Wild-type Adenomatous Polyposis Coli Research Articles

Statin Treatment as a Targeted Therapy for APC-Mutated Colorectal Cancer.

BackgroundMutations in the tumor suppressor gene Adenomatous Polyposis Coli (APC) are found in 80% of sporadic colorectal cancer (CRC) tumors and are also responsible for the inherited form of CRC, Familial adenomatous polyposis (FAP).MethodsTo identify novel therapeutic strategies for the treatment of APC mutated CRC, we generated a drug screening platform that incorporates a human cellular model of APC mutant CRC using CRISPR-cas9 gene editing and performed an FDA-approved drug screen targeting over 1000 compounds.ResultsWe have identified the group of HMG-CoA Reductase (HMGCR) inhibitors known as statins, which cause a significantly greater loss in cell viability in the APC mutated cell lines and in in vivo APC mutated patient derived xenograft (PDX) models, compared to wild-type APC cells. Mechanistically, our data reveals this new synthetic lethal relationship is a consequence of decreased Wnt signalling and, ultimately, a reduction in the level of expression of the anti-apoptotic protein Survivin, upon statin treatment in the APC-mutant cells only. This mechanism acts via a Rac1 mediated control of beta-catenin.ConclusionSignificantly, we have identified a novel synthetic lethal dependence between APC mutations and statin treatment, which could potentially be exploited for the treatment of APC mutated cancers.

Predicting Agents That Can Overcome 5-FU Resistance in Colorectal Cancers via Pharmacogenomic Analysis.

5-Fluorouracil (5-FU) is one of several chemotherapeutic agents in clinical use as a standard of care to treat colorectal cancers (CRCs). As an antimetabolite, 5-FU inhibits thymidylate synthase to disrupt the synthesis and repair of DNA and RNA. However, only a small proportion of patients benefit from 5-FU treatment due to the development of drug resistance. This study applied pharmacogenomic analysis using two public resources, the Genomics of Drug Sensitivity in Cancer (GDSC) and the Connectivity Map, to predict agents overcoming 5-FU resistance in CRC cells based on their genetic background or gene expression profile. Based on the genetic status of adenomatous polyposis coli (APC), the most frequent mutated gene found in CRC, we found that combining a MEK inhibitor with 5-FU exhibited synergism effects on CRC cells with APC truncations. While considering the gene expression in 5-FU resistant cells, we demonstrated that targeting ROCK is a potential avenue to restore 5-FU response to resistant cells with wild-type APC background. Our results reveal MEK signaling plays a pivotal role in loss-of-function, APC-mediated 5-FU resistance, and ROCK activation serves as a signature in APC-independent 5-FU resistance. Through the use of these available database resources, we highlight possible approaches to predict potential drugs for combinatorial therapy for patients developing resistance to 5-FU treatment.

ELEVATED ADENOMATOUS POLYPOSIS COLI IN GOBLET CELLS IS ASSOCIATED WITH INFLAMMATION IN MOUSE AND HUMAN COLON

Adenomatous Polyposis Coli (APC) functions as an essential colon tumor suppressor. Roles for APC in other disease states such as Inflammatory Bowel Disease (IBD) remain less defined. In the process of characterizing Apc protein in gastrointestinal tissues from human patients with active IBD, we found a subset of goblet cells with elevated Apc staining intensity. While normal colon tissue was only sparsely populated with these “APChigh” goblet cells, tissue from patients with Ulcerative Colitis and Crohn’s Disease contained entire regions where almost every goblet cell was APChigh. In the descending colon, the APChigh goblet cells were prominent in patients with active Ulcerative Colitis but were mostly lacking in normal samples. In mice, APChigh cells were observed only in the small intestines and proximal/medial colons. Upon induction of colitis with Dextran Sodium Sulfate (DSS), the APChigh goblet cells remained in the proximal and medial colon, but also appeared in the distal colon. To better understand the link between APC expression, goblet cells, and inflammation, cultured human colon cells derived from normal tissue were depleted of APC and RNAseq analysis was performed. APC depletion resulted in reduced expression of mRNAs encoding IL1 signaling pathway components IL1b and IL1R, known regulators of Muc2 expression. Muc2 is the main constituent of goblet cell mucus, which is secreted to form a protective barrier for the epithelial cells lining the large intestine. We found that treating cancer cells lacking wild-type APC with IL1b resulted in increased IL1R and MUC2 expression. Induction of full-length APC in these cells led to a similar phenotype. Combining IL1β treatment with APC induction led to an increase of MUC2 expression greater than expected for additive affects, suggesting that APC sensitized these cells to IL1 signaling. These results illuminate a novel role for APC in goblet cells under conditions of inflammation. We postulate that the higher amount of APC in a subset of goblet cells might sensitize them to IL-1 signaling. During times of inflammation, such as active Ulcerative Colitis, goblet cells with higher APC levels would be more sensitive to IL-1-induced MUC2 expression than other goblet cells, perhaps protecting the intestinal lining from further barrier breaches.

APC regulation of ESRP1 and p120-catenin isoforms in colorectal cancer cells.

The adenomatous polyposis coli (APC) tumor suppressor protein is associated with the regulation of Wnt signaling; however, APC also controls other cellular processes including the regulation of cell adhesion and migration. The expression of full-length APC in SW480 colorectal cancer cells (SW480+APC) not only reduces Wnt signaling, but increases membrane E-cadherin and restores cell–cell adhesion. This report describes the effects of full-length, wild-type APC (fl-APC) on cell–cell adhesion genes and p120-catenin isoform switching in SW480 colon cancer cells: fl-APC increased the expression of genes implicated in cell–cell adhesion, whereas the expression of negative regulators of E-cadherin was decreased. Analysis of cell–cell adhesion-related proteins in SW480+APC cells revealed an increase in p120-catenin isoform 3A; similarly, depletion of APC altered the p120-catenin protein isoform profile. Expression of ESRP1 (epithelial splice regulatory protein 1) is increased in SW480+APC cells, and its depletion results in reversion to the p120-catenin isoform 1A phenotype and reduced cell–cell adhesion. The ESRP1 transcript is reduced in primary colorectal cancer, and its expression correlates with the level of APC. Pyrvinium pamoate, which inhibits Wnt signaling, promotes ESRP1 expression. We conclude that re-expression of APC restores the cell–cell adhesion gene and posttranscriptional regulatory programs leading to p120-catenin isoform switching and associated changes in cell–cell adhesion.

Elevated adenomatous polyposis coli in goblet cells is associated with inflammation in mouse and human colon.

What is the central question of this study? What is the localization and distribution pattern of adenomatous polyposis coli (APC) in intestinal epithelial cells? Does this distribution change in different regions of the colon or in the condition of inflammation? What is the main finding and its importance? Colonic epithelia from mice and humans contain a subset of goblet cells displaying high APC levels. The number of APChigh goblet cells increases in inflamed tissue, which also displays increased GRP78, indicating potential stress from mucin production. In cultured human colon cells, expression of interleukin 1 pathway components (inducers of MUC2 expression) is reduced upon APC depletion raising the potential for APC participation in an inflammatory response. Adenomatous polyposis coli (APC) serves as a gatekeeper of intestinal homeostasis by promoting cellular differentiation and maintaining crypt architecture. Although appreciated as a critical colon tumour suppressor, roles for APC in disease states such as inflammation have yet to be fully delineated. This study aimed to characterize the localization of APC protein in gastrointestinal tissues from human patients with active inflammatory bowel disease and mice with dextran sodium sulfate (DSS)-induced colitis. Fluorescence immunohistochemistry revealed a subset of goblet cells with elevated Apc staining intensity in the small intestines and proximal/medial colons of mice. Upon induction of colitis with DSS, these 'APChigh ' goblet cells remained in the proximal and medial colon, but now were also observed in the distal colon. This phenotype was recapitulated in humans, with APChigh goblet cells observed only in the descending colons of patients with active ulcerative colitis. In cultured human colon cells derived from normal tissue, APC depletion reduced expression of mRNAs encoding the interleukin 1 (IL1) signalling pathway components IL1β and interleukin-1 receptor (IL1R), known regulators of Muc2 expression. Treating cancer cells lacking wild-type APC with IL1β, or induction of full-length APC in these cells led to increases in IL1R and MUC2 expression. Combining IL1β treatment with APC induction led to an increase of MUC2 expression greater than expected for additive affects, suggesting that APC sensitizes cells to IL1 signalling. These findings suggest that APC has novel roles in maintaining proper goblet cell function, thus providing further evidence for APC as an important factor in intestinal tissue homeostasis and disease.

Adenomatous Polyposis Coli as a Major Regulator of Human Embryonic Stem Cells Self-Renewal.

Human embryonic stem cells (hESCs) provide an essential tool to investigate early human development, study disease pathogenesis, and examine therapeutic interventions. Adenomatous polyposis coli (APC) is a negative regulator of Wnt/β-catenin signaling, implicated in the majority of sporadic colorectal cancers and in the autosomal dominant inherited syndrome familial adenomatous polyposis (FAP). Studies into the role of Wnt/β-catenin signaling in hESCs arrived at conflicting results, due at least in part to variations in culture conditions and the use of external inhibitors and agonists. Here, we directly targeted APC in hESCs carrying a germline APC mutation, derived from affected blastocysts following preimplantation genetic diagnosis (PGD) for FAP, in order to answer open questions regarding the role of APC in regulating pluripotency and differentiation potential of hESCs. Using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated protein 9 (Cas9), we generated second hit APC mutations in FAP-hESCs. Despite high CRISPR/Cas9 targeting efficiency and the successful isolation of many clones, none of the isolated clones carried a loss of function mutation in the wild-type (WT) APC allele. Using a fluorescent β-catenin reporter and analysis of mutated-allele frequencies in the APC locus, we show that APC double mutant hESCs robustly activate Wnt/β-catenin signaling that results in rapid differentiation to endodermal and mesodermal lineages. Here, we provide direct evidence for a strict requirement for constant β-catenin degradation through the APC destruction complex in order to maintain pluripotency, highlighting a fundamental role for APC in self-renewal of hESCs. Stem Cells 2019;37:1505-1515.

Phase II study of nab-paclitaxel in refractory small bowel adenocarcinoma and CpG island methylator phenotype (CIMP)-high colorectal cancer

Hypermethylation of promoter CpG islands [CpG island methylator phenotype (CIMP)] represents a unique pathway for the development of colorectal cancer (CRC), characterized by lack of chromosomal instability and a low rate of adenomatous polyposis coli (APC) mutations, which have both been correlated with taxane resistance. Similarly, small bowel adenocarcinoma (SBA), a rare tumor, also has a low rate of APC mutations. This phase II study evaluated taxane sensitivity in SBA and CIMP-high CRC. The primary objective was Response Evaluation Criteria in Solid Tumors version 1.1 response rate. Eligibility included Eastern Cooperative Oncology Group performance status 0/1, refractory disease, and SBA or CIMP-high metastatic CRC. Nab-paclitaxel was initially administered at a dose of 260 mg/m2 every 3 weeks but was reduced to 220 mg/m2 owing to toxicity. A total of 21 patients with CIMP-high CRC and 13 with SBA were enrolled from November 2012 to October 2014. The efficacy-assessable population (patients who received at least three doses of the treatment) comprised 15 CIMP-high CRC patients and 10 SBA patients. Common grade 3 or 4 toxicities were fatigue (12%), neutropenia (9%), febrile neutropenia (9%), dehydration (6%), and thrombocytopenia (6%). No responses were seen in the CIMP-high CRC cohort and two partial responses were seen in the SBA cohort. Median progression-free survival was significantly greater in the SBA cohort than in the CIMP-high CRC cohort (3.2 months compared with 2.1 months, P = 0.03). Neither APC mutation status nor CHFR methylation status correlated with efficacy in the CIMP-high CRC cohort. In vivo testing of paclitaxel in an SBA patient-derived xenograft validated the activity of taxanes in this disease type. Although preclinical studies suggested taxane sensitivity was associated with chromosomal stability and wild-type APC, we found that nab-paclitaxel was inactive in CIMP-high metastatic CRC. Nab-paclitaxel may represent a novel therapeutic option for SBA.

Abstract A31: Targeting APC loss using synthetic lethality in Colorectal Cancer

Abstract Background: Mutations in the tumor suppressor gene Adenomatous Polyposis Coli (APC) are found in 80% of sporadic colorectal cancer (CRC) tumors and are also responsible for the inherited form of CRC, Familial Adenomatous Polyposis (FAP). APC mutations typically occur early in the development of CRC, followed by mutations in KRAS, SMAD2/3/4 and TP53. The majority of mutations in APC occur in a region known as the mutation cluster region (MCR). This region is responsible for negatively regulating levels of B-catenin and therefore the level of Wnt signaling activation. In APC mutated tumors, B-catenin is not tightly regulated resulting in hyperactivation of the Wnt signaling pathway leading to uncontrolled cellular proliferation, differentiation, migration and apoptosis. Aim: We aim to use the concept of synthetic lethality to identify novel therapeutic targets for the treatment of APC mutated CRC. Results: In order to identify novel therapeutic targets for the treatment of APC mutated CRC, we have generated an in vitro model of APC mutant CRC using a lentiviral CRISPR-cas9 system. Using the APC wildtype colorectal carcinoma cell line RKO, we targeted the cells with a guide RNA targeting the start of the final exon of APC, which covers 80% of the coding region. These cell lines allow us to identify targets, which are synthetically lethal with the APC mutation. To identify novel potential drug targets, we have used two parallel screening approaches. Firstly, we have screened our cell lines with a library of siRNA silencing over 700 kinases. Typically kinases are easy to target pharmaceutically, with many kinase inhibitors already clinically available. Upon analysis, we have identified seven genes which show synthetic lethality with the APC mutation, whilst not harming the control wildtype APC cells. In parallel, we have screened over 1000 FDA-approved compounds to identify drugs which cause increased selective lethality in APC mutant cells. From screening our FDA-approved compounds, we have identified a number of compounds which display synthetic lethality with the APC mutation. Conclusions: We have identified seven genes as potential therapeutic targets and a number of FDA-approved compounds, which could potentially be new selective therapies for 80% of CRC patients. Currently we are validating these findings and investigating the mechanism of synthetic lethality with APC mutation. To further validate our findings we are also exploring whether these results extend to other CRC cell lines with different mutational backgrounds, this will help us access how many patients may benefit from our novel therapeutic targets. Acknowledgments: We would like to thank Bowel and Cancer Research and The Rosetree Trust for co-funding this project. Citation Format: Hannah Shailes, Gemma Bridge, Daniel Foxler, Tyson V. Sharp, Andrew Silver, Sarah A. Martin. Targeting APC loss using synthetic lethality in Colorectal Cancer [abstract]. In: Proceedings of the AACR Precision Medicine Series: Opportunities and Challenges of Exploiting Synthetic Lethality in Cancer; Jan 4-7, 2017; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2017;16(10 Suppl):Abstract nr A31.

Adenomatous polyposis coli nucleates actin assembly to drive cell migration and microtubule-induced focal adhesion turnover.

Cell motility depends on tight coordination between the microtubule (MT) and actin cytoskeletons, but the mechanisms underlying this MT-actin cross talk have remained poorly understood. Here, we show that the tumor suppressor protein adenomatous polyposis coli (APC), which is a known MT-associated protein, directly nucleates actin assembly to promote directed cell migration. By changing only two residues in APC, we generated a separation-of-function mutant, APC (m4), that abolishes actin nucleation activity without affecting MT interactions. Expression of full-length APC carrying the m4 mutation (APC (m4)) rescued cellular defects in MT organization, MT dynamics, and mitochondrial distribution caused by depletion of endogenous APC but failed to restore cell migration. Wild-type APC and APC (m4) localized to focal adhesions (FAs), and APC (m4) was defective in promoting actin assembly at FAs to facilitate MT-induced FA turnover. These results provide the first direct evidence for APC-mediated actin assembly in vivo and establish a role for APC in coordinating MTs and actin at FAs to direct cell migration.

Novel APC gene mutations associated with protein alteration in diffuse type gastric cancer

BackgroundThe role of adenomatous polyposis coli (APC) gene in mitosis might be critical for regulation of genomic stability and chromosome segregation. APC gene mutations have been associated to have a role in colon cancer and since gastric and colon tumors share some common genetic lesions, it is relevant to investigate the role of APC tumor suppressor gene in gastric cancer.MethodsWe investigated for somatic mutations in the Exons 14 and 15 of APC gene from 40 diffuse type gastric cancersamples. Rabbit polyclonal anti-APC antibody was used, which detects the wild-type APC protein and was recommended for detection of the respective protein in human tissues. Cell cycle analysis was done from tumor and adjacent normal tissue.ResultsAPC immunoreactivity showed positive expression of the protein in stages I, II, III and negative expression in Stages III and IV. Two novel deleterious variations (g.127576C > A, g.127583C > T) in exon 14 sequence were found to generate stop codon (Y622* and Q625*)in the tumor samples. Due to the generation of stop codon, the APC protein might be truncated and all the regulatory features could be lost which has led to the down-regulation of protein expression. Our results indicate that aneuploidy might occurdue to the codon 622 and 625 APC-driven gastric tumorigenesis, in agreement with our cell cycle analysis. The APC gene function in mitosis and chromosomal stability might be lost and G1 might be arrested with high quantity of DNA in the S phase. Six missense somatic mutations in tumor samples were detected in exon 15 A-B, twoof which showed pathological and disease causing effects based on SIFT, Polyphen2 and SNPs & GO score and were not previously reported in the literature or the public mutation databases.ConclusionThe two novel pathological somatic mutations (g.127576C > A, g.127583C > T) in exon 14 might be altering the protein expression leading to development of gastric cancer in the study population. Our study showed that mutations in the APC gene alter the protein expression and cell cycle regulation in diffuse type gastric adenocarcinoma.

Genetic analysis of intestinal polyp development in Collaborative Cross mice carrying the Apc (Min/+) mutation.

BackgroundColorectal cancer is an abnormal tissue development in the colon or rectum. Most of CRCs develop due to somatic mutations, while only a small proportion is caused by inherited mutations. Familial adenomatous polyposis is an inherited genetic disease, which is characterized by colorectal polyps. It is caused by inactivating mutations in the Adenomatous polyposis coli gene. Mice carrying and non-sense mutation in Adenomatous polyposis coli gene at site R850, which designated ApcR850X/+ (Min), develop intestinal adenomas, while the bulk of the disease is in the small intestine. A number of genetic modifier loci of Min have been mapped, but so far most of the underlying genes have not been identified. In our previous studies, we have shown that Collaborative Cross mice are a powerful tool for mapping loci responsible for phenotypic variation. As a first step towards identification of novel modifiers of Min, we assessed the phenotypic variation between 27 F1 crosses between different Collaborative cross mice and C57BL/6-Min lines.ResultsHere, C57BL/6-Min male mice were mated with females from 27 Collaborative cross lines. F1 offspring were terminated at 23 weeks old and multiple phenotypes were collected: polyp counts, intestine length, intestine weight, packed cell volume and spleen weight. Additionally, in eight selected F1 Collaborative cross-C57BL/6-Min lines, body weight was monitored and compared to control mice carry wildtype Adenomatous polyposis coli gene. We found significant (p < 0.05) phenotypic variation between the 27 F1 Collaborative cross-C57BL/6-Min lines for all the tested phenotypes, and sex differences with traits; Colon, body weight and intestine length phenotypes, only. Heritability calculation showed that these phenotypes are mainly controlled by genetic factors.ConclusionsVariation in polyp development is controlled, an appreciable extent, by genetic factors segregating in the Collaborative cross population and suggests that it is suited for identifying modifier genes associated with ApcMin/+ mutation, after assessing sufficient number of lines for quantitative trait loci analysis.Electronic supplementary materialThe online version of this article (doi:10.1186/s12863-016-0349-6) contains supplementary material, which is available to authorized users.

Detection of a Tumor Suppressor Gene Variant Predisposing to Colorectal Cancer in an 18th Century Hungarian Mummy

Mutations of the Adenomatous polyposis coli (APC) gene are common and strongly associated with the development of colorectal adenomas and carcinomas. While extensively studied in modern populations, reports on visceral tumors in ancient populations are scarce. To the best of our knowledge, genetic characterization of mutations associated with colorectal cancer in ancient specimens has not yet been described. In this study we have sequenced hotspots for mutations in the APC gene isolated from 18th century naturally preserved human Hungarian mummies. While wild type APC sequences were found in two mummies, we discovered the E1317Q missense mutation, known to be a colorectal cancer predisposing mutation, in a large intestine tissue of an 18th century mummy. Our data suggests that this genetic predisposition to cancer already existed in the pre-industrialization era. This study calls for similar investigations of ancient specimens from different periods and geographical locations to be conducted and shared for the purpose of obtaining a larger scale analysis that will shed light on past cancer epidemiology and on cancer evolution.

APC binds the Miro/Milton motor complex to stimulate transport of mitochondria to the plasma membrane.

Mutations in adenomatous polyposis coli (APC) disrupt regulation of Wnt signaling, mitosis, and the cytoskeleton. We describe a new role for APC in the transport of mitochondria. Silencing of wild-type APC by small interfering RNA caused mitochondria to redistribute from the cell periphery to the perinuclear region. We identified novel APC interactions with the mitochondrial kinesin-motor complex Miro/Milton that were mediated by the APC C-terminus. Truncating mutations in APC abolished its ability to bind Miro/Milton and reduced formation of the Miro/Milton complex, correlating with disrupted mitochondrial distribution in colorectal cancer cells that could be recovered by reconstitution of wild-type APC. Using proximity ligation assays, we identified endogenous APC-Miro/Milton complexes at mitochondria, and live-cell imaging showed that loss of APC slowed the frequency of anterograde mitochondrial transport to the membrane. We propose that APC helps drive mitochondria to the membrane to supply energy for cellular processes such as directed cell migration, a process disrupted by cancer mutations.

Adenomatous polyposis coli (APC)-induced apoptosis of HT29 colorectal cancer cells depends on mitochondrial oxidative metabolism

Adenomatous polyposis coli (APC) is a tumor suppressor involved in the Wnt signaling, the primary driving force of the intestinal epithelium homeostasis. Alterations of components of the Wnt pathway, and in most cases mutations of APC, have been reported to promote colorectal cancer (CRC). During differentiation the enterocytes migrate from the crypt to the tip of the villus where they undergo apoptosis thus ensuring the continual renewal of the intestinal mucosa. The differentiation process is characterized by an activation gradient of the Wnt signaling pathway accompanied by a metabolic switch from glycolysis to mitochondrial oxidative phosphorylation along the crypt–villus axis. In the present work, we study the relationship between the expression of wild type APC protein and mitochondrial oxidative metabolism in HT29 colorectal cancer cells, originally carrying endogenous inactive APC alleles. By generating mtDNA-depleted (rho0) APC-inducible HT29 cells, we demonstrate for the first time that the APC-dependent apoptosis requires the production of reactive oxygen species (ROS) by the mitochondrial respiratory chain. The possible role of mitochondria as putative target in the prevention and/or therapy of colorectal cancer is herein discussed.

Targeting the DNA replication checkpoint by pharmacologic inhibition of Chk1 kinase: a strategy to sensitize APC mutant colon cancer cells to 5-fluorouracil chemotherapy.

5-fluorouracil (5-FU) is the first line component used in colorectal cancer (CRC) therapy however even in combination with other chemotherapeutic drugs recurrence is common. Mutations of the adenomatous polyposis coli (APC) gene are considered as the initiating step of transformation in familial and sporadic CRCs. We have previously shown that APC regulates the cellular response to DNA replication stress and recently hypothesized that APC mutations might therefore influence 5-FU resistance. To test this, we compared CRC cell lines and show that those expressing truncated APC exhibit a limited response to 5-FU and arrest in G1/S-phase without undergoing lethal damage, unlike cells expressing wild-type APC. In SW480 APC-mutant CRC cells, 5-FU-dependent apoptosis was restored after transient expression of full length APC, indicating a direct link between APC and drug response. Furthermore, we could increase sensitivity of APC truncated cells to 5-FU by inactivating the Chk1 kinase using drug treatment or siRNA-mediated knockdown. Our findings identify mutant APC as a potential tumor biomarker of resistance to 5-FU, and importantly we show that APC-mutant CRC cells can be made more sensitive to 5-FU by use of Chk1 inhibitors.

Therapeutic targeting truncated adenomatous polyposis coli (APC) proteins for the selective killing of colorectal cancer cells

The adenomatous polyposis coli (APC) gene is a multifunctional tumor suppressor mutated in over 80% of colorectal cancers (CRC). Mutations in APC are believed to be one of the earliest events that contribute to CRC initiation. APC has been implicated in the negative regulation of the canonical Wnt signaling pathway, cell cycle control, cell migration, differentiation, and apoptosis. However, there remain many unanswered questions about the precise roles of APC in CRC progression. For example, over 90% of APC mutations result in truncated proteins, among which termination mutations at codons 1309 and 1450 occur the most frequently. It is completely unclear why the vast majority of human colon cancers would retain truncated APC proteins unless there was some survival/growth advantage to the emerging tumor. We hypothesized that these truncated APC proteins may actually play a dominant (gain of function) role in the initiation and/or progression of CRC and have conducted experiments to test this idea. Our rationale for these experiments is there are no disease-specific targeted treatments for CRC and therapeutic agents targeting APC truncations could be beneficial. We developed a unique series of telomerase (TERT) and CDK4 immortalized human colonic epithelial cell (HCEC) lines and experimentally made isogenic derivatives by ectopic expression of the most commonly observed APC truncations found in patients. In addition, we made TERT and CDK4 expressing HCECs with TP53 and APC knockdowns as well as ectopic expression of oncogenic KRASv12. We have completed a cell-based high-throughput screen within UT Southwestern's 200,000 compound library utilizing the most cancer progressed isogenic cell line and tested the initial hits against the TERT immortalized normal diploid HCECs. A small molecule lead compound, TASIN-1 (truncated APC selective inhibitor), was identified from this screen that is selectively toxic towards a panel of colon cancer cell lines with APC truncations while sparing normal diploid HCECs and cancer cells with wild type APC. TASIN-1 and its analogs (with IC50s from 0.01nM to 5µM) represent a novel strategy for the treatment of colon cancer. In vitro and in vivo preclinical results will be presented.

Adenomatous polyposis coli determines sensitivity to the EGFR tyrosine kinase inhibitor gefitinib in colorectal cancer cells

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) have been used to treat colorectal cancer (CRC). However, resistance to EGFR-TKIs presents a great challenge for the treatment of CRC, and the mechanisms of resistance are poorly understood. The adenomatous polyposis coli (APC) protein has been known to contribute to the carcinogenesis of CRC. However, its role in the sensitivity of CRC cells to gefitinib has not been investigated. Human CRC HCT-116 (wild-type APC) and HT-29 (mutant APC) cells were used to investigate the effect of APC on the sensitivity of CRC cells to gefitinib. The MTT assay was used to measure cell viability after exposure to gefitinib. Cell apoptosis, migration and invasion were determined by flow cytometry, wound healing assay and transwell assay, respectively. Knockdown and overexpression of APC were performed, and activation of the EGFR and its downstream pathway was determined. Gefinitib inhibited viability, promoted apoptosis, and reduced the migration of HCT-116 and HT-29 cells. HT-29 cells exhibited increased sensitivity to gefinitib when compared to HCT-116 cells. Knockdown of APC expression increased the sensitivity of HCT-16 cells to gefitinib, accompanied by downregulation of pEGFR, p-AKT and pERK1/2. In contrast, overexpression of APC decreased the sensitivity of HT-29 cells to gefitinib, accompanied by upregulation of pEGFR, p-AKT and pERK1/2. APC plays an important role in the sensitivity of CRC cells to gefitinib. APC may represent a potential therapeutic target for the treatment of CRC.

A Porcine Model of Familial Adenomatous Polyposis

We created gene-targeted pigs with mutations in the adenomatous polyposis coli (APC) gene (APC) that are orthologous to those responsible for human familial adenomatous polyposis (FAP). One-year-old pigs with the APC(1311) mutation (orthologous to human APC(1309)) have aberrant crypt foci and low- and high-grade dysplastic adenomas in the large intestine, similar to the precancerous lesions that develop in patients with FAP. Dysplastic adenomas accumulate β-catenin and lose heterozygosity of APC. This large-animal, genetic model of FAP will be useful in the development of diagnostics and therapeutics for colorectal cancer. DNA sequence data: NCBI accession number GU951771.

Regulation of Wnt signaling by the tumor suppressor adenomatous polyposis coli does not require the ability to enter the nucleus or a particular cytoplasmic localization

Wnt signaling plays key roles in development and disease. The tumor suppressor adenomatous polyposis coli (APC) is an essential negative regulator of Wnt signaling. Its best-characterized role is as part of the destruction complex, targeting the Wnt effector β-catenin (βcat) for phosphorylation and ultimate destruction, but several studies suggested APC also may act in the nucleus at promoters of Wnt-responsive genes or to shuttle βcat out for destruction. Even in its role in the destruction complex, APC's mechanism of action remains mysterious. We have suggested APC positions the destruction complex at the appropriate subcellular location, facilitating βcat destruction. In this study, we directly tested APC's proposed roles in the nucleus or in precisely localizing the destruction complex by generating a series of APC2 variants to which we added tags relocalizing otherwise wild-type APC to different cytoplasmic locations. We tested these for function in human colon cancer cells and Drosophila embryos. Strikingly, all rescue Wnt regulation and down-regulate Wnt target genes in colon cancer cells, and most restore Wnt regulation in Drosophila embryos null for both fly APCs. These data suggest that APC2 does not have to shuttle into the nucleus or localize to a particular subcellular location to regulate Wnt signaling.

A Common Role for Various Human Truncated Adenomatous Polyposis Coli Isoforms in the Control of Beta-Catenin Activity and Cell Proliferation

The tumour suppressor gene adenomatous polyposis coli (APC) is mutated in most colorectal cancer cases, leading to the synthesis of truncated APC products and the stabilization of β-catenin. Truncated APC is almost always retained in tumour cells, suggesting that it serves an essential function. Here, RNA interference has been used to down-regulate truncated APC in several colorectal cancer cell lines expressing truncated APCs of different lengths, thereby performing an analysis covering most of the mutation cluster region (MCR). The consequences on proliferation in vitro, tumour formation in vivo and the level and transcriptional activity of β-catenin have been investigated. Down-regulation of truncated APC results in an inhibition of tumour cell population expansion in vitro in 6 cell lines out of 6 and inhibition of tumour outgrowth in vivo as analysed in one of these cell lines, HT29. This provides a general rule explaining the retention of truncated APC in colorectal tumours and defines it as a suitable target for therapeutic intervention. Actually, we also show that it is possible to design a shRNA that targets a specific truncated isoform of APC without altering the expression of wild-type APC. Down-regulation of truncated APC is accompanied by an up-regulation of the transcriptional activity of β-catenin in 5 out of 6 cell lines. Surprisingly, the increased signalling is associated in most cases (4 out of 5) with an up-regulation of β-catenin levels, indicating that truncated APC can still modulate wnt signalling through controlling the level of β-catenin. This control can happen even when truncated APC lacks the β-catenin inhibiting domain (CiD) involved in targeting β-catenin for proteasomal degradation. Thus, truncated APC is an essential component of colorectal cancer cells, required for cell proliferation, possibly by adjusting β-catenin signalling to the “just right” level.