Function of Ras as a molecular switch in signal transduction

K15 promoter-driven enforced expression of NKIRAS exhibits tumor suppressive activity against the development of DMBA/TPA-induced skin tumors

NKIRAS1 and NKIRAS2 (also called as κB-Ras) were identified as members of the atypical RAS family that suppress the transcription factor NF-κB. However, their function in carcinogenesis is still controversial. To clarify how NKIRAS acts on cellular transformation, we generated transgenic mice in which NKIRAS2 was forcibly expressed using a cytokeratin 15 (K15) promoter, which is mainly activated in follicle bulge cells. The ectopic expression of NKIRAS2 was mainly detected in follicle bulges of transgenic mice with NKIRAS2 but not in wild type mice. K15 promoter-driven expression of NKIRAS2 failed to affect the development of epidermis, which was evaluated using the expression of K10, K14, K15 and filaggrin. However, K15 promoter-driven expression of NKIRAS2 effectively suppressed the development of skin tumors induced by treatment with 7,12-dimethylbenz(a)anthracene (DMBA)/12-O-tetradecanoylphorbol 13-acetate (TPA). This observation suggested that NKIRAS seemed to function as a tumor suppressor in follicle bulges. However, in the case of oncogenic HRAS-driven cellular transformation of murine fibroblasts, knockdown of NKIRAS2 expression drastically suppressed HRAS-mutant-provoked cellular transformation, suggesting that NKIRAS2 was required for the cellular transformation of murine fibroblasts. Furthermore, moderate enforced expression of NKIRAS2 augmented oncogenic HRAS-provoked cellular transformation, whereas an excess NKIRAS2 expression converted its functional role into a tumor suppressive phenotype, suggesting that NKIRAS seemed to exhibit a biphasic bell-shaped enhancing effect on HRAS-mutant-provoked oncogenic activity. Taken together, the functional role of NKIRAS in carcinogenesis is most likely determined by not only cellular context but also its expression level.

Kras-Deficient T Cells Attenuate Graft-versus-Host Disease but Retain Graft-versus-Leukemia Activity

Acute graft-versus-host disease (aGVHD) is one major serious complication that is induced by alloreactive donor T cells recognizing host Ags and limits the success of allogeneic hematopoietic stem cell transplantation. In the current studies, we identified a critical role of Kras in regulating alloreactive T cell function during aGVHD. Kras deletion in donor T cells dramatically reduced aGVHD mortality and severity in an MHC-mismatched allogeneic hematopoietic stem cell transplantation mouse model but largely maintained the antitumor capacity. Kras-deficient CD4 and CD8 T cells exhibited impaired TCR-induced activation of the ERK pathway. Kras deficiency altered TCR-induced gene expression profiles, including the reduced expression of various inflammatory cytokines and chemokines. Moreover, Kras deficiency inhibited IL-6-mediated Th17 cell differentiation and impaired IL-6-induced ERK activation and gene expression in CD4 T cells. These findings support Kras as a novel and effective therapeutic target for aGVHD.

Oncogenic Ras mutant causes the hyperactivation of NF-κB via acceleration of its transcriptional activation

It is well established that nuclear factor κB (NF-κB) acts as one of the most important transcription factors for tumor initiation and progression, as it both protects cells from apoptotic/necrotic signals and accelerates angiogenesis and tumor metastasis, which is mediated via the expression of target genes. However, it has not yet been clarified how oncogenic signals accelerate the activation of NF-κB. In the current study, we utilized untransformed NIH-3T3 cells stably harboring a κB-driven luciferase gene to show that an oncogenic mutant of Ras GTPase augmented TNFα-induced NF-κB activation. Notably, enforced expression of cyclin-dependent kinase inhibitors, such as p27^Kip1 and p21^Cip1 , effectively canceled the accelerated activation of NF-κB, suggesting that oncogenic Ras-induced cell cycle progression is essential for the hyperactivation of NF-κB. Furthermore, we found that Ras (G12V) augmented the transcriptional activation of NF-κB, and this activation required the p38 MAP kinase. We observed that a downstream kinase of p38 MAP kinase, MSK1, was activated by Ras (G12V) and catalyzed the phosphorylation of p65/RelA at Ser-276, which is critical for its transcriptional activation. Significantly, phosphorylation of the p65/RelA subunit at Ser-276 was elevated in patient samples of colorectal cancer harboring oncogenic mutations of the K-Ras gene, and the expression levels of NF-κB target genes were drastically enhanced in several cancer tissues. These observations strongly suggest that oncogenic signal-induced acceleration of NF-κB activation is caused by activation of the p38 MAP kinase-MSK1 signaling axis and by cell cycle progression in cancer cells.

The role of the interleukin (IL)-6/IL-6 receptor axis in cancer

Interleukin-6 (IL-6) is a pleiotropic cytokine that activates a classic signalling pathway upon binding to its membrane-bound receptor (IL-6R). Alternatively, IL-6 may 'trans-signal' in a manner that is facilitated by its binding to a soluble derivative of the IL-6 receptor (sIL-6R). Resultant signal transduction is, respectively, driven by the association of IL-6/IL-6R or IL-6/sIL-6R complex with the membrane-associated signal transducer, gp130 (Glycoprotein 130). Distinct JAK (Janus tyrosine kinase)/STAT (signal transducers and activators of transcription) and other signalling pathways are activated as a consequence. Of translational relevance, overexpression of IL-6 has been documented in several neoplastic disorders, including but not limited to colorectal, ovarian and breast cancer and several haematological malignancies. This review attempts to summarise our current understanding of the role of IL-6 in cancer development. In short, these studies have shown important roles for IL-6 signalling in tumour cell growth and survival, angiogenesis, immunomodulation of the tumour microenvironment, stromal cell activation, and ultimate disease progression. Given this background, we also consider the potential for therapeutic targeting of this system in cancer.

Small GTPase R-Ras participates in neural tube formation in zebrafish embryonic spinal cord

Ras related (R-Ras), a small GTPase, is involved in the maintenance of apico-basal polarity in neuroepithelial cells of the zebrafish hindbrain, axonal collapse in cultured murine hippocampal neurons, and maturation of blood vessels in adult mice. However, the role of R-Ras in neural tube formation remains unknown. Using antisense morpholino oligonucleotides (AMOs), we found that in the spinal cord of zebrafish embryos, the lumen was formed bilaterally in rras morphants, whereas it was formed at the midline in control embryos. As AMO can cause off-target effects, we generated rras mutant zebrafish lines using CRISPR/Cas9 technology. Although these rras mutant embryos did not have a bilateral lumen in the spinal cord, the following findings suggest that the phenotype is unlikely due to an off-target effect of rras AMO: 1) The rras morphant phenotype was rescued by an injection of AMO-resistant rras mRNA, and 2) a bilaterally segregated spinal cord was not observed in rras mutant embryos injected with rras AMO. The results suggest that the function of other ras family genes may be redundant in rras mutants. Previous research reported a bilaterally formed lumen in the spinal cord of zebrafish embryos with a mutation in a planar cell polarity (PCP) gene, van gogh-like 2 (vangl2). In the present study, in cultured cells, R-Ras was co-immunoprecipitated with Vangl2 but not with another PCP regulator, Pricke1. Interestingly, the interaction between R-Ras and Vangl2 was stronger in guanine-nucleotide free point mutants of R-Ras than in wild-type or constitutively active (GTP-bound) forms of R-Ras. R-Ras may regulate neural tube formation in cooperation with Vangl2 in the developing zebrafish spinal cord.

