The APC tumor suppressor controls entry into S-phase through its ability to regulate the cyclin D/RB pathway

Differences in cell shape, motility, and growth reflect chromosomal number variations that can be visualized with live-cell ChReporters

Chromosome numbers often change dynamically in tumors and cultured cells, which complicates therapy as well as understanding genotype-mechanotype relationships. Here we use a live-cell "ChReporter" method to identify cells with a single chromosomal loss in efforts to better understand differences in cell shape, motility, and growth. We focus on a standard cancer line and first show clonal populations that retain the ChReporter exhibit large differences in cell and nuclear morphology as well as motility. Phenotype metrics follow simple rules, including migratory persistence scaling with speed, and cytoskeletal differences are evident from drug responses, imaging, and single-cell RNA sequencing. However, mechanotype-genotype relationships between fluorescent ChReporter-positive clones proved complex and motivated comparisons of clones that differ only in loss or retention of a Chromosome-5 ChReporter. When lost, fluorescence-null cells show low expression of Chromosome-5 genes, including a key tumor suppressor APC that regulates microtubules and proliferation. Colonies are compact, nuclei are rounded, and cells proliferate more, with drug results implicating APC, and patient survival data indicating an association in multiple tumor-types. Visual identification of genotype with ChReporters can thus help clarify mechanotype and mechano-evolution.

The Impact of ETV6-NTRK3 Oncogenic Gene Fusions on Molecular and Signaling Pathway Alterations

Chromosomal translocations creating fusion genes are common cancer drivers. The oncogenic ETV6-NTRK3 (EN) gene fusion joins the sterile alpha domain of the ETV6 transcription factor with the tyrosine kinase domain of the neurotrophin-3 receptor NTRK3. Four EN variants with alternating break points have since been detected in a wide range of human cancers. To provide molecular level insight into EN oncogenesis, we employed a proximity labeling mass spectrometry approach to define the molecular context of the fusions. We identify in total 237 high-confidence interactors, which link EN fusions to several key signaling pathways, including ERBB, insulin and JAK/STAT. We then assessed the effects of EN variants on these pathways, and showed that the pan NTRK inhibitor Selitrectinib (LOXO-195) inhibits the oncogenic activity of EN2, the most common variant. This systems-level analysis defines the molecular framework in which EN oncofusions operate to promote cancer and provides some mechanisms for therapeutics.

The preventive and therapeutic effects of anthocyanins on colorectal cancer: A comprehensive review based on up-to-date experimental studies

Colorectal cancer (CRC) is the second most lethal and the third most diagnosed type of cancer worldwide. More than 75% of CRC cases are sporadic and lifestyle-related. Risk factors include diet, physical inactivity, genetics, smoking, alcohol, changes in the intestinal microbiota, and inflammation-related diseases such as obesity, diabetes, and inflammatory bowel diseases. The limits of conventional treatments (surgery, chemotherapy, radiotherapy), as demonstrated by the side effects and resistance of many CRC patients, are making professionals search for new chemopreventive alternatives. In this context, diets rich in fruits and vegetables or plant-based products, which contain high levels of phytochemicals, have been postulated as complementary therapeutic options. Anthocyanins, phenolic pigments responsible for the vivid colors of most red, purple, and blue fruits and vegetables, have been shown protective effects on CRC. Berries, grapes, Brazilian fruits, and vegetables such as black rice and purple sweet potato are examples of products rich in anthocyanins, which have been able to reduce cancer development by modulating signaling pathways associated with CRC. Therefore, this review has as main objective to present and discuss the potential preventive and therapeutic effects of anthocyanins present in fruits and vegetables, in plant extracts, or in their pure form on CRC, taking into account up-to-date experimental studies (2017-2023). Additionally, a highlight is given towards the mechanisms of action of anthocyanins on CRC.

Mouse models in colon cancer, inferences, and implications

Mouse models of colorectal cancer (CRC) have been crucial in the identification of the role of genes responsible for the full range of pathology of the human disease and have proved to be dependable for testing anti-cancer drugs. Recent research points toward the relevance of tumor, angiogenic, and immune microenvironments in CRC progression to late-stage disease, as well as the treatment of it. This study examines important mouse models in CRC, discussing inherent strengths and weaknesses disclosed during their construction. It endeavors to provide both a synopsis of previous work covering how investigators have defined various models and to evaluate critically how researchers are most likely to use them in the future. Accumulated evidence regarding the metastatic process and the hope of using checkpoint inhibitors and immunological inhibitor therapies points to the need for a genetically engineered mouse model that is both immunocompetent and autochthonous.

Identification of dynamic driver sets controlling phenotypical landscapes

Controlling phenotypical landscapes is of vital interest to modern biology. This task becomes highly demanding because cellular decisions involve complex networks engaging in crosstalk interactions. Previous work on control theory indicates that small sets of compounds can control single phenotypes. However, a dynamic approach is missing to determine the drivers of the whole network dynamics. By analyzing 35 biologically motivated Boolean networks, we developed a method to identify small sets of compounds sufficient to decide on the entire phenotypical landscape. These compounds do not strictly prefer highly related compounds and show a smaller impact on the stability of the attractor landscape. The dynamic driver sets include many intervention targets and cellular reprogramming drivers in human networks. Finally, by using a new comprehensive model of colorectal cancer, we provide a complete workflow on how to implement our approach to shift from in silico to in vitro guided experiments.

Adenomatous polyposis coli in cancer and therapeutic implications

Inactivating mutations of the adenomatous polyposis coli (APC) gene and consequential upregulation of the Wnt signaling pathway are critical initiators in the development of colorectal cancer (CRC), the third most common cancer in the United States for both men and women. Emerging evidence suggests APCmutations are also found in gastric, breast and other cancers. The APC gene, located on chromosome 5q, is responsible for negatively regulating the b-catenin/Wnt pathway by creating a destruction complex with Axin/Axin2, GSK-3b, and CK1. In the event of an APC mutation, b-catenin accumulates, translocates to the cell nucleus and increases the transcription of Wnt target genes that have carcinogenic consequences in gastrointestinal epithelial stem cells. A literature review was conducted to highlight carcinogenesis related to APC mutations, as well as preclinical and clinical studies for potential therapies that target steps in inflammatory pathways, including IL-6 transduction, and Wnt pathway signaling regulation. Although a range of molecular targets have been explored in murine models, relatively few pharmacological agents have led to substantial increases in survival for patients with colorectal cancer clinically. This article reviews a range of molecular targets that may be efficacious targets for tumors with APC mutations.

Investigation of the expression levels of CPEB4, APC, TRIP13, EIF2S3, EIF4A1, IFNg, PIK3CA and CTNNB1 genes in different stage colorectal tumors

Background/aim

The aim of the study is to assess expression levels of CPEB4, APC, TRIP13, EIF2S3, EIF4A1, IFNg, PIK3CA and CTNNB1 genes in tumors and peripheral bloods of colorectal cancer patients in stages I–IV.

Materials and methods

The mRNA levels of the genes were determined in tumor tissues and peripheral blood samples of 45 colorectal cancer patients and colon tissues and peripheral blood samples of 5 healthy individuals. Real-time polymerase chain reaction method was used for the analysis.

Results

The mRNA level of the CPEB4 gene was significantly downregulated in colorectal tumor tissues and was upregulated in the peripheral blood of colorectal cancer patients relative to the controls (P < 0.05). APC mRNA level was significantly downregulated in tissues and upregulated in the peripheral blood (P < 0.05). TRIP13 mRNA level was upregulated in peripheral blood and also significantly upregulated in colorectal tumor tissues (P < 0.05). EIF2S3 mRNA level was upregulated in tissues and also significantly upregulated in peripheral blood (P < 0.05). PIK3CA mRNA level was downregulated in tissues and upregulated in peripheral blood. EIF4A1 mRNA level was downregulated in tissues and significantly upregulated in peripheral blood (P < 0.05). CTNNB1 mRNA level was downregulated in tissues and upregulated in peripheral blood. IFNg mRNA level was upregulated in both colorectal cancer tumor tissues and peripheral blood.

Conclusion:

TRIP13 and CPEB4 mRNA up regulation in the peripheral blood of patients with colorectal cancer may be a potential target for early stage diagnosis. In addition to this evaluation, although there is not much study on EIF2S3 and EIF4A1 mRNA changes in cases with colorectal cancer, upregulation in peripheral blood draws attention in our study. These data will shed light on the new comprehensive studies.

