Colocalization of APC and DLG at the tips of cellular protrusions in cultured epithelial cells and its dependency on cytoskeletons

LDL receptor related protein 1 requires the I3 domain of discs-large homolog 1/DLG1 for interaction with the kinesin motor protein KIF13B

KIF13B, a kinesin-3 family motor, was originally identified as GAKIN due to its biochemical interaction with human homolog of Drosophila discs-large tumor suppressor (hDLG1). Unlike its homolog KIF13A, KIF13B contains a carboxyl-terminal CAP-Gly domain. To investigate the function of the CAP-Gly domain, we developed a mouse model that expresses a truncated form of KIF13B protein lacking its CAP-Gly domain (KIF13BΔCG), whereas a second mouse model lacks the full-length KIF13A. Here we show that the KIF13BΔCG mice exhibit relatively higher serum cholesterol consistent with the reduced uptake of [³H]CO-LDL in KIF13BΔCG mouse embryo fibroblasts. The plasma level of factor VIII was not significantly elevated in the KIF13BΔCG mice, suggesting that the CAP-Gly domain region of KIF13B selectively regulates LRP1-mediated lipoprotein endocytosis. No elevation of either serum cholesterol or plasma factor VIII was observed in the full length KIF13A null mouse model. The deletion of the CAP-Gly domain region caused subcellular mislocalization of truncated KIF13B concomitant with the mislocalization of LRP1. Mechanistically, the cytoplasmic domain of LRP1 interacts specifically with the alternatively spliced I₃ domain of DLG1, which complexes with KIF13B via their GUK-MBS domains, respectively. Importantly, double mutant mice generated by crossing KIF13A null and KIF13BΔCG mice suffer from perinatal lethality showing potential craniofacial defects. Together, this study provides first evidence that the carboxyl-terminal region of KIF13B containing the CAP-Gly domain is important for the LRP1-DLG1-KIF13B complex formation with implications in the regulation of metabolism, cell polarity, and development.

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.

Mutational Mechanisms That Activate Wnt Signaling and Predict Outcomes in Colorectal Cancer Patients

APC biallelic loss-of-function mutations are the most prevalent genetic changes in colorectal tumors, but it is unknown whether these mutations phenocopy gain-of-function mutations in the CTNNB1 gene encoding β-catenin that also activate canonical WNT signaling. Here we demonstrate that these two mutational mechanisms are not equivalent. Furthermore, we show how differences in gene expression produced by these different mechanisms can stratify outcomes in more advanced human colorectal cancers. Gene expression profiling in Apc-mutant and Ctnnb1-mutant mouse colon adenomas identified candidate genes for subsequent evaluation of human TCGA (The Cancer Genome Atlas) data for colorectal cancer outcomes. Transcriptional patterns exhibited evidence of activated canonical Wnt signaling in both types of adenomas, with Apc-mutant adenomas also exhibiting unique changes in pathways related to proliferation, cytoskeletal organization, and apoptosis. Apc-mutant adenomas were characterized by increased expression of the glial nexin Serpine2, the human ortholog, which was increased in advanced human colorectal tumors. Our results support the hypothesis that APC-mutant colorectal tumors are transcriptionally distinct from APC-wild-type colorectal tumors with canonical WNT signaling activated by other mechanisms, with possible implications for stratification and prognosis.Significance: These findings suggest that colon adenomas driven by APC mutations are distinct from those driven by WNT gain-of-function mutations, with implications for identifying at-risk patients with advanced disease based on gene expression patterns. Cancer Res; 78(3); 617-30. ©2017 AACR.

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.

Requirement of DLG1 for cardiovascular development and tissue elongation during cochlear, enteric, and skeletal development: possible role in convergent extension

The Dlg1 gene encodes a member of the MAGUK protein family involved in the polarization of epithelial cells. Null mutant mice for the Dlg1 gene (Dlg1^-/- mice) exhibit respiratory failure and cyanosis, and die soon after birth. However, the cause of this neonatal lethality has not been determined. In the present study, we further examined Dlg1^-/- mice and found severe defects in the cardiovascular system, including ventricular septal defect, persistent truncus arteriosus, and double outlet right ventricle, which would cause the neonatal lethality. These cardiovascular phenotypes resemble those of mutant mice lacking planar cell polarity (PCP) genes and support a recent notion that DLG1 is involved in the PCP pathway. We assessed the degree of involvement of DLG1 in the development of other organs, as the cochlea, intestine, and skeleton, in which PCP signaling has been suggested to play a role. In the organ of Corti, tissue elongation was inhibited accompanied by disorganized arrangement of the hair cell rows, while the orientation of the stereocilia bundle was normal. In the sternum, cleft sternum, abnormal calcification pattern of cartilage, and disorganization of chondrocytes were observed. Furthermore, shortening of the intestine, sternum, and long bones of the limbs was observed. These phenotypes of Dlg1^-/- mice involving cellular disorganization and insufficient tissue elongation strongly suggest a defect in the convergent extension movements in these mice. Thus, our present results provide a possibility that DLG1 is particularly required for convergent extension among PCP signaling-dependent processes.

