Isoprenylcysteine carboxyl methyltransferase activity modulates endothelial cell apoptosis

Network analysis identifies a gene biomarker panel for sepsis-induced acute respiratory distress syndrome

BACKGROUND

Acute respiratory distress syndrome (ARDS) is characterized by non-cardiogenic pulmonary edema caused by inflammation, which can lead to serious respiratory complications. Due to the high mortality of ARDS caused by sepsis, biological markers that enable early diagnosis are urgently needed for clinical treatment.

METHODS

In the present study, we used the public microarray data of whole blood from patients with sepsis-induced ARDS, patients with sepsis-alone and healthy controls to perform an integrated analysis based on differential expressed genes (DEGs) and co-expression network to identify the key genes and pathways related to the development of sepsis into ARDS that may be key targets for diagnosis and treatment.

RESULTS

Compared with controls, we identified 180 DEGs in the sepsis-alone group and 152 DEGs in the sepsis-induced ARDS group. About 70% of these genes were unique to the two groups. Functional analysis of DEGs showed that neutrophil-mediated inflammation and mitochondrial dysfunction are the main features of ARDS induced by sepsis. Gene network analysis identified key modules and screened out key regulatory genes related to ARDS. The key genes and their upstream regulators comprised a gene panel, including EOMES, LTF, CSF1R, HLA-DRA, IRF8 and MPEG1. Compared with the healthy controls, the panel had an area under the curve (AUC) of 0.900 and 0.914 for sepsis-alone group and sepsis-induced ARDS group, respectively. The AUC was 0.746 between the sepsis-alone group and sepsis-induced ARDS group. Moreover, the panel of another independent blood transcriptional expression profile dataset showed the AUC was 0.769 in diagnosing sepsis-alone group and sepsis-induced ARDS group.

CONCLUSIONS

Taken together, our method contributes to the diagnosis of sepsis and sepsis-induced ARDS. The biological pathway involved in this gene biomarker panel may also be a critical target in combating ARDS caused by sepsis.

3-Deazaadenosine, an S-adenosylhomocysteine hydrolase inhibitor, attenuates lipopolysaccharide-induced inflammatory responses via inhibition of AP-1 and NF-κB signaling

3-Deazadenosine (3-DA) is a general methylation inhibitor that depletes S-adenosylmethionine, a methyl donor, by blocking S-adenosylhomocysteine hydrolase (SAHH). In this study, we investigated the inhibitory activity and molecular mechanisms of 3-DA in inflammatory responses. 3-DA suppressed the secretion of inflammatory mediators such as nitric oxide (NO) and prostaglandin E₂ (PGE₂) in lipopolysaccharide-treated RAW264.7 cells and phorbol 12-myristate 13-acetate (PMA)-differentiated U937 cells. It also reduced mRNA expression of inducible nitric oxide synthase, cyclooxygenase-2, tumor necrosis factor-α, interleukin-1β (IL-1 β), and IL-6, indicating that 3-DA has anti-inflammatory properties in murine and human macrophages. Moreover, 3-DA strongly blocked AP-1 and NF-κB luciferase activity under PMA-, MyD88-, and TRIF-stimulated conditions and decreased the translocation of c-Jun, c-Fos, p65, and p50 into the nucleus. In addition, the p-ERK level in AP-1 signaling and the p-IκBα level in NF-kB signaling were diminished by 3-DA treatment. Interestingly, 3-DA did not alter the phosphorylation of MEK1/2, an ERK modulator, or IKKα/β, an IκBα regulator. Instead, 3-DA prevented MEK1/2 and IKKα/β from combining with ERK and IκBα, respectively, and directly suppressed MEK1/2 and IKKα/β kinase activity. These results indicate that MEK1/2 and IKKα/β are direct targets of 3-DA. In addition, suppression of SAHH by siRNA or treatment with adenosine dialdehyde, another SAHH inhibitor, showed inhibitory patterns against p-ERK and IκBα similar to those of 3-DA. Taken together, this study demonstrates that 3-DA inhibits AP-1 and NF-κB signaling by directly blocking MEK1/2 and IKKα/β or indirectly mediating SAHH, resulting in anti-inflammatory activity.

Pulmonary Endothelial Cell Apoptosis in Emphysema and Acute Lung Injury

Apoptosis plays an essential role in homeostasis and pathogenesis of a variety of human diseases. Endothelial cells are exposed to various environmental and internal stress and endothelial apoptosis is a pathophysiological consequence of these stimuli. Pulmonary endothelial cell apoptosis initiates or contributes to progression of a number of lung diseases. This chapter will focus on the current understanding of the role of pulmonary endothelial cell apoptosis in the development of emphysema and acute lung injury (ALI) and the factors controlling pulmonary endothelial life and death.

Defining a role for lung function associated gene GSTCD in cell homeostasis

Genome wide association (GWA) studies have reproducibly identified signals on chromosome 4q24 associated with lung function and COPD. GSTCD (Glutathione S-transferase C-terminal domain containing) represents a candidate causal gene in this locus, however little is currently known about the function of this protein. We set out to further our understanding of the role of GSTCD in cell functions and homeostasis using multiple molecular and cellular approaches in airway relevant cells. Recombinant expression of human GSTCD in conjunction with a GST activity assay did not identify any enzymatic activity for two GSTCD isoforms questioning the assignment of this protein to this family of enzymes. Protein structure analyses identified a potential methyltransferase domain contained within GSTCD, with these enzymes linked to cell viability and apoptosis. Targeted knockdown (siRNA) of GSTCD in bronchial epithelial cells identified a role for GSTCD in cell viability as proliferation rates were not altered. To provide greater insight we completed transcriptomic analyses on cells with GSTCD expression knocked down and identified several differentially expressed genes including those implicated in airway biology; fibrosis e.g. TGFBR1 and inflammation e.g. IL6R. Pathway based transcriptomic analyses identified an over-representation of genes related to adipogenesis which may suggest additional functions for GSTCD. These findings identify potential additional functions for GSTCD in the context of airway biology beyond the hypothesised GST activity and warrant further investigation.

Betaine in Inflammation: Mechanistic Aspects and Applications

Betaine is known as trimethylglycine and is widely distributed in animals, plants, and microorganisms. Betaine is known to function physiologically as an important osmoprotectant and methyl group donor. Accumulating evidence has shown that betaine has anti-inflammatory functions in numerous diseases. Mechanistically, betaine ameliorates sulfur amino acid metabolism against oxidative stress, inhibits nuclear factor-κB activity and NLRP3 inflammasome activation, regulates energy metabolism, and mitigates endoplasmic reticulum stress and apoptosis. Consequently, betaine has beneficial actions in several human diseases, such as obesity, diabetes, cancer, and Alzheimer's disease.

