The RalGEF/Ral pathway: evaluating an intervention opportunity for Ras cancers

RALGAPA1 Deletion in Belgian Shepherd Dogs with Cerebellar Ataxia

Several genetically distinct forms of cerebellar ataxia exist in Belgian shepherd dogs. We investigated a litter in which two puppies developed cerebellar ataxia. The clinical signs stabilized at around six weeks of age, but remained visible into adulthood. Combined linkage and homozygosity mapping delineated a 5.5 Mb critical interval. The comparison of whole-genome sequence data of one affected dog to 929 control genomes revealed a private homozygous ~4.8 kb deletion in the critical interval, Chr8:14,468,376_14,473,136del4761. The deletion comprises exon 35 of the RALGAPA1 gene, XM_038544497.1:c.6080-2893_6944+1003del. It is predicted to introduce a premature stop codon into the transcript, truncating ~23% of the wild-type open reading frame of the encoded Ral GTPase-activating protein catalytic subunit α 1, XP_038400425.1:(p.Val2027Glnfs*7). Genotypes at the deletion showed the expected co-segregation with the phenotype in the family. Genotyping additional ataxic Belgian shepherd dogs revealed three additional homozygous mutant dogs from a single litter, which had been euthanized at five weeks of age due to their severe clinical phenotype. Histopathology revealed cytoplasmic accumulation of granular material within cerebellar Purkinje cells. Genotyping a cohort of almost 900 Belgian shepherd dogs showed the expected genotype-phenotype association and a carrier frequency of 5% in the population. Human patients with loss-of-function variants in RALGAPA1 develop psychomotor disability and early-onset epilepsy. The available clinical and histopathological data, together with current knowledge about RALGAPA1 variants and their functional impact in other species, suggest the RALGAPA1 deletion is the likely causative defect for the observed phenotype in the affected dogs.

The strategic roles of four enzymes in the interconnection between metabolism and oncogene activation in non-small cell lung cancer: Therapeutic implications

NSCLC is the leading cause of cancer mortality and represents a major challenge in cancer therapy. Intrinsic and acquired anticancer drug resistance are promoted by hypoxia and HIF-1α. Moreover, chemoresistance is sustained by the activation of key signaling pathways (such as RAS and its well-known downstream targets PI3K/AKT and MAPK) and several mutated oncogenes (including KRAS and EGFR among others). In this review, we highlight how these oncogenic factors are interconnected with cell metabolism (aerobic glycolysis, glutaminolysis and lipid synthesis). Also, we stress the key role of four metabolic enzymes (PFK1, dimeric-PKM2, GLS1 and ACLY), which promote the activation of these oncogenic pathways in a positive feedback loop. These four tenors orchestrating the coordination of metabolism and oncogenic pathways could be key druggable targets for specific inhibition. Since PFK1 appears as the first tenor of this orchestra, its inhibition (and/or that of its main activator PFK2/PFKFB3) could be an efficacious strategy against NSCLC. Citrate is a potent physiologic inhibitor of both PFK1 and PFKFB3, and NSCLC cells seem to maintain a low citrate level to sustain aerobic glycolysis and the PFK1/PI3K/EGFR axis. Awaiting the development of specific non-toxic inhibitors of PFK1 and PFK2/PFKFB3, we propose to test strategies increasing citrate levels in NSCLC tumors to disrupt this interconnection. This could be attempted by evaluating inhibitors of the citrate-consuming enzyme ACLY and/or by direct administration of citrate at high doses. In preclinical models, this "citrate strategy" efficiently inhibits PFK1/PFK2, HIF-1α, and IGFR/PI3K/AKT axes. It also blocks tumor growth in RAS-driven lung cancer models, reversing dedifferentiation, promoting T lymphocytes tumor infiltration, and increasing sensitivity to cytotoxic drugs.

