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The partial success of tumor immunotherapy induced by checkpoint blockade, which is not antigen-specific, suggests that the immune system of some patients contain antigen receptors able to specifically identify tumor cells. Here we focused on T-cell receptor (TCR) repertoires associated with spontaneous breast cancer. We studied the alpha and beta chain CDR3 domains of TCR repertoires of CD4 T cells using deep sequencing of cell populations in mice and applied the results to published TCR sequence data obtained from human patients. We screened peripheral blood T cells obtained monthly from individual mice spontaneously developing breast tumors by 5 months. We then looked at identical TCR sequences in published human studies; we used TCGA data from tumors and healthy tissues of 1,256 breast cancer resections and from 4 focused studies including sequences from tumors, lymph nodes, blood and healthy tissues, and from single cell dataset of 3 breast cancer subjects. We now report that mice spontaneously developing breast cancer manifest shared, Public CDR3 regions in both their alpha and beta and that a significant number of women with early breast cancer manifest identical CDR3 sequences. These findings suggest that the development of breast cancer is associated, across species, with biomarker, exclusive TCR repertoires., Author summary More than 1,100 cancer treatments are currently in clinical testing. Of these, 295 are immune-oncology medicines and vaccines. For Checkpoint Immunotherapy alone, 52,539 patients were enrolled in 2017. Of these treatments, 108 are for breast cancer, the leading cancer diagnosed in women. Although checkpoint immunotherapy has yet to be proven beneficial in most types of breast cancer, current observations of which specific T cell go into the tumor, and how these cells are connected to the response to treatment, have lead to a new understating of the role of the immune system. Yet, and in spite of this intense research into the role of T cells in tumors, very little is known about how clones of T cells behave during tumor formation. The paper we present here studies this clonal behavior over time. We study it during mammary tumor development in mice. We see that a set of T cell clones, which comes from a diversity of different nucleotide sequences, stands out in its behavior compared with other T cell clones. Importantly, we show that these mouse T cell clones have a strong connection to human breast cancer. The specific identification of a subset of T cell clones, together with the behavior of these clones over time, is critical to our understanding of the effect of modifications to the immune system, such as the modifications made by immunotherapy treatments, and to our understanding of how to better control the behavior of the immune system.

Summary Biology of the response to anti-CTLA-4 involves the dynamics of specific T cell clones. Reasons for clinical success and failure of this treatment are still largely unknown. Here, we quantified the dynamics of the T cell receptor (TCR) repertoire, throughout 4 weeks involving treatment with anti-CTLA-4, in a syngeneic mouse model for colorectal cancer. These dynamics show an initial increase in clonality in tandem with a decrease in diversity, effects which gradually subside. Furthermore, response to treatment is tightly connected to the shared and public parts of the T cell repertoire. We were able to recognize time-dependent behaviors of specific TCR sequences and cell types and to show the response is dominated by specific motifs. We see that a single, specific time point might be useful to inform a physician of the true response to treatmentThe research further highlights the importance of temporal analyses of the immune response., Graphical Abstract, Highlights • Response to ICI is associated with pre-treatment TCR repertoire in mice • TCR repertoire goes through distinct, ICI-dependent changes with time • Tumor size and its response to ICI can be tracked by TCR repertoire metrics • A single time point is found to be a focal point of the immune response, Immunology; Cell Biology: Bioinformatics