Isoprenyl carboxyl methyltransferase inhibitors: a brief review including recent patents

Among the enzymes involved in the post-translational modification of Ras, isoprenyl carboxyl methyltransferase (ICMT) has been explored by a number of researchers as a significant enzyme controlling the activation of Ras. Indeed, inhibition of ICMT exhibited promising anti-cancer activity against various cancer cell lines. This paper reviews patents and research articles published between 2009 and 2016 that reported inhibitors of ICMT as potential chemotherapeutic agents targeting Ras-induced growth factor signaling. Since ICMT inhibitors can modulate Ras signaling pathway, it might be possible to develop a new class of anti-cancer drugs targeting Ras-related cancers. Researchers have discovered indole-based small-molecular ICMT inhibitors through high-throughput screening. Researchers at Duke University identified a prototypical inhibitor, cysmethynil. At Singapore University, Ramanujulu and his colleagues patented more potent compounds by optimizing cysmethynil. In addition, Rodriguez and Stevenson at Universidad Complutense De Madrid and Cancer Therapeutics CRC PTY Ltd., respectively, have developed inhibitors based on formulas other than the indole base. However, further optimization of chemicals targeted to functional groups is needed to improve the characteristics of ICMT inhibitors related to their application as drugs, such as solubility, effectiveness, and safety, to facilitate clinical use.

6-C-(E-phenylethenyl)naringenin induces cell growth inhibition and cytoprotective autophagy in colon cancer cells

6-C-(E-phenylethenyl)naringenin (6-CEPN) is a small molecule found in naringenin fortified fried beef. It has been shown to suppress colon cancer cell proliferation, but the underlying mechanisms are not fully understood. Here we demonstrate that 6-CEPN suppresses tumour cell proliferation through cell cycle arrest in G1 phase, induces necrotic cell death and autophagy in colon cancer cells. Blockade of autophagy by knockdown of the essential autophagy proteins, Atg7 or beclin-1, resulted in aggravated cell death in response to 6-CEPN treatment. In addition, genome-wide transcriptome expression profiling by RNA-sequencing revealed that 6-CEPN-mediated gene expression pattern was extremely similar to the transcriptome response induced by a RAS inhibitor salirasib (farnesylthiosalicylic acid [FTS; salirasib]). Subsequent molecular biological and biochemical experiments demonstrated that 6-CEPN indeed strongly inhibited RAS activation, leading to the inhibition of the downstream effector pathways c-Raf/mitogen-activated protein kinase (MEK)/extracellular signal-regulated kinase kinase and phosphoinositide 3-kinase/AKT/mammalian target of rapamycin. More importantly, our computational molecular docking data showed that 6-CEPN could bind to the active site of isoprenylcysteine carboxyl methyltransferase (Icmt), a critical enzyme for the activation of RAS. Icmt activity assay showed that 6-CEPN inhibited its activity significantly. Knockdown of Icmt by siRNA attenuated 6-CEPN-mediated autophagy and cell death. The present study demonstrates that 6-CEPN induces cell growth inhibition and cytoprotective autophagy in colon cancer cells, at least in part, though inhibition of the Icmt/RAS signalling pathways.

Occupancy of human EPCR by protein C induces β-arrestin-2 biased PAR1 signaling by both APC and thrombin

Activation of protease-activated receptor 1 (PAR1) by activated protein C (APC) and thrombin elicits paradoxical cytoprotective and cytotoxic signaling responses in vascular endothelial cells through cleavage of the receptor at Arg-46 and Arg-41 protease recognition sites, respectively. It has been reported that unlike a disruptive G-protein-mediated PAR1 signaling by thrombin, APC induces a protective β-arrestin-2 biased PAR1 signaling by unknown mechanisms. We hypothesize that the occupancy of endothelial protein C receptor (EPCR) by the Gla-domain of protein C/APC is responsible for the β-arrestin-2 biased PAR1 signaling independent of the protease cleavage site. To test this hypothesis, we monitored the signaling specificity of thrombin in endothelial cells in response to lipopolysaccharide (LPS) with or without pretreatment of cells with protein C-S195A. The PAR1-dependent recruitment of β-arrestin-2 in response to LPS by both APC and thrombin was analyzed by functional, gene silencing, and signaling assays. Results indicate that similar to APC, thrombin exerts cytoprotective effects via β-arrestin-2 biased PAR1 signaling. Similar to APC, thrombin triggered β-arrestin-2-dependent recruitment of disheveled 2 (Dvl-2) in PC-S195A pretreated cells. Further studies in HeLa cells transfected with PAR1 constructs revealed that EPCR occupancy initiates β-arrestin-2 biased PAR1 signaling independent of the protease cleavage sites. We demonstrate that EPCR occupancy recruits G-protein coupled receptor kinase 5, thereby inducing β-arrestin-2 biased PAR1 signaling by both APC and thrombin. In support of a physiological relevance for these results, intraperitoneal administration of PC-S195A conferred a cytoprotective effect for thrombin in an in vivo inflammatory model.

Non-Substrate Based, Small Molecule Inhibitors of the Human Isoprenylcysteine Carboxyl Methyltransferase

Activating mutations of human K-Ras proteins are among the most common oncogenic mutations, present in approximately 30% of all human cancers. Posttranslational modifications to K-Ras guide it to the plasma membrane and disruption of this localization inhibits the growth of Ras-driven cancers. The human isoprenylcysteine carboxyl methyltransferase (hIcmt) enzyme catalyzes the final α-carboxyl methylesterification of the C-terminal farnesyl cysteine of K-Ras, which is necessary for its proper localization. Thus, hIcmt inhibition is a regarded as a promising cancer therapy. A high quality inhibitor of hIcmt with in vivo activity would advance hIcmt research and drug development. Herein, Wwe report the results of a screen for small molecule hIcmt inhibitors in a library of molecules that were not hIcmt substrate analogs. The lead compound identified by this screen (1) was modified to remove chemical liabilities and to increase potency. The most potent resulting compound (5) inhibited hIcmt in vitro with low micromolar potency (IC₅₀ = 1.5 ± 0.2 μM) and was kinetically characterized as a competitive inhibitor for prenylated substrates and a non-competitive inhibitor for the cofactor and methyl donor S-adenosylmethionine (SAM). These inhibitors offer important structure activity relationships for the future development of hIcmt inhibitors with in vivo activity.