Dysregulation of RalA signaling through dual regulatory mechanisms exerts its oncogenic functions in hepatocellular carcinoma

BACKGROUND AND AIMS

Ras-like (Ral) small guanosine triphosphatases (GTPases), RalA and RalB, are proto-oncogenes directly downstream of Ras and cycle between the active guanosine triphosphate-bound and inactive guanosine diphosphate-bound forms. RalGTPase-activating protein (RalGAP) complex exerts a negative regulation. Currently, the role of Ral up-regulation in cancers remains unclear. We aimed to examine the clinical significance, functional implications, and underlying mechanisms of RalA signaling in HCC.

APPROACH AND RESULTS

Our in-house and The Cancer Genome Atlas RNA sequencing data and quantitative PCR data revealed significant up-regulation of RalA in patients' HCCs. Up-regulation of RalA was associated with more aggressive tumor behavior and poorer prognosis. Consistently, knockdown of RalA in HCC cells attenuated cell proliferation and migration in vitro and tumorigenicity and metastasis in vivo. We found that RalA up-regulation was driven by copy number gain and uncovered that SP1 and ETS proto-oncogene 2 transcription factor cotranscriptionally drove RalA expression. On the other hand, RalGAPA2 knockdown increased the RalA activity and promoted intrahepatic and extrahepatic metastasis in vivo. Consistently, we observed significant RalGAPA2 down-regulation in patients' HCCs. Intriguingly, HCC tumors showing simultaneous down-regulation of RalGAPA2 and up-regulation of RalA displayed a significant association with more aggressive tumor behavior in terms of more frequent venous invasion, more advanced tumor stage, and poorer overall survival. Of note, Ral inhibition by a Ral-specific inhibitor RBC8 suppressed the oncogenic functions in a dose-dependent manner and sensitized HCC cells to sorafenib treatment, with an underlying enhanced inhibition of mammalian target of rapamycin signaling.

CONCLUSIONS

Our results provide biological insight that dysregulation of RalA signaling through dual regulatory mechanisms supports its oncogenic functions in HCC. Targeting RalA may serve as a potential alternative therapeutic approach alone or in combination with currently available therapy.

Ras Multimers on the Membrane: Many Ways for a Heart-to-Heart Conversation

Formation of Ras multimers, including dimers and nanoclusters, has emerged as an exciting, new front of research in the ‘old’ field of Ras biomedicine. With significant advances made in the past few years, we are beginning to understand the structure of Ras multimers and, albeit preliminary, mechanisms that regulate their formation in vitro and in cells. Here we aim to synthesize the knowledge accrued thus far on Ras multimers, particularly the presence of multiple globular (G-) domain interfaces, and discuss how membrane nanodomain composition and structure would influence Ras multimer formation. We end with some general thoughts on the potential implications of Ras multimers in basic and translational biology.

Exocyst protein subnetworks integrate Hippo and mTOR signaling to promote virus detection and cancer

The exocyst is an evolutionarily conserved protein complex that regulates vesicular trafficking and scaffolds signal transduction. Key upstream components of the exocyst include monomeric RAL GTPases, which help mount cell-autonomous responses to trophic and immunogenic signals. Here, we present a quantitative proteomics-based characterization of dynamic and signal-dependent exocyst protein interactomes. Under viral infection, an Exo84 exocyst subcomplex assembles the immune kinase Protein Kinase R (PKR) together with the Hippo kinase Macrophage Stimulating 1 (MST1). PKR phosphorylates MST1 to activate Hippo signaling and inactivate Yes Associated Protein 1 (YAP1). By contrast, a Sec5 exocyst subcomplex recruits another immune kinase, TANK binding kinase 1 (TBK1), which interacted with and activated mammalian target of rapamycin (mTOR). RALB was necessary and sufficient for induction of Hippo and mTOR signaling through parallel exocyst subcomplex engagement, supporting the cellular response to virus infection and oncogenic signaling. This study highlights RALB-exocyst signaling subcomplexes as mechanisms for the integrated engagement of Hippo and mTOR signaling in cells challenged by viral pathogens or oncogenic signaling.

NMR resonance assignments for the active and inactive conformations of the small G protein RalA

The Ral proteins (RalA and RalB) are small G proteins of the Ras family that have been implicated in exocytosis, endocytosis, transcriptional regulation and mitochondrial fission, as well as having a role in tumourigenesis. RalA and RalB are activated downstream of the master regulator, Ras, which causes the nucleotide exchange of GDP for GTP. Here we report the ¹H, ¹⁵ N and ¹³C resonance assignments of RalA in its active form bound to the GTP analogue GMPPNP. We also report the backbone assignments of RalA in its inactive, GDP-bound form. The assignments give insight into the switch regions, which change conformation upon nucleotide exchange. These switch regions are invisible in the spectra of the active, GMPPNP bound form but the residues proximal to the switches can be monitored. RalA is also an important drug target due to its over activation in some cancers and these assignments will be extremely useful for NMR-based screening approaches.

Bi-allelic Variants in RALGAPA1 Cause Profound Neurodevelopmental Disability, Muscular Hypotonia, Infantile Spasms, and Feeding Abnormalities

Ral (Ras-like) GTPases play an important role in the control of cell migration and have been implicated in Ras-mediated tumorigenicity. Recently, variants in RALA were also described as a cause of intellectual disability and developmental delay, indicating the relevance of this pathway to neuropediatric diseases. Here, we report the identification of bi-allelic variants in RALGAPA1 (encoding Ral GTPase activating protein catalytic alpha subunit 1) in four unrelated individuals with profound neurodevelopmental disability, muscular hypotonia, feeding abnormalities, recurrent fever episodes, and infantile spasms . Dysplasia of corpus callosum with focal thinning of the posterior part and characteristic facial features appeared to be unifying findings. RalGAPA1 was absent in the fibroblasts derived from two affected individuals suggesting a loss-of-function effect of the RALGAPA1 variants. Consequently, RalA activity was increased in these cell lines, which is in keeping with the idea that RalGAPA1 deficiency causes a constitutive activation of RalA. Additionally, levels of RalGAPB, a scaffolding subunit of the RalGAP complex, were dramatically reduced, indicating a dysfunctional RalGAP complex. Moreover, RalGAPA1 deficiency clearly increased cell-surface levels of lipid raft components in detached fibroblasts, which might indicate that anchorage-dependence of cell growth signaling is disturbed. Our findings indicate that the dysregulation of the RalA pathway has an important impact on neuronal function and brain development. In light of the partially overlapping phenotype between RALA- and RALGAPA1-associated diseases, it appears likely that dysregulation of the RalA signaling pathway leads to a distinct group of genetic syndromes that we suggest could be named RALopathies.

K-Ras-ERK1/2 accelerates lung cancer cell development via mediating H3K18ac through the MDM2-GCN5-SIRT7 axis

Context: H3^K18ac is linked to gene expression and DNA damage. Nevertheless, whether H3^K18ac participates in regulating Ras-ERK1/2-affected lung cancer cell phenotypes remains unclear. Objective: We explored the effects of H3^K18ac on Ras-ERK1/2-affected lung cancer cell phenotypes. Material and methods: NCI-H2126 cells were transfected with, pEGFP-K-Ras^WT and pEGFP-K-Ras^G12V/T35S plasmids for 48 h, and transfection with pEGFP-N1 served as a blank control. Then H3^K18ac and AKT and ERK1/2 pathways-associated factors were examined. Different amounts of the H3^K18Q (0.5, 1, and 2 μg) plasmids and Ras^G12V/T35S were co-transfected into NCI-H2126 cells, cell viability, cell colonies and migration were analyzed for exploring the biological functions of H3^K18ac in NCI-H2126 cells. The ERK1/2 pathway downstream factors were detected by RT-PCR and ChIP assays. The regulatory functions of SIRT7, GCN5 and MDM2 in Ras-ERK1/2-regulated H3^K18ac expression were finally uncovered. Results: Ras^G12V/T35S transfection decreased the expression of H3^K18ac about 2.5 times compared with the pEGFP-N1 transfection group, and activated ERK1/2 and AKT pathways. Moreover, H3^K18ac reduced cell viability, colonies, migration, and altered ERK1/2 downstream transcription in NCI-H2126 cells. Additionally, SIRT7 knockdown increased H3^K18ac expression and repressed cell viability, migration and the percentage of cells in S phase by about 50% compared to the control group, as well as changed ERK1/2 downstream factor expression. Besides, Ras-ERK1/2 decreased H3^K18ac was linked to MDM2-regulated GCN5 degradation. Conclusion: These observations disclosed that Ras-ERK1/2 promoted the development of lung cancer via decreasing H3^K18ac through MDM2-mediated GCN5 degradation. These findings might provide a new therapeutic strategy for lung cancer.

K-ras-ERK1/2 down-regulates H2A.XY142ph through WSTF to promote the progress of gastric cancer

Background

Histone H2AX phosphorylation at the site of Tyr-142 can participates in multiple biological progressions, which is including DNA repair. Ras pathway is closely involved in human cancers. Our study investigated the effects of Ras pathway via regulating H2AX.^Y142ph.

Methods

Gastric cancer cell line SNU-16 and MKN1 cells were transfected with Ras for G12D and T35S site mutation. The phosphorylation of H2A.X^Y142 and ERK1/2, WSTF and MDM2 was detected by western blot. Cell viability, cell colonies and migration was analyzed by MTT assay, soft-agar colony formation assay, and Transwell assay, respectively. The expression of Ras pathway related downstream factors, EYA3 and WSTF was detected by qRT-PCR. The relationship between Ras and downstream factors were detected by ChIP. The cell cycle progression was measured by flow cytometry.

Results

Ras^G12D/T35V transection decreased the phosphorylation of H2A.X^Y142 and activated phosphorylation of ERK-1/2. H2A.X^Y142 inhibited cell viability, colonies and migration. H2A.X^Y142ph altered the expression of Ras downstream factors. CHIP assay revealed that Ras^G12D/T35V could bind to the promoters of these Ras pathway downstream factors. Silence of EYA3 increased H2A.X^Y142ph and inhibited cell viability, migration and percent cells in S stage. Furthermore, silence of EYA3 also changed the downstream factors expression. WSTF and H2A.X^Y142ph revealed the similar trend and MDM2 on the opposite.

Conclusion

Ras/ERK signal pathway decreased H2A.X^Y142ph and promoted cell growth and metastasis. This Ras regulation process was down-regulated by the cascade of MDM2-WSTF-EYA3 to decrease H2A.X^Y142ph in SNU-16 cells.

ATP1A1 Integrates AKT and ERK Signaling via Potential Interaction With Src to Promote Growth and Survival in Glioma Stem Cells

Glioma stem cells (GSCs) have been considered to be responsible for treatment failure due to their self-renewal and limitless proliferative property. Recently, the Na⁺/K⁺-ATPase a1 (ATP1A1) subunit was described as a novel therapeutic target for gliomas. Interestingly, our previous proteomics study revealed that ATP1A1 is remarkably overexpressed in GSCs. In the current study, we investigated the role of ATP1A1 in regulating growth, survival, and tumorigenicity of primary human GSCs and the underlying molecular mechanism. We tested RNA and protein expression of ATP1A1 in glioma tissues and GSCs. In addition, we knocked down ATP1A1 in GSCs and assessed the effects thereof on growth, survival, and apoptosis. The role of ATP1A1 in signaling pathways was investigated in vitro. We found that the ATP1A1 expression level was associated with the grade of glioma. Knockdown of ATP1A1 in GSCs in vitro inhibited cell proliferation and survival, increased apoptosis, and halted cell-cycle progression at the G1 phase. Cell proliferation and survival were resumed upon rescue of ATP1A1 expression in ATP1A1-knockdown GSCs. The ERK1/2 and AKT pathways were inhibited through suppression of Src phosphorylation by ATP1A1 knockdown. Collectively, our findings suggest that ATP1A1 overexpression promotes GSC growth and proliferation by affecting Src phosphorylation to activate the ERK1/2 and AKT signaling pathways.

