors used worldwide to manage dyslipidaemia and thus limit the development of atherosclerotic disease and its complications. These atheroprotective drugs are now known to exert pleiotropic actions outside of their cholesterol-lowering activity, including altering immune cell function. Macrophages are phagocytic leukocytes that play critical functional roles in the pathogenesis of atherosclerosis and are directly targeted by statins. Early studies documented the anti-inflammatory effects of statins on macrophages, but emerging evidence suggests that these drugs can also enhance pro-inflammatory macrophage responses, creating an unresolved paradox. This review comprehensively examines the in vitro, in vivo, and clinical literature to document the statin-induced changes in macrophage polarization and immunomodulatory functions, explore the underlying mechanisms involved, and offer potential explanations for this paradox. A better understanding of the immunomodulatory actions of statins on macrophages should pave the way for the development of novel therapeutic approaches to manage atherosclerosis and other chronic diseases and conditions characterised by unresolved inflammation.

Genetic Markers PLEKHA7, ABCC5, and KALRN Are Not Associated With the Progression of Primary Angle Closure Glaucoma (PACG) in Malays

Introduction PLEKHA7, ABCC5, and KALRN have been identified as susceptible genetic markers related to glaucoma. We aimed to investigate the association between the identified susceptible genetic markers PLEKHA7 rs11024102, ABCC5 rs17217796, and KALRN rs1392912 in the progression of primary angle-closure glaucoma (PACG) in Malay patients. Methods For this study, 163 Malay patients with PACG were recruited from April 2015 to April 2017 at Hospital Universiti Sains Malaysia and Hospital Raja Perempuan Zainab II, Kota Bharu. Venesection was performed. DNA was extracted using a commercial DNA extraction kit. The primer was optimized for rs11024102, rs17217796, and rs1392912 of the PLEKHA7, ABCC5, and KALRN genes, respectively. Polymerase chain reaction (PCR) was performed, and PCR products were purified. A DNA sequencer was used to identify polymorphisms. Progression was based on the agreement between the Advanced Glaucoma Intervention Study scoring system and the Hodapp-Parrish and Anderson staging system. The scoring was conducted on two reliable consecutive Humphrey visual fields (HVFs) during the recruitment period and two baseline HVFs obtained when the diagnosis was made. Based on the scoring, patients were grouped into progressed and non-progressed. A chi-square test was used to analyze the association between the genetic markers and the progression of PACG. Results One hundred and sixty-three Malay patients with PACG (58 men and 105 women) were recruited. Twenty-nine patients (18%) had visual field progression of PACG after a mean (SD) follow-up of 6.0 (1.0) years. The minor allele frequencies for PLEKHA7 rs11024102 (G/A), ABCC5 rs17217796 (C/G), and KALRN rs1392912 (A/G) were 0.44, 0.08, and 0.48, respectively. We found that rs11024102 (p=0.828), rs17217796 (p=0.865), and rs1392912 (p=0.684) were not associated with PACG progression in the Malay patients. Conclusion Although PLEKHA7 and ABCC5 were found to be genetic markers associated with the risk of PACG, they played no roles in PACG progression in the Malay population. Moreover, KALRN was not significantly associated with PACG progression. Other susceptible genetic markers may be responsible for PACG progression.

ArhGAP15, a RacGAP, Acts as a Temporal Signaling Regulator of Mac-1 Affinity in Sterile Inflammation

