Adenomatous polyposis coli (APC) plays multiple roles in the intestinal and colorectal epithelia

Altered microbiota caused by disordered gut motility leads to an overactivation of intestinal immune system in APC1638T mice

Adenomatous polyposis coli (APC) is recognized as an antioncogene related to familial adenomatous polyposis and colorectal cancers. However, APC is a large protein with multiple binding partners, indicating APC has diverse roles besides as a tumor suppressor. We have ever studied the roles of APC by using APC1638T/1638T (APC1638T) mice. Through those studies, we have noticed stools of APC1638T mice were smaller than those of APC+/+ mice and hypothesized there be a disturbance in fecal formation processes in APC1638T mice. The gut motility was morphologically analyzed by immunohistochemical staining of the Auerbach's plexus. Gut microbiota was analyzed by terminal restriction fragment length polymorphism (T-RFLP). IgA concentration in stools was determined by enzyme-linked immunosorbent assay (ELISA). As results, macroscopic findings suggestive of large intestinal dysmotility and microscopic findings of disorganization and inflammation of the plexus were obtained in APC1638T mice. An alteration of microbiota composition, especially increased Bacteroidetes population was observed. Increases in IgA positive cells and dendritic cells in the ileum with high fecal IgA concentration were also confirmed, suggesting over-activation of gut immunity. Our findings will contribute to our understanding of APC's functions in the gastrointestinal motility, and lead to a development of novel therapies for gut dysmotility-related diseases.

Decreased Podocyte Vesicle Transcytosis and Albuminuria in APC C-Terminal Deficiency Mice with Puromycin-Induced Nephrotic Syndrome

In minimal change nephrotic syndrome, podocyte vesicle transport is enhanced. Adenomatous polyposis coli (APC) anchors microtubules to cell membranes and plays an important role in vesicle transport. To clarify the role of APC in vesicle transport in podocytes, nephrotic syndrome was induced by puromycin amino nucleoside (PAN) injection in mice expressing APC1638T lacking the C-terminal of microtubule-binding site (APC1638T mouse); this was examined in renal tissue changes. The kidney size and glomerular area of APC1638T mice were reduced (p = 0.014); however, the number of podocytes was same between wild-type (WT) mice and APC1638T mice. The ultrastructure of podocyte foot process was normal by electron microscopy. When nephrotic syndrome was induced, the kidneys of WT+PAN mice became swollen with many hyaline casts, whereas these changes were inhibited in the kidneys of APC1638T+PAN mice. Electron microscopy showed foot process effacement in both groups; however, APC1638T+PAN mice had fewer vesicles in the basal area of podocytes than WT+PAN mice. Cytoplasmic dynein-1, a motor protein for vesicle transport, and α-tubulin were significantly reduced in APC1638T+PAN mice associated with suppressed urinary albumin excretion compared to WT+PAN mice. In conclusion, APC1638T mice showed reduced albuminuria associated with suppressed podocyte vesicle transport when minimal change nephrotic syndrome was induced.

Gut-Restricted Selective Cyclooxygenase-2 (COX-2) Inhibitors for Chemoprevention of Colorectal Cancer

Selective cyclooxygenase (COX)-2 inhibitors have been extensively studied for colorectal cancer (CRC) chemoprevention. Celecoxib has been reported to reduce the incidence of colorectal adenomas and CRC but is also associated with an increased risk of cardiovascular events. Here, we report a series of gut-restricted, selective COX-2 inhibitors characterized by high colonic exposure and minimized systemic exposure. By establishing acute ex vivo ¹⁸F-FDG uptake attenuation as an efficacy proxy, we identified a subset of analogues that demonstrated statistically significant in vivo dose-dependent inhibition of adenoma progression and survival extension in an APC^min/+ mouse model. However, in vitro-in vivo correlation analysis showed their chemoprotective effects were driven by residual systemic COX-2 inhibition, rationalizing their less than expected efficacies and highlighting the challenges associated with COX-2-mediated CRC disease chemoprevention.

Immune Microenvironment: New Insight for Familial Adenomatous Polyposis

Currently, the main treatment for familial adenomatous polyposis (FAP) is surgery, however, surgery is far from ideal as there are many complications such as uncontrollable bowel movements, pouch inflammation, anastomotic stricture, and secondary fibroids. Therefore, it is necessary to further expand the understanding of FAP and develop new treatments for FAP. The immune microenvironment including immune cells and cytokines, plays an important role in FAP and the progression of FAP to adenocarcinoma, thus it may be a promising treatment for FAP. In the current review, we summarized the recent progress in the immune microenvironment of FAP.

A further study on a disturbance of intestinal epithelial cell population and kinetics in APC1638T mice

Adenomatous polyposis coli (APC), a well-known anti-oncogene, is considered to have multiple functions through its several binding domains. We have continuingly studied APC^1638T/1638T mice (APC1638T mice) to elucidate the functions of APC other than tumor suppression. A distinctive feature of the APC1638T mice is they are tumor free and live as long as APC^+/+ mice (WT mice). Previously, we found the length of crypt-villus axis in the jejunum was significantly elongated in APC1638T mice compared with that of WT mice. The populations of goblet cells, Paneth cells, and enteroendocrine cells were also disordered in APC1638T mice. Here, we further analyzed the intestinal dyshomeostasis in APC1638T mice, focusing on the proliferation and differentiation of intestinal stem cell (ISC) lineages, and apoptotic cell shedding at the villus tips. We found that the proliferation of ISC lineages was normally controlled; however, the shedding process of apoptosis cells was significantly delayed in the APC1638T mouse jejunum. Furthermore, the number of microfold cells (M cells) was significantly increased in the APC1638T mouse jejunum. Our data suggested both differentiation process of ISCs and turnover process of intestinal epithelia were disturbed in APC1638T mice, and that contributed to the villus elongation in the APC1638T mouse jejunum.

Nod1 promotes colorectal carcinogenesis by regulating the immunosuppressive functions of tumor-infiltrating myeloid cells

Pioneering studies from the early 1980s suggested that bacterial peptidoglycan-derived muramyl peptides (MPs) could exert either stimulatory or immunosuppressive functions depending, in part, on chronicity of exposure. However, this Janus-faced property of MPs remains largely unexplored. Here, we demonstrate the immunosuppressive potential of Nod1, the bacterial sensor of diaminopimelic acid (DAP)-containing MPs. Using a model of self-limiting peritonitis, we show that systemic Nod1 activation promotes an autophagy-dependent reprogramming of macrophages toward an alternative phenotype. Moreover, Nod1 stimulation induces the expansion of myeloid-derived suppressor cells (MDSCs) and maintains their immunosuppressive potential via arginase-1 activity. Supporting the role of MDSCs and tumor-associated macrophages in cancer, we demonstrate that myeloid-intrinsic Nod1 expression sustains intra-tumoral arginase-1 levels to foster an immunosuppressive and tumor-permissive microenvironment during colorectal cancer (CRC) development. Our findings support the notion that bacterial products, via Nod1 detection, modulate the immunosuppressive activity of myeloid cells and fuel tumor progression in CRC.