We describe and provide an array of diverse methods to predict cellular positions in tissue from RNA-seq data selecting mapping genes according to their spatial/statistical properties and their effect on improving the cell positioning., Single-cell RNA-sequencing (scRNAseq) technologies are rapidly evolving. Although very informative, in standard scRNAseq experiments, the spatial organization of the cells in the tissue of origin is lost. Conversely, spatial RNA-seq technologies designed to maintain cell localization have limited throughput and gene coverage. Mapping scRNAseq to genes with spatial information increases coverage while providing spatial location. However, methods to perform such mapping have not yet been benchmarked. To fill this gap, we organized the DREAM Single-Cell Transcriptomics challenge focused on the spatial reconstruction of cells from the Drosophila embryo from scRNAseq data, leveraging as silver standard, genes with in situ hybridization data from the Berkeley Drosophila Transcription Network Project reference atlas. The 34 participating teams used diverse algorithms for gene selection and location prediction, while being able to correctly localize clusters of cells. Selection of predictor genes was essential for this task. Predictor genes showed a relatively high expression entropy, high spatial clustering and included prominent developmental genes such as gap and pair-rule genes and tissue markers. Application of the top 10 methods to a zebra fish embryo dataset yielded similar performance and statistical properties of the selected genes than in the Drosophila data. This suggests that methods developed in this challenge are able to extract generalizable properties of genes that are useful to accurately reconstruct the spatial arrangement of cells in tissues.

The introduction of novel cancer drugs and innovative treatments brings great hope for cancer patients, but also an urgent need to match drugs to suitable patients, since certain drugs that benefit one patient may actually harm others. The newly developed poly-ADP ribose polymerase (PARP) inhibitors (PARPis) are a group of pharmacological enzyme inhibitors used clinically for multiple indications. Several forms of cancer tend to be PARP dependent, making PARP an attractive target for cancer therapy. Specifically, PARPis are commonly used in BRCA-associated breast cancers patients, since unrepaired single-strand breaks are converted into double-strand breaks and BRCA-associated tumors cannot repair them by homologous recombination so that PARPi leads to tumor cell death, by a mechanism called “Synthetic Lethality”. Unfortunately, not all patients respond to PARPi, and it is not currently possible to predict who will or will not respond. Here, we present a specific genomic marker, which reflects a single-nucleotide polymorphism of human PARP1 and correlates in vitro with response to PARPi, throughout all indications. In addition, we report that this SNP is associated with re-shaping mRNA, and mRNA levels, and influences the final protein structure to expose new binding sites while hiding others. The status of the SNP is therefore critical to patients’ care, as it relates responses to PARPi to the PARP1-SNP carried.

Paclitaxel, the most commonly used form of chemotherapy, is utilized in curative protocols in different types of cancer. The response to treatment differs among patients. Biological interpretation of a mechanism to explain this personalized response is still unavailable. Since paclitaxel is known to target BCL2 and TUBB1, we used pan-cancer genomic data from hundreds of patients to show that a single-nucleotide variant in the BCL2 sequence can predict a patient’s response to paclitaxel. Here, we show a connection between this BCL2 genomic variant, its transcript structure, and protein abundance. We demonstrate these findings in silico, in vitro, in formalin-fixed paraffin-embedded (FFPE) tissue, and in patient lymphocytes. We show that tumors with the specific variant are more resistant to paclitaxel. We also show that tumor and normal cells with the variant express higher levels of BCL2 protein, a phenomenon that we validated in an independent cohort of patients. Our results indicate BCL2 sequence variations as determinants of chemotherapy resistance. The knowledge of individual BCL2 genomic sequences prior to the choice of chemotherapy may improve patient survival. The current work also demonstrates the benefit of community-wide, integrative omics data sources combined with in-lab experimentation and validation sets.

// Rotem Ben-Hamo 1 , Alona Zilberberg 1 , Helit Cohen 1 and Sol Efroni 1 1 The Mina and Everard Goodman Faculty of Life Science, Bar Ilan University, Ramat-Gan, Israel Correspondence to: Sol Efroni, email: // Keywords : MAPKAP signaling, cytoskeleton, pathways, glioblastoma, metastasis, hsa-miR9 Received : July 23, 2015 Accepted : December 05, 2015 Published : December 21, 2015 Abstract Background: Glioblastoma Multiforme (GBM) is the most common and lethal primary tumor of the brain. GBM is associated with one of the worst 5-year survival rates among all human cancers, despite much effort in different modes of treatment. Results: Here, we demonstrate specific GBM cancer phenotypes that are governed by modifications to the MAPAKAP network. We then demonstrate a novel regulation mode by which a set of five key factors of the MAPKAP pathway are regulated by the same microRNA, hsa-miR-9. We demonstrate that hsa-miR-9 overexpression leads to MAPKAP signaling inhibition, partially by interfering with the MAPK14/MAPKAP3 complex. Further, hsa-miR-9 overexpression initiates re-arrangement of actin filaments, which leads us to hypothesize a mechanism for the observed phenotypic shift. Conclusion: The work presented here exposes novel microRNA features and situates hsa-miR-9 as a therapeutic target, which governs metastasis and thus determines prognosis in GBM through MAPKAP signaling.

