H-Ras G12V Research Articles

Regulation of alternative polyadenylation isoforms of Timp2 is an effector event of RAS signaling in cell transformation.

Alternative polyadenylation (APA) generates mRNA isoforms with different lengths of the 3' untranslated region (3' UTR). The tissue inhibitor of metalloproteinase 2 (TIMP2) plays a key role in extracellular matrix remodeling under various developmental and disease conditions. Both human and mouse genes encoding TIMP2 contain two highly conserved 3'UTR APA sites, leading to mRNA isoforms that differ substantially in 3'UTR size. APA of Timp2 is one of the most significantly regulated events in multiple cell differentiation lineages. Here we show that Timp2 APA is highly regulated in transformation of NIH3T3 cells by the oncogene HRAS G12V . Perturbations of isoform expression with long 3'UTR isoform-specific knockdown or genomic removal of the alternative UTR (aUTR) region indicate that the long 3'UTR isoform contributes to the secreted Timp2 protein much more than the short 3'UTR isoform. The short and long 3'UTR isoforms differ in subcellular localization to endoplasmic reticulum (ER). Strikingly, Timp2 aUTR enhances secreted protein expression but no effect on intracellular proteins in reporter assays. Furthermore, downregulation of Timp2 long isoform mitigates gene expression changes elicited by HRAS G12V . Together, our data indicate that regulation of Timp2 protein expression through APA isoform changes is an integral part of RAS-mediated cell transformation and 3'UTR isoforms of Timp2 can have distinct impacts on expression of secreted vs. intracellular proteins.

Abstract A144: HM99462, a Novel & potent SOS1 inhibitor, induces tumor regressions in combination with KRAS G12C inhibitor, MEK inhibitor, or EGFR mutant inhibitor

Abstract Son of sevenless homolog 1 (SOS1) is one of guanine nucleotide exchange factor (GEF) responsible for a binary molecular switch to activate KRAS as well as a node in the negative feedback loop in the RTK-KRAS-MAPK signaling pathway. Therefore, combination strategies with a SOS1 inhibitor are being explored as a promising therapeutic options to target the MAPK-mediated bypass, which may improve antitumor activity or delay the induction of resistance after treatment. Herein, we presented a novel and potent SOS1 inhibitor, HM99462, which abrogates GTP-binding to KRAS and the profile of drug potency and mechanism of action was examined with in vitro and in vivo models. Biochemical activity on SOS1 was evaluated by a GTP-exchange assay on diverse KRAS G12X mutant types, NRAS Q61H, and HRAS G12V, and HM99462 showed excellent inhibitory activity, while SOS2 action was not affected. Moreover, HM99462 decreased ERK phosphorylation in various cancer cell lines harboring different major KRAS mutation statuses such as KRAS G12C, G12D, G12V, or G13D. Growth inhibition assay was performed using a three-dimensional (3D) conformation culture that mimics the complexity and heterogeneity of tumors and has elevated p-ERK. In this 3D spheroid growth inhibition assay, HM99462 demonstrated significantly effective GI50 against various KRAS mutant cancer cell lines. Additionally, HM99462 was evaluated in cancer cell xenograft mouse models harboring KRAS or EGFR mutation. The combination of HM99462 with KRAS G12C, MEK, or EGFR mutant inhibitor led to significantly synergistic anti-tumor activity in both in vitro and in vivo models with several KRAS or EGFR mutations. Based on our exploratory study, a novel and potent SOS1 inhibitor, HM99462 could be suggested as an appropriate therapeutic agent for diverse inhibitory activity against cancers causing by the hyperactivation of oncogenic KRAS or RTK signaling. And it has the potential to overcome the limitations of KRAS G12C, MEK or EGFR inhibitor through combination. IND enabling GLP-toxicity studies with HM99462 are currently underway, and we planned to initiate clinical study in early 2024. Citation Format: Jaeyul Choi, Seung Hyun Jung, Wongi Park, Jooyun Byun, Semi Lim, Youngjoo Lee, Soye Jeon, Yu-Yon Kim, Young Gil Ahn, Young Hoon Kim, Kwee Hyun Suh. HM99462, a Novel & potent SOS1 inhibitor, induces tumor regressions in combination with KRAS G12C inhibitor, MEK inhibitor, or EGFR mutant inhibitor [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A144.