Importance of an Orchestrate Participation of each Individual Residue Present at a Catalytic Site

GTP hydrolysis is indispensable to keep a living cell healthy. Nature has evolved so many enzymes to enhance the slow GTP hydrolysis. Rab GTPases are evolved to regulate vesicle trafficking. GTPase activating proteins (GAPs) accelerates their intrinsic slow GTP hydrolysis in order to maintain the sustainability between cellular events. Any malfunction/interference in this hydrolysis disrupts normal cellular events and causes severe diseases. In this study, GTP hydrolysis mechanism of Rab33B catalyzed by TBC-domain GAP protein Gyp1p has been decoded using extensive ab initio QM/MM metadynamics simulations. An organized coupled movement of individual residues present at the catalytic site is found to be the key factor for this reaction. An unorganized coupled movement leads the hydrolysis through very high energy pathways. This also reveals that the chemical transformations occurring at a catalytic site are residue specific.

In situ detection of the activation of Rac1 and RalA small GTPases in mouse adipocytes by immunofluorescent microscopy following in vivo and ex vivo insulin stimulation

Rac1 has been implicated in insulin-dependent glucose uptake by mechanisms involving plasma membrane translocation of the glucose transporter GLUT4 in skeletal muscle. Although the uptake of glucose is also stimulated by insulin in adipose tissue, the role for Rac1 in adipocyte insulin signaling remains controversial. As a step to reveal the role for Rac1 in adipocytes, we aimed to establish immunofluorescent microscopy to detect the intracellular distribution of activated Rac1. The epitope-tagged Rac1-binding domain of a Rac1-specific target was utilized as a probe that specifically recognizes the activated form of Rac1. Rac1 activation in response to ex vivo and in vivo insulin stimulations in primary adipocyte culture and mouse white adipose tissue, respectively, was successfully observed by immunofluorescent microscopy. These Rac1 activations were mediated by phosphoinositide 3-kinase. Another small GTPase RalA has also been implicated in insulin-stimulated glucose uptake in skeletal muscle and adipose tissue. Similarly to Rac1, immunofluorescent microscopy using an activated RalA-specific polypeptide probe allowed us to detect intracellular distribution of insulin-activated RalA in adipocytes. These novel approaches to visualize the activation status of small GTPases in adipocytes will largely contribute to the understanding of signal transduction mechanisms particularly for insulin action.

Covalent Guanosine Mimetic Inhibitors of G12C KRAS

Ras proteins are members of a large family of GTPase enzymes that are commonly mutated in cancer where they act as dominant oncogenes. We previously developed an irreversible guanosine-derived inhibitor, SML-8-73-1, of mutant G12C RAS that forms a covalent bond with cysteine 12. Here we report exploration of the structure-activity relationships (SAR) of hydrolytically stable analogues of SML-8-73-1 as covalent G12C KRAS inhibitors. We report the discovery of difluoromethylene bisphosphonate analogues such as compound 11, which, despite exhibiting reduced efficiency as covalent G12C KRAS inhibitors, remove the liability of the hydrolytic instability of the diphosphate moiety present in SML-8-73-1 and provide the foundation for development of prodrugs to facilitate cellular uptake. The SAR and crystallographic results reaffirm the exquisite molecular recognition that exists in the diphosphate region of RAS for guanosine nucleotides which must be considered in the design of nucleotide-competitive inhibitors.

Targeting the KRAS variant for treatment of non-small cell lung cancer: potential therapeutic applications

Lung cancer is the leading cause of cancer deaths worldwide, with non-small cell lung cancer (NSCLC) accounting for 80% of all lung cancers. Kirsten rat sarcoma viral oncogene homolog (KRAS) is one of the deadliest cancer-related proteins and plays a pivotal role in the most aggressive and lethal human cancers, including lung adenocarcinoma where it represents one of the most frequently mutated oncogene. Although therapeutic progresses have made an impact over the last decade, median survival for patients with advanced lung cancer remains disappointing, with a 5-year worldwide survival rate of <15%. For more than 20 years it has been recognized that constitutively active signaling downstream of KRAS is a fundamental driver of lung tumorigenesis. However, years of pursuit have failed to yield a drug that can safely curb KRAS activity; up to now no approved therapies exist for KRAS-mutant NSCLC. The aim of this review is to discuss the current knowledge of KRAS-mutated NSCLC, touching upon KRAS clinical relevance as a prognostic and predictive biomarker, with an emphasis on novel therapeutic approaches for the treatment of KRAS-variant NSCLC.

Modeling the mechanisms of biological GTP hydrolysis

Enzymes that hydrolyze GTP are currently in the spotlight, due to their molecular switch mechanism that controls many cellular processes. One of the best-known classes of these enzymes are small GTPases such as members of the Ras superfamily, which catalyze the hydrolysis of the γ-phosphate bond in GTP. In addition, the availability of an increasing number of crystal structures of translational GTPases such as EF-Tu and EF-G have made it possible to probe the molecular details of GTP hydrolysis on the ribosome. However, despite a wealth of biochemical, structural and computational data, the way in which GTP hydrolysis is activated and regulated is still a controversial topic and well-designed simulations can play an important role in resolving and rationalizing the experimental data. In this review, we discuss the contributions of computational biology to our understanding of GTP hydrolysis on the ribosome and in small GTPases.

Simvastatin interacts synergistically with tipifarnib to induce apoptosis in leukemia cells through the disruption of RAS membrane localization and ERK pathway inhibition

Tipifarnib, a farnesyltransferase inhibitor (FTI), was initially designed to disrupt RAS farnesylation and membrane localization necessary for RAS function. However, alternative geranylgeranylation has been postulated as an escape mechanism by which RAS bypasses the effect of FTI treatment. In this study, we demonstrate that simvastatin, an HMG-CoA reductase inhibitor, augments the cytotoxic effect of tipifarnib by blocking the alternative geranylgeranylation of RAS. Notably, this effect was accompanied by disruption of RAS membrane localization and ERK downregulation. In addition, the apoptotic effect of this combination was associated with downregulation of the antiapoptotic Mcl-1 protein and activation of the caspase cascade. These findings demonstrate that combining tipifarnib and simvastatin was successful in targeting RAS/ERK signaling and inducing apoptosis in leukemia cells. Both simvastatin and tipifarnib were used at clinically achievable doses, which make the combination promising for future clinical studies.

Dynamics of Ras complexes observed in living cells

K-Ras works as a switch in many important intracellular signaling pathways and plays important roles in cell growth, proliferation, differentiation and carcinogenesis. For signal transduction from K-Ras to Raf1, the best-characterized effector of K-Ras, the general view is that Ras recruits Raf1 from the cytoplasm to the cell membrane. To elucidate this process, we constructed a series of fusion proteins (including Raf1 and K-Ras fused with either fluorescent proteins or fluorescent protein fragments) to compare subcellular localizations of these proteins. Bimolecular fluorescence complementation (BiFC) and a co-transfection system were used. In the BiFC system, the K-Ras/Raf1 complexes were mainly located in the cell membrane, while the Raf1 control was uniformly distributed in the cytoplasm. However, the complexes of Raf1 and K-RasC185S, a K-Ras mutant which loses membrane-localization, were also able to accumulate in the cell membrane. In contrast, an apparent cytosolic distribution pattern was observed in cells co-transfected with mcerulean-Raf1 and EGFP-K-RasC185S, suggesting that the membrane localization of K-Ras/Raf1 complexes is not entirely dependent on K-Ras, and that other factors, such as the irreversible conformation formed between K-Ras and Raf1 may play a role. This study sheds light on the interaction between K-Ras and Raf1 and provides a practical method to elucidate the mechanism underlying K-Ras and Raf1 binding to the cell membrane.