Cancer immunotherapy by checkpoint blockade proves that an effective immune response to a tumor can be induced clinically. However, little is known about the evolution of tumor-associated T-cell receptor (TCR) repertoires without intervention. Here we studied TCR repertoire evolution in mice spontaneously developing mammary tumors; we sequenced peripheral blood alpha and beta TCRs of CD4+CD62L+CD44− T cells monthly for 8 months in 10 FVB/NJ mice transgenic at the Erbb2 locus, all developing tumors; 5 FVB/NJ mice without the transgene were age-matched controls. Sequences were either private (restricted to one mouse) or public (shared among mice); public sequences were either exclusive to the tumor group or inclusive among different groups. We now report that 1), public AA sequences were each encoded by many different nucleotide sequences (NT) recombinations (convergent recombination; CR); 2) mice developing tumors evolved tumor-exclusive public sequences, derived initially from private or from inclusive public sequences; and 3) tumor-exclusive public sequences in mice were also present among published public TCR sequences from human breast cancer patients. These cross-species tumor-exclusive TCR sequences manifested high CR; but the AA sequences shared by mice and humans did not share NT sequences. Thus, tumor-exclusive TCR AA sequences across species are selected from different NT recombination events. The roles of tumor-exclusive TCR repertoires in advancing or inhibiting tumor development and the effects of tumor immunotherapy on these T cells remain to be seen.

Increased expression of CD24 is seen in a large variety of solid tumors, including up to 90% of gastrointestinal (GI) tumors. Stable derivatives of SW480 colorectal cancer (CRC) cells that overexpress CD24 proliferate faster, and increase cell motility, saturation density, plating efficiency, and growth in soft agar. They also produce larger tumors in nude mice as compared to the parental SW480 cells. Most significantly, even depletion of one copy of the CD24 allele in the APC(Min/+) mice of a transgenic mouse model led to a dramatic reduction in tumor burden in all sections of the small intestine. Homozygous deletion of both CD24 alleles resulted in complete abolishment of tumor formation. Moreover, CD24 knockout mice exhibited resistance to chemically induced inflammation-associated CRC. Finally, a new signal transduction pathway is suggested: namely, CD24 expression downstream to COX2 and PGE2 synthesis, which is directly regulated by β-catenin. CD24 is shown in vitro and in vivo as being an important oncogene in the gut, and one that plays a critical role in the initiation and progression of carcinogenesis.

The effector protein of the canonical Wnt pathway is β-catenin, which is regulated by the ubiquitin system. This study shows that the E3 ubiquitin ligase EDD ubiquitinates β-catenin, leading to up-regulation of β-catenin's expression levels and activity. Thus the results demonstrate a role for the ubiquitin system in up-regulation of the Wnt pathway., Wnt/β-catenin signaling plays a central role in development and is also involved in a diverse array of diseases. β-Catenin activity is tightly regulated via a multiprotein complex that includes the kinase glycogen synthase kinase-3β (GSK-3β). GSK-3β phosphorylates β-catenin, marking it for ubiquitination and degradation via the proteasome. Thus in regulation of the Wnt pathway, the ubiquitin system is known to be involved mostly in mediating the turnover of β-catenin, resulting in reduced Wnt signaling levels. Here we report that an arm of the ubiquitin system increases β-catenin protein levels. We show that GSK-3β directly interacts with the E3 ubiquitin ligase identified by differential display (EDD) that also binds β-catenin. Expression of EDD leads to enhanced nuclear accumulation of both GSK-3β and β-catenin and results in up-regulation of β-catenin expression levels and activity. Importantly, EDD ubiquitinates β-catenin through Lys29- or Lys11-linked ubiquitin chains, leading to enhanced stability of β-catenin. Our results demonstrate a role for the ubiquitin system in up-regulation of the Wnt signaling pathway, suggesting that EDD could function as a colorectal oncogene.