Expression of oncogenic HRAS G12V causes defects in control of cell size in NIH 3T3 cells.

Severe defects in control of cell size are closely associated with cancer. However, the mechanisms that drive cell size defects in cancer remain unknown and it is unclear whether they are a direct consequence of signals from primary oncogenic drivers or a secondary consequence of mutations that accumulate during evolution of cancer cells. Here, we report that expression of oncogenic HRAS G12V is sufficient to cause cell size defects in NIH 3T3 cells, which suggests that the cell size defects of cancer cells are a direct consequence of primary oncogenic drivers.

Increased osteoclastogenesis contributes to bone loss in the Costello syndrome Hras G12V mouse model.

RAS GTPases are ubiquitous GDP/GTP-binding proteins that function as molecular switches in cellular signalling and control numerous signalling pathways and biological processes. Pathogenic mutations in RAS genes severely affect cellular homeostasis, leading to cancer when occurring in somatic cells and developmental disorders when the germline is affected. These disorders are generally termed as RASopathies and among them Costello syndrome (CS) is a distinctive entity that is caused by specific HRAS germline mutations. The majority of these mutations affect residues 12 and 13, the same sites as somatic oncogenic HRAS mutations. The hallmarks of the disease include congenital cardiac anomalies, impaired thriving and growth, neurocognitive impairments, distinctive craniofacial anomalies, and susceptibility to cancer. Adult patients often present signs of premature aging including reduced bone mineral density and osteoporosis. Using a CS mouse model harbouring a Hras G12V germline mutation, we aimed at determining whether this model recapitulates the patients' bone phenotype and which bone cells are driving the phenotype when mutated. Our data revealed that Hras G12V mutation induces bone loss in mice at certain ages. In addition, we identified that bone loss correlated with an increased number of osteoclasts in vivo and Hras G12V mutations increased osteoclastogenesis in vitro. Last, but not least, mutant osteoclast differentiation was reduced by treatment in vitro with MEK and PI3K inhibitors, respectively. These results indicate that Hras is a novel regulator of bone homeostasis and an increased osteoclastogenesis due to Hras G12V mutation contributes to bone loss in the Costello syndrome.

Inhibition of Calcineurin/NFAT Signaling Blocks Oncogenic H-Ras Induced Autophagy in Primary Human Keratinocytes

Mutations of H-Ras, a member of the RAS family, are preferentially found in cutaneous squamous cell carcinomas (SCCs). H-Ras has been reported to induce autophagy, which plays an essential role in tissue homeostasis in multiple types of cancer cells and in fibroblasts, however, the potential role of H-Ras in regulating autophagy in human keratinocytes has not been reported. In this study, we found that the stable expression of the G12V mutant of H-RAS (H-RasG12V) induced autophagy in human keratinocytes, and interestingly, the induction of autophagy was strongly blocked by inhibiting the calcineurin/nuclear factor of activated T cells (NFAT) pathway with either a calcineurin inhibitor (Cyclosporin A) or a NFAT inhibitor (VIVIT), or by the small interfering RNA (siRNA) mediated knockdown of calcineurin B1 or NFATc1 in vitro, as well as in vivo. To characterize the role of the calcineurin/NFAT pathway in H-Ras induced autophagy, we found that H-RasG12V promoted the nuclear translocation of NFATc1, an indication of the activation of the calcineurin/NFAT pathway, in human keratinocytes. However, activation of NFATc1 either by the forced expression of NFATc1 or by treatment with phenformin, an AMPK activator, did not increase the formation of autophagy in human keratinocytes. Further study revealed that inhibiting the calcineurin/NFAT pathway actually suppressed H-Ras expression in H-RasG12V overexpressing cells. Finally, chromatin immunoprecipitation (ChIP) assays showed that NFATc1 potentially binds the promoter region of H-Ras and the binding efficiency was significantly enhanced by the overexpression of H-RasG12V, which was abolished by treatment with the calcineurin/NFAT pathway inhibitors cyclosporine A (CsA) or VIVIT. Taking these data together, the present study demonstrates that the calcineurin/NFAT signaling pathway controls H-Ras expression and interacts with the H-Ras pathway, involving the regulation of H-Ras induced autophagy in human keratinocytes.

Overexpression of oncogenic H-Ras in hTERT-immortalized and SV40-transformed human cells targets replicative and specialized DNA polymerases for depletion

DNA polymerases play essential functions in replication fork progression and genome maintenance. DNA lesions and drug-induced replication stress result in up-regulation and re-localization of specialized DNA polymerases η and κ. Although oncogene activation significantly alters DNA replication dynamics, causing replication stress and genome instability, little is known about DNA polymerase expression and regulation in response to oncogene activation. Here, we investigated the consequences of mutant H-RAS G12V overexpression on the regulation of DNA polymerases in h-TERT immortalized and SV40-transformed human cells. Focusing on DNA polymerases associated with the replication fork, we demonstrate that DNA polymerases are depleted in a temporal manner in response to H-RAS G12V overexpression. The polymerases targeted for depletion, as cells display markers of senescence, include the Pol α catalytic subunit (POLA1), Pol δ catalytic and p68 subunits (POLD1 and POLD3), Pol η, and Pol κ. Both transcriptional and post-transcriptional mechanisms mediate this response. Pol η (POLH) depletion is sufficient to induce a senescence-like growth arrest in human foreskin fibroblast BJ5a cells, and is associated with decreased Pol α expression. Using an SV-40 transformed cell model, we observed cell cycle checkpoint signaling differences in cells with H-RasG12V-induced polymerase depletion, as compared to Pol η-deficient cells. Our findings contribute to our understanding of cellular events following oncogene activation and cellular transformation.

Studying Metabolic Abnormalities in the Costello Syndrome HRAS G12V Mouse Model: Isolation of Mouse Embryonic Fibroblasts and Their In Vitro Adipocyte Differentiation.

Costello syndrome (CS), characterized by a developmental delay and a failure to thrive, is also associated with an impaired lipid and energy metabolism. White adipose tissue is a central sensor of whole-body energy homeostasis, and HRAS hyperactivation may affect adipocyte differentiation and mature adipocyte homeostasis. An extremely useful tool for delineating in vitro intrinsic cellular signaling leading to metabolic alterations during adipogenesis is mouse embryonic fibroblasts, known to differentiate into adipocytes in response to adipogenesis-stimulating factors. Here, we describe in detail the isolation and maintenance of CS HRAS G12V mouse embryonic fibroblasts, their differentiation into adipocytes, and an assessment of adipocyte differentiation.

Cohesin Is Out for Stalled Replication Fork Restart.

Replication stress underlies many genomic alterations in cancer cells. In this issue of Developmental Cell, Benedict etal. show that WAPL-dependent cohesin removal is needed to restart DNA synthesis at stalled forks and promote survival following replication stress, uncovering an unexpected link between stress and sister chromatid cohesion loss.

Abstract 1791: RADIL regulates RAS downstream signaling

Abstract RAS proteins regulate a variety of cellular processes including cell survival, proliferation, and differentiation. RAS genes are among the most frequently mutated oncogenes in human malignancies. To date, there are no successful anti-cancer drugs in the clinic that target RAS proteins or their pathways. Therefore, it is imperative to identify and characterize new components that regulate RAS activity or mediates its downstream signaling. Recently, we identified a series of proteins that are associated with HRAS using a combination of immunoprecipitation and mass spectrometry. We first focused on RADIL, a gene product with Ras-Association (RA) and DIL domains. RADIL is known to be a downstream effector of RAP1, inhibiting RhoA signaling in the regulation of cell survival, adhesion, and migration. We demonstrated that RADIL interacted with all three isoforms of RAS, including H, N, and KRAS. Interestingly, constitutively active HRAS (HRASG12V) was strongly associated with RADIL whereas dominant negative HRAS (HRASS17N) displayed a compromised association with RADIL, suggesting that RADIL may be required for RAS activation. We also found that Radil Knockout cells had weakened ERK phosphorylation whereas induced expression of RADIL promoted ERK phosphorylation, suggesting that RADIL is required for the RAS-MEK-ERK signaling cascade in vitro. Taken together, our current studies strongly suggest that RADIL may be important for regulating RAS signaling. Citation Format: Byeong Hyeok Choi, Ziyue Kou, Mark R. Philips, Wei Dai. RADIL regulates RAS downstream signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1791.

Abstract PR02: Capturing the integration of Ras-mutant cells into normal epithelial tissue using live imaging

Abstract Healthy tissues are frequently subject to oncogenic mutations that result in abnormal cellular behaviors, yet do not always produce malignancy or even macroscopic phenotypes. Specifically, cancer-associated mutations have frequently been identified in phenotypically “normal” skin; however, the mechanism by which the skin epithelium responds to these mutant cells in order to maintain normalcy has been poorly understood. One challenge to understanding this phenomenon has been the inability to follow the same tissue and cells over time in an intact mammal. To overcome this, we have established a novel live-imaging approach to track over time skin epithelial tissue that has been burdened with varying amounts of two distinct activating mutations: Hras G12V and β-Catenin. My previous work has demonstrated that the skin has a robust capacity for coping with and even reversing disruptions to normal tissue architecture produced by either mutational insult (Brown* and Pineda* et al. Nature in press). Intriguingly, our current work, using the hair follicle epithelium as a model system, demonstrates that while β-Catenin driven aberrancies are corrected through the elimination of mutant cells from the tissue, correction of Hras-driven aberrancies does not require mutant cell elimination. Instead, through live imaging and biochemical analysis, we found that the Hras pathway is active over time, resulting in the expansion of mutant cells and enhanced tissue function including more frequent as well as forced hair follicle cycling. While hair cycling is orchestrated by a specialized mesenchyme, called the dermal papilla (DP), these data instead suggest a model whereby the mutant epithelium can influence the nearby wild-type mesenchymal tissue. Preliminary immunofluorescence stains revealed a non-cell autonomous effect by the Hras epithelium on the neighboring mesenchymal cells whereby its molecular and proliferative behaviors are upregulated. Furthermore, mesenchymal laser ablation experiments show that DPs regenerate faster in Hras-mutant follicles compared to wild-type follicles and quickly restore normal hair cycling. We are currently investigating molecular links identified through our proteomic and cytokine analyses that mediate Hras-mutant epithelium communication with its adjacent mesenchyme while maintaining proper hair follicle function. Altogether, these findings indicate an unexpected relationship by which mutant epithelial tissue is able to non-autonomously influence and enhance adjacent mesenchymal behavior in prephenotypic tissue, establishing a tissue crosstalk that appears to buffer mutant cell potential. This abstract is also being presented as Poster A13. Citation Format: Cristiana M. Pineda, Valentina Greco. Capturing the integration of Ras-mutant cells into normal epithelial tissue using live imaging [abstract]. In: Proceedings of the AACR Special Conference: Advances in Modeling Cancer in Mice: Technology, Biology, and Beyond; 2017 Sep 24-27; Orlando, Florida. Philadelphia (PA): AACR; Cancer Res 2018;78(10 Suppl):Abstract nr PR02.

Abstract 3162: HRAS G12V predicts for innate resistance to PI3Kα inhibition in head and neck squamous cell cancer

Abstract Introduction: Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide, with an incidence of ~600 000 new cases per year and a 50% mortality rate for advanced disease. The mutational landscape of HNSCC has been recently elucidated, introducing the possibility for targeted therapeutic approaches. PIK3CA—which encodes the α-catalytic subunit of PI3K (PI3Kα)—is the most frequently altered actionable target in HNSCC, however it is not presently clear which patients benefit most from PI3Kα-inhibition. BYL719 is a leading PI3Kα inhibitor in clinical development for HNSCC. We previously examined the responses of a large panel of genetically-characterized HNSCC cell lines to BYL719 and identified activating HRAS G12V mutations as strong predictors for BYL719 resistance. Here we examine if this mutation is able to individually modulate BYL719 response through overexpression and knockdown studies. Methods: To determine if HRAS G12V was able to modulate BYL719 sensitivity, we knocked down HRAS in HRAS G12V and HRAS wild-type (WT) cell lines using RNA interference, and then treated cells over 10-point dose ranges with BYL719. Sensitivity was determined by calculating IC50 (half-maximal inhibitory concentration) values at 72 hours using PrestoBlue®. Constructs expressing wildtype (WT) HRAS or HRAS G12V were transfected into BYL719-sensitive cells for overexpression studies and cells were selected using G418 Sulfate for 1 month. Proliferation and BYL719 sensitivity (IC50 values) were measured as described. Immunoblotting was used to examine activity of the PI3K-AKT axis with and without BYL719 (1μM) for 24 hours. Results & Conclusions: HRAS knockdown sensitized HRAS G12V lines to BYL719 (lower IC50), but did not affect the response of WT HRAS cells. WT HRAS and HRAS G12V overexpression significantly increased cellular proliferation and promoted BYL719 resistance. In HRAS G12V cell lines, we observed high levels of active phosphorylated AKT (S473/T308), even in the presence of BYL719. Collectively these findings highlight the predictive role of HRAS G12V for innate BYL719 resistance and contribute to our understanding of which patients may respond best on BYL719 therapy. Citation Format: Kara M. Ruicci, Ren Sun, Morgan Black, Nicole Pinto, John Yoo, Kevin Fung, Danielle Macneil, Lauire Aillies, Joseph S. Mymryk, Paul C. Boutros, John W. Barrett, Anthony C. Nichols. HRAS G12V predicts for innate resistance to PI3Kα inhibition in head and neck squamous cell cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3162. doi:10.1158/1538-7445.AM2017-3162

Roles of the PDZ-binding motif of HPV 16 E6 protein in oncogenic transformation of human cervical keratinocytes.

The high‐risk human papillomavirus E6 proteins have been shown to interact with and lead to degradation of PDZ‐domain‐containing proteins through its carboxy‐terminal motif. This PDZ‐binding motif plays important roles in transformation of cultured cells and carcinogenesis of E6‐transgenic mice. However, its biological effects on the natural host cells have not been elucidated. We have examined its roles in an in vitro carcinogenesis model for cervical cancer, in which E6 and E7 together with activated HRAS (HRASG 12V) can induce tumorigenic transformation of normal human cervical keratinocytes. In this model, E6Δ151 mutant, which is defective in binding to PDZ domains, almost lost tumorigenic ability, whereas E6SAT mutant, which is defective in p53 degradation showed activity close to wild‐type E6. Interestingly, we found decreased expression of PAR3 in E6‐expressing cells independently of E6AP, which has not been previously recognized. Therefore, we knocked down several PDZ‐domain containing proteins including PAR3 in human cervical keratinocytes expressing E7, HRASG 12V and E6Δ151 to examine whether depletion of these proteins can restore the tumorigenic ability. Single knockdown of SCRIB, MAGI1 or PAR3 significantly but partially restored the tumorigenic ability. The combinatorial knockdown of SCRIB and MAGI1 cooperatively restored the tumorigenic ability, and additional depletion of PAR3 further enhanced the tumorigenic ability surpassing that induced by wild‐type E6. These data highlight the importance of the carboxy‐terminal motif of the E6 protein and downregulation of PAR3 in tumorigenic transformation of human cervical keratinocytes.

A cellular model reflecting the phenotypic heterogeneity of mutant HRAS driven squamous cell carcinoma.

Squamous cell carcinomas have a range of histopathological manifestations. The parameters that determine this clinically observed heterogeneity are not fully understood. Here, we report the generation of a cell culture model that reflects part of this heterogeneity. We have used the catalytic subunit of human telomerase hTERT and large T to immortalize primary UV-unexposed keratinocytes. Then, mutant HRAS G12V has been introduced to transform these immortal keratinocytes. When injected into immunosuppressed mice, transformed cells grew as xenografts with distinct histopathological characteristics. We observed three major tissue architectures: solid, sarcomatoid and cystic growth types, which were primarily composed of pleomorphic and basaloid cells but in some cases displayed focal apocrine differentiation. We demonstrate that the cells generated represent different stages of skin cancerogenesis and as such can be used to identify novel tumor-promoting alterations such as the overexpression of the PADI2 oncogene in solid-type SCC. Importantly, the cultured cells maintain the characteristics from the xenograft they were derived from while being amenable to manipulation and analysis. The availability of cell lines representing different clinical manifestations opens a new tool to study the stochastic and deterministic factors that cause case-to-case heterogeneity despite departing from the same set of oncogenes and the same genetic background.

Abstract A47: Expression of oncogenic alleles induces multiple blocks to HCMV infection

Abstract Human cytomegalovirus (HCMV) poses serious threats to newborns and immune-compromised individuals. In contrast to most viruses studied, HCMV is unable to replicate in cancerous cells, but the mechanisms of this restriction are unclear. We explored these mechanisms by determining whether defined oncogenic alleles including the simian virus 40 (SV40) T antigens and oncogenic HRas G12V could inhibit HCMV replication. Our results show that the expression of SV40 T antigens blocks HCMV replication. In contrast, the replication of a related herpes virus, herpes simplex virus I, is not impacted by T antigen expression. The earliest restriction of HCMV infection involves a block of viral entry, as T antigen expression prevents viral tegument protein delivery. Subsequently we find that T antigen expression reduces the accumulation of platelet-derived growth factor receptor (PDGFR) alpha, a host protein that facilitates HCMV entry. Viral entry, gene expression and DNA replication could be partially rescued by PDGFR alpha over-expression. However, production of infectious viral progeny is not restored by PDGFR alpha over-expression in T antigen-expressing fibroblasts. Analysis of viral gene expression indicates that the accumulation of immediate early 2 (IE2), the major viral transcriptional activator, is inhibited by T antigen expression. Restoration of IE2 expression markedly increases downstream HCMV gene expression but not virion production, suggesting additional viral restrictions induced by T antigen. Similarly, PDGFR alpha over-expression in Hela cells markedly increases HCMV gene expression and DNA replication but not virion production. Combined, our results indicate that oncogenic alleles induce multiple restrictions to HCMV infection. Citation Format: Shihao Xu, Xenia Schafer, Joshua Munger. Expression of oncogenic alleles induces multiple blocks to HCMV infection. [abstract]. In: Proceedings of the Fourth AACR International Conference on Frontiers in Basic Cancer Research; 2015 Oct 23-26; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2016;76(3 Suppl):Abstract nr A47.

Mutant HRAS as novel target for MEK and mTOR inhibitors.

HRAS is a frequently mutated oncogene in cancer. However, mutant HRAS as drug target has not been investigated so far. Here, we show that mutant HRAS hyperactivates the RAS and the mTOR pathway in various cancer cell lines including lung, bladder and esophageal cancer. HRAS mutation sensitized toward growth inhibition by the MEK inhibitors AZD6244, MEK162 and PD0325901. Further, we found that MEK inhibitors induce apoptosis in mutant HRAS cell lines but not in cell lines lacking RAS mutations. In addition, knockdown of HRAS by siRNA blocked cell growth in mutant HRAS cell lines. Inhibition of the PI3K pathway alone or in combination with MEK inhibitors did not alter signaling nor had an impact on viability. However, inhibition of mTOR or combined inhibition of MEK and mTOR reduced cell growth in a synergistic manner. Finally, Ba/F3 cells transformed with mutant HRAS isoforms Q61L, Q61R and G12V demonstrated equal sensitivity towards MEK and mTOR inhibition. Our results show that HRAS mutations in cancer activate the RAS and mTOR pathways which might serve as a therapeutic option for patients with HRAS mutant tumors.

H-RAS mutation is a key molecular feature of pediatric urothelial bladder cancer. A detailed report of three cases

Urothelial carcinoma (UC) of the bladder is a rare entity in the pediatric population, with an incidence of less than 0.4% in patients younger than 20 years. These patients overwhelmingly present with non-muscle-invasive low-grade disease and an indolent behavior. The aim was to determine the source of the different natural history between pediatric population and adults; we hypothesized that pediatric bladder cancer may stem from different molecular pathways. Our objective with this descriptive case series was to study the main genes involved in pediatric urothelial bladder carcinoma using immunohistochemical (IHC) and mutational analysis. By studying the genetic alterations and immunophenotype of the most commonly altered genes in bladder urothelial cancer in three pediatric tumors we could gain better understanding of the molecular pathogenesis in this rare disease. Formalin-fixed paraffin-embedded (FFPE) tissue slides of urothelial bladder tumors from three pediatric patients were retrospectively identified at Columbia University pathology archives (1990-2011) and re-evaluated. FGFR3, H-RAS, and PI3K hotspots mutational analyses were conducted by polymerase chain reaction amplification and Sanger sequencing from the FFPE tissue blocks. IHC analysis was conducted using antibodies against p53, PTEN, RB, EGFR, and HER2. Proliferative rate was assessed by Ki-67 expression. Two patients had low-grade Ta disease, whereas the other tumor was classified as a papillary urothelial neoplasm of low malignant potential. None of the lesions recurred. Notably, all specimens showed H-RAS G12V mutation, whereas they were characterized by wild-type FGFR3 and PI3K. Nuclear p53 was not detected, whereas PTEN and RB expression were maintained. EGFR was expressed in the three cases and HER2 was negative. The proliferation rate was very low in all cases. It is difficult to draw strong conclusions from the study of three tumors treated at the same institution and from the same referral population, and a multicentric study should be performed to confirm these preliminary results. However, we propose that H-RAS mutation analysis could be performed on urothelial bladder tumors of pediatric patients. The knowledge in the molecular basis of urothelial bladder tumors in children opens a promising field which could lead us to establish different guidelines for surveillance and follow-up of pediatric urothelial bladder cancer patients. Pediatric tumors are characterized by a consistent H-RAS mutation status, whereas FGFR3 and p53 pathways are not involved in this tumor initiation. These results may explain the few recurrences seen in this population.

KRAS and HRAS mutations confer resistance to MET targeting in preclinical models of MET-expressing tumor cells

The MET receptor tyrosine kinase is often deregulated in human cancers and several MET inhibitors are evaluated in clinical trials. Similarly to EGFR, MET signals through the RAS-RAF-ERK/MAPK pathway which plays key roles in cell proliferation and survival. Mutations of genes encoding for RAS proteins, particularly in KRAS, are commonly found in various tumors and are associated with constitutive activation of the MAPK pathway. It was shown for EGFR, that KRAS mutations render upstream EGFR inhibition ineffective in EGFR-positive colorectal cancers. Currently, there are no clinical studies evaluating MET inhibition impairment due to RAS mutations. To test the impact of RAS mutations on MET targeting, we generated tumor cells responsive to the MET inhibitor EMD1214063 that express KRAS G12V, G12D, G13D and HRAS G12V variants. We demonstrate that these MAPK-activating RAS mutations differentially interfere with MET-mediated biological effects of MET inhibition. We report increased residual ERK1/2 phosphorylation indicating that the downstream pathway remains active in presence of MET inhibition. Consequently, RAS variants counteracted MET inhibition-induced morphological changes as well as anti-proliferative and anchorage-independent growth effects. The effect of RAS mutants was reversed when MET inhibition was combined with MEK inhibitors AZD6244 and UO126. In an in vivo mouse xenograft model, MET-driven tumors harboring mutated RAS displayed resistance to MET inhibition. Taken together, our results demonstrate for the first time in details the role of KRAS and HRAS mutations in resistance to MET inhibition and suggest targeting both MET and MEK as an effective strategy when both oncogenic drivers are expressed.

Characterization of molecular features of pediatric urothelial bladder carcinomas.

345 Background: Bladder cancer is a rare entity in the pediatric population making it difficult to define surveillance protocols and long term outcomes. Notably, most pediatric tumors are low grade and non-muscle invasive and do not recur. In order to determine the source of the different natural history between pediatric population and adults, we hypothesized that pediatric bladder cancer may potentially stem from different molecular pathways than its adult form. Our main objective was to study the molecular pathogenesis in this rare disease using immunohistochemical (IHC) and mutational analysis of the main known genes involved in bladder cancer. Methods: Paraffin-embedded tissue slides of bladder tumors from three pediatric patients were retrospectively identified from our institution's pathology archives (1990-present) and re-evaluated. Clinical data was reviewed. FGFR3, H-RAS, and PI3K mutational analysis of the most well-known mutated spots was conducted by PCR amplification and Sanger sequencing. IHC analysis was conducted using antibodies against p53, Pten, Rb, EGFR, Her2Neu and ki-67. Results: Two patients had low-grade Ta disease, whereas the other tumor was classified as a Papillary Urothelial Neoplasm of Low Malignant Potential (PUNLMP). None of the lesions recurred. Two patients were female and one was male. The ages at diagnosis were 13, 11, and 17, with a mean follow-up of 5.2 years (Range: 1.5-8.0 years). All specimens showed H-RAS G12V mutation, whereas they were characterized by wild-type FGFR3 and PI3K. Nuclear p53 was not detected, whereas PTEN and Rb expression were maintained. EGFR was homogenously expressed in the three cases, and Her2Neu was negative. The proliferation rate analyzed by Ki-67 expression was very low in all cases (<5%). Conclusions: Pediatric tumors may arise from a pathway that is not initiated by FGFR3 or p53 mutations, but by H-RAS mutations. This distinction may explain the relatively few recurrences seen in the pediatric population. Molecular investigation of larger series of pediatric tumors is warranted, and will aid in determining the surveillance and the clinical follow up, if any, needed in this rare entity.