Dynamic association with donor cell filopodia and lipid-modification are essential features of Wnt8a during patterning of the zebrafish neuroectoderm

BACKGROUND

Wnt proteins are conserved signaling molecules that regulate pattern formation during animal development. Many Wnt proteins are post-translationally modified by addition of lipid adducts. Wnt8a provides a crucial signal for patterning the anteroposterior axis of the developing neural plate in vertebrates. However, it is not clear how this protein propagates from its source, the blastoderm margin, to the target cells in the prospective neural plate, and how lipid-modifications might influence Wnt8a propagation and activity.

RESULTS

We have dynamically imaged biologically active, fluorescently tagged Wnt8a in living zebrafish embryos. We find that Wnt8a localizes to membrane-associated, punctate structures in live tissue. In Wnt8a expressing cells, these puncta are found on filopodial cellular processes, from where the protein can be released. In addition, Wnt8a is found colocalized with Frizzled receptor-containing clusters on signal receiving cells. Combining in vitro and in vivo assays, we compare the roles of conserved Wnt8a residues in cell and non-cell-autonomous signaling activity and secretion. Non-signaling Wnt8 variants show these residues can regulate Wnt8a distribution in producing cell membranes and filopodia as well as in the receiving tissue.

CONCLUSIONS

Together, our results show that Wnt8a forms dynamic clusters found on filopodial donor cell and on signal receiving cell membranes. Moreover, they demonstrate a differential requirement of conserved residues in Wnt8a protein for distribution in producing cells and receiving tissue and signaling activity during neuroectoderm patterning.

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

Background

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

Methods

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

Results

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

Conclusions

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

Structure of the human discs large 1 PDZ2- adenomatous polyposis coli cytoskeletal polarity complex: insight into peptide engagement and PDZ clustering

The membrane associated guanylate kinase (MAGUK) family member, human Discs Large 1 (hDlg1) uses a PDZ domain array to interact with the polarity determinant, the Adenomatous Polyposis Coli (APC) microtubule plus end binding protein. The hDLG1-APC complex mediates a dynamic attachment between microtubule plus ends and polarized cortical determinants in epithelial cells, stem cells, and neuronal synapses. Using its multi-domain architecture, hDlg1 both scaffolds and regulates the polarity factors it engages. Molecular details underlying the hDlg1-APC interaction and insight into how the hDlg1 PDZ array may cluster and regulate its binding factors remain to be determined. Here, I present the crystal structure of the hDlg1 PDZ2-APC complex and the molecular determinants that mediate APC binding. The hDlg1 PDZ2-APC complex also provides insight into potential modes of ligand-dependent PDZ domain clustering that may parallel Dlg scaffold regulatory mechanisms. The hDlg1 PDZ2-APC complex presented here represents a core biological complex that bridges polarized cortical determinants with the dynamic microtubule cytoskeleton.

Targeting and transport: how microtubules control focal adhesion dynamics

Directional cell migration requires force generation that relies on the coordinated remodeling of interactions with the extracellular matrix (ECM), which is mediated by integrin-based focal adhesions (FAs). Normal FA turnover requires dynamic microtubules, and three members of the diverse group of microtubule plus-end-tracking proteins are principally involved in mediating microtubule interactions with FAs. Microtubules also alter the assembly state of FAs by modulating Rho GTPase signaling, and recent evidence suggests that microtubule-mediated clathrin-dependent and -independent endocytosis regulates FA dynamics. In addition, FA-associated microtubules may provide a polarized microtubule track for localized secretion of matrix metalloproteases (MMPs). Thus, different aspects of the molecular mechanisms by which microtubules control FA turnover in migrating cells are beginning to emerge.

Loss of adenomatous poliposis coli-α3 integrin interaction promotes endothelial apoptosis in mice and humans

RATIONALE

Pulmonary hypertension (PH) is characterized by progressive elevation in pulmonary pressure and loss of small pulmonary arteries. As bone morphogenetic proteins promote pulmonary angiogenesis by recruiting the Wnt/β-catenin pathway, we proposed that β-catenin activation could reduce loss and induce regeneration of small pulmonary arteries (PAs) and attenuate PH.