Focal adhesion kinase and endothelial cell apoptosis

Focal adhesion kinase (FAK) is a key component of cell-substratum adhesions, known as focal adhesion complexes. Growing evidence indicates that FAK is important in maintenance of normal cell survival and that disruption of FAK signaling results in loss of substrate adhesion and anoikis (apoptosis) of anchorage-dependent cells, such as endothelial cells. Basal FAK activity in non-stimulated endothelial cells is important in maintaining cell adhesion to integrins via PI3 kinase/Akt signaling. FAK activity is dependent upon small GTPase signaling. FAK also appears to be important in cardiomyocyte hypertrophy and hypoxia/reoxygenation-induced cell death. This review summarizes the signaling pathways of FAK in prevention of apoptosis and the role of FAK in mediating adenosine and homocysteine-induced endothelial cell apoptosis and in cardiovascular diseases.

Discovery and SAR of methylated tetrahydropyranyl derivatives as inhibitors of isoprenylcysteine carboxyl methyltransferase (ICMT)

A series of tetrahydropyranyl (THP) derivatives has been developed as potent inhibitors of isoprenylcysteine carboxyl methyltransferase (ICMT) for use as anticancer agents. Structural modification of the submicromolar hit compound 3 led to the potent 3-methoxy substituted analogue 27. Further SAR development around the THP ring resulted in an additional 10-fold increase in potency, exemplified by analogue 75 with an IC(50) of 1.3 nM. Active and potent compounds demonstrated a dose-dependent increase in Ras cytosolic protein. Potent ICMT inhibitors also reduced cell viability in several cancer cell lines with growth inhibition (GI(50)) values ranging from 0.3 to >100 μM. However, none of the cellular effects observed using ICMT inhibitors were as pronounced as those resulting from a farnesyltransferase inhibitor.

RAS-converting enzyme 1-mediated endoproteolysis is required for trafficking of rod phosphodiesterase 6 to photoreceptor outer segments

Prenylation is the posttranslational modification of a carboxyl-terminal cysteine residue of proteins that terminate with a CAAX motif. Following prenylation, the last three amino acids are cleaved off by the endoprotease, RAS-converting enzyme 1 (RCE1), and the prenylcysteine residue is methylated. Although it is clear that prenylation increases membrane affinity of CAAX proteins, less is known about the importance of the postprenylation processing steps. RCE1 function has been studied in a variety of tissues but not in neuronal cells. To approach this issue, we generated mice lacking Rce1 in the retina. Retinal development proceeded normally in the absence of Rce1, but photoreceptor cells failed to respond to light and subsequently degenerated in a rapid fashion. In contrast, the inner nuclear and ganglion cell layers were unaffected. We found that the multimeric rod phosphodiesterase 6 (PDE6), a prenylated protein and RCE1 substrate, was unable to be transported to the outer segments in Rce1-deficient photoreceptor cells. PDE6 present in the inner segment of Rce1-deficient photoreceptor cells was assembled and functional. Synthesis and transport of transducin, and rhodopsin kinase 1 (GRK1), also prenylated substrates of RCE1, was unaffected by Rce1 deficiency. We conclude that RCE1 is essential for the intracellular trafficking of PDE6 and survival of photoreceptor cells.

Biochemical and docking analysis of substrate interactions with polyisoprenylated methylated protein methyl esterase

Polyisoprenylated proteins (PPs) methylation by polyisoprenylated protein methyl transferase (PPMTase) is counteracted by polyisoprenylated methylated protein methyl esterase (PMPMEase). This is the only reversible step of the polyisoprenylation pathway as the relative amounts of the acid and ester forms are determined by the two competing reactions. Since PMPMEase and PPMTase may influence both the structural/functional conformations of PPs, a thorough study of these enzymes is essential to our understanding of the structural/functional features of PPs. PMPMEase has been reported under such pseudonyms as human carboxylesterase 1 (hCE1) because of its apparent broad substrate spectrum. The current study aimed to show the complementarity between its active site and the polyisoprenylated substrates that it metabolizes. Kinetics analysis was conducted with N-, S- and O-substituted substrates using porcine liver PMPMEase and docking analysis using Arguslab. Consistent with the biochemical analysis, the S-ethyl analog yielded an AScore binding energy of -11.32 compared to -13.48, -14.88, -16.15, and -16.81 kcal/mol for S-prenyl (C-5), S-trans-geranyl (C-10), S-trans,trans-farnesyl (C-15) and S-all trans-geranylgeranyl (C-20), respectively. The all trans-geranylgeranyl moiety provides the optimal size for active site interactions. The data reveal that the trans,trans-farnesyl and all trans-geranylgeranyl groups, which are reminiscent of endogenous PPs modifications, have the highest affinity for PMPMEase. Since PPs such as monomeric G-proteins are oncogenic, PMPMEase may be viewed as a viable target for anticancer drug development. The analyses reveal the important structural elements for the design of specific PMPMEase inhibitors to serve in the modulation of oncogenic PPs activities. The results also show that hCE1's repertoire of substrates extends beyond xenobiotics to include PPs as its endogenous substrates.

Involvement and mechanism of DGAT2 upregulation in the pathogenesis of alcoholic fatty liver disease

The mechanisms involved in the development of alcoholic liver disease (ALD) are not well established. We investigated the involvement of acyl-CoA: diacylglycerol acyltransferase 2 (DGAT2) upregulation in mediating hepatic fat accumulation induced by chronic alcohol consumption. Chronic alcohol feeding caused fatty liver and increased hepatic DGAT2 gene and protein expression, concomitant with a significant suppression of hepatic MAPK/ERK kinase/extracellular regulated kinase 1/2 (MEK/ERK1/2) activation. In vitro studies demonstrated that specific inhibitors of the MEK/ERK1/2 pathway increased DGAT2 gene expression and triglyceride (TG) contents in HepG2 cells, whereas epidermal growth factor, a strong ERK1/2 activator, had the opposite effect. Moreover, chronic alcohol feeding decreased hepatic S-adenosylmethionine (SAM): S-adenosylhomocysteine (SAH) ratio, an indicator of disrupted transmethylation reactions. Mechanistic investigations revealed that N-acetyl-S-farnesyl-L-cysteine, a potent inhibitor of isoprenylcysteine carboxyl methyltransferase, suppressed ERK1/2 activation, followed by an enhanced DGAT2 expression and an elevated TG content in HepG2 cells. Lastly, we demonstrated that the beneficial effects of betaine supplementation in ALD were associated with improved SAM/SAH ratio, alleviated ERK1/2 inhibition, and attenuated DGAT2 upregulation. In conclusion, our data suggest that upregulation of DGAT2 plays an important role in the pathogenesis of ALD, and that abnormal methionine metabolism contributes, at least partially, to DGAT2 upregulation via suppression of MEK/ERK1/2 activation.