Beta-catenin is the central signalling molecule of the canonical Wnt pathway, where it activates target genes in a complex with lymphoid enhancer factor/T-cell factor transcription factors in the nucleus. The regulation of beta-catenin activity is thought to occur via a cytoplasmatic multiprotein complex that includes the serine/threonine kinase glycogen synthase kinase-3beta (GSK-3beta) that phosphorylates beta-catenin, marking it for degradation by the proteasome. Here, we provide evidence showing that GSK-3beta has a nuclear function in downregulating the activity of beta-catenin. Using colorectal cell lines that express a mutant form of beta-catenin, which cannot be phosphorylated by GSK-3beta and ectopically expressed mutant beta-catenin protein, we show that nuclear GSK-3beta functions in a mechanism that does not involve beta-catenin phosphorylation to reduce the levels of Wnt signalling. We show that GSK-3beta enters the nucleus, forms a complex with beta-catenin and lowers the levels of beta-catenin/TCF-dependent transcription in a mechanism that involves GSK-3beta-Axin binding.

Melanoma originates in the epidermis and becomes metastatic after invasion into the dermis. Prior interactions between melanoma cells and dermis are poorly studied. Here, we show that melanoma cells directly affect the formation of the dermal tumour niche by microRNA trafficking before invasion. Melanocytes, cells of melanoma origin, are specialized in releasing pigment vesicles, termed melanosomes. In melanoma in situ, we found melanosome markers in distal fibroblasts before melanoma invasion. The melanosomes carry microRNAs into primary fibroblasts triggering changes, including increased proliferation, migration and pro-inflammatory gene expression, all known features of cancer-associated fibroblasts (CAFs). Specifically, melanosomal microRNA-211 directly targets IGF2R and leads to MAPK signalling activation, which reciprocally encourages melanoma growth. Melanosome release inhibitor prevented CAF formation. Since the first interaction of melanoma cells with blood vessels occurs in the dermis, our data suggest an opportunity to block melanoma invasion by preventing the formation of the dermal tumour niche.

Introduction GATA binding protein 3 (GATA3) is a regulator of mammary luminal cell differentiation, and an estrogen receptor (ER) associated marker in breast cancer. Tumor suppressor functions of GATA3 have been demonstrated primarily in basal-like breast cancers. Here, we focused on its function in luminal breast cancer, where GATA3 is frequently mutated, and its levels are significantly elevated. Methods GATA3 target genes were identified in normal- and luminal cancer- mammary cells by ChIP-seq, followed by examination of the effects of GATA3 expressions and mutations on tumorigenesis-associated genes and processes. Additionally, mutations and expression data of luminal breast cancer patients from The Cancer Genome Atlas were analyzed to characterize genetic signatures associated with GATA3 mutations. Results We show that some GATA3 effects shift from tumor suppressing to tumor promoting during tumorigenesis, with deregulation of three genes, BCL2, DACH1, THSD4, representing major GATA3-controlled processes in cancer progression. In addition, we identify an altered activity of mutant GATA3, and distinct associated genetic signatures. These signatures depend on the functional domain mutated; and, for a specific subgroup, are shared with basal-like breast cancer patients, who are a clinical group with regard to considerations of mode of treatment. Conclusions The GATA3 dependent mechanisms may call for special considerations for proper prognosis and treatment of patients. Electronic supplementary material The online version of this article (doi:10.1186/s13058-014-0464-0) contains supplementary material, which is available to authorized users.