During inflammation, leukocyte recruitment has to be tightly controlled to prevent overwhelming leukocyte infiltration, activation, and, consequently, organ damage. A central regulator of leukocyte recruitment is Rac1. In this study, we analyzed the effects of the RacGAP ArhGAP15 on leukocyte recruitment. Using ArhGAP15-deficient mice, reduced neutrophil adhesion and transmigration in the TNF-α-inflamed cremaster muscle and a prolongation of chemokine-dependent leukocyte adhesion could be observed. In a murine model of sterile kidney injury, reduced neutrophil infiltration, and serum creatinine levels were apparent. Further in vitro and in vivo analyses revealed a defective intravascular crawling capacity, resulting from increased affinity of the β₂-integrin Mac-1 after prolonged chemokine stimulation of neutrophils. LFA-1 activity regulation was not affected. Summarizing, ArhGAP15 specifically regulates Mac-1, but not LFA-1, and affects leukocyte recruitment by controlling postadhesion strengthening and intravascular crawling in a Mac-1-dependent manner. In conclusion, ArhGAP15 is involved in the time-dependent regulation of leukocyte postadhesion in sterile inflammation.

Microglial polarization: novel therapeutic mechanism against Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease that results in progressive dementia, and exhibits high disability and fatality rates. Recent evidence has demonstrated that neuroinflammation is critical in the pathophysiological processes of AD, which is characterized by the activation of microglia and astrocytes. Under different stimuli, microglia are usually activated into two polarized states, termed the classical 'M1' phenotype and the alternative 'M2' phenotype. M1 microglia are considered to promote inflammatory injury in AD; in contrast, M2 microglia exert neuroprotective effects. Imbalanced microglial polarization, in the form of excessive activation of M1 microglia and dysfunction of M2 microglia, markedly promotes the development of AD. Furthermore, an increasing number of studies have shown that the transition of microglia from the M1 to M2 phenotype could potently alleviate pathological damage in AD. Hence, this article reviews the current knowledge regarding the role of microglial M1/M2 polarization in the pathophysiology of AD. In addition, we summarize several approaches that protect against AD by altering the polarization states of microglia. This review aims to contribute to a better understanding of the pathogenesis of AD and, moreover, to explore the potential of novel drugs for the treatment of AD in the future.

Systematic functional analysis of the Ras GTPase family unveils a conserved network required for anterograde protein trafficking

Phylogeny is often used to compare entire families of genes/proteins. We previously showed that classification of Caenorhabditis elegans Rho GTPases on the basis of their enzymatic properties was significantly different from sequence alignments. To further develop this concept, we have developed an integrated approach to classify C. elegans small GTPases based on functional data comprising affinity for GTP, sub-cellular localization, tissue distribution and silencing impact. This analysis led to establish a novel functional classification for small GTPases. To test the relevance of this classification in mammals, we focused our attention on the human orthologs of small GTPases from a specific group comprising arf-1.2, evl-20, arl-1, Y54E10BR.2, unc-108 and rab-7. We then tested their involvement in protein secretion and membrane traffic in mammalian systems. Using this approach we identify a novel network containing 18 GTPases, and 23 functionally interacting proteins, conserved between C. elegans and mammals, which is involved in membrane traffic and protein secretion.

Dietary flavonoid luteolin attenuates uropathogenic Escherichia. Coli invasion of the urinary bladder

Uropathogenic Escherichia coli (UPEC), the primary uropathogen, adhere to and invade bladder epithelial cells (BECs) to establish a successful urinary tract infection (UTI). Emerging antibiotic resistance requires novel nonantibiotic strategies. Our previous study indicated that luteolin attenuated adhesive and invasive abilities as well as cytotoxicity of UPEC on T24 BECs through down-regulating UPEC virulence factors. The aims of this study were to investigate the possible function of the flavonoid luteolin and the mechanisms by which luteolin functions in UPEC-induced bladder infection. Firstly, obvious reduction of UPEC invasion but not adhesion were observed in luteolin-pretreated 5637 and T24 BECs sa well as mice bladder via colony counting. The luteolin-mediated suppression of UPEC invasion was linked to elevated levels of intracellular cAMP induced by inhibiting the activity of cAMP-phosphodiesterases (cAMP-PDEs), which resulting activation of protein kinase A, thereby negatively regulating Rac1-GTPase-mediated actin polymerization. Furthermore, p38 MAPK was primarily and ERK1/2 was partially involved in luteolin-mediated suppression of UPEC invasion and actin polymerization, as confirmed with chemical activators of p38 MAPK and ERK1/2. These data suggest that luteolin can protect bladder epithelial cells against UPEC invasion. Therefore, luteolin or luteolin-rich products as dietary supplement may be beneficial to control the UPEC-related bladder infections, and cAMP-PDEs may be a therapy target for UTIs treatment. © 2016 BioFactors, 42(6):674-685, 2016.