Sasanquasaponin up-regulates anion exchanger 3 expression and elicits cardioprotection via NO/RAS/ERK1/2 pathway

We have shown recently that sasanquasaponin (SQS) can inhibit ischemia/reperfusion-induced elevation of intracellular Cl(-) concentration ([Cl(-)](i)) and elicit cardioprotection by up-regulating anion exchanger 3 (AE(3)) expression. In the present study, we futher analysed the intracellular signal transduction pathways by which SQS up-regulates AE(3) expression and elicits cardioprotection. Cardiomyocytes were incubated for 24 h with or without 10 µmol/L SQS, followed by simulated ischemia/reperfusion (sI/R). NO formation, Ras activity, and extracellular-regulated kinase 1/2 (ERK1/2) phosphorylation were measured appropriately. We showed that SQS pretreatment efficiently attenuated viability loss and lactate dehydrogenase leakage induced by sI/R in cardiomyocytes. Moreover, SQS induced NO production and promoted Ras activation, which futher promoted extracellular-regulated kinase 1/2 (ERK1/2) phosphorylation. These effects were paralleled by an increase in AE(3) expression. However, when the cardiomyocytes were treated with 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-l-oxyl-3-oxide (c-PTIO; an NO scavenger), S-trans-trans-farnesylthiosalicylic acid (FTS) (a Ras inhibitor), U0126 (an ERK1/2 inhibitor), respectively, the increase in AE(3) expression occurring during SQS pretreatment was almost completely abolished and, as a result, SQS-induced cardioprotection was prevented. Our findings indicate that SQS might up-regulate AE(3) expression through NO/Ras/ERK1/2 signal pathway to elicit cardioprotection in cultured cardiomyocytes.

Raf activation by Ras and promotion of cellular metastasis require phosphorylation of prohibitin in the raft domain of the plasma membrane

Prohibitin (PHB) is indispensable for Ras-induced Raf-1 activation, cell migration and growth; however, the exact role of PHB in the molecular pathogenesis of cancer metastasis remains largely unexamined. Here, we found a positive correlation between plasma membrane-associated PHB and the clinical stages of cancer. The level of PHB phosphorylated at threonine 258 (T258) and tyrosine 259 (Y259) in human cancer-cell membranes correlated with the invasiveness of cancer cells. Overexpression of phosphorylated PHB (phospho-PHB) in the lipid-raft domain of the cell membrane enhanced cell migration/invasion through PI3K/Akt and Raf-1/ERK activation. It also enhanced epithelial-mesenchymal transition, matrix metalloproteinase-2 activity and invasiveness of cancer cells in vitro. Immunoprecipitation analysis demonstrated that phospho-PHB associated with Raf-1, Akt and Ras in the membrane and was essential for the activation of Raf-1 signaling by Ras. Mice implanted with cancer cells stably overexpressing PHB in the plasma membrane showed enlarged cervical tumors, enhanced metastasis and shorter survival time compared with mice implanted with cancer cells without PHB overexpression. Dephosphorylation of PHB at T258 by site-directed mutagenesis diminished the in vitro and in vivo effects of PHB. These results suggest that increase in phospho-PHB T258 in the raft domain of the plasma membrane has a role in the Ras-driven activation of PI3K/Akt and Raf-1/ERK-signaling cascades and results in the promotion of cancer metastasis.

Molecular assessment of c-H-ras p21 expression in Helicobacter pylori-mediated gastric carcinogenesis

Helicobacter pylori (H. pylori) infection plays a significant role in causing gastric cancer; the exact molecular mechanisms of gastric carcinogenesis have not yet been fully determined. Therefore, this study was planned to examine the role of c-H-ras p21 expression in H. pylori infection at different stages of disease progression from precursor lesions to gastric carcinoma. This study was carried out in 200 patients, consisting of normal gastric mucosa (n = 20), mucosa with chronic gastritis (n = 63), intestinal metaplasia (n = 20), dysplasia (n = 11), and gastric adenocarcinoma (n = 86), in which the H. pylori status have been analysed. The expression of c-H-ras p21 was studied at mRNA as well as protein level using RT-PCR and western blotting, respectively. The localization of c-H-ras p21 was also studied semiquantitatively by immunohistochemistry. The RT-PCR and western blotting results of c-H-ras p21 mRNA and protein expressions were significantly increased in chronic gastritis, intestinal metaplasia, dysplasia, and gastric adenocarcinoma patients, respectively. Immunohistochemical study also showed the increased expression of c-H-ras p21 in the similar way. Overexpression of c-H-ras p21 might be due to H-ras mutation at codon 12 of ras gene family in H. pylori infection. The rate of expression of ras p21 was higher in the H. pylori-infected precursor lesions, chronic gastritis 49/56 (87.5%), intestinal metaplasia 16/17 (94%), and dysplasia 9/11(82%) whereas in the case of H. pylori negative cases these groups, show 12.5, 5.9, and 18.2%, respectively. The data suggested that H. pylori infection may increase the expression of c-H-ras p21 early in the process of gastric carcinogenesis.

Triggering Ras signalling by intracellular Francisella tularensis through recruitment of PKCα and βI to the SOS2/GrB2 complex is essential for bacterial proliferation in the cytosol

Intracellular proliferation of Francisella tularensis is essential for manifestation of the fatal disease tularaemia, and is classified as a category A bioterrorism agent. The F. tularensis-containing phagosome (FCP) matures into a late endosome-like phagosome with limited fusion to lysosomes, followed by rapid bacterial escape into the cytosol. The Francisella pathogenicity island (FPI) encodes a type VI-like secretion system, and the FPI-encoded IglC is essential for evasion of lysosomal fusion and phagosomal escape. Many host signalling events are likely to be modulated by F. tularensis to render the cell permissive for intracellular proliferation but they are not fully understood. Here we show that within 15 min of infection, intracellular F. tularensis ssp. novicida triggers IglC-dependent temporal activation of Ras, but attached extracellular bacteria fail to trigger Ras activation, which has never been shown for other intracellular pathogens. Intracellular F. tularensis ssp. novicida triggers activation of Ras through recruitment of PKCα and PKCβI to the SOS2/GrB2 complex. Silencing of SOS2, GrB2 and PKCα and PKCβI by RNAi has no effect on evasion of lysosomal fusion and bacterial escape into the cytosol but renders the cytosol non-permissive for replication of F. tularensis ssp. novicida. Since Ras activation promotes cell survival, we show that silencing of SOS2, GrB2 and PKCα and βI is associated with rapid early activation of caspase-3 within 8 h post infection. However, silencing of SOS2, GrB2 and PKCα and βI does not affect phosphorylation of Akt or Erk, indicating that activation of the PI3K/Akt and the Erk signalling cascade are independent of the F. tularensis-triggered Ras activation. We conclude that intracellular F. tularensis ssp. novicida triggers temporal and early activation of Ras through the SOS2/GrB2/PKCα/PKCβI quaternary complex. Temporal and rapid trigger of Ras signalling by intracellular F. tularensis is essential for intracellular bacterial proliferation within the cytosol, and this is associated with downregulation of early caspase-3 activation.

IL-6 increases MMP-13 expression and motility in human chondrosarcoma cells

Chondrosarcoma is a type of highly malignant tumor with a potent capacity to invade locally and cause distant metastasis. Chondrosarcoma shows a predilection for metastasis to the lungs. IL-6 is a multifunctional cytokine that is associated with the disease status and outcomes of cancers. However, the effect of IL-6 on the migration activity of human chondrosarcoma cells is mostly unknown. Here, we found that IL-6 increased the migration and expression of MMP-13 in human chondrosarcoma cells. We also found that human chondrosarcoma tissues had significant expression of IL-6, which was higher than that in normal cartilage. IL-6-mediated migration and MMP-13 up-regulation were attenuated by anti-IL-6 receptor antibody, Ras, Raf-1, and a MEK inhibitor. Activation of the Ras, Raf-1, MEK, ERK, and NF-κB signaling pathways after IL-6 treatment was demonstrated, and IL-6-induced MMP-13 expression and migration activity were inhibited by the specific inhibitor and mutant Ras, Raf-1, MEK, ERK, and NF-κB cascades. In addition, migration-prone sublines demonstrated that cells with increasing migration ability had greater expression of IL-6 and MMP-13. Taken together, these results indicate that IL-6 and IL-6 receptor interaction enhances migration of chondrosarcoma through an increase in MMP-13 production.