Mutational screening through comprehensive bioinformatics analysis to detect novel germline mutations in the APC gene in patients with familial adenomatous polyposis (FAP)

Background

Familial adenomatous polyposis (FAP) as a colon cancer predisposition syndrome is an autosomal‐dominant inherited condition and is diagnosed by the progress of hundreds or thousands of adenomatous colonic polyps in the colon. This study aims at the nature and effect of Adenomatous Polyposis Coli (APC) gene mutations in FAP tumorigenesis.

Methods

The genetic screening of 59 FAP Iranian patients in 10 families was performed by polymerase chain reactions and the direct sequencing of the entire coding exons of the APC gene. To do linkage haplotype analysis and multiplex PCR‐based microsatellite examination, six short tandem repeat loci were selected in this gene. To evaluate and predict the potentially deleterious effects, comprehensive bioinformatics pathogenicity assays were used.

Results

A total of 12 germline heterozygous and homozygous nucleotide variations were identified. They included two missense mutations, four nonsense mutations, which would lead to the truncated and nonfunctional protein products, four synonymous or silent variations, and two nucleotide deletions of 1 to 5 bp or frameshift mutations. In addition, three novel heterozygous nonsense mutations were found in exons 10, 14, and 15 of the gene. There was also p.Arg653Met as a novel heterozygote mutation in exon 14 of the gene.

Conclusions

Bioinformatics analysis and three‐dimensional structural modeling predicted that these missense and nonsense mutations generally are associated with the deleted or truncated domains of APC and have functional importance and mainly affected the APC protein. These findings may provide evidence for the progress of potential biomarkers and help to understand the role of the APC gene in FAP.

The Role of Noncoding RNAs in the Regulation of Anoikis and Anchorage-Independent Growth in Cancer

Cancer is a global health concern, and the prognosis of patients with cancer is associated with metastasis. Multistep processes are involved in cancer metastasis. Accumulating evidence has shown that cancer cells acquire the capacity of anoikis resistance and anchorage-independent cell growth, which are critical prerequisite features of metastatic cancer cells. Multiple cellular factors and events, such as apoptosis, survival factors, cell cycle, EMT, stemness, autophagy, and integrins influence the anoikis resistance and anchorage-independent cell growth in cancer. Noncoding RNAs (ncRNAs), such as microRNAs (miRNAs) and long noncoding RNAs (lncRNAs), are dysregulated in cancer. They regulate cellular signaling pathways and events, eventually contributing to cancer aggressiveness. This review presents the role of miRNAs and lncRNAs in modulating anoikis resistance and anchorage-independent cell growth. We also discuss the feasibility of ncRNA-based therapy and the natural features of ncRNAs that need to be contemplated for more beneficial therapeutic strategies against cancer.

Molecular Mechanisms of Colon Cancer Progression and Metastasis: Recent Insights and Advancements

Colorectal cancer (CRC), the third most common type of cancer, is the second leading cause of cancer-related mortality rates worldwide. Although modern research was able to shed light on the pathogenesis of CRC and provide enhanced screening strategies, the prevalence of CRC is still on the rise. Studies showed several cellular signaling pathways dysregulated in CRC, leading to the onset of malignant phenotypes. Therefore, analyzing signaling pathways involved in CRC metastasis is necessary to elucidate the underlying mechanism of CRC progression and pharmacotherapy. This review focused on target genes as well as various cellular signaling pathways including Wnt/β-catenin, p53, TGF-β/SMAD, NF-κB, Notch, VEGF, and JAKs/STAT3, which are associated with CRC progression and metastasis. Additionally, alternations in methylation patterns in relation with signaling pathways involved in regulating various cellular mechanisms such as cell cycle, transcription, apoptosis, and angiogenesis as well as invasion and metastasis were also reviewed. To date, understanding the genomic and epigenomic instability has identified candidate biomarkers that are validated for routine clinical use in CRC management. Nevertheless, better understanding of the onset and progression of CRC can aid in the development of early detection molecular markers and risk stratification methods to improve the clinical care of CRC patients.

The Role of Carcinogenesis-Related Biomarkers in the Wnt Pathway and Their Effects on Epithelial-Mesenchymal Transition (EMT) in Oral Squamous Cell Carcinoma

As oral squamous cell carcinoma (OSCC) can develop from potentially malignant disorders (PMDs), it is critical to develop methods for early detection to improve the prognosis of patients. Epithelial-mesenchymal transition (EMT) plays an important role during tumor progression and metastasis. The Wnt signaling pathway is an intercellular pathway in animals that also plays a fundamental role in cell proliferation and regeneration, and in the function of many cell or tissue types. Specific components of master regulators such as epithelial cadherin (E-cadherin), Vimentin, adenomatous polyposis coli (APC), Snail, and neural cadherin (N-cadherin), which are known to control the EMT process, have also been implicated in the Wnt cascade. Here, we review recent findings on the Wnt signaling pathway and the expression mechanism. These regulators are known to play roles in EMT and tumor progression, especially in OSCC. Characterizing the mechanisms through which both EMT and the Wnt pathway play a role in these cellular pathways could increase our understanding of the tumor genesis process and may allow for the development of improved therapeutics for OSCC.

Development and Characterization of a Genetic Mouse Model of KRAS Mutated Colorectal Cancer

Patients with KRAS mutated colorectal cancer (CRC) represent a cohort with unmet medical needs, with limited options of FDA-approved therapies. Representing 40-45% of all CRC patients, they are considered ineligible to receive anti-EGFR monoclonal antibodies that have added a significant therapeutic benefit for KRAS wild type CRC patients. Although several mouse models of CRC have been developed during the past decade, one genetically resembling the KRAS mutated CRC is yet to be established. In this study C57 BL/6 mice with truncated adenomatous polyposis coli (APC) floxed allele was crossed with heterozygous KRAS floxed outbred mice to generate an APCf/f KRAS+/f mouse colony. In another set of breeding, APC floxed mice were crossed with CDX2-Cre-ERT2 mice and selected for APCf/f CDX2-Cre-ERT2 after the second round of inbreeding. The final model of the disease was generated by the cross of the two parental colonies and viable APC f/f KRAS +/f CDX2-Cre-ERT2 (KPC: APC) were genotyped and characterized. The model animals were tamoxifen (TAM) induced to generate tumors. Micro-positron emission tomography (PET) scan was used to detect and measure tumor volume and standard uptake value (SUV). Hematoxylin and eosin (H&E) staining was performed to establish neoplasm and immunohistochemistry (IHC) was performed to determine histological similarities with human FFPE biopsies. The MSI/microsatellite stable (MSS) status was determined. Finally, the tumors were extensively characterized at the molecular level to establish similarities with human CRC tumors. The model KPC: APC animals are conditional mutants that developed colonic tumors upon induction with tamoxifen in a dose-dependent manner. The tumors were confirmed to be malignant within four weeks of induction by H&E staining and higher radioactive [18F] fluoro-2-deoxyglucose (FDG) uptake (SUV) in micro-PET scan. Furthermore, the tumors histologically and molecularly resembled human colorectal carcinoma. Post tumor generation, the KPC: APC animals died of cachexia and rectal bleeding. Implications: This model is an excellent preclinical platform to molecularly characterize the KRAS mutated colorectal tumors and discern appropriate therapeutic strategies to improve disease management and overall survival.

Functions of the APC tumor suppressor protein dependent and independent of canonical WNT signaling: implications for therapeutic targeting. Cancer Metastasis Rev. 2018;37:159-172. [PMID: 29318445 DOI: 10.1007/s10555-017-9725-6]

The acquisition of biallelic mutations in the APC gene is a rate-limiting step in the development of most colorectal cancers and occurs in the earliest lesions. APC encodes a 312-kDa protein that localizes to multiple subcellular compartments and performs diverse functions. APC participates in a cytoplasmic complex that promotes the destruction of the transcriptional licensing factor β-catenin; APC mutations that abolish this function trigger constitutive activation of the canonical WNT signaling pathway, a characteristic found in almost all colorectal cancers. By negatively regulating canonical WNT signaling, APC counteracts proliferation, promotes differentiation, facilitates apoptosis, and suppresses invasion and tumor progression. APC further antagonizes canonical WNT signaling by interacting with and counteracting β-catenin in the nucleus. APC also suppresses tumor initiation and progression in the colorectal epithelium through functions that are independent of canonical WNT signaling. APC regulates the mitotic spindle to facilitate proper chromosome segregation, localizes to the cell periphery and cell protrusions to establish cell polarity and appropriate directional migration, and inhibits DNA replication by interacting directly with DNA. Mutations in APC are often frameshifts, insertions, or deletions that introduce premature stop codons and lead to the production of truncated APC proteins that lack its normal functions and possess tumorigenic properties. Therapeutic approaches in development for the treatment of APC-deficient tumors are focused on the inhibition of canonical WNT signaling, especially through targets downstream of APC in the pathway, or on the restoration of wild-type APC expression.