The Canonical Wnt Signaling (Wnt/β-Catenin Pathway): A Potential Target for Cancer Prevention and Therapy

Precise regulation of signal transduction pathways is crucial for normal animal development and for maintaining cellular and tissue homeostasis in adults. The Wnt/Frizzled-mediated signaling includes canonical and non-canonical signal transduction pathways. Upregulation or downregulation of the canonical Wnt signaling (or the Wnt/β-Catenin signal transduction) leads to a variety of human diseases, including cancers, neurodegenerative disorders, skin and bone diseases, and heart deficiencies. Therefore, Wnt/β-Catenin signal transduction is a potential clinical target for the treatment of not only human cancers but also some other human chronic diseases. Here, some recent results including those from my laboratory highlighting the role of Wnt/β-Catenin signal transduction in human cancers will be reviewed. After a brief overview on canonical Wnt signaling and introducing some critical β-Catenin/T-cell factor-target genes, the interaction of canonical Wnt signaling with some common human cancers will be discussed. In the end, the different segments of the aforesaid signaling pathway, which have been considered as targets for clinical purposes, will be scrutinized.

Morphological and functional abnormalities of hippocampus in APC1638T/1638T mice

In the present study, we examined morphology and function of hippocampus in the APC^1638T/1638T mouse. Expression levels of the APC mRNA and protein were both identical in the hippocampus of the APC^+/+ and APC^1638T/1638T mice. The dentate gyrus of the APC^1638T/1638T hippocampus was thicker, and has more densely-populated granule cells in the APC^1638T/1638T mouse hippocampus. Immunoelectron microscopy revealed co-localization of APC with alpha-amino-3- hydroxy-5-methyl- isoxazole-4-propionate receptor (AMPA-R) and with PSD-95 at post-synapse in the APC^+/+ hippocampus, while APC1638T was co-localized with neither AMPA-R nor PSD-95 in the APC^1638T/1638T hippocampus. By immunoprecipitation assay, full-length APC expressed in the APC ^+/+ mouse was co-immunoprecipitated with AMPA-R and PSD-95. In contrast, APC1638T expressed in the APC^1638T/1638T mouse was not co-immunoprecipitated with AMPA-R and PSD-95. In the hippocampal CA1 region of the APC^1638T/1638T mouse, c-Fos expression after electric foot shock was decreased compared with the APC^+/+ mouse. The present study showed some abnormalities on morphology of the hippocampus caused by a truncated APC (APC1638T). Also, our findings suggest that failure in APC binding to AMPA-R and PSD-95 may bring about less activities of hippocampal neurons in the APC^1638T/1638T mouse.

The Role of the Gut Microbiome in Colorectal Cancer: Where Are We? Where Are We Going?

Microbiome (microbiota) is a community of all microorganisms inhabiting a specific site of the body, including pathogens, which distinguishes it from the physiological microflora. Intestinal dysbiosis plays a key role in the development of colorectal cancer. In the process of carcinogenesis, inflammation, immune response, and toxic metabolites play a significant role. Specific species of bacteria might affect the risk of colorectal cancer and growth of tumor already present. Assessment of changes in the intestinal microbiome during the development and progression of colorectal cancer might create a simple diagnostic tool, a useful biomarker, or might influence treatment strategies in colorectal cancer patients. Analysis of the gut microbiome provides the potential to develop noninvasive diagnostic tests that would be useful as new protective markers of colorectal cancer, prognostic markers in already present colorectal cancer, and predictive markers of response to treatment, especially immunotherapy.

Gastric precancerous lesions present in ApcMin/+ mice

The Apc^Min/+ mouse is an animal model for familial adenomatous polyposis, and aged Apc^Min/+ mice also spontaneously develop multiple tumors in their stomachs. However, gastric premalignant lesions in Apc^Min/+ mice have not been well characterized. The stomachs of Apc^Min/+ mice were compared with those of their wild type littermates at 24 weeks with hematoxylin and eosin (H&E) staining and alcian blue staining. Ki67, CD68 and CA199 expression was analyzed by immunohistochemistry. The results revealed the presence of epithelial proliferation and inflammatory infiltration in the forestomachs, glandular atrophy and intestinal metaplasia in the gastric bodies, and dysplasia in the gastric antra. The effect of mutations in the Apc gene on chronic gastritis and gastric precancerous lesions was characterized in Apc^Min/+ mice. These results suggest that Apc^Min/+ mice represent a genetic model for mechanistic studies and drug discovery in gastric precancerous lesions.

Adenomatous polyposis coli as a predictor of environmental chemical-induced transgenerational effects related to male infertility

Exposure to toxic environmental chemicals during pregnancy is a ubiquitous threat to health with potentially transgenerational consequences. However, the underlying mechanism of how transgenerational effects occur as part of environmental chemical exposure are not well understood. We investigated the potential molecular changes associated with dibutyl phthalate exposure that induced transgenerational effects, using a rat model. Through the analysis of the Gene Expression Omnibus database, we found some similar studies of environmental exposure induced transgenerational effects. Then, we analyzed one of the studies and our results to identify the adenomatous polyposis coli (APC) gene. This gene participated the most of the pathways and was upregulated in both studies. We used the miRWALK data set to predict the microRNAs which targeted the APC gene. We confirmed the miR-30 family were significantly downregulated in F3 testis tissues and targeted the APC gene. In conclusion, the miR-30 family/APC interaction is a potential mechanism for the transgenerational effects induced by the environmental chemical.

Functions of the APC tumor suppressor protein dependent and independent of canonical WNT signaling: implications for therapeutic targeting

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.

Protective and Restorative Effects of Nutrients and Phytochemicals

Intoroduction:

Dietary intake fundamentally provides reintegration of energy and essential nutrients to human organisms. However, its qualitative and quantitative composition strongly affects individual’s health, possibly being either a preventive or a risk factor. It was shown that nutritional status resulting from long-term exposition to specific diet formulations can outstandingly reduce incidences of most common and most important diseases of the developed world, such as cardiovascular and neoplastic diseases. Diet formulations result from different food combinations which bring specific nutrient molecules. Numerous molecules, mostly but not exclusively from vegetal foods, have been characterized among nutritional components as being particularly responsible for diet capabilities to exert risk reduction. These “bioactive nutrients” are able to produce effects which go beyond basic reintegration tasks, i.e. energetic and/or structural, but are specifically pharmacologically active within pathophysiological pathways related to many diseases, being able to selectively affect processes such as cell proliferation, apoptosis, inflammation, differentiation, angiogenesis, DNA repair and carcinogens activation.

Conclusion:

The present review was aimed to know the molecular mechanisms and pathways of activity of bioactive molecules; which will firstly allow search for optimal food composition and intake, and then use them as possible therapeutical targets and/or diagnostics. Also, the present review discussed the therapeutic effect of both nutrients and phytochemicals.

Insights into the role of the intestinal microbiota in colon cancer

The intestinal microbiota consists of a dynamic organization of bacteria, viruses, archaea, and fungal species essential for maintaining gut homeostasis and protecting the host against pathogenic invasion. When dysregulated, the intestinal microbiota can contribute to colorectal cancer development. Though the microbiota is multifaceted in its ability to induce colorectal cancer, this review will focus on the capability of the microbiota to induce colorectal cancer through the modulation of immune function and the production of microbial-derived metabolites. We will also explore an experimental technique that is revolutionizing intestinal research. By elucidating the interactions of microbial species with epithelial tissue, and allowing for drug screening of patients with colorectal cancers, organoid development is a novel culturing technique that is innovating intestinal research. As a cancer that remains one of the leading causes of cancer-related deaths worldwide, it is imperative that scientific findings are translated into the creation of effective therapeutics to treat colorectal cancer.

A disturbance of intestinal epithelial cell population and kinetics in APC1638T mice

The adenomatous polyposis coli (APC) is a multifunctional protein as well as a tumor suppressor. To determine the functions of the C-terminal domain of APC, we explored APC ^1638T/1638T (APC1638T) mice that express a truncated APC lacking the C-terminal domain. The APC1638T mice were tumor free and exhibited growth retardation. In the present study, we compared small intestinal crypt-villus cells homeostasis in APC ^+/+ (WT) mice and APC1638T mice. The body weight of APC1638T mice was significantly smaller than that of WT mice at all ages. The length of small intestine of APC1638T mice was significantly shorter than that of WT mice. The crypt-villus axis was significantly elongated, and the number of intestinal epithelial cells also increased in APC1638T mice compared with those in WT mice. However, the number of intestinal epithelial cells per 100 µm of villi was not different between WT and APC1638T mice. Migration and proliferation of intestinal epithelial cells in APC1638T mice were faster than that in WT mice. The population of Goblet cells, Paneth cells, and enteroendocrine cells was significantly altered in APC1638T mice. These results indicate that C-terminal domain of APC has a role in the regulation of intestinal epithelium homeostasis.

Beta-catenin Forms Protein Aggregation at High Concentrations in HEK293TCells

BACKGROUND

The canonical Wnt signal transduction (or the Wnt/β-catenin pathway) plays a crucial role in the development of animals and in carcinogenesis. Beta-catenin is the central component of this signaling pathway. The activation of Wnt/β-catenin signaling results in the cytoplasmic and nuclear accumulation of β-catenin. In the nucleus, β-catenin interacts with the TCF/LEF transcription factors and, therefore, participates in the upregulation or downregulation of some important genes involved in diverse cellular activities. In addition, β-catenin is a critical component of the cadherin-mediated cell adherens junction. We had previously noticed that very high cellular concentrations of β-catenin had a negative effect on the transcriptional activity of this protein and, therefore, the aim of this study was to find a mechanism for this negative interaction.

METHODS

Cell fractionation, western blotting, and immunofluorescence microscopy experiments were performed to measure β-catenin protein levels and β-catenin cellular localization in HEK293Tcells transfected with various amounts of a β-catenin-encoding plasmid. Also, total RNA was extracted from the cells and used for reverse transcriptase-PCR experiments to measure the expression of the β-catenin target genes. SPSS, version 16, was used to analyze the results statistically.

RESULTS

We demonstrated that overexpression of β-catenin led to the formation of rod-shaped protein aggregates. The aggregate structures were mainly formed in the cell nucleus and were heavy enough to be isolated by centrifugation. Beta-catenin aggregate formation was accompanied by a decrease in the expression of the β-catenin target genes used in this study.

CONCLUSION

Since deregulation of β-catenin function occurs in several human diseases, including cancer and neurological disorders, the results of this paper further support the possible biological and clinical significance of β-catenin aggregate formation.

Regulatory single nucleotide polymorphisms (rSNPs) at the promoters 1A and 1B of the human APC gene

Background

Germline mutations in the coding sequence of the tumour suppressor APC gene give rise to familial adenomatous polyposis (which leads to colorectal cancer) and are associated with many other oncopathologies. The loss of APC function because of deletion of putative promoter 1A or 1B also results in the development of colorectal cancer. Since the regions of promoters 1A and 1B contain many single nucleotide polymorphisms (SNPs), the aim of this study was to perform functional analysis of some of these SNPs by means of an electrophoretic mobility shift assay (EMSA) and a luciferase reporter assay.

Results

First, it was shown that both putative promoters of APC (1A and 1B) drive transcription in an in vitro reporter experiment. From eleven randomly selected SNPs of promoter 1A and four SNPs of promoter 1B, nine and two respectively showed differential patterns of binding of nuclear proteins to oligonucleotide probes corresponding to alternative alleles. The luciferase reporter assay showed that among the six SNPs tested, the rs75612255 C allele and rs113017087 C allele in promoter 1A as well as the rs138386816 T allele and rs115658307 T allele in promoter 1B significantly increased luciferase activity in the human erythromyeloblastoid leukaemia cell line K562. In human colorectal cancer HCT-116 cells, none of the substitutions under study had any effect, with the exception of minor allele G of rs79896135 in promoter 1B. This allele significantly decreased the luciferase reporter’s activity

Conclusion

Our results indicate that many SNPs in APC promoters 1A and 1B are functionally relevant and that allele G of rs79896135 may be associated with the predisposition to colorectal cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12863-016-0460-8) contains supplementary material, which is available to authorized users.

Inactivation of Adenomatous Polyposis Coli Reduces Bile Acid/Farnesoid X Receptor Expression through Fxr gene CpG Methylation in Mouse Colon Tumors and Human Colon Cancer Cells

BACKGROUND

The farnesoid X receptor (FXR) regulates bile acid (BA) metabolism and possesses tumor suppressor functions. FXR expression is reduced in colorectal tumors of subjects carrying inactivated adenomatous polyposis coli (APC). Identifying the mechanisms responsible for this reduction may offer new molecular targets for colon cancer prevention.