Dynamic palmitoylation and the role of DHHC proteins in T cell activation and anergy

Although protein S-palmitoylation was first characterized >30 years ago, and is implicated in the function, trafficking, and localization of many proteins, little is known about the regulation and physiological implications of this posttranslational modification. Palmitoylation of various signaling proteins required for TCR-induced T cell activation is also necessary for their proper function. Linker for activation of T cells (LAT) is an essential scaffolding protein involved in T cell development and activation, and we found that its palmitoylation is selectively impaired in anergic T cells. The recent discovery of the DHHC family of palmitoyl acyl transferases and the establishment of sensitive and quantitative proteomics-based methods for global analysis of the palmitoyl proteome led to significant progress in studying the biology and underlying mechanisms of cellular protein palmitoylation. We are using these approaches to explore the palmitoyl proteome in T lymphocytes and, specifically, the mechanistic basis for the impaired palmitoylation of LAT in anergic T cells. This chapter reviews the history of protein palmitoylation and its role in T cell activation, the DHHC family and new methodologies for global analysis of the palmitoyl proteome, and summarizes our recent work in this area. The new methodologies will accelerate the pace of research and provide a greatly improved mechanistic and molecular understanding of the complex process of protein palmitoylation and its regulation, and the substrate specificity of the novel DHHC family. Reversible protein palmitoylation will likely prove to be an important posttranslational mechanism that regulates cellular responses, similar to protein phosphorylation and ubiquitination.

Salirasib in the treatment of pancreatic cancer

The Ras family of genes is involved in the cellular regulation of proliferation, differentiation, cell adhesion and apoptosis. The K-ras gene is mutated in over 90% of pancreatic cancer cases. Salirasib (S-trans,trans-farnesylthiosalycilic acid [FTS]) is a synthetic small molecule that acts as a potent Ras inhibitor. It is a farnesylcysteine mimetic that selectively disrupts the association of active RAS proteins with the plasma membrane. Animal studies demonstrated that salirasib inhibited tumor growth, downregulated gene expression in the cell cycle and Ras signaling pathways. In a clinical study of salirasib combined with standard doses of gemcitabine, it was demonstrated that the two drugs have no overlapping pharmacokinetics. The salirasib recommended dose was 600 mg twice daily and the progression-free survival was 4.7 months. Future studies will determine whether salirasib adds to the anti-tumor activity of drugs approved by the US FDA for pancreatic cancer.

KappaB-Ras is a nuclear-cytoplasmic small GTPase that inhibits NF-kappaB activation through the suppression of transcriptional activation of p65/RelA

NF-κB is an important transcription factor involved in various biological responses, including inflammation, cell differentiation, and tumorigenesis. κB-Ras was identified as an IκB-interacting small GTPase and is reported to disturb cytokine-induced NF-κB activation. In this study, we established that κB-Ras is a novel type of nuclear-cytoplasmic small GTPase that mainly binds to GTP, and its localization seemed to be regulated by its GTP/GDP-binding state. Unexpectedly, the GDP-binding form of the κB-Ras mutant exhibited a more potent inhibitory effect on NF-κB activation, and this inhibitory effect seemed to be due to suppression of the transactivation of a p65/RelA NF-κB subunit. κB-Ras suppressed phosphorylation at serine 276 on the p65/RelA subunit, resulting in decreased interaction between p65/RelA and the transcriptional coactivator p300. Interestingly, the GDP-bound κB-Ras mutant exhibited higher interactive affinity with p65/RelA and inhibited the phosphorylation of p65/RelA more potently than wild-type κB-Ras. Taken together, these findings suggest that the GDP-bound form of κB-Ras in cytoplasm suppresses NF-κB activation by inhibiting its transcriptional activation.

Regulation of smooth muscle contraction by small GTPases

Next to changes in cytosolic [Ca(2+)], members of the Rho subfamily of small GTPases, in particular Rho and its effector Rho kinase, also known as ROK or ROCK, emerged as key regulators of smooth muscle function in health and disease. In this review, we will focus on the regulation of the contractile machinery by Rho/ROK signaling and its interaction with PKC and cyclic nucleotide signaling. We will briefly discuss the emerging evidence that remodeling of cortical actin is necessary for contraction.

Early endosome localization and activity of RasGEF1b, a toll-like receptor-inducible Ras guanine-nucleotide exchange factor

Guanine-nucleotide exchange factors (GEFs) stimulate the intrinsic GDP/GTP exchange activity of Ras and promote the formation of active Ras-GTP, which in turn controls diverse signalling networks important for the regulation of cell proliferation, survival, differentiation, vesicular trafficking, and gene expression. RasGEF1b is a GEF, whose expression is induced in macrophages on stimulation with toll-like receptor (TLR) agonists. Here, we showed that in vitro RasGEF1b expression by macrophages is mostly induced by TLR3 (poly I:C) and TLR4 (lipopolysaccharyde) through the MyD88-independent pathway. In vivo infection with the protozoan parasites Trypanosoma cruzi and Plasmodium chabaudi induced RasGEF1b in an MyD88-, TRIF-, and IFN-gamma-dependent manner. Ectopically expressed RasGEF1b was found, mostly, in the heavy membrane fraction of HEK 293T, and by confocal microscopy, it was found to be located at early endosomes. Computational modelling of the RasGEF1b-Ras interaction revealed that RasGEF1b interacts with the binding domain site of Ras, a critical region for interacting with GEFs involved in the activation of Ras-Raf-MEK-ERK pathway. More important, RasGEF1b was found to be closely associated with Ras in live cells and to trigger Ras activity. Altogether, these results indicate that on TLR activation, RasGEF1b may trigger Ras-like proteins and regulate specific biological activities described for this subtype of GTPases.

Human papillomavirus and mutated H-ras oncogene in cervical carcinomas and pathological negative pelvic lymph nodes: a retrospective follow-up

The metastasis status of pelvic lymph nodes (PLNs) seems to be a predictive factor of survival. It was suggested that the presence of HPV DNA and other biological markers in PLN may indicate a sub clinical early metastasis. The aim was to describe the prevalence and distribution patterns of HPV DNA and H-ras mutations in intra operatively obtained cervical tumors and PLN. Thirty-seven cervical tumors and 61 lymph node biopsies from 37 patients with cervical cancer were selected. HPV typing and location were performed by PCR/dot blot and in situ hybridization (ISH) respectively. PCR/RFLP was used to scan for mutations in H-ras. Hundred percent of the cervical cancers and 85% of the PLN were HPV positive; co-infection with more than one type was 27%. HPV 16 was detected alone or co-infecting with other types in 84% of tumors and 46% of PLN; the second most frequent viral type was HPV 18 (tumor: 27%; PLN: 20%). In PLN, HPV was located in nuclei or/and cytoplasm of lymphocytes, macrophages, endothelial, and /or stromal cells. H-ras mutations were identified in 5/24 (21%) of patients with cervical tumors showing poor or moderated differentiation. HPV DNA in histological tumor-free PLN not necessary indicate metastasis, but it may be associated to an active immune reaction. Mutated H-ras is probably involved in cervical carcinogenesis and its detection in tumor and metastasis free PLN may be related to early metastasis or recurrence in at least a subset of poorly differentiated cervical tumors.