Co‑expression of Axin and APC gene fragments inhibits colorectal cancer cell growth via regulation of the Wnt signaling pathway

Adenomatous polyposis coli (APC) and Axin interactions serve an important role in colorectal cancer (CRC) pathogenesis. The aim of the present study was to assess the combined effects of Axin and APC co-expression in CRC cells, and to determine the underlying mechanisms involved. SW480 cells were divided into the following groups: Untransfected (SW480 group), transfected with pEGFP-N₃plus pCS2-MT (SW480/vector-vector), transfected with pEGFP-N₃-APC5 (SW480/APC5), and transfected with pEGFP-N₃-APC5 pluspCS2-MT-Axin (SW480/APC5-Axin). APC5 and Axin mRNA levels were determined by reverse transcription-polymerase chain reaction. MTT assays and flow cytometry analysis were performed to assess cell growth and cell cycle distribution, respectively. Quantitative PCR and western blot analyses were conducted to evaluate the mRNA and protein levels, respectively, of Wnt signaling effectors, including β-catenin, c-myc and survivin. Successful transfection of SW480 cells was determined with APC and APC-Axin plasmids as indicated by the green fluorescence signals. Notably, SW480/APC5 cell growth was inhibited by 40.33%, and cells co-expressing APC5 and Axin demonstrated 61.27% inhibition of cell growth compared with SW480 control cells. The results demonstrate that APC5 may induce G1/S arrest in SW480 cells, and Axin may enhance cell growth arrest induced by APC5. The mRNA and protein levels of β-catenin, c-myc and survivin were significantly reduced in SW480/APC-Axin cells when compared with the SW480/APC group. In conclusion, co-expression of APC5 and Axin genes significantly downregulated Wnt signaling in human SW480 CRC cells and inhibited cell growth, when compared with cells transfected with APC5 alone. These results may provide experimental evidence to support combined gene therapy in CRC.

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

BACKGROUND

The 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.

METHODS

We 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.

RESULTS

APC 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.

CONCLUSION

The 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.

Multiple Roles of APC and its Therapeutic Implications in Colorectal Cancer

Adenomatous polyposis coli (APC) is widely accepted as a tumor suppressor gene highly mutated in colorectal cancers (CRC). Mutation and inactivation of this gene is a key and early event almost uniquely observed in colorectal tumorigenesis. Alterations in the APC gene generate truncated gene products, leading to activation of the Wnt signaling pathway and deregulation of multiple other cellular processes. It has been a mystery why most patients with CRC retain a truncated APC protein, but accumulating evidence suggest that these C terminally truncated APC proteins may have gain of function properties beyond the well-established loss of tumor suppressive function. Here, we will review the evidence for both the loss of function and the gain of function of APC truncations and how together they contribute to CRC initiation and progression.

Redeployment of Myc and E2f1-3 drives Rb-deficient cell cycles

Robust mechanisms to control cell proliferation have evolved to maintain the integrity of organ architecture. Here, we investigated how two critical proliferative pathways, Myc and E2f, are integrated to control cell cycles in normal and Rb-deficient cells using a murine intestinal model. We show that Myc and E2f1-3 have little impact on normal G1-S transitions. Instead, they synergistically control an S-G2 transcriptional program required for normal cell divisions and maintaining crypt-villus integrity. Surprisingly, Rb deficiency results in the Myc-dependent accumulation of E2f3 protein and chromatin repositioning of both Myc and E2f3, leading to the 'super activation' of a G1-S transcriptional program, ectopic S phase entry and rampant cell proliferation. These findings reveal that Rb-deficient cells hijack and redeploy Myc and E2f3 from an S-G2 program essential for normal cell cycles to a G1-S program that re-engages ectopic cell cycles, exposing an unanticipated addiction of Rb-null cells on Myc.

Effect of lentiviral-mediated delivery of Survivin shRNA with adenomatous polyposis coli fragment in HT-29 cells

AIM: To observe the effect of Survivin shRNA combined with adenomatous polyposis coli (APC) fragment on the expression of Survivin and cell proliferation in HT-29 cells.

METHODS: Lentiviral vectors for Survivin shRNA and APC fragment were constructed and transfected into HT-29 cells, alone or in combination. Cells were divided into a negative control group, an empty vector group, an shRNA group, an APC group, and an shRNA + APC group. After 48 h of infection, the Survivin mRNA and protein expression was detected by real-time PCR and Western blot, respectively. The proliferation of cells was assayed by CCK8.

RESULTS: ShRNA + APC significantly decreased the expression of Survivin mRNA and protein and cell proliferation compared with the other groups (P < 0.05 for all).

CONCLUSION: Survivin shRNA combined with APC fragment can inhibit the expression of Survivin mRNA and protein and down-regulate cell proliferation in HT-29 cells.

Targeting lung cancer stem-like cells with TRAIL gene armed oncolytic adenovirus

Lung cancer stem cell (LCSC) is critical in cancer initiation, progression, drug resistance and relapse. Disadvantages showed in conventional lung cancer therapy probably because of its existence. In this study, lung cancer cell line A549 cells propagated as spheroid bodies (named as A549 sphere cells) in growth factors-defined serum-free medium. A549 sphere cells displayed CSC properties, including chemo-resistance, increased proportion of G0/G1 cells, slower proliferation rate, ability of differentiation and enhanced tumour formation ability in vivo. Oncolytic adenovirus ZD55 carrying EGFP gene, ZD55-EGFP, infected A549 sphere cells and inhibited cell growth. Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) armed oncolytic adenovirus, ZD55-TRAIL, exhibited enhanced cytotoxicity and induced A549 sphere cells apoptosis through mitochondrial pathway. Moreover, small molecules embelin, LY294002 and resveratrol improved the cytotoxicity of ZD55-TRAIL. In the A549 sphere cells xenograft models, ZD55-TRAIL significantly inhibited tumour growth and improved survival status of mice. These results suggested that gene armed oncolytic adenovirus is a potential approach for lung cancer therapy through targeting LCSCs.

The APC tumor suppressor is required for epithelial cell polarization and three-dimensional morphogenesis

The Adenomatous Polyposis Coli (APC) tumor suppressor has been previously implicated in the control of apical-basal polarity; yet, the consequence of APC loss-of-function in epithelial polarization and morphogenesis has not been characterized. To test the hypothesis that APC is required for the establishment of normal epithelial polarity and morphogenesis programs, we generated APC-knockdown epithelial cell lines. APC depletion resulted in loss of polarity and multi-layering on permeable supports, and enlarged, filled spheroids with disrupted polarity in 3D culture. Importantly, these effects of APC knockdown were independent of Wnt/β-catenin signaling, but were rescued with either full-length or a carboxy (c)-terminal segment of APC. Moreover, we identified a gene expression signature associated with APC knockdown that points to several candidates known to regulate cell-cell and cell-matrix communication. Analysis of epithelial tissues from mice and humans carrying heterozygous APC mutations further supports the importance of APC as a regulator of epithelial behavior and tissue architecture. These data also suggest that the initiation of epithelial-derived tumors as a result of APC mutation or gene silencing may be driven by loss of polarity and dysmorphogenesis.

The deubiquitinase USP28 controls intestinal homeostasis and promotes colorectal cancer

Colorectal cancer is the third most common cancer worldwide. Although the transcription factor c-MYC is misregulated in the majority of colorectal tumors, it is difficult to target directly. The deubiquitinase USP28 stabilizes oncogenic factors, including c-MYC; however, the contribution of USP28 in tumorigenesis, particularly in the intestine, is unknown. Here, using murine genetic models, we determined that USP28 antagonizes the ubiquitin-dependent degradation of c-MYC, a known USP28 substrate, as well as 2 additional oncogenic factors, c-JUN and NOTCH1, in the intestine. Mice lacking Usp28 had no apparent adverse phenotypes, but exhibited reduced intestinal proliferation and impaired differentiation of secretory lineage cells. In a murine model of colorectal cancer, Usp28 deletion resulted in fewer intestinal tumors, and importantly, in established tumors, Usp28 deletion reduced tumor size and dramatically increased lifespan. Moreover, we identified Usp28 as a c-MYC target gene highly expressed in murine and human intestinal cancers, which indicates that USP28 and c-MYC form a positive feedback loop that maintains high c-MYC protein levels in tumors. Usp28 deficiency promoted tumor cell differentiation accompanied by decreased proliferation, which suggests that USP28 acts similarly in intestinal homeostasis and colorectal cancer models. Hence, inhibition of the enzymatic activity of USP28 may be a potential target for cancer therapy.