Inhibition of isoprenylcysteine carboxylmethyltransferase induces autophagic-dependent apoptosis and impairs tumor growth

Inhibition of isoprenylcysteine carboxylmethyltransferase (Icmt), which catalyzes the final step in the post-translational C-terminal processing of prenylated proteins, suppresses tumor cell growth and induces cell death. Icmt inhibition by either a small molecule inhibitor termed as cysmethynil or inhibitory RNA induces marked autophagy leading to cell death. HepG2 cells were used to investigate the function of autophagy in tumor cell death. Suppression of autophagy, either pharmacologically or through knockdown of the autophagy essential proteins, Atg5 or Atg1, inhibits not only cysmethynil-induced autophagy, but also apoptosis in HepG2 cells. The dependence of cysmethynil-induced apoptosis on autophagy was further shown using autophagy-deficient mouse embryonic fibroblast (MEF) cells. Atg5(-/-) MEF cells were found to be resistant to cysmethynil-induced apoptosis, whereas wild-type MEFs showed high sensitivity to apoptosis induction. These data indicate that inhibition of Icmt can elicit cell death through two linked mechanisms, autophagy and apoptosis, and that autophagy can be an active player upstream of apoptosis in cell types capable of apoptotic cell death, such as HepG2 and MEFs. Further, treatment of mice-bearing HepG2-derived tumors with cysmethynil resulted in marked inhibition of tumor growth; analysis of tumor tissue from these mice revealed markers consistent with autophagy induction and cell growth arrest.

Clostridium difficile toxin B differentially affects GPCR-stimulated Ca2+ responses in macrophages: independent roles for Rho and PLA2

Clostridium difficile toxins cause acute colitis by disrupting the enterocyte barrier and promoting inflammation. ToxB from C. difficile inactivates Rho family GTPases and causes release of cytokines and eicosanoids by macrophages. We studied the effects of ToxB on GPCR signaling in murine RAW264.7 macrophages and found that ToxB elevated Ca(2+) responses to Galphai-linked receptors, including the C5aR, but reduced responses to Galphaq-linked receptors, including the UDP receptors. Other Rho inhibitors also reduced UDP Ca(2+) responses, but they did not affect C5a responses, suggesting that ToxB inhibited UDP responses by inhibiting Rho but enhanced C5a responses by other mechanisms. By using PLCbeta isoform-deficient BMDM, we found that ToxB inhibited Ca(2+) signaling through PLCbeta4 but enhanced signaling through PLCbeta3. Effects of ToxB on GPCR Ca(2+) responses correlated with GPCR use of PLCbeta3 versus PLCbeta4. ToxB inhibited UDP Ca(2+) signaling without reducing InsP3 production or the sensitivity of cellular Ca(2+) stores to exogenous InsP3, suggesting that ToxB impairs UDP signaling at the level of InsP3/Ca(2+)coupling. In contrast, ToxB elevated InsP3 production by C5a, and the enhancement of Ca(2+) signaling by C5a was prevented by inhibition of PLA(2) or 5-LOX but not COX, implicating LTs but not prostanoids in the mechanism. In sum, ToxB has opposing, independently regulated effects on Ca(2+) signaling by different GPCR-linked PLCbeta isoforms in macrophages.

Alterations in molecular chaperones and eIF2alpha during lung endothelial cell apoptosis

We have previously demonstrated that inhibition of CAAX carboxyl methylation with AGGC caused redistribution and condensation of the ER molecular chaperones, glucose-regulated protein (GRP)-94 and calnexin; an effect that was attenuated by overexpression of dominant active RhoA. We have also shown that AGGC decreased GRP94 protein level; an effect that was dependent on caspase activity. In the present study, we tested the effects of inhibition of posttranslational processing of CAAX proteins on localization and protein levels of molecular chaperones and phosphorylation and protein level of eIF2alpha. We found that both AGGC, which inhibits CAAX carboxyl methylation, and simvastatin, which inhibits CAAX geranylgeranylation, caused relocalization of GRP94, calnexin, and calreticulin, effects that were not seen during endothelial apoptosis induced by TNF-alpha or ultraviolet (UV) irradiation. These results suggest that posttranslational processing of CAAX proteins is important in maintaining localization of molecular chaperones normally found in the ER. We also noted that AGGC, but not simvastatin, TNF-alpha, or UV irradiation, decreased protein levels of most molecular chaperones. Increased eIF2alpha phosphorylation was observed in the early stages of apoptosis, which was independent of the cause of apoptosis. These results suggest that eIF2alpha phosphorylation is a common early response to apoptosis-inducing stimuli. Interestingly, eIF2alpha protein level was decreased in the late stages of apoptosis induced by AGGC, TNF-alpha, and UV irradiation: an effect that was prevented by caspase inhibition. Thus we speculate that caspase(s)-dependent proteolysis of molecular chaperones and eIF2alpha may be novel signaling pathways of apoptosis. We also speculate that increased eIF2alpha phosphorylation is a defensive response against endothelial cell apoptosis.

