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The adenomatous polyposis coli gene (Apc) is mutated in most colorectal cancers. The multifunctional character of the Apc protein in the regulation of β-catenin-mediated gene transcription and cytoskeletal proteins has been well described. An important question is how this protein affects the behaviour of cells within a tumour and how its mutational status influences the prognosis for these tumours. Here we provide an overview of the functions of Apc and examine how this information can be used in the prognosis and development of directed therapy in colorectal cancer. [ABSTRACT FROM AUTHOR]

One of the most important properties of intrinsically disordered proteins is their ability to undergo liquid-liquid phase separation and form droplets. The Adenomatous Polyposis Coli (APC) protein is an IDP that plays a key role in Wnt signaling and mutations in Apc initiate cancer. APC forms droplets via its 20R domains and self-association domain (ASAD) and in the context of Axin. However, the mechanism involved is unknown. Here, we used peptides to study the molecular mechanism and regulation of APC droplet formation. We found that a peptide derived from the ASAD of APC-formed droplets. Peptide array screening showed that the ASAD bound other APC peptides corresponding to the 20R3 and 20R5 domains. We discovered that the 20R3/5 peptides also formed droplets by themselves and mapped specific residues within 20R3/5 that are necessary for droplet formation. When incubated together, the ASAD and 20R3/5 did not form droplets. Thus, the interaction of the ASAD with 20R3 and 20R5 may regulate the droplet formation as a means of regulating different cellular functions. Phosphorylation of 20R3 or 20R5 at specific residues prevented droplet formation of 20R3/5. Our results reveal that phosphorylation and the ability to undergo liquid-liquid phase separation, which are both important properties of intrinsically disordered proteins, are related to each other in APC. Phosphorylation inhibited the liquid-liquid phase separation of APC, acting as an 'on-off' switch for droplet formation. Phosphorylation may thus be a common mechanism regulating LLPS in intrinsically disordered proteins.

Biologic drugs, defined as therapeutic agents produced from or containing components of a living organism, are of growing importance to the pharmaceutical industry. Though oral delivery of medicine is convenient, biologics require invasive injections because of their poor bioavailability via oral routes. Delivery of biologics to the small intestine using electronic delivery with devices that are similar to capsule endoscopes is a promising means of overcoming this limitation and does not require reformulation of the therapeutic agent. The efficacy of such capsule devices for drug delivery could be further improved by increasing the permeability of the intestinal tract lining with an integrated ultrasound transducer to increase uptake. This paper describes a novel proof of concept capsule device capable of electronic application of focused ultrasound and delivery of therapeutic agents. Fluorescent markers, which were chosen as a model drug, were used to demonstrate in vivo delivery in the porcine small intestine with this capsule. We show that the fluorescent markers can penetrate the mucus layer of the small intestine at low acoustic powers when combining microbubbles with focused ultrasound during in vivo experiments using porcine models. This study illustrates how such a device could be potentially used for gastrointestinal drug delivery and the challenges to be overcome before focused ultrasound and microbubbles could be used with this device for the oral delivery of biologic therapeutics.

Adenomatous Polyposis Coli ( APC ) is the most frequently mutated gene in colorectal cancer. APC negatively regulates the Wnt signaling pathway by promoting the degradation of β-catenin, but the extent to which APC exerts Wnt/β-catenin-independent tumor-suppressive activity is unclear. To identify interaction partners and β-catenin-independent targets of endogenous, full-length APC, we applied label-free and multiplexed tandem mass tag-based mass spectrometry. Affinity enrichment-mass spectrometry identified more than 150 previously unidentified APC interaction partners. Moreover, our global proteomic analysis revealed that roughly half of the protein expression changes that occur in response to APC loss are independent of β-catenin. Combining these two analyses, we identified Misshapen-like kinase 1 (MINK1) as a putative substrate of an APC-containing destruction complex. We validated the interaction between endogenous MINK1 and APC and further confirmed the negative, and β-catenin-independent, regulation of MINK1 by APC. Increased Mink1/Msn levels were also observed in mouse intestinal tissue and Drosophila follicular cells expressing mutant Apc/APC when compared with wild-type tissue/cells. Collectively, our results highlight the extent and importance of Wnt-independent APC functions in epithelial biology and disease. IMPLICATIONS: The tumor-suppressive function of APC, the most frequently mutated gene in colorectal cancer, is mainly attributed to its role in β-catenin/Wnt signaling. Our study substantially expands the list of APC interaction partners and reveals that approximately half of the changes in the cellular proteome induced by loss of APC function are mediated by β-catenin-independent mechanisms., (©2019 American Association for Cancer Research.)