Extensive telomere erosion in the initiation of colorectal adenomas and its association with chromosomal instability

BACKGROUND

Telomere shortening, dysfunction, and fusion may facilitate the acquisition of large-scale genomic rearrangements, driving clonal evolution and tumor progression. The relative contribution that telomere dysfunction and/or APC mutation play in the chromosome instability that occurs during colorectal tumorigenesis is not clear.

METHODS

We used high-resolution telomere length and fusion analysis to analyze 85 adenomatous colorectal polyps obtained from 10 patients with familial adenomatous polyposis and a panel of 50 colorectal carcinomas with patient-matched normal colonic mucosa. Telomerase activity was determined using the telomeric repeat amplification protocol. Array-CGH was used to detect large-scale genomic rearrangements. Pearson correlation and Student t test were used, and all statistical tests were two-sided.

RESULTS

Despite the presence of telomerase activity, we observed apparent telomere shortening in colorectal polyps that correlated with large-scale genomic rearrangements (P < .0001) but was independent of polyp size and indistinguishable from that observed in colorectal carcinomas (P = .82). We also observed apparent lengthening of telomeres in both polyps and carcinomas. The extensive differences in mean telomere length of up to 4.6kb between patient-matched normal mucosa and polyps were too large to be accounted for by replicative telomere erosion alone. Telomere fusion events were detected in both polyps and carcinomas; the mutational spectrum accompanying fusion was consistent with alternative nonhomologous end joining.

CONCLUSIONS

Telomere length distributions observed in colorectal polyps reflect the telomere length composition of the normal originating cells from which clonal growth was initiated. Originating cells containing both short telomeres and APC mutations may give rise to polyps that exhibit short telomeres and are prone to telomere dysfunction, driving genomic instability and progression to malignancy. J Natl Cancer Inst;2013;105:1202-1211.

Apc regulates the function of hematopoietic stem cells largely through β-catenin-dependent mechanisms

Emerging evidence suggests that adenomatous polyposis coli (Apc) plays a critical role in the maintenance of hematopoietic stem/progenitor cells (HSCs/HPCs). The molecular pathways responsible for the function of Apc in HSCs/HPCs remain unclear. By genetic approach, we demonstrated that inactivation of β-catenin rescued the exhaustion of Apc-deficient HSCs/HPCs, thereby preventing bone marrow failure in Apc-deficient mice. β-catenin loss inhibited the excessive proliferation and apoptosis of Apc-deficient HSCs/HPCs, as well as their defects in myeloid and erythroid differentiation. In addition, loss of β-catenin reversed the down-regulation of Cdkn1a, Cdkn1b, and Mcl1 induced by Apc ablation in Lin(-)Sca(+)c-Kit(+). In assays of long-term stem cell function, the HSCs with deficiency of both Apc and β-catenin displayed a significantly enhanced self-renewal capacity compared with β-catenin-deficient and control HSCs. Our findings suggest that Apc regulates the survival, proliferation, and differentiation of HSCs/HPCs largely through a β-catenin-mediated pathway. They also indicate that multiple downstream targets of Apc including β-catenin may coordinately regulate HSC self-renewal.

Chemoprevention utility of silibinin and Cdk4 pathway inhibition in Apc(-/+) mice

Background

Colorectal cancer (CRC) is the second leading cause of death from cancer in the United States. Colorectal cancers have a prolonged latency following initiation that may span decades providing ample time for implementing a chemoprevention strategy that could block or reverse the progression to CRC. Cdk4 pathway alterations have been linked to a number of cancers including CRC. In these experiments we focused on the Cdk4 pathway and its role in intestinal tumorigenesis as a possible target in chemoprevention strategies.

Methods

We evaluated the effect of Cdk4 blockade on the prevention of intestinal tumor formation by crossing Cdk4^−/− mice to Apc^−/+ mice. In addition, we tested the effect of the dietary compound silibinin on the Cdk4 pathway in Apc^−/+ mice and HT-29 colon cancer cells in culture.

Results

Cdk4^−/− mice backcrossed to Apc^−/+ mice reduced intestinal adenoma formation compared to Apc^−/+ controls. Silibinin effectively targeted the Cdk4 pathway causing hypophosphorylation of the retinoblastoma protein, inhibited cell growth, and induced apoptosis. As a result silibinin blocked the development of intestinal adenomas by 52% in this genetic model (Apc^−/+ mice) of early events in colorectal cancer formation. No toxic abnormalities were detected in mice which received silibinin.

Conclusions

Modification of the Cdk4 pathway using a natural plant-derived compound such as silibinin may be a useful chemopreventive strategy for colorectal carcinomas.

APC/β-catenin-rich complexes at membrane protrusions regulate mammary tumor cell migration and mesenchymal morphology

Background

The APC tumor suppressor is mutated or downregulated in many tumor types, and is prominently localized to punctate clusters at protrusion tips in migratory cells, such as in astrocytes where it has been implicated in directed cell motility. Although APC loss is considered an initiating event in colorectal cancer, for example, it is less clear what role APC plays in tumor cell motility and whether loss of APC might be an important promoter of tumor progression in addition to initiation.

Methods

The localization of APC and β-catenin was analyzed in multiple cell lines, including non-transformed epithelial lines treated with a proteasome inhibitor or TGFβ to induce an epithelial-to-mesenchymal transition (EMT), as well as several breast cancer lines, by immunofluorescence. APC expression was knocked down in 4T07 mammary tumor cells using lentiviral-mediated delivery of APC-specific short-hairpin (sh) RNAs, and assessed using quantitative (q) reverse-transcriptase (RT)-PCR and western blotting. Tumor cell motility was analyzed by performing wound-filling assays, and morphology via immunofluorescence (IF) and phase-contrast microscopy. Additionally, proliferation was measured using BrdU incorporation, and TCF reporter assays were performed to determine β-catenin/TCF-mediated transcriptional activity.

Results

APC/β-catenin-rich complexes were observed at protrusion ends of migratory epithelial cells treated with a proteasome inhibitor or when EMT has been induced and in tumor cells with a mesenchymal, spindle-like morphology. 4T07 tumor cells with reduced APC levels were significantly less motile and had a more rounded morphology; yet, they did not differ significantly in proliferation or β-catenin/TCF transcriptional activity. Furthermore, we found that APC/β-catenin-rich complexes at protrusion ends were dependent upon an intact microtubule cytoskeleton.

Conclusions

These findings indicate that membrane protrusions with APC/β-catenin-containing puncta control the migratory potential and mesenchymal morphology of mammary tumor cells and suggest that APC loss during later stages of tumor progression might impact tumor cell dissemination or colonization.

Apc mutation enhances PyMT-induced mammary tumorigenesis

The Adenomatous Polyposis Coli (APC) tumor suppressor gene is silenced by hypermethylation or mutated in up to 70% of human breast cancers. In mouse models, Apc mutation disrupts normal mammary development and predisposes to mammary tumor formation; however, the cooperation between APC and other mutations in breast tumorigenesis has not been studied. To test the hypothesis that loss of one copy of APC promotes oncogene-mediated mammary tumorigenesis, Apc^Min/+ mice were crossed with the mouse mammary tumor virus (MMTV)-Polyoma virus middle T antigen (PyMT) or MMTV-c-Neu transgenic mice. In the PyMT tumor model, the Apc^Min/+ mutation significantly decreased survival and tumor latency, promoted a squamous adenocarcinoma phenotype, and enhanced tumor cell proliferation. In tumor-derived cell lines, the proliferative advantage was a result of increased FAK, Src and JNK signaling. These effects were specific to the PyMT model, as no changes were observed in MMTV-c-Neu mice carrying the Apc^Min/+ mutation. Our data indicate that heterozygosity of Apc enhances tumor development in an oncogene-specific manner, providing evidence that APC-dependent pathways may be valuable therapeutic targets in breast cancer. Moreover, these preclinical model systems offer a platform for dissection of the molecular mechanisms by which APC mutation enhances breast carcinogenesis, such as altered FAK/Src/JNK signaling.