OBJECTIVE

We investigated how APC inactivation influences the regulation of FXR expression in colonic mucosal cells. We hypothesized that APC inactivation would epigenetically repress nuclear receptor subfamily 1, group H, member 4 (FXR gene name) expression through increased CpG methylation.

METHODS

Normal proximal colonic mucosa and normal-appearing adjacent colonic mucosa and colon tumors were collected from wild-type C57BL/6J and Apc-deficient (Apc(Min) (/+)) male mice, respectively. The expression of Fxr, ileal bile acid-binding protein (Ibabp), small heterodimer partner (Shp), and cyclooxygenase-2 (Cox-2) were determined by real-time polymerase chain reaction. In both normal and adjacent colonic mucosa and colon tumors, we measured CpG methylation of Fxr in bisulfonated genomic DNA. In vitro, we measured the impact of APC inactivation and deoxycholic acid (DCA) treatment on FXR expression in human colon cancer HCT-116 cells transfected with silencing RNA for APC and HT-29 cells carrying inactivated APC.

RESULTS

In Apc(Min) (/+) mice, constitutive CpG methylation of the Fxrα3/4 promoter was linked to reduced (60-90%) baseline Fxr, Ibabp, and Shp and increased Cox-2 expression in apparently normal adjacent mucosa and colon tumors. Apc knockdown in HCT-116 cells increased cellular myelocytomatosis (c-MYC) and lowered (∼50%) FXR expression, which was further reduced (∼80%) by DCA. In human HCT-116 but not HT-29 colon cancer cells, DCA induced FXR expression and lowered CpG methylation of FXR.

CONCLUSIONS

We conclude that the loss of APC function favors the silencing of FXR expression through CpG hypermethylation in mouse colonic mucosa and human colon cells, leading to reduced expression of downstream targets (SHP, IBABP) involved in BA homeostasis while increasing the expression of factors (COX-2, c-MYC) that contribute to inflammation and colon cancer.

Tankyrase Inhibition Causes Reversible Intestinal Toxicity in Mice with a Therapeutic Index < 1

Activated Wnt/β-catenin signaling is frequently associated with colorectal cancer. Wnt inhibitors, including tankyrase inhibitors, are being explored as potential anticancer agents. Wnt signaling is also critical for intestinal tissue homeostasis, and Wnt inhibitors have been shown to cause intestinal toxicity in mice by affecting intestinal stem cells. This study sought to characterize the intestinal toxicity of tankyrase inhibitors, including reversibility, and to assess their therapeutic index. Novel tankyrase inhibitor G-631 caused dose-dependent intestinal toxicity with a therapeutic index < 1 after 14 days of dosing in mice. At a tolerated subtherapeutic dose level, the intestinal toxicity was composed of enteritis characterized by villus blunting, epithelial degeneration, and inflammation, which fully reversed after 14 days of recovery. Doubled exposure showed weak antitumor activity in a xenograft colorectal cancer model but also caused more severe intestinal toxicity characterized by multifocal-regionally extensive necrotizing and ulcerative enteritis leading to morbidity or moribundity in some animals. This toxicity was only partially reversed after 14 days of recovery, with evidence of crypt and villus regeneration, mildly blunted villi, and/or scarring in association with chronic inflammation of the submucosa. Therefore, the clinical utility of tankyrase inhibitors is likely limited by the on-target intestinal toxicity and a therapeutic index < 1 in mice.

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

The role of adenomatous polyposis coli (APC) tumor suppressor at mitochondria is unclear. We show that APC associates with the Miro/Milton/kinesin complex to stimulate anterograde transport of mitochondria. This identifies the first regulatory role of APC in organelle transport. APC cancer mutations block this activity.

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

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

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

Mieap suppresses murine intestinal tumor via its mitochondrial quality control

Mieap, a novel p53-inducible protein, plays a key role in maintaining healthy mitochondria in various pathophysiological states. Here, we show that Mieap deficiency in Apc^Min/+ mice is strikingly associated with the malignant progression of murine intestinal tumors. To understand the role that Mieap plays in in vivo tumorigenesis, we generated Mieap heterozygous (Apc^Min/+ Mieap^+/−) and homozygous (Apc^Min/+ Mieap^−/−) Apc^Min/+ mice. Interestingly, the Apc^Min/+ mice with the Mieap^+/− and Mieap^−/− genetic background revealed remarkable shortening of the lifetime compared to Apc^Min/+ mice because of severe anemia. A substantial increase in the number and size of intestinal polyps was associated with Mieap gene deficiency. Histopathologically, intestinal tumors in the Mieap-deficient Apc^Min/+ mice clearly demonstrated advanced grades of adenomas and adenocarcinomas. We demonstrated that the significant increase in morphologically unhealthy mitochondria and trace accumulations of reactive oxygen species may be mechanisms underlying the increased malignant progression of the intestinal tumors of Mieap-deficient Apc^Min/+ mice. These findings suggest that the Mieap-regulated mitochondrial quality control plays a critical role in preventing mouse intestinal tumorigenesis.

Altered Interactions between the Gut Microbiome and Colonic Mucosa Precede Polyposis in APCMin/+ Mice

Mutation of the adenomatous polyposis coli (APC gene), an early event in the adenoma-carcinoma sequence, is present in 70-80% of sporadic human colorectal adenomas and carcinomas. To test the hypothesis that mutation of the APC gene alters microbial interactions with host intestinal mucosa prior to the development of polyposis, culture-independent methods (targeted qPCR assays and Illumina sequencing of the 16S rRNA gene V1V2 hypervariable region) were used to compare the intestinal microbial composition of 30 six-week old C57BL/6 APCMin/+ and 30 congenic wild type (WT) mice. The results demonstrate that similar to 12-14 week old APCMin/+ mice with intestinal neoplasia, 6 week old APCMin/+ mice with no detectable neoplasia, exhibit an increased relative abundance of Bacteroidetes spp in the colon. Parallel mouse RNA sequence analysis, conducted on a subset of proximal colonic RNA samples (6 APCMin/+, 6 WT) revealed 130 differentially expressed genes (DEGs, fold change ≥ 2, FDR <0.05). Hierarchical clustering of the DEGs was carried out by using 1-r dissimilarity measurement, where r stands for the Pearson correlation, and Ward minimum variance linkage, in order to reduce the number of input variables. When the cluster centroids (medians) were included along with APC genotype as input variables in a negative binomial (NB) regression model, four of seven mouse gene clusters, in addition to APC genotype, were significantly associated with the increased relative abundance of Bacteroidetes spp. Three of the four clusters include several downregulated genes encoding immunoglobulin variable regions and non-protein coding RNAs. These results support the concept that mutation of the APC gene alters colonic-microbial interactions prior to polyposis. It remains to be determined whether interventions directed at ameliorating dysbiosis in APCMin/+mice, such as through probiotics, prebiotics or antibiotics, could reduce tumor formation.

Genetic dissection of the Mom5 modifier locus and evaluation of Mom5 candidate genes

Germline mutations in the adenomatous polyposis coli (APC) gene cause familial adenomatous polyposis (FAP), a hereditary colon cancer syndrome in which affected individuals may develop 100-1000s of colonic adenomas. In families affected by FAP, adenoma number can vary markedly between individuals, despite the fact that these individuals carry the same APC mutation. In at least some FAP pedigrees, evidence suggests that these phenotypic differences are caused by segregating modifier alleles that impact adenoma number. However, identifying these modifiers in the human population is difficult, therefore mouse models are essential. Using the Apc (Min/+) mouse colon cancer model, we previously mapped one such modifier, Mom5, to a 25 Mbp region of chromosome 5 that contains hundreds of genes. The purpose of the present study was to refine the Mom5 interval and evaluate candidate genes for the Mom5 modifier of intestinal neoplasia. Recombinant mice were used to narrow the Mom5 interval to 8.1 Mbp containing 70 genes. In silico and gene expression analyses were utilized to identify and evaluate potential candidate genes that reside within this interval. These analyses identified seven genes within the Mom5 interval that contain variants between the B6 and 129P2 strains. These genes represent the most likely candidates for the Mom5 modifier.

Gut microbial metabolism drives transformation of MSH2-deficient colon epithelial cells

The etiology of colorectal cancer (CRC) has been linked to deficiencies in mismatch repair and adenomatous polyposis coli (APC) proteins, diet, inflammatory processes, and gut microbiota. However, the mechanism through which the microbiota synergizes with these etiologic factors to promote CRC is not clear. We report that altering the microbiota composition reduces CRC in APC(Min/+)MSH2(-/-) mice, and that a diet reduced in carbohydrates phenocopies this effect. Gut microbes did not induce CRC in these mice through an inflammatory response or the production of DNA mutagens but rather by providing carbohydrate-derived metabolites such as butyrate that fuel hyperproliferation of MSH2(-/-) colon epithelial cells. Further, we provide evidence that the mismatch repair pathway has a role in regulating β-catenin activity and modulating the differentiation of transit-amplifying cells in the colon. These data thereby provide an explanation for the interaction between microbiota, diet, and mismatch repair deficiency in CRC induction. PAPERCLIP:

The comparative study of acetyl-11-keto-beta-boswellic acid (AKBA) and aspirin in the prevention of intestinal adenomatous polyposis in APC(Min/+) mice

Acetyl-11-keto-beta-BA (AKBA), a component of the gum resin of Boswellia serrata, has been recognized as a promising agent for the prevention of intestinal tumorigenesis. Aspirin, a non-steroidal anti-inflammatory drug (NSAID), has also been considered to have the activity against intestinal tumorigenesis. However, the prevention of colonic cancer is insufficient and no definitive recommendation has been made for clinic use. Herein, we compared the efficacy of AKBA with that of aspirin in an adenomatous polyposis coli intestinal neoplasia consecutive weeks. Mice were sacrificed by anesthetizing. The whole intestine was removed from each mouse. The number, size and histopathology of intestinal adenomatous polyps were examined under microscopy. The adenomatous polyps were removed for further analysis by the assays of western blotting and immunohistochemical staining. AKBA significantly prevented the formation of intestinal adenomatous polyps without toxicity to mice. Statistical analysis indicated that AKBA's activity both in the prevention of small intestinal and colonic polyps was more potently than aspirin. Histopathologic examination revealed that AKBA's effect, that is the reduction of polyp size and degree of dysplasia, was more prominent in larger sized polyps, especially those originating in colon. These effects of AKBA were associated with its role in the induction of apoptosis in carcinomas. The assays of western blotting and immunohistochemistry staining indicated that the efficacy of AKBA might arise from its activity in the modulation of the Wnt/β-catenin pathway and NF-κB/COX-2 pathway in adenomatous polyps. Conclusion, AKBA by oral application prevented intestinal tumorigenesis more potential than aspirin.

Inhibition of CRM1-dependent nuclear export sensitizes malignant cells to cytotoxic and targeted agents

Nuclear-cytoplasmic trafficking of proteins is a significant factor in the development of cancer and drug resistance. Subcellular localization of exported proteins linked to cancer development include those involved in cell growth and proliferation, apoptosis, cell cycle regulation, transformation, angiogenesis, cell adhesion, invasion, and metastasis. Here, we examined the basic mechanisms involved in the export of proteins from the nucleus to the cytoplasm. All proteins over 40kDa use the nuclear pore complex to gain entry or exit from the nucleus, with the primary nuclear export molecule involved in these processes being chromosome region maintenance 1 (CRM1, exportin 1 or XPO1). Proteins exported from the nucleus must possess a hydrophobic nuclear export signal (NES) peptide that binds to a hydrophobic groove containing an active-site Cys528 in the CRM1 protein. CRM1 inhibitors function largely by covalent modification of the active site Cys528 and prevent binding to the cargo protein NES. In the absence of a CRM1 inhibitor, CRM1 binds cooperatively to the NES of the cargo protein and RanGTP, forming a trimer that is actively transported out of the nucleus by facilitated diffusion. Nuclear export can be blocked by CRM1 inhibitors, NES peptide inhibitors or by preventing post-translational modification of cargo proteins. Clinical trials using the classic CRM1 inhibitor leptomycin B proved too toxic for patients; however, a new generation of less toxic small molecule inhibitors is being used in clinical trials in patients with both hematological malignancies and solid tumors. Additional trials are being initiated using small-molecule CRM1 inhibitors in combination with chemotherapeutics such as pegylated liposomal doxorubicin. In this review, we present evidence that combining the new CRM1 inhibitors with other classes of therapeutics may prove effective in the treatment of cancer. Potential combinatorial therapies discussed include the use of CRM1 inhibitors and the addition of alkylating agents (melphalan), anthracyclines (doxorubicin and daunomycin), BRAF inhibitors, platinum drugs (cisplatin and oxaliplatin), proteosome inhibitors (bortezomib and carfilzomib), or tyrosine-kinase inhibitors (imatinib). Also, the sequence of treatment may be important for combination therapy. We found that the most effective treatment regimen involved first priming the cancer cells with the CRM1 inhibitor followed by doxorubicin, bortezomib, carfilzomib, or melphalan. This order sensitized both de novo and acquired drug-resistant cancer cell lines.