3-Deazaadenosine prevents smooth muscle cell proliferation and neointima formation by interfering with Ras signaling

3-Deazaadenosine (c3Ado) is a potent inhibitor of S-adenosylhomocysteine hydrolase, which regulates cellular methyltransferase activity. In the present study, we sought to determine the effect of c3Ado on vascular smooth muscle cell (VSMC) function and neointima formation in vivo. c3Ado dose-dependently prevented the proliferation and migration of human coronary VSMCs in vitro. This was accompanied by an increased expression of the cyclin-dependent kinase inhibitors p21(WAF1/Cip1), p27(Kip1), a decreased expression of G(1)/S phase cyclins, and a lack of retinoblastoma protein hyperphosphorylation. In accordance with these findings, fluorescence-activated cell-sorting analysis of propidium iodide-stained cells indicated a cell cycle arrest in the G(0)/G(1) phase. Importantly, c3Ado did not affect the number of viable (trypan blue exclusion) or apoptotic cells (TUNEL). Mechanistically, c3Ado prevented FCS-induced Ras carboxyl methylation and membrane translocation and activity by inhibiting isoprenylcysteine carboxyl methyltransferase and reduced FCS-induced extracellular signal-regulated kinase (ERK)1/2 and Akt phosphorylation in a dose-dependent manner. Conversely, rescuing signal transduction by overexpression of a constitutive active Ras mutant abrogated c3Ado's effect on proliferation. For in vivo studies, the femoral artery of C57BL/6 mice was dilated and mice were fed a diet containing 150 microg of c3Ado per day. c3Ado prevented dilation-induced Ras activation, as well as ERK1/2 and Akt phosphorylation in vivo. At day 21, VSMC proliferation (proliferating-cell nuclear antigen [PCNA]-positive cells), as well as the neointima/media ratio (0.7+/-0.2 versus 1.6+/-0.4; P<0.05) were significantly reduced, without any changes in the number of apoptotic cells. Our data indicate that c3Ado interferes with Ras methylation and function and thereby with mitogenic activation of ERK1/2 and Akt, preventing VSMC cell cycle entry and proliferation and neointima formation in vivo. Thus, therapeutic inhibition of S-adenosylhomocysteine hydrolase by c3Ado may represent a save and effective novel approach to prevent vascular proliferative disease.

RAS: target for cancer therapy

The RAS protein controls signaling pathway are major player in cell growth, its regulation and malignant transformation. Any activation in RAS brings alteration in upstream or downstream signaling component. Activating mutation in RAS is found in approximately 30% of human cancer. RAS plays essential role in tumor maintenance and is therefore an appropriate target for anticancer therapy. Among the anti-RAS strategies that are under evaluation in the clinic are pharmacologic inhibitors designed to prevent: (1) association with the plasma membrane (prenylation and post prenylation inhibitors). (2) Downstream signaling (kinase inhibitor), (3) upstream pathway (kinase inhibitor and monoclonal antibody), (4) Expression of RAS or other component of pathway (siRNA and antisense oligonucleotide). Several of these new therapeutic agents are showing promising result in the clinic and many more are on the way. Here, we review the current status and new hopes for targeting RAS as an anticancer drug.

Transforming growth factor-beta1 protects against pulmonary artery endothelial cell apoptosis via ALK5

Transforming growth factor (TGF)-beta1 has been reported to cause endothelial cell apoptosis. However, conflicting data have also demonstrated that TGF-beta1 promotes endothelial cell survival. In this study, the effect of TGF-beta1 on apoptosis of cultured bovine pulmonary artery endothelial cells (PAEC) induced by multiple stimuli was investigated. TGF-beta1 protected against apoptosis of bovine PAEC induced by serum deprivation or the VEGF receptor inhibitor SU-5416, but not by UV light exposure or TNFalpha. Neither caspase-8 nor caspase-12 was activated by serum deprivation or the VEGF receptor blocker. However, blockade of VEGF receptors activated caspase-9, an effect that was abolished by TGF-beta1. Furthermore, serum deprivation and inhibition of VEGF receptors significantly decreased the protein level of Bcl-2, an effect that was also abrogated by TGF-beta1. In addition, the baseline level of Bcl-2 was enhanced by TGF-beta1 and reduced by inhibition of activin receptor-like kinase 5 (ALK5), a TGF-beta1 type I receptor. Furthermore, inhibition of ALK5 caused apoptosis of bovine PAEC. These results suggest that TGF-beta1 signaling is critical for maintenance of bovine PAEC survival. Finally, the protective effects of TGF-beta1 on bovine PAEC apoptosis and Bcl-2 reduction were abolished by ALK5 inhibition, but not by inhibition of non-SMAD signaling pathways. Also, TGF-beta1 activated SMAD2 and SMAD1/5, an effect that was abolished by ALK5 inhibition. The results of this study suggest that TGF-beta1 protects against bovine PAEC apoptosis, possibly through ALK5-mediated Bcl-2 induction and subsequent inhibition of the mitochondria-mediated intrinsic pathway of apoptosis. Understanding the mechanism by which TGF-beta1 promotes endothelial cell survival may provide a better treatment for apoptosis-dependent vascular diseases, such as emphysema.

Pulmonary endothelial cell signaling and function

RhoA is an important modulator of endothelial monolayer permeability. Posttranslational carboxyl methylation of small GTPases, such as RhoA and Ras, regulates subcellular localization and GTPase activity, resulting in altered cellular function. In this study, we investigated the role of RhoA carboxyl methylation in modulating endothelial monolayer permeability. We found that inhibition of isoprenylcysteine-O-carboxyl methyltransferase (ICMT) with adenosine plus homocysteine (Ado/HC) or N-acetyl-S-geranylgeranyl-L-cysteine (AGGC) decreased RhoA carboxyl methylation and activation, which correlated with decreased monolayer permeability of bovine pulmonary artery endothelial cells (BPAEC). Conversely, BPAEC stably overexpressing ICMT had enhanced endothelial monolayer permeability, associated with elevated RhoA carboxyl methylation and activation. These results suggest that ICMT modulates endothelial monolayer permeability by altering RhoA carboxyl methylation and activation. In addition, we demonstrated that adenosine deaminase inhibitor not only attenuated, but also rescued, lung edema induced by a non-inflammatory edemagenic agent. Our data suggest that increasing intracellular adenosine is a useful therapeutic strategy against diseases characterized by increased vascular permeability.

Role of transmethylation reactions in alcoholic liver disease

Alcoholic liver disease is a major health care problem worldwide. Findings from many laboratories, including ours, have demonstrated that ethanol feeding impairs several of the many steps involved in methionine metabolism. Ethanol consumption predominantly results in a decrease in the hepatocyte level of S-adenosylmethionine and the increases in two toxic metabolites, homocysteine and S-adenosylhomocysteine. These changes, in turn, result in serious functional consequences which include decreases in essential methylation reactions via inhibition of various methyltransferases. Of particular interest to our laboratory is the inhibition of three important enzymes, phosphatidylethanolamine methyltransferase, isoprenylcysteine carboxyl methyltransferase and protein L-isoaspartate methyltransferase. Decreased activity of these enzymes results in increased fat deposition, increased apoptosis and increased accumulation of damaged proteins-all of which are hallmark features of alcoholic liver injury. Of all the therapeutic modalities available, betaine has been shown to be the safest, least expensive and most effective in attenuating ethanol-induced liver injury. Betaine, by virtue of aiding in the remethylation of homocysteine, removes both toxic metabolites (homocysteine and S-adenosylhomocysteine), restores S-adenosylmethionine level, and reverses steatosis, apoptosis and damaged proteins accumulation. In conclusion, betaine appears to be a promising therapeutic agent in relieving the methylation and other defects associated with alcoholic abuse.

