APC at a glance

Gardner syndrome in a Tunisian family: Identification of a rare APC mutation through targeted NGS

Gardner syndrome (GS) is a subtype of familial adenomatous polyposis (FAP) characterized by colorectal polyps, multiple osteomas, soft tissue tumors, and specific oral manifestations, such as jaw osteomas. GS is caused by mutations in the APC gene, resulting in a nonfunctional protein. This study reports a comprehensive clinical evaluation and genetic analysis of a Tunisian family affected by GS. Targeted exome sequencing and Sanger sequencing techniques were employed to identify and validate mutations in the APC gene. Clinical observations of the patient revealed multiple sebaceous cysts, frontal and maxillary osteomas, and several gastrointestinal polyps. Genetic analysis revealed a pathogenic variant (c.4652-4655del) in the APC gene, leading to a truncated protein. Additionally, genetic testing of the patient's child indicated that the child does not carry the APC pathogenic variant. In conclusion, our study highlights the importance of genetic testing in raising awareness of GS among clinicians to ensure early diagnosis and effective management, thereby reducing the risk of development and progression of colorectal cancer.

Mechanisms of Action of Phytoestrogens and Their Role in Familial Adenomatous Polyposis

Familial adenomatous polyposis (FAP) is a rare disease characterized by the development of adenomatous polyps in the colon and rectum already in adolescence. If left untreated, patients develop colorectal cancer (CRC) with a 100% probability. To date, the gold standard of FAP management is surgery, which is associated with morbidity and mortality. A chemopreventive agent capable of delaying, preventing and reversing the development of CRC has been sought. Several classes of drugs have been used but to date no chemopreventive drug has been found for the management of this disease. In recent years, the importance of estrogen receptors in FAP and CRC, particularly the β subtype, has emerged. Indeed, the expression of the latter is strongly reduced in adenomatous polyps and CRC and is inversely correlated with the aggressiveness of the disease. Since phytoestrogens have a high affinity for this receptor, they have been suggested for use as chemopreventive agents in FAP and CRC. A combination of phytoestrogens and insoluble fibres has proved particularly effective. In this review, the various mechanisms of action of phytoestrogens were analyzed and the effectiveness of using phytoestrogens as an effective chemopreventive strategy was discussed.

Possible Role of Wnt Signaling Pathway in Diabetic Retinopathy

The core of impaired vision in working people suffering from insulin-dependent and noninsulin- dependent diabetes mellitus is diabetic retinopathy (DR). The Wnt Protein Ligands family influences various processes; this ensures the cells are able to interact and co-ordinate various mobile functions, including cell growth, division, survival, apoptosis, migration, and cell destiny. The extracellular Wnt signal activates other signals. It is seen that Wnt pathways play an important role in inflammation, oxidative stress, and angiogenesis. It has been illustrated that the canonically preserved Wnt signaling system has a vital role in the homeostasis of adulthood. Developmental disorders in each of these stages will lead to serious eye problems and eventually blindness. There is, therefore, a need to specifically organize and regulate the growth of ocular tissues. In tissue specification and polarities, axonal exhaust, and maintenance of cells, especially in the central nervous system, Wnt/frizzled pathways play an important role. Thus, Wnt route antagonists may act as have been possible therapeutic options in DR by inhibiting aberrant Wnt signals. Elaborative and continued research in this area will help in the advancement of current knowledge in the field of DR, and eventually, this can lead to the development of new therapeutic approaches.

Impact of Epithelial Cell Shedding on Intestinal Homeostasis

The gut barrier acts as a first line of defense in the body, and plays a vital role in nutrition and immunoregulation. A layer of epithelial cells bound together via intercellular junction proteins maintains intestinal barrier integrity. Based on a tight equilibrium between cell extrusion and cell restitution, the renewal of the epithelium (epithelial turnover) permits the preservation of cell numbers. As the last step within the epithelial turnover, cell shedding occurs due to the pressure of cell division and migration from the base of the crypt. During this process, redistribution of tight junction proteins enables the sealing of the epithelial gap left by the extruded cell, and thereby maintains barrier function. Disturbance in cell shedding can create transient gaps (leaky gut) or cell accumulation in the epithelial layer. In fact, numerous studies have described the association between dysregulated cell shedding and infection, inflammation, and cancer; thus epithelial cell extrusion is considered a key defense mechanism. In the gastrointestinal tract, altered cell shedding has been observed in mouse models of intestinal inflammation and appears as a potential cause of barrier loss in human inflammatory bowel disease (IBD). Despite the relevance of this process, there are many unanswered questions regarding cell shedding. The investigation of those mechanisms controlling cell extrusion in the gut will definitely contribute to our understanding of intestinal homeostasis. In this review, we summarized the current knowledge about intestinal cell shedding under both physiological and pathological circumstances.

