Ral Guanine Nucleotide Dissociation Stimulator Research Articles

RILP inhibits proliferation, migration, and invasion of PC3 prostate cancer cells

RILP (Rab-interacting lysosomal protein) is a key regulator of lysosomal transport and a potential tumor suppressor. However, the role of RILP in prostate cancer and the underlying mechanism of RILP in regulating the proliferation, migration, and invasion of prostate cancer cells remain to be studied. In this study, we confirmed RalGDS (Ral guanine nucleotide dissociation stimulator) as the interaction partner of RILP in PC3 prostate cancer cells. Immunofluorescence microscopy showed that RILP recruits RalGDS to the lysosomal compartment. We found that RILP inhibits the activation of RalA and downstream effector RalBP1, and negatively regulates the downstream molecular phosphorylation of Ras. We showed that RILP inhibits the proliferation, migration, and invasion of PC3 prostate cancer cells, which may give rise to novel ideas for cancer treatment.

Identification of key genes related to immune cells in patients with gram-negative sepsis based on weighted gene co-expression network analysis.

BackgroundGram-negative sepsis is closely related to the immune response, involving collaborative efforts of different immune cells. However, the mechanisms underlying immune cell regulation in gram-negative sepsis remain unclear. Therefore, this study investigated the potential regulatory mechanisms and identified the key genes related to immune cells in gram-negative sepsis.MethodsThe RNA-sequencing data for gram-negative sepsis samples and normal samples were collected from the Gene Expression Omnibus (GEO) dataset GSE9960. CIBERSORT was performed to analyze the proportion of 22 types of immune cells in gram-negative sepsis and normal samples. Weighted gene co-expression network analysis (WGCNA) was used to determine the networks that are associated with the differentially distributed immune cells in the two groups. Differentially expressed genes were identified using the limma package. The least absolute shrinkage and selection operator (LASSO) and support vector machine-recursive feature elimination (SVM-RFE) algorithms were applied to ascertain hub gene signatures. The gene interaction network of hub gene signatures was determined by ingenuity pathway analysis. Furthermore, the expression levels of the key genes were verified using quantitative real-time polymerase chain reaction (qRT-PCR).ResultsCIBERSORT analysis showed that the proportions of plasma cells, resting CD4+ memory T cells, M1 macrophages, and eosinophils were significantly different between gram-negative sepsis and normal samples. WGCNA identified 1,100 genes in the most relevant modules associated with these immune cells. In addition, 87 differentially expressed genes were identified. By overlapping the genes found in the WGCNA and the differentially expressed genes, a total of 46 genes related to immune cells were identified. Integrative analysis of LASSO and SVM-RFE identified NLR family CARD domain-containing 4 (NLRC4) and ral guanine nucleotide dissociation stimulator like 4 (RGL4) as key gene signatures related to immune cells in gram-negative sepsis. The qRT-PCR results demonstrated that both NLRC4 and RGL4 were upregulated in peripheral blood mononuclear cells (PBMCs) from patients with sepsis.ConclusionsThis investigation provides novel insights into the molecular mechanisms of immune cells involved in the pathogenesis of gram-negative sepsis. NLRC4 and RGL4 were identified as key gene signatures related to immune cells and may act as potential diagnostic biomarkers for gram-negative sepsis.

Structures of RGL1 RAS-Association Domain in Complex with KRAS and the Oncogenic G12V Mutant

Ral Guanine Nucleotide Dissociation Stimulator Like 1 (RGL1) is a RAS effector protein that activates Ral GTPase by stimulating nucleotide exchange. Most structures of RAS-effector complexes are for the HRAS isoform; relatively few KRAS-effector structures have been solved, even though KRAS mutations are more frequent in human cancers. We determined crystal structures of KRAS/RGL1-RAS-association (RA) domain complexes and characterized the interaction in solution using nuclear magnetic resonance spectroscopy, size-exclusion chromatography combined with multi-angle light scattering and biolayer interferometry. We report structures of wild-type KRAS and the oncogenic G12V mutant in complex with the RA domain of RGL1 at < 2 Å resolution. KRASWT/RGL1-RA crystallized as a 1:1 heterodimer, whilst KRASG12V/RGL1-RA crystallized as a heterotetrameric structure in which RGL1-RA dimerized via domain-swapping the C-terminal beta-strand. Solution data indicated that KRASWT and KRASG12V in complex with RGL1-RA both exist predominantly as 1:1 dimers, while tetramerization occurs through very slow association. Through detailed structural analyses, the distance and angle between RAS α1 helix and RBD/RA α1 helix were found to differ significantly among RAS and RBD/RA complexes. The KRAS/RGL1-RA structures possess some of the largest α1RAS/α1Effector distances (21.7–22.2 Å), whereas the corresponding distances in previously reported RAS/RAF complexes are significantly shorter (15.2–17.7 Å). Contact map analysis identified unique structural signatures involving contacts between the β1-β2 loop of RA and the α1 helix of RAS, clearly distinguishing the KRAS/RGL1-RA (and other RAS/RA complexes) from RAS/RBD complexes. These results demonstrate that RAS effectors employ an assortment of finely-tuned docking surfaces to achieve optimal interactions with RAS.