Bilobol inhibits the lipopolysaccharide-induced expression and distribution of RhoA in HepG2 human hepatocellular carcinoma cells

Recent studies have revealed the localization of RhoA protein in the cell nucleus, in addition to its distribution in the cytosol and cell membrane. The results of previous studies by our group indicated that nuclear RhoA expression is increased, or RhoA is transported into the nucleus, when cells become cancerous or damaged. Furthermore, application of the anticancer agent Taxol appeared to reduce nuclear RhoA localization, indicating an association between the nuclear translocation of RhoA and tumor progression. Bilobol is a traditional Chinese medicine ingredient, however, its anticancer effect has remained unclear. The present study aimed to demonstrate the anticarcinogenic action of bilobol against hepatocellular carcinoma, in order to lay the foundations for subsequent research into the mechanisms underlying its anticancer effects. In the present study, HepG2 cells were treated with lipopolysaccharide (LPS), to induce inflammation, and/or bilobol. By performing an ELISA, it was observed that bilobol was able to suppress the inflammation induced by LPS. In addition, immunofluorescence and western blot analyses indicated that bilobol may reduce the expression of RhoA, suppress translocation of RhoA into the nucleus and inhibit the RhoA/Rho-associated protein kinase signaling pathway. In conclusion, the present study revealed the potential anticancer effects of bilobol.

Significance of expression of ECT2 in gastric cancer

AIM: To investigate the expression of epithelial cell transforming sequence 2 (ECT2) in gastric cancer (GC) and to analyze its correlation with clinicopathological characteristics.

METHODS: Immunohistochemistry (IHC) and RT-PCR were used to examine the expression of ECT2 protein and mRNA in GC tissues and paired adjacent normal tissues. The correlation between ECT2 expression and clinicopathological characteristics was then analyzed.

RESULTS: In comparison with adjacent normal tissues (36.0%), the expression of ECT2 protein in GC tissues (76.0%) was significantly higher (P < 0.01), and the expression of ECT2 mRNA in GC tissues was also significantly higher in GC tissues than in adjacent normal tissues. The expression of ECT2 protein and mRNA was related to histologic differentiation, TNM stage and lymph node metastasis in GC (P < 0.05), but not to gender, age or tumor size (P > 0.05).

CONCLUSION: Both ECT2 protein and mRNA are overexpressed in GC, and ECT2 expression correlates with the histologic differentiation, TNM stage and lymph node metastasis in GC. ECT2 may play an important role during GC progression, and may serve as a good factor to indicate biologic behavior of GC.

Rho/ROCK signaling in motility and metastasis of gastric cancer

Gastric cancer is one of the most frequent and lethal malignancies worldwide because of high frequency of metastasis. Tumor cell motility and invasion play fundamental roles in cancer metastasis. Recent studies have revealed that the Rho/Rho-associated protein kinases (ROCK) pathway plays a critical role in the regulation of cancer cell motility and invasion. In addition, the Rho/ROCK pathway plays important roles in invasion and metastasis on the basis of its predominant function of cell cytoskeletal regulation in gastric cancer. According to the current understanding of tumor motility, there are two modes of tumor cell movement: mesenchymal and amoeboid. In addition, cancer cell movement can be interchangeable between the mesenchymal and amoeboid movements under certain conditions. Control of cell motility through the actin cytoskeleton creates the potential for regulating tumor cell metastasis. In this review we discuss Rho GTPases and ROCK signaling and describe the mechanisms of Rho/ROCK activity with regard to motility and metastasis in gastric cancer. In addition, we provide an insight of the therapeutic potential of targeting the Rho/ROCK pathway.