Adenomatous polyposis coli protein regulates the cellular response to DNA replication stress

The adenomatous polyposis coli (APC) tumor suppressor traffics between nucleus and cytoplasm to perform distinct functions. Here we identify a specific role for APC in the DNA replication stress response. The silencing of APC caused an accumulation of asynchronous cells in early S phase and delayed S phase progression in cells released from hydroxyurea-mediated replication arrest. Immunoprecipitation assays revealed a selective binding of APC to replication protein A 32kDa subunit (RPA32), and the APC-RPA32 complex increased at chromatin after hydroxyurea treatment. Interestingly, APC knock-down prevented accumulation at chromatin of the stress-induced S33- and S29-phosphorylated forms of RPA32, and reduced the expression of ATR-phosphorylated forms of S317-phospho-Chk1 and γ-H2AX. Using RPA32-inducible cells we showed that reconstitution of RPA32 diminished the S-phase delay caused by loss of APC. In contrast to full-length APC, the truncated APC mutant protein expressed in SW480 colon cancer cells was impaired in its binding and regulation of RPA32, and failed to regulate cell cycle after replication stress. We propose that APC associates with RPA at stalled DNA replication forks and promotes the ATR-dependent phosphorylation of RPA32, Chk1 and γ-H2AX in response to DNA replication stress, thereby influencing the rate of re-entry into the cell cycle.

Mechanisms Regulating Microtubule Binding, DNA Replication, and Apoptosis are Controlled by the Intestinal Tumor Suppressor APC. Curr Colorectal Cancer Rep. 2011;7:145-151. [PMID: 23308069 DOI: 10.1007/s11888-011-0088-z]

Colorectal cancer (CRC) results from the progressive accumulation of both genetic and epigenetic alterations that lead to the transformation of normal colorectal epithelium to benign (adenoma) and invasive (carcinoma) disease. Since its discovery in mutated form as the causative gene for familial adenomatous polyposis coli (FAP), as well as in many sporadic CRCs, the APC tumor suppressor has been shown to possess numerous functions within the cell including regulation of WNT signaling pathways and its transcriptional effects, cell migration, and chromosome separation. In recent years, other novel roles for APC have been investigated and suggest that APC can also repress DNA replication and enhance apoptosis. Further insights into the mechanisms by which APC contributes to tumor suppression will accelerate the diagnosis and treatment of CRC.

Rho GTPase Cdc42 is a direct interacting partner of Adenomatous Polyposis Coli protein and can alter its cellular localization

Adenomatous Polyposis Coli (APC) is a tumor suppressor gene product involved in colon cancer. APC is a large multidomain molecule of 2843 amino acid residues and connects cell-cell adhesion, the F-actin/microtubule cytoskeleton and the nucleus. Here we show that Cdc42 interacts directly with the first three armadillo repeats of APC by yeast two-hybrid screens. We confirm the Cdc42-APC interaction using pulldown assays in vitro and FRET assays in vivo. Interestingly, Cdc42 interacts with APC at leading edge sites where F-actin is enriched. In contrast, Cdc42 interacts with the truncated mutant APC^1–1638 in cellular puncta associated with the golgi-lysozome pathway in transfected CHO cells. In HCT116 and SW480 cells, Cdc42 induces the relocalization of endogenous APC and the mutant APC^1–1338 to the plasma membrane and cellular puncta, respectively. Taken together, these data indicate that the Cdc42-APC interaction induces localization of both APC and mutant APC and may thus play a direct role in the functions of these proteins.

Topoisomerase IIalpha binding domains of adenomatous polyposis coli influence cell cycle progression and aneuploidy

BACKGROUND

Truncating mutations in the tumor suppressor gene APC (Adenomatous Polyposis Coli) are thought to initiate the majority of colorectal cancers. The 15- and 20-amino acid repeat regions of APC bind beta-catenin and have been widely studied for their role in the negative regulation of canonical Wnt signaling. However, functions of APC in other important cellular processes, such as cell cycle control or aneuploidy, are only beginning to be studied. Our previous investigation implicated the 15-amino acid repeat region of APC (M2-APC) in the regulation of the G2/M cell cycle transition through interaction with topoisomerase IIalpha (topo IIalpha).

METHODOLOGY/PRINCIPAL FINDINGS

We now demonstrate that the 20-amino acid repeat region of APC (M3-APC) also interacts with topo IIalpha in colonic epithelial cells. Expression of M3-APC in cells with full-length endogenous APC causes cell accumulation in G2. However, cells with a mutated topo IIalpha isoform and lacking topo IIbeta did not arrest, suggesting that the cellular consequence of M2- or M3-APC expression depends on functional topoisomerase II. Both purified recombinant M2- and M3-APC significantly enhanced the activity of topo IIalpha. Of note, although M3-APC can bind beta-catenin, the G2 arrest did not correlate with beta-catenin expression or activity, similar to what was seen with M2-APC. More importantly, expression of either M2- or M3-APC also led to increased aneuploidy in cells with full-length endogenous APC but not in cells with truncated endogenous APC that includes the M2-APC region.

CONCLUSIONS/SIGNIFICANCE

Together, our data establish that the 20-amino acid repeat region of APC interacts with topo IIalpha to enhance its activity in vitro, and leads to G2 cell cycle accumulation and aneuploidy when expressed in cells containing full-length APC. These findings provide an additional explanation for the aneuploidy associated with many colon cancers that possess truncated APC.

Ablation of IL-17A abrogates progression of spontaneous intestinal tumorigenesis. Proc Natl Acad Sci U S A. 2010;107:5540-5544. [PMID: 20212110 DOI: 10.1073/pnas.0912675107]

The intrinsic role of endogenous IL-17A in spontaneous intestinal tumorigenesis has not been addressed previously to our knowledge. Ablation of IL-17A significantly reduced tumor development in mice bearing a heterozygote mutation in the adenomatous polyposis coli (APC) gene (Apc(Min/+) mice). There was also a decrease in inflammatory cytokines and proinflammatory mediators, reduced infiltration of lymphocytes including T cells, and preservation of intestinal architecture and the presence of APC protein in intestinal epithelial cells. Interestingly, IL-17A ablation also corrected immunological abnormalities such as splenomegaly and thymic atrophy in Apc(Min/+) mice. CD4 T cells from Apc(Min/+) mice showed hyperproliferative potential in vitro and in vivo and increased levels of IL-17A and IL-10. The effector CD4 T cells from Apc(Min/+) mice were more resistant to regulatory T cell-mediated suppression. Finally, these CD4 T cells induced colitis in immunodeficient mice upon adoptive transfer, whereas the ablation of IL-17A in CD4 T cells in Apc(Min/+) mice completely abolished this pathogenic potential in vivo. Taken together, our results show that CD4 T cell-derived IL-17A promotes spontaneous intestinal tumorigenesis with altered functions of CD4 T cells in Apc(Min/+) mice.

The APC tumor suppressor is required for epithelial integrity in the mouse mammary gland

Inactivation of the adenomatous polyposis coli (APC) tumor suppressor has been associated with mammary tumorigenesis in mouse models and through epidemiological studies of human breast cancers, but the normal role for APC in mammary development has not been thoroughly characterized. We report here that Apc(Min/+) mice containing one functional allele of Apc have severely disrupted lobuloalveolar development during pregnancy and lactation, time points at which Apc gene expression is at its highest levels in normal mice. This phenotype was accompanied by altered proliferation during pregnancy and involution, increased apoptosis throughout lactation, the formation of preneoplastic lesions and changes in specific genes associated with each of these processes. Neither modifications in beta-catenin localization, nor the expression of beta-catenin transcriptional target genes, were observed in Apc(Min/+) mammary tissues; however, tissues from lactating Apc(Min/+) mice had a significantly altered epithelial architecture, including disrupted localization of junctional proteins and polarization. Consistent with these findings, APC knockdown in non-transformed mouse mammary epithelial cells in vitro resulted in altered monolayer formation and proliferation without changes in beta-catenin-mediated transcription. These results suggest that APC expression is tightly regulated during mammary gland development and is required for normal mammary homeostasis and tumor suppression primarily through maintaining epithelial integrity.

Loss of Rb1 in the gastrointestinal tract of Apc1638N mice promotes tumors of the cecum and proximal colon

To examine the role of Rb1 in gastrointestinal (GI) tumors, we generated mice with an Apc(1638N) allele, Rb(tm2brn) floxed alleles, and a villin-cre transgene (RBVCA). These animals had exon 19 deleted from Rb1 throughout the GI tract. We have shown previously that Rb1 deficiency is insufficient for GI tumor initiation, with inactivation of an Apc allele capable of overcoming the insufficiency. In this study we demonstrate that RBVCA mice have reduced median survival because of an increase in tumor incidence and multiplicity in the cecum and the proximal colon. Large intestinal tumors are predominantly adenomas, whereas the tumors of the small intestine are a mixture of adenomas and adenocarcinomas. We find truncation mutations to the second Apc allele in tumors of both the large and small intestine. Expression profiles of duodenal and cecal tumors relative to each other show unique gene subsets up and down regulated. Substantial expression patterns compare to human colorectal cancer, including recapitulation of embryonic genes. Our results indicate that Rb1 has significant influence over tumor location in the GI tract, and that both cecal and duodenal tumors initiate through inactivation of Apc. Expression profile analysis indicates the two tumor types differentially regulate distinct sets of genes that are over-expressed in a majority of human colorectal carcinomas.

Interaction between tumor suppressor adenomatous polyposis coli and topoisomerase IIalpha: implication for the G2/M transition

The tumor suppressor adenomatous polyposis coli (APC) is implicated in regulating multiple stages of the cell cycle. APC participation in G1/S is attributed to its recognized role in Wnt signaling. APC function in the G2/M transition is less well established. To identify novel protein partners of APC that regulate the G2/M transition, APC was immunoprecipitated from colon cell lysates and associated proteins were analyzed by matrix-assisted laser desorption ionization/time of flight (MALDI-TOF). Topoisomerase IIalpha (topo IIalpha) was identified as a potential binding partner of APC. Topo IIalpha is a critical regulator of G2/M transition. Evidence supporting an interaction between endogenous APC and topo IIalpha was obtained by coimmunoprecipitation, colocalization, and Förster resonance energy transfer (FRET). The 15-amino acid repeat region of APC (M2-APC) interacted with topo IIalpha when expressed as a green fluorescent protein (GFP)-fusion protein in vivo. Although lacking defined nuclear localization signals (NLS) M2-APC predominantly localized to the nucleus. Furthermore, cells expressing M2-APC displayed condensed or fragmented nuclei, and they were arrested in the G2 phase of the cell cycle. Although M2-APC contains a beta-catenin binding domain, biochemical studies failed to implicate beta-catenin in the observed phenotype. Finally, purified recombinant M2-APC enhanced topo IIalpha activity in vitro. Together, these data support a novel role for APC in the G2/M transition, potentially through association with topo IIalpha.

The APC tumor suppressor inhibits DNA replication by directly binding to DNA via its carboxyl terminus

BACKGROUND & AIMS

The APC tumor suppressor is well known for its ability to regulate Wnt signaling through mediation of beta-catenin levels in the cell. Transient over expression of the tumor suppressor gene APC in colon cancer cells prevents entry into S phase of the cell cycle, a phenotype only partially restored by cotransfection of a transcriptionally active form of beta-catenin. In an attempt to define its transcription-independent tumor suppressor functions, we tested whether APC directly affects DNA replication.

METHODS

A transcriptionally quiescent in vitro DNA replication system, the polymerase chain reaction, DNA binding assays, and transient transfections in colon cancer cell lines were used to determine the effects of APC on DNA replication and the mechanism by which it works.

RESULTS

We report that exogenous full-length APC inhibits replication of template DNA through a function that maps to amino acids 2140-2421, a region of the protein commonly lost by somatic or germline mutation. This segment of APC directly interacts with DNA, while mutation of the DNA-binding S(T)PXX motifs within it abolishes DNA binding and reduces inhibition of DNA replication. Phosphorylation of this segment by cyclin-dependent kinases also reduces inhibition of DNA replication. Furthermore, transient transfection of an APC segment encoding amino acids 2140-2421 into a colon cancer cell line with mutant APC prevents cell cycle progression into or through S phase.

CONCLUSIONS

Our results suggest that APC can negatively regulate cell cycle progression through inhibition of DNA replication by direct interaction with DNA.

Haploinsufficiency of Krüppel-like factor 4 promotes adenomatous polyposis coli dependent intestinal tumorigenesis

The zinc finger transcription factor Krüppel-like factor 4 (KLF4) is frequently down-regulated in colorectal cancer. Previous studies showed that the expression of KLF4 was activated by the colorectal cancer tumor suppressor adenomatous polyposis coli (APC) and that KLF4 repressed the Wnt/beta-catenin pathway. Here, we examined whether KLF4 plays a role in modulating intestinal tumorigenesis by comparing the tumor burdens in mice heterozygous for the Apc(Min) allele (Apc(Min/+)) and those heterozygous for both the Apc(Min) and Klf4 alleles (Klf4(+/-)/Apc(Min/+)). Between 10 and 20 weeks of age, Klf4(+/-)/Apc(Min/+) mice developed, on average, 59% more intestinal adenomas than Apc(Min/+) mice (P < 0.0001). Immunohistochemical staining showed that Klf4 protein levels were lower in the normal-appearing intestinal tissues of Klf4(+/-)/Apc(Min/+) mice compared with wild-type, Klf4(+/-), or Apc(Min/+) mice. In contrast, the levels of beta-catenin and cyclin D1 were higher in the normal-appearing intestinal tissues of Klf4(+/-)/Apc(Min/+) mice compared with the other three genotypes. Klf4 levels were further decreased in adenomas from both Apc(Min/+) and Klf4(+/-)/Apc(Min/+) mice compared with their corresponding normal-appearing tissues. Reverse transcription-PCR showed an inverse correlation between adenoma size and Klf4 mRNA levels in both Klf4(+/-)/Apc(Min/+) and Apc(Min/+) mice. There was also a progressive loss of heterozygosity of the wild-type Apc allele in adenomas with increasing size from Klf4(+/-)/Apc(Min/+) and Apc(Min/+) mice. Results from this study show that KLF4 plays an important role in promoting the development of intestinal adenomas in the presence of Apc(Min) mutation.

Blockade of tumor necrosis factor-induced Bid cleavage by caspase-resistant Rb

Tumor necrosis factor-alpha (TNF) activates caspase-8 to cleave effector caspases or Bid, resulting in type-1 or type-2 apoptosis, respectively. We show here that TNF also induces caspase-8-dependent C-terminal cleavage of the retinoblastoma protein (Rb). Interestingly, fibroblasts from Rb(MI/MI) mice, in which the C-terminal caspase cleavage site is mutated, exhibit a defect in Bid cleavage despite caspase-8 activation. Recent results suggest that TNF receptor endocytosis is required for the activation of caspase-8. Consistent with this notion, inhibition of V-ATPase, which plays an essential role in acidification and degradation of endosomes, specifically restores Bid cleavage in Rb(MI/MI) cells. Inhibition of V-ATPase sensitizes Rb(MI/MI) but not wild-type fibroblasts to TNF-induced apoptosis and stimulates inflammation-associated colonic apoptosis in Rb(MI/MI) but not wild-type mice. These results suggest that Rb cleavage is required for Bid cleavage in TNF-induced type-2 apoptosis, and this requirement can be supplanted by the inhibition of V-ATPase.

Human homolog of Drosophila tumor suppressor Scribble negatively regulates cell-cycle progression from G1 to S phase by localizing at the basolateral membrane in epithelial cells

Drosophila tumor suppressor Scribble has been identified as an apical-basolateral polarity determinant in epithelia. A human homolog of Drosophila Scribble, human Scribble (hScrib), has been identified as a protein targeted by human papillomavirus E6 for the ubiquitin-mediated degradation dependent on E6AP, a cellular ubiquitin-protein ligase. Human Scribble is classified as a LAP protein, having leucine-rich repeats (LRRs) and PDZ domains. We investigated whether hScrib, which is thought to have a role in polarity determination based on the data of its Drosophila homolog, is involved in cell-cycle regulation and proliferation control of epithelia. Transfection of hScrib inhibits cell-cycle progression from G1 to S phase, and it up- and down-regulates expression of adenomatous polyposis coli and cyclins A and D1, respectively. Knockdown of hScrib expression by siRNA leads to cell-cycle progression from G1 to S phase. We explored functional domain mapping to reveal which domains of hScrib are critical for its cellular proliferation control and localization at the basolateral membrane. We found that LRRs and PDZ domain 1 are indispensable for hScrib to inhibit cell growth by blocking cell-cycle progression and to keep its proper localization. These data indicate that basolateral membrane localization of hScrib is closely related to its proliferation control. Our findings suggest the possibility that hScrib is involved in signal transduction to negatively regulate cell proliferation by localizing at the basolateral membrane of epithelial cells through LRRs and PDZ domains.

beta-Catenin/Wnt signaling regulates expression of the membrane type 3 matrix metalloproteinase in gastric cancer

Activation of Wnt signaling through beta-catenin dysregulation occurs in numerous human tumors, including gastric cancer. The specific consequences of Wnt signaling in gastric cancer, however, are not well characterized. This study shows that the introduction of mutant beta-catenin into gastric cancer cell lines by adenoviral infection enhances invasiveness and proliferation and up-regulates the expression of the gene encoding the matrix metalloproteinase (MMP) family member membrane type 3 MMP (MT3-MMP). Up-regulation of MT3-MMP is critical to the invasive phenotype as shown by small interfering RNA (siRNA) studies. Immunohistochemical staining also showed that MT3-MMP was highly expressed in gastric cancers with activating beta-catenin mutations. These observations suggest that Wnt activation may contribute to gastric cancer progression by increasing the invasiveness of neoplastic cells in the stomach via up-regulation of MT3-MMP expression.