RGL2 Drives the Metastatic Progression of Colorectal Cancer via Preventing the Protein Degradation of β-Catenin and KRAS.

Simple SummaryAberrant activation of the Wnt/β-catenin pathway due to APC (adenomatous polyposis coli) loss and Kirsten ras (KRAS) mutation is highly associated with malignant evolution, e.g., metastasis, of colorectal cancer (CRC). Ral guanine nucleotide dissociation stimulator-like (RGL) proteins, such as RGL2, regulate RAS activity via controlling the exchange between GTP and GDP. Although the cross-talk between β-catenin and KRAS has been reported to promote cancer metastasis, the functional role of RGL2 remains largely unknown. Here we show that RGL2 is significantly upregulated in primary tumors compared to normal tissues and serves as a poor prognostic marker in CRC patients. Cell-based and animal experiments further demonstrate that RGL2 acts as a driver to promote the metastatic progression of CRC, most likely via preventing the protein degradation of β-catenin and KRAS. Our findings not only unveil the oncogenic function of RGL2 but also provide a new strategy to combat metastatic CRC by targeting RGL2 activity.Colorectal cancer (CRC) is one of the most common cancers and results in high mortality worldwide, owing to cancer progression, i.e., metastasis. However, the molecular mechanism underlying the metastatic evolution of CRC remains largely unknown. Here, we find that the upregulation of Ral Guanine Nucleotide Dissociation Stimulator Like 2 (RGL2) is commonly detected in primary tumors compared normal tissues and is significantly associated with a poorer prognosis in CRC patients. Moreover, RGL2 expression appeared to positively correlate with the metastatic potentials of CRC cells. Whereas RGL2 knockdown dramatically suppresses the metastatic potentials of CRC cells in vitro and in vivo, RGL2 overexpression in the poorly metastatic CRC cells and reconstitution in the RGL2-silenced CRC cells enhanced and rescued the cellular metastatic ability, respectively. Computational simulation using Gene Set Enrichment Analysis program and cell-based assays demonstrated that RGL2 expression causally associated with the activity of Wnt/β-catenin signaling axis and Kirsten ras (KRAS)S, as well as the progression of epithelial-mesenchymal transition (EMT) in the detected CRC cells. Importantly, RGL2 upregulation was capable of preventing the protein degradation of β-catenin and KRAS in CRC cells. These findings suggest that RGL2 acts as a driver to promote the metastatic progression of CRC and also serves as a poor prognostic biomarker in CRC patients.

RGL4 over Expression Correlates with Variation in Midostaurin Response in FLT3-ITD Mutant AML Samples

