RhoA Mutant Research Articles

Abstract P221: Discovery of a covalent inhibitor for an oncogenic mutant RhoAY42C

Abstract Ras homolog family member A (RhoA) is a member of a larger family of Rho proteins of small GTPases, with structural and signaling similarities to Ras proteins. RhoA is involved in multiple cellular processes including cytoskeleton regulation and actin-myosin contractility, etc. Recent studies have shown that the most common RhoA mutation in diffuse gastric cancer (DGC), Y42C, causes a gain-of-function and is associated with the loss of the E-cadherin gene CDH (CDH1). Inhibitors of RhoAY42C could be promising agents for treating DGC that harbors CDH1 mutation/deletion. BridGene expressed RhoAY42C in cells, screened our proprietary covalent library against the RhoAY42C live cells, and employed our chemoproteomic platform IMTACTM (Isobaric Mass Tagged Affinity Characterization) to detect covalent labeling of the mutant RhoA protein. A pilot screening led to the successful identification of a covalent ligand of RhoAY42C, BGS1933. Mass spec analysis has confirmed the covalent modification of Cys42 in RhoA by BGS1933. Dose-dependent binding of BGS1933 to RhoAY42C was measured using an orthogonal fluorescence-based assay. The Cancer Genome Atlas (TCGA) study shows that ~1% DGC patients harbor the oncogenic mutant RhoAY42C. The discovery of a covalent inhibitor of RhoAY42C will enable us to validate the role of RhoAY42C in DGC and facilitate the development of new first-in-class targeted therapies for the treatment of gastric cancer. Citation Format: Shirley Guo, Ping Cao. Discovery of a covalent inhibitor for an oncogenic mutant RhoAY42C [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P221.

Variants identified by next-generation sequencing cause endoplasmic reticulum stress in Rhodopsin-associated retinitis pigmentosa

BackgroundRhodopsin (RHO) is the most well-known genetic cause of autosomal dominant retinitis pigmentosa (adRP). This study aimed to investigate the genetic cause of a large Chinese adRP family and assess the pathogenicity of the detected RHO mutant.MethodsRoutine ocular examinations were conducted on all participants. Next-generation sequencing with targeted capture was performed to screen mutations in 179 genes associated with hereditary retinal diseases and 10 candidate genes. Variants detected by NGS were validated by Sanger sequencing and evaluated for pathogenicity. Fragments of mutant and wild-type RHO were cloned into the pEGFP-N1 vector and were transfected into different cell lines to observe the cellular localization of the Rhodopsin-GFP fusion protein and evaluate the expression of endoplasmic reticulum (ER) stress markers. RT-PCR analysis was used to detect transfected the splicing of X box-binding protein 1 (XBP1) mRNA, which is a critical factor affecting ER stress.ResultsGenetic analysis identified a heterozygous missense variant, RHO, c.284 T > C (p.L95P) in this adRP family. Another RHO variant (p.P53R) that we reported previously was also included in further functional assessment. Both misfolded mutant proteins accumulated in the ER in a manner similar to that noted for the classic mutant P23H. Spliced XBP1 was observed in cells transfected with mutants, indicating an increase in ER stress.ConclusionsAlthough the p.L95P variant is not a novel change, it was the first variant to be functionally evaluated and reported in Chinese RP patients. The results in our study provide significant evidence to classify the p.L95P mutation as a class II mutation.

Identification of a novel RHO heterozygous nonsense mutation in a Chinese family with autosomal dominant retinitis pigmentosa

BackgroundTo explore the molecular genetic cause of a four-generation autosomal dominant retinitis pigmentosa family in China.MethodsTargeted region sequencing was performed to detect the potential mutation, and Sanger sequencing was used to validate the mutation. Multiple sequence alignment from different species was performed by CLUSTALW. The structures of wild-type and the mutant RHO were modeled by Swiss-Model Server and shown using a PyMOL Molecular Graphic system.ResultsA novel heterozygous nonsense mutation (c.1015 A > T, p.Lys339Ter, p.K339X) within RHO, which cosegregated with retinitis pigmentosa phenotype was detected in this family. Bioinformatics analysis showed the mutation was located in a highly conserved region, and the mutation was predicted to be pathogenic.ConclusionsWe identified a novel heterozygous nonsense mutation of RHO gene in a Chinese family with retinitis pigmentosa by target region sequencing and our bioinformatics analysis indicated that the mutation is pathogenic. Our results can broaden the spectrum of RHO gene mutation and enrich the phenotype-genotype correlation of retinitis pigmentosa.

Cold Regulation of Genes Encoding Ion Transport Systems in the Oligotrophic Bacterium Caulobacter crescentus.

ABSTRACTIn this study, we characterize the response of the free-living oligotrophic alphaproteobacterium Caulobacter crescentus to low temperatures by global transcriptomic analysis. Our results showed that 656 genes were upregulated and 619 were downregulated at least 2-fold after a temperature downshift. The identified differentially expressed genes (DEG) belong to several functional categories, notably inorganic ion transport and metabolism, and a subset of these genes had their expression confirmed by reverse transcription quantitative real-time PCR (RT-qPCR). Several genes belonging to the ferric uptake regulator (Fur) regulon were downregulated, indicating that iron homeostasis is relevant for adaptation to cold. Several upregulated genes encode proteins that interact with nucleic acids, particularly RNA: cspA, cspB, and the DEAD box RNA helicases rhlE, dbpA, and rhlB. Moreover, 31 small regulatory RNAs (sRNAs), including the cell cycle-regulated noncoding RNA (ncRNA) CcnA, were upregulated, indicating that posttranscriptional regulation is important for the cold stress response. Interestingly, several genes related to transport were upregulated under cold stress, including three AcrB-like cation/multidrug efflux pumps, the nitrate/nitrite transport system, and the potassium transport genes kdpFABC. Further characterization showed that kdpA is upregulated in a potassium-limited medium and at a low temperature in a SigT-independent way. kdpA mRNA is less stable in rho and rhlE mutant strains, but while the expression is positively regulated by RhlE, it is negatively regulated by Rho. A kdpA-deleted strain was generated, and its viability in response to osmotic, acidic, or cold stresses was determined. The implications of such variation in the gene expression for cold adaptation are discussed.IMPORTANCE Low-temperature stress is an important factor for nucleic acid stability and must be circumvented in order to maintain the basic cell processes, such as transcription and translation. The oligotrophic lifestyle presents further challenges to ensure the proper nutrient uptake and osmotic balance in an environment of slow nutrient flow. Here, we show that in Caulobacter crescentus, the expression of the genes involved in cation transport and homeostasis is altered in response to cold, which could lead to a decrease in iron uptake and an increase in nitrogen and high-affinity potassium transport by the Kdp system. This previously uncharacterized regulation of the Kdp transporter has revealed a new mechanism for adaptation to low temperatures that may be relevant for oligotrophic bacteria.

Rho-dependent transcription termination regulates the toxin-antitoxin modules of cryptic prophages to silence their expression in Escherichia coli.

Bacterial Rho-dependent transcription termination regulates many physiological processes. Here, we report that it controls the expression of toxin-antitoxin (TA) modules of cryptic prophages in E.coli. Microarray profiles of Rho mutants showed upregulation of genes of the CP4-6 and CP4-44 prophages, including their TA modules, that were validated by RT-qPCR. Analysis of the invivo termination efficiency and the mRNA sequences of these prophages revealed the presence of many Rho-dependent terminators. The prophage TA modules exhibited synthetic lethality with the Rho mutants, indicating functional involvement of Rho-dependent termination in controlling these modules. Rho-dependent termination does not regulate most of the chromosomal TA modules. We conclude that Rho-dependent termination specifically silences the TA modules of prophages, thereby augmenting bacterial innate immunity.

Targeting T-Cell Receptor Signaling Pathway in Angioimmunoblastic T-Cell Lymphoma

[Backgrounds] Angioimmunoblastic T-cell lymphoma (AITL) belongs to nodal T-cell lymphoma with T follicular helper (TFH) phenotype. Both the G17V RHOA mutation and the loss-of-function TET2 mutation have been identified in 70% of AITLs. We previously demonstrated that G17V mutant RHOA augmented T-cell receptor (TCR) signaling though binding to VAV1, an essential component of the T-cell signaling pathway (Leukemia, in press). However, it remains elusive whether inhibition of TCR pathway serves as an effective treatment in AITL. [Methods] Activation of VAV1 and PLCgamma1 in response to TCR stimulation was examined in Jurkat cells inducibly expressing wild-type and G17V mutant RHOA under the treatment with dasatinib, a multi-kinase inhibitor. Nuclear factor of activated T cell (NFAT) activity was similarly examined in Jurkat cells transiently transfected with wild-type and G17V mutant RHOA. Mice expressing G17V RHOA under CD2 promoter (G17VRHOA mice) were crossed with MxCre Tet2f/f mice and pIpC was given to the offspring 4 weeks after birth to obtain Tet2-/- and Tet2-/-G17VRHOA mice. Whole transcriptome analysis was performed for CD4+ T cells purified from the spleen of tumor developed mice. Serum cytokines were examined by BD Cytometric Beads Assay. Cells derived from tumors developed in Tet2-/-G17VRHOA mice were transplanted into nude mice. Dasatinib was orally given at 5 mg/kg/day for 14 days. [Results] The G17V mutant RHOA enhanced phosphorylation of VAV1 and PLCgamma1, and NFAT reporter activity in Jurkat cells. The phosphorylation and the NFAT activity were efficiently blocked by dasatinib at 10 nM. Approximately 70% of Tet2-/-G17VRHOA mice died around 40 wo, while 14% of Tet2-/- and none of G17VRHOA mice died at the same age (p<0.05). All the moribund Tet2-/-G17VRHOA mice presented splenomegaly and lymphadenopathy. The lymph nodes and the spleens showed diffuse infiltration of tumor cells expressing TFH markers, i.e., CD4, PD1, and ICOS. The aberrant increase of high endothelial venules was observed in the swollen lymph nodes, mimicking human AITL. Whole transcriptome analysis followed by gene-set enrichment analysis revealed enrichment of Il-2/STAT5, Il-6/JAK-STAT3, and TNFα/NFκB signaling pathways in Tet2-/-G17VRHOA CD4+ spleen cells. The serum concentrations of Il-2, Il6, and TNFα in Tet2-/-G17VRHOA were significantly higher than control at the same age (p<0.05). The CD4+ cells in the enlarged spleen and the swollen lymph nodes in Tet2-/-G17VRHOA mice at 40 wo showed oligoclonal rearrangement of TCR genes. Nude mice transplanted with tumor-derived cells showed splenomegaly and lymphadenopathy preceded by elevation ofthe serum concentrations of Il-2, Il-6 and TNFα (before vs. after the transplantation, 4.33±0.14 vs. 4.80±0.37, 5.85±2.96 vs. 34.92±15.49, and 7.68±2.08 vs. 45.70±33.72, p<0.01, respectively). Mice given with dasatinib starting at 10 days after the transplantation showed higher overall survival compared to the vehicle control (p<0.05, Figure 1). The serum concentrations of Il-2, Il-6, and TNFα were decreased in dasatinib group (before vs. after the dasatinib treatment, 4.85±0.40 vs. 4.28±0.18, 38.23±18.74 vs. 10.01±7.38, and 48.37±34.6 vs. 18.67±12.37, p<0.05, respectively).Discussions and Conclusion: The combination of G17V mutantRHOAexpression and Tet2 deletion led to development of AITL-like tumors in mice, which were hughly effectively treated by dasatinib. This model may also be useful to examine novel treatment strategies for AITL, other than dasatinib. [Display omitted] DisclosuresChiba:Nippon Shinyaku: Honoraria, Research Funding.

C-Jun N-terminal kinase (JNK) pathway activation is essential for dental papilla cells polarization.

During tooth development, dental papilla cells differentiate into odontoblasts with polarized morphology and cell function. Our previous study indicated that the C-Jun N-terminal kinase (JNK) pathway regulates human dental papilla cell adhesion, migration, and formation of focal adhesion complexes. The aim of this study was to further examine the role of the JNK pathway in dental papilla cell polarity formation. Histological staining, qPCR, and Western Blot suggested the activation of JNK signaling in polarized mouse dental papilla tissue. After performing an in vitro tooth germ organ culture and cell culture, we found that JNK inhibitor SP600125 postponed tooth germ development and reduced the polarization, migration and differentiation of mouse dental papilla cells (mDPCs). Next, we screened up-regulated polarity-related genes during dental papilla development and mDPCs or A11 differentiation. We found that Prickle3, Golga2, Golga5, and RhoA were all up-regulated, which is consistent with JNK signaling activation. Further, constitutively active RhoA mutant (RhoA Q63L) partly rescued the inhibition of SP600125 on cell differentiation and polarity formation of mDPCs. To sum up, this study suggests that JNK signaling has a positive role in the formation of dental papilla cell polarization.

PLCε1 mediates one-lung ventilation injury by regulating the p38/RhoA/NFκB activation loop

BackgroundPhospholipase C epsilon-1 (PLCε1) might be a novel and potential target in treating inflammatory conditions. In the present study, we aimed to clarify whether PLCε1 is involved in lung injury caused by one-lung ventilation (OLV) and to elucidate the potential molecular mechanism of PLCε1-mediated signaling pathway on OLV induced inflammatory response and injury. MethodsMale Sprague-Dawley (SD) rats were divided into wide-type (PLCε1-WT) group and PLCε1-KO group, and were treated with OLV for 0.5 h, 1 h, and 2 h respectively. Observation of lung tissue injury in rats was performed by Hematoxylin and eosin (HE) staining and Wet/dry (W/D) radios. In addition, pulmonary microvascular endothelial cells (PMVECs) transfected with PLCε1-si RNA, were stimulated by lipopolysaccharide (LPS). To explore the possible roles of PLCε1 in the OLV induced inflammatory injury and the involved pathway underlying, the lung tissue and bronchoalveolar lavage fluids (BALF) of OLV rats, as well as the PMVECs were prepared for further analysis. Enzyme-linked immunoassay (ELISA) was used to detect the expression of pro-inflammatory factors. The activities of related pathway proteins (NF-κB, phospho-p38, p38, phospho-ERK1/2, ERK1/2, RhoA and ROCK) were also detected by reverse transcription quantitative polymerase chain reaction (RT-qPCR) and western blot analysis. ResultsCompared to the PLCε1-WT rats, PLCε1-KOrats exhibited marked alleviation of lung inflammation as shown by great reduction in lung wet/dry weight ratios, decreases in the expressions of pro-inflammatory mediators, and declines in the number of neutrophils and the protein concentration in bronchoalveolar lavage fluid (BALF). Moreover, the increased expressions of RhoA and NF-κB p65 mRNA induced by OLV were significantly inhibited in PLCε1-KO rats. In LPS treated PMVECs, PLCε1-si RNA transfection ones also showed the decrease expression of proinflammatory mediators, reduction in p38 phosphorylation levels and downregulation of RhoA/ROCK signaling activation. Co-cultured with PLCε1-si RNA and BTRB796 (p38 inhibitors) in LPS-stimulated PMVECs resulted in a significant reduction in RhoA and NF-κB activity. In addition, treatment with either ROCK inhibitor (Y-27632) or dominant negative mutant of RhoA (RhoT19 N) significantly reduced the expression of NF-κB in PLCε1-si RNA treated PMVECs. ConclusionThe results indicated that PLCε1 played an important role in the inflammatory response induced by OLV. Moreover, through promoting p38/RhoA/ROCK activation loop, PLCε1 promoted NF-κB activation and thereby increased the expressions of inflammatory mediators, which induced the PMVECs inflammation and subsequent injury. The results of this study provide a potential therapeutic target for the reduction of inflammatory response in patients with OLV.

FRET Sensors Reveal the Retinal Entry Pathway in the G Protein-Coupled Receptor Rhodopsin

The visual photoreceptor rhodopsin (Rho) represents a curious case among G protein-coupled receptors (GPCRs) because its primary ligand 11-cis-retinal (11CR) is an inverse agonist, which partitions into the bilayer and enters through an intermembranous pathway. Light activates Rho by converting 11CR to all-trans-retinal (ATR), which serves as an agonist ligand. We used genetic code expansion and bioorthogonal labeling to engineer Rho mutants that serve as FRET sensors for measuring 11CR binding kinetics and energetics. We found mutations that alter a channel between transmembrane helices 5 and 6 (TM5/6) dramatically affect 11CR binding kinetics, but not ATR release kinetics. Our data provide direct experimental evidence for 11CR entry between TM5/6 in Rho that involves dynamic allosteric control of the ligand entry channel. Our findings can be extended to other visual pigments and a wide range of GPCRs with hydrophobic ligands that are hypothesized to enter their binding pockets through transmembrane pores.

The Rho-Dependent Transcription Termination Is Involved in Broad-Spectrum Antibiotic Susceptibility in Escherichia coli.

One of the major ways of acquiring multidrug resistance in bacteria is via drug influx and efflux pathways. Here, we show that E. coli with compromised Rho-dependent transcription termination function has enhanced broad-spectrum antibiotic susceptibility, which arises from the inefficient TolC-efflux process and increased permeability of the membrane. The Rho mutants have altered morphology, distinct cell surface, and increased levels of lipopolysaccharide in their outer membrane, which might have rendered the TolC efflux pumps inefficient. These alterations are due to the upregulations of poly-N-acetyl-glucosamine and lipopolysaccharide synthesis operons because of inefficient Rho functions. The Rho mutants are capable of growing on various dipeptides and carbohydrate sources, unlike their WT counterpart. Dipeptides uptake arises from the upregulations of the di-peptide permease operon in these mutants. The metabolomics of the Rho mutants revealed the presence of a high level of novel metabolites. Accumulation of these metabolites in these Rho mutants might titrate out the TolC-efflux pumps, which could further reduce their efficiency. We conclude that the transcription termination factor, Rho, regulates the broad-spectrum antibiotic susceptibility of E. coli through multipartite pathways in a TolC-dependent manner. The involvement of Rho-dependent termination in multiple pathways and its association with antibiotic susceptibility should make Rho-inhibitors useful in the anti-bacterial treatment regimen.

Identification of Rho GEF and RhoA Activation by Pull-Down Assays.

The small GTPase RhoA participates in actin and microtubule machinery, cell migration and invasion, gene expression, vesicular trafficking and cell cycle, and its dysregulation is a determining factor in many pathological conditions. Similar to other Rho GTPases, RhoA is a key component of the wound-healing process, regulating the activity of different participating cell types. RhoA gets activated upon binding to guanine nucleotide exchange factors (GEFs), which catalyze the exchange of guanosine diphosphate (GDP) for guanosine triphosphate (GTP). GTPase-activating proteins (GAPs) mediate the exchange of GTP to GDP, inactivating RhoA, whereas guanine nucleotide dissociation inhibitors (GDIs) preserve the inactive pool of RhoA proteins in the cytosol. RhoA and Rho GEF activation is detected by protein pull-down assays, which use chimeric proteins with Rhotekin and G17A mutant RhoA as "bait" to pull down active RhoA and RhoA GEFs, respectively. In this chapter, we describe an optimized protocol for performing RhoA and GEF pull-down assays.

Abstract 2586: Identification of cancer-associated RhoA mutants and analogous K-Ras mutants that induce gain-of function despite low GTP binding

Abstract While the Ras GTPases are frequently mutated, especially at codons 12, 13, or 61, the structurally related Rho GTPases, although they are implicated in tumor invasion and metastasis, are rarely mutated in solid tumors, except for diffuse gastric cancer. The vast majority of cancer-associated RHO mutations are not located in codons 14, 15, or 63, which correspond to the 3 canonical mutant Ras codons. Here we have evaluated the biological and biochemical phenotypes of several cancer-associated RhoA mutants, which indicated that some RhoA mutants have unusual phenotypes and therefore prompted us to generalize our findings to other small GTPases by constructing and analyzing the analogous mutants in K-Ras. We constructed 8 cancer-associated RhoA mutants from the TCGA database, and found that each was gain-of-function biologically. Using the Rhotekin binding assay to infer RhoGTP levels, 5 mutants (Y42C, L57V, D59G, A61D, D76G), had higher binding than WT RhoA. However, 3 mutants (G62E. L69P and L69R) did not bind Rhotekin, but did bind strongly to Citron, a Rho-dependent kinase implicated in cytokinesis and cell cycle regulation. Because the three mutants were highly transforming, we directly determined GTP/GDP binding levels, the “gold-standard” assay, for all mutants, which indicated G62E had high GTP-binding and low GDP-binding, in contrast to its negative binding to Rhotekin, while L69P and L69R had high GDP-binding and low GTP-binding similar to WT. Purified GDP-bound L69P and L69R formed a complex with Citron more efficiently than did WT GTP-bound or GDP-bound RhoA. Endogenous Citron and CDK1 contribute to anchorage-independent growth, as siRNA knockdown of either gene in lines transformed by G62E, L69R or L69P inhibited this phenotype. The cancer-associated K-Ras mutants G60E and M67L (which correspond to RhoA G62E and L69R) and also K-Ras M67R displayed gain-of-function biologically, and the GTP/GDP-binding phenotype of each was analogous to the respective RhoA mutant: high GTP-binding for G60E, and low Raf-RBD binding and high GDP-binding for M67L and M67R. The low GTP K-Ras mutants bound more strongly to the RBD domain of Ras effectors other than Raf, resulting in activation of RAP and AKT in transfected cells. Our microarray data revealed that these GDP-bound mutant K-Ras or RhoA can up-regulate cell-cycle progression genes and down-regulate tumor suppressor genes compared to WT, which may account for their transforming phenotype. We conclude that some cancer-associated RhoA mutants are transforming when GDP-bound, a phenotype that has not been described for any small GTPase. The equivalent K-Ras mutants display a similar phenotype, which implies the findings should be extrapolatable to many small GTPases. Such mutants can be strongly transforming, although they only bind a subset of preferred downstream effectors and activate their respective pathways. In addition, the widely used Rhotekin binding assay to infer RhoGTP levels may give misleading results for some mutants. Citation Format: Xiaolan Qian, Alex Papageorge, Dunrui Wang, Brajendra Tripathi, Yucheng Gao, Marian Durkin, Beatriz Sanchez-Solana, Dominic Esposito, Timothy Waybright, Andrew Stephen, Douglas R. Lowy. Identification of cancer-associated RhoA mutants and analogous K-Ras mutants that induce gain-of function despite low GTP binding [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2586.

Abstract 5112: Interaction between RHOA mutated gastric cancer cells and cancer associated fibroblasts promotes tumorigenesis

Abstract Background: We previously observed that RHOA-mutated gastric cancer has desmoplastic morphological feature. Although desmoplastic reaction is known to consist mainly of cancer associated fibroblasts (CAF), the relationship cancer cells with RHOA mutation and CAF have not been reported. Thus, in this study, we investigated the interaction between RHOA-mutated gastric cancer cells and CAF and its underlying mechanism. Methods: We established stable gastric cell lines (AGS, MKN-45) expressing RHOA wild type (WT) of mutation (G17E, T37I, E40K, Y42C) using lentiviral vector and cocultured these cells with CAF using transwell. And proliferation and migration of RHOA-mutated gastric cancer cells were examined. To understand molecular mechanism of RHOA-mutated gastric cancer cells proliferation and migration, RNA-sequencing was conducted and the results were analyzed and validated. Results: Cocultivation of gastric cancer cells expressing RHOA WT or mutation (G17E, T37I, E40K, Y42C) with CAF increased proliferation relative to cells expressing an empty vector (EV). In addition, migration of RHOA mutant cells, except for cells with RHOA WT and Y42C, was increased by CAF relative to EV cells. Genes related to IL-17, IL-15, and IGF-1 signaling pathways were differentially expressed between RHOA WT or mutant cells and EV cells, suggesting that proliferation and migration of RHOA mutant cells promoted by CAF through these pathways. Furthermore, we identified CXCL1 and IGFBP2 as mediator of interaction between RHOA mutated gastric cancer cells and CAF. Conclusion: In summary, we found that gastric cancer cells with RHOA mutation have tumor-promoting activity by interaction with CAF. Thus, molecules for impairing their interactions could be potential therapeutic targets in gastric cancer patients with RHOA mutation. Citation Format: Daye Jeon, Yuri Choi, Seon Jin Lee, Kyung Un Choi, Do Youn Park, Chae Hwa Kwon. Interaction between RHOA mutated gastric cancer cells and cancer associated fibroblasts promotes tumorigenesis [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 5112.

Rho factor mediates flagellum and toxin phase variation and impacts virulence in Clostridioides difficile.

The intestinal pathogen Clostridioides difficile exhibits heterogeneity in motility and toxin production. This phenotypic heterogeneity is achieved through phase variation by site-specific recombination via the DNA recombinase RecV, which reversibly inverts the “flagellar switch” upstream of the flgB operon. A recV mutation prevents flagellar switch inversion and results in phenotypically locked strains. The orientation of the flagellar switch influences expression of the flgB operon post-transcription initiation, but the specific molecular mechanism is unknown. Here, we report the isolation and characterization of spontaneous suppressor mutants in the non-motile, non-toxigenic recV flg OFF background that regained motility and toxin production. The restored phenotypes corresponded with increased expression of flagellum and toxin genes. The motile suppressor mutants contained single-nucleotide polymorphisms (SNPs) in rho, which encodes the bacterial transcription terminator Rho factor. Analyses using transcriptional reporters indicate that Rho contributes to heterogeneity in flagellar gene expression by preferentially terminating transcription of flg OFF mRNA within the 5’ leader sequence. Additionally, Rho is important for initial colonization of the intestine in a mouse model of infection, which may in part be due to the sporulation and growth defects observed in the rho mutants. Together these data implicate Rho factor as a regulator of gene expression affecting phase variation of important virulence factors of C. difficile.

An Oncogenic Alteration Creates a Microenvironment that Promotes Tumor Progression by Conferring a Metabolic Advantage to Regulatory T Cells

Only a small percentage of patients afflicted with gastric cancer (GC) respond to immune checkpoint blockade (ICB). To study the mechanisms underlying this resistance, we examined the immune landscape of GC. A subset of these tumors was characterized by high frequencies of regulatory T (Treg) cells and low numbers of effector Tcells. Genomic analyses revealed that these tumors bore mutations in RHOA that are known to drive tumor progression. RHOA mutations in cancer cells activated the PI3K-AKT-mTOR signaling pathway, increasing production of free fatty acids that are more effectively consumed by Treg cells than effector Tcells. RHOA mutant tumors were resistant to PD-1 blockade but responded to combination of PD-1 blockade with inhibitors of the PI3K pathway or therapies targeting Treg cells. We propose that the metabolic advantage conferred by RHOA mutations enables Treg cell accumulation within GC tumors, generating an immunosuppressive TME that underlies resistance to ICB.

Abstract A29: The gastric cancer-associated mutations R5W and Y42C in the RAS homologous RHOA protein cause distinct biochemical alterations, exhibit gain-of-function signaling and oncogenic activities

Abstract Missense mutations of the RAS homologous RHOA gene have recently been identified in ~25% of diffuse gastric cancer (DGC). Unexpectedly, in contrast to the gain-of-function hotspot mutations found in RAS in cancer, DGC-associated RHOA mutations (e.g., R5W, Y42C) are localized at different hotspots that instead suggest loss-of-function alterations. First, we utilized bacterially expressed recombinant proteins and determined the biochemical consequences of these mutations on RHOA function. We found that RHOA WT and Y42C, but not R5W nucleotide exchange, was catalyzed by the ECT2 RhoGEF. Similarly, WT and Y42C, but not R5W GTP hydrolysis activity, was stimulated by the p190RhoGAP. Surprisingly, Y42C and to a lesser degree R5W exhibited impaired intrinsic GTP hydrolysis activity. Interestingly, Y42C showed both loss- and gain-of-function interaction with effectors. Second, we ectopically expressed WT and mutant RHOA proteins in NIH/3T3 fibroblast, and surprisingly, found that Y42C and R5W, similar to the lab-generated constitutively GTP-bound Q63L mutant (analogous to RAS Q61L), stimulated actin stress fiber formation and focal adhesion assembly. Finally, when ectopically expressed in beta-catenin-deficient (another mutation found in gastric cancer) mouse gastric organoids, Y42C disrupted the 3D architecture and induced a DGC-like phenotype in vitro and in vivo. In summary, our studies suggest mutation-specific biochemical defects that act as gain-of-function oncogenic RHOA mutations. Citation Format: Antje Schaefer, Richard G. Hodge, Devon R. Blake, Haisheng Zhang, Adam J. Bass, Channing J. Der. The gastric cancer-associated mutations R5W and Y42C in the RAS homologous RHOA protein cause distinct biochemical alterations, exhibit gain-of-function signaling and oncogenic activities [abstract]. In: Proceedings of the AACR Special Conference on Targeting RAS-Driven Cancers; 2018 Dec 9-12; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(5_Suppl):Abstract nr A29.

The Inhibition of Wnt Restrain KRASG12V-Driven Metastasis in Non-Small-Cell Lung Cancer.

The KRAS mutations have been an obstacle to identify therapeutic targets in cancer treatment. In this work, we clarified the distinct metastasis pattern of non-small-cell lung carcinoma (NSCLC) induced by KRASG12V/KRASG12D mutations and inhibited the KRASG12V mediated metastasis by Wnt inhibitor. First, we found that KRASG12V induced more aggressive phenotype in vitro and in vivo experiments. The Gene Set Enrichment Analysis (GSEA) results of H838 KRASG12V cells showed a significant negative correlation with RhoA-related signaling. Following this clue, we observed KRASG12D induced higher activation of RhoA and suppressed activation of Wnt/β-catenin in H838KRASG12D cells. The restored activation of Wnt/β-catenin in H838KRASG12D cells could be detected when expression with a dominant-negative mutant of RhoA or treatment with RhoA inhibitor. Furthermore, the Wnt inhibitor abolished the KRASG12V-induced migration. We elucidated the importance of the axis of RhoA/Wnt in regulatory NSCLC metastasis driven by KRAS mutations. Our data indicate that KRASG12V driven NSCLC metastasis is Wnt-dependent and the mechanisms of NSCLC metastasis induced by KRASG12V/KRASG12D is distinct.

Angioimmunoblastic T-cell lymphoma-like lymphadenopathy in mice transgenic for human RHOA with p.Gly17Val mutation

ABSTRACT A missense mutation in RHOA encoding p.Gly17 Val has been reported to occur frequently in angioimmunoblastic T-cell lymphoma (AITL). Here, we describe a murine model which expresses the human RHOA mutant gene product in a T-cell specific manner and develops AITL-like symptoms. Most transgenic mice feature with latency one or two enlarged lymph nodes characterized by aberrant lymph node architecture, extensive lymphocytic infiltration, extrafollicular meshwork of follicular dendritic cells (FDC) and arborized endothelial venules. Importantly, we provide evidence for expansion of PD-1+ follicular helper T (Tfh) cells which are the neoplastic cells of AITL. In addition, we saw proliferation of B-cells leading to hypergammaglobulinemia and the presence of dominant T cell clonal populations. Transplantation of lymph node cells to immunocompromised mice partly recreated lymphadenopathy after a long latency and with low penetrance suggesting that cells have undergone partial transformation to a premalignant state. Transcriptomic profiling revealed that the gene expression pattern within affected lymph nodes of the mice closely resembles that of AITL patients with the identical RHOA p.Gly17 Val mutation. The murine model should, therefore, be useful in dissecting pathogenesis of AITL at the molecular level particularly for the cases with the RHOA p.Gly17Val mutation.

Key roles of Rho GTPases, YAP, and Mutant P53 in anti‐neoplastic effects of statins

Emerging epidemiological and preclinical studies have focused on statins and mevalonate pathway to identify potential therapeutic target and clarify the underlying mechanism of the anti-neoplastic effects. Reductions of mevalonate or isoprenoids, caused by statins, would further decrease the isoprenylation of Rho GTPases which is the crucial step for Rho GTPases to anchor on inner cellular membrane. Following anchoring, activated Rho GTPases can mediate a series of cellular activities such as cytoskeleton reprogramming, front-rear polarity, and cell-ECM adhesion. These changes not only facilitate tumor cell detachment and migration but also bring great mechanical changes to directly activate YAP, the major nuclear mechanotransducer, to translocate into nucleus. Recently, statins have been identified as potent inhibitors of YAP. Once entering nucleus, YAP would combine TEADs to promote the transcription of about 100 genes, which are involved in cell proliferation, cell cycle regulation, stemness, invasion, and metastasis. Besides, statins are able to promote the degradation of misfolded mutant p53 (mutp53), which is an oncogene in a variety of human malignancies. Reduction in mevalonate-5-phosphate (MVP), also induced by statins, would impair the stability of DNAJA1-mutp53 complex; then, elevated C terminus of Hsc70-interacting protein (CHIP) mediates the nuclear export and degradation of misfolded mutp53 through ubiquitin-proteasome pathway. It is worth noted that YAP, mutp53, and mevalonate pathway form two positive feedback loops. It is reasonable to believe that Rho GTPases, YAP, and mutp53 are determinants for statins as anti-cancer agents: tumor cells harboring mutp53 and nuclear-located YAP would be more sensitive to statins.

PS1308 TARGETING T‐CELL RECEPTOR SIGNALING PATHWAY BY DASATINIB IN RELAPSED/REFRACTORY ANGIOIMMUNOBLASTIC T‐CELL LYMPHOMA

Background:Angioimmunoblastic T‐cell lymphoma (AITL) is an intractable T‐cell lymphoma. The recurrent hotspot (p.Gly17Val) mutations in RHOAencoding a small GTPase, together with the loss‐of‐function mutations in TET2encoding an epigenetic regulator, are the genetic hallmark in AITL. We previously identified that the p. Gly17Val RHOA mutant hyperactivates T‐cell receptor (TCR) signaling through direct binding to VAV1, a component of the TCR pathway. VAV1mutations were also found in RHOA‐negative AITL cases. The phosphorylation of VAV1 induced by the RHOA binding or its own amino acid changes was effectively inhibited by dasatinib at low concentrations. Dasatinib also prolonged the survival of AITL model mice (ASH 2017).Aims:Here, we performed a phase I clinical trial of dasatinib monotherapy in relapsed/refractory AITL patients.Methods:Five patients (one male and four females; 51–72 y/o; median, 65 y/o) being diagnosed with AITL were enrolled. Written informed consent was obtained from all the patients.Results:The median number of prior chemotherapies was 2 (range, 1–5). Two patients (Patient 1 and 2) were refractory to the latest chemotherapies. One patient (Patient 3) relapsed after the autologous transplantation. The performance status was 0‐ 2 (Table 1). Dasatinib was started at a dose of 100 mg/body q.d. and continued until days 10–78 (median day 58). Patient 2 withdrew the consent on day 10 and thus the response was not evaluable. In the remaining four patients, dasatinib was continued until day 54 or later and the response evaluation was possible. The trial was ultimately discontinued due to further treatment with allogeneic hematopoietic stem cell transplantation, disease progression, or severe adverse event in these four patients. Grade3/4 adverse drug reactions were observed in one case (Patient 5). The other adverse events were attributable to exacerbation of the diseases. There were no new safety concerns other than reported in BCR‐ABL‐positive chronic myelogenous leukemia/acute lymphoblastic leukemia. The maximum response was partial responses (PR) in all these four patients. The response at the discontinuation of trial was PR in two (Patient 1 and 5) and progressive disease (PD) in two (Patient 3 and 4).Targeted sequencing using a panel for 427 genes identified 34 candidate mutations including 22 nonsilent single nucleotide variants (SNVs), 2 nonsense mutations, 3 frameshift deletions, 2 frameshift insertions, 2 nonframeshift deletions, and one nonframeshift insertion. Two TET2 mutations were found in 4 samples (PAT1, PAT2, PAT4, and PAT5). The Gly17Val RHOA mutations were found by targeted sequencing in 2 samples (PAT3 and PAT4). VAV1 mutations were found in 2 samples (PAT2 and PAT5). Additionally one tandem duplication involving VAV1 locus was also identified by manual inspection of Integral Genome Viewer (IGV) in PAT5.Summary/Conclusion:AITL is highly dependent on TCR signaling, and dasatinib appears to be a promising candidate treatment modality in AITL.