OBJECTIVE

This study aims to establish the role of β-catenin in protecting the pulmonary endothelium and stimulating compensatory angiogenesis after injury.

METHODS AND RESULTS

To assess the impact of β-catenin activation on chronic hypoxia-induced PH, we used the adenomatous polyposis coli (Apc(Min/+)) mouse, where reduced APC causes constitutive β-catenin elevation. Surprisingly, hypoxic Apc(Min/+) mice displayed greater PH and small PA loss compared with control C57Bl6J littermates. PA endothelial cells isolated from Apc(Min/+) demonstrated reduced survival and angiogenic responses along with a profound reduction in adhesion to laminin. The mechanism involved failure of APC to interact with the cytoplasmic domain of the α3 integrin, to stabilize focal adhesions and activate integrin-linked kinase-1 and phospho Akt. We found that PA endothelial cells from lungs of patients with idiopathic PH have reduced APC expression, decreased adhesion to laminin, and impaired vascular tube formation. These defects were corrected in the cultured cells by transfection of APC.

CONCLUSIONS

We show that APC is integral to PA endothelial cells adhesion and survival and is reduced in PA endothelial cells from PH patient lungs. The data suggest that decreased APC may be a cause of increased risk or severity of PH in genetically susceptible individuals.

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.

Adenomatous polyposis coli regulates axon arborization and cytoskeleton organization via its N-terminus

Conditional deletion of APC leads to marked disruption of cortical development and to excessive axonal branching of cortical neurons. However, little is known about the cell biological basis of this neuronal morphological regulation. Here we show that APC deficient cortical neuronal growth cones exhibit marked disruption of both microtubule and actin cytoskeleton. Functional analysis of the different APC domains revealed that axonal branches do not result from stabilized β-catenin, and that the C-terminus of APC containing microtubule regulatory domains only partially rescues the branching phenotype. Surprisingly, the N-terminus of APC containing the oligomerization domain and the armadillo repeats completely rescues the branching and cytoskeletal abnormalities. Our data indicate that APC is required for appropriate axon morphological development and that the N-terminus of APC is important for regulation of the neuronal cytoskeleton.

Tumor suppressor interactions with microtubules: keeping cell polarity and cell division on track

Tumor suppressor proteins protect cells and tissues from malignant transformation. Among their diverse actions, many of these proteins interact with the microtubule cytoskeleton. This review focuses on the interactions of several tumor suppressors with microtubules and speculates on how disruption of microtubule-dependent processes may contribute to cancer development and spread. We conclude that several tumor suppressors stabilize microtubules and organize microtubule arrays, functions that are likely to be important in preventing tumorigenesis. How tumor suppressors link microtubule stability with cell fate, and how their mutation affects the response of cancer cells to anti-microtubule chemotherapy drugs, remains unclear; these should prove fertile areas for future research.

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

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

Novel self-association of the APC molecule affects APC clusters and cell migration

Truncation mutations in the adenomatous polyposis coli (APC) gene are responsible for familial and sporadic colorectal cancer. APC is a multifunctional protein involved in cell migration, proliferation and differentiation. The APC protein forms specific clusters in the cell periphery that correlate with sites of active cell migration. Little is known about the molecular mechanisms that govern these clusters. Here, we identify a novel interaction of an N-terminal region of APC with the extreme C-terminal 300 amino acids of APC and also with itself. The latter interaction is phospho-sensitive and is enhanced by 14-3-3 (YWHA) protein. These interactions modulate the clustering of APC at the ends of membrane protrusions. Overexpressing this domain or inhibiting 14-3-3 proteins disperses APC clusters and leads to decreased cell migration. Moreover, deleting this domain from full-length APC results in less-dynamic clusters compared with wild-type APC. Our data indicate that this newly identified regions in the N-terminal third of APC contributes to the regulation of APC clusters, thus providing a molecular clue for how locally regulated phosphorylation events could mediate the dynamics of APC clusters and contribute to cell migration.

Role of adenomatous polyposis coli (APC) and microtubules in directional cell migration and neuronal polarization

In response to extracellular signals during embryonic development, cells undergo directional movements to specific sites and establish proper connections to other cells to form organs and tissues. Cell extension and migration in the direction of extracellular cues is mediated by the actin and microtubule cytoskeletons, and recent results have shed new light on how these pathways are activated by neurotrophins, Wnt or extracellular matrix. These signals lead to modifications of microtubule-associated proteins (MAPs) and point to glycogen synthase kinase (GSK) 3beta as a key regulator of microtubule function during directional migration. This review will summarize these results and then focus on the role of microtubule-binding protein adenomatous polyposis coli (APC) in neuronal polarization and directed migration, and on its regulation by GSK3beta.