Mutational inactivation of Apc in the intestinal epithelia compromises cellular organisation

The adenomatous polyposis coli (Apc) protein regulates diverse effector pathways essential for tissue homeostasis. Truncating oncogenic mutations in Apc removing its Wnt pathway and microtubule regulatory domains drives intestinal epithelia tumorigenesis. Exuberant cell proliferation is one well-established consequence of oncogenic Wnt pathway activity; however, the contribution of other deregulated molecular circuits to tumorigenesis has not been fully examined. Using in vivo and organoid models of intestinal epithelial tumorigenesis we found that Wnt pathway activity controls intestinal epithelial villi and crypt structure, morphological features lost upon Apc inactivation. Although the Wnt pathway target gene c-Myc (also known as Myc) has critical roles in regulating cell proliferation and tumorigenesis, Apc specification of intestinal epithelial morphology is independent of the Wnt-responsive Myc-335 (also known as Rr21) regulatory element. We further demonstrate that Apc inactivation disrupts the microtubule cytoskeleton and consequently localisation of organelles without affecting the distribution of the actin cytoskeleton and associated components. Our data indicates the direct control over microtubule dynamics by Apc through an independent molecular circuit. Our study stratifies three independent Apc effector pathways in the intestinal epithelial controlling: (1) proliferation, (2) microtubule dynamics and (3) epithelial morphology.This article has an associated First Person interview with the first author of the paper.

Cytoskeletal Control and Wnt Signaling-APC's Dual Contributions in Stem Cell Division and Colorectal Cancer

Intestinal epithelium architecture is sustained by stem cell division. In principle, stem cells can divide symmetrically to generate two identical copies of themselves or asymmetrically to sustain tissue renewal in a balanced manner. The choice between the two helps preserve stem cell and progeny pools and is crucial for tissue homeostasis. Control of spindle orientation is a prime contributor to the specification of symmetric versus asymmetric cell division. Competition for space within the niche may be another factor limiting the stem cell pool. An integrative view of the multiple links between intracellular and extracellular signals and molecular determinants at play remains a challenge. One outstanding question is the precise molecular roles of the tumour suppressor Adenomatous polyposis coli (APC) for sustaining gut homeostasis through its respective functions as a cytoskeletal hub and a down regulator in Wnt signalling. Here, we review our current understanding of APC inherent activities and partners in order to explore novel avenues by which APC may act as a gatekeeper in colorectal cancer and as a therapeutic target.

Identification a nonsense mutation of APC gene in Chinese patients with familial adenomatous polyposis

Familial adenomatous polyposis (FAP; Mendelian of Inherintance in Man ID, 175100) is a rare autosomal dominant disorder characterized by the development of numerous adenomatous polyps throughout the colon and rectum associated with an increased risk of colorectal cancer. FAP is at time accompanied with certain extraintestinal manifestations such as congenital hypertrophy of the retinal pigment epithelium, dental disorders and desmoid tumors. It is caused by mutations in the adenomatous polyposis coli (APC) gene. The present study reported on a Chinese family with FAP. Polymerase chain reaction and direct sequencing of the full coding sequence of the APC gene were performed to identify the mutation in this family. A nonsense mutation of the APC gene was identified in this pedigree. It is a heterozygous G>T substitution at position 2,971 in exon 15 of the APC gene, which formed a premature stop codon at amino acid residue 991 (p.Glu991*). The resulting truncated protein lacked 1,853 amino acids. The present study expanded the database on APC gene mutations in FAP and enriched the spectrum of known germline mutations of the APC gene. Prophylactic proctocolectomy may be considered as a possible treatment for carriers of the mutation.