Identification of novel genetic Loci associated with thyroid peroxidase antibodies and clinical thyroid disease

Autoimmune thyroid diseases (AITD) are common, affecting 2-5% of the general population. Individuals with positive thyroid peroxidase antibodies (TPOAbs) have an increased risk of autoimmune hypothyroidism (Hashimoto's thyroiditis), as well as autoimmune hyperthyroidism (Graves' disease). As the possible causative genes of TPOAbs and AITD remain largely unknown, we performed GWAS meta-analyses in 18,297 individuals for TPOAb-positivity (1769 TPOAb-positives and 16,528 TPOAb-negatives) and in 12,353 individuals for TPOAb serum levels, with replication in 8,990 individuals. Significant associations (P<5×10(-8)) were detected at TPO-rs11675434, ATXN2-rs653178, and BACH2-rs10944479 for TPOAb-positivity, and at TPO-rs11675434, MAGI3-rs1230666, and KALRN-rs2010099 for TPOAb levels. Individual and combined effects (genetic risk scores) of these variants on (subclinical) hypo- and hyperthyroidism, goiter and thyroid cancer were studied. Individuals with a high genetic risk score had, besides an increased risk of TPOAb-positivity (OR: 2.18, 95% CI 1.68-2.81, P = 8.1×10(-8)), a higher risk of increased thyroid-stimulating hormone levels (OR: 1.51, 95% CI 1.26-1.82, P = 2.9×10(-6)), as well as a decreased risk of goiter (OR: 0.77, 95% CI 0.66-0.89, P = 6.5×10(-4)). The MAGI3 and BACH2 variants were associated with an increased risk of hyperthyroidism, which was replicated in an independent cohort of patients with Graves' disease (OR: 1.37, 95% CI 1.22-1.54, P = 1.2×10(-7) and OR: 1.25, 95% CI 1.12-1.39, P = 6.2×10(-5)). The MAGI3 variant was also associated with an increased risk of hypothyroidism (OR: 1.57, 95% CI 1.18-2.10, P = 1.9×10(-3)). This first GWAS meta-analysis for TPOAbs identified five newly associated loci, three of which were also associated with clinical thyroid disease. With these markers we identified a large subgroup in the general population with a substantially increased risk of TPOAbs. The results provide insight into why individuals with thyroid autoimmunity do or do not eventually develop thyroid disease, and these markers may therefore predict which TPOAb-positives are particularly at risk of developing clinical thyroid dysfunction.

LPS-induced nuclear translocation of RhoA is dependent on NF-κB in the human lung cancer cell line A549

RhoA, an extensively studied member of the Rho GTPase family, has been identified as a mediator of pro-inflammatory responses and aggressive carcinogenesis. Bacterial lipopolysaccharide (LPS) is known to be a potent stimulator of inflammatory cytokine production. LPS is able to alter the activity of RhoA and the subcellular distribution of RhoA is altered according to its activity. In this study, we investigated a possible link between RhoA and the LPS/nuclear factor (NF)-κB signaling pathway. In the present study, western blotting and pull-down and immunofluorescence assays were performed to investigate the activity of RhoA in A549 cells following LPS stimulation. The results showed that LPS was able to activate RhoA. Furthermore, western blotting and an immunofluorescence assay were carried out to investigate the nuclear expression of RhoA in A549 cells following LPS stimulation. The results indicated that LPS triggers the nuclear translocation of RhoA. Furthermore, western blotting, NF-κB small interfering RNA (siRNA) transfection and an immunofluorescence assay were performed to investigate the role of NF-κB in LPS-induced RhoA nuclear translocation in A549 cells. The results showed that LPS-induced RhoA nuclear translocation was inhibited by NF-κB depletion in A549 cells. RhoA and NF-κB siRNA transfection, western blotting and ELISA were carried out to investigate the role of RhoA in the LPS-induced secretion of interleukin (IL)-6 and IL-8 in A549 cells. The depletion of RhoA using RhoA siRNA decreased the LPS-induced secretion of IL-6 and IL-8, similar to the effect of NF-κB depletion. These results demonstrate that LPS is able to activate RhoA and trigger its nuclear translocation, which is dependent on NF-κB, and that RhoA plays a significant role in the LPS/NF-κB signaling pathway.