Morphoregulation by acetylcholinesterase in fibroblasts and astrocytes

Acetylcholinesterase (AChE) terminates neurotransmission at cholinergic synapses by hydrolysing acetylcholine, but also has non-enzymatic morphoregulatory effects on neurons such as stimulation of neurite outgrowth. It is widely expressed outside the nervous system, but its function in non-neuronal cells is unclear. Here we have investigated the distribution and function of AChE in fibroblasts and astrocytes. We show that these cells express high levels of AChE protein that co-migrates with recombinant AChE but contains little catalytic activity. Fibroblasts express transcripts encoding the synaptic AChE-T isoform and its membrane anchoring peptide PRiMA-I. AChE is strikingly distributed in arcs, rings and patches at the leading edge of spreading and migrating fibroblasts and astrocytes, close to the cell-substratum interface, and in neuronal growth cones. During in vivo healing of mouse skin, AChE becomes highly expressed in re-epithelialising epidermal keratinocytes 1 day after wounding. AChE appears to be functionally important for polarised cell migration, since an AChE antibody reduces substratum adhesion of fibroblasts, and slows wound healing in vitro as effectively as a beta1-integrin antibody. Moreover, elevation of AChE expression increases fibroblast wound healing independently of catalytic activity. Interestingly, AChE surface patches precisely co-localise with amyloid precursor protein and the extracellular matrix protein perlecan, but not focal adhesions or alpha-dystroglycan, and contain a high concentration of tyrosine phosphorylated proteins in spreading cells. These findings suggest that cell surface AChE, possibly in a novel signalling complex containing APP and perlecan, contributes to a generalised mechanism for polarised membrane protrusion and migration in all adherent cells.

Changes in localization of human discs large (hDlg) during keratinocyte differentiation is associated with expression of alternatively spliced hDlg variants

Alternative spliced variants of the human discs large (hDlg) tumour suppressor are characterized by combinations of insertions. Here, using insertions I2- and I3-specific antibodies, we show that I2 and I3 variants have distinct distributions in epidermal and cervical epithelia. In skin and cervix, I3 variants are found in the cytoplasm. Cytoplasmic localization of I3 variants decreases as cervical keratinocytes differentiate, concomitant with relocalization to the cell periphery. I2 variants are found at the cell periphery of differentiated epidermal and cervical keratinocytes. Nuclear localization of I2 variants was evident in both tissues, with concentration of nuclear I2 variants in basal and parabasal cervical keratinocytes. A prominent nuclear localization of hDlg in cells of hyperproliferative layers of psoriatic lesions, but not in mature differentiated keratinocytes, together with I2 redistribution in differentiating keratinocytes, suggests that nuclear hDlg functions may be pertinent to growth of undifferentiated cells. Supporting our findings in squamous tissues, a decrease of nuclear hDlg and an increase of membrane-bound and cytoplasmic hDlg upon calcium-induced keratinocyte differentiation were not concomitant processes. Furthermore, we confirm that the exit of I2 variants from the nucleus is linked to stimulation of epithelial differentiation. The dynamic redistribution of hDlg also correlated with a marked increase in the expression of I3 variants while the level of I2 variants showed only a moderate decrease. Because changes in the intracellular distribution of hDlg splice variants, and in their expression levels, correlate with changes in differentiation state we hypothesize that the different hDlg isoforms play distinct roles at various stages of epithelial 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.

Abnormal development of urogenital organs in Dlgh1-deficient mice

Dlgh1 (discs large homolog 1) is a mammalian homolog of the Drosophila tumor suppressor Discs large 1, and is a member of the membrane-associated guanylate kinase (MAGUK) scaffolding proteins that contain three PSD-95/Dlg/ZO-1 (PDZ) domains. Discs large 1 is involved in epithelial polarization and cell-cell adhesion complex formation during Drosophila development. However, the functions of Dlgh1 during mammalian development remain to be elucidated. We generated Dlgh1-knockout mice and found that homozygous Dlgh1-knockout mice developed various abnormalities in their renal and urogenital organs. The kidneys and ureters were hypoplastic and the lower ends of the ureters were ectopic. In addition, the vagina and seminal vesicle, which are derived from the lower part of the Müllerian and Wolffian duct, respectively, were absent. Unexpectedly, loss of Dlgh1 function in the developing ureters did not disrupt cell-cell junctional complexes, but did impair cellular proliferation in the epithelium. These results suggest a novel role for Dlgh1 in regulating epithelial duct formation and morphogenesis during mammalian development. Although congenital absence of the vagina associated with other variable Müllerian duct abnormalities has been reported in humans, its mechanism has not yet been clarified. Our findings might contribute to a better understanding of such abnormalities.