Aspirin augments the expression of Adenomatous Polyposis Coli protein by suppression of IKKβ

Aspirin has been widely used as analgesic, antipyretic and anti-inflammatory medicine for long. In addition to these traditional effects, clinical studies suggest that aspirin can protect against cancer, but its mechanism has not been explored. To unveil it, we identified the proteins up- or down-regulated after incubation with aspirin by using proteomics analysis with Nano-flow LC/MALDI-TOF system. Interestingly, the analysis identified the protein of Adenomatous Polyposis Coli (APC) as one of the most up-regulated protein. APC regulates cell proliferation or angiogenesis, and is widely known as a tumor-suppressing gene which can cause colorectal cancer when it is mutated. Western blots confirmed this result, and real-time PCR indicated it is transcriptionally regulated. We further tried to elucidate the molecular mechanism with focusing on IKKβ. IKKβ is the essential kinase in activation of nuclear factor-kappa B (NF-κB), major transcriptional factors that regulate genes responsible for inflammation or immune response. Previous reports indicated that aspirin specifically inhibits IKKβ activity, and constitutively active form of IKKβ accelerates APC loss. We found that aspirin suppressed the expression of IKKβ, and the deletion of IKKβ by siRNA increases the expression of APC in HEK294 cells. Finally, we observed similar effects of aspirin in human umbilical vein endothelial cells. Taken together, these results reveal that aspirin up-regulates the expression of APC via the suppression of IKKβ. This can be a mechanism how aspirin prevents cancer at least in part, and a novel link between inflammatory NF-κB signaling and cancer.

Targeted deletion of the C-terminus of the mouse adenomatous polyposis coli tumor suppressor results in neurologic phenotypes related to schizophrenia

Background

Loss of adenomatous polyposis coli (APC) gene function results in constitutive activation of the canonical Wnt pathway and represents the main initiating and rate-limiting event in colorectal tumorigenesis. APC is likely to participate in a wide spectrum of biological functions via its different functional domains and is abundantly expressed in the brain as well as in peripheral tissues. However, the neuronal function of APC is poorly understood. To investigate the functional role of Apc in the central nervous system, we analyzed the neurological phenotypes of Apc^1638T/1638T mice, which carry a targeted deletion of the 3′ terminal third of Apc that does not affect Wnt signaling.

Results

A series of behavioral tests revealed a working memory deficit, increased locomotor activity, reduced anxiety-related behavior, and mildly decreased social interaction in Apc^1638T/1638T mice. Apc^1638T/1638T mice showed abnormal morphology of the dendritic spines and impaired long-term potentiation of synaptic transmission in the hippocampal CA1 region. Moreover, Apc^1638T/1638T mice showed abnormal dopamine and serotonin distribution in the brain. Some of these behavioral and neuronal phenotypes are related to symptoms and endophenotypes of schizophrenia.

Conclusions

Our results demonstrate that the C-terminus of the Apc tumor suppressor plays a critical role in cognitive and neuropsychiatric functioning. This finding suggests a potential functional link between the C-terminus of APC and pathologies of the central nervous system.

Wnt signaling proteins associate with the nuclear pore complex: implications for cancer

Several components of the Wnt signaling pathway have in recent years been linked to the nuclear pore complex. β-catenin, the primary transducer of Wnt signals from the plasma membrane to the nucleus, has been shown to transiently associate with different FG-repeat containing nucleoporins (Nups) and to translocate bidirectionally through pores of the nuclear envelope in a manner independent of classical transport receptors and the Ran GTPase. Two key regulators of β-catenin, IQGAP1 and APC, have also been reported to bind specific Nups or to locate at the nuclear pore complex. The interaction between these Wnt signaling proteins and different Nups may have functional implications beyond nuclear transport in cellular processes that include mitotic regulation, centrosome positioning and cell migration, nuclear envelope assembly/disassembly, and the DNA replication checkpoint. The broad implications of interactions between Wnt signaling proteins and Nups will be discussed in the context of cancer.

Animal models of colorectal cancer

Colorectal cancer is a heterogeneous disease that afflicts a large number of people in the USA. The use of animal models has the potential to increase our understanding of carcinogenesis, tumor biology, and the impact of specific molecular events on colon biology. In addition, animal models with features of specific human colorectal cancers can be used to test strategies for cancer prevention and treatment. In this review, we provide an overview of the mechanisms driving human cancer, we discuss the approaches one can take to model colon cancer in animals, and we describe a number of specific animal models that have been developed for the study of colon cancer. We believe that there are many valuable animal models to study various aspects of human colorectal cancer. However, opportunities for improving upon these models exist.

Tissue-dependent consequences of Apc inactivation on proliferation and differentiation of ciliated cell progenitors via Wnt and notch signaling

The molecular signals that control decisions regarding progenitor/stem cell proliferation versus differentiation are not fully understood. Differentiation of motile cilia from progenitor/stem cells may offer a simple tractable model to investigate this process. Wnt and Notch represent two key signaling pathways in progenitor/stem cell behavior in a number of tissues. Adenomatous Polyposis Coli, Apc is a negative regulator of the Wnt pathway and a well known multifunctional protein. Using the cre-LoxP system we inactivated the Apc locus via Foxj1-cre, which is expressed in cells committed to ciliated cell lineage. We then characterized the consequent phenotype in two select tissues that bear motile cilia, the lung and the testis. In the lung, Apc deletion induced β-catenin accumulation and Jag1 expression in ciliated cells and by lateral induction, triggered Notch signaling in adjacent Clara cells. In the bronchiolar epithelium, absence of Apc blocked the differentiation of a subpopulation of cells committed to the ciliogenesis program. In the human pulmonary adenocarcinoma cells, Apc over-expression inhibited Jag1 expression and promoted motile ciliogenic gene expression program including Foxj1, revealing the potential mechanism. In the testis, Apc inactivation induced β-catenin accumulation in the spermatogonia, but silenced Notch signaling and depleted spermatogonial stem cells, associated with reduced proliferation, resulting in male infertility. In sum, the present comparative analysis reveals the tissue-dependent consequences of Apc inactivation on proliferation and differentiation of ciliated cell progenitors by coordinating Wnt and Notch signaling.