During late mitosis and the early G 1 phase, the origins of replication are licensed by binding to double hexamers of MCM2-7. In this study, we investigated how licensing and proliferative commitment are coupled in the epithelium of the small intestine. We developed a method for identifying cells in intact tissue containing DNA-bound MCM2-7. Interphase cells above the transit-amplifying compartment had no DNA-bound MCM2-7, but still expressed the MCM2-7 protein, suggesting that licensing is inhibited immediately upon differentiation. Strikingly, we found most proliferative Lgr5 + stem cells are in an unlicensed state. This suggests that the elongated cell-cycle of intestinal stem cells is caused by an increased G 1 length, characterized by dormant periods with unlicensed origins. Significantly, the unlicensed state is lost in Apc -mutant epithelium, which lacks a functional restriction point, causing licensing immediately upon G 1 entry. We propose that the unlicensed G 1 phase of intestinal stem cells creates a temporal window when proliferative fate decisions can be made., (© 2018 Carroll et al.)

More than 90% of colorectal cancers carry mutations in Apc that drive tumourigenesis. A 'just-right' signalling model proposes that Apc mutations stimulate optimal, but not excessive Wnt signalling, resulting in a growth advantage of Apc mutant over wild-type cells. Reversal of this growth advantage constitutes a potential therapeutic approach. We utilised intestinal organoids to compare the growth of Apc mutant and wild-type cells. Organoids derived from Apc Min/+ mice recapitulate stages of intestinal polyposis in culture. They eventually form spherical cysts that reflect the competitive growth advantage of cells that have undergone loss of heterozygosity (LOH). We discovered that this emergence of cysts was inhibited by Chiron99021 and Valproic acid, which potentiates Wnt signalling. Chiron99021 and Valproic acid restrict the growth advantage of Apc mutant cells while stimulating that of wild-type cells, suggesting that excessive Wnt signalling reduces the relative fitness of Apc mutant cells. As a proof of concept, we demonstrated that Chiron99021-treated Apc mutant organoids were rendered susceptible to TSA-induced apoptosis, while wild-type cells were protected.