Rit mutants confirm role of MEK/ERK signaling in neuronal differentiation and reveal novel Par6 interaction

Rit is a novel member of the Ras superfamily of small GTP-binding proteins that regulates signaling pathways controlling cellular fate determination. Constitutively activated mutants of Rit induce terminal differentiation of pheochromocytoma (PC6) cells resulting in a sympathetic neuron-like phenotype characterized by the development of highly-branched neurites. Rit signaling has been found to activate several downstream pathways including MEK/ERK, p38 MAPK, Ral-specific guanine nucleotide exchange factors (GEFs), and Rit associates with the Par6 cell polarity machinery. In this study, a series of Rit effector loop mutants was generated to test the importance of these cellular targets to Rit-mediated neuronal differentiation. We find that Rit-mediated neuritogenesis is dependent upon MEK/ERK MAP kinase signaling but independent of RalGEF activation. In addition, in vivo binding studies identified a novel mechanism of Par6 interaction, suggesting that the cell polarity machinery may serve to spatially restrict Rit signaling.

Thirty-one flavors of Drosophila rab proteins

Rab proteins are small GTPases that play important roles in transport of vesicle cargo and recruitment, association of motor and other proteins with vesicles, and docking and fusion of vesicles at defined locations. In vertebrates, >75 Rab genes have been identified, some of which have been intensively studied for their roles in endosome and synaptic vesicle trafficking. Recent studies of the functions of certain Rab proteins have revealed specific roles in mediating developmental signal transduction. We have begun a systematic genetic study of the 33 Rab genes in Drosophila. Most of the fly proteins are clearly related to specific vertebrate proteins. We report here the creation of a set of transgenic fly lines that allow spatially and temporally regulated expression of Drosophila Rab proteins. We generated fluorescent protein-tagged wild-type, dominant-negative, and constitutively active forms of 31 Drosophila Rab proteins. We describe Drosophila Rab expression patterns during embryogenesis, the subcellular localization of some Rab proteins, and comparisons of the localization of wild-type, dominant-negative, and constitutively active forms of selected Rab proteins. The high evolutionary conservation and low redundancy of Drosophila Rab proteins make these transgenic lines a useful tool kit for investigating Rab functions in vivo.

Loss of RAB25 expression in breast cancer

A novel breast cancer cell line (RAO-3) was established by transduction of the Q61L mutant RAS into human mammary epithelial cells that were immortalized with catalytic subunit of telomerase (hTERT). The cells displayed anchorage-independent growth and proliferation, and formed human mammary spindle cell carcinoma when injected into nude mice. Chromosome locus 1q22-23 was partially duplicated and inverted on one of the 3 chromosomes present in the cell line. We report here that mutations of chromosome 1q22-23 locus have resulted in the loss of RAB25 expression in the breast cancer cell line. Transduction of RAB25 into the breast cancer cell line arrests anchorage-independent growth. We have also demonstrated loss of RAB25 in human breast tumor tissue. These data suggest that loss of RAB25 might contribute to tumorigenesis of breast cancer, and RAB25 is likely to be an important factor in the development of breast cancer. RAB25 could be used as biological marker of breast cancer and provides a target for gene replacement therapy.

Cross-talk among gp130 cytokines in adipocytes

The interleukin-6 (IL-6) family of cytokines is a family of structurally and functionally related proteins, including IL-6, IL-11, leukemia inhibitory factor (LIF), oncostatin M (OSM), ciliary neurotrophic factor (CNTF), and cardiotrophin-1 (CT-1). These proteins are also known as gp130 cytokines because they all share gp130 as a common transducer protein within their functional receptor complexes. Several of these cytokines (LIF, OSM, CNTF, and CT-1) also utilize the LIF receptor (LIFR) as a component of their receptor complex. We have shown that all of these cytokines are capable of activating both the JAK/STAT and p42/44 mitogen-activated protein kinase signaling pathways in 3T3-L1 adipocytes. By performing a variety of preincubation studies and examining the ability of these cytokines to activate STATs, ERKs, and induce transcription of SOCS-3 mRNA, we have also examined the ability of gp130 cytokines to modulate the action of their family members. Our results indicate that a subset of gp130 cytokines, in particular CT-1, LIF, and OSM, has the ability to impair subsequent signaling activity initiated by gp130 cytokines. However, IL-6 and CNTF do not exhibit this cross-talk ability. Moreover, our results indicate that the cross-talk among gp130 cytokines is mediated by the ability of these cytokines to induce ligand-dependent degradation of the LIFR, in a proteasome-independent manner, which coincides with decreased levels of LIFR at the plasma membrane. In summary, our results demonstrate that an inhibitory cross-talk among specific gp130 cytokines in 3T3-L1 adipocytes occurs as a result of specific degradation of LIFR via a lysosome-mediated pathway.

Tfs1p, a member of the PEBP family, inhibits the Ira2p but not the Ira1p Ras GTPase-activating protein in Saccharomyces cerevisiae

Ras proteins are guanine nucleotide-binding proteins that are highly conserved among eukaryotes. They are involved in signal transduction pathways and are tightly regulated by two sets of antagonistic proteins: GTPase-activating proteins (GAPs) inhibit Ras proteins, whereas guanine exchange factors activate them. In this work, we describe Tfs1p, the first physiological inhibitor of a Ras GAP, Ira2p, in Saccharomyces cerevisiae. TFS1 is a multicopy suppressor of the cdc25-1 mutation in yeast and corresponds to the so-called Ic CPY cytoplasmic inhibitor. Moreover, Tfs1p belongs to the phosphatidylethanolamine-binding protein (PEBP) family, one member of which is RKIP, a kinase and serine protease inhibitor and a metastasis inhibitor in prostate cancer. In this work, the results of (i) a two-hybrid screen of a yeast genomic library, (ii) glutathione S-transferase pulldown experiments, (iii) multicopy suppressor tests of cdc25-1 mutants, and (iv) stress resistance tests to evaluate the activation level of Ras demonstrate that Tfs1p interacts with and inhibits Ira2p. We further show that the conserved ligand-binding pocket of Tfs1-the hallmark of the PEBP family-is important for its inhibitory activity.

Mitogen-activated 3p kinase is active in the nucleus

The MAPK-activated kinase 3pK (chromosome 3p kinase), also known as MAPKAPK-3, is a member of a family of kinases that are activated by more than one mitogen-activated protein kinase (MAPK). 3pK is unique since it was shown to be activated by three members of the MAPK family, namely extracellular-signal-regulated kinase (ERK), p38, and Jun-N-terminal kinase (JNK). Accordingly, 3pK is highly activated both by mitogens and by stress-inducing agents or proinflammatory cytokines. Studies utilizing dominant interfering mutants and pharmacological agents revealed that upon mitogenic stimulation, 3pK is exclusively activated via the classical MAPK cascade, while stress-induced activation of 3pK is mainly mediated by p38. The mechanism defining the specificity of kinase action in response to mitogenic versus stress activation remains unknown. Here we show that 3pK is transported to the cytoplasm upon both stress and mitogenic stimulation. While kinetics of nuclear export are similar in both situations, the activation pattern differs substantially. In the mitogenic situation, active 3pK remains in the nucleus for a significant time and there may fulfill mitogen-specific functions. These data not only show that nuclear export of the kinase is mechanistically uncoupled from its activation, but also provide a novel mechanism by which cells may modulate enzyme activity toward a stimulus-specific response.