Identifying novel mechanisms, which are at the core of breast cancer biology, is of critical importance. Such mechanisms may explain response to treatment, reveal novel targets or drive detection assays. To uncover such novel mechanisms, we used survival analysis on gene expression datasets encompassing 1363 patients. By iterating over the compendia of genes, we screened for their significance as prognosis biomarkers and identified SUMO-specific protease 5 (SENP5) to significantly stratify patients into two survival groups across five unrelated tested datasets. According to these findings, low expression of SENP5 is associated with good prognosis among breast cancer patients. Following these findings, we analyzed SENP5 silencing and show it is followed by inhibition of anchorage-independence growth, proliferation, migration and invasion in breast cancer cell lines. We further show that these changes are conducted via regulation of TGFβRI levels. These data relate to recent reports about the SUMOylation of TGFβRI. Following TGFβRI changes in expression, we show that one of its target genes, MMP9, which plays a key role in degrading the extracellular matrix and contributes to TGFβ-induced invasion, is dramatically down regulated upon SENP5 silencing. This is the first report represents SENP5-TGFβ-MMP9 cascade and its mechanistic involvement in breast cancer.

Aberrant activation of the canonical Wnt signal transduction pathway is involved in a large number of human diseases. β-catenin, the key effector protein of the canonical Wnt pathway, functions in the nucleus with T-cell factor/lymphoid enhancer factor (TCF/LEF) to activate expression of Wnt target genes. Here we show that members of the 14-3-3 protein family bind disheveled-2 (Dvl-2) and glycogen synthase-3β (GSK-3β) to attenuate the interaction between GSK-3β and β-catenin. Importantly, 14-3-3 and β-catenin form "bleb-like" structures and are secreted via extracellular vesicles to induce Wnt signaling activity in target cells. Our data suggest a novel way of transducing the oncogenic Wnt signal in which β-catenin is regulated by 14-3-3ζ through the formation of "oncosomes" that contain both the 14-3-3 and β-catenin proteins.

During organogenesis, PAX6 is required for establishment of various progenitor subtypes within the central nervous system, eye and pancreas. PAX6 expression is maintained in a variety of cell types within each organ, although its role in each lineage and how it acquires cell-specific activity remain elusive. Herein, we aimed to determine the roles and the hierarchical organization of the PAX6-dependent gene regulatory network during the differentiation of the retinal pigmented epithelium (RPE). Somatic mutagenesis of Pax6 in the differentiating RPE revealed that PAX6 functions in a feed-forward regulatory loop with MITF during onset of melanogenesis. PAX6 both controls the expression of an RPE isoform of Mitf and synergizes with MITF to activate expression of genes involved in pigment biogenesis. This study exemplifies how one kernel gene pivotal in organ formation accomplishes a lineage-specific role during terminal differentiation of a single lineage., Author Summary It is currently poorly understood how a single developmental transcription regulator controls early specification as well as a broad range of highly specialized differentiation schemes. PAX6 is one of the most extensively investigated factors in central nervous system development, yet its role in execution of lineage-specific programs remains mostly elusive. Here, we directly investigated the involvement of PAX6 in the differentiation of one lineage, the retinal pigmented epithelium (RPE), a neuroectodermal-derived tissue that is essential for retinal development and function. We revealed that PAX6 accomplishes its role through a unique regulatory interaction with the transcription factor MITF, a master regulator of the pigmentation program. During the differentiation of the RPE, PAX6 regulates the expression of an RPE-specific isoform of Mitf and importantly, at the same time, PAX6 functions together with MITF to directly activate the expression of downstream genes required for pigment biogenesis. These findings provide comprehensive insight into the gene hierarchy that controls RPE development: from a kernel gene (a term referring to the upper-most gene in the gene regulatory network) that is broadly expressed during CNS development through a lineage-specific transcription factor that together with the kernel gene creates cis-regulatory input that contributes to transcriptionally activate a battery of terminal differentiation genes.