Downregulation of anti-oncomirs miR-143/145 cluster occurs before APC gene aberration in the development of colorectal tumors

Accumulating data indicate that some microRNAs (miRNAs or miRs) can function as tumor suppressors or oncogenes and as such are important in cancer development. We previously reported that miR-143 and -145 are frequently downregulated in colon adenomas and cancers, acting as tumor suppressors. In this present study, we investigated the relationship between the downregulation of the miR-143/145 cluster and genetic aberrations of adenomatous polyposis coli (APC), which are early genetic events in the development of colorectal tumors. The expression levels of both miRs were determined by performing real-time PCR on tissue samples of familial adenomatous polyposis (FAP), colorectal adenoma, colorectal cancer, and paired non-tumorous tissues. Also, the expression of C- or N-terminus of the APC protein and that of the p53 protein in these tissues were examined immunohistochemically. Our data clearly indicated that the decreased expression of miR-143 and -145 frequently occurred before APC gene aberrations. The downregulation of miR-143 and -145 is thus an important genetic event for the initiation step in colorectal tumor development.

Tumor suppressor APC protein is essential in mucosal repair from colonic inflammation through angiogenesis

Mucosal repair after acute colonic inflammation is central to maintaining mucosal homeostasis. Failure of mucosal repair often leads to chronic inflammation, sometimes associated with inflammatory bowel disease (IBD). The adenomatous polyposis coli (APC) tumor suppressor gene regulates the Wnt signaling pathway, which is essential for epithelial development, and inactivation of APC facilitates colorectal cancer. Our previous study suggested that APC is involved in pathogenesis of colonic inflammation; however, its role in mucosal repair remains unknown. In this article, we report that colitis induced by dextran sodium sulfate persisted with delayed mucosal repair in Kyoto Apc Delta (KAD) rats lacking the APC C terminus. Defects in the repair process were accompanied by an absence of a fibrin layer covering damaged mucosa and reduced microvessel angiogenesis. APC was up-regulated in vascular endothelial cells (VECs) in inflamed mucosa in KAD and F344 (control) rats. The VECs of KAD rats revealed elevated cell adhesion and low-branched and short-length tube formation. We also found that DLG5, which is associated with IBD pathogenesis, was up-regulated in VECs in inflamed mucosa and interacted with the C terminus of APC. This finding suggests that loss of interaction between the APC C terminus and DLG5 affects VEC morphology and function and leads to persistence of colitis. Therefore, APC is essential for maintenance of intestinal mucosal homeostasis and can consequently contribute to IBD pathogenesis.

More than two decades of Apc modeling in rodents

Mutation of tumor suppressor gene adenomatous polyposis coli (APC) is an initiating step in most colon cancers. This review summarizes Apc models in mice and rats, with particular concentration on those most recently developed, phenotypic variation among different models, and genotype/phenotype correlations.

Chemoprevention of intestinal adenomatous polyposis by acetyl-11-keto-beta-boswellic acid in APC(Min/+) mice

Acetyl-11-keto-beta-boswellic acid (AKBA) is a derivative of boswellic acid, which is an active component of the gum resin of Boswellia serrata. AKBA has been used as an adjuvant medication for treatment of inflammatory diseases. In this study, we aimed to evaluate the efficacy of AKBA as a chemopreventive agent against intestinal adenomatous polyposis in the adenomatous polyposis coli multiple intestinal neoplasia (APC(Min/+) ) mouse model. APC(Min/+) mice were administered AKBA by p.o. gavage for 8 consecutive weeks. The mice were sacrificed and the number, size and histopathology of intestinal polyps were examined by light microscopy. AKBA decreased polyp numbers by 48.9% in the small intestine and 60.4% in the colon. An even greater AKBA effect was observed in preventing the malignant progression of these polyps. The number of large (>3 cm) colonic polyposis was reduced by 77.8%. Histopathologic analysis demonstrated a significant reduction in the number of dysplastic cells and in the degree of dysplasia in each polyp after AKBA treatment. There was no evidence of high grade dysplasia or intramucosal carcinoma in any of the polyps examined within the treated group. More interestingly, interdigitated normal appearing intestinal villi were observed in the polyps of the treated group. During the course of the study, AKBA was well tolerated by the mice with no obvious signs of toxicity. Results from immunohistochemical staining, Western blotting and enzyme-linked immunosorbent assay indicated that the chemopreventive effect of AKBA was attributed to a collection of activities including antiproliferation, apoptosis induction, antiangiogenesis and anti-inflammation. AKBA was found to exert its chemopreventive action through the inhibition of the Wnt/β-catenin and NF-κB/cyclooxygenase-2 signaling pathways. Our findings suggest that AKBA could be a promising regimen in chemoprevention against intestinal tumorigenesis.

Some fine-structural findings on the thyroid gland in Apc1638T/1638T mice that express a C-terminus lacking truncated Apc

Adenomatous polyposis coli (Apc) is a multifunctional protein as well as a tumor suppressor. To determine the functions of the C-terminal domain of Apc, we examined Apc(1638T/1638T) mice that express a truncated Apc lacking the C-terminal domain. The Apc(1638T/1638T) mice were tumor free and exhibited growth retardation. We recently reported abnormalities in thyroid morphology and functions of Apc(1638T/1638T) mice, although the mechanisms underlying these abnormalities are not known. In the present study, we further compared thyroid gland morphology in Apc(1638T/1638T) and Apc(+/+) mice. The diameters of thyroid follicles in the left and right lobes of the same thyroid gland of Apc(1638T/1638T) mice were significantly different whereas the Apc(+/+) mice showed no significant differences in thyroid follicle diameter between these lobes. To assess the secretory activities of thyroid follicular cells, we performed double-immunostaining of thyroglobulin, a major secretory protein of these cells, and the rough endoplasmic reticulum (rER) marker calreticulin. In the Apc(1638T/1638T) follicular epithelial cells, thyroglobulin was mostly colocalized with calreticulin whereas in the Apc(+/+) follicular epithelial cells, a significant amount of the cytoplasmic thyroglobulin did not colocalize with calreticulin. In addition, in thyroid-stimulating hormone (TSH)-treated Apc(1638T/1638T) mice, electron microscopic analysis indicated less frequent pseudopod formation at the apical surface of the thyroid follicular cells than in Apc(+/+) mice, indicating that reuptake of colloid droplets containing iodized thyroglobulin is less active. These results imply defects in intracellular thyroglobulin transport and in pseudopod formation in the follicular epithelial cells of Apc(1638T/1638T) mice and suggest suppressed secretory activities of these cells.