NO stimulation of ATP-sensitive potassium channels: Involvement of Ras/mitogen-activated protein kinase pathway and contribution to neuroprotection

ATP-sensitive potassium (K(ATP)) channels regulate insulin release, vascular tone, and neuronal excitability. Whether these channels are modulated by NO, a membrane-permeant messenger in various physiological and pathological processes, is not known. The possibility of NO signaling via K(ATP) channel modulation is of interest because both NO and K(ATP) have been implicated in physiological functions such as vasodilation and neuroprotection. In this report, we demonstrate a mechanism that leads to K(ATP) activation via NO/Ras/mitogen-activated protein kinase pathway. By monitoring K(ATP) single-channel activities from human embryonic kidney 293 cell-attached patches expressing sulfonylurea receptor 2B and Kir6.2, we found K(ATP) stimulation by NO donor Noc-18, a specific NO effect abolished by NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (PTIO) but not guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). NO stimulation of K(ATP) is indirect and requires Ras and mitogen-activated protein kinase kinase activities. Blockade of Ras activation by pharmacological means or by coexpressing either a dominant-negative or an S-nitrosylation-site mutant Ras protein significantly abrogates the effects of NO. Inhibition of mitogen-activated protein kinase kinase abolishes the NO activation of K(ATP) but suppression of phosphatidylinositol 3-kinase does not. The NO precursor l-Arg also stimulates K(ATP) via endogenous NO synthase and the Ras signaling pathway. In addition, in rat hippocampal neurons, the protective effect of ischemic preconditioning induced by oxygen-glucose deprivation requires K(ATP) and NO synthase activity during preconditioning. Thus, neuroprotection caused by NO released during the short episode of sublethal ischemia may be mediated partly by K(ATP) stimulation.

Single-molecule imaging analysis of Ras activation in living cells

A single-molecule fluorescence resonance energy transfer (FRET) method has been developed to observe the activation of the small G protein Ras at the level of individual molecules. KB cells expressing H- or K-Ras fused with YFP (donor) were microinjected with the fluorescent GTP analogue BodipyTR-GTP (acceptor), and the epidermal growth factor-induced binding of BodipyTR-GTP to YFP-(H or K)-Ras was monitored by single-molecule FRET. On activation, Ras diffusion was greatly suppressed/immobilized, suggesting the formation of large, activated Ras-signaling complexes. These complexes may work as platforms for transducing the Ras signal to effector molecules, further suggesting that Ras signal transduction requires more than simple collisions with effector molecules. GAP334-GFP recruited to the membrane was also stationary, suggesting its binding to the signaling complex. The single-molecules FRET method developed here provides a powerful technique to study the signal-transduction mechanisms of various G proteins.

Identification of a novel domain of Ras and Rap1 that directs their differential subcellular localizations

The small GTPase Ha-Ras and Rap1A exhibit high mutual sequence homology and share various target proteins. However, they exert distinct biological functions and exhibit differential subcellular localizations; Rap1A is predominantly localized in the perinuclear region including the Golgi apparatus and endosomes, whereas Ha-Ras is predominantly localized in the plasma membrane. Here, we have identified a small region in Rap1A that is crucial for its perinuclear localization. Analysis of a series of Ha-Ras-Rap1A chimeras shows that Ha-Ras carrying a replacement of amino acids 46-101 with that of Rap1 exhibits the perinuclear localization. Subsequent mutational studies indicate that Rap1A-type substitutions within five amino acids at positions 85-89 of Ha-Ras, such as NNTKS85-89TAQST, NN85-86TA, and TKS87-89QST, are sufficient to induce the perinuclear localization of Ha-Ras. In contrast, substitutions of residues surrounding this region, such as FAI82-84YSI and FEDI90-93FNDL, have no effect on the plasma membrane localization of Ha-Ras. A chimeric construct consisting of amino acids 1-134 of Rap1A and 134-189 of Ha-Ras, which harbors both the palmitoylation and farnesylation sites of Ha-Ras, exhibits the perinuclear localization like Rap1A. Introduction of a Ha-Ras-type substitution into amino acids 85-89 (TAQST85-89NNTKS) of this chimeric construct causes alteration of its predominant subcellular localization site from the perinuclear region to the plasma membrane. These results indicate that a previously uncharacterized domain spanning amino acids 85-89 of Rap1A plays a pivotal role in its perinuclear localization. Moreover, this domain acts dominantly over COOH-terminal lipid modification of Ha-Ras, which has been considered to be essential and sufficient for the plasma membrane localization.

Somatostatin receptors

In 1972, Brazeau et al. isolated somatostatin (somatotropin release-inhibiting factor, SRIF), a cyclic polypeptide with two biologically active isoforms (SRIF-14 and SRIF-28). This event prompted the successful quest for SRIF receptors. Then, nearly a quarter of a century later, it was announced that a neuropeptide, to be named cortistatin (CST), had been cloned, bearing strong resemblance to SRIF. Evidence of special CST receptors never emerged, however. CST rather competed with both SRIF isoforms for specific receptor binding. And binding to the known subtypes with affinities in the nanomolar range, it has therefore been acknowledged to be a third endogenous ligand at SRIF receptors. This review goes through mechanisms of signal transduction, pharmacology, and anatomical distribution of SRIF receptors. Structurally, SRIF receptors belong to the superfamily of G protein-coupled (GPC) receptors, sharing the characteristic seven-transmembrane-segment (STMS) topography. Years of intensive research have resulted in cloning of five receptor subtypes (sst(1)-sst(5)), one of which is represented by two splice variants (sst(2A) and sst(2B)). The individual subtypes, functionally coupled to the effectors of signal transduction, are differentially expressed throughout the mammalian organism, with corresponding differences in physiological impact. It is evident that receptor function, from a physiological point of view, cannot simply be reduced to the accumulated operations of individual receptors. Far from being isolated functional units, receptors co-operate. The total receptor apparatus of individual cell types is composed of different-ligand receptors (e.g. SRIF and non-SRIF receptors) and co-expressed receptor subtypes (e.g. sst(2) and sst(5) receptors) in characteristic proportions. In other words, levels of individual receptor subtypes are highly cell-specific and vary with the co-expression of different-ligand receptors. However, the question is how to quantify the relative contributions of individual receptor subtypes to the integration of transduced signals, ultimately the result of collective receptor activity. The generation of knock-out (KO) mice, intended as a means to define the contributions made by individual receptor subtypes, necessarily marks but an approximation. Furthermore, we must now take into account the stunning complexity of receptor co-operation indicated by the observation of receptor homo- and heterodimerisation, let alone oligomerisation. Theoretically, this phenomenon adds a novel series of functional megareceptors/super-receptors, with varied pharmacological profiles, to the catalogue of monomeric receptor subtypes isolated and cloned in the past. SRIF analogues include both peptides and non-peptides, receptor agonists and antagonists. Relatively long half lives, as compared to those of the endogenous ligands, have been paramount from the outset. Motivated by theoretical puzzles or the shortcomings of present-day diagnostics and therapy, investigators have also aimed to produce subtype-selective analogues. Several have become available.

Ha-ras oncogene mutation associated to progression of papillomavirus induced lesions of uterine cervix

BACKGROUND

Epidemiological and virological surveys suggest that the HPV presence is not enough condition to generate anogenital cancer, others factors (genetic, environmental, hormonal, etc) may have an important role. Mutations of ras genes were observed in several human neoplasias, including cervical cancer.

OBJECTIVE

The aim of the study was to assess the frequency of Ha-ras oncogene mutations in cervical intraepithelial neoplasia (CIN) grade III and invasive squamous cell carcinomas and to examine this genetic factor in relation to HPV infection and the clinical evolution of cervical lesions.