Objective: Colorectal cancer (CRC) leads to significant morbidity/mortality worldwide. Defining critical research gaps (RG), their prioritisation and resolution, could improve patient outcomes., Design: RG analysis was conducted by a multidisciplinary panel of patients, clinicians and researchers (n=71). Eight working groups (WG) were constituted: discovery science; risk; prevention; early diagnosis and screening; pathology; curative treatment; stage IV disease; and living with and beyond CRC. A series of discussions led to development of draft papers by each WG, which were evaluated by a 20-strong patient panel. A final list of RGs and research recommendations (RR) was endorsed by all participants., Results: Fifteen critical RGs are summarised below: RG1 : Lack of realistic models that recapitulate tumour/tumour micro/macroenvironment; RG2 : Insufficient evidence on precise contributions of genetic/environmental/lifestyle factors to CRC risk; RG3 : Pressing need for prevention trials; RG4 : Lack of integration of different prevention approaches; RG5 : Lack of optimal strategies for CRC screening; RG6 : Lack of effective triage systems for invasive investigations; RG7 : Imprecise pathological assessment of CRC; RG8 : Lack of qualified personnel in genomics, data sciences and digital pathology; RG9 : Inadequate assessment/communication of risk, benefit and uncertainty of treatment choices; RG10 : Need for novel technologies/interventions to improve curative outcomes; RG11 : Lack of approaches that recognise molecular interplay between metastasising tumours and their microenvironment; RG12 : Lack of reliable biomarkers to guide stage IV treatment; RG13 : Need to increase understanding of health related quality of life (HRQOL) and promote residual symptom resolution; RG14 : Lack of coordination of CRC research/funding; RG15 : Lack of effective communication between relevant stakeholders., Conclusion: Prioritising research activity and funding could have a significant impact on reducing CRC disease burden over the next 5 years., Competing Interests: Competing interests: ML reports support from Pfizer, outside the submitted work; DA reports grants from the Norman Foster Foundation, grants from the Tom Simms Memorial Fund at Queen’s University Belfast, during the conduct of the study; Dr Andreyev reports other from Entrinsic Health Solutions, Inc and personal fees from Macmillan Cancer Support, outside the submitted work; Professor Atkin reports grants from Cancer Research UK, outside the submitted work; Mr Bach reports personal fees from Ethicon Inc, outside the submitted work; Professor Burn has a patent A novel panel of short coding repeats suitable for high-throughput detection of microsatellite instability pending to Newcastle University; Dr Chau reports grants from Eli-Lily, Janssen-Cilag, Sanofi Oncology, Merck-Serono, and Novartis, personal fees from Taiho, Pfizer, Amgen, Eli-Lily, outside the submitted work; Professor Cheadle has a patent MUTYH gene variants licensed to Myriad Genetics and receives royalties; Professor Cunningham reports grants from Amgen, AstraZeneca, Bayer, Celgene, Medimmune, Merck Serono, Merrimack, and Sanofi, outside the submitted work; Professor Fraser reports personal fees from Immunostics Inc, Ocean, NJ, USA, Kyowa, Tokyo, Japan, and support for travel from Alpha Labs Ltd, Eastleigh, Hants, UK, during the conduct of the study; DH reports MRC CASE Award with Merck Serono for project unrelated to this submission and research support from Merck Serono for project unrelated to this submission; MH reports other from consultancy for Thetis Pharma, outside the submitted work; CN reports personal fees from Takeda and Ferring, outside the submitted work; Dr Sharma reports grants, personal fees and other from Sirtex, grants, personal fees and other from BTG, during the conduct of the study; AT reports personal fees from BMS Advisory Board, Roche Speaker Panel, Amgen Advisory Board, and Servier Advisory Board, outside the submitted work; LMW reports personal fees from Atticus Consultants Ltd, during the conduct of the study; RW reports personal fees from BMS Advisory Board, Clovis Oncology Advisory Board, Halozyme Advisory Board, Amgen Advisory Board, Servier Advisory Board, and Sirtex Independent Data Monitoring and Safety Committee, all outside the submitted work. RA, Professor Ahmedzai, ASA, Mr Arbuthnot, Mrs Berkman, Miss Bloor, Mr Boulter, Mrs Cole, Dr Brewster, GB, Professor Cazier, Dr Coyle, Mr Davies, Professor Downward, Professor Dunlop, NSF, SF, Dr Gerlinger, Dr Glaser, Professor Goh, Professor González De Castro, Dr Graham, Mr Griffith, Professor Halligan, SPH, Professor Hamilton, Mrs Hepburn, Dr Hold, Mr Holden, Professor Houlston, Dr Hubbard, Dr Iqbal, Dr Irvine, Dr Iveson, Mr Jackson, Mr Jakowiw, Mrs Jefford, Professor Longley, Dr McDermott, AGKM, Mr Machesney, Professor Maher, Professor Marchesi, Professor Maughan, Professor Middleton, Mr Moss, Mrs Moss, KJM, Dr Murchie, IN, MRN, Mr O’Sullivan, Mr Robertson, Professor Rutter, Dr Sansom, Dr Samuel, Professor Saxton, Dr Seward, Mrs Smith, Dr Sottoriva, RS, Professor Steward, Mr Stocker, Mrs Sweetman, IT, Dr Von Wagner and Professor Williams have nothing to disclose., (© Article author(s) (or their employer(s) unless otherwise stated in the text of the article) 2018. All rights reserved. No commercial use is permitted unless otherwise expressly granted.)