Epithelial cell extrusion: Pathways and pathologies

To remove dying or unwanted cells from an epithelium while preserving the barrier function of the layer, epithelia use a unique process called cell extrusion. To extrude, the cell fated to die emits the lipid Sphingosine 1 Phosphate (S1P), which binds the G-protein-coupled receptor Sphingosine 1 Phosphate receptor 2 (S1P₂) in the neighboring cells that activates Rho-mediated contraction of an actomyosin ring circumferentially and basally. This contraction acts to squeeze the cell out apically while drawing together neighboring cells and preventing any gaps to the epithelial barrier. Epithelia can extrude out cells targeted to die by apoptotic stimuli to repair the barrier in the face of death or extrude live cells to promote cell death when epithelial cells become too crowded. Indeed, because epithelial cells naturally turn over by cell death and division at some of the highest rates in the body, epithelia depend on crowding-induced live cell extrusion to preserve constant cell numbers. If extrusion is defective, epithelial cells rapidly lose contact inhibition and form masses. Additionally, because epithelia act as the first line of defense in innate immunity, preservation of this barrier is critical for preventing pathogens from invading the body. Given its role in controlling constant cell numbers and maintaining barrier function, a number of different pathologies can result when extrusion is disrupted. Here, we review mechanisms and signaling pathways that control epithelial extrusion and discuss how defects in these mechanisms can lead to multiple diseases. We also discuss tactics pathogens have devised to hijack the extrusion process to infect and colonize epithelia.

Molecular Heterogeneity of Ewing Sarcoma as Detected by Ion Torrent Sequencing

Ewing sarcoma (ES) is the second most common malignant bone and soft tissue tumor in children and adolescents. Despite advances in comprehensive treatment, patients with ES metastases still suffer poor outcomes, thus, emphasizing the need for detailed genetic profiles of ES patients to identify suitable molecular biomarkers for improved prognosis and development of effective and targeted therapies. In this study, the next generation sequencing Ion AmpliSeq^™ Cancer Hotspot Panel v2 was used to identify cancer-related gene mutations in the tissue samples from 20 ES patients. This platform targeted 207 amplicons of 2800 loci in 50 cancer-related genes. Among the 20 tissue specimens, 62 nonsynonymous hotspot mutations were identified in 26 cancer-related genes, revealing the molecular heterogeneity of ES. Among these, five novel mutations in cancer-related genes (KDR, STK11, MLH1, KRAS, and PTPN11) were detected in ES, and these mutations were confirmed with traditional Sanger sequencing. ES patients with KDR, STK11, and MLH1 mutations had higher Ki-67 proliferation indices than the ES patients lacking such mutations. Notably, more than half of the ES patients harbored one or two possible ‘druggable’ mutations that have been previously linked to a clinical cancer treatment option. Our results provided the foundation to not only elucidate possible mechanisms involved in ES pathogenesis but also indicated the utility of Ion Torrent sequencing as a sensitive and cost-effective tool to screen key oncogenes and tumor suppressors in order to develop personalized therapy for ES patients.

Crosstalk between Agrin and Wnt signaling pathways in development of vertebrate neuromuscular junction

Neuromuscular junction (NMJ) is a cholinergic synapse where motor neurons elicit muscle contraction. Agrin and its coreceptors LRP4 and MuSK are critical for vertebrate NMJ formation. This paper reviews recent evidence for Wnts and Wnt signaling molecules in NMJ formation including a possible retrograde mechanism by muscle β-catenin. We also present data that Wnt3a, 7a, 8a and 10b could inhibit agrin-mediated AChR clustering. Together with the stimulating effect of Wnt9a, 9b, 10b, 11 and 16 on AChR clustering in the absence of agrin, these results suggest diverse roles for Wnt ligands in NMJ development.

Novel insertion mutation p.Asp610GlyfsX23 in APC gene causes familial adenomatous polyposis in Chinese families

OBJECTIVE

The aim of the study was to identify the causative gene defects associated with familial adenomatous polyposis (FAP) in two Chinese pedigrees.

METHODS

The diagnosis of FAP patients was confirmed by clinical manifestations, family histories, colonoscopy and pathology examinations. Blood samples were collected and genomic DNA was extracted. The mutation analysis of the adenomatous polyposis coli (APC) and human mutY homolog (MUTYH) genes was conducted by direct polymerase chain reaction (PCR) sequencing and multiplex ligation-dependent probe amplification (MLPA).

RESULTS

In pedigree A, the results of direct PCR sequencing revealed a heterozygous insertion mutation at codon 610 in exon 15 of APC gene (c.1828_1829insG), which resulted in frameshift change (p.Asp610GlyfsX23) in all 4 patients, but was absent in the unaffected familial members and controls. In pedigree B, we didn't identify that causative mutations cosegregated with the clinical phenotype in the APC and MUTYH genes.