Validation study of genetic associations with coronary artery disease on chromosome 3q13-21 and potential effect modification by smoking

The CATHGEN study reported associations of chromosome 3q13-21 genes (KALRN, MYLK, CDGAP, and GATA2) with early-onset coronary artery disease (CAD). This study attempted to independently validate those associations. Eleven single nucleotide polymorphisms (SNPs) were examined (rs10934490, rs16834817, rs6810298, rs9289231, rs12637456, rs1444768, rs1444754, rs4234218, rs2335052, rs3803, rs2713604) in patients (N = 1618) from the Intermountain Heart Collaborative Study (IHCS). Given the higher smoking prevalence in CATHGEN than IHCS (41% vs. 11% in controls, 74% vs. 29% in cases), smoking stratification and genotype-smoking interactions were evaluated. Suggestive association was found for GATA2 (rs2713604, p = 0.057, OR = 1.2). Among smokers, associations were found in CDGAP (rs10934490, p = 0.019, OR = 1.6) and KALRN (rs12637456, p = 0.011, OR = 2.0) and suggestive association was found in MYLK (rs16834871, p = 0.051, OR = 1.8, adjusting for gender). No SNP association was found among non-smokers, but smoking/SNP interactions were detected for CDGAP (rs10934491, p = 0.017) and KALRN (rs12637456, p = 0.010). Similar differences in SNP effects by smoking status were observed on re-analysis of CATHGEN. CAD associations were suggestive for GATA2 and among smokers significant post hoc associations were found in KALRN, MYLK, and CDGAP. Genetic risk conferred by some of these genes may be modified by smoking. Future CAD association studies of these and other genes should evaluate effect modification by smoking.

Dexamethasone suppresses infiltration of RhoA+ cells into early lesions of rat traumatic brain injury

Inflammatory cell infiltration is a major part of secondary tissue damage in traumatic brain injury (TBI). RhoA is an important member of Rho GTPases and is involved in leukocyte migration. Inhibition of RhoA and its downstream target, Rho-associated coiled kinase (ROCK), has been proven to promote axon regeneration and function recovery following injury in the central nervous system (CNS). Previously, we showed that dexamethasone, an immunosuppressive corticosteroid, attenuated early expression of three molecules associated with microglia/macrophages activation following TBI in rats. Here, the effects of dexamethasone on the early expression of RhoA have been investigated in brains of TBI rats by immunohistochemistry. In brains of rats treated with TBI alone, significant RhoA+ cell accumulation was observed at 18 h post-injury and continuously increased during our observed time period. The accumulated RhoA+ cells were distributed to the areas of pannecrosis and selective neuronal loss. Most accumulated RhoA+ cells were identified as active microglia/macrophages by double-labelling. Dexamethasone (1 mg/kg body weight) was intraperitoneally injected on day 0 and 2 immediately following brain injury. Numbers of RhoA+ cells were significantly reduced on day 1 and 2 following administration of dexamethasone but returned to vehicle control level on day 4. However, dexamethasone treatment did not change the proportion of RhoA+ cells. These observations suggest that dexamethasone has only a transient effect on early leukocyte recruitment.