Homeostasis of renewing tissues requires balanced proliferation, differentiation and movement. This is particularly important in the intestinal epithelium where lineage tracing suggests that stochastic differentiation choices are intricately coupled to the position of a cell relative to a niche. To determine how position is achieved, we followed proliferating cells in intestinal organoids and discovered that the behaviour of mitotic sisters predicted long-term positioning. We found that, normally, 70% of sisters remain neighbours, while 30% lose contact and separate after cytokinesis. These post-mitotic placements predict longer term differences in positions assumed by sisters: adjacent sisters reach similar positions over time; in a pair of separating sisters, one remains close to its birthplace while the other is displaced upward. Computationally modelling crypt dynamics confirmed that post-mitotic separation leads to sisters reaching different compartments. We show that interkinetic nuclear migration, cell size and asymmetric tethering by a process extending from the basal side of cells contribute to separations. These processes are altered in adenomatous polyposis coli ( Apc ) mutant epithelia where separation is lost. We conclude that post-mitotic placement contributes to stochastic niche exit and, when defective, supports the clonal expansion of Apc mutant cells., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2017. Published by The Company of Biologists Ltd.)

New work shows that the actin-nucleating ability of the adenomatous polyposis coli protein is required for disassembly of focal adhesions. Loss of this function in Apc mutant cells reduces directed cell migration, potentially explaining the decreased migration of colon cancer cells., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Video capsule endoscopy (VCE) is now a clinically accepted diagnostic modality in which miniaturized technology, an on-board power supply and wireless telemetry stand as technological foundations for other capsule endoscopy (CE) devices. However, VCE does not provide therapeutic functionality, and research towards therapeutic CE (TCE) has been limited. In this paper, a route towards viable TCE is proposed, based on multiple CE devices including important acoustic sensing and drug delivery components. In this approach, an initial multimodal diagnostic device with high-frequency quantitative microultrasound that complements video imaging allows surface and subsurface visualization and computer-assisted diagnosis. Using focused ultrasound (US) to mark sites of pathology with exogenous fluorescent agents permits follow-up with another device to provide therapy. This is based on an US-mediated targeted drug delivery system with fluorescence imaging guidance. An additional device may then be utilized for treatment verification and monitoring, exploiting the minimally invasive nature of CE. While such a theranostic patient pathway for gastrointestinal treatment is presently incomplete, the description in this paper of previous research and work under way to realize further components for the proposed pathway suggests it is feasible and provides a framework around which to structure further work., Competing Interests: The authors declare no conflict of interest.

Video capsule endoscopy (VCE) has been of immense benefit in the diagnosis and management of gastrointestinal (GI) disorders since its introduction in 2001. However, it suffers from a number of well recognized deficiencies. Amongst these is the limited capability of white light imaging, which is restricted to analysis of the mucosal surface. Current capsule endoscopes are dependent on visual manifestation of disease and limited in regards to transmural imaging and detection of deeper pathology. Ultrasound capsule endoscopy (USCE) has the potential to overcome surface only imaging and provide transmural scans of the GI tract. The integration of high frequency microultrasound (µUS) into capsule endoscopy would allow high resolution transmural images and provide a means of both qualitative and quantitative assessment of the bowel wall. Quantitative ultrasound (QUS) can provide data in an objective and measurable manner, potentially reducing lengthy interpretation times by incorporation into an automated diagnostic process. The research described here is focused on the development of USCE and other complementary diagnostic and therapeutic modalities. Presently investigations have entered a preclinical phase with laboratory investigations running concurrently., Competing Interests: Conflicts of Interest: The authors have no conflicts of interest to declare.