Post-translational modifications and regulation of the RAS superfamily of GTPases as anticancer targets

The involvement of the RAS superfamily of monomeric GTPases in carcinogenesis is increasingly being appreciated. A complex array of post-translational modifications and a highly sophisticated protein network regulate the spatio-temporal activation of these GTPases. Previous attempts to pharmacologically target this family have focused on the development of farnesyltransferase inhibitors, but the performance of such agents in cancer clinical trials has not been as good as hoped. Here, we review emerging druggable targets and novel therapeutic approaches targeting prenylation and post-prenylation modifications and the functional regulation of GDP/GTP exchange as exciting alternatives for anticancer therapy.

Role of S-adenosylmethionine, folate, and betaine in the treatment of alcoholic liver disease: summary of a symposium

This report is a summary of a symposium on the role of S-adenosylmethionine (SAM), betaine, and folate in the treatment of alcoholic liver disease (ALD), which was organized by the National Institute on Alcohol Abuse and Alcoholism in collaboration with the Office of Dietary Supplements and the National Center for Complementary and Alternative Medicine of the National Institutes of Health (Bethesda, MD) and held on 3 October 2005. SAM supplementation may attenuate ALD by decreasing oxidative stress through the up-regulation of glutathione synthesis, reducing inflammation via the down-regulation of tumor necrosis factor-alpha and the up-regulation of interleukin-10 synthesis, increasing the ratio of SAM to S-adenosylhomocysteine (SAH), and inhibiting the apoptosis of normal hepatocytes and stimulating the apoptosis of liver cancer cells. Folate deficiency may accelerate or promote ALD by increasing hepatic homocysteine and SAH concentrations; decreasing hepatic SAM and glutathione concentrations and the SAM-SAH ratio; increasing cytochrome P4502E1 activation and lipid peroxidation; up-regulating endoplasmic reticulum stress markers, including sterol regulatory element-binding protein-1, and proapoptotic gene caspase-12; and decreasing global DNA methylation. Betaine may attenuate ALD by increasing the synthesis of SAM and, eventually, glutathione, decreasing the hepatic concentrations of homocysteine and SAH, and increasing the SAM-SAH ratio, which can trigger a cascade of events that lead to the activation of phosphatidylethanolamine methyltransferase, increased phosphatidylcholine synthesis, and formation of VLDL for the export of triacylglycerol from the liver to the circulation. Additionally, decreased concentrations of homocysteine can down-regulate endoplasmic reticulum stress, which leads to the attenuation of apoptosis and fatty acid synthesis.

Inhibition of ICMT induces endothelial cell apoptosis through GRP94

Isoprenylcysteine-O-carboxyl methyltransferase (ICMT) catalyzes methylation of proteins containing a C-terminal CAAX motif. We have previously shown that chemical inhibition of ICMT caused endothelial cell apoptosis, an effect correlated with decreased Ras and RhoA carboxyl methylation and GTPase activities. In the current study, proteomic analysis of pulmonary artery endothelial cells (PAEC) exposed to the ICMT inhibitor, N-acetyl-geranylgeranyl-cysteine (AGGC), demonstrated a shift in the isoelectric points (pI) of the glucose-regulated protein (GRP) 94. Two-dimensional PAGE and immunoblot analysis further documented that ICMT inhibition caused multiple changes in the pI of GRP94. GRP94 is an endoplasmic reticulum molecular chaperone, a component of the unfolded protein response (UPR), and is involved in apoptosis. Immunofluorescence analyses revealed redistribution and aggregation of GRP94 after 3 h exposure to AGGC. A similar finding was noted with calnexin. In addition, GRP94 protein levels were significantly diminished upon 18 h AGGC exposure or ICMT suppression. The effects of ICMT inhibition on changes in GRP94 subcellular localization and protein content were blunted by overexpression of constitutively active RhoA or a caspase inhibitor. Furthermore, GRP94 depletion augmented endothelial cell apoptosis induced by ICMT inhibition. These results indicate that ICMT inhibition leads to GRP94 relocalization, aggregation, and degradation; effects were dependent upon the activities of RhoA and caspases. We speculate that changes in the pI, subcellular localization, and protein level of GRP94 cause endothelial cell apoptosis, possibly through UPR dysfunction. These studies suggest a novel link between RhoA GTPases and the UPR.

Release of soluble E-selectin from activated endothelial cells upon apoptosis

Circulating soluble E-selectin is increased in diseases associated with endothelial apoptosis such as sepsis and acute respiratory distress syndrome. We investigated the mechanism by which endothelial cell (EC) apoptosis may promote soluble E-selectin release. We found that serum deprivation of EC caused apoptosis, yet it did not induce E-selectin EC surface expression. Tumor necrosis factor-alpha (TNFalpha) significantly increased EC E-selectin surface expression. Soluble E-selectin was noted, however, only in the medium of TNFalpha-activated, apoptotic EC. Preincubation of the EC with the caspase inhibitor z-VAD-fmk significantly attenuated soluble E-selectin levels in the culture medium of TNFalpha-activated, apoptotic EC, but it had no effect on E-selectin surface expression. These results indicate that TNFalpha activation, but not apoptosis, is necessary for E-selectin surface expression in EC. Furthermore, E-selectin release from EC requires caspase-3 activation. Thus, increased concentrations of circulating E-selectin in serum may serve as a marker for endothelial apoptosis in certain disease states.