Expression of RhoA by inflammatory macrophages and T cells in rat experimental autoimmune neuritis

RhoA is one of the best-studied members of Rho GTPases. Experimental autoimmune neuritis (EAN), which is characterized by infiltration of T cells and macrophages into the peripheral nervous system, is an autoantigen-specific T-cell-mediated animal model of human Guillain-Barré Syndrome. In this study, RhoA expression has been investigated in the dorsal/ventral roots of EAN rats by immunohistochemistry. A significant accumulation of RhoA+ cells was observed on Day 12, with a maximum around Day 15, correlating to the clinical severity of EAN. In dorsal/ventral roots of EAN, RhoA+ cells were seen in perivascular areas but also in the parenchyma. Furthermore, double-labelling experiments showed that the major cellular sources of RhoA were reactive macrophages and T cells. In conclusion, this is the first demonstration of the presence of RhoA in the dorsal/ventral roots of EAN. The time courses and cellular sources of RhoA together with the functions of RhoA indicate that RhoA may function to facilitate macrophage and T-cell infiltration in EAN and therefore could be a potential therapeutic target.

Peakwide mapping on chromosome 3q13 identifies the kalirin gene as a novel candidate gene for coronary artery disease

A susceptibility locus for coronary artery disease (CAD) has been mapped to chromosome 3q13-21 in a linkage study of early-onset CAD. We completed an association-mapping study across the 1-LOD-unit-down supporting interval, using two independent white case-control data sets (CATHGEN, initial and validation) to evaluate association under the peak. Single-nucleotide polymorphisms (SNPs) evenly spaced at 100-kb intervals were screened in the initial data set (N=468). Promising SNPs (P<.1) were then examined in the validation data set (N=514). Significant findings (P<.05) in the combined initial and validation data sets were further evaluated in multiple independent data sets, including a family-based data set (N=2,954), an African American case-control data set (N=190), and an additional white control data set (N=255). The association between genotype and aortic atherosclerosis was examined in 145 human aortas. The peakwide survey found evidence of association in SNPs from multiple genes. The strongest associations were found in three SNPs from the kalirin (KALRN) gene, especially in patients with early-onset CAD (P=.00001-00028 in the combined CATHGEN data sets). In-depth investigation of the gene found that an intronic SNP, rs9289231, was associated with early-onset CAD in all white data sets examined (P<.05). In the joint analysis of all white early-onset CAD cases (N=332) and controls (N=546), rs9289231 was highly significant (P=.00008), with an odds-ratio estimate of 2.1. Furthermore, the risk allele of this SNP was associated with atherosclerosis burden (P=.03) in 145 human aortas. KALRN is a protein with many functions, including the inhibition of inducible nitric oxide synthase and guanine-exchange-factor activity. KALRN and two other associated genes identified in this study (CDGAP and MYLK) belong to the Rho GTPase-signaling pathway. Our data suggest the importance of the KALRN gene and the Rho GTPase-signaling pathway in the pathogenesis of CAD.

Drug Insight: statins and gastrointestinal cancer

Statins are popular lipid-lowering drugs that have had a great impact on the primary and secondary prevention of cardiovascular diseases. Basic and clinical research have also revealed that statins have biologic activities that go beyond lipid lowering, and suggest that they might have other therapeutic benefits. Perhaps the most exciting of these additional biologic effects is the finding that statins can exert an anticancer effect on cultured cancer cells, and in animal models. Clinical studies of statins for the treatment and prevention of cancer have, however, produced conflicting results. This review critically evaluates the current body of literature on the role of statins in the treatment and prevention of gastrointestinal cancers, with particular focus on clinical and observational studies.