STUDY DESIGN

They were selected for (a) evaluation of the frequency of Ha-ras mutations: 39 cases of invasive carcinomas (InCa), 47 CIN III and 12 normal tissues taken from areas adjacent to the tumor (NT). (b) Retrospective follow-up: 18 cases of lesion progression; 9 cases of persistence and 12 of regression to mature or immature metaplasia after specific treatment. All biopsies obtained from each patient during the follow-up done between 5 and 10 years were included. HPV typing and scanning of possible mutations in Ha-ras were made by single-strand conformation polymorphism analysis/polymerase chain reaction.

RESULTS

HPV-DNA was detected in 95% of InCa and 84% of CIN III; HPV 16/18 was found in 65% of patients, mainly associated with persistent infection and lesion progression. The undetermined HPV types (18%) could indicate the circulation in our country of types other than those screened (6, 11, 16, 18, 31 and 33). Twenty percent of CIN III and 41% of InCa had patterns compatible with Ha-ras mutations. Mutated Ha-ras was detected in 61 and 44% of progression and persistence cases, respectively, including early stages of progression.

CONCLUSIONS

Ha-ras mutations were detected in CIN II-III lesions; in mutated cases, the progression took place in under 2 years, then this detection may be an early predictive marker of rapid progression.

Bradykinin B2 receptor-mediated proliferation via activation of the Ras/Raf/MEK/MAPK pathway in rat vascular smooth muscle cells

It has been suggested that bradykinin (BK) plays an important role in regulating neointimal formation after vascular injury. However, implication of BK in the growth of rat vascular smooth muscle cells (VSMCs) is controversial. Therefore, we examined the mitogenic effect of BK on VSMCs associated with activation of mitogen-activated protein kinase (MAPK). Both [(3)H]thymidine incorporation and p42/p44 MAPK phosphorylation were activated by BK in time- and concentration-dependent manners. Pretreatment of these cells with neither pertussis toxin nor cholera toxin attenuated the BK-induced responses. Pretreatment of VSMCs with Hoe 140 (a selective B(2) receptor antagonist), U73122 (an inhibitor of phospholipase C), and BAPTA/AM (an intracellular Ca(2+) chelator) inhibited both [(3)H]thymidine incorporation and p42/p44 MAPK phosphorylation in response to BK. BK-induced [(3)H]thymidine incorporation and p42/p44 MAPK phosphorylation were inhibited by pretreatment of VSMCs with tyrosine kinase inhibitors (genistein and herbimycin A), protein kinase C (PKC) inhibitors (staurosporine, Go-6976, and Ro-318220), an MAPK kinase inhibitor (PD98059), and a p38 MAPK inhibitor (SB203580). Overexpression of the dominant negative mutants, H-Ras-15A and Raf-N4, suppressed p42/p44 MAPK activation induced by BK and PDGF-BB, indicating that Ras and Raf may be required for activation of these kinases. From these results, we concluded that the mitogenic effect of BK is mediated through activation of the Ras/Raf/MEK/MAPK pathway similar to that of PDGF-BB. BK-mediated MAPK activation was modulated by Ca(2+), PKC, and tyrosine kinase all of which are associated with cell proliferation in rat cultured VSMCs.

Brain-metastatic melanoma: a neurotrophic perspective

The brain is a unique microenvironment enclosed by the skull and maintaining a highly regulated vascular transport barrier. To metastasize to the brain, malignant tumor cells must attach to microvessel endothelial cells, invade the blood-brain barrier (BBB), and respond to brain survival and growth factors. Neurotrophins (NT) are important in brain invasion because they stimulate this process. In brain-metastatic melanoma cells, NT can promote invasion by enhancing the production of extracellular matrixdegradative enzymes such as heparanase, an enzyme capable of locally destroying both the extracellular matrix and the basement membrane of the BBB. We have examined human and murine melanoma cell lines exhibiting varying abilities to form brain metastases, and have found that they express low-affinity neurotrophin receptor p75NTR in relation to their brain-metastatic potentials. They do not, however, express trkA, the gene encoding the tyrosine kinase receptor TrkA, the high-affinity receptor for nerve growth factor (NGF), the prototypic NT. Presence of functional TrkC, the putative receptor for the invasion-promoting neurotrophin NT-3, was also expressed in these cells. Brain-metastatic melanoma cells can also produce autocrine factors and inhibitors that influence their growth, invasion, and survival in the brain. Synthesis of these factors may influence NT production by brain cells adjacent to the neoplastic invasion front, such as oligodendrocytes and astrocytes. In brain biopsies, we observed increased amounts of NGF and NT-3 in tumor-adjacent tissues at the invasion front of human melanoma tumors. Additionally, we found that astrocytes contribute to the brain-metastatic specificity of melanoma cells by producing NT-regulated heparanase. Trophic, autocrine, and paracrine growth factors may therefore determine whether metastatic cells can successfully invade, colonize, and grow in the central nervous system (CNS).

Purification and characterization of a UDP-glucosyltransferase produced by Legionella pneumophila

Legionella pneumophila is the agent of Legionnaires' disease. It invades and replicates within eukaryotic cells, including aquatic protozoans, mammalian macrophages, and epithelial cells. The molecular mechanisms of the Legionella interaction with target cells are not fully defined. In an attempt to discover novel virulence factors of L. pneumophila, we searched for bacterial enzymes with transferase activity. Upon screening ultrasonic extracts of virulent legionellae, we identified a uridine diphospho (UDP)-glucosyltransferase activity, which was capable of modifying a 45-kDa substrate in host cells. An approximately 60-kDa UDP-glucosyltransferase was purified from L. pneumophila and subjected to microsequencing. An N-terminal amino acid sequence, as well as the sequence of an internal peptide, allowed us to identify the gene for the enzyme within the unfinished L. pneumophila genome database. The intact gene was cloned and expressed in Escherichia coli, and the recombinant protein was purified and confirmed to possess an enzymatic activity similar to that of the native UDP-glucosyltransferase. We designated this gene ugt (UDP-glucosyltransferase). The Legionella enzyme did not exhibit significant homology with any known protein, suggesting that it is novel in structure and, perhaps, in function. Based on PCR data, an enzyme assay, and an immunoblot analysis, the glucosyltransferase appeared to be conserved in L. pneumophila strains but was absent from the other Legionella species. This study represents the first identification of a UDP-glucosyltransferase in an intracellular parasite, and therefore modification of a eukaryotic target(s) by this enzyme may influence host cell function and promote L. pneumophila proliferation.

Angiogenic oligosaccharides of hyaluronan induce multiple signaling pathways affecting vascular endothelial cell mitogenic and wound healing responses

Hyaluronan (HA) is a large nonsulfated glycosaminoglycan and an important regulator of angiogenesis, in particular, the growth and migration of vascular endothelial cells. We have identified some of the key intermediates responsible for induction of mitogenesis and wound recovery. Treatment of bovine aortic endothelial cells with oligosaccharides of hyaluronan (o-HA) resulted in rapid tyrosine phosphorylation and plasma membrane translocation of phospholipase Cgamma1 (PLCgamma1). Cytoplasmic loading with inhibitory antibodies to PLCgamma1, Gbeta, and Galpha(i/o/t/z) inhibited activation of extracellular-regulated kinase 1/2 (ERK1/2). Treatment with the Galpha(i/o) inhibitor, pertussis toxin, reduced o-HA-induced PLCgamma1 tyrosine phosphorylation, protein kinase C (PKC) alpha and beta1/2 membrane translocation, ERK1/2 activation, mitogenesis, and wound recovery, suggesting a mechanism for o-HA-induced angiogenesis through G-proteins, PLCgamma1, and PKC. In particular, we demonstrated a possible role for PKCalpha in mitogenesis and PKCbeta1/2 in wound recovery. Using antisense oligonucleotides and the Ras farnesylation inhibitor FTI-277, we showed that o-HA-induced bovine aortic endothelial cell proliferation, wound recovery, and ERK1/2 activation were also partially dependent on Ras activation, and that o-HA-stimulated tyrosine phosphorylation of the adapter protein Shc, as well as its association with Sos1. Binding of Src to Shc was required for its activation and for Ras-dependent activation of ERK1/2, cell proliferation, and wound recovery. Neither Src nor Ras activation was inhibited by pertussis toxin, suggesting that their activation was independent of heterotrimeric G-proteins. However, the specific Src kinase inhibitor PP2 inhibited Gbeta subunit co-precipitation with PLCgamma1, suggesting a possible role for Src in activation of PLCgamma1 and interaction between two distinct o-HA-induced signaling pathways.