Background & Aims: Chronic hepatitis C virus (HCV) infection is strongly associated with insulin resistance and diabetes mellitus. Peroxisome proliferator-activated receptor-gamma co-activator 1a (PGC-1a) is a transcriptional co-activator involved in the initiation of gluconeogenesis in the liver. Increased hepatic expression of PGC-1a has been implicated in insulin resistance. We investigated whether modulation of PGC-1a levels following HCV infection underlies HCV-associated hepatic insulin resistance. Methods: HCV genomes were expressed in hepatoma cells followed by analysis of PGC-1a and gluconeogenesis levels. Results: PGC-1a was robustly induced in HCV infected cells. PGC-1a induction was accompanied by an elevated expression of the gluconeogenic gene glucose-6 phosphatase (G6Pase) and increased glucose production. The induction of gluconeogenesis is HCV dependent, since interferon treatment abolishes PGC-1a and G6Pase elevation and decreases glucose output. Moreover, PGC-1a knockdown resulted in a significant reduction of G6Pase levels in HCV full length replicon cells, emphasizing the central role of PGC-1a in the exaggerated gluconeogenic response observed in HCV patients. Treatment of HCV replicon cells with the antioxidant N-acetylcysteine resulted in reduction of PGC1a levels, suggesting that HCV-induced oxidative stress promoted PGC-1a upregulation. Finally, both PGC-1a and G6Pase RNA levels were significantly elevated in liver samples of HCV infected patients, highlighting the clinical relevance of these results. Conclusions: PGC-1a is robustly induced following HCV infection, resulting in an upregulated gluconeogenic response, thereby linking HCV infection to hepatic insulin resistance. Our results suggest that PGC-1a is a potential molecular target for the treatment of HCV-associated insulin resistance. 2012 European Association for the Study of the Liver. Published

Adenomatous polyposis coli (APC) is a multifunctional tumour suppressor protein that negatively regulates the Wnt signalling pathway. The APC gene is ubiquitously expressed in tissues and organs, including the large intestine and central nervous system. The majority of patients with sporadic and hereditary colorectal cancer have mutations in the gene encoding APC. Approximately 30% of these mutations are single nucleotide changes that result in premature stop codons (nonsense mutations). A potential therapeutic approach for treatment of this subset of patients is the use of aminoglycosides and macrolides that induce nonsense mutation read-through and restore levels of full-length protein. We have used reporter plasmids and colorectal cancer cell lines to demonstrate that several aminoglycosides and tylosin, a member of the macrolide family, induced read-through of nonsense mutations in the APC gene. In xenograft experiments and in the Apc(Min/+) mouse model, these compounds ameliorated the tumorigenic clinical symptoms caused by nonsense mutations in the APC gene.

Adenomatous polyposis coli (APC) is a multifunctional tumor suppressor protein that negatively regulates the Wnt signaling pathway. The APC gene is ubiquitously expressed in various tissues, especially throughout the large intestine and central nervous system. Mutations in the gene encoding APC have been found in most colorectal cancers and in other types of cancer. The APC gene product is a large multidomain protein that interacts with a variety of proteins, many of which bind to the well conserved armadillo repeat domain of APC. Through its binding partners, APC affects a large number of important cellular processes, including cell–cell adhesion, cell migration, organization of the actin and microtubule cytoskeletons, spindle formation and chromosome segregation. The molecular mechanisms that control these diverse APC functions are only partly understood. Here we describe the identification of an additional APC armadillo repeat binding partner — the Striatin protein. The Striatin family members are multidomain molecules that are mainly neuronal and are thought to function as scaffolds. We have found that Striatin is expressed in epithelial cells and co-localizes with APC in the epithelial tight junction compartment and in neurite tips of PC12 cells. The junctional localization of APC and Striatin is actin-dependent. Depletion of APC or Striatin affected the localization of the tight junction protein ZO-1 and altered the organization of F-actin. These results raise the possibility that the contribution of APC to cell-cell adhesion may be through interaction with Striatin in the tight junction compartment of epithelial cells.