Establishing and maintaining cell fate in the right place at the right time is a key requirement for normal tissue maintenance. Stem cells are at the core of this process. Understanding how stem cells balance self-renewal and production of differentiating cells is key for understanding the defects that underpin many diseases. Both, external cues from the environment and cell intrinsic mechanisms can control the outcome of stem cell division. The role of the orientation of stem cell division has emerged as an important mechanism for specifying cell fate decisions. Although, the alignment of cell divisions can dependent on spatial cues from the environment, maintaining stemness is not always linked to positioning of stem cells in a particular microenvironment or `niche'. Alternate mechanisms that could contribute to cellular memory include differential segregation of centrosomes in asymmetrically dividing cells., (Copyright © 2014 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Most cancers arise in epithelia, the tissue type that lines all body cavities. The organization of epithelia enables them to act as a barrier and perform vectorial transport of molecules between body compartments. Crucial for their organization and function is a highly specialized network of cell adhesion and polarity proteins aligned along the apical-basal axis. Comparing breast and intestinal tissue as examples of common cancer sites, reveals an important contribution of polarity proteins to the initiation and progression of cancer. Defects in polarity are induced directly by mutations in polarity proteins, but also indirectly by changes in the expression of specific microRNAs and altered transcriptional programs that drive cellular differentiation from epithelial to more mesenchymal characteristics. The latter is particularly important in the metastatic process., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Epidemiological data reveals the gastrointestinal (GI) tract as one of the main sites for low-LET radiation-induced cancers. Importantly, the use of particle therapy is increasing, but cancer risk by high-LET particles is still poorly understood. This gap in our knowledge also remains a major limiting factor in planning long-term space missions. Therefore, assessing risks and identifying predisposing factors for carcinogenesis induced by particle radiation is crucial for both astronauts and cancer survivors. We have previously shown that exposure to relatively high doses of high-energy (56)Fe ions induced higher intestinal tumor frequency and grade in the small intestine of Apc(Min/+) mice than γ rays. However, due to the high number of spontaneous lesions (∼30) that develop in Apc(Min/+) animals, this Apc mutant model is not suitable to investigate effects of cumulative doses <1 Gy, which are relevant for risk assessment in astronauts and particle radiotherapy patients. However, Apc(1638N/+) mice develop a relatively small number of spontaneous lesions (∼3 per animal) in both small intestine and colon, and thus we propose a better model for studies on radiation-induced carcinogenesis. Here, we investigated model particle radiation increases tumor frequency and grade in the entire gastrointestinal tract (stomach and more distal intestine) after high- and low-radiation doses whether in the Apc(1638N/+). We have previously reported that an increase in small intestinal tumor multiplicity after exposure to γ rays was dependent on gender in Apc(1638N/+) mice, and here we investigated responses to particle radiation in the same model. Phenotypical and histopathological observations were accompanied by late changes in number and position of mitotic cells in intestinal crypts from animals exposed to different radiation types.

Ubiquitin-binding domains (UBDs) are crucial for recruiting many proteins to sites of DNA damage. Here we characterize C1orf124 (Spartan; referred to as DVC1), which has an UBZ4-type UBD found predominantly in DNA repair proteins. DVC1 associates with DNA replication factories and localizes to sites of DNA damage in human cells, in a manner that requires the ability of the DVC1 UBZ domain to bind to ubiquitin polymers in vitro and a conserved PCNA-interacting motif. DVC1 interacts with the p97 protein 'segregase'. We show that DVC1 recruits p97 to sites of DNA damage, where we propose that p97 facilitates the extraction of the translesion synthesis (TLS) polymerase (Pol) η during DNA repair to prevent excessive TLS and limit the incidence of mutations induced by DNA damage. We introduce DVC1 as a regulator of cellular responses to DNA damage that prevents mutations when DNA damage occurs.

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.