CONCLUSIONS

We identified a novel insertion mutation as the pathogenic gene of FAP in Chinese population, which could enrich the germline mutation spectrum of APC gene, and the prophylactic proctocolectomy for the mutation carrier in family should be considered.

EB1 is required for spindle symmetry in mammalian mitosis

Most information about the roles of the adenomatous polyposis coli protein (APC) and its binding partner EB1 in mitotic cells has come from siRNA studies. These suggest functions in chromosomal segregation and spindle positioning whose loss might contribute to tumourigenesis in cancers initiated by APC mutation. However, siRNA-based approaches have drawbacks associated with the time taken to achieve significant expression knockdown and the pleiotropic effects of EB1 and APC gene knockdown. Here we describe the effects of microinjecting APC- or EB1- specific monoclonal antibodies and a dominant-negative EB1 protein fragment into mammalian mitotic cells. The phenotypes observed were consistent with the roles proposed for EB1 and APC in chromosomal segregation in previous work. However, EB1 antibody injection also revealed two novel mitotic phenotypes, anaphase-specific cortical blebbing and asymmetric spindle pole movement. The daughters of microinjected cells displayed inequalities in microtubule content, with the greatest differences seen in the products of mitoses that showed the severest asymmetry in spindle pole movement. Daughters that inherited the least mobile pole contained the fewest microtubules, consistent with a role for EB1 in processes that promote equality of astral microtubule function at both poles in a spindle. We propose that these novel phenotypes represent APC-independent roles for EB1 in spindle pole function and the regulation of cortical contractility in the later stages of mitosis. Our work confirms that EB1 and APC have important mitotic roles, the loss of which could contribute to CIN in colorectal tumour cells.

The tumor suppressor adenomatous polyposis coli controls the direction in which a cell extrudes from an epithelium

Adenomatous polyposis coli (APC) controls the direction in which cells extrude from epithelia. APC acts in the dying cell to control where microtubules target actomyosin contraction in neighboring cells that squeeze out the dying cell. APC mutations that frequently occur in colon cancer cause cells to extrude aberrantly beneath epithelia, which could enable tumor cell invasion.

Despite high rates of cell death, epithelia maintain intact barriers by squeezing dying cells out using a process termed cell extrusion. Cells can extrude apically into the lumen or basally into the tissue the epithelium encases, depending on whether actin and myosin contract at the cell base or apex, respectively. We previously found that microtubules in cells surrounding a dying cell target p115 RhoGEF to the actin cortex to control where contraction occurs. However, what controls microtubule targeting to the cortex and whether the dying cell also controls the extrusion direction were unclear. Here we find that the tumor suppressor adenomatous polyposis coli (APC) controls microtubule targeting to the cell base to drive apical extrusion. Whereas wild-type cells preferentially extrude apically, cells lacking APC or expressing an oncogenic APC mutation extrude predominantly basally in cultured monolayers and zebrafish epidermis. Thus APC is essential for driving extrusion apically. Surprisingly, although APC controls microtubule reorientation and attachment to the actin cortex in cells surrounding the dying cell, it does so by controlling actin and microtubules within the dying cell. APC disruptions that are common in colon and breast cancer may promote basal extrusion of tumor cells, which could enable their exit and subsequent migration.

MUTYH Associated Polyposis (MAP)

MUTYH Associated Polyposis (MAP), a Polyposis predisposition caused by biallelic mutations in the Base Excision Repair (BER) gene MUTYH, confers a marked risk of colorectal cancer (CRC). The MAP phenotype is difficult to distinguish from other hereditary CRC syndromes. Especially from Familial Adenomatous Polyposis (FAP) and to a lesser extend Lynch Syndrome, which are caused by germline mutations in the APC and Mismatch Repair (MMR) genes, respectively.

Here we review research findings regarding MUTYH interactions, genotypic and phenotypic characteristics of MAP, as well as surveillance and treatment of the disease. The applied papers, published between 1/1 2002- 1/2 2008, were found through PubMed.

The exact role of MUTYH in CRC tumorgenesis is still uncertain, although MAP tumors show distinct molecular features, including somatic G:C>T:A transversions in the APC gene. Furthermore, cooperation between the BER and the MMR systems exists, as MUTYH interacts with MMR gene-products. Possibly, monoallelic defects in both pathways are of significance to CRC development.

Specific MUTYH variants are found to be characteristic in distinct ethnic populations, which could facilitate future genetic screening. Knowledge concerning functional consequences of many MUTYH germline mutations remains sparse. Most thoroughly investigated are the two most common MUTYH variants, Y179C and G396D, both generating dysfunctional gene products.

Phenotypic features of MAP include: development of 10-100 colorectal adenomas, debuting at 46-47 years, often CRC at time of clinical diagnosis, and in some, development of extracolonic manifestations.

Assembly of the base excision repair complex on abasic DNA and role of adenomatous polyposis coli on its functional activity

The assembly and stability of base excision repair (BER) proteins in vivo with abasic DNA and the role of adenomatous polyposis coli (APC) protein in this process are currently unclear. We have studied the assembly of a multiprotein BER complex onto abasic DNA (F-DNA) and characterized the physical and functional activity of the associated proteins. We found that the BER complex contained all the essential components of the long-patch BER system, such as APE1, Pol-β, Fen1, and DNA ligase I. Interestingly, wild-type APC was also present in the BER complex. Kinetics of the assembly of BER proteins onto the F-DNA were rapid and appeared in sequential order depending upon their requirement in the repair process. The presence of wild-type APC in the BER complex caused a decrease in the level of assembly of BER proteins and negatively affected long-patch BER. These results suggest that major BER proteins in the complex are assembled onto F-DNA and are competent in performing DNA repair. Wild-type APC in the BER complex reduces the repair activity, probably because of interaction with multiple components of the system.

Complete deletion of Apc results in severe polyposis in mice

The adenomatous polyposis coli (APC) gene product is mutated in the vast majority of human colorectal cancers. APC negatively regulates the WNT pathway by aiding in the degradation of beta-catenin, which is the transcription factor activated downstream of WNT signaling. APC mutations result in beta-catenin stabilization and constitutive WNT pathway activation, leading to aberrant cellular proliferation. APC mutations associated with colorectal cancer commonly fall in a region of the gene termed the mutation cluster region and result in expression of an N-terminal fragment of the APC protein. Biochemical and molecular studies have revealed localization of APC/Apc to different sub-cellular compartments and various proteins outside of the WNT pathway that associate with truncated APC/Apc. These observations and genotype-phenotype correlations have led to the suggestion that truncated APC bears neomorphic and/or dominant-negative function that support tumor development. To analyze this possibility, we have generated a novel allele of Apc in the mouse that yields complete loss of Apc protein. Our studies reveal that whole-gene deletion of Apc results in more rapid tumor development than the APC multiple intestinal neoplasia (Apc(Min)) truncation. Furthermore, we found that adenomas bearing truncated Apc had increased beta-catenin activity when compared with tumors lacking Apc protein, which could lead to context-dependent inhibition of tumorigenesis.

Changes in CpG islands promoter methylation patterns during ductal breast carcinoma progression

Aberrant promoter methylation of several known or putative tumor suppressor genes occurs frequently during carcinogenesis, and this epigenetic change has been considered as a potential molecular marker for cancer. We examined the methylation status of nine genes (APC, CDH1, CTNNB1, TIMP3, ESR1, GSTP1, MGMT, THBS1, and TMS1), by quantitative methylation specific PCR. Synchronous preinvasive lesions (atypical ductal hyperplasia and/or ductal carcinoma in situ) and invasive ductal breast carcinoma from 52 patients, together with pure lesions from 24 patients and 12 normal tissues paired to tumor and 20 normal breast distant from tumor were analyzed. Aberrant promoter methylation was detected in both preinvasive and invasive lesions for genes APC, CDH1, CTNNB1, TIMP3, ESR1, and GSTP1. However, hierarchical mixed model and Generalized Estimating Equations model analyses showed that only APC, CDH1, and CTNNB1 promoter regions showed a higher frequency and methylation levels in pathologic samples when compared with normal breast. Whereas APC and CTNNB1 did not show differences in methylation levels or frequencies, CDH1 showed higher methylation levels in invasive tumors as compared with preinvasive lesions (P < 0.04, Mann-Whitney test with permutation correction). The analysis of APC, CDH1, and CTNNB1 methylation status was able to distinguish between normal and pathologic samples with a sensitivity of 67% (95% confidence interval, 60-71%) and a specificity of 75% (95% confidence interval, 69-81%). Our data point to the direct involvement of APC, CDH1, and CTNNB1 promoter methylation in the early stages of breast cancer progression and suggest that they may represent a useful tool for the detection of tumor cells in clinical specimens.