Members of the low density lipoprotein receptor family (LDLR), LRP5/6, were shown to interact with the Frizzled (Fz) receptors and to function as Wnt coreceptors. Here we show that mLRP4T100, a minireceptor of LRP1, another member of the LDLR family, interacts with the human Fz-1 (HFz1), previously shown to serve as a receptor transmitting the canonical Wnt-3a-induced signaling cascade. However, in contrast to LRP5/6, mLRP4T100, as well as the full-length LRP1, did not cooperate with HFz1 in transmitting the Wnt-3a signaling but rather repressed it. mLRP4T100 inhibitory effect was displayed also by endocytosis-defective mLRP4T100 mutants, suggesting that LRP1 repressive effect is not attributable to LRP1-mediated enhanced HFz1 internalization and subsequent degradation. Enforced expression of mLRP4T100 decreased the capacity of HFz1 cysteine-rich domain (CRD) to interact with LRP6, in contrast to HFz1-CRD/Wnt-3a interaction that was not disrupted by overexpressing mLRP4T100. These data suggest that LRP1, by sequestering HFz1, disrupts the receptor/coreceptor complex formation, leading to the repression of the canonical Wnt signaling. Thus, this study implies that the ability to interact with Fz receptors is shared by several members of the LDLR family. However, whereas some members of the LDLR family, such as LRP5/6, interact with Fz and serve as Wnt coreceptors, others negatively regulate Wnt signaling, presumably by sequestering Fz.

Background: Previous studies in our lab have shown that CD24 is a potential oncogene in the colon. CD24, a mucin-like glycoprotein, is overexpressed in 90% of colorectal cancer (CRC) tumors at a fairly early stage in the multistep process of CR carcinogenesis (Sagiv et al., Gastroenterology, 2006). We have also shown that CD24 downregulation by shRNA interference (Sagiv et al., Can Res, 2008) or anti-CD24 mAb targeting (Shapira et al., Gastroenterology, 2011) retarded tumorigenicity of human CRC cell lines and/or reduced tumor volume in nude mice. The APCmin/+ is a popular animal model for studies of human colon carcinogenesis and the molecular changes associated with neoplasia in this system have been partially characterized. These mice have a germline nonsense mutation at codon 850 of the APC gene and spontaneously develop hundreds of polyps, mostly in the small intestine at the age of 10-12 weeks. Aim: To validate the importance of CD24 in intestinal carcinogenesis using a transgenic mouse model with a double knockout (KO) of CD24−/+ /CD24+/− and APCMin/+ alleles. Methods: We generated the CD24−/+/APCMin/+ double KO by crossing the mice with each of the single gene knockouts, in order to obtain both CD24+/−/APCMin/+ and CD24−/+ APCMin/+ genotypes. The double KO mice were followed up thrice a week and sacrificed at 12 weeks of age. Tumors from the entire small and large intestine were counted and verified by histological analysis Results: There was almost a complete absence of polyps in the small intestine in APCMin/+/CD24+/− double heterozygotes compared to that of the parental APCMin/+, CD24+/+ animals: 273±55.4 vs. 6±1.7 polyps, respectively (P=0.0001). APCMin/+and CD24−/+ homozygotes showed a striking lack of polyps (P< 0.0001). This reduction occurred in all sections of the small intestine. Histophatological analysis confirmed the absence of malignant lesions in the double KO mice as compared to the parental mice. Conclusions: 1. A deficiency of only one CD24 allele is sufficient to suppress almost completely polyp formation in the APCMin/+ mice that normally develop hundreds of polyps. 2. Although the mechanism/s underlying the pathophysiologic role of CD24 in the development of CRC are still unknown, these studies suggest that CD24 plays a critical role in the proliferation and progression of CRC and is a potential important target for the prevention and treatment of intestinal neoplasia. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1338. doi:1538-7445.AM2012-1338