Binding of Manumycin A Inhibits IκB Kinase β Activity

IkappaB kinase (IKK) catalytic subunits play a key role in cytokinemediated nuclear factor (NF)-kappaB signaling, and a loss of NF-kappaB function appears to inhibit inflammation and oncogenesis. Manumycin A is a potent and selective farnesyltransferase inhibitor with antitumor activity. We found that manumycin A caused a rapid and potent inhibition of IKK activity induced by tumor necrosis factor alpha in a number of cell types. Most unexpectedly, other classes of farnesyltransferase inhibitors had no inhibitory effect. To identify the molecular mechanisms of manumycin A action, cultured human HepG2 hepatoma cells were transiently transfected with various IKKalpha and IKKbeta constructs, and a striking difference in manumycin A sensitivity was observed. Furthermore, cells expressing wild-type IKKbeta and IKKbeta mutated in the activation loop at Cys-179 exhibited covalent homotypic dimerization of IKKbeta in response to manumycin A, whereas substitution of Cys-662 and -716 conferred protection against dimer formation. Direct inhibition of IKK activity and formation of stable IKKbeta dimers were observed in the presence of manumycin A that could be blocked by dithiothreitol. IKK interaction with the adaptor protein IKKgamma/NEMO was disrupted in manumycin A-treated cells. Most importantly, administration of manumycin A to mice xenografted with murine B16F10 tumors caused potent IKK-suppressive effects. Thus, manumycin A with its epoxyquinoid moieties plays an important regulatory function in IKK signaling through pathways distinct from its role as a protein farnesylation inhibitor.

Lesional Expression of RhoA and RhoB following Traumatic Brain Injury in Humans

Inhibition of the small GTPase Rho or of its downstream target Rho-associated kinase (ROCK) has been shown to promote axon regeneration and to improve functional recovery following traumatic CNS lesions in the adult rat. In order to determine the expression pattern of RhoA and RhoB following human traumatic brain injury (TBI) and to assess whether Rho is a possible target for pharmacological intervention in humans, we investigated expression patterns of RhoA and RhoB in brain specimens from 25 patients who died after closed TBI in comparison to brain tissue derived from four neuropathologically unaffected control patients by immunohistochemistry. A highly significant lesional upregulation of both RhoA and RhoB was observed beginning several hours after the traumatic event and continuing for months after TBI. The cellular sources of both molecules included polymorphonuclear granulocytes, monocytes/macrophages, and reactive astrocytes. Additionally, expression of RhoA was also detected in neuronal cells in some of the cases. From our data, we conclude that inhibition of Rho is a promising mechanism for the development of new pharmacological interventions in human TBI. As the observed upregulation of RhoA and RhoB was still detectable months after TBI, we speculate that even delayed treatment with Rho inhibitors might be a therapeutic option.

Scambio, a novel guanine nucleotide exchange factor for Rho

Background

Small GTPases of the Rho family are critical regulators of various cellular functions including actin cytoskeleton organization, activation of kinase cascades and mitogenesis. For this reason, a major objective has been to understand the mechanisms of Rho GTPase regulation. Here, we examine the function of a novel protein, Scambio, which shares homology with the DH-PH domains of several known guanine nucleotide exchange factors for Rho family members.

Results

Scambio is located on human chromosome 14q11.1, encodes a protein of around 181 kDa, and is highly expressed in both heart and skeletal muscle. In contrast to most DH-PH-domain containing proteins, it binds the activated, GTP-bound forms of Rac and Cdc42. However, it fails to associate with V14RhoA. Immunofluorescence studies indicate that Scambio and activated Rac3 colocalize in membrane ruffles at the cell periphery. In accordance with these findings, Scambio does not activate either Rac or Cdc42 but rather, stimulates guanine nucleotide exchange on RhoA and its close relative, RhoC.

Conclusion

Scambio associates with Rac in its activated conformation and functions as a guanine nucleotide exchange factor for Rho.

Cytotoxic necrotizing factor 1 enhances reactive oxygen species-dependent transcription and secretion of proinflammatory cytokines in human uroepithelial cells

Uropathogenic Escherichia coli strains frequently produce a Rho-activating protein toxin named cytotoxic necrotizing factor type 1 (CNF1). We herein report that CNF1 promotes transcription and release of tumor necrosis factor alpha, gamma interferon, interleukin-6 (IL-6), and IL-8 proinflammatory cytokines and increases the production of reactive oxygen species (ROS) in uroepithelial T24 cells. The antioxidant N-acetyl-L-cysteine counteracts these phenomena, a fact which suggests a role for ROS-mediated signaling in CNF1-induced proinflammatory cytokine production.

Rho kinase blockade prevents inflammation via nuclear factor kappa B inhibition: evidence in Crohn's disease and experimental colitis

BACKGROUND & AIMS

Rho proteins are involved in the regulation of several cellular functions. Data from in vitro studies suggest that RhoA could be involved in the inflammatory response. We investigated the role of RhoA and its downstream effector Rho kinase in intestinal inflammation.

METHODS

Activation of RhoA was assessed by pull-down assays. A specific inhibitor of Rho kinase, Y-27632, was used to examine the role of Rho kinase in inflammatory response in vivo and in vitro by molecular biology and by immunological and biochemical approaches.

RESULTS

Increased activation of RhoA was found in inflamed intestinal mucosa of patients with Crohn's disease and of rats with 2,4,6-trinitrobenzene sulfonic acid-induced colitis. Oral administration of Y-27632 in rats significantly reduced the colonic inflammation. In vitro, activation of RhoA alone was sufficient to induce tumor necrosis factor production. Y-27632 inhibited production of tumor necrosis factor-alpha and interleukin-1 beta by lamina propria and peripheral blood mononuclear cells. Rho kinase inhibition prevented nuclear factor kappa B activation and I-kappa B phosphorylation and degradation. We showed that Rho kinase associates with and activates I-kappa B kinase alpha and that Y-27632 prevents I-kappa B kinase activation.

CONCLUSIONS

Our study provides the first evidence that Rho kinase activates I-kappa B kinase and, thus, nuclear factor kappa B, suggesting a key role of Rho kinase in inflammatory responses and intestinal inflammation. Specific inhibition of Rho kinase may be a promising approach for the treatment of patients with Crohn's disease.

An Escherichia coli cytotoxin increases superoxide anion generation via rac in epithelial cells

Cytotoxic Necrotizing Factor 1 (CNF1) is a protein toxin from Escherichia coli that induces the activation of Rho, Rac, and Cdc42 GTPases, all involved in actin reorganization. Rac plays a further role in oxidase function. In epithelial cells, CNF1 has been reported to induce a phagocytic-like behavior in terms of a ruffle-driven ingestion of large material. We herein show that CNF1-activated epithelial cells may exert additional cell responses typical of professional phagocytes following stimulation, i.e., an increase in oxygen consumption and the generation of superoxide anions. Such effects were triggered by the contact of latex beads with epithelial cells and were significantly augmented by CNF1-induced Rac activation. Altogether our data indicate that Rac, one of the targets of CNF1, plays a pivotal role in these phenomena, suggesting the involvement in epithelial cells of a Rac-dependent NADPH-oxidase complex similar to that employed by professional phagocytes.

Rho signals to cell growth and apoptosis

Ras and Rho GTPases are among the best studied signaling molecules in molecular biology. Essential cellular processes, such as cell growth, lipid metabolism, cytoarchitecture, membrane trafficking, transcriptional regulation, apoptosis, and response to genotoxic agents, are directly modulated by different members of this superfamily of proteins. Not until recently have we begun to understand the physiological implications of Ras and Rho GTPases, linking them to processes such as embryonic development, tissue remodeling, tumorigenesis and metastasis. In this sense, uncontrolled activation, due to overexpression of different members of the Rho family in a variety of tissues, leads to uncontrolled proliferation and invasiveness of human tumors. In this review, an attempt to briefly integrate recent findings in transcriptional regulation by Rho GTPases in the context of carcinogenesis and metastasis as well as apoptosis is made.