Nup358 interacts with APC and plays a role in cell polarization

Asymmetric localization of adenomatous polyposis coli (APC) to the ends of a subset of microtubules located in the leading edges is essential for the establishment of front-rear polarity during cell migration. APC is known to associate with microtubules in three ways: through interaction with the plus-end tracking protein EB1, direct binding through a C-terminal basic region, and through interaction with the plus-end motor kinesin-2. Here we report that the middle region of APC has a previously unidentified microtubule plus-end-targeting function, suggesting an additional microtubule-binding mode for APC. Through the same region, APC interacts with Nup358 (also called RanBP2), a microtubule-binding nucleoporin. Ectopic expression of the middle region of APC is sufficient to recruit endogenous Nup358 to the plus ends of microtubules. Furthermore, our results indicate that Nup358 cooperates with kinesin-2 to regulate the localization of APC to the cell cortex through a nuclear-transport-independent mechanism. Using RNA interference and a scratch-induced wound-healing assay we demonstrate that Nup358 functions in polarized cell migration. These results reveal a more active role for structural nucleoporins in regulating fundamental cellular processes than previously anticipated.

Cadherin-bound beta-catenin feeds into the Wnt pathway upon adherens junctions dissociation: evidence for an intersection between beta-catenin pools

β-catenin is an essential component of two cellular systems: cadherin-based adherens junctions (AJ) and the Wnt signaling pathway. A functional or physical connection between these β-catenin pools has been suggested in previous studies, but not conclusively demonstrated to date. To further examine this intersection, we treated A431 cell colonies with lysophosphatidic acid (LPA), which forces rapid and synchronized dissociation of AJ. A combination of immunostaining, time-lapse microscopy using photoactivatable-GFP-tagged β-catenin, and image analyses indicate that the cadherin-bound pool of β-catenin, internalized together with E-cadherin, accumulates at the perinuclear endocytic recycling compartment (ERC) upon AJ dissociation, and can be translocated into the cell nucleus upon Wnt pathway activation. These results suggest that the ERC may be a site of residence for β-catenin destined to enter the nucleus, and that dissociation of AJ may influence β-catenin levels in the ERC, effectively affecting β-catenin substrate levels available downstream for the Wnt pathway. This intersection provides a mechanism for integrating cell-cell adhesion with Wnt signaling and could be critical in developmental and cancer processes that rely on β-catenin-dependent gene expression.

Somatic mutations of adenomatous polyposis coli gene and nuclear b-catenin accumulation have prognostic significance in invasive urothelial carcinomas: evidence for Wnt pathway implication

Wnt pathway signaling is crucial in many cancers and data indicate crosstalk with other key cancer pathways, however in urothelial carcinogenesis it has not been extensively studied. We searched for mutations in adenomatous polyposis coli (APC), a key regulator of the pathway, and studied b-catenin expression and interactions with the expression of other markers of apoptosis, angiogenesis, and proliferation in patients with invasive urothelial cancer. The mutation cluster region of APC was directly sequenced in 70 patients with muscle invasive disease who were treated with surgery and adjuvant chemotherapy. COX-2, p53, Ki67, and b-catenin were studied immunohistochemically and micro vessel density was quantified by CD105 expression. Single somatic amino-acid substitutions (missense) were found in 9 (13%) and frameshift deletions in 2 (3%) tumors, all located in regions adjacent to b-catenin binding sites. Patients having either APC missense mutations or b-catenin nuclear accumulation had less frequent COX-2 overexpression (24% vs. 76%, p = 0.043) and more frequent lymph node involvement (75% vs. 38%, p = 0.023). Patients with either APC mutations or b-catenin accumulation had shorter disease-free interval (13.4 vs. 28 months, p = 0.07), whereas in multivariate analysis they had shorter disease-specific survival (60.5 vs. 20.6 months, p = 0.048). Somatic APC missense mutations are not rare in advanced urothelial neoplasms. Either APC mutations and/or aberrant expression of b-catenin are associated with worse outcome. Further study of the role of the Wnt pathway, potential crosstalk with other pathways and potential candidate therapeutic targets in urothelial cancer is needed.