Truncated APC is required for cell proliferation and DNA replication

The tumour suppressor APC is truncated in most colon cancers, which leads to the stabilization of beta-catenin and to the constitutive activation of Wnt signalling. However, it is not clear why colon cancer cells retain the truncated APC fragment. Here, we show that a decrease of APC levels achieved by RNA interference impairs cell proliferation and DNA replication, not only in 293 cells that express a wild-type protein, but also in SW480 colon cancer cells that express exclusively a truncated APC fragment. This correlates with a reduction of the levels of cyclin A, cyclin A-dependent kinase activity, p27(kip1) and the catalytic subunit of DNA polymerase delta. Thus, our data suggest that colon cancer cells retain a truncated APC fragment because it is essential for cell proliferation.

APC inhibits ERK pathway activation and cellular proliferation induced by RAS

Inactivating mutations in the adenomatous polyposis coli gene (APC), and activating mutations in RAS, occur in a majority of colorectal carcinomas. However, the relationship between these changes and tumorigenesis is poorly understood. RAS-induced activation of the ERK pathway was reduced by overexpressing APC in DLD-1 colorectal cancer cells. ERK activity was increased by Cre-virus-induced Apc knockout in primary Apc(flox/flox) mouse embryonic fibroblasts, indicating that APC inhibits ERK activity. ERK activity was increased by overexpression and decreased by knock down of beta-catenin. The activation of Raf1, MEK and ERK kinases by beta-catenin was reduced by co-expression of APC. These results indicate that APC inhibits the ERK pathway by an action on beta-catenin. RAS-induced activation of the ERK pathway was reduced by the dominant negative form of TCF4, indicating that the ERK pathway regulation by APC/beta-catenin signaling is, at least, partly caused by effects on beta-catenin/TCF4-mediated gene expression. The GTP loading and the protein level of mutated RAS were decreased in cells with reduced ERK activity as a result of APC overexpression, indicating that APC regulates RAS-induced ERK activation at least partly by reduction of the RAS protein level. APC regulates cellular proliferation and transformation induced by activation of both RAS and beta-catenin signaling.

Nitric oxide-donating aspirin induces apoptosis in human colon cancer cells through induction of oxidative stress

Nitric oxide-donating aspirin (NO-ASA) is a promising chemoprevention agent against colon cancer and other cancers. It consists of traditional ASA to which a NO-releasing moiety is bound through a spacer. NO-ASA inhibits colon cancer cell growth several hundred times more potently than does ASA. In Min mice, NO-ASA inhibited intestinal carcinogenesis without affecting cell proliferation. Thus, we examined whether NO-ASA's most important cell kinetic effect is the induction of apoptosis. After confirming induction of apoptosis in Min mice, we studied the underlying mechanism in human colon adenocarcinoma cells. NO-ASA's spacer formed a conjugate with glutathione, depleting glutathione stores. This induced oxidative stress (increased intracellular levels of peroxides and O(2)(.-)) leads to apoptosis by activating the intrinsic apoptosis pathway. NO-ASA disrupted adherens junctions by inducing cleavage of beta- and gamma-catenin, resulting in cell detachment. NO-ASA inhibited Wnt signaling by a dual mechanism: at low concentrations it blocked the formation of beta-catenin/Tcf complexes (dominant mechanism), and at higher concentrations it also cleaved beta-catenin. These findings provide a mechanism of action by a potent chemopreventive agent, underscore the significance of these pathways in regulating cell death in the context of cancer chemoprevention, and present a paradigm for developing agents with enhanced cancer cell growth inhibitory properties.

7,12-Dimethylbenzanthracene-dependent transcriptional regulation of adenomatous polyposis coli (APC) gene expression in normal breast epithelial cells is mediated by GC-box binding protein Sp3

In the present investigation, we have examined the transcriptional regulation of adenomatous polyposis coli (APC) gene expression in the spontaneously immortalized human normal breast epithelial cell line, MCF10A, in response to carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) treatment. The APC mRNA levels and the APC gene's promoter (pAPCP) activity were increased in MCF10A cells after treatment with DMBA. A sequential deletion analysis and site-directed mutagenesis of the pAPCP promoter revealed that the DMBA response is mediated through a GC-box element. Also, the GC-box binding agent mithramycin A, which prevents binding of proteins to the GC-box region, abolished DMBA-mediated increase of the pAPCP promoter activity. The specificity of the proteins binding to the GC-box region was characterized by gel-shift analysis. An increased binding of the GC-box binding proteins was observed in the gel-shift analysis with nuclear extracts from DMBA-treated MCF10A cells, which corresponded to the increased levels of Sp1 and Sp3 proteins. However, a super-shift of the DNA-protein complexes was observed with only anti-Sp3 antibody. Based on the chromatin-immunoprecipitation assay results, the Sp3 appeared to be a genuine protein binding to the GC-box site of the pAPCP promoter. In RNA interference experiments, in which the Sp3 expression was knocked down, the DMBA response on the pAPCP promoter activity was reduced, suggesting that the binding of Sp3 to the GC-box site is critical for DMBA-induced pAPCP promoter activity. From these results we conclude that the increased pAPCP promoter activity in the MCF10A cell line in response to DMBA treatment is mediated by Sp3.

The APC tumor suppressor promotes transcription-independent apoptosis in vitro

The APC tumor suppressor is found in nonproliferating epithelial cells of the colonic crypts and is mutated in most colorectal tumors. To understand the function of APC in normal epithelium and how its loss leads to tumor formation, we tested whether APC is a mediator of apoptosis using an in vitro assay that monitors caspase-3-mediated cleavage of lamin B protein or a colorimetric substrate in a cell-free Xenopus egg extract. Recombinant APC protein accelerates apoptosis-associated caspase activity independently of ongoing transcription and protein synthesis. Conversely, the addition of mutant APC and immunodepletion of Xenopus APC decelerates apoptosis-associated caspase activity. Acceleration of apoptosis by APC is abolished by the caspase-8 inhibitor Z-IETD-FMK, demonstrating that caspase-8 is an essential component of APC-mediated apoptosis. These results suggest that the induction of apoptosis may be one role of APC in tumor suppression and that this mechanism is independent of beta-catenin-mediated effects on transcription.

Global gene expression analysis in time series following N-acetyl L-cysteine induced epithelial differentiation of human normal and cancer cells in vitro

Background

Cancer prevention trials using different types of antioxidant supplements have been carried out at several occasions and one of the investigated compounds has been the antioxidant N-acetyl-L-cysteine (NAC). Studies at the cellular level have previously demonstrated that a single supplementation of NAC induces a ten-fold more rapid differentiation in normal primary human keratinocytes as well as a reversion of a colon carcinoma cell line from neoplastic proliferation to apical-basolateral differentiation [1]. The investigated cells showed an early change in the organization of the cytoskeleton, several newly established adherens junctions with E-cadherin/β-catenin complexes and increased focal adhesions, all features characterizing the differentiation process.

Methods

In order to investigate the molecular mechanisms underlying the proliferation arrest and accelerated differentiation induced by NAC treatment of NHEK and Caco-2 cells in vitro, we performed global gene expression analysis of NAC treated cells in a time series (1, 12 and 24 hours post NAC treatment) using the Affymetrix GeneChip™ Human Genome U95Av2 chip, which contains approximately 12,000 previously characterized sequences. The treated samples were compared to the corresponding untreated culture at the same time point.

Results

Microarray data analysis revealed an increasing number of differentially expressed transcripts over time upon NAC treatment. The early response (1 hour) was transient, while a constitutive trend was commonly found among genes differentially regulated at later time points (12 and 24 hours). Connections to the induction of differentiation and inhibition of growth were identified for a majority of up- and down-regulated genes. All of the observed transcriptional changes, except for seven genes, were unique to either cell line. Only one gene, ID-1, was mutually regulated at 1 hour post treatment and might represent a common mediator of early NAC action.

The detection of several genes that previously have been identified as stimulated or repressed during the differentiation of NHEK and Caco-2 provided validation of results. In addition, real-time kinetic PCR analysis of selected genes also verified the differential regulation as identified by the microarray platform.

Conclusion

NAC induces a limited and transient early response followed by a more consistent and extensively different expression at later time points in both the normal and cancer cell lines investigated. The responses are largely related to inhibition of proliferation and stimulation of differentiation in both cell types but are almost completely lineage specific. ID-1 is indicated as an early mediator of NAC action.

Targeting the beta-catenin/APC pathway: a novel mechanism to explain the cyclooxygenase-2-independent anticarcinogenic effects of celecoxib in human colon carcinoma cells

Celecoxib, a cyclooxygenase-2 (COX-2) selective nonsteroidal anti-inflammatory drug, is a new anticarcinogenic agent. Its antitumor effects depend on the one hand on its COX-2-inhibiting potency, but on the other hand on COX-2-independent mechanisms, which until now have not been fully understood. Here, we investigated whether celecoxib has an impact on the APC/beta-catenin pathway, which has been shown to play a pivotal role in the development of various cancers, especially of the colon. After only 2 h of treatment of human Caco-2 colon carcinoma cells with 100 muM celecoxib, we observed a rapid translocation of beta-catenin from its predominant membrane localization to the cytoplasm. Inhibition of the glycogen-synthase-kinase-3beta (GSK-3beta) by LiCl prevented this celecoxib-induced translocation, suggesting that phosphorylation of beta-catenin by the GSK-3beta kinase was essential for this release. Furthermore, the cytosolic accumulation was accompanied by a rapid increase of beta-catenin in the nuclei, starting already 30 min after celecoxib treatment. The DNA binding activity of beta-catenin time dependently decreased 2 h after celecoxib treatment. After this cellular reorganization, we observed a caspase- and proteasome-dependent degradation of beta-catenin after 8 h of drug incubation. Celecoxib-induced beta-catenin degradation was also observed in various other tumor cell lines (HCT-116, MCF-7, and LNCAP) but was not seen after treatment of Caco-2 cells with either the anticarcinogenic nonsteroidal anti-inflammatory drug R-flurbiprofen or the highly COX-2-selective inhibitor rofecoxib. These findings indicate that the anticarcinogenic effects of celecoxib can be explained, at least partly, by an extensive degradation of beta-catenin in human colon carcinoma cells.

Zinc stabilizes adenomatous polyposis coli (APC) protein levels and induces cell cycle arrest in colon cancer cells

In the present study, we investigated the mechanisms by which zinc causes growth arrest in colon cancer cells. The results suggest that zinc treatment stabilizes the levels of the wild-type adenomatous polyposis coli (APC) protein at the post-translational level since the APC mRNA levels and the promoter activity of the APC gene were decreased in HCT-116 cells (which express the wild-type APC gene) after treatment with ZnCl2. Increased levels of wild-type but not truncated APC proteins were required for the ZnCl2-mediated G2/M phase arrest in different colon cancer cell lines. We further tested whether serum-stimulation, which induces cell cycle arrest in the S phase, can relieve ZnCl2-induced G2/M phase arrest of HCT-116 cells. Results showed that in the HCT-116 cells pretreated with ZnCl2, the serum-stimulation neither changed the distribution of G2/M phase arrested cells nor the increased levels of APC protein. The G2/M phase arrest correlated with retarded growth of HCT-116 cells. To further establish that wild-type APC protein plays a role in ZnCl2-induced G2/M arrest, we treated SW480 colon cancer cells that express truncated APC protein. We found that ZnCl2 treatment did not induce G2/M phase arrest in SW480 cells; however, the cell growth was retarded due to the loss of E-cadherin and alpha-tubulin levels. These results suggest that ZnCl2 inhibits the proliferation of colon cancer cells (which carry the wild-type APC gene) through stabilization of the APC protein and cell cycle arrest in the G2/M phase. On the other hand, ZnCl2 inhibits the proliferation of colon cancer cells (which carry the mutant APC gene) by disrupting cellular attachment and microtubule stability.

Isoforms of the APC tumor suppressor and their ability to inhibit cell growth and tumorigenicity

Mutation of the APC tumor suppressor gene is one of the earliest events in the development of most colorectal tumors. The APC gene encodes multiple protein isoforms through a complicated pattern of expression and alternative splicing. The role that each isoform plays in cellular physiology is unknown, although the presence of some of these isoforms in postmitotic cells suggests a role in controlling cell growth or promoting differentiation. Three APC isoforms that differ in their amino-terminal domains were evaluated by gene transfer experiments using a colon cancer cell line that lacks functional APC. All three isoforms alter cellular morphology and affect cell growth by elongating the G1 phase of the cell cycle. The conventional APC and brain-specific APC isoforms suppress the tumorigenic phenotype of cultured cells, while the 0.3 APC isoform does not. In support of these experiments, BrdU incorporation as a marker for S-phase entry occurs at a higher level in transiently transfected cells with 0.3 APC when compared to cells transfected with the other isoforms. All three APC isoforms colocalize with microtubules and dramatically reduce beta-catenin activity to the same extent in transiently transfected cancer cells, suggesting that the different effects of each isoform on tumorigenesis may be nontranscriptional in origin.

Aberrant methylation of the cyclin D2 promoter in primary small cell, nonsmall cell lung and breast cancers

DNA methylation alteration of several genes contributes to human tumorigenesis. Cyclin D2, a member of the D-type cyclins, is implicated in cell cycle regulation and malignant transformation. In our study, we examined the methylation status of the cyclin D2 promoter in small cell lung cancer (SCLC), nonsmall cell lung cancer (NSCLC), breast tumors and tumor cell lines. We observed that aberrant methylation of cyclin D2 was present in 32 of 56 (57%) SCLC cell lines, 7 of 32 (22%) SCLC tumor tissues; 25 of 61 (47%) NSCLC cell lines, 19 of 48 (40%) NSCLC tumor tissues; 18 of 30 (60%) breast tumor cell lines and 19 of 63 (30%) breast tumor tissues. Methylation was more frequent in the tumor cell lines compared to the primary breast and SCLC tumors (p = 0.007 and p = 0.001, respectively). Methylation was rare in the control tissue samples; 0 of 12 peripheral blood lymphocytes; 0 of 12 buccal epithelial cells; 0 of 18 nonmalignant lung tissues and 3 of 28 (11%) nonmalignant breast tissues. Promoter methylation correlated with loss of transcript by reverse transcription PCR (RT-PCR) in 9 of 11 (6 lung, 5 breast) tumor cell lines tested. Two cell lines that were not methylated also lacked expression, suggesting that other mechanisms of inactivation may be involved. Expression was restored by treatment with the demethylating agent, 5 aza 2' deoxycytidine, in all 9 methylated cell lines. Our results confirm earlier reports in breast cancer and indicate that aberrant methylation of cyclin D2 may contribute to the pathogenesis of the 2 major types of lung cancers.

Nitric oxide-donating aspirin inhibits beta-catenin/T cell factor (TCF) signaling in SW480 colon cancer cells by disrupting the nuclear beta-catenin-TCF association

Dysregulation of the Wnt pathway and altered Beta-catenin expression are central early events in colorectal carcinogenesis. We studied the ortho, meta, and para (o-, m-, and p-) positional isomers of NO-donating aspirin (NO-ASA), a chemopreventive agent against colon cancer, for their effect on Beta-catenin/T cell factor (TCF) signaling. In human SW480 colon carcinoma cells, cell-growth inhibition by NO-ASA [IC50 values for p-, o-, and m- were 48.1 +/- 4.3 (mean +/-SEM), 60.4 +/- 2.1, and 900 +/-50 microM, respectively] was accompanied by significant inhibition of Beta-catenin signaling. We determined Beta-catenin-dependent TCF-4 transcriptional activity by measuring the activity of the luciferase gene placed under the control of TCF-4 regulatory sequences. The IC50 values for Beta-catenin/TCF-4-signaling inhibition by NO-ASA were: o-, 2.6 +/- 0.4; m-, 15 +/- 5; p-, 1.1 +/- 0.1 microM; and for ASA, >5,000 microM. Total or nuclear levels of Beta-catenin and its distribution in the cell were not altered by NO-ASA, as judged by protein expression levels and semiquantitative immunofluorescence analysis. NO-ASA disrupted the association of Beta-catenin and TCF-4 in the nucleus, whereas ASA did not affect it. NO-ASA reduced the expression of cyclin D1, a downstream target gene that plays an important role in colon carcinogenesis. In contrast, a structural analog of NO-ASA lacking the -NO2 moiety did not affect TCF-4 transcriptional activity. Thus, NO-ASA inhibits Beta-catenin-mediated TCF activity by preventing the formation of the Beta-catenin/TCF-4 complex. This effect, occurring at NO-ASA concentrations far below those required to inhibit cell growth, may be a critical early event in the chemopreventive activity of NO-ASA against colon cancer.