Most colorectal cancers have mutations in the tumor suppressor APC. The best-understood function of APC is its participation in a protein complex that regulates the availability of β-catenin. Solid tumors are characterized by the presence of hypoxia as well as inflammation, which leads to the upregulation of Hypoxia Inducible Factors like HIF-1α. We recently demonstrated a novel antagonistic link between APC and HIF-1α. We found that hypoxia results in reduced levels of APC mRNA and protein via a direct HIF-1α-dependent mechanism. Similarly, APC mediates the repression of HIF-1α. However, this requires wild-type APC, low levels of β-catenin and NFκB activity. These results reveal the downregulation of APC as a novel mechanism that contributes to the survival advantage induced by hypoxia and cytokines such as TNFα. Our data indicate that loss-of-function mutations in APC result in the engagement of the hypoxia response. Importantly, this suggests that other stimuli that induce HIF, such as inflammatory cytokines and oncogenes, alter APC function.

The tumor suppressor adenomatous polyposis coli (APC) is mutated in the majority of colorectal cancers and is best known for its role as a scaffold in a Wnt-regulated protein complex that determines the availability of β-catenin. Another common feature of solid tumors is the presence of hypoxia as indicated by the up-regulation of hypoxia-inducible factors (HIFs) such as HIF-1α. Here, we demonstrate a novel link between APC and hypoxia and show that APC and HIF-1α antagonize each other. Hypoxia results in reduced levels of APC mRNA and protein via a HIF-1α-dependent mechanism. HIF-1α represses the APC gene via a functional hypoxia-responsive element on the APC promoter. In contrast, APC-mediated repression of HIF-1α requires wild-type APC, low levels of β-catenin, and nuclear factor-κB activity. These results reveal down-regulation of APC as a new mechanism that contributes to the survival advantage induced by hypoxia and also show that loss of APC mutations produces a survival advantage by mimicking hypoxic conditions.

The adenomatous polyposis coli gene (Apc) is mutated in most colorectal cancers. The multifunctional character of the Apc protein in the regulation of beta-catenin-mediated gene transcription and cytoskeletal proteins has been well described. An important question is how this protein affects the behaviour of cells within a tumour and how its mutational status influences the prognosis for these tumours. Here we provide an overview of the functions of Apc and examine how this information can be used in the prognosis and development of directed therapy in colorectal cancer.

The development of cancer is a multistep process in which the DNA of a single cell accumulates mutations in genes that control essential cellular processes. Loss of cell-cell adhesion and cell polarity is commonly observed in advanced tumours and correlates well with their invasion into adjacent tissues and the formation of metastases. Growing evidence indicates that loss of cell-cell adhesion and cell polarity may also be important in early stages of cancer. The strongest hints in this direction come from studies on tumour suppressor genes in the fruitfly Drosophila melanogaster, which have revealed their importance in the control of apical-basal cell polarity.

Truncation mutations in the adenomatous polyposis coli protein (APC) are responsible for familial and sporadic colonic tumours. APC is best known for its role in regulating beta-catenin, an important mediator of cell adhesion and a transcriptional activator. However, recent studies indicate that APC has additional roles in cytoskeletal regulation. It binds to microtubules directly and indirectly. Furthermore, indirect connections between APC and the actin cytoskeleton have also been described. Here, we integrate recent information describing the association between APC and the cytoskeleton to illustrate how this multifaceted protein might link different cytoskeletal elements to each other and to cellular signaling pathways.

Mutations in the Adenomatous Polyposis Coli (APC) gene are responsible for familial colon cancer and also occur in the early stages of sporadic colon cancer. APC functions in the Wnt signalling pathway to regulate the degradation of beta-catenin (reviewed in refs 1-3). APC also binds to and stabilizes microtubules in vivo and in vitro, localizes to clusters at the ends of microtubules near the plasma membrane of interphase cells, and is an important regulator of cytoskeletal function. Here we show that cells carrying a truncated APC gene (Min) are defective in chromosome segregation. Moreover, during mitosis, APC localizes to the ends of microtubules embedded in kinetochores and forms a complex with the checkpoint proteins Bub1 and Bub3. In vitro, APC is a high-affinity substrate for Bub kinases. Our data are consistent with a role for APC in kinetochore-microtubule attachment and suggest that truncations in APC that eliminate microtubule binding may contribute to chromosomal instability in cancer cells.