Polarity Regulators and the Control of Epithelial Architecture, Cell Migration, and Tumorigenesis

A large body of work on Drosophila melanogaster has identified and characterized a number of key polarity regulators, many of which are required for the regulation of multiple other processes including proliferation, migration, invasion, and tumorigenesis. Humans possess either single or multiple homologues of each of the Drosophila polarity proteins, and in most cases, these are highly conserved between species, implying an important and conserved function for each of the polarity complexes. Recent studies in cultured mammalian epithelial cells have shed some light on the requirement for the polarity complexes in the regulation of epithelial cell function, including an unexpected link to the regulation of directed cell migration. However, many questions still remain regarding the molecular mechanisms of polarity regulation and whether disruption of polarity protein function is an important step in the development of human cancers. Here we will review what is currently understood about the regulation of cell polarity, migration, and invasion and the level of functional conservation between Drosophila and mammalian tissues. Particular reference will be made as to how the Scribble and Par polarity complexes may be involved in the regulation of apical-basal polarity, migration, and tumorigenesis.

Cytoskeleton out of the cupboard: colon cancer and cytoskeletal changes induced by loss of APC

Mutation of APC (adenomatous polyposis coli) is a common factor in most colorectal cancers. APC has many functions, the most prominent is its capacity to regulate beta-catenin-mediated gene transcription in response to Wnt signalling. Loss of APC leads to deregulated beta-catenin and this is intimately linked with tumour formation. However, recent evidence indicates that the interaction of APC with the cytoskeleton might also contribute to tumour initiation and progression. How does APC interact with the cytoskeleton and how could this play a part in colorectal tumorigenesis?

The histochemistry and cell biology vade mecum: a review of 2005–2006

The procurement of new knowledge and understanding in the ever expanding discipline of cell biology continues to advance at a breakneck pace. The progress in discerning the physiology of cells and tissues in health and disease has been driven to a large extent by the continued development of new probes and imaging techniques. The recent introduction of semi-conductor quantum dots as stable, specific markers for both fluorescence light microscopy and electron microscopy, as well as a virtual treasure-trove of new fluorescent proteins, has in conjunction with newly introduced spectral imaging systems, opened vistas into the seemingly unlimited possibilities for experimental design. Although it oftentimes proves difficult to predict what the future will hold with respect to advances in disciplines such as cell biology and histochemistry, it is facile to look back on what has already occurred. In this spirit, this review will highlight some advancements made in these areas in the past 2 years.

Membrane localization of adenomatous polyposis coli protein at cellular protrusions: targeting sequences and regulation by beta-catenin

Adenomatous polyposis coli protein (APC) translocates to, and stabilizes, the plus-ends of microtubules. In microtubule-dependent cellular protrusions, APC frequently accumulates in peripheral clusters at the basal membrane. APC targeting to membrane clusters is important for cell migration, but the localization mechanism is poorly understood. In this study, we performed deletion mapping and defined a minimal sequence (amino acids 1-2226) that efficiently targets APC to membrane clusters. This sequence lacks DLG-1 and EB1 binding sites, suggesting that these partners are not absolutely required for APC membrane targeting. A series of APC sequences were transiently expressed in cells and compared for their ability to compete endogenous APC at the membrane; potent inhibition of endogenous APC targeting was elicited by the Armadillo- (binds KAP3A, B56alpha, and ASEF) and beta-catenin-binding domains. The Armadillo domain was predicted to inhibit APC membrane localization through sequestration of the kinesin-KAP3A complex. The role of beta-catenin in APC membrane localization was unexpected but affirmed by overexpressing the APC binding sequence of beta-catenin, which similarly reduced APC membrane staining. Furthermore, we used RNA interference to show that loss of beta-catenin reduced APC at membrane clusters in migrating cells. In addition, we report that transiently expressed APC-yellow fluorescent protein co-localized with beta-catenin, KAP3A, EB1, and DLG-1 at membrane clusters, but only beta-catenin stimulated APC anchorage at the membrane. Our findings identify beta-catenin as a regulator of APC targeting to membrane clusters and link these two proteins to cell migration.

Vangl1 protein acts as a downstream effector of intestinal trefoil factor (ITF)/TFF3 signaling and regulates wound healing of intestinal epithelium

The intestinal trefoil factor (ITF/TFF3) protects intestinal epithelia from a range of insults and contributes to mucosal repair. However, the signaling events that mediate healing responses are only partially understood. To identify ITF signaling pathways, