Ral GTPases in tumorigenesis: emerging from the shadows. Exp Cell Res. 2013;319:2337-2342. [PMID: 23830877 DOI: 10.1016/j.yexcr.2013.06.020]

RAL-1 signaling regulates lipid composition in C. elegans

Signaling by the Ral small GTPase is poorly understood in vivo . Caenorhabditis elegans animals with constitutively activated RAL-1 or deficient for the inhibitory RalGAP, HGAP-1 /2, display pale intestines. Staining with Oil Red O detected decreased intestinal lipids in the hgap-1 deletion mutant relative to the wild type. Constitutively activated RAL-1 decreased lipid detected by stimulated Raman scattering (SRS) microscopy, a label-free method of detecting lipid by laser excitation and detection. A signaling-deficient missense mutant for RAL-1 also displayed reduced lipid staining via SRS. We conclude that RAL-1 signaling regulates lipid homeostasis, biosynthesis or storage in live animals.

RAS-targeted cancer therapy: Advances in drugging specific mutations

Rat sarcoma (RAS), as a frequently mutated oncogene, has been studied as an attractive target for treating RAS-driven cancers for over four decades. However, it is until the recent success of kirsten-RAS (KRAS)G12C inhibitor that RAS gets rid of the title "undruggable". It is worth noting that the therapeutic effect of KRASG12C inhibitors on different RAS allelic mutations or even different cancers with KRASG12C varies significantly. Thus, deep understanding of the characteristics of each allelic RAS mutation will be a prerequisite for developing new RAS inhibitors. In this review, the structural and biochemical features of different RAS mutations are summarized and compared. Besides, the pathological characteristics and treatment responses of different cancers carrying RAS mutations are listed based on clinical reports. In addition, the development of RAS inhibitors, either direct or indirect, that target the downstream components in RAS pathway is summarized as well. Hopefully, this review will broaden our knowledge on RAS-targeting strategies and trigger more intensive studies on exploiting new RAS allele-specific inhibitors.

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.

A signalling cascade for Ral

Ras is the most mutated oncoprotein in cancer. Among the three oncogenic effectors of Ras - Raf, PI3 Kinase and RalGEF>Ral - signalling through RalGEF>Ral (Ras-like) is by far the least well understood. A variety of signals and binding partners have been defined for Ral, yet we know little of how Ral functions in vivo. This review focuses on previous research in Drosophila that defined a function for Ral in apoptosis and established indirect relationships among Ral, the CNH-domain MAP4 Kinase misshapen, and the JNK MAP kinase basket. Most of the described signalling components are not essential in C. elegans, facilitating subsequent analysis using developmental patterning of the C. elegans vulval precursor cells (VPCs). The functions of two paralogous CNH-domain MAP4 Kinases were defined relative to Ras>Raf, Notch and Ras>RalGEF>Ral signalling in VPCs. MIG-15, the nematode ortholog of misshapen, antagonizes both the Ral-dependent and Ras>Raf-dependent developmental outcomes. In contrast, paralogous GCK-2, the C. elegans ortholog of Drosophila happyhour, propagates the 2°-promoting signal of Ral. Manipulations via CRISPR of Ral signalling through GCK-2 coupled with genetic epistasis delineated a Ras>RalGEF>Ral>Exo84>GCK-2>MAP3K^MLK-1> p38^PMK-1 cascade. Thus, genetic analysis using invertebrate experimental organisms defined a cascade from Ras to p38 MAP kinase.

Targeting KRAS in NSCLC: Old Failures and New Options for "Non-G12c" Patients

Kirsten Rat Sarcoma Viral Oncogene Homolog (KRAS) gene mutations are among the most common driver alterations in non-small cell lung cancer (NSCLC). Despite their high frequency, valid treatment options are still lacking, mainly due to an intrinsic complexity of both the protein structure and the downstream pathway. The increasing knowledge about different mutation subtypes and co-mutations has paved the way to several promising therapeutic strategies. Despite the best results so far having been obtained in patients harbouring KRAS exon 2 p.G12C mutation, even the treatment landscape of non-p.G12C KRAS mutation positive patients is predicted to change soon. This review provides a comprehensive and critical overview of ongoing studies into NSCLC patients with KRAS mutations other than p.G12C and discusses future scenarios that will hopefully change the story of this disease.

The small G-protein RalA promotes progression and metastasis of triple-negative breast cancer

Background

Breast cancer (BC) is the most common cancer in women and the leading cause of cancer-associated mortality in women. In particular, triple-negative BC (TNBC) has the highest rate of mortality due in large part to the lack of targeted treatment options for this subtype. Thus, there is an urgent need to identify new molecular targets for TNBC treatment. RALA and RALB are small GTPases implicated in growth and metastasis of a variety of cancers, although little is known of their roles in BC.

Methods

The necessity of RALA and RALB for TNBC tumor growth and metastasis were evaluated in vivo using orthotopic and tail-vein models. In vitro, 2D and 3D cell culture methods were used to evaluate the contributions of RALA and RALB during TNBC cell migration, invasion, and viability. The association between TNBC patient outcome and RALA and RALB expression was examined using publicly available gene expression data and patient tissue microarrays. Finally, small molecule inhibition of RALA and RALB was evaluated as a potential treatment strategy for TNBC in cell line and patient-derived xenograft (PDX) models.

Results

Knockout or depletion of RALA inhibited orthotopic primary tumor growth, spontaneous metastasis, and experimental metastasis of TNBC cells in vivo. Conversely, knockout of RALB increased TNBC growth and metastasis. In vitro, RALA and RALB had antagonistic effects on TNBC migration, invasion, and viability with RALA generally supporting and RALB opposing these processes. In BC patient populations, elevated RALA but not RALB expression is significantly associated with poor outcome across all BC subtypes and specifically within TNBC patient cohorts. Immunohistochemical staining for RALA in patient cohorts confirmed the prognostic significance of RALA within the general BC population and the TNBC population specifically. BQU57, a small molecule inhibitor of RALA and RALB, decreased TNBC cell line viability, sensitized cells to paclitaxel in vitro and decreased tumor growth and metastasis in TNBC cell line and PDX models in vivo.

Conclusions

Together, these data demonstrate important but paradoxical roles for RALA and RALB in the pathogenesis of TNBC and advocate further investigation of RALA as a target for the precise treatment of metastatic TNBC.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13058-021-01438-3.

The Crossroads between RAS and RHO Signaling Pathways in Cellular Transformation, Motility and Contraction

Ras and Rho proteins are GTP-regulated molecular switches that control multiple signaling pathways in eukaryotic cells. Ras was among the first identified oncogenes, and it appears mutated in many forms of human cancer. It mainly promotes proliferation and survival through the MAPK pathway and the PI3K/AKT pathways, respectively. However, the myriad proteins close to the plasma membrane that activate or inhibit Ras make it a major regulator of many apparently unrelated pathways. On the other hand, Rho is weakly oncogenic by itself, but it critically regulates microfilament dynamics; that is, actin polymerization, disassembly and contraction. Polymerization is driven mainly by the Arp2/3 complex and formins, whereas contraction depends on myosin mini-filament assembly and activity. These two pathways intersect at numerous points: from Ras-dependent triggering of Rho activators, some of which act through PI3K, to mechanical feedback driven by actomyosin action. Here, we describe the main points of connection between the Ras and Rho pathways as they coordinately drive oncogenic transformation. We emphasize the biochemical crosstalk that drives actomyosin contraction driven by Ras in a Rho-dependent manner. We also describe possible routes of mechanical feedback through which myosin II activation may control Ras/Rho activation.

Parallel Rap1>RalGEF>Ral and Ras signals sculpt the C. elegans nervous system

Ras is the most commonly mutated oncogene in humans and uses three oncogenic effectors: Raf, PI3K, and RalGEF activation of Ral. Understanding the importance of RalGEF>Ral signaling in cancer is hampered by the paucity of knowledge about their function in animal development, particularly in cell movements. We found that mutations that disrupt function of RalGEF or Ral enhance migration phenotypes of mutants for genes with established roles in cell migration. We used as a model the migration of the canal associated neurons (CANs), and validated our results in HSN cell migration, neurite guidance, and general animal locomotion. These functions of RalGEF and Ral are specific to their control of Ral signaling output rather than other published functions of these proteins. In this capacity Ral functions cell autonomously as a permissive developmental signal. In contrast, we observed Ras, the canonical activator of RalGEF>Ral signaling in cancer, to function as an instructive signal. Furthermore, we unexpectedly identified a function for the close Ras relative, Rap1, consistent with activation of RalGEF>Ral. These studies define functions of RalGEF>Ral, Rap1 and Ras signaling in morphogenetic processes that fashion the nervous system. We have also defined a model for studying how small GTPases partner with downstream effectors. Taken together, this analysis defines novel molecules and relationships in signaling networks that control cell movements during development of the nervous system.

Regulator of Chromosome Condensation 2 Modulates Cell Cycle Progression, Tumorigenesis, and Therapeutic Resistance

Accurate regulation of cell cycle is important for normal tissue development and homeostasis. RCC2 (Regulator of Chromosome Condensation 2) play a role as chromosomal passenger complex (CPC) implicated in all cell cycle phases. RCC2 was initially identified as Ran guanine exchange factor (GEF) for small G proteins. Therefore, RCC2 plays a key role in oncogenesis of most cancers. RCC2 is implicated in Colorectal Cancer (CRC), Lung Adenocarcinoma (LUAD), breast cancer, and ovarian cancer. Expression level of RCC2 protein determines regulation of tumor cell proliferation, invasion, metastasis, and radio-chemotherapeutic resistance. In this review, we explored proteins that interact with RCC2 to modulate tumor development and cancer therapeutic resistance by regulation of cell cycle process through various signaling pathways.

Proteogenomic Characterization Reveals Therapeutic Vulnerabilities in Lung Adenocarcinoma

To explore the biology of lung adenocarcinoma (LUAD) and identify new therapeutic opportunities, we performed comprehensive proteogenomic characterization of 110 tumors and 101 matched normal adjacent tissues (NATs) incorporating genomics, epigenomics, deep-scale proteomics, phosphoproteomics, and acetylproteomics. Multi-omics clustering revealed four subgroups defined by key driver mutations, country, and gender. Proteomic and phosphoproteomic data illuminated biology downstream of copy number aberrations, somatic mutations, and fusions and identified therapeutic vulnerabilities associated with driver events involving KRAS, EGFR, and ALK. Immune subtyping revealed a complex landscape, reinforced the association of STK11 with immune-cold behavior, and underscored a potential immunosuppressive role of neutrophil degranulation. Smoking-associated LUADs showed correlation with other environmental exposure signatures and a field effect in NATs. Matched NATs allowed identification of differentially expressed proteins with potential diagnostic and therapeutic utility. This proteogenomics dataset represents a unique public resource for researchers and clinicians seeking to better understand and treat lung adenocarcinomas.

Kirsten Rat Sarcoma Viral Oncogene Homologue (KRAS) Mutations in the Occurrence and Treatment of Pancreatic Cancer

Pancreatic cancer is a highly malignant tumor with a 5-year survival rate of less than 6%, and incidence increasing year by year globally. Pancreatic cancer has a poor prognosis and a high recurrence rate, almost the same as the death rate. However, the available effective prevention and treatment measures for pancreatic cancer are still limited. The genome variation is one of the main reasons for the development of pancreatic cancer. In recent years, with the development of gene sequencing technology, in-depth research on pancreatic cancer gene mutation presents that a growing number of genetic mutations are confirmed to be in a close relationship with invasion and metastasis of pancreatic cancer. Among them, KRAS mutation is a special one. Therefore, it is particularly important to understand the mechanism of the KRAS mutation in the occurrence and development of pancreatic cancer, and to explore the method of its transformation into clinical tumor molecular targeted treatment sites, to further improve the therapeutic effect on pancreatic cancer. Therefore, to better design chemical drugs, this review based on the biological functions of KRAS, summarized the types of KRAS mutations and their relationship with pancreatic cancer and included the downstream signaling pathway Raf-MEK-ERK, PI3K-AKT, RalGDS-Ral of KRAS and the current medicinal treatment methods for KRAS mutations. Moreover, drug screening and clinical treatment for KRAS mutated cell and animal models of pancreatic cancer are also reviewed along with the prospect of targeted medicinal chemistry therapy for precision treatment of pancreatic cancer in the future.

Conserved aging-related signatures of senescence and inflammation in different tissues and species

Increasing evidence indicates that chronic inflammation and senescence are the cause of many severe age-related diseases, with both biological processes highly upregulated during aging. However, until now, it has remained unknown whether specific inflammation- or senescence-related genes exist that are common between different species or tissues. These potential markers of aging could help to identify possible targets for therapeutic interventions of aging-associated afflictions and might also deepen our understanding of the principal mechanisms of aging. With the objective of identifying such signatures of aging and tissue-specific aging markers, we analyzed a multitude of cross-sectional RNA-Seq data from four evolutionarily distinct species (human, mouse and two fish) and four different tissues (blood, brain, liver and skin). In at least three different species and three different tissues, we identified several genes that displayed similar expression patterns that might serve as potential aging markers. Additionally, we show that genes involved in aging-related processes tend to be tighter controlled in long-lived than in average-lived individuals. These observations hint at a general genetic level that affect an individual’s life span. Altogether, this descriptive study contributes to a better understanding of common aging signatures as well as tissue-specific aging patterns and supplies the basis for further investigative age-related studies.

Genome-wide DNA methylation changes in transformed foci induced by nongenotoxic carcinogens

In vitro cell transformation assays (CTA) have been proposed as a method to identify possible nongenotoxic carcinogens. However, the current protocols do not provide information on the mechanism of action of the test articles. In this study, we combined an in vitro Bhas 42 CTA and sequencing-based DNA methylation profiling analysis to elucidate the carcinogenic mechanism associated with nongenotoxic carcinogens. Three nongenotoxic carcinogens were evaluated: cadmium chloride, methyl carbamate, and lithocholic acid. Methylation profiles were generated for the two nongenotoxic carcinogens (cadmium chloride and lithocholic acid) that were positive in Bhas 42 CTA. Methyl carbamate did not exhibit any promoter activity. Approximately 9.8% of all differentially methylated regions (DMRs) identified in cadmium chloride-induced transformed foci overlapped with DMRs in lithocholic acid-induced transformed foci. Interestingly, overlapping DMRs showed more hypermethylation than individual DMRs. In addition, the DMRs in CpG island elements common to both nongenotoxic carcinogens showed considerably more bias toward hypermethylated DMRs than those unique to either cadmium chloride or lithocholic acid. Pathway enrichment analysis revealed that genes harboring hypermethylated DMRs were significantly enriched in Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways including pathways in cancer, basal cell carcinoma, and Wnt signaling. The genes harboring hypomethylated DMRs were significantly related to mRNA surveillance pathway, RNA transport, and autophagy. Taken together, our preliminary results on genome-wide methylation analysis of cell clones from nongenotoxic carcinogen-induced foci could be exploited for CTAs improvement, but further research will be required to standardize and assess the specificity and sensitivity of this combined approach. Environ. Mol. Mutagen. 2019. © 2019 Wiley Periodicals, Inc.

Therapeutic strategies to target RAS-mutant cancers

RAS genes are the most commonly mutated oncogenes in cancer, but effective therapeutic strategies to target RAS-mutant cancers have proved elusive. A key aspect of this challenge is the fact that direct inhibition of RAS proteins has proved difficult, leading researchers to test numerous alternative strategies aimed at exploiting RAS-related vulnerabilities or targeting RAS effectors. In the past few years, we have witnessed renewed efforts to target RAS directly, with several promising strategies being tested in clinical trials at different stages of completion. Important advances have also been made in approaches designed to indirectly target RAS by improving inhibition of RAS effectors, exploiting synthetic lethal interactions or metabolic dependencies, using therapeutic combination strategies or harnessing the immune system. In this Review, we describe historical and ongoing efforts to target RAS-mutant cancers and outline the current therapeutic landscape in the collective quest to overcome the effects of this crucial oncogene.

RCC2, a regulator of the RalA signaling pathway, is identified as a novel therapeutic target in cisplatin-resistant ovarian cancer

Currently, cisplatin (DDP) is the first-line chemotherapeutic agent used for treatment of ovarian cancer, but gradually acquired drug resistance minimizes its therapeutic outcomes. We aimed to identify crucial genes associated with DDP resistance in ovarian cancer and uncover potential mechanisms. Two sets of gene expression data were downloaded from Gene Expression Omnibus, and bioinformatics analysis was conducted. In our study, the differentially expressed genes between DDP-sensitive and DDP-resistant ovarian cancer were screened in GSE15709 and GSE51373 database, and chromosome condensation 2 regulator (RCC2) and nucleoporin 160 were identified as 2 genes that significantly up-regulated in DDP-resistant ovarian cancer cell lines compared with DDP-sensitive cell lines. Moreover, RCC2, Ral small GTPase (RalA), and Ral binding protein-1 (RalBP1) expression was found to be significantly higher in DDP-resistant ovarian cancer tissues than in DDP-sensitive tissues. RCC2 plays a positive role in cell proliferation, apoptosis, and migration in DDP-resistant ovarian cancer cell lines in vitro and in vivo. Furthermore, RCC2 could interact with RalA, thus promoting its downstream effector RalBP1. RalA knockdown could reverse the effects of RCC2 overexpression on DDP-resistant ovarian cancer cell proliferation, apoptosis, and migration. Similarly, RalA overexpression could alleviate the effects of RCC2 knockdown in DDP-resistant ovarian cancer cells. Taken together, RCC2 may function as an oncogene, regulating the RalA signaling pathway, and intervention of RCC2 expression might be a promising therapeutic strategy for DDP-resistant ovarian cancer.-Gong, S., Chen, Y., Meng, F., Zhang, Y., Wu, H., Li, C., Zhang, G. RCC2, a regulator of the RalA signaling pathway, is identified as a novel therapeutic target in cisplatin-resistant ovarian cancer.

Two high-risk susceptibility loci at 6p25.3 and 14q32.13 for Waldenström macroglobulinemia

Waldenström macroglobulinemia (WM)/lymphoplasmacytic lymphoma (LPL) is a rare, chronic B-cell lymphoma with high heritability. We conduct a two-stage genome-wide association study of WM/LPL in 530 unrelated cases and 4362 controls of European ancestry and identify two high-risk loci associated with WM/LPL at 6p25.3 (rs116446171, near EXOC2 and IRF4; OR = 21.14, 95% CI: 14.40-31.03, P = 1.36 × 10-54) and 14q32.13 (rs117410836, near TCL1; OR = 4.90, 95% CI: 3.45-6.96, P = 8.75 × 10-19). Both risk alleles are observed at a low frequency among controls (~2-3%) and occur in excess in affected cases within families. In silico data suggest that rs116446171 may have functional importance, and in functional studies, we demonstrate increased reporter transcription and proliferation in cells transduced with the 6p25.3 risk allele. Although further studies are needed to fully elucidate underlying biological mechanisms, together these loci explain 4% of the familial risk and provide insights into genetic susceptibility to this malignancy.

Ral Signals through a MAP4 Kinase-p38 MAP Kinase Cascade in C. elegans Cell Fate Patterning

C. elegans vulval precursor cell (VPC) fates are patterned by an epidermal growth factor (EGF) gradient. High-dose EGF induces 1° VPC fate, and lower dose EGF contributes to 2° fate in support of LIN-12/Notch. We previously showed that the EGF 2°-promoting signal is mediated by LET-60/Ras switching effectors, from the canonical Raf-MEK-ERK mitogen-activated protein (MAP) kinase cascade that promotes 1° fate to the non-canonical RalGEF-Ral that promotes 2° fate. Of oncogenic Ras effectors, RalGEF-Ral is by far the least well understood. We use genetic analysis to identify an effector cascade downstream of C. elegans RAL-1/Ral, starting with an established Ral binding partner, Exo84 of the exocyst complex. Additionally, RAL-1 signals through GCK-2, a citron-N-terminal-homology-domain-containing MAP4 kinase, and PMK-1/p38 MAP kinase cascade to promote 2° fate. Our study delineates a Ral-dependent developmental signaling cascade in vivo, thus providing the mechanism by which lower EGF dose is transduced.

Structure, signaling and the drug discovery of the Ras oncogene protein

Mutations in Ras GTPase are among the most common genetic alterations in human cancers. Despite extensive research investigating Ras proteins, their functions still remain a challenge over a long period of time. The currently available data suggests that solving the outstanding issues regarding Ras could lead to development of effective drugs that could have a significant impact on cancer treatment. Developing a better understanding of their biochemical properties or modes of action, along with improvements in their pharmacologic profiles, clinical design and scheduling will enable the development of more effective therapies.

Evaluation and characterization of anti-RalA autoantibody as a potential serum biomarker in human prostate cancer

Autoantibodies against intracellular tumor-associated antigens (TAAs) are commonly found in human cancers. In this study, we characterized the serum autoantibody response to the RalA, Ras-like GTPase, in patients with prostate cancer (PCa). The autoantibodies were detected by immunofluorescence assay in PCa cell lines, ELISA, and immunoblotting in 339 serum samples from patients with PCa and benign prostatic hyperplasia (BPH), and in normal human sera (NHS). The expression of RalA in prostate tumor tissues was evaluated by immunohistochemistry (IHC) in tumor microarrays. The autoantibody level to RalA (median) in NHS was significantly lower than in PCa (0.053 vs 0.138; P < 0.001) and BPH (0.053 vs 0.132; P < 0.005) groups. The circulating anti-RalA autoantibody could distinguish PCa patients from normal individuals with the area under the receiver operating characteristic (ROC) curve (AUC) performing at 0.861, with sensitivity of 52.9% and specificity of 91.0%. Elevation in serum immunoreactivity was observed in PCa patients after radical prostatectomy. The combined use of both anti-RalA autoantibody and PSA showed a significantly higher discriminatory ability compared with either of those markers alone. RalA protein expression was detected by IHC in 85.3% of tumor tissues from PCa patients, but without significant difference compared to BPH or normal control tissues. Together, our study shows the additional benefits of anti-RalA autoantibody as a potential serological biomarker for PCa, particularly in patients with normal PSA, and further demonstrate the utility of biomarker combinations in the immunodiagnosis of PCa.

Ral signaling pathway in health and cancer

The Ral (Ras-Like) signaling pathway plays an important role in the biology of cells. A plethora of effects is regulated by this signaling pathway and its prooncogenic effectors. Our team has demonstrated the overactivation of the RalA signaling pathway in a number of human malignancies including cancers of the liver, ovary, lung, brain, and malignant peripheral nerve sheath tumors. Additionally, we have shown that the activation of RalA in cancer stem cells is higher in comparison with differentiated cancer cells. In this article, we review the role of Ral signaling in health and disease with a focus on the role of this multifunctional protein in the generation of therapies for cancer. An improved understanding of this pathway can lead to development of a novel class of anticancer therapies that functions on the basis of intervention with RalA or its downstream effectors.

Overexpression of RCC2 Enhances Cell Motility and Promotes Tumor Metastasis in Lung Adenocarcinoma by Inducing Epithelial-Mesenchymal Transition

Purpose: Investigate the role of regulator of chromosome condensation 2 (RCC2) on lung adenocarcinoma (LUAD) metastasis.Experimental Design: Clinical specimens were used to assess the impact of RCC2 on LUAD metastasis. Mouse models, cytobiology, and molecular biology assays were performed to elucidate the function and underlying mechanisms of RCC2 in LUAD.Results: RCC2 expression was frequently increased in LUADs (88/122, 72.13%). It was confirmed by analysis of a larger cohort of TCGA RNA-seq data containing 488 LUADs and 58 normal lung tissues (P < 0.001). Importantly, increased level of RCC2 was significantly associated with T status of tumor (P = 0.002), lymph node metastasis (P = 0.004), and advanced clinical stage (P = 0.001). Patients with LUAD with higher expression of RCC2 had shorter overall survival. Cox regression analysis demonstrated that RCC2 was an independent poorer prognostic factor for patients with LUAD. Moreover, forced expression of RCC2 promoted intrapulmonary metastasis in vivo and significantly enhanced LUAD cell migration, invasion, and proliferation in vitro Further study found that RCC2 induced epithelial-mesenchymal transition (EMT) and also stimulated the expression of MMP-2 and MMP-9. In addition, RCC2 was able to activate JNK, while inhibition of JNK suppressed the effect of RCC2 on LUAD cell migration, invasion, EMT, and the expression of MMP-2 and MMP-9.Conclusions: RCC2 plays a pivotal role in LUAD metastasis by inducing EMT via activation of MAPK-JNK signaling. Clin Cancer Res; 23(18); 5598-610. ©2017 AACR.

RalBP1 and p19-VHL play an oncogenic role, and p30-VHL plays a tumor suppressor role during the blebbishield emergency program

Cancer stem cells evade apoptotic death by blebbishield emergency program, which constructs blebbishields from apoptotic bodies and drives cellular transformation. Von Hippel-Lindau (VHL) plays both tumor suppressor and oncogenic roles, and the reason behind is poorly understood. Here we demonstrate that dimers and trimers of p19-VHL interact with RalBP1 to construct blebbishields. Expression of RalBP1, p19-VHL, and high-molecular weight VHL is required to evade apoptosis by blebbishield-mediated transformation. In contrast, p30-VHL plays a tumor suppressor role by inhibiting blebbishield-mediated transformation. Furthermore, target genes of VHL that suppress oxidative stress were elevated during blebbishield-mediated cellular transformation. Thus, RalBP1 and p19-VHL play an oncogenic role, whereas p30-VHL plays a tumor suppressor role during the blebbishield emergency program by regulating oxidative stress management genes.

Cathepsin F Knockdown Induces Proliferation and Inhibits Apoptosis in Gastric Cancer Cells

Gastric cancer (GC) is one of the most common cancers in the world. The cathepsin F (CTSF) gene has recently been found to participate in the progression of several types of cancer. However, the clinical characteristics and function of CTSF in GC as well as its molecular mechanisms are not clear. Six GC cell lines and 44 paired adjacent noncancerous and GC tissue samples were used to assess CTSF expression by quantitative polymerase chain reaction (qPCR). We used lentivirus-mediated small hairpin RNA (Lenti-shRNA) against CTSF to knock down the expression of CTSF in GC cells. Western blot and qPCR were used to analyze the mRNA and related protein expression. The biological phenotypes of gastric cells were examined by cell proliferation and apoptosis assays. Microarray-based mRNA expression profile screening was also performed to evaluate the potential molecular pathways in which CTSF may be involved. The CTSF mRNA level was associated with tumor differentiation, depth of tumor invasion, and lymph node metastasis. Downregulation of CTSF expression efficiently inhibited apoptosis and promoted the proliferation of GC cells. Moreover, a total of 1,117 upregulated mRNAs and 1,143 downregulated mRNAs were identified as differentially expressed genes (DEGs). Further analysis identified the involvement of these mRNAs in cancer-related pathways and various other biological processes. Nine DEGs in cancer-related pathways and three downstream genes in the apoptosis pathway were validated by Western blot, which was mainly in agreement with the microarray data. To our knowledge, this is the first report investigating the effect of CTSF on the growth and apoptosis in GC cells and its clinical significance. The CTSF gene may function as a tumor suppressor in GC and may be a potential therapeutic target in the treatment of GC.

Quantitative Proteomics Reveals Fundamental Regulatory Differences in Oncogenic HRAS and Isocitrate Dehydrogenase (IDH1) Driven Astrocytoma

Glioblastoma multiformes (GBMs) are high-grade astrocytomas and the most common brain malignancies. Primary GBMs are often associated with disturbed RAS signaling, and expression of oncogenic HRAS results in a malignant phenotype in glioma cell lines. Secondary GBMs arise from lower-grade astrocytomas, have slower progression than primary tumors, and contain IDH1 mutations in over 70% of cases. Despite significant amount of accumulating genomic and transcriptomic data, the fundamental mechanistic differences of gliomagenesis in these two types of high-grade astrocytoma remain poorly understood. Only a few studies have attempted to investigate the proteome, phosphorylation signaling, and epigenetic regulation in astrocytoma. In the present study, we applied quantitative phosphoproteomics to identify the main signaling differences between oncogenic HRAS and mutant IDH1-driven glioma cells as models of primary and secondary GBM, respectively. Our analysis confirms the driving roles of the MAPK and PI3K/mTOR signaling pathways in HRAS driven cells and additionally uncovers dysregulation of other signaling pathways. Although a subset of the signaling changes mediated by HRAS could be reversed by a MEK inhibitor, dual inhibition of MEK and PI3K resulted in more complete reversal of the phosphorylation patterns produced by HRAS expression. In contrast, cells expressing mutant IDH1 did not show significant activation of MAPK or PI3K/mTOR pathways. Instead, global downregulation of protein expression was observed. Targeted proteomic analysis of histone modifications identified significant histone methylation, acetylation, and butyrylation changes in the mutant IDH1 expressing cells, consistent with a global transcriptional repressive state. Our findings offer novel mechanistic insight linking mutant IDH1 associated inhibition of histone demethylases with specific histone modification changes to produce global transcriptional repression in secondary glioblastoma. Our proteomic datasets are available for download and provide a comprehensive catalogue of alterations in protein abundance, phosphorylation, and histone modifications in oncogenic HRAS and IDH1 driven astrocytoma cells beyond the transcriptomic level.

RalA is overactivated in medulloblastoma

Medulloblastoma (MDB) represents a major form of malignant brain tumors in the pediatric population. A vast spectrum of research on MDB has advanced our understanding of the underlying mechanism, however, a significant need still exists to develop novel therapeutics on the basis of gaining new knowledge about the characteristics of cell signaling networks involved. The Ras signaling pathway, one of the most important proto-oncogenic pathways involved in human cancers, has been shown to be involved in the development of neurological malignancies. We have studied an important effector down-stream of Ras, namely RalA (Ras-Like), for the first time and revealed overactivation of RalA in MDB. Affinity precipitation analysis of active RalA (RalA-GTP) in eight MDB cell lines (DAOY, RES256, RES262, UW228-1, UW426, UW473, D283 and D425) revealed that the majority contained elevated levels of active RalA (RalA-GTP) as compared with fetal cerebellar tissue as a normal control. Additionally, total RalA levels were shown to be elevated in 20 MDB patient samples as compared to normal brain tissue. The overall expression of RalA, however, was comparable in cancerous and normal samples. Other important effectors of RalA pathway including RalA binding protein-1 (RalBP1) and protein phosphatase A (PP2A) down-stream of Ral and Aurora kinase A (AKA) as an upstream RalA activator were also investigated in MDB. Considering the lack of specific inhibitors for RalA, we used gene specific silencing in order to inhibit RalA expression. Using a lentivirus expressing anti-RalA shRNA we successfully inhibited RalA expression in MDB and observed a significant reduction in proliferation and invasiveness. Similar results were observed using inhibitors of AKA and geranyl-geranyl transferase (non-specific inhibitors of RalA signaling) in terms of loss of in vivo tumorigenicity in heterotopic nude mouse model. Finally, once tested in cells expressing CD133 (a marker for MDB cancer stem cells), higher levels of RalA activation was observed. These data not only bring RalA to light as an important contributor to the malignant phenotype of MDB but introduces this pathway as a novel target in the treatment of this malignancy.

Ral-Arf6 crosstalk regulates Ral dependent exocyst trafficking and anchorage independent growth signalling

Integrin dependent regulation of growth factor signalling confers anchorage dependence that is deregulated in cancers. Downstream of integrins and oncogenic Ras the small GTPase Ral is a vital mediator of adhesion dependent trafficking and signalling. This study identifies a novel regulatory crosstalk between Ral and Arf6 that controls Ral function in cells. In re-adherent mouse fibroblasts (MEFs) integrin dependent activation of RalA drives Arf6 activation. Independent of adhesion constitutively active RalA and RalB could both however activate Arf6. This is further conserved in oncogenic H-Ras containing bladder cancer T24 cells, which express anchorage independent active Ral that supports Arf6 activation. Arf6 mediates active Ral-exocyst dependent delivery of raft microdomains to the plasma membrane that supports anchorage independent growth signalling. Accordingly in T24 cells the RalB-Arf6 crosstalk is seen to preferentially regulate anchorage independent Erk signalling. Active Ral we further find uses a Ral-RalBP1-ARNO-Arf6 pathway to mediate Arf6 activation. This study hence identifies Arf6, through this regulatory crosstalk, to be a key downstream mediator of Ral isoform function along adhesion dependent pathways in normal and cancer cells.

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Ral mediates Arf6 activation downstream of integrins and oncogenic Ras.

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Arf6 mediates Ral-exocyst dependent delivery of raft microdomains.

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Active Ral supports anchorage independent Arf6 activation in bladder cancer T24 cells.

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Ral-Arf6 crosstalk in T24 cells regulates anchorage independent Erk signalling.

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A Ral-RalBP1-ARNO-Arf6 pathway mediates the Ral-Arf6 crosstalk.

Mutant K-RAS Promotes Invasion and Metastasis in Pancreatic Cancer Through GTPase Signaling Pathways

Pancreatic ductal adenocarcinoma is one of the most aggressive malignancies, characterized by the local invasion into surrounding tissues and early metastasis to distant organs. Oncogenic mutations of the K-RAS gene occur in more than 90% of human pancreatic cancers. The goal of this study was to investigate the functional significance and downstream effectors of mutant K-RAS oncogene in the pancreatic cancer invasion and metastasis. We applied the homologous recombination technique to stably disrupt K-RAS oncogene in the human pancreatic cell line MiaPaCa-2, which carries the mutant K-RAS (G12C) oncogene in both alleles. Using in vitro assays, we found that clones with disrupted mutant K-RAS gene exhibited low RAS activity, reduced growth rates, increased sensitivity to the apoptosis inducing agents, and suppressed motility and invasiveness. In vivo assays showed that clones with decreased RAS activity had reduced tumor formation ability in mouse xenograft model and increased survival rates in the mouse orthotopic pancreatic cancer model. We further examined molecular pathways downstream of mutant K-RAS and identified RhoA GTP activating protein 5, caveolin-1, and RAS-like small GTPase A (RalA) as key effector molecules, which control mutant K-RAS-dependent migration and invasion in MiaPaCa-2 cells. Our study provides rational for targeting RhoA and RalA GTPase signaling pathways for inhibition of pancreatic cancer metastasis.

Bridging the Gap: A Regulator of NF-κB Linking Inflammation and Cancer

BACKGROUND

A close connection between inflammation and cancer has now been firmly established. While tumor initiation is typically independent of inflammatory events, immune cells infiltrating the tumor microenvironment secrete inflammatory cytokines that enhance the aberrant growth of tumor cells and thus facilitate tumor progression. Therefore, inflammation and tumor growth are usually interpreted as closely related on a systemic level but as distinct, independently regulated processes at a molecular level.

HIGHLIGHT

Recently, we reported that a sub-class of small GTPases, namely κB-Ras1 and κB-Ras2, regulate both inflammation and tumor growth, thereby providing a unique molecular bridge between the two biological processes.

CONCLUSION

Here, we briefly summarize the known contact points between inflammation and cancer, including oral cancers, and put into context the identification of κB-Ras proteins as molecular link between two independent pathways important for tumor growth.

Divergent roles of CAAX motif-signaled posttranslational modifications in the regulation and subcellular localization of Ral GTPases

The Ras-like small GTPases RalA and RalB are well validated effectors of RAS oncogene-driven human cancer growth, and pharmacologic inhibitors of Ral function may provide an effective anti-Ras therapeutic strategy. Intriguingly, although RalA and RalB share strong overall amino acid sequence identity, exhibit essentially identical structural and biochemical properties, and can utilize the same downstream effectors, they also exhibit divergent and sometimes opposing roles in the tumorigenic and metastatic growth of different cancer types. These distinct biological functions have been attributed largely to sequence divergence in their carboxyl-terminal hypervariable regions. However, the role of posttranslational modifications signaled by the hypervariable region carboxyl-terminal tetrapeptide CAAX motif (C = cysteine, A = aliphatic amino acid, X = terminal residue) in Ral isoform-selective functions has not been addressed. We determined that these modifications have distinct roles and consequences. Both RalA and RalB require Ras converting CAAX endopeptidase 1 (RCE1) for association with the plasma membrane, albeit not with endomembranes, and loss of RCE1 caused mislocalization as well as sustained activation of both RalA and RalB. In contrast, isoprenylcysteine carboxylmethyltransferase (ICMT) deficiency disrupted plasma membrane localization only of RalB, whereas RalA depended on ICMT for efficient endosomal localization. Furthermore, the absence of ICMT increased stability of RalB but not RalA protein. Finally, palmitoylation was critical for subcellular localization of RalB but not RalA. In summary, we have identified striking isoform-specific consequences of distinct CAAX-signaled posttranslational modifications that contribute to the divergent subcellular localization and activity of RalA and RalB.

TD-60 links RalA GTPase function to the CPC in mitosis

TD-60 (also known as RCC2) is a highly conserved protein that structurally resembles the Ran guanine exchange factor (GEF) RCC1, but has not previously been shown to have GEF activity. TD-60 has a typical chromosomal passenger complex (CPC) distribution in mitotic cells, but associates with integrin complexes and is involved in cell motility during interphase. Here we show that TD-60 exhibits GEF activity, in vitro and in cells, for the small GTPase RalA. TD-60 or RalA depletion causes spindle abnormalities in prometaphase associated with abnormal centromeric accumulation of CPC components. TD-60 and RalA apparently work together to contribute to the regulation of kinetochore-microtubule interactions in early mitosis. Importantly, several mitotic phenotypes caused by TD-60 depletion are reverted by the expression of a GTP-locked mutant, RalA (Q72L). The demonstration that a small GTPase participates in the regulation of the CPC reveals a level of mitotic regulation not suspected in previous studies.

Early Steps of Jaagsiekte Sheep Retrovirus-Mediated Cell Transformation Involve the Interaction between Env and the RALBP1 Cellular Protein

Ovine pulmonary adenocarcinoma is a naturally occurring lung cancer in sheep induced by the Jaagsiekte sheep retrovirus (JSRV). Its envelope glycoprotein (Env) carries oncogenic properties, and its expression is sufficient to induce in vitro cell transformation and in vivo lung adenocarcinoma. The identification of cellular partners of the JSRV envelope remains crucial for deciphering mechanisms leading to cell transformation. We initially identified RALBP1 (RalA binding protein 1; also known as RLIP76 or RIP), a cellular protein implicated in the ras pathway, as a partner of JSRV Env by yeast two-hybrid screening and confirmed formation of RALBP1/Env complexes in mammalian cells. Expression of the RALBP1 protein was repressed in tumoral lungs and in tumor-derived alveolar type II cells. Through its inhibition using specific small interfering RNA (siRNA), we showed that RALBP1 was involved in envelope-induced cell transformation and in modulation of the mTOR (mammalian target of rapamycin)/p70S6K pathway by the retroviral envelope.

IMPORTANCE

JSRV-induced lung adenocarcinoma is of importance for the sheep industry. While the envelope has been reported as the oncogenic determinant of the virus, the cellular proteins directly interacting with Env are still not known. Our report on the formation of RALBP/Env complexes and the role of this interaction in cell transformation opens up a new hypothesis for the dysregulation observed upon virus infection in sheep.

The RAS-RAL axis in cancer: evidence for mutation-specific selectivity in non-small cell lung cancer

Activating RAS mutations are common in human tumors. These mutations are often markers for resistance to therapy and subsequent poor prognosis. So far, targeting the RAF-MEK-ERK and PI3K-AKT signaling pathways downstream of RAS is the only promising approach in the treatment of cancer patients harboring RAS mutations. RAL GTPase, another downstream effector of RAS, is also considered as a therapeutic option for the treatment of RAS-mutant cancers. The RAL GTPase family comprises RALA and RALB, which can have either divergent or similar functions in different tumor models. Recent studies on non-small cell lung cancer (NSCLC) have showed that different RAS mutations selectively activate specific effector pathways. This observation requires broader validation in other tumor tissue types, but if true, will provide a new approach to the treatment of RAS-mutant cancer patients by targeting specific downstream RAS effectors according to the type of RAS mutation. It also suggests that RAL GTPase inhibition will be an important treatment strategy for tumors harboring RAS glycine to cysteine (G12C) or glycien to valine (G12V) mutations, which are commonly found in NSCLC and pancreatic cancer.

Thermodynamic mapping of effector protein interfaces with RalA and RalB

RalA and RalB are members of the Ras family of small G proteins and are activated downstream of Ras via RalGEFs. The RalGEF-Ral axis represents one of the major effector pathways controlled by Ras and as such is an important pharmacological target. RalA and RalB are approximately 80% identical at the amino acid level; despite this, they have distinct roles both in normal cells and in the disease state. We have used our structure of RalB-RLIP76 to guide an analysis of Ral-effector interaction interfaces, creating panels of mutant proteins to probe the energetics of these interactions. The data provide a physical mechanism that underpins the effector selective mutations commonly employed to dissect Ral G protein function. Comparing the energetic landscape of the RalB-RLIP76 and RalB-Sec5 complexes reveals mutations in RalB that lead to differential binding of the two effector proteins. A panel of RLIP76 mutants was used to probe the interaction between RLIP76 and RalA and -B. Despite 100% sequence identity in the RalA and -B contact residues with RLIP76, differences still exist in the energetic profiles of the two complexes. Therefore, we have revealed properties that may account for some of the functional separation observed with RalA and RalB at the cellular level. Our mutations, in both the Ral isoforms and RLIP76, provide new tools that can be employed to parse the complex biology of Ral G protein signaling networks. The combination of these thermodynamic and structural data can also guide efforts to ablate RalA and -B activity with small molecules and peptides.

MS/MS-based strategies for proteomic profiling of invasive cell structures

Acquired capacity of cancer cells to penetrate through the extracellular matrix of surrounding tissues is a prerequisite for tumour metastatic spread - the main source of cancer-associated mortality. Through combined efforts of many research groups, we are beginning to understand that the ability of cells to invade through the extracellular matrix is a multi-faceted phenomenon supported by variety of specialised protrusive cellular structures, primarily pseudopodia, invadopodia and podosomes. Additionally, secreted extracellular vesicles are being increasingly recognised as important mediators of invasive cell phenotypes and therefore may be considered bona fide invasive cell structures. Dissection of the molecular makings underlying biogenesis and function of all of these structures is crucial to identify novel targets for specific anti-metastatic therapies. Rapid advances and growing accessibility of MS/MS-based protein identification made this family of techniques a suitable and appropriate choice for proteomic profiling of invasive cell structures. In this review, we provide a summary of current progress in the characterisation of protein composition and topology of protein interaction networks of pseudopodia, invadopodia, podosomes and extracellular vesicles, as well as outline challenges and perspectives of the field.

Genome-wide association study identifies multiple susceptibility loci for diffuse large B cell lymphoma

Diffuse large B cell lymphoma (DLBCL) is the most common lymphoma subtype and is clinically aggressive. To identify genetic susceptibility loci for DLBCL, we conducted a meta-analysis of 3 new genome-wide association studies (GWAS) and 1 previous scan, totaling 3,857 cases and 7,666 controls of European ancestry, with additional genotyping of 9 promising SNPs in 1,359 cases and 4,557 controls. In our multi-stage analysis, five independent SNPs in four loci achieved genome-wide significance marked by rs116446171 at 6p25.3 (EXOC2; P = 2.33 × 10(-21)), rs2523607 at 6p21.33 (HLA-B; P = 2.40 × 10(-10)), rs79480871 at 2p23.3 (NCOA1; P = 4.23 × 10(-8)) and two independent SNPs, rs13255292 and rs4733601, at 8q24.21 (PVT1; P = 9.98 × 10(-13) and 3.63 × 10(-11), respectively). These data provide substantial new evidence for genetic susceptibility to this B cell malignancy and point to pathways involved in immune recognition and immune function in the pathogenesis of DLBCL.

Novel therapeutic targets for pancreatic cancer

Pancreatic cancer has become the fourth leading cause of cancer death in the last two decades. Only 3%-15% of patients diagnosed with pancreatic cancer had 5 year survival rate. Drug resistance, high metastasis, poor prognosis and tumour relapse contributed to the malignancies and difficulties in treating pancreatic cancer. The current standard chemotherapy for pancreatic cancer is gemcitabine, however its efficacy is far from satisfactory, one of the reasons is due to the complex tumour microenvironment which decreases effective drug delivery to target cancer cell. Studies of the molecular pathology of pancreatic cancer have revealed that activation of KRAS, overexpression of cyclooxygenase-2, inactivation of p16^INK4A and loss of p53 activities occurred in pancreatic cancer. Co-administration of gemcitabine and targeting the molecular pathological events happened in pancreatic cancer has brought an enhanced therapeutic effectiveness of gemcitabine. Therefore, studies looking for novel targets in hindering pancreatic tumour growth are emerging rapidly. In order to give a better understanding of the current findings and to seek the direction in future pancreatic cancer research; in this review we will focus on targets suppressing tumour metastatsis and progression, KRAS activated downstream effectors, the relationship of Notch signaling and Nodal/Activin signaling with pancreatic cancer cells, the current findings of non-coding RNAs in inhibiting pancreatic cancer cell proliferation, brief discussion in transcription remodeling by epigenetic modifiers (e.g., HDAC, BMI1, EZH2) and the plausible therapeutic applications of cancer stem cell and hyaluronan in tumour environment.

A role for Ral GTPase-activating protein subunit β in mitotic regulation

Ral proteins are small GTPases that play critical roles in normal physiology and in oncogenesis. There is little information on the GTPase-activating proteins (GAPs) that downregulate their activity. Here, we provide evidence that the noncatalytic β subunit of RalGAPα1/2 β complexes is involved in mitotic control. RalGAPβ localizes to the Golgi and nucleus during interphase, and relocalizes to the mitotic spindle and cytokinetic intercellular bridge during mitosis. Depletion of RalGAPβ causes chromosome misalignment and decreases the amount of mitotic cyclin B1, disturbing the metaphase-to-anaphase transition. Overexpression of RalGAPβ interferes with cell division, leading to binucleation and multinucleation, and cell death. We propose that RalGAPβ plays an essential role in the sequential progression of mitosis by controlling the spatial and temporal activation of Ral GTPases in the spindle assembly checkpoint (SAC) and cytokinesis. Deregulation of RalGAPβ might cause genomic instability, leading to human carcinogenesis.

Nodal signals via β-arrestins and RalGTPases to regulate trophoblast invasion

Placentation is critical for establishing a healthy pregnancy. Trophoblasts mediate implantation and placentation and certain subtypes, most notably extravillous cytotrophoblast, are highly invasive. Trophoblast invasion is tightly regulated by microenvironmental cues that dictate placental morphology and depth. In choriocarcinomas, malignant trophoblast cells become hyperinvasive, breaching the myometrium and leading to major complications. Nodal, a member of the TGF-β superfamily, is expressed throughout the endometrium during the peri-implantation period and in invasive trophoblast cells. Nodal promotes the invasion of numerous types of cancer cells. However, Nodal's role in trophoblast and choriocarcinoma cell invasion is unclear. Here we show that Nodal stimulates the invasion of both the non-malignant HTR-8SV/neo trophoblast and JAR choriocarcinoma cells in a dose-dependent manner. We found that endogenous β-arrestins and Ral GTPases, key regulators of the cell cytoskeleton, are constitutively associated with Nodal receptors (ALK4 and ALK7) in trophoblast cells and that RalA is colocalized with ALK4 in endocytic vesicles. Nodal stimulates endogenous β-arrestin2 to associate with phospho-ERK1/2, and knockdown of β-arrestin or Ral proteins impairs Nodal-induced trophoblast and choriocarcinoma cell invasion. These results demonstrate, for the first time, that β-arrestins and RalGTPases are important regulators of Nodal-induced invasion.

Not just gRASping at flaws: finding vulnerabilities to develop novel therapies for treating KRAS mutant cancers

Mutations in Kirsten rat-sarcoma (KRAS) are well appreciated to be major drivers of human cancers through dysregulation of multiple growth and survival pathways. Similar to many other non-kinase oncogenes and tumor suppressors, efforts to directly target KRAS pharmaceutically have not yet materialized. As a result, there is broad interest in an alternative approach to develop therapies that induce synthetic lethality in cancers with mutant KRAS, therefore exposing the particular vulnerabilities of these cancers. Fueling these efforts is our increased understanding into the biology driving KRAS mutant cancers, in particular the important pathways that mutant KRAS governs to promote survival. In this mini-review, we summarize the latest approaches to treat KRAS mutant cancers and the rationale behind them.

Dragging ras back in the ring

Ras proteins play a major role in human cancers but have not yielded to therapeutic attack. Ras-driven cancers are among the most difficult to treat and often excluded from therapies. The Ras proteins have been termed "undruggable," based on failures from an era in which understanding of signaling transduction, feedback loops, redundancy, tumor heterogeneity, and Ras' oncogenic role was poor. Structures of Ras oncoproteins bound to their effectors or regulators are unsolved, and it is unknown precisely how Ras proteins activate their downstream targets. These knowledge gaps have impaired development of therapeutic strategies. A better understanding of Ras biology and biochemistry, coupled with new ways of targeting undruggable proteins, is likely to lead to new ways of defeating Ras-driven cancers.

An orthosteric inhibitor of the RAS-SOS interaction

Rat sarcoma (RAS) proteins are signaling nodes that transduce extracellular cues into precise alterations in cellular physiology by engaging effector pathways. RAS signaling thus regulates diverse cell processes including proliferation, migration, differentiation, and survival. Owing to this central role in governing mitogenic signals, RAS pathway components are often dysregulated in human diseases. Targeted therapy of RAS pathways has generally not been successful, largely because of the robust biochemistry of the targets and their multifaceted network of molecular regulators. The rate-limiting step of RAS activation is Son of Sevenless (SOS)-mediated nucleotide exchange involving a single evolutionarily conserved catalytic helix from SOS. Structure function data of this mechanism provided a strong platform to design an SOS-derived, helically constrained peptide mimic as an inhibitor of the RAS-SOS interaction. In this chapter, we review RAS-SOS signaling dynamics and present evidence supporting the novel paradigm of inhibiting their interaction as a therapeutic strategy. We then describe a method of generating helically constrained peptide mimics of protein surfaces, which we have employed to inhibit the RAS-SOS active site interaction. The biochemical and functional properties of this SOS mimic support the premise that inhibition of RAS-nucleotide exchange can effectively block RAS activation and downstream signaling.