Does the coronary risk factor low density lipoprotein alter growth and signaling in vascular smooth muscle cells?

There is increasing evidence that hypertension promotes low density lipoprotein (LDL) transportation into the subendothelial space of the vascular wall. Vascular smooth muscle cell (VSMC) proliferation plays an important role in the development and progression of cardiovascular diseases. Recently, several studies have demonstrated that LDL acts as a classic growth factor promoting VSMC growth via mitogenic signals normally elicited by classic growth factors. The present work summarizes current nontraditional concepts regarding possible cellular mechanisms through which hypertension and LDL may promote the development of atherosclerosis. Especially addressed are the possible effects of an elevated blood pressure in combination with LDL on VSMC growth. The new research concept concerning LDL as a growth factor and carrier for biological active phospholipids such as sphingosine-1-phosphate and sphingosylphosphorylcholine may contribute to an understanding of the pathogenesis of atherosclerosis by elevated high blood pressure.

Phosphorylation of Saccharomyces cerevisiae choline kinase on Ser30 and Ser85 by protein kinase A regulates phosphatidylcholine synthesis by the CDP-choline pathway

The Saccharomyces cerevisiae CKI-encoded choline kinase is phosphorylated on a serine residue and stimulated by protein kinase A. We examined the hypothesis that amino acids Ser(30) and Ser(85) contained in a protein kinase A sequence motif in choline kinase are target sites for protein kinase A. The synthetic peptides SQRRHSLTRQ (V(max)/K(m) = 10.8 microm(-1) nmol min(-1) mg(-1)) and GPRRASATDV (V(max)/K(m) = 0.15 microm(-1) nmol min(-1) mg(-1)) containing the protein kinase A motif for Ser(30) and Ser(85), respectively, within the choline kinase protein were substrates for protein kinase A. Choline kinase with Ser(30) to Ala (S30A) and Ser(85) to Ala (S85A) mutations were constructed alone and in combination by site-directed mutagenesis and expressed in a cki1Delta eki1Delta double mutant that lacks choline kinase activity. The mutant enzymes were expressed normally, but the specific activity of choline kinase in cells expressing the S30A, S85A, and S30A,S85A mutant enzymes was reduced by 44, 8, and 60%, respectively, when compared with the control. In vivo labeling experiments showed that the extent of phosphorylation of the S30A, S85A, and S30A,S85A mutant enzymes was reduced by 70, 17, and 83%, respectively. Phosphorylation of the S30A, S85A, and S30A,S85A mutant enzymes by protein kinase A in vitro was reduced by 60, 7, and 96%, respectively, and peptide mapping analysis of the mutant enzymes confirmed the phosphorylation sites in the enzyme. The incorporation of (3)H-labeled choline into phosphocholine and phosphatidylcholine in cells bearing the S30A, S85A, and S30A,S85A mutant enzymes was reduced by 56, 27, and 81%, respectively, and by 58, 33, and 84%, respectively, when compared with control cells. These data supported the conclusion that phosphorylation of choline kinase on Ser(30) and Ser(85) by protein kinase A regulates PC synthesis by the CDP-choline pathway.

Early embryonic expression ofFGF4/6/9gene and its role in the induction of mesenchyme and notochord inCiona savignyiembryos

In early Ciona savignyi embryos, nuclear localization of β-catenin is the first step of endodermal cell specification, and triggers the activation of various target genes. A cDNA for Cs-FGF4/6/9, a gene activated downstream of β-catenin signaling, was isolated and shown to encode an FGF protein with features of both FGF4/6 and FGF9/20. The early embryonic expression of Cs-FGF4/6/9 was transient and the transcript was seen in endodermal cells at the 16- and 32-cell stages, in notochord and muscle cells at the 64-cell stage, and in nerve cord and muscle cells at the 110-cell stage; the gene was then expressed again in cells of the nervous system after neurulation. When the gene function was suppressed with a specific antisense morpholino oligo, the differentiation of mesenchyme cells was completely blocked, and the fate of presumptive mesenchyme cells appeared to change into that of muscle cells. The inhibition of mesenchyme differentiation was abrogated by coinjection of the morpholino oligo and synthetic Cs-FGF4/6/9 mRNA. Downregulation of β-catenin nuclear localization resulted in the absence of mesenchyme cell differentiation due to failure of the formation of signal-producing endodermal cells. Injection of synthetic Cs-FGF4/6/9 mRNA in β-catenin-downregulated embryos evoked mesenchyme cell differentiation. These results strongly suggest that Cs-FGF4/6/9 produced by endodermal cells acts an inductive signal for the differentiation of mesenchyme cells. On the other hand, the role of Cs-FGF4/6/9 in the induction of notochord cells is partial; the initial process of the induction was inhibited by Cs-FGF4/6/9 morpholino oligo, but notochord-specific genes were expressed later to form a partial notochord.

Regulation of the cell cycle in normal and pathological glia

Precise regulation of the glial cell cycle is essential during nervous system development and in response to injury, whereas disruption of cell cycle control is associated with malignant glial tumors and other nervous system diseases. The Ras signaling pathway plays a central role in regulating the mammalian cell cycle, and uncontrolled Ras signaling has been implicated in a wide range of human cancers, including malignant gliomas. Recent studies in glia have demonstrated that activation of Ras can either induce or inhibit proliferation through complex interactions among downstream signaling pathways impinging on cell cycle regulatory proteins. Studies in Schwann cells have begun to delineate the pathways by which Ras regulates the cell cycle in normal and pathological glia, and have identified promising targets for therapeutic intervention in the treatment of PNS and CNS malignant glial tumors.

High-efficiency solid-phase capture using glass beads bonded to microcentrifuge tubes: immunoprecipitation of proteins from cell extracts and assessment of ras activation

We have bonded glass microbeads (425-600 microm diameter) to the inner walls of polypropylene microcentrifuge tubes. In addition to increasing the surface area of the tubes manyfold, the beads provide surface Si groups which can be reacted with a silane compound such as aminopropyltriethoxysilane, yielding a free amino group. The amino group is reacted with another cross-linking reagent, for example, the homobifunctional compound dimethyl suberimidate, which can form a covalent bond with amine groups of proteins. After binding protein A or G to the dimethyl suberimidate, the beads were used to immunoprecipitate proteins from cell extracts; we show that the protein A/G-coated glass beads yield similar amounts of immunoprecipitated proteins as a standard method using protein A- or G-agarose beads, but with fewer contaminating proteins. In addition, we show that when immunoprecipitating Ras from cell extracts and measuring the amounts of Ras-bound GTP and GDP, the new method yielded higher guanine nucleotide levels than protein G-agarose beads, suggesting that it caused less denaturation of Ras. Because the glass beads are bonded to the walls of the tubes, the immunoprecipitates can be washed rapidly and efficiently, and we show that 20-30 tubes can be washed in 1/10 the time required to wash immunoprecipitates on protein A- or G-agarose beads.