Calcium, calcium-sensing receptor and colon cancer

There is much evidence that dietary Ca(2+) loading reduces colon cell proliferation and carcinogenesis in humans and rodents, but during carcinogenesis it becomes ineffective or even tumor-promoting. We are beginning to see how Ca(2+) balances the continuous massive cell production in colon crypts by driving the terminal differentiation and eventually the apoptosis of the cells mainly on the mucosal surface, and how this Ca(2+) control is lost during colon carcinogenesis. The rapid proliferation of the transit-amplifying (TA) progeny of the colon stem cells is driven by the so-called "Wnt" signaling mechanism, which involves the stimulation of proliferogenic genes such as those for c-Myc and cyclin D1 and the silencing of the gene for the cell cycle-stopping p21(Cip1/WAF1) protein by nuclear beta-catenin*Tcf-4 complexes. TA cells avoid mitotic damage and premature apoptosis by expressing the protein survivin. It appears that TA cell cycling stops and terminal differentiation starts when the cells reach a higher level in the crypt where there is enough lumenal Ca(2+) to stimulate the expression and activation of CaSRs (Ca(2+)-sensing receptors), the signals from which stimulate the expression of E-cadherin. Along with this, the APC (adenomatous polyposis coli) protein appears and some of it enters the nucleus. There it makes the TA cells susceptible to the eventual apoptotic balancing by stopping survivin expression and the beta-catenin*Tcf-4 complex from driving further cell cycling by releasing beta-catenin from the nucleus, and delivering it to cytoplasmic APC*axin*GSK-3beta complexes for ultimate proteasomal destruction. Cytoplasmic beta-catenin is then prevented from returning to the nucleus by either being intercepted and destroyed by APC*axin*GSK-3beta complexes or locked by the emerging E-cadherin into membrane adherens junctions which tie the cell into the sheet of proliferatively shut-down cells with APC-dependent cytoskeletons moving to the mouth of the crypt and onto the flat mucosal surface. A common first step in sporadic colon carcinogenesis is the loss of functional APC which disorients upwardly directed migration and causes the retention of nuclear beta-catenin and proliferogenic beta-catenin*Tcf-4 complexes as well as genomic instability. Eventually the balance between cell proliferation and terminal differentiation and death is radically tipped in favour of proliferation by the appearance of apoptosis-resistant, survivin-expressing clones of Ca(2+)-insensitive cells which are locked into the proliferative, mutation-prone mode because of CaSR-disabling gene mutations which prevent the stimulation of E-cadherin expression and terminal differentiation.

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

The adenomatous polyposis coli (APC) gene is mutated in familial adenomatous polyposis and in most sporadic colorectal tumors. During both embryonic and postnatal periods, APC is widely expressed in a variety of tissues, including the brain and gastrointestinal tract. The APC gene product (APC) is a large multidomain protein consisting of 2843 amino acids. APC downregulates the Wnt signaling pathway through its binding to beta-catenin and Axin. Most mutated APC proteins in colorectal tumors lack the beta-catenin-binding regions and fail to inhibit Wnt signaling, leading to the overproliferation of tumor cells. Several mouse models (APC580D, APCDelta716, APC1309, APCMin, APC1638T) have been established to investigate carcinogenesis caused by APC mutations. APC also binds to APC-stimulated guanine nucleotide exchange factor, the kinesin superfamily-associated protein 3, IQGAP1, microtubules, EB1, and discs large (DLG). APC has both nuclear localization signals and nuclear export signals in its molecule, suggesting its occasional nuclear localization and export of beta-catenin from the nucleus. APC is highly expressed in the intestinal and colorectal epithelia and may be involved in homeostasis of the enterocyte renewal phenomena, in which proliferation, migration, differentiation, and apoptosis are highly regulated both temporally and spatially. Through the many binding proteins mentioned, APC can exert multiple functions involved in epithelial homeostasis.

Polarity and intracellular compartmentalization of Drosophila neurons

Background

Proper neuronal function depends on forming three primary subcellular compartments: axons, dendrites, and soma. Each compartment has a specialized function (the axon to send information, dendrites to receive information, and the soma is where most cellular components are produced). In mammalian neurons, each primary compartment has distinctive molecular and morphological features, as well as smaller domains, such as the axon initial segment, that have more specialized functions. How neuronal subcellular compartments are established and maintained is not well understood. Genetic studies in Drosophila have provided insight into other areas of neurobiology, but it is not known whether flies are a good system in which to study neuronal polarity as a comprehensive analysis of Drosophila neuronal subcellular organization has not been performed.

Results

Here we use new and previously characterized markers to examine Drosophila neuronal compartments. We find that: axons and dendrites can accumulate different microtubule-binding proteins; protein synthesis machinery is concentrated in the cell body; pre- and post-synaptic sites localize to distinct regions of the neuron; and specializations similar to the initial segment are present. In addition, we track EB1-GFP dynamics and determine microtubules in axons and dendrites have opposite polarity.