Truncation mutations in the adenomatous polyposis coli protein (APC) are responsible for familial polyposis, a form of inherited colon cancer. In addition to its role in mediating beta-catenin degradation in the Wnt signaling pathway, APC plays a role in regulating microtubules. This was suggested by its localization to the end of dynamic microtubules in actively migrating areas of cells and by the apparent correlation between the dissociation of APC from polymerizing microtubules and their subsequent depolymerization [1, 2]. The microtubule binding domain is deleted in the transforming mutations of APC [3, 4]; however, the direct effect of APC protein on microtubules has never been examined. Here we show that binding of APC to microtubules increases microtubule stability in vivo and in vitro. Deleting the previously identified microtubule binding site from the C-terminal domain of APC does not eliminate its binding to microtubules but decreases the ability of APC to stabilize them significantly. The interaction of APC with microtubules is decreased by phosphorylation of APC by GSK3 beta. These data confirm the hypothesis that APC is involved in stabilizing microtubule ends. They also suggest that binding of APC to microtubules is mediated by at least two distinct sites and is regulated by phosphorylation.

Mutations in the adenomatous polyposis coli (APC) gene are associated with most colorectal cancers. The APC protein has been implicated in many aspects of tumour development. This article will discuss recent data suggesting that APC may have multiple functions in the cell. First, APC is a component of the Wnt signalling pathway; second, APC may have a role in cell migration; finally, APC may regulate proliferation and apoptosis.

Cadherins play important roles in cell-cell adhesion during tissue differentiation. Cadherins are linked to the actin cytoskeleton by catenins (beta-catenin/armadillo, plakoglobin, and alpha-catenin). Recent results show that beta-catenin also binds to another cytoskeletal complex containing the adenomatous polyposis coli protein and microtubules, and interacts with several signaling pathways that include tyrosine kinases and phosphatases and Wnt/Wingless. Interplay between these cytoskeletal complexes and signaling pathways may regulate morphogenesis.

Beta-catenin is a cytosolic protein originally identified through its association with the cadherin class of cell-adhesion proteins. However, recent studies have demonstrated that there are cadherin-independent pools of beta-catenin and that beta-catenin binds at least one other protein, the product of the tumor-suppressor gene APC. Furthermore, beta-catenin is the target of two signal transduction pathways mediated by the proto-oncogenes src and wnt-1. This raises the possibility that beta-catenin plays a pivotal role in balancing cellular responses to both adhesive and proliferative signals.

Epithelial cell adhesion is principally regulated by calcium-dependent cell adhesion proteins, termed cadherins. Recent studies indicate that cadherin function is modulated by a class of proteins, termed catenins, that bind to the cytoplasmic domain of cadherin. Here we review the evidence that catenins regulate cadherin function in cell-cell adhesion, and discuss their role in initiating cell surface polarity in epithelial cells.

The triskelion shape of the clathrin molecule enables it to form the polyhedral protein network that covers clathrin-coated pits and vesicles. Domains within the clathrin heavy chain that are responsible for maintaining triskelion shape and function were identified and localized. Sequences that mediate trimerization are distal to the carboxyl terminus and are adjacent to a domain that mediates both light chain binding and clathrin assembly. Structural modeling predicts that within this domain, the region of heavy chain-light chain interaction is a bundle of three or four alpha helices. These studies establish a low resolution model of clathrin subunit folding in the central portion (hub) of the triskelion, thus providing a basis for future mutagenesis experiments.

Polymerization of clathrin triskelions into clathrin coats and subsequent disassembly by the heat shock protein hsc70 control receptor-mediated pathways of intracellular transport. The clathrin light chains are major regulatory elements in these processes. These polypeptides consist of linear arrays of functional domains with distinctive sequence motifs. Comparison of unicellular and multicellular eukaryotes reveals differences in the numbers of clathrin light chains and in the functional domains they contain.