Nuclear export of proteins and drug resistance in cancer

The intracellular location of a protein is crucial to its normal functioning in a cell. Cancer cells utilize the normal processes of nuclear-cytoplasmic transport through the nuclear pore complex of a cell to effectively evade anti-neoplastic mechanisms. CRM1-mediated export is increased in various cancers. Proteins that are exported in cancer include tumor-suppressive proteins such as retinoblastoma, APC, p53, BRAC1, FOXO proteins, INI1/hSNF5, galectin-3, Bok, nucleophosmin, RASSF2, Merlin, p21(CIP), p27(KIP1), N-WASP/FAK, estradiol receptor and Tob, drug targets topoisomerase I and IIα and BCR-ABL, and the molecular chaperone protein Hsp90. Here, we review in detail the current processes and known structures involved in the export of a protein through the nuclear pore complex. We also discuss the export receptor molecule CRM1 and its binding to the leucine-rich nuclear export signal of the cargo protein and the formation of a nuclear export trimer with RanGTP. The therapeutic potential of various CRM1 inhibitors will be addressed, including leptomycin B, ratjadone, KOS-2464, and specific small molecule inhibitors of CRM1, N-azolylacrylate analogs, FOXO export inhibitors, valtrate, acetoxychavicol acetate, CBS9106, and SINE inhibitors. We will also discuss examples of how drug resistance may be reversed by targeting the exported proteins topoisomerase IIα, BCR-ABL, and galectin-3. As effective and less toxic CRM1 export inhibitors become available, they may be used as both single agents and in combination with current chemotherapeutic drugs. We believe that the future development of low-toxicity, small-molecule CRM1 inhibitors may provide a new approach to treating cancer.

Adenomatous polyposis coli heterozygous knockout mice display hypoactivity and age-dependent working memory deficits

A tumor suppressor gene, Adenomatous polyposis coli (Apc), is expressed in the nervous system from embryonic to adulthood stages, and transmits the Wnt signaling pathway in which schizophrenia susceptibility genes, including T-cell factor 4 (TCF4) and calcineurin (CN), are involved. However, the functions of Apc in the nervous system are largely unknown. In this study, as the first evaluation of Apc function in the nervous system, we have investigated the behavioral significance of the Apc gene, applying a battery of behavioral tests to Apc heterozygous knockout (Apc(+/-)) mice. Apc(+/-) mice showed no significant impairment in neurological reflexes or sensory and motor abilities. In various tests, including light/dark transition, open-field, social interaction, eight-arm radial maze, and fear conditioning tests, Apc(+/-) mice exhibited hypoactivity. In the eight-arm radial maze, Apc(+/-) mice 6-7 weeks of age displayed almost normal performance, whereas those 11-12 weeks of age showed a severe performance deficit in working memory, suggesting that Apc is involved in working memory performance in an age-dependent manner. The possibility that anemia, which Apc(+/-) mice develop by 17 weeks of age, impairs working memory performance, however, cannot be excluded. Our results suggest that Apc plays a role in the regulation of locomotor activity and presumably working memory performance.

The C-terminal domain of the adenomatous polyposis coli (Apc) protein is involved in thyroid morphogenesis and function

Adenomatous polyposis coli (APC) is a multifunctional protein as well as a tumor suppressor. To determine the functions of the C-terminal domain of Apc, we have investigated Apc ( 1638T/1638T ) mice, which express a truncated Apc that lacks the C-terminal domain. Apc ( 1638T/1638T ) mice are tumor free and exhibit growth retardation. In the present study, we analyzed the morphology and functions of the thyroid gland in Apc ( 1638T/1638T ) mice. There was no significant difference in the basal concentration of serum thyroid hormones between Apc ( 1638T/1638T ) and Apc (+/+) mice. Thyroid follicle size was significantly larger in Apc ( 1638T/1638T ) mice than in Apc (+/+) mice. The extent of serum T4 elevation following exogenous thyroid-stimulating hormone (TSH) injection was lower in Apc ( 1638T/1638T ) mice than in Apc (+/+) mice. TSH also induced a greater reduction in thyroid follicle size in Apc ( 1638T/1638T ) mice than in Apc (+/+) mice. Analyses using immunohistochemistry and electron microscopy indicated that follicular epithelial cells in Apc ( 1638T/1638T ) mice had an enlarged rough endoplasmic reticulum of irregular shape. These results suggest that the C-terminal domain of Apc is involved in thyroid morphology and function.

APC as a mobile scaffold: regulation and function at the nucleus, centrosomes, and mitochondria

Genetic mutations of adenomatous polyposis coli (APC) predispose to high risk of human colon cancer. APC is a large tumor suppressor protein and truncating mutations disrupt its normal roles in regulating cell migration, DNA replication/repair, mitosis, apoptosis, and turnover of oncogenic β-catenin. APC is targeted to multiple subcellular sites, and here we discuss recent evidence implicating novel protein interactions and functions of APC in the nucleus and at centrosomes and mitochondria. The ability of APC to shuttle between these and other cell locations is hypothesized to be integral to its cellular function.

Crystal structure of the armadillo repeat domain of adenomatous polyposis coli which reveals its inherent flexibility

The conserved armadillo repeat (ARM) domain of adenomatous polyposis coli (APC) protein plays an important role in the recognition of its binding partners. In this study, we report the crystal structure of APC-ARM (residues 407-775), which was determined to 2.9 Å resolution. Our structure shows that the seven armadillo repeats of APC-ARM fold together into a compact domain, with Arm2 and Arm5 presenting some deviations from canonical armadillo repeats. There is a positively charged groove on the surface of APC-ARM, which might be the recognition site for APC-binding partners. Comparison of this structure with our previously reported structure of APC (407-751), together with normal mode analysis, reveals that the APC-ARM domain possesses a limited intrinsic flexibility. We propose that this intrinsic flexibility might be an inherent property of ARM domains in general.

Mitotic spindle misorientation in cancer--out of alignment and into the fire

Mitotic spindle orientation can influence tissue organization and vice versa. Cells orient their spindles by rotating them parallel or perpendicular to the cell--and hence the tissue--axis. Spindle orientation in turn controls the placement of daughter cells within a tissue, influencing tissue morphology. Recent findings implicating tumor suppressor proteins in spindle orientation bring to the forefront a connection between spindle misorientation and cancer. In this Commentary, we focus on the role of three major human tumor suppressors--adenomatous polyposis coli (APC), E-cadherin and von Hippel-Lindau (VHL)--in spindle orientation. We discuss how, in addition to their better-known functions, these proteins affect microtubule stability and cell polarity, and how their loss of function causes spindles to become misoriented. We also consider how other cancer-associated features, such as oncogene mutations, centrosome amplification and the tumor microenvironment, might influence spindle orientation. Finally, we speculate on the role of spindle misorientation in cancer development and progression. We conclude that spindle misorientation alone is unlikely to be tumorigenic, but it has the potential to synergize with cancer-associated changes to facilitate genomic instability, tissue disorganization, metastasis and expansion of cancer stem cell compartments.