Role of S-adenosylhomocysteine hydrolase in adenosine-induced apoptosis in HepG2 cells

Adenosine has been shown to initiate apoptosis through different mechanisms: (i) activation of adenosine receptors, (ii) intracellular conversion to AMP and stimulation of AMP-activated kinase, (iii) conversion to S-adenosylhomocysteine (AdoHcy), which is an inhibitor of S-adenosylmethionine (AdoMet)-dependent methyltransferases. Since the pathways involved are still not completely understood, we further investigated the role of AdoHcy hydrolase in adenosine-induced apoptosis. In HepG2 cells, adenosine induced caspase-like activity and DNA fragmentation, a marker of apoptosis. These effects were potentiated by co-incubation with homocysteine or adenosine deaminase inhibitor, pentostatin, and were mimicked by inhibition of AdoHcy hydrolase by adenosine-2',3'-dialdehyde (Adox). Adenosine-induced effects were significantly inhibited by dipyridamole, an inhibitor of adenosine transporter, whereas inhibitors of adenosine kinase did not affect adenosine-induced changes. Various adenosine receptor agonists and AICAR, an activator of AMP-activated kinase, did not mimic the effect of adenosine. Thus, adenosine-induced apoptosis is likely due to intracellular action of AdoHcy and independent of AMP-activated kinase and adenosine receptors. Because elevated AdoHcy levels are associated with reduced mRNA methylation, we studied mRNA expression in Adox-treated cells by microarray analysis. Since several p53-target genes and other apoptosis-related genes were up-regulated by Adox, we conclude that AdoHcy is involved in adenosine-induced apoptosis by altering gene expression.

Apoptosis and lung injury

Apoptosis is important in developmental biology and in remodeling of tissues during repair. Apoptosis also plays important roles in the progression of many diseases. The cellular and molecular mechanisms of apoptosis, in general, have been extensively demonstrated. However, the causes and the roles of apoptosis of various cell types in the lung are not well understood. We have determined that adenosine/homocysteine causes lung vascular endothelial cell apoptosis by inhibition of carboxyl methylation of the small GTPase, Ras, through inhibition of isoprenylcysteine carboxyl methyltransferase(ICMT) activity, leading to inactivation of Ras and the subsequent disruption of focal adhesion complexes, resulting in cell-extracellular matrix detachment and anoikis. Apoptosis can either ameliorate or exacerbate lung injury, depending upon the cell type. Although apoptosis of polymorphonuclear leukocytes in the lung prevents inflammation and the development of acute respiratory distress syndrome during acute lung injury, Fas/FasL-mediated alveolar epithelial cell apoptosis promotes acute lung injury and pulmonary fibrosis. Lung epithelial and endothelial cell apoptosis also contributes to the development of emphysema. This article focuses on elucidating the mechanisms of adenosine/homocysteine-induced endothelial cell apoptosis. We also review the current understanding of the role of lung cell apoptosis in acute lung injury, pulmonary fibrosis and emphysema.

Mining literature for a comprehensive pathway analysis: a case study for retrieval of homocysteine related genes for genetic and epigenetic studies

Homocysteine is an independent risk factor for cardiovascular diseases. It is also known to be associated with a variety of complex disorders. While there are a large number of independent studies implicating homocysteine in isolated pathways, the mechanism of homocysteine induced adverse effects are not clear. Homocysteine-induced modulation of gene expression through alteration of methylation status or by hitherto unknown mechanisms is predicted to lead to several pathological conditions either directly or indirectly. In the present manuscript, using literature mining approach, we have identified the genes that are modulated directly or indirectly by an elevated level of homocysteine. These genes were then placed in appropriate pathways in an attempt to understand the molecular basis of homocysteine induced complex disorders and to provide a resource for selection of genes for polymorphism screening and analysis of mutations as well as epigenetic modifications in relation to hyperhomocysteinemia. We have identified 135 genes in 1137 abstracts that either modulate the levels of homocysteine or are modulated by elevated levels of homocysteine. Mapping the genes to their respective pathways revealed that an elevated level of homocysteine leads to the atherosclerosis either by directly affecting lipid metabolism and transport or via oxidative stress and/or Endoplasmic Reticulum (ER) stress. Elevated levels of homocysteine also decreases the bioavailability of nitric oxide and modulates the levels of other metabolites including S-adenosyl methionine and S-adenosyl homocysteine which may result in cardiovascular or neurological disorders. The ER stress emerges as the common pathway that relates to apoptosis, atherosclerosis and neurological disorders and is modulated by levels of homocysteine. The comprehensive network collated has lead to the identification of genes that are modulated by homocysteine indicating that homocysteine exerts its effect not only through modulating the substrate levels for various catalytic processes but also through regulation of expression of genes involved in complex diseases.

Mechanisms of adenosine-induced cytotoxicity and their clinical and physiological implications

Extracellular ATP (ATPo) and adenosine are cytotoxic to several cancer cell lines, suggesting their potential use for anticancer therapy. Adenosine causes cytotoxicity, either when added exogenously or when generated from ATPo hydrolysis, via mechanisms which are not mutually exclusive and which involve, adenosine receptor activation, pyrimidine starvation and/or increases in intracellular S-adenosylhomocysteine: S-adenosylmethionine ratio. Given that adenosine also appears to protect against cytotoxicity via mechanisms including immunity against damage by oxygen free radicals, an understanding of the contribution of adenosine to ATPo-induced cytotoxicity is thus crucial, when considering any potential therapeutic use for these compounds. However, such an understanding has been largely hindered by the fact that many studies have not focused enough on the possibility that both ATPo and adenosine may mediate cytotoxicity in the same system. Such studies can benefit from use a range of ATPo concentrations when assessing the contribution of adenosine to ATPo-induced cytotoxicity. Whilst future molecular and pharmacological studies are needed to establish the nature of the cytotoxic adenosine receptor, it is possible that more than just one adenosine receptor type is involved and that the cytotoxic receptor(s) type is more likely to have a low affinity for adenosine. Activation of the adenosine receptor(s) would thus lead to cytotoxicity only at relatively high adenosine concentrations, while lower adenosine concentrations mediate non-cytotoxic physiological effects.

Role of elevated S-adenosylhomocysteine in rat hepatocyte apoptosis: protection by betaine

Previous studies from our laboratory have shown that ethanol consumption results in an increase in hepatocellular S-adenosylhomocysteine levels. Because S-adenosylhomocysteine is a potent inhibitor of methylation reactions, we propose that increased intracellular S-adenosylhomocysteine levels could be a major contributor to ethanol-induced pathologies. To test this hypothesis, hepatocytes isolated from rat livers were grown on collagen-coated plates in Williams' medium E containing 5% FCS and exposed to varying concentrations of adenosine in order to increase intracellular S-adenosylhomocysteine levels. We observed increases in caspase-3 activity following exposure to adenosine. This increase in caspase activity correlated with increases in intracellular S-adenosylhomocysteine levels and DNA hypoploidy. The adenosine-induced changes could be significantly attenuated by betaine administration. The mechanism of betaine action appeared to be via the methylation reaction catalyzed by betaine-homocysteine-methyltransferase. To conclude, our results indicate that the elevation of S-adenosylhomocysteine levels in the liver by ethanol is a major factor in altering methylation reactions and in increasing apoptosis in the liver. We conclude that ethanol-induced alteration in methionine metabolic pathways may play a crucial role in the pathologies associated with alcoholic liver injury and that betaine administration may have beneficial therapeutic effects.