Conclusion

We conclude that Drosophila will be a powerful system to study the establishment and maintenance of neuronal compartments.

Familial adenomatous polyposis

Familial adenomatous polyposis (FAP) is an autosomal-dominant colorectal cancer syndrome, caused by a germline mutation in the adenomatous polyposis coli (APC) gene, on chromosome 5q21. It is characterized by hundreds of adenomatous colorectal polyps, with an almost inevitable progression to colorectal cancer at an average age of 35 to 40 yr. Associated features include upper gastrointestinal tract polyps, congenital hypertrophy of the retinal pigment epithelium, desmoid tumors, and other extracolonic malignancies. Gardner syndrome is more of a historical subdivision of FAP, characterized by osteomas, dental anomalies, epidermal cysts, and soft tissue tumors. Other specified variants include Turcot syndrome (associated with central nervous system malignancies) and hereditary desmoid disease. Several genotype-phenotype correlations have been observed. Attenuated FAP is a phenotypically distinct entity, presenting with fewer than 100 adenomas. Multiple colorectal adenomas can also be caused by mutations in the human MutY homologue (MYH) gene, in an autosomal recessive condition referred to as MYH associated polyposis (MAP). Endoscopic screening of FAP probands and relatives is advocated as early as the ages of 10-12 yr, with the objective of reducing the occurrence of colorectal cancer. Colectomy remains the optimal prophylactic treatment, while the choice of procedure (subtotal vs proctocolectomy) is still controversial. Along with identifying better chemopreventive agents, optimizing screening of extracolonic cancers and applying new radiological and endoscopic technology to the diagnosis and management of extracolonic features are the major challenges for the future.

IQGAP1: a key regulator of adhesion and migration

The dynamic rearrangement of cell-cell adhesion is one of the major physiological events in tissue development and tumor metastasis. Polarized cell migration, another key event, is a tightly regulated process that occurs during tissue development, chemotaxis and wound healing. Rho-family small GTPases, especially Rac1 and Cdc42, play pivotal roles in these processes through one of their effectors, IQGAP1. Recent studies reveal that IQGAP1 regulates cadherin-mediated cell-cell adhesion both positively and negatively. It captures and stabilizes microtubules through the microtubule-binding protein CLIP-170 near the cell cortex, leading to establishment of polarized cell morphology and directional cell migration. Furthermore, Rac1 and Cdc42 link the adenomatous polyposis coli (APC) protein to actin filaments through IQGAP1 at the leading edge and thereby regulate polarization and directional migration.

Hypermethylation ofhMLH1,HPP1,p14ARF,p16INK4A andAPC in primary adenocarcinomas of the small bowel

Small bowel adenocarcinoma (SB-AC) is a very rare tumor entity. Epigenetic alterations, including hypermethylation of DNA mismatch repair genes and tumor suppressor genes, seem to be important for carcinogenesis in tumors of the gastrointestinal tract, but have not yet been investigated in SB-AC. In the current study, the prevalence of hypermethylation in a panel of genes involved in gastrointestinal carcinogenesis (hMLH1, HPP1, p14(ARF), p16(INK4A), APC) was determined in a series of SB-AC. Paraffin-embedded tumor samples from 56 patients with SB-AC who underwent surgical resection between January 1985 and December 2003 were investigated for hypermethylation by means of methylation-specific real-time PCR, and compared with our findings in a previously investigated series of 50 gastric adenocarcinomas. In comparison with adenocarcinomas of the stomach, SB-AC revealed a significantly higher rate of hypermethylation of HPP1 (86% versus 54%, p = 0.0003), p16(INK4A) (32% versus 10%, p = 0.0006), and a significantly lower rate of hypermethylation of APC (48% versus 84%, p = 0.0001). Hypermethylation of hMLH1 and p14(ARF) was present in 23% and 9% of SB-AC, respectively. Locally advanced tumor categories (pT3/4) showed a higher rate of hypermethylation of HPP1 (90%) than did early tumor categories (pT1/2 categories, 40%; p = 0.0036). This was also reflected by the correlation between the HPP1 hypermethylation and high UICC stage (p = 0.02). No correlation was found between hypermethylation and other clinicopathologic parameters such as age, tumor grade and nodal status. Our findings suggest that hypermethylation of hMLH1, HPP1, p16(INK4A) and APC is frequent in primary adenocarcinomas of the small bowel. The differences in the hypermethylation spectrum of small bowel and stomach cancer indicate significant epigenetic differences between these tumors.