The Emerging Role of LPA as an Oncometabolite

Lysophosphatidic acid (LPA) is a phospholipid that displays potent signalling activities that are regulated in both an autocrine and paracrine manner. It can be found both extra- and intracellularly, where it interacts with different receptors to activate signalling pathways that regulate a plethora of cellular processes, including mitosis, proliferation and migration. LPA metabolism is complex, and its biosynthesis and catabolism are under tight control to ensure proper LPA levels in the body. In cancer patient specimens, LPA levels are frequently higher compared to those of healthy individuals and often correlate with poor responses and more aggressive disease. Accordingly, LPA, through promoting cancer cell migration and invasion, enhances the metastasis and dissemination of tumour cells. In this review, we summarise the role of LPA in the regulation of critical aspects of tumour biology and further discuss the available pre-clinical and clinical evidence regarding the feasibility and efficacy of targeting LPA metabolism for effective anticancer therapy.

Vitamin B5 supports MYC oncogenic metabolism and tumor progression in breast cancer

Tumors are intrinsically heterogeneous and it is well established that this directs their evolution, hinders their classification and frustrates therapy1-3. Consequently, spatially resolved omics-level analyses are gaining traction4-9. Despite considerable therapeutic interest, tumor metabolism has been lagging behind this development and there is a paucity of data regarding its spatial organization. To address this shortcoming, we set out to study the local metabolic effects of the oncogene c-MYC, a pleiotropic transcription factor that accumulates with tumor progression and influences metabolism10,11. Through correlative mass spectrometry imaging, we show that pantothenic acid (vitamin B5) associates with MYC-high areas within both human and murine mammary tumors, where its conversion to coenzyme A fuels Krebs cycle activity. Mechanistically, we show that this is accomplished by MYC-mediated upregulation of its multivitamin transporter SLC5A6. Notably, we show that SLC5A6 over-expression alone can induce increased cell growth and a shift toward biosynthesis, whereas conversely, dietary restriction of pantothenic acid leads to a reversal of many MYC-mediated metabolic changes and results in hampered tumor growth. Our work thus establishes the availability of vitamins and cofactors as a potential bottleneck in tumor progression, which can be exploited therapeutically. Overall, we show that a spatial understanding of local metabolism facilitates the identification of clinically relevant, tractable metabolic targets.

Abstract PO-042: A multimodal analysis in breast cancer: Revealing metabolic heterogeneity using DESI-MS imaging with Laser-microdissection coupled transcriptome approach

Introduction

A multi-modal analysis approach using desorption electrospray ionization (DESI-MSI) and RNA-Seq can envision a complete metabolic and genetic information from clinical specimens revealing tumour heterogeneity. Coupled with laser capture microdissection (LCM) provides a compelling opportunity for molecular sub-characterizing of the tumour tissues. The envisioned combination analysis raises special requirements, including short LCM time, to prevent RNA degradation during microdissection at room temperature. The isolated RNA must have sufficient quality and quantity to carry out RNA seq for transcriptomics.

Objectives

The aim of this study was developing a multi-modal analysis protocol obtaining metabolic clusters to get a more in-depth knowledge for tumour-heterogeneity from Patient-derived Xenografts (PDXs) and clinical specimens.

Methods

PDXs and primary tissue biopsies from patients with Breast cancer were cryosectioned at ten μm and mounted on PEN membrane glass slides, which are unique slides for LASER Capture Microdissection (LDM). The DESI imaging analysis area was obtained line-by-line using the DEFFI sprayer. The analyzed tissue sections were stained with H&E and annotated by a histopathologist to allow the alignment of optical and MSI images. Next, the areas of interest in the same slide were microdissected by Laser Capture Microdissection for LC-MS and RNA-seq (Leica LDM 7000). RNA was isolated with a commercial kit (Qiagen RNeasy Micro Kit). Finally, standardization of RNA quality control was done by the Agilent 2100 Bioanalyzer System and followed by RNA Sequencing.

Results

Preliminary results showed that the extracted samples from microdissected sections using Laser Capture Microdissected for LC-MS could be used to validate the metabolites and lipids, which already had been imaged by DESI-MSI. These DESI-MSI and LC-MS results, which obtained from specific areas on the tissue sections can be attributed to identifying metabolically different sub-clones in the adjacent tumour sections.

The next identification method for sub-cloning is a transcriptomic approach. For the transcriptomic study, the results of Agilent showed that the RNA quality of samples was sufficiently competent to carry out downstream analysis, including RNA seq. RNA seq can identify specific gene expression of the pathways, which are related to the identified metabolic profiling by DESI-MSI and LC-MS.

Conclusion:

We found that developing a multi-modal analysis protocol coupled to Laser capture microdissection is a promising approach for the identification of metabolic heterogeneity in the cancerous specimens.

Citation Format: Emine Kazanc, Evi Karali, Vincen Wu, Paolo Inglese, James McKenzie, Aurelien Tripp, Nikos Koundouros, Thanasis Tsalikis, Hiromi Kudo, George Poulogiannis, Zoltan Takats. A multimodal analysis in breast cancer: Revealing metabolic heterogeneity using DESI-MS imaging with Laser-microdissection coupled transcriptome approach [abstract]. In: Proceedings of the AACR Virtual Special Conference on Tumor Heterogeneity: From Single Cells to Clinical Impact; 2020 Sep 17-18. Philadelphia (PA): AACR; Cancer Res 2020;80(21 Suppl):Abstract nr PO-042.

Universal Sample Preparation Unlocking Multimodal Molecular Tissue Imaging

A new tissue sample embedding and processing method is presented that provides downstream compatibility with numerous different histological, molecular biology, and analytical techniques. The methodology is based on the low temperature embedding of fresh frozen specimens into a hydrogel matrix composed of hydroxypropyl methylcellulose (HPMC) and polyvinylpyrrolidone (PVP) and sectioning using a cryomicrotome. The hydrogel was expected not to interfere with standard tissue characterization methods, histologically or analytically. We assessed the compatibility of this protocol with various mass spectrometric imaging methods including matrix-assisted laser desorption ionization (MALDI), desorption electrospray ionization (DESI) and secondary ion mass spectrometry (SIMS). We also demonstrated the suitability of the universal protocol for extraction based molecular biology techniques such as rt-PCR. The integration of multiple analytical modalities through this universal sample preparation protocol offers the ability to study tissues at a systems biology level and directly linking results to tissue morphology and cellular phenotype.

Metabolic Fingerprinting Links Oncogenic PIK3CA with Enhanced Arachidonic Acid-Derived Eicosanoids

Oncogenic transformation is associated with profound changes in cellular metabolism, but whether tracking these can improve disease stratification or influence therapy decision-making is largely unknown. Using the iKnife to sample the aerosol of cauterized specimens, we demonstrate a new mode of real-time diagnosis, coupling metabolic phenotype to mutant PIK3CA genotype. Oncogenic PIK3CA results in an increase in arachidonic acid and a concomitant overproduction of eicosanoids, acting to promote cell proliferation beyond a cell-autonomous manner. Mechanistically, mutant PIK3CA drives a multimodal signaling network involving mTORC2-PKCζ-mediated activation of the calcium-dependent phospholipase A2 (cPLA2). Notably, inhibiting cPLA2 synergizes with fatty acid-free diet to restore immunogenicity and selectively reduce mutant PIK3CA-induced tumorigenicity. Besides highlighting the potential for metabolic phenotyping in stratified medicine, this study reveals an important role for activated PI3K signaling in regulating arachidonic acid metabolism, uncovering a targetable metabolic vulnerability that largely depends on dietary fat restriction. VIDEO ABSTRACT.

Reprogramming of fatty acid metabolism in cancer

A common feature of cancer cells is their ability to rewire their metabolism to sustain the production of ATP and macromolecules needed for cell growth, division and survival. In particular, the importance of altered fatty acid metabolism in cancer has received renewed interest as, aside their principal role as structural components of the membrane matrix, they are important secondary messengers, and can also serve as fuel sources for energy production. In this review, we will examine the mechanisms through which cancer cells rewire their fatty acid metabolism with a focus on four main areas of research. (1) The role of de novo synthesis and exogenous uptake in the cellular pool of fatty acids. (2) The mechanisms through which molecular heterogeneity and oncogenic signal transduction pathways, such as PI3K-AKT-mTOR signalling, regulate fatty acid metabolism. (3) The role of fatty acids as essential mediators of cancer progression and metastasis, through remodelling of the tumour microenvironment. (4) Therapeutic strategies and considerations for successfully targeting fatty acid metabolism in cancer. Further research focusing on the complex interplay between oncogenic signalling and dysregulated fatty acid metabolism holds great promise to uncover novel metabolic vulnerabilities and improve the efficacy of targeted therapies.

Metabolic adaptability in metastatic breast cancer by AKR1B10-dependent balancing of glycolysis and fatty acid oxidation

The different stages of the metastatic cascade present distinct metabolic challenges to tumour cells and an altered tumour metabolism associated with successful metastatic colonisation provides a therapeutic vulnerability in disseminated disease. We identify the aldo-keto reductase AKR1B10 as a metastasis enhancer that has little impact on primary tumour growth or dissemination but promotes effective tumour growth in secondary sites and, in human disease, is associated with an increased risk of distant metastatic relapse. AKR1B10^High tumour cells have reduced glycolytic capacity and dependency on glucose as fuel source but increased utilisation of fatty acid oxidation. Conversely, in both 3D tumour spheroid assays and in vivo metastasis assays, inhibition of fatty acid oxidation blocks AKR1B10^High-enhanced metastatic colonisation with no impact on AKR1B10^Low cells. Finally, mechanistic analysis supports a model in which AKR1B10 serves to limit the toxic side effects of oxidative stress thereby sustaining fatty acid oxidation in metabolically challenging metastatic environments.

Cancer cells must develop distinct metabolic adaptations to survive in challenging metastatic environments. Here, the authors find, via an in vivo RNAi screen, that the aldo-keto reductase AKR1B10 limits the toxic side effects of oxidative stress to sustain fatty acid oxidation and promote metastatic colonisation.

Nonsteroidal anti-inflammatory drugs and pain in cancer patients: a systematic review and reappraisal of the evidence

BACKGROUND

Emerging data highlights the potential role of cyclooxygenase (COX) inhibitors in the primary prevention of malignancy, reducing metastatic spread and improving overall mortality. Despite nonsteroidal anti-inflammatory drugs (NSAIDs) forming a key component of the WHO analgesic ladder, their use in cancer pain management remains relatively low. This review re-appraises the current evidence regarding the efficacy of COX inhibitors as analgesics in cancer pain, providing a succinct resource to aid clinicians' decision making when determining treatment strategies.

METHODS

Medline® and Embase® databases were searched for publications up to November 2018. Randomised controlled trials (RCTs) and double-blind controlled studies considering the use of NSAIDs for management of cancer-related pain in adults were included. Animal studies, case reports, and retrospective observational data were excluded.

RESULTS

Thirty studies investigating the use of NSAIDs in cancer pain management were identified. There is a lack of high-quality evidence regarding the analgesic efficacy of NSAIDs in cancer pain, with short study durations and heterogeneity in outcome measures limiting the ability to draw meaningful conclusions.

CONCLUSIONS

Despite the renewed interest in these cost-effective, well-established medications in cancer treatment outcomes, there is a paucity of data from the past 15 yr regarding their efficacy in cancer pain management. However, when analgesic strategies in the cancer population are being formulated, it is important that the potential benefits of this class of drug are considered. Further work investigating the role of NSAIDs in cancer pain management is undoubtedly warranted.

Phosphoinositide 3-Kinase/Akt Signaling and Redox Metabolism in Cancer

Metabolic rewiring and the consequent production of reactive oxygen species (ROS) are necessary to promote tumorigenesis. At the nexus of these cellular processes is the aberrant regulation of oncogenic signaling cascades such as the phosphoinositide 3-kinase and AKT (PI3K/Akt) pathway, which is one of the most frequently dysregulated pathways in cancer. In this review, we examine the regulation of ROS metabolism in the context of PI3K-driven tumors with particular emphasis on four main areas of research. (1) Stimulation of ROS production through direct modulation of mitochondrial bioenergetics, activation of NADPH oxidases (NOXs), and metabolic byproducts associated with hyperactive PI3K/Akt signaling. (2) The induction of pro-tumorigenic signaling cascades by ROS as a consequence of phosphatase and tensin homolog and receptor tyrosine phosphatase redox-dependent inactivation. (3) The mechanisms through which PI3K/Akt activation confers a selective advantage to cancer cells by maintaining redox homeostasis. (4) Opportunities for therapeutically exploiting redox metabolism in PIK3CA mutant tumors and the potential for implementing novel combinatorial therapies to suppress tumor growth and overcome drug resistance. Further research focusing on the multi-faceted interactions between PI3K/Akt signaling and ROS metabolism will undoubtedly contribute to novel insights into the extensive pro-oncogenic effects of this pathway, and the identification of exploitable vulnerabilities for the treatment of hyperactive PI3K/Akt tumors.

Erratum: Asparagine bioavailability governs metastasis in a model of breast cancer

This corrects the article DOI: 10.1038/nature25465.

Asparagine bioavailability governs metastasis in a model of breast cancer

Using a functional model of breast cancer heterogeneity, we previously showed that clonal sub-populations proficient at generating circulating tumour cells were not all equally capable of forming metastases at secondary sites. A combination of differential expression and focused in vitro and in vivo RNA interference screens revealed candidate drivers of metastasis that discriminated metastatic clones. Among these, asparagine synthetase expression in a patient's primary tumour was most strongly correlated with later metastatic relapse. Here we show that asparagine bioavailability strongly influences metastatic potential. Limiting asparagine by knockdown of asparagine synthetase, treatment with l-asparaginase, or dietary asparagine restriction reduces metastasis without affecting growth of the primary tumour, whereas increased dietary asparagine or enforced asparagine synthetase expression promotes metastatic progression. Altering asparagine availability in vitro strongly influences invasive potential, which is correlated with an effect on proteins that promote the epithelial-to-mesenchymal transition. This provides at least one potential mechanism for how the bioavailability of a single amino acid could regulate metastatic progression.

DNA Damage, Repair, and Cancer Metabolism

Although there has been a renewed interest in the field of cancer metabolism in the last decade, the link between metabolism and DNA damage/DNA repair in cancer has yet to be appreciably explored. In this review, we examine the evidence connecting DNA damage and repair mechanisms with cell metabolism through three principal links. (1) Regulation of methyl- and acetyl-group donors through different metabolic pathways can impact DNA folding and remodeling, an essential part of accurate double strand break repair. (2) Glutamine, aspartate, and other nutrients are essential for de novo nucleotide synthesis, which dictates the availability of the nucleotide pool, and thereby influences DNA repair and replication. (3) Reactive oxygen species, which can increase oxidative DNA damage and hence the load of the DNA-repair machinery, are regulated through different metabolic pathways. Interestingly, while metabolism affects DNA repair, DNA damage can also induce metabolic rewiring. Activation of the DNA damage response (DDR) triggers an increase in nucleotide synthesis and anabolic glucose metabolism, while also reducing glutamine anaplerosis. Furthermore, mutations in genes involved in the DDR and DNA repair also lead to metabolic rewiring. Links between cancer metabolism and DNA damage/DNA repair are increasingly apparent, yielding opportunities to investigate the mechanistic basis behind potential metabolic vulnerabilities of a substantial fraction of tumors.

Discovery of naturally occurring ESR1 mutations in breast cancer cell lines modelling endocrine resistance

Resistance to endocrine therapy remains a major clinical problem in breast cancer. Genetic studies highlight the potential role of estrogen receptor-α (ESR1) mutations, which show increased prevalence in the metastatic, endocrine-resistant setting. No naturally occurring ESR1 mutations have been reported in in vitro models of BC either before or after the acquisition of endocrine resistance making functional consequences difficult to study. We report the first discovery of naturally occurring ESR1 Y537C and ESR1 Y537S mutations in MCF7 and SUM44 ESR1-positive cell lines after acquisition of resistance to long-term-estrogen-deprivation (LTED) and subsequent resistance to fulvestrant (ICIR). Mutations were enriched with time, impacted on ESR1 binding to the genome and altered the ESR1 interactome. The results highlight the importance and functional consequence of these mutations and provide an important resource for studying endocrine resistance.

PARK2 loss promotes cancer progression via redox-mediated inactivation of PTEN

Cancer and Parkinson disease (PD) derive from distinct alterations in cellular processes, yet there are pathogenic mutations that are unequivocally linked to both diseases. Here we expand on our recent findings that loss of parkin RBR E3 ubiquitin protein ligase (PRKN, best known as PARK2)—which is genetically linked to PD—promotes cancer progression via redox-mediated inactivation of phosphatase and tensin homolog (PTEN) by S-nitrosylation.

PARK2 Depletion Connects Energy and Oxidative Stress to PI3K/Akt Activation via PTEN S-Nitrosylation

PARK2 is a gene implicated in disease states with opposing responses in cell fate determination, yet its contribution in pro-survival signaling is largely unknown. Here we show that PARK2 is altered in over a third of all human cancers, and its depletion results in enhanced phosphatidylinositol 3-kinase/Akt (PI3K/Akt) activation and increased vulnerability to PI3K/Akt/mTOR inhibitors. PARK2 depletion contributes to AMPK-mediated activation of endothelial nitric oxide synthase (eNOS), enhanced levels of reactive oxygen species, and a concomitant increase in oxidized nitric oxide levels, thereby promoting the inhibition of PTEN by S-nitrosylation and ubiquitination. Notably, AMPK activation alone is sufficient to induce PTEN S-nitrosylation in the absence of PARK2 depletion. Park2 loss and Pten loss also display striking cooperativity to promote tumorigenesis in vivo. Together, our findings reveal an important missing mechanism that might account for PTEN suppression in PARK2-deficient tumors, and they highlight the importance of PTEN S-nitrosylation in supporting cell survival and proliferation under conditions of energy deprivation.

Deconstructing the Metabolic Networks of Oncogenic Signaling Using Targeted Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS)

Metabolic reprogramming is recognized as an emerging hallmark of oncogenic signaling and cancer development. Hence the need to identify novel quantitative analytical platforms for studying metabolism in vitro and in vivo has dramatically increased. Here, we describe the experimental workflow for a targeted liquid chromatography-tandem mass spectrometry (LC-MS/MS) approach involving positive/negative ion switching to analyze >250 metabolites of central carbon metabolism, nucleotides, and amino acids.

Proteomics profiling of interactome dynamics by colocalisation analysis (COLA)

Localisation and protein function are intimately linked in eukaryotes, as proteins are localised to specific compartments where they come into proximity of other functionally relevant proteins. Significant co-localisation of two proteins can therefore be indicative of their functional association. We here present COLA, a proteomics based strategy coupled with a bioinformatics framework to detect protein-protein co-localisations on a global scale. COLA reveals functional interactions by matching proteins with significant similarity in their subcellular localisation signatures. The rapid nature of COLA allows mapping of interactome dynamics across different conditions or treatments with high precision.

Abstract A34: Oncogenic KRAS regulates pancreatic cancer cell signaling via stromal reciprocation

Pancreatic Ductal Adenocarcinoma is characterized by a reactive stroma, which modifies tumor progression and response to therapy. Oncogenic mutations regulate signaling both within tumor cells and adjacent stromal cells. However, defining whether oncogenes can regulate tumor cell signaling and phenotypic behavior via stromal cells is of importance to understand mechanisms of disease progression and response to therapy. Here we show that oncogenic KRAS (KRASG12D) regulates pancreatic cancer cell signaling via stromal stellate cells. By combining cell-specific proteome labeling with multivariate phosphoproteomics, we analyzed heterocellular KRASG12D signaling in Pancreatic Ductal Adenocarcinoma (PDA) cells. Tumor cell KRASG12D engages heterotypic stellate cells, which subsequently instigate reciprocal signaling in the tumor cells. Reciprocal signaling employs additional kinases and doubles the number of regulated signaling nodes from cell-autonomous KRASG12D. Consequently, reciprocal KRASG12D produces a tumor cell phosphoproteome and total proteome that is distinct from cell-autonomous KRASG12D alone. Reciprocal signaling regulates tumor cell proliferation, apoptosis, and increases mitochondrial capacity via an IGF1R/AXL-AKT axis. These results demonstrate that oncogene signaling should be viewed as a heterocellular process and that our existing cell-autonomous perspective underrepresents the extent of oncogene signaling in cancer.

Citation Format: Christopher Tape, Stephanie Ling, Maria Dimitriadi, Kelly McMahon, Jonathan Worboys, Hui S. Leong, Ida Norrie, Crispin Miller, George Poulogiannis, Douglas Lauffenburger, Claus Jorgensen.{Authors}. Oncogenic KRAS regulates pancreatic cancer cell signaling via stromal reciprocation. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr A34.

Decreased function of survival motor neuron protein impairs endocytic pathways

Spinal muscular atrophy (SMA) is caused by depletion of the ubiquitously expressed survival motor neuron (SMN) protein, with 1 in 40 Caucasians being heterozygous for a disease allele. SMN is critical for the assembly of numerous ribonucleoprotein complexes, yet it is still unclear how reduced SMN levels affect motor neuron function. Here, we examined the impact of SMN depletion in Caenorhabditis elegans and found that decreased function of the SMN ortholog SMN-1 perturbed endocytic pathways at motor neuron synapses and in other tissues. Diminished SMN-1 levels caused defects in C. elegans neuromuscular function, and smn-1 genetic interactions were consistent with an endocytic defect. Changes were observed in synaptic endocytic proteins when SMN-1 levels decreased. At the ultrastructural level, defects were observed in endosomal compartments, including significantly fewer docked synaptic vesicles. Finally, endocytosis-dependent infection by JC polyomavirus (JCPyV) was reduced in human cells with decreased SMN levels. Collectively, these results demonstrate for the first time, to our knowledge, that SMN depletion causes defects in endosomal trafficking that impair synaptic function, even in the absence of motor neuron cell death.

Oncogenic KRAS Regulates Tumor Cell Signaling via Stromal Reciprocation

Oncogenic mutations regulate signaling within both tumor cells and adjacent stromal cells. Here, we show that oncogenic KRAS (KRAS(G12D)) also regulates tumor cell signaling via stromal cells. By combining cell-specific proteome labeling with multivariate phosphoproteomics, we analyzed heterocellular KRAS(G12D) signaling in pancreatic ductal adenocarcinoma (PDA) cells. Tumor cell KRAS(G12D) engages heterotypic fibroblasts, which subsequently instigate reciprocal signaling in the tumor cells. Reciprocal signaling employs additional kinases and doubles the number of regulated signaling nodes from cell-autonomous KRAS(G12D). Consequently, reciprocal KRAS(G12D) produces a tumor cell phosphoproteome and total proteome that is distinct from cell-autonomous KRAS(G12D) alone. Reciprocal signaling regulates tumor cell proliferation and apoptosis and increases mitochondrial capacity via an IGF1R/AXL-AKT axis. These results demonstrate that oncogene signaling should be viewed as a heterocellular process and that our existing cell-autonomous perspective underrepresents the extent of oncogene signaling in cancer. VIDEO ABSTRACT.

Loss of INPP4B causes a DNA repair defect through loss of BRCA1, ATM and ATR and can be targeted with PARP inhibitor treatment

Treatment options for ovarian cancer patients remain limited and overall survival is less than 50% despite recent clinical advances. The lipid phosphatase inositol polyphosphate 4-phosphatase type II (INPP4B) has been described as a tumor suppressor in the PI3K/Akt pathway with loss of expression found most pronounced in breast, ovarian cancer and melanoma. Using microarray technology we identified a DNA repair defect in INPP4B-deficient cells, which we further characterized by comet assays and quantification of γH2AX, RAD51 and 53BP1 foci formation. INPP4B loss resulted in significantly increased sensitivity towards PARP inhibition, comparable to loss of BRCA1 in two- and three-dimensional in vitro models, as well as in in vivo xenograft models. Mechanistically, we discovered that INPP4B forms a protein complex with the key players of DNA repair, ATR and BRCA1, in GST pulldown and 293T overexpression assays, and INPP4B loss affects BRCA1, ATM and ATR protein stability resulting in the observed DNA repair defect. Given that INPP4B loss has been found in 40% of ovarian cancer patients, this study provides the rationale for establishing INPP4B as a biomarker of PARP inhibitor response, and consequently offers novel therapeutic options for a significant subset of patients. Loss of the tumor suppressor inositol polyphosphate 4-phosphatase type II (INPP4B) results in a DNA repair defect due to concomitant loss of BRCA1, ATR and ATM and can be therapeutically targeted with PARP inhibitors.

Abstract NG05: Depletion of a putatively druggable class of phosphatidylinositol kinases inhibits growth of p53 null tumors

The phosphoinositide family of lipids includes seven derivatives of phosphatidylinositol (PI) that are formed through the phosphorylation of the 3-, 4-, and 5-positions on the inositol ring. Phosphoinositides have distinct biological roles and regulate many cellular processes, including proliferation, survival, glucose uptake, and migration. Phosphoinositide kinases, phosphatases, and phospholipases spatially and temporally regulate the generation of the different phosphoinositide species, which localize to different subcellular compartments. Phosphatidylinositol-3,4,5-trisphosphate (PI-3,4,5-P3) is synthesized by phosphoinositide 3-kinase (PI3K) and serves as the plasma membrane docking site for a subset of proteins that have pleckstrin-homology (PH) domains that bind this lipid, including the serine/threonine protein kinase AKT (also known as protein kinase B or PKB). AKT is a proto-oncogene that has critical regulatory roles in insulin signaling and cancer progression. Phosphatidylinositol-4,5-bisphosphate (PI-4,5-P2) is the major substrate for Class I PI3Ks and has a significant role itself in mediating the localization of proteins to the plasma membrane and in nucleating cortical actin polymerization (1).

Until 1997 it was thought that PI-4,5-P2 was produced exclusively by phosphorylation of phosphatidylinositol-4-phosphate (PI-4-P) at the 5 position of the inositol ring, a reaction catalyzed by the Type 1 PI-4-P 5-kinases (encoded by the genes PIP5K1A, B and C). Unexpectedly, a second highly-related family of PIP kinases (called Type 2) was found to produce PI-4,5-P2 by phosphorylating the 4 position of phosphatidylinositol-5-phosphate (PI-5-P), a lipid that had been previously overlooked due to its co-migration with the much more abundant PI-4-P (2-3). The Type 2 PIP kinases are not present in yeast but are conserved in higher eukaryotes from worms and flies to mammals. Humans and mice have three distinct genes, PIP4K2A, B and C encoding enzymes called PI5P4Kα, β, and γ, respectively. The bulk of PI-4,5-P2 in most tissues is almost certainly derived from the Type 1 PIP5Ks, yet recent quantitative proteomic studies on cell lines have revealed a higher abundance of PI5P4Ks than PI4P5Ks (4). This high abundance of the Type 2 enzymes may, in part, explain why the substrate, PI-5-P is present at very low levels. While the Type 1 PIP kinases generate PI-4,5-P2 at the plasma membrane, the Type 2 kinases are located at internal membranes, including the ER, Golgi and nucleus and probably generate PI-4,5-P2 at those locations (5-8). The vast majority of PI-4,5-P2 is located at the plasma membrane and it is not clear whether the critical function of the Type 2 PIP kinases is to generate PI-4,5-P2 at intracellular sites or to maintain low levels of PI-5-P (or both).

In a previous study we generated mice in which one of the Type 2 PIP kinase genes (PIP4K2B) was deleted in the germline. These mice were viable, exhibited enhanced insulin sensitivity and enhanced insulin-dependent activation of AKT in skeletal muscle (9). Paradoxically, despite increased AKT activation the mice were smaller and had decreased adiposity on a high fat diet. Cell based assays revealed that PI5P4Kβ (encoded by PIP4K2B) becomes phosphorylated by p38 at Ser326 in response to cellular stresses, such as UV and H2O2, and that this causes inhibition of the PI5P 4-kinase activity and results in increased cellular PI-5-P levels (10). These studies suggest that the Type 2 PIP kinases mediate cellular stress responses downstream of p38 (presumably by altering the PI-5-P/PI-4,5-P2 ratio at intracellular locations) and that under conditions of low stress, these enzymes suppress the PI3K/AKT signaling pathway. It should be pointed out that the Type 2 PIP kinases are unlikely to supply PI-4,5-P2 as a substrate for PI3K since activation of AKT correlates with loss of PI5P4K activity rather than gain.

In this study we have interrogated the potential role of Type 2 PIP kinases in cancers. We found high levels of either PI5P4Kα or PI5P4Kβ enzymes or both in a number of breast cancer cell lines, and more importantly, found amplification of the PIP4K2B gene and high levels of both the PI5P4Kα and PI5P4Kβ proteins in a subset of human breast tumors. We found that knocking down the levels of both PI5P4Kα and PI5P4Kβ in a TP53 deficient breast cancer cell line blocked growth on plastic and in xenografts. This impaired growth correlated with impaired glucose metabolism and enhanced levels of reactive oxygen species (ROS) leading to senescence. The impaired glucose metabolism, despite activation of the PI3K-AKT pathway (which typically enhances glucose metabolism) was paradoxical. The results indicate that PI3K activation is not driving the ROS production, but may be an inadequate feedback attempt to restore glucose uptake and metabolism.

To assess the role of Type 2 PIP kinases in tumor formation, we generated mice with germline deletions of PIP4K2A and PIP4K2B and crossed these with TP53-/- mice and evaluated tumor formation in all the viable genotypes. We found that mice with homozygous deletion of both TP53 and PIP4K2B were not viable, indicating a synthetic lethality for loss of these two genes. Importantly, mice with the genotype PIP4K2A-/-, PIP4KB+/-, TP53-/- were viable and had a dramatic reduction in tumor formation compared to siblings that were TP53-/- and wild type for PIP4K2B and/or PIP4K2A genes. The decreased tumor incidence in the background of PIP4K2A-/-, PIP4K2B+/-, TP53-/- compared to TP53-/- alone is particularly interesting in respect to Li Fraumeni Syndrome (germline TP53 mutations). Our results indicate that expression of PI5P4Kα and/or β is critical for the growth of tumors with TP53 mutations or deletions. Thus, co-amplification of PIP4K2B with ERBB2 might explain why breast cancers in patients with Li Fraumeni syndrome show ERBB2 amplifications (HER2-positive) in over 83% of cases as opposed to 16% of age-matched patients with wild type TP53 (11).

The results that we present here suggest that PI5P4Kα and β play a critical role in mediating changes in metabolism in response to stress, and in particular ROS stress that occurs in the absence of p53. Germ-line deletion of either PIP4K2A or PIP4K2B alone resulted in mice with normal lifespans, and germ-line deletion of both PIP4K2A and PIP4K2B resulted in full-term embryos of normal size and appearance at birth, indicating that these genes do not play a major role in normal embryonic growth and development. Yet the PIP4K2A-/-, PIP4K2B-/- pups die shortly after birth, consistent with these genes having a role in mediating stress responses known to occur following birth. Importantly, germ-line deletion of both PIP4K2B and TP53 resulted in lethality while germ-line deletion of either gene alone resulted in Mendelian ratios of viable pups. Thus, the genetic studies suggest that TP53 and PIP4K2B have overlapping roles in mediating cellular responses to stress and that, while neither gene alone is essential, loss of both genes is not tolerated.

The most exciting observation from these studies in regard to potentially new therapies for p53 mutant tumors is that germ-line deletion of both alleles of PIP4K2A and one allele of PIP4K2B in the context of TP53-/- results in a viable mouse with a dramatic reduction in tumor-dependent death compared to TP53-/- mice that are wild type for PIP4K2A and B. These results (and studies of the PIP4K2A-/-, PIP4K2B+/- or PIP4K2A+/-, PIP4K2B-/- mice in the context of wild type TP53) indicate that normal tissues tolerate well the loss of three out of four alleles of the PIP4K2A and PIP4K2B genes, but that tumors are not viable in this context. PI5P4Kα and β are kinases and pharmaceutical companies have shown that it is possible to develop highly specific inhibitors of both protein kinases and lipid kinases. The synthetic lethality that we observe between TP53 loss and loss of these kinases indicates that drugs that target either the enzyme PI5P4Kβ alone or that target both PI5P4Kα and β are likely to be well-tolerated and very effective on tumors that have loss of function mutations or deletions of TP53. Our observations with BT474 cells suggest that HER2 positive tumors that have amplifications of PIP4K2B and mutations in TP53 may be particularly sensitive to PI5P4Kα,β inhibitors. The ERBB2 (Her2) amplicon on chromosome 17 is variable in size and can contain a number of cancer-related genes in addition to the ERBB2 locus. Clinically, patients who have tumors with small amplicons confined to the ERBB2 locus have the greatest benefit from ERBB2-directed therapies such as Trastuzumab, while tumors with wider ERBB2 amplicons have poor responses, suggesting co-amplification of genes that contribute to Trastuzumab resistance (11). PIP4K2B, which is located in a chromosomal region (17q12) close to ERBB2, may be a candidate for an adjacent co-amplified gene that confers Trastuzumab resistance, and, conversely, concomitant inhibition of ERBB2 and PIP4K2B could be a highly effective treatment option for ERBB2 (Her2) positive tumors that are p53-mutant and PIP4K2B-amplified.

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9. Lamia, K.A., Peroni, O.D., Kim, Y.B., Rameh, L.E., Kahn, B.B., and Cantley, L.C. Increased insulin sensitivity and reduced adiposity in phosphatidylinositol 5-phosphate 4-kinase beta-/- mice. Mol Cell Biol 2004;24:5080-5087.

10. Jones, D.R., Bultsma, Y., Keune, W.J., Halstead, J.R., Elouarrat, D., Mohammed, S., Heck, A.J., D'Santos, C.S., and Divecha, N. Nuclear PtdIns5P as a transducer of stress signaling: an in vivo role for PIP4Kbeta. Mol Cell 2006;23:685-695.

11. Morrison, L.E., Jewell, S.S., Usha, L., Blondin, B.A., Rao, R.D., Tabesh, B., Kemper, M., Batus, M., and Coon, J.S. Effects of ERBB2 amplicon size and genomic alterations of chromosomes 1, 3, and 10 on patient response to trastuzumab in metastatic breast cancer. Genes Chromosomes Cancer 2007;46:397-405.

Citation Format: Brooke M. Emerling, Jonathan B. Hurov, George Poulogiannis, Rayman Choo-Wing, Gerburg M. Wulf, Hye-Seok Shim, Katja A. Lamia, Lucia E. Rameh, Xin Yuan, Andrea Bullock, Gina M. DeNicola, Jiaxi Song, Sabina Signoretti, Lewis C. Cantley. Depletion of a putatively druggable class of phosphatidylinositol kinases inhibits growth of p53 null tumors. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr NG05. doi:10.1158/1538-7445.AM2014-NG05

Depletion of a putatively druggable class of phosphatidylinositol kinases inhibits growth of p53-null tumors

Here, we show that a subset of breast cancers express high levels of the type 2 phosphatidylinositol-5-phosphate 4-kinases α and/or β (PI5P4Kα and β) and provide evidence that these kinases are essential for growth in the absence of p53. Knocking down PI5P4Kα and β in a breast cancer cell line bearing an amplification of the gene encoding PI5P4K β and deficient for p53 impaired growth on plastic and in xenografts. This growth phenotype was accompanied by enhanced levels of reactive oxygen species (ROS) leading to senescence. Mice with homozygous deletion of both TP53 and PIP4K2B were not viable, indicating a synthetic lethality for loss of these two genes. Importantly however, PIP4K2A(-/-), PIP4K2B(+/-), and TP53(-/-) mice were viable and had a dramatic reduction in tumor formation compared to TP53(-/-) littermates. These results indicate that inhibitors of PI5P4Ks could be effective in preventing or treating cancers with mutations in TP53.

Wild-type K-ras has a tumour suppressor effect on carcinogen-induced murine colorectal adenoma formation

K-ras mutations are found in ~40% of human colorectal adenomas and carcinomas and contribute to colorectal tumour formation at an early stage. Wild-type K-ras has been reported to be deleted in some tumours, but the consequences of changes in wild-type K-ras copy number for experimental colorectal carcinogenesis have not been investigated. To characterize the effects of K-ras copy number changes on formation of carcinogen-induced colorectal neoplasms in mice, wild-type (K-ras(+/+) ) and heterozygous K-ras exon 1 knockout (K-ras(+/-) ) mice were given 10 weekly treatments of 1, 2-dimethylhydrazine (DMH) to induce colorectal tumours. Colorectal expression levels of K-ras 4A and 4B transcripts in K-ras(+/-) mice were ~50% decreased compared with K-ras(+/+) mice. One year after DMH treatment, survival of K-ras(+/-) mice decreased from 88 to 82% compared with wild-type mice. Colorectal adenomas significantly increased from 0.52 ± 0.15 in K-ras(+/+) mice to 0.87 ± 0.14 in K-ras(+/-) mice (mean ± SEM per mouse, P < 0.01); total tumour volume increased 2.13-fold (P < 0.05). Comparing K-ras(+/+) with K-ras(+/-) murine adenomas, Ki-67-positive proliferating tumour cells significantly increased from 7.77 ± 0.64% to 9.15 ± 0.92% and cleaved caspase-3-positive apoptotic tumour cells decreased from 1.40 ± 0.37% to 0.80 ± 0.22% (mean ± SEM, P < 0.05 for both). No K-ras or B-raf mutations were detected in the adenomas. Immunohistochemical studies showed no significant changes in extracellular signal regulating kinase/mitogen-activated protein kinase (Erk/MapK) or PI3K/Akt pathway activation in the adenomas. In conclusion, the data collectively show that a 50% reduction in K-ras gene dosage and RNA expression promoted experimental colorectal tumourigenesis, consistent with wild-type K-ras having a tumour suppressor effect on carcinogen-induced murine colorectal adenoma formation.

The mTORC1 pathway stimulates glutamine metabolism and cell proliferation by repressing SIRT4

Proliferating mammalian cells use glutamine as a source of nitrogen and as a key anaplerotic source to provide metabolites to the tricarboxylic acid cycle (TCA) for biosynthesis. Recently, mammalian target of rapamycin complex 1 (mTORC1) activation has been correlated with increased nutrient uptake and metabolism, but no molecular connection to glutaminolysis has been reported. Here, we show that mTORC1 promotes glutamine anaplerosis by activating glutamate dehydrogenase (GDH). This regulation requires transcriptional repression of SIRT4, the mitochondrial-localized sirtuin that inhibits GDH. Mechanistically, mTORC1 represses SIRT4 by promoting the proteasome-mediated destabilization of cAMP-responsive element binding 2 (CREB2). Thus, a relationship between mTORC1, SIRT4, and cancer is suggested by our findings. Indeed, SIRT4 expression is reduced in human cancer, and its overexpression reduces cell proliferation, transformation, and tumor development. Finally, our data indicate that targeting nutrient metabolism in energy-addicted cancers with high mTORC1 signaling may be an effective therapeutic approach.

IRS2 is a candidate driver oncogene on 13q34 in colorectal cancer

Copy number alterations are frequently found in colorectal cancer (CRC), and recurrent gains or losses are likely to correspond to regions harbouring genes that promote or impede carcinogenesis respectively. Gain of chromosome 13q is common in CRC but, because the region of gain is frequently large, identification of the driver gene(s) has hitherto proved difficult. We used array comparative genomic hybridization to analyse 124 primary CRCs, demonstrating that 13q34 is a region of gain in 35% of CRCs, with focal gains in 4% and amplification in a further 1.6% of cases. To reduce the number of potential driver genes to consider, it was necessary to refine the boundaries of the narrowest copy number changes seen in this series and hence define the minimal copy region (MCR). This was performed using molecular copy-number counting, identifying IRS2 as the only complete gene, and therefore the likely driver oncogene, within the refined MCR. Analysis of available colorectal neoplasia data sets confirmed IRS2 gene gain as a common event. Furthermore, IRS2 protein and mRNA expression in colorectal neoplasia was assessed and was positively correlated with progression from normal through adenoma to carcinoma. In functional in vitro experiments, we demonstrate that deregulated expression of IRS2 activates the oncogenic PI3 kinase pathway and increases cell adhesion, both characteristics of invasive CRC cells. Together, these data identify IRS2 as a likely driver oncogene in the prevalent 13q34 region of gain/amplification and suggest that IRS2 over-expression may provide an additional mechanism of PI3 kinase pathway activation in CRC.

Abstract 4588: Identification of CDCP1 as a HIF-2α target gene involved in the regulation of cancer cell migration and metastasis

CUB domain-containing protein 1 (CDCP1) is a transmembrane protein that is highly expressed in stem cells and frequently overexpressed and tyrosine phosphorylated in cancer. CDCP1 promotes cancer cell metastasis. However, the mechanisms that regulate CDCP1 are not well defined. Studies from our laboratory revealed a biochemical pathway by which CDCP1 participates in the activation of Src-family kinase (SFK) members and the coupling of SFK-activation to the phosphorylation and regulation of protein kinase C-delta (PKC-δ). Here we show that hypoxia induces CDCP1 expression and tyrosine phosphorylation in a HIF-2α, but not HIF-1α, dependent fashion. shRNA knockdown of CDCP1 impairs cancer cell migration under hypoxic conditions, while overexpression of HIF-2α promotes the growth of tumor xenografts in association with enhanced CDCP1 expression and tyrosine phosphorylation, as well as, significantly promotes lung metastases in NOD/SCID mice. To investigate the relationship between HIF-2α and CDCP1 expression, we performed a correlation analysis in the largest up-to-date collection (Sanger Cell Line Project) of cancer cell line microarray data (n=732). We found a dramatic concordance in the expression of HIF-2α and CDCP1 (Pearson's correlation, P &lt;1x10-20), indicating that cancers with high HIF-2α expression tend to have high levels of CDCP1 expression. We next asked whether other known HIF-2α target genes also correlate in this expression analysis. Remarkably, MET and EGFR, which are hypoxia regulated and known HIF-2α target genes, also displayed a strong correlation with HIF-2α and CDCP1 expression. Immunohistochemistry analysis of tissue microarray samples from tumors of patients with clear cell renal cell carcinoma (ccRCC) shows that increased CDCP1 expression correlates with decreased overall survival. Interestingly, high-grade ccRCCs (G3, G4) expressed significantly higher (P = 0.03, t-test) levels of CDCP1 protein compared to lower grade tumors (G1, G2), suggesting that CDCP1 expression increases progressively with higher ccRCC tumor grade. Furthermore, hypoxia activates Src signaling and the Src inhibitor (Dasatinib) prevents the hypoxia-induced phosphorylation of CDCP1. Thereby, reinforcing that CDCP1 is an SFK-associated receptor, which promotes migration and metastasis and suggests that hypoxia-induced CDCP1 signaling may further stimulate a more aggressive cancer phenotype. Together, these data support a critical role for CDCP1 as a unique HIF-2α target gene involved in the regulation of cancer metastasis, and suggest that therapeutic approaches targeting CDCP1, such as monoclonal antibodies, could be beneficial in the treatment of metastatic cancers.

Supported by NIH grant 5R01GM056203-15 to L.C.C and Dana Farber/Harvard Cancer Center Career Development Award to B.M.E.

Citation Format: Brooke M. Emerling, Cyril Benes, Eric Bell, George Poulogiannis, Kevin Courtney, Hui Lui, Rayman Choo-Wing, Gary Bellinger, Stephen Soltoff, Lewis Cantley. Identification of CDCP1 as a HIF-2α target gene involved in the regulation of cancer cell migration and metastasis. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4588. doi:10.1158/1538-7445.AM2013-4588

Loss of RASSF1A synergizes with deregulated RUNX2 signaling in tumorigenesis

The tumor suppressor gene RASSF1A is inactivated through point mutation or promoter hypermethylation in many human cancers. In this study, we conducted a Sleeping Beauty transposon-mediated insertional mutagenesis screen in Rassf1a-null mice to identify candidate genes that collaborate with loss of Rassf1a in tumorigenesis. We identified 10 genes, including the transcription factor Runx2, a transcriptional partner of Yes-associated protein (YAP1) that displays tumor suppressive activity through competing with the oncogenic TEA domain family of transcription factors (TEAD) for YAP1 association. While loss of RASSF1A promoted the formation of oncogenic YAP1-TEAD complexes, the combined loss of both RASSF1A and RUNX2 further increased YAP1-TEAD levels, showing that loss of RASSF1A, together with RUNX2, is consistent with the multistep model of tumorigenesis. Clinically, RUNX2 expression was frequently downregulated in various cancers, and reduced RUNX2 expression was associated with poor survival in patients with diffuse large B-cell or atypical Burkitt/Burkitt-like lymphomas. Interestingly, decreased expression levels of RASSF1 and RUNX2 were observed in both precursor T-cell acute lymphoblastic leukemia and colorectal cancer, further supporting the hypothesis that dual regulation of YAP1-TEAD promotes oncogenic activity. Together, our findings provide evidence that loss of RASSF1A expression switches YAP1 from a tumor suppressor to an oncogene through regulating its association with transcription factors, thereby suggesting a novel mechanism for RASSF1A-mediated tumor suppression.

Nuclear receptor binding protein 1 regulates intestinal progenitor cell homeostasis and tumour formation

Genetic screens in simple model organisms have identified many of the key components of the conserved signal transduction pathways that are oncogenic when misregulated. Here, we identify H37N21.1 as a gene that regulates vulval induction in let-60(n1046gf), a strain with a gain-of-function mutation in the Caenorhabditis elegans Ras orthologue, and show that somatic deletion of Nrbp1, the mouse orthologue of this gene, results in an intestinal progenitor cell phenotype that leads to profound changes in the proliferation and differentiation of all intestinal cell lineages. We show that Nrbp1 interacts with key components of the ubiquitination machinery and that loss of Nrbp1 in the intestine results in the accumulation of Sall4, a key mediator of stem cell fate, and of Tsc22d2. We also reveal that somatic loss of Nrbp1 results in tumourigenesis, with haematological and intestinal tumours predominating, and that nuclear receptor binding protein 1 (NRBP1) is downregulated in a range of human tumours, where low expression correlates with a poor prognosis. Thus NRBP1 is a conserved regulator of cell fate, that plays an important role in tumour suppression.

Increased tumorigenesis associated with loss of the tumor suppressor gene Cadm1

Background

CADM1 encodes an immunoglobulin superfamily (IGSF) cell adhesion molecule. Inactivation of CADM1, either by promoter hypermethylation or loss of heterozygosity, has been reported in a wide variety of tumor types, thus it has been postulated as a tumor suppressor gene.

Findings

We show for the first time that Cadm1 homozygous null mice die significantly faster than wildtype controls due to the spontaneous development of tumors at an earlier age and an increased tumor incidence of predominantly lymphomas, but also some solid tumors. Tumorigenesis was accelerated after irradiation of Cadm1 mice, with the reduced latency in tumor formation suggesting there are genes that collaborate with loss of Cadm1 in tumorigenesis. To identify these co-operating genetic events, we performed a Sleeping Beauty transposon-mediated insertional mutagenesis screen in Cadm1 mice, and identified several common insertion sites (CIS) found specifically on a Cadm1-null background (and not wildtype background).

Conclusion

We confirm that Cadm1 is indeed a bona fide tumor suppressor gene and provide new insights into genetic partners that co-operate in tumorigenesis when Cadm1-expression is lost.

Inhibition of pyruvate kinase M2 by reactive oxygen species contributes to cellular antioxidant responses

Control of intracellular reactive oxygen species (ROS) concentrations is critical for cancer cell survival. We show that, in human lung cancer cells, acute increases in intracellular concentrations of ROS caused inhibition of the glycolytic enzyme pyruvate kinase M2 (PKM2) through oxidation of Cys(358). This inhibition of PKM2 is required to divert glucose flux into the pentose phosphate pathway and thereby generate sufficient reducing potential for detoxification of ROS. Lung cancer cells in which endogenous PKM2 was replaced with the Cys(358) to Ser(358) oxidation-resistant mutant exhibited increased sensitivity to oxidative stress and impaired tumor formation in a xenograft model. Besides promoting metabolic changes required for proliferation, the regulatory properties of PKM2 may confer an additional advantage to cancer cells by allowing them to withstand oxidative stress.

Phosphoproteomic analysis identifies Grb10 as an mTORC1 substrate that negatively regulates insulin signaling

The evolutionarily conserved serine-threonine kinase mammalian target of rapamycin (mTOR) plays a critical role in regulating many pathophysiological processes. Functional characterization of the mTOR signaling pathways, however, has been hampered by the paucity of known substrates. We used large-scale quantitative phosphoproteomics experiments to define the signaling networks downstream of mTORC1 and mTORC2. Characterization of one mTORC1 substrate, the growth factor receptor-bound protein 10 (Grb10), showed that mTORC1-mediated phosphorylation stabilized Grb10, leading to feedback inhibition of the phosphatidylinositol 3-kinase (PI3K) and extracellular signal-regulated, mitogen-activated protein kinase (ERK-MAPK) pathways. Grb10 expression is frequently down-regulated in various cancers, and loss of Grb10 and loss of the well-established tumor suppressor phosphatase PTEN appear to be mutually exclusive events, suggesting that Grb10 might be a tumor suppressor regulated by mTORC1.

Synergism between K-rasVal12 and mutant Apc accelerates murine large intestinal tumourigenesis

K-ras (KRAS) is mutated in 40-50% of human colorectal adenomas and carcinomas and plays key roles in cell proliferation, apoptosis, motility and differentiation, but its functional contribution to intestinal tumourigenesis in vivo remains incompletely understood. We have previously crossed K-rasVal12 transgenic mice with Ah-Cre mice to produce K-rasVal12/Cre offspring that inducibly express K-rasVal12 4A and 4B in the intestines, but this alone showed no significant effect on intestinal adenoma formation. Here, we crossed these mice with Min mice to evaluate the effect of K-rasVal12 and Apc mutation on intestinal tumourigenesis in vivo. The double mutant K-rasVal12/Cre/ApcMin/+ mice showed a moderate (1.86-fold) increase in adenomas in the small intestines, but a striking acceleration (6-fold increase) of large intestinal adenoma formation (P<0.01) and significantly reduced survival (by ~5 weeks) compared with control ApcMin/+ mice (P<0.01). There was recombination of the mutant K-rasVal12 transgene in 80% of large intestinal adenomas with expression of both K-rasVal12 4A and 4B isoform transcripts and expression of K-RasVal12 protein. The large intestinal adenomas showed immunohistochemical evidence of activation of MapK, Akt and Wnt signaling pathways and this was confirmed by quantitative RT-PCR analysis of relative transcript expression levels of target genes using a panel of 23 selected genes evaluated in both adenomas and non-tumour-bearing intestines. Several genes including Tiam1, Gastrin, CD44, uPA, Igfbp4, VEGF and Cox-2 that are known to be transcriptionally regulated by activation of the Wnt signaling pathway were found to be expressed at higher levels in the large intestinal adenomas from K-rasVal12/Cre/ApcMin/+ mice compared with those from controls, although other Wnt signaling pathway target genes remained unchanged. These data show that intestinal expression of K-rasVal12 accelerates Apc-initiated intestinal adenomagenesis in vivo with particularly striking tumour promotion in the large intestines and indicate synergistic effects between mutant K-ras and mutant Apc in this process.

Mutant K-ras promotes carcinogen-induced murine colorectal tumourigenesis, but does not alter tumour chromosome stability

K-ras (KRAS) mutations are observed in around 40% of human colorectal adenomas and carcinomas. Previously, we developed and characterized a strain of transgenic mice with inducible intestinal epithelial expression of K-ras{Val12} via a Cre/LoxP system. To evaluate the influence of mutant K-ras on carcinogen-induced colorectal tumourigenesis, we induced neoplastic alterations in the large intestines of wild-type and K-ras{Val12} mice using the colon-selective carcinogen 1,2-dimethylhydrazine (DMH), which has been widely used to induce colorectal tumours that are histopathologically similar to those observed in humans. K-ras{Val12} expression significantly promoted DMH-induced colorectal tumourigenesis: the average lifespan of the mice decreased from 38.52 ± 1.97 weeks for 40 control mice to 32.42 ± 2.17 weeks for 26 K-ras{Val12} mice (mean ± SEM, p < 0.05) and the abundance of large intestinal tumours increased from 2.27 ± 0.15 per control mouse to 3.85 ± 0.20 in K-ras{Val12} mice (mean ± SEM, p < 0.01). Adenomas from DMH-treated K-ras{Val12} mice showed significantly higher proportions of Ki-67-positive proliferating cells (10.9 ± 0.69%) compared with those from DMH-treated wild-type mice (7.77 ± 0.47%) (mean ± SEM, p < 0.01) and a mild increase in apoptotic nuclei staining for cleaved caspase-3 (1.94 ± 0.21% compared with 1.15 ± 0.14%, mean ± SEM, p < 0.01). In the adenomas from DMH-treated K-ras{Val12} mice, K-ras{Val12} transgene recombination and expression were confirmed, with immunohistochemical evidence of strong Erk/MapK and mild PI3K/Akt pathway activation compared with adenomas from DMH-treated wild-type mice. Microarray hybridization and clustering analysis demonstrated different expression profiles in adenomas from DMH-treated wild-type and DMH-treated K-ras{Val12} mice, indicating involvement of different molecular mechanisms including Erk/MapK and PI3K/Akt signalling in K-ras{Val12}-expressing adenomas. Array-comparative genomic hybridization analysis showed chromosome stability in both cohorts, with only a very few tiny alterations observed in one adenoma from a DMH-treated K-ras{Val12} mouse. Taken together, these data show that mutant K-ras significantly promotes DMH-induced colorectal tumourigenesis, resulting in distinct changes in cell signalling and proliferation, but does not alter chromosome stability in the tumours.

DNA mismatch repair deficiency in sporadic colorectal cancer and Lynch syndrome

DNA mismatch repair (MMR) deficiency is one of the best understood forms of genetic instability in colorectal cancer (CRC), and is characterized by the loss of function of the MMR pathway. Failure to repair replication-associated errors due to a defective MMR system allows persistence of mismatch mutations all over the genome, but especially in regions of repetitive DNA known as microsatellites, giving rise to the phenomenon of microsatellite instability (MSI). A high frequency of instability at microsatellites (MSI-H) is the hallmark of the most common form of hereditary susceptibility to CRC, known as Lynch syndrome (LS) (previously known as hereditary non-polyposis colorectal cancer syndrome), but is also observed in approximately 15-20% of sporadic colonic cancers (and rarely in rectal cancers). Tumour analysis by both MMR protein immunohistochemistry and DNA testing for MSI is necessary to provide a comprehensive picture of molecular abnormality, for use in conjunction with family history data and other clinicopathological features, in order to distinguish LS from sporadic MMR-deficient CRC. Identification of the gene targets that become mutated in MMR-deficient tumours may explain, at least in part, some of the clinical, pathological and biological features of MSI-H CRCs and holds promise for developing novel therapeutics.

K-ras exon 4A has a tumour suppressor effect on carcinogen-induced murine colonic adenoma formation

K-ras encodes two isoforms, K-ras 4A and 4B, that are jointly affected by K-ras activating mutations, which are prevalent in colorectal cancer (CRC). CRC shows alterations in the expressed K-ras 4A : 4B isoform ratio in favour of K-ras 4B, in tumours both with and without K-ras mutations. The present study evaluated whether K-ras 4A expression can suppress colonic adenoma development in the absence of its oncogenic allele. Mice with homozygous targeted deletions of K-ras exon 4A (K-ras(tmDelta4A/tmDelta4A)) that can express the K-ras 4B isoform only, along with heterozygous K-ras(tmDelta4A/+) and wild-type mice, were given ten weekly 1,2-dimethylhydrazine (DMH) treatments to induce colonic adenomas. There was a significant increase in both the number and the size of colonic adenomas in DMH-treated K-ras(tmDelta4A/tmDelta4A) mice, with reduced survival, compared with heterozygous and wild-type mice. No K-ras mutations were found in any of the 30 tumours tested from the three groups. Lack of expression of K-ras 4A transcripts was confirmed, whereas the relative expression levels of K-ras 4B transcripts were significantly increased in the adenomas of K-ras(tmDelta4A/tmDelta4A) mice compared with K-ras(tmDelta4A/+) and wild-type mice. Immunohistochemical studies showed that adenomas of K-ras(tmDelta4A/tmDelta4A) mice had significantly increased cell proliferation and significantly decreased apoptosis with evidence of activation of MapKinase and Akt pathways, with increased phospho-Erk1/2 and both phospho-Akt-Thr308 and phospho-Akt-Ser473 immunostaining, compared with adenomas from K-ras(tmDelta4A/+) and wild-type mice. In conclusion, following DMH treatment, K-ras exon 4A deletion promoted increased number and size of colonic adenomas showing increased K-ras 4B expression, increased proliferation, decreased apoptosis, and activation of MapKinase and Akt pathways, in the absence of K-ras mutations. Therefore, K-ras 4A expression had a tumour suppressor effect on carcinogen-induced murine colonic adenoma formation, explaining the selective advantage of the altered K-ras 4A : 4B isoform ratio found in human colorectal cancer.

Prognostic relevance of DNA copy number changes in colorectal cancer

In a study of 109 colorectal cancers, DNA copy number aberrations were identified by comparative genomic hybridization using a DNA microarray covering the entire genome at an average interval of less than 1 Mbase. Four patterns were revealed by unsupervised clustering analysis, one of them associated with significantly better prognosis than the others. This group contained tumours with short, dispersed, and relatively few regions of copy number gain or loss. The good prognosis of this group was not attributable to the presence of tumours showing microsatellite instability (MSI-H). Supervised methods were employed to determine those genomic regions where copy number alterations correlate significantly with multiple indices of aggressive growth (lymphatic spread, recurrence, and early death). Multivariate analysis identified DNA copy number loss at 18q12.2, harbouring a single gene, BRUNOL4 that encodes the Bruno-like 4 splicing factor, as an independent prognostic indicator. The data show that the different patterns of DNA copy number alterations in primary tumours reveal prognostic information and can aid identification of novel prognosis-associated genes.

Mutated K-ras(Asp12) promotes tumourigenesis in Apc(Min) mice more in the large than the small intestines, with synergistic effects between K-ras and Wnt pathways

Summary K-ras mutations are found in 40-50% of human colorectal adenomas and carcinomas, but their functional contribution remains incompletely understood. Here, we show that a conditional mutant K-ras mouse model (K-ras(Asp12)/Cre), with transient intestinal Cre activation by beta-Naphthoflavone (beta-NF) treatment, displayed transgene recombination and K-ras(Asp12) expression in the murine intestines, but developed few intestinal adenomas over 2 years. However, when crossed with Apc(Min/+) mice, the K-ras(Asp12)/Cre/Apc(Min/+) offspring showed acceleration of intestinal tumourigenesis with significantly changed average lifespan (P < 0.05) decreased to 18.4 +/- 5.4 weeks from 20.9 +/- 4.7 weeks (control Apc(Min/+) mice). The numbers of adenomas in the small intestine and large intestine were significantly (P < 0.01) increased by 1.5-fold and 5.7-fold, respectively, in K-ras(Asp12)/Cre/Apc(Min/+) mice compared with Apc(Min/+) mice, with the more marked increase in adenoma prevalence in the large intestine. To explore possible mechanisms for K-ras(Asp12) and Apc(Min) co-operation, the Mitogen-activated protein kinase (Mapk), Akt and Wnt signalling pathways, including selected target gene expression levels, were evaluated in normal large intestine and large intestinal tumours. K-ras(Asp12) increased activation of Mapk and Akt signalling pathway targets phospho-extracellular signal-regulated kinase (pErk) and pAkt, and increased relative expression levels of Wnt pathway targets vascular endothelial growth factor (VEGF), gastrin, cyclo-oxygenase 2 (Cox2) and T-cell lymphoma invasion and metastasis 1 (Tiam1) in K-ras(Asp12)/Cre/Apc(Min/+) adenomas compared with that of Apc(Min/+) adenomas, although other Wnt signalling pathway target genes such as Peroxisome proliferator-activated receptor delta (PPARd), matrix metalloproteinase 7 (MMP7), protein phosphatase 1 alpha (PP1A) and c-myc remained unchanged. In conclusion, intestinal expression of K-ras(Asp12) promotes mutant Apc-initiated intestinal adenoma formation in vivo more in the large intestine than the small intestine, with evidence of synergistic co-operation between mutant K-ras and Apc involving increased expression of some Wnt-pathway target genes.

Conditional expression of mutated K-ras accelerates intestinal tumorigenesis in Msh2-deficient mice

K-ras mutation occurs in 40-50% of human colorectal adenomas and carcinomas, but its contribution to intestinal tumorigenesis in vivo is unclear. We developed K-ras(V12) transgenic mice that were crossed with Ah-Cre mice to generate K-ras(V12)/Cre mice, which showed beta-naphthoflavone-induction of Cre-mediated LoxP recombination that activated intestinal expression of K-ras(V12) 4A and 4B transcripts and proteins. Only very occasional intestinal adenomas were observed in beta-naphthoflavone-treated K-ras(V12)/Cre mice aged up to 2 years, suggesting that mutated K-ras expression alone does not significantly initiate intestinal tumourigenesis. To investigate the effects of mutated K-ras on DNA mismatch repair (MMR)-deficient intestinal tumour formation, these mice were crossed with Msh2(-/-) mice to generate K-ras(V12)/Cre/Msh2(-/-) offspring. After beta-naphthoflavone treatment, K-ras(V12)/Cre/Msh2(-/-) mice showed reduced average lifespan of 17.3+/-5.0 weeks from 26.9+/-6.8 (control Msh2(-/-) mice) (P<0.01). They demonstrated increased adenomas in the small intestine from 1.41 (Msh2(-/-) controls) to 7.75 per mouse (increased fivefold, P<0.01). In the large intestine, very few adenomas were found in Msh2(-/-) mice (0.13 per mouse) whereas K-ras(V12)/Cre/Msh2(-/-) mice produced 2.70 adenomas per mouse (increased 20-fold, P<0.01). Over 80% adenomas from K-ras(V12)/Cre/Msh2(-/-) mice showed transgene recombination with expression of K-ras(V12) 4A and 4B transcripts and proteins. Sequencing of endogenous murine K-ras showed mutations in two out of 10 tumours examined from Msh2(-/-) mice, but no mutations in 17 tumours from K-ras(V12)/Cre/Msh2(-/-) mice. Expression of K-ras(V12) in tumours caused activation of the mitogen-activated protein kinase and Akt/protein kinase B signaling pathways, demonstrated by phosphorylation of p44MAPK, Akt and GSK3beta, as well as transcriptional upregulation of Pem, Tcl-1 and Trap1a genes (known targets of K-ras(V12) expression in stem cells). Thus, mutated K-ras cooperates synergistically with MMR deficiency to accelerate intestinal tumorigenesis, particularly in the large intestine.