Small-Molecule Inhibition of Axl Targets Tumor Immune Suppression and Enhances Chemotherapy in Pancreatic Cancer

Activation of the receptor tyrosine kinase Axl is associated with poor outcomes in pancreatic cancer (PDAC), where it coordinately mediates immune evasion and drug resistance. Here, we demonstrate that the selective Axl kinase inhibitor BGB324 targets the tumor-immune interface to blunt the aggressive traits of PDAC cells in vitro and enhance gemcitibine efficacy in vivo Axl signaling stimulates the TBK1-NFκB pathway and innate immune suppression in the tumor microenvironment. In tumor cells, BGB324 treatment drove epithelial differentiation, expression of nucleoside transporters affecting gemcitabine response, and an immune stimulatory microenvironment. Our results establish a preclinical mechanistic rationale for the clinical development of Axl inhibitors to improve the treatment of PDAC patients.Significance: These results establish a preclinical mechanistic rationale for the clinical development of AXL inhibitors to improve the treatment of PDAC patients. Cancer Res; 78(1); 246-55. ©2017 AACR.

TBK1 Provides Context-Selective Support of the Activated AKT/mTOR Pathway in Lung Cancer

Emerging observations link dysregulation of TANK-binding kinase 1 (TBK1) to developmental disorders, inflammatory disease, and cancer. Biochemical mechanisms accounting for direct participation of TBK1 in host defense signaling have been well described. However, the molecular underpinnings of the selective participation of TBK1 in a myriad of additional cell biological systems in normal and pathophysiologic contexts remain poorly understood. To elucidate the context-selective role of TBK1 in cancer cell survival, we employed a combination of broad-scale chemogenomic and interactome discovery strategies to generate data-driven mechanism-of-action hypotheses. This approach uncovered evidence that TBK1 supports AKT/mTORC1 pathway activation and function through direct modulation of multiple pathway components acting both upstream and downstream of the mTOR kinase itself. Furthermore, we identified distinct molecular features in which mesenchymal, Ras-mutant lung cancer is acutely dependent on TBK1-mediated support of AKT/mTORC1 pathway activation for survival. Cancer Res; 77(18); 5077-94. ©2017 AACR.

Novel p21-Activated Kinase 4 (PAK4) Allosteric Modulators Overcome Drug Resistance and Stemness in Pancreatic Ductal Adenocarcinoma

The p21-activated kinase 4 (PAK4) is a key downstream effector of the Rho family GTPases and is found to be overexpressed in pancreatic ductal adenocarcinoma (PDAC) cells but not in normal human pancreatic ductal epithelia (HPDE). Gene copy number amplification studies in PDAC patient cohorts confirmed PAK4 amplification making it an attractive therapeutic target in PDAC. We investigated the antitumor activity of novel PAK4 allosteric modulators (PAM) on a panel of PDAC cell lines and chemotherapy-resistant flow-sorted PDAC cancer stem cells (CSC). The toxicity and efficacy of PAMs were evaluated in multiple subcutaneous mouse models of PDAC. PAMs (KPT-7523, KPT-7189, KPT-8752, KPT-9307, and KPT-9274) show antiproliferative activity in vitro against different PDAC cell lines while sparing normal HPDE. Cell growth inhibition was concurrent with apoptosis induction and suppression of colony formation in PDAC. PAMs inhibited proliferation and antiapoptotic signals downstream of PAK4. Co-immunoprecipitation experiments showed disruption of PAK4 complexes containing vimentin. PAMs disrupted CSC spheroid formation through suppression of PAK4. Moreover, PAMs synergize with gemcitabine and oxaliplatin in vitro KPT-9274, currently in a phase I clinical trial (clinicaltrials.gov; NCT02702492), possesses desirable pharmacokinetic properties and is well tolerated in mice with the absence of any signs of toxicity when 200 mg/kg daily is administered either intravenously or orally. KPT-9274 as a single agent showed remarkable antitumor activity in subcutaneous xenograft models of PDAC cell lines and CSCs. These proof-of-concept studies demonstrated the antiproliferative effects of novel PAMs in PDAC and warrant further clinical investigations. Mol Cancer Ther; 16(1); 76-87. ©2016 AACR.