Targeting Ras and Rho GTPases as opportunities for cancer therapeutics

The Ras and Rho GTPases contribute to the initiation and progression of cancer by subverting the normal regulation of specific intracellular signalling pathways. As a result, Ras and Rho play significant roles in the development of numerous aspects of the malignant phenotype by promoting cell cycle progression, resistance to apoptotic stimuli, neo-vascularisation and tumour cell motility, invasiveness and metastasis. With these GTPases contributing at so many levels, they are appealing targets for the development of cancer chemotherapeutic agents.

A small-molecule inhibitor of isoprenylcysteine carboxyl methyltransferase with antitumor activity in cancer cells

Many key regulatory proteins, including members of the Ras family of GTPases, are modified at their C terminus by a process termed prenylation. This processing is initiated by the addition of an isoprenoid lipid, and the proteins are further modified by a proteolytic event and methylation of the C-terminal prenylcysteine. Although the biological consequences of prenylation have been characterized extensively, the contributions of prenylcysteine methylation to the functions of the modified proteins are not well understood. This reaction is catalyzed by the enzyme isoprenylcysteine carboxyl methyltransferase (Icmt). Recent genetic disruption studies have provided strong evidence that blocking Icmt activity has profound consequences on oncogenic transformation. Here, we report the identification of a selective small-molecule inhibitor of Icmt, 2-[5-(3-methylphenyl)-1-octyl-1H-indol-3-yl]acetamide (cysmethynil). Cysmethynil treatment results in inhibition of cell growth in an Icmt-dependent fashion, demonstrating mechanism-based activity of the compound. Treatment of cancer cells with cysmethynil results in mislocalization of Ras and impaired epidermal growth factor signaling. In a human colon cancer cell line, cysmethynil treatment blocks anchorage-independent growth, and this effect is reversed by overexpression of Icmt. These findings provide a compelling rationale for development of Icmt inhibitors as another approach to anticancer drug development.

Post-prenylation-processing enzymes as new targets in oncogenesis

RAS and many other oncogenic proteins undergo a complex series of post-translational modifications that are initiated by the addition of an isoprenoid lipid through a process known as prenylation. Following prenylation, these proteins usually undergo endoproteolytic processing by the RCE1 protease and then carboxyl methylation by a unique methyltransferase known as isoprenylcysteine carboxyl methyltransferase (ICMT). Although inhibitors that have been designed to target the prenylation step are now in advanced-stage clinical trials, their utility and efficacy seem to be limited. Recent findings, however, indicate that the inhibition of these post-prenylation-processing steps--particularly that of ICMT-catalysed methylation--might provide a better approach to the control of cancer-cell proliferation.

Barrier dysfunction and RhoA activation are blunted by homocysteine and adenosine in pulmonary endothelium

RhoA GTPases modulate endothelial permeability. We have previously shown that adenosine and homocysteine enhance basal barrier function in pulmonary artery endothelial cells by a mechanism involving diminution of RhoA carboxyl methylation and activity. In the current study, we investigated the effects of adenosine and homocysteine on endothelial monolayer permeability in cultured monolayers. Adenosine and homocysteine significantly attenuated thrombin-induced endothelial barrier dysfunction and intercellular gap formation. We found significantly diminished RhoA associated with the membrane subcellular fraction in endothelial cells pretreated with adenosine and homocysteine, compared with vehicle-treated endothelial cells. Additionally, adenosine and homocysteine significantly blunted RhoA activation following thrombin exposure. Incubation with adenosine and homocysteine also enhanced in vitro interactions between RhoA and RhoGDI, as well as subcellular translocation of p190RhoGAP to the cytosol. These data demonstrate that elevated intracellular concentrations of homocysteine and adenosine enhance endothelial barrier function in cultured endothelial cells isolated from the main pulmonary artery and lung microvasculature, suggesting a potentially protective effect against pulmonary edema in response to lung injury. We speculate that homocysteine and adenosine modulate the level of endothelial barrier dysfunction through modulation of RhoA posttranslational processing resulting in diminished GTPase activity through altered interactions with modulators of RhoA activation.

Isoprenylcysteine Carboxyl Methyltransferase Modulates Endothelial Monolayer Permeability

RhoA and Rac1 regulate formation of stress fibers and intercellular junctions, thus modulating endothelial monolayer permeability. Posttranslational modifications of RhoA and Rac1 regulate enzyme activity and subcellular localization, resulting in altered cellular function. The role of RhoA and Rac1 carboxyl methylation in modulating endothelial monolayer permeability is not known. In this study, we found that inhibition of isoprenylcysteine-O-carboxyl methyltransferase (ICMT) with adenosine plus homocysteine or N-acetyl-S-geranylgeranyl-l-cysteine decreased RhoA carboxyl methylation, RhoA activity, and endothelial monolayer permeability, suggesting that RhoA carboxyl methylation may play a role in the ICMT-modulated monolayer permeability. Similar studies showed no effect of ICMT inhibition on Rac1 carboxyl methylation or localization. Bovine pulmonary artery endothelial cells (PAECs) stably overexpressing ICMT-GFP cDNA were established to determine if increased ICMT expression could alter RhoA or Rac1 carboxyl methylation, activation, and endothelial monolayer permeability. PAECs stably overexpressing ICMT demonstrated increased RhoA carboxyl methylation, membrane-bound RhoA, and RhoA activity. Additionally, PAECs stably overexpressing ICMT had diminished VE-cadherin and beta-catenin at intercellular junctions, with resultant intercellular gap formation, as well as enhanced monolayer permeability. These effects were blunted by adenosine plus homocysteine and by inhibition of RhoA, but not by inhibition of Rac1. These results indicate that ICMT modulates endothelial monolayer permeability by altering RhoA carboxyl methylation and activation, thus changing the organization of intercellular junctions. Therefore, carboxyl methylation of RhoA may modulate endothelial barrier function.