Introduction: Acute Myeloid Leukemia (AML) is a heterogenous malignancy with the most common genomic alterations including mutations in NPM1, DNMT3A, and FLT3. Multiple FLT3-inhibitors have been developed and Midostaurin is the first to be FDA approved. However, while Midostaurin is now part of standard of care for FLT3 mutant AML patients undergoing induction chemotherapy, there is still a spectrum of clinical response. We hypothesized that additional biological factors could play a role in this variation of response. We previously observed that FLT3-ITD wildtype samples with KRAS mutations correlated with increased resistance to Midostaurin (1). Here, we utilized the Beat AML dataset containing over 900 AML patient samples processed through an ex vivo drug sensitivity screen to understand further whether genomic alterations could influence the range of Midostaurin response.Methods:We identified 180 (46 FLT3-ITD positive, 134 FLT3-ITD negative) de-novo primary AML peripheral blood or bone marrow samples from distinct patients within the Beat AML dataset. All samples included RNA-Sequencing profiling, mutational analyses, and ex-vivo Midostaurin drug screening data. Drug sensitivity was measured as area under a seven-point drug concentration curve (AUC). AUC was calculated as the area under the fitted probit curve (via direct integration) using all seven dose ranges as x-values and cell viability with limits from 0 to 100% as the y-value. RNA-Sequencing was normalized to counts per million (cpm) and the overall gene expression was chosen as the transcript of that gene with greatest average expression across the cohort. Differential gene expression was performed with the EdgeR package in R version 3.4.0.Results: As expected FLT3-ITD mutant samples, on average, are more sensitive to Midostaurin than FLT3-ITD wildtype sample. However, within the FLT3-ITD mutant cohort we observed a distribution of sensitivity responses (AUC mean of 55.4, IQR 35.5 - 75.3). Analysis of differential gene expression performed on the top 20% and bottom 20% of AUC values identified RGL4 over-expression across the entire resistant cohort (n = 9; Figure A). This was validated in an orthogonal data-set of 79 samples (21 mutant FLT3-ITD, 58 wildtype FLT3-ITD). To gain even more power within the validation set, we looked at all FLT3-ITD positive AUC values and observed a positive correlation between Midostaurin AUC and RGL4 expression (Spearman's rank correlation coefficient of 0.72, p < 0.05).Conclusions: In summary, we found that RGL4 over-expression correlated with resistance to Midostaurin in FLT3-ITD mutant samples in our ex vivo drug screen. RGL4 (ral guanine nucleotide dissociation stimulator like 4) encodes a protein similar to the guanine nucleotide exchange factor for Ral known as Ral GDS (guanine dissociation stimulator). It is highly expressed in the bone marrow and has the potential to activate the Ras-Raf-MEK-ERK pathway. As we had previously observed KRAS mutations correlating with resistance in FLT3-WT samples, this additional finding of RGL4 over expression supports the involvement of RAS pathway activation as a potential mechanism of resistance to Midostaurin. Additional in vitro studies are necessary to establish and further understand this mechanism as well as to test the efficacy of a Midostaurin / MEK inhibitor combination to treat resistant samples.1. Watanabe-Smith, K., Rosenberg, M., Bucy, T., Tyner, J. W., & Borate, U.(2017). Factors Predicting Response and Resistance to Midostaurin in FLT3 Positive and FLT3 Negative AML in 483 Primary AML Patient Samples. Blood,130(Suppl 1), 296. [Display omitted] DisclosuresBorate:Novartis: Consultancy; Agios: Consultancy.

RAS-mediated oncogenic signaling pathways in human malignancies.

Abnormally activated RAS proteins are the main oncogenic driver that governs the functioning of major signaling pathways involved in the initiation and development of human malignancies. Mutations in RAS genes and or its regulators, most frequent in human cancers, are the main force for incessant RAS activation and associated pathological conditions including cancer. In general, RAS is the main upstream regulator of the highly conserved signaling mechanisms associated with a plethora of important cellular activities vital for normal homeostasis. Mutated or the oncogenic RAS aberrantly activates a web of interconnected signaling pathways including RAF-MEK (mitogen-activated protein kinase kinase)-ERK (extracellular signal-regulated kinase), phosphoinositide-3 kinase (PI3K)/AKT (protein kinase B), protein kinase C (PKC) and ral guanine nucleotide dissociation stimulator (RALGDS), etc., leading to uncontrolled transcriptional expression and reprogramming in the functioning of a range of nuclear and cytosolic effectors critically associated with the hallmarks of carcinogenesis. This review highlights the recent literature on how oncogenic RAS negatively use its signaling web in deregulating the expression and functioning of various effector molecules in the pathogenesis of human malignancies.

Abstract 5161: Inhibition of TBK1/IKBKE impacts tumor growth of KRAS-mutant colorectal cancers

Abstract Mutations in RAS occur in an estimated one third of all human cancers. While direct targeting of RAS remains challenging, targeting downstream RAS effector molecules has been shown to impact the oncogenic function of RAS and elicit anti-tumor activity. TANK Binding Kinase 1 (TBK1) and I-Kappa B Kinase Epsilon (IKBKE) serine/threonine kinases are non-canonical IKK family members. TBK1 is directly downstream of the RAS effector Ral Guanine Nucleotide Dissociation Stimulator (RALGDS) and may be required for RAS to elicit its full oncogenic potential. To explore this possibility, we identified a potent and selective TBK1/IKBKE inhibitor to determine whether inhibition of TBK1 impacts the growth of RAS-mutant cancer models. KRAS-mutant cancer cell lines showed preferential sensitivity to TBK1/IKBKE inhibition over KRAS wild-type cell lines. The TBK1/IKBKE inhibitor was then evaluated in vivo with two KRAS-mutant colorectal cancer patient-derived xenograft (PDX) models, one of which harbors co-occurring PIK3CA and KRAS mutations. The TBK1/IKBKE inhibitor caused moderate tumor growth inhibition in comparison to vehicle in both PDX models. Since RAS exerts its oncogenic effects via additional effectors, such as RAF, and that inhibition of MEK1/2 resulted in compensatory activation of TBK1 in a KRAS-mutant cancer cell line, we tested if inhibition of TBK1/IKBKE in combination with the MEK inhibitor, trametinib, would result in superior efficacy in PDX models. The combination of a TBK1/IKBKE inhibitor and trametinib resulted in greater than 90% tumor growth inhibition within both of these KRAS mutant PDX models compared to either single agent alone. We also tested TBK1/IKBKE inhibition in a KRAS wild-type colorectal PDX model containing a BRAF mutation. In this model, TBK1/IKBKE did not inhibit tumor growth and, although there was significant tumor growth inhibition with trametinib alone, there was no further enhancement of efficacy with the addition of a TBK1/IKBKE inhibitor. Together, these data suggest that a TBK1/IKBKE inhibitor in combination with a MEK inhibitor may impact KRAS-mutant cancers. Citation Format: Susanna Stinson, Jianhua He, Zhiheng Jia, Katie S. Walker, Zhi-Hua Cui, Joshua A. Kaplan, Chandrasekar Venkataramani, Yujin Wang, Fatima Guevara, Timothy Nelson, Ewa Sicinska, Kimmie Ng, Charles S. Fuchs, David Dornan. Inhibition of TBK1/IKBKE impacts tumor growth of KRAS-mutant colorectal cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5161. doi:10.1158/1538-7445.AM2017-5161

RILP suppresses invasion of breast cancer cells by modulating the activity of RalA through interaction with RalGDS.

RILP (Rab7-interacting lysosomal protein) is a key regulator for late endosomal/lysosomal trafficking, and probably a tumor suppressor in prostate cancer. However, the role of RILP in other cancers and the underlying mechanism for RILP in regulating the invasion of cancer cells remain to be investigated. In this study, we showed that overexpression of RILP in breast cancer cells inhibits the migration and invasion, whereas the depletion of RILP by RNAi-mediated knockdown promotes the migration and invasion. We identified RalGDS (Ral guanine nucleotide dissociation stimulator) as a novel interacting partner for RILP, and truncation analysis revealed the N-terminal region of RILP is responsible for interacting with the guanine nucleotide exchange factor (GEF) domain of RalGDS. Immunofluorescence microscopy revealed that RalGDS can be recruited to the late endosomal compartments by RILP. Further investigations indicated that the overexpression of RILP inhibits the activity of RalA, a downstream target of RalGDS. Our data suggest that RILP suppresses the invasion of breast cancer cells by interacting with RalGDS to inhibit its GEF activity for RalA.

The Small GTPase RALA Controls c-Jun N-terminal Kinase-mediated FOXO Activation by Regulation of a JIP1 Scaffold Complex

FOXO (forkhead box O) transcription factors are tumor suppressors and increase the life spans of model organisms. Cellular stress, in particular oxidative stress caused by an increase in levels of reactive oxygen species (ROS), activates FOXOs through JNK-mediated phosphorylation. Importantly, JNK regulation of FOXO is evolutionarily conserved. Here we identified the pathway that mediates ROS-induced JNK-dependent FOXO regulation. Following increased ROS, RALA is activated by the exchange factor RLF (RalGDS-like factor), which is in complex with JIP1 (C-Jun-amino-terminal-interacting protein 1) and JNK. Active RALA consequently regulates assembly and activation of MLK3, MKK4, and JNK onto the JIP1 scaffold. Furthermore, regulation of FOXO by RALA and JIP1 is conserved in C. elegans, where both ral-1 and jip-1 depletion impairs heat shock-induced nuclear translocation of the FOXO orthologue DAF16.

Functional analysis of a duplication (p.E63_D69dup) in the switch II region of HRAS: new aspects of the molecular pathogenesis underlying Costello syndrome

Costello syndrome is a congenital disorder comprising a characteristic face, severe feeding difficulties, skeletal, cardiac and skin abnormalities, intellectual disability and predisposition to malignancies. It is caused by heterozygous germline HRAS mutations mostly affecting Gly(12) or Gly(13), which impair HRAS-GTPase activity and result in increased downstream signal flow independent of incoming signals. Functional analyses of rarer HRAS mutations identified in individuals with attenuated Costello syndrome phenotypes revealed altered GDP/GTP nucleotide affinities (p.K117R) and inefficient effector binding (p.E37dup). Thus, both phenotypic and functional variability associated with HRAS mutations are evident. Here, we report on a novel heterozygous HRAS germline mutation (c.187_207dup, p.E63_D69dup) in a girl presenting with a phenotype at the milder end of the Costello syndrome spectrum. The p.E63_D69dup mutation impaired co-precipitation of recombinant HRAS with NF1 GTPase-activating protein (GAP) suggesting constitutive HRAS(E63_D69dup) activation due to GAP insensitivity. Indeed, we identified strongly augmented active HRAS(E63_D69dup) that co-precipitated with effectors RAF1, RAL guanine nucleotide dissociation stimulator and phospholipase C1. However, we could not pull down active HRAS(E63_D69dup) using the target protein PIK3CA, indicating a compromised association between active HRAS(E63_D69dup) and PIK3CA. Accordingly, overexpression of HRAS(E63_D69dup) increased steady-state phosphorylation of MEK1/2 and ERK1/2 downstream of RAF, whereas AKT phosphorylation downstream of phosphoinositide 3-kinase (PI3K) was not enhanced. By analyzing signaling dynamics, we found that HRAS(E63_D69dup) has impaired reagibility to stimuli resulting in reduced and disrupted capacity to transduce incoming signals to the RAF-MAPK and PI3K-AKT cascade, respectively. We suggest that disrupted HRAS reagibility, as we demonstrate for the p.E63_D69dup mutation, is a previously unappreciated molecular pathomechanism underlying Costello syndrome.

Role of Electrostatics in Differential Binding of RalGDS to Rap Mutations E30D and K31E Investigated by Vibrational Spectroscopy of Thiocyanate Probes

The human protein Rap1A (Rap) is a member of the Ras superfamily of GTPases that binds to the downstream effector Ral guanine nucleotide dissociation stimulator (RalGDS). Although Ras and Rap have nearly identical amino acid sequences and structures along the effector binding surface, the charge reversal mutation Rap K31E has previously been shown to increase the dissociation constant of Rap-RalGDS docking to values similar to that of Ras-RalGDS docking. This indicates that the difference in charge at position 31 could provide a mechanism for Ral to distinguish two structurally similar but functionally distinct GTPases, which would be of vital importance for appropriate biological function. In this report, vibrational Stark effect spectroscopy, dissociation constant measurements, and molecular dynamics simulations were used to investigate the role that electrostatic field differences caused by the charge reversal mutation Rap K31E play in determining the binding specificity of RalGDS to Rap versus Ras. To do this, six variants of RalGDS carrying a thiocyanate electrostatic probe were docked with three Rap mutants, E30D, K31E, and E30D/K31E. The change in absorption energy of the thiocyanate probe caused by RalGDS docking to these Rap variants was then compared to that observed with wild-type Ras. Three trends emerged: the expected reversion behavior, an additive behavior of the two single mutations, and cancelation of the effects of each single mutation in the double mutant. These observations are explained with a physical model of the position of the thiocyanate probe with respect to the mutated residue based on molecular dynamics simulations.

Electrostatic Effects of Mutations of Ras Glutamine 61 Measured Using Vibrational Spectroscopy of a Thiocyanate Probe

Mutations of human oncoprotein p21(Ras) (hereafter Ras) at glutamine 61 are known to slow the rate of guanosine triphosphate (GTP) hydrolysis and transform healthy cells into malignant cells. It has been hypothesized that this glutamine plays a role in the intrinsic mechanism of GTP hydrolysis by interacting with an active site water molecule that electrostatically stabilizes the formation of the charged transition state at the γ-phosphate during hydrolysis. We have tested the interactions between amino acids at this position and water by measuring changes in the electrostatic field experienced by a nitrile probe positioned near Ras Q61 using vibrational Stark effect (VSE) spectroscopy. We mutated this glutamine to every amino acid except cysteine and proline and then incubated these mutants with a Ral guanine nucleotide dissociation stimulator (Ral) containing the I18C mutation that was chemically labeled with a thiocyanate vibrational spectroscopic probe. The formation of the docked Ras Q61X-labeled Ral complex was confirmed by measurement of the dissociation constant of the interaction. We measured the absorption energy of this nitrile to determine any differences in electrostatic environment in the immediate vicinity of the thiocyanate probe between wild type and mutants of Ras. For each Ras Q61X mutant, we correlate the change in electrostatic field at position 61 with the solvent accessible surface area of polar components of the mutant side chain determined from a Boltzmann-weighted ensemble of structures, as well as the residue's hydration potential. These results support the hypothesis that the role of Ras Q61 is to stabilize water in or near the active site during GTP hydrolysis. The substantial effect that nonpolar side chains of Ras Q61X have on the absorption energy of the thiocyanate must be investigated with further experiments.

Factors determining electrostatic fields in molecular dynamics simulations of the ras/effector interface

Using molecular dynamics simulations, we explore geometric and physical factors contributing to calculated electrostatic fields at the binding surface of the GTPase Ras with a spectroscopically labeled variant of a downstream effector, the Ras-binding domain of Ral guanine nucleotide dissociation stimulator (RalGDS). A related system (differing by mutation of one amino acid) has been studied in our group using vibrational Stark effect spectroscopy, a technique sensitive to electrostatic fields. Electrostatic fields were computed using the AMBER 2003 force field and averaged over snapshots from molecular dynamics simulation. We investigate geometric factors by exploring how the orientation of the spectroscopic probe changes on Ras-effector binding. In addition, we explore the physical origin of electrostatic fields at our spectroscopic probe by comparing contributions to the field from discrete components of the system, such as explicit solvent, residues on the Ras surface, and residues on the RalGDS surface. These models support our experimental hypothesis that vibrational Stark shifts are caused by Ras binding to its effector and not the structural rearrangements of the effector surface or probe reorientation on Ras-effector binding, for at least some of our experimental probes. These calculations provide physical insight into the origin, magnitude, and importance of electrostatic fields in protein-protein interactions and suggest new experiments to probe the field's role in protein docking.

Vibrational Stark Effect Spectroscopy at the Interface of Ras and Rap1A Bound to the Ras Binding Domain of RalGDS Reveals an Electrostatic Mechanism for Protein−Protein Interaction

Electrostatic fields at the interface of the Ras binding domain of the protein Ral guanine nucleotide dissociation stimulator (RalGDS) with the structurally analogous GTPases Ras and Rap1A were measured with vibrational Stark effect (VSE) spectroscopy. Eleven residues on the surface of RalGDS that participate in this protein-protein interaction were systematically mutated to cysteine and subsequently converted to cyanocysteine in order to introduce a nitrile VSE probe in the form of the thiocyanate (SCN) functional group. The measured SCN absorption energy on the monomeric protein was compared with solvent-accessible surface area (SASA) calculations and solutions to the Poisson-Boltzmann equation using Boltzmann-weighted structural snapshots from molecular dynamics simulations. We found a weak negative correlation between SASA and measured absorption energy, indicating that water exposure of protein surface amino acids can be estimated from experimental measurement of the magnitude of the thiocyanate absorption energy. We found no correlation between calculated field and measured absorption energy. These results highlight the complex structural and electrostatic nature of the protein-water interface. The SCN-labeled RalGDS was incubated with either wild-type Ras or wild-type Rap1A, and the formation of the docked complex was confirmed by measurement of the dissociation constant of the interaction. The change in absorption energy of the thiocyanate functional group due to complex formation was related to the change in electrostatic field experienced by the nitrile functional group when the protein-protein interface forms. At some locations, the nitrile experiences the same shift in field when bound to Ras and Rap1A, but at others, the change in field is dramatically different. These differences identify residues on the surface of RalGDS that direct the specificity of RalGDS binding to its in vivo binding partner, Rap1A, through an electrostatic mechanism.

Expression of tumour‐suppressing chemokine BRAK/CXCL14 reduces cell migration rate of HSC‐3 tongue carcinoma cells and stimulates attachment to collagen and formation of elongated focal adhesions in vitro

BRAK/CXCL14 (breast- and kidney-expressed chemokine/CXC chemokine ligand 14) is a chemokine that is expressed in many normal cells and tissues but is absent from or expressed at very low levels in transformed cells and cancerous tissues, including HNSCC (head and neck squamous cell carcinoma). We reported previously that the forced expression of BRAK/CXCL14 in HNSCC (HSC-3 BRAK) cells decreased the rate of tumour formation and size of tumour xenografts compared with mock-vector-introduced (HSC-3 Mock) cells in athymic nude mice, even though the growth rates of these cells were the same under in vitro culture conditions, suggesting that high-level expression of the gene is important for the suppression of tumour establishment in vivo. For the first step to study the mechanisms of BRAK-dependent tumour suppression, we compared characteristics between HSC-3 BRAK and HSC-3 Mock cells under in vitro culture conditions. The cell migration rate was lower in HSC-3 BRAK cells than in HSC-3 Mock cells. Also, HSC-3 BRAK cells showed more rapid adhesion than HSC-3 Mock cells when cultured on type I collagen-coated dishes but not on fibronectin or laminin 1-coated ones. This adhesion was mediated by alpha2beta1 integrin. Immunofluorescent analysis of the cells cultured on type I collagen showed that HSC-3 BRAK cells formed much more elongated focal adhesions co-localized with paxillin and actin stress fibres than did HSC-3 Mock cells. Treatment of parental HSC-3 cells with recombinant BRAK stimulated the activation of Rap1, which is a ras family small GTPase, and formation of elongated focal adhesions, indicating that the difference in cell character observed between HSC-3 Mock and HSC-3 BRAK was not due to selection of clones of different character but due to expression of BRAK in the cells. The characteristic morphology of focal adhesions in HSC-3 BRAK cells was perturbed by the introduction of an expression vector of the Rap-binding domain of the Ral guanine nucleotide dissociation stimulator, a target of Rap1, into HSC-3 BRAK cells, suggesting that Rap1 regulated the formation of the morphology of the focal adhesions. These data indicate that the expression of BRAK stimulated the formation of elongated focal adhesions of the HSC-3 cells in an autocrine or paracrine fashion, in which stimulation may be responsible for the reduced migration of the cells.

The Small GTPase Ral Couples the Angiotensin II Type 1 Receptor to the Activation of Phospholipase C-δ1

The angiotensin II type 1 receptor (AT(1)R) plays an important role in cardiovascular function and as such represents a primary target for therapeutic intervention. The AT(1)R has traditionally been considered to be coupled to the activation of phospholipase C (PLC) beta via its association with G alpha(q/11), leading to increases in intracellular inositol phosphate (IP) and release of calcium from intracellular stores. In the present study, we investigated whether the small GTPase RalA contributed to the regulation of AT(1)R endocytosis and signaling. We find that neither RalA nor RalB is required for the endocytosis of the AT(1)R, but that RalA expression is required for AT(1)R-stimulated IP formation but not 5-HT(2A) receptor-mediated IP formation. AT(1)R-activated IP formation is lost in the absence of Ral guanine nucleotide dissociation stimulator (RalGDS), and requires the beta-arrestin-dependent plasma membrane translocation of RalGDS. G alpha(q/11) small interfering RNA (siRNA) treatment also significantly attenuates both AT(1)R- and 5-HT(2A) receptor-stimulated IP formation after 30 min of agonist stimulation. PLC-delta1 has been reported to be activated by RalA, and we show that AT(1)R-stimulated IP formation is attenuated after PLC-delta 1 siRNA treatment. Taken together, our results provide evidence for a G protein-coupled recepto-activated and RalGDS/Ral-mediated mechanism for PLC-delta 1 stimulation.

G-protein binding features and regulation of the RalGDS family member, RGL2

RGL2 [RalGDS (Ral guanine nucleotide dissociation stimulator)-like 2] is a member of the RalGDS family that we have previously isolated and characterized as a potential effector for Ras and the Ras analogue Rap1b. The protein shares 89% sequence identity with its mouse orthologue Rlf (RalGDS-like factor). In the present study we further characterized the G-protein-binding features of RGL2 and also demonstrated that RGL2 has guanine-nucleotide-exchange activity toward the small GTPase RalA. We found that RGL2/Rlf properties are well conserved between human and mouse species. Both RGL2 and Rlf have a putative PKA (protein kinase A) phosphorylation site at the C-terminal of the domain that regulates the interaction with small GTPases. We demonstrated that RGL2 is phosphorylated by PKA and phosphorylation reduces the ability of RGL2 to bind H-Ras. As RGL2 and Rlf are unique in the RalGDS family in having a PKA site in the Ras-binding domain, the results of the present study indicate that Ras may distinguish between the different RalGDS family members by their phosphorylation by PKA.

Identification of Genes that May Play Critical Roles in Phenobarbital (PB)-Induced Liver Tumorigenesis due to Altered DNA Methylation

Aberrant DNA methylation plays important roles in tumorigenesis, and the nongenotoxic rodent tumor promoter phenobarbital (PB) alters methylation patterns to a greater extent in liver tumor susceptible as compared to resistant mice (Watson and Goodman, 2002). Unique hepatic regions of altered DNA methylation (RAMs) were identified in sensitive B6C3F1, as compared to resistant C57BL/6, mice at 2 or 4 weeks of PB treatment using a novel approach involving methylation-sensitive restriction digestion, arbitrarily primed PCR, and capillary electrophoresis (Bachman et al., 2006b). PCR products representing 90 of 170 (53%) total unique B6C3F1 RAMs at 2 or 4 weeks were cloned and subjected to BLAST-like alignment tool searches that resulted in 51 gene matches; some of these have documented oncogenic or tumor suppressor roles. Importantly, uniquely hypomethylated genes play roles in angiogenesis (e.g., chymase 1, tyrosine kinase nonreceptor 2, and possibly ephrin B2 and triple functional domain, PTPRF interacting) and invasion and metastasis, including those involved in the epithelial-mesenchymal transition (transcription factor 4, transforming growth factor beta receptor II, and ral guanine nucleotide dissociation stimulator). Common cellular targets and regulators of the genes representing unique B6C3F1 RAMs were uncovered, indicating that they might act in concert to more efficiently promote tumorigenesis. Genes not previously associated with mouse liver tumorigenesis exhibited altered methylation at these very early times following PB treatment. We hypothesize that at least some of the unique PB-induced B6C3F1 RAMs represent key events facilitating transformation, which is consistent with a causative role of altered DNA methylation during early stages of tumorigenesis.

Oog1, an oocyte-specific protein, interacts with Ras and Ras-signaling proteins during early embryogenesis

We previously identified an oocyte-specific gene, Oogenesin 1 (Oog1), that encodes 326 amino acids containing a leucine zipper structure and a leucine-rich repeat. In the present study, to identify the interacting proteins of Oog1, we performed a yeast two-hybrid screening using a GV-oocyte cDNA library and found that Ral guanine nucleotide dissociation stimulator (RalGDS) is the binding partner of Oog1. Coimmunoprecipitation assay confirmed the interaction between Oog1 and RalGDS proteins. Colocalization experiments provide the evidence that the nuclear localization of RalGDS depends on the expression of Oog1. Interestingly, RalGDS protein localized in the nucleus rather than the cytoplasm between late 1-cell and early 2-cell stages, the time when Oog1 localizes in the nucleus. We also examined the interaction between Oog1 and Ras by GST pull-down assay and revealed that Oog1 interacts with Ras in a GTP-dependent manner. These findings suggest a role of Oog1 as a Ras-binding protein.

Inhibition of maladaptive cardiac hypertrophy by the Ras effector protein Rlf

The monomeric G-protein Ras has been shown to have an obligatory role in the cardiac hypertrophic response by coordinating the activity of the mitogen activated protein kinases (MAPKs). Ras activation of ERK is associated with an adaptive hypertrophic response while JNK activation is associated with maladaptive hypertrophy. We identified the Ral guanine nucleotide dissociation stimulator like factor (Rlf) as a protein that binds to and interacts with Ras in cardiomyocytes. To understand the role of Rlf in regulating cardiomyocyte signaling, we assessed MAPK activation in neonatal rat ventricular myocytes (NRVMs) infected with adenoviruses encoding Rlf, or co-infected with constitutively active (V12-Ras) and Rlf. Rlf overexpression in NRVMs decreased agonist (endothelin-1 or phenylephrine) and V12-Ras mediated JNK activation without significantly altering ERK activation. To determine the effect of Rlf on cardiac hypertrophy in vivo, we generated transgenic mice with cardiac-specific overexpression of Rlf. Transgenic and nontransgenic male mice were treated with isoproteronol (ISO; 30 mg/kg/day) for 14 days. ISO treatment increased heart weight in transgenic and nontransgenic littermates to a similar extent. However, the hearts of Rlf transgenic mice treated with ISO displayed decreased fibrosis and myocardial cell loss compared to nontransgenic mice. Furthermore, Rlf transgenic mice were protected from ISO-mediated decreased SERCA2a expression. Overall, our results demonstrate that Rlf attenuates Ras-mediated activation of the JNK pathway and protects from maladaptive cardiac hypertrophy. (Supported by grants from the NIH and AHA)