Increased susceptibility of H-Ras(G12V)-transformed human urothelial cells to the genotoxic effects of sodium arsenite.

Inorganic arsenite (iAs) is a human carcinogen. Numerous studies have shown that mutation-activated H-Ras is frequently observed in human urothelial carcinomas. The interaction between iAs, an environmental factor, and H-Ras, an oncogene, is not clear. In this study, we explored the genotoxic effects of iAs in human urothelial cells ectopically expressing H-Ras (G12V) an activated H-Ras oncogene. Our results showed that H-Ras(G12V)-transformed human urothelial cells (HUC-RAS) were more susceptible to arsenite-induced cell death, DNA damage, micronuclei formation and anchorage-independent growth than control cells (HUC-neo). Furthermore, iAs treatment induced higher intracellular levels of reactive oxygen species (ROS) in the HUC-RAS cells than in the HUC-neo cells. N-acetyl-L-cysteine could suppress the iAs-induced increases in ROS and genetic damage. We further demonstrated that the intracellular glutathione levels were significantly elevated by the iAs treatment of the HUC-neo cells, but that this effect was not observed in the HUC-RAS cells. The iAs treatment induced higher superoxide dismutase activity in the HUC-neo cells than in the HUC-RAS cells. Alternatively, catalase activity was higher in the HUC-RAS cells than in the HUC-neo cells, but this enzyme was significantly suppressed by iAs. Moreover, iAs activated the ERK and JNK signaling pathways, which are involved in iAs-induced ROS production and genetic damage. Taken together, our present results suggest that elevated catalase activity in H-Ras(G12V)-transformed cells is significantly suppressed by iAs via activation of ERK and JNK signaling pathways and hence attenuate the defense of the neoplastic transformed cells against iAs-induced oxidative injuries.

A Novel Mechanism by Which Tissue Transglutaminase Activates Signaling Events That Promote Cell Survival

Tissue transglutaminase (tTG) functions as a GTPase and an acyl transferase that catalyzes the formation of protein cross-links. tTG expression is frequently up-regulated in human cancer, where it has been implicated in various aspects of cancer progression, including cell survival and chemo-resistance. However, the extent to which tTG cooperates with other proteins within the context of a cancer cell, versus its intrinsic ability to confer transformed characteristics to cells, is poorly understood. To address this question, we asked what effect the ectopic expression of tTG in a non-transformed cellular background would have on the behavior of the cells. Using NIH3T3 fibroblasts stably expressing a Myc-tagged form of tTG, we found that tTG strongly protected these cells from serum starvation-induced apoptosis and triggered the activation of the PI3-kinase/mTOR Complex 1 (mTORC1)/p70 S6-kinase pathway. We determined that tTG forms a complex with the non-receptor tyrosine kinase c-Src and PI3-kinase, and that treating cells with inhibitors to block tTG function (monodansylcadaverine; MDC) or c-Src kinase activity (PP2) disrupted the formation of this complex, and prevented tTG from activating the PI3-kinase pathway. Moreover, treatment of fibroblasts over-expressing tTG with PP2, or with inhibitors that inactivate components of the PI3-kinase pathway, including PI3-kinase (LY294002) and mTORC1 (rapamycin), ablated the tTG-promoted survival of the cells. These findings demonstrate that tTG has an intrinsic capability to stimulate cell survival through a novel mechanism that activates PI3-kinase signaling events, thus highlighting tTG as a potential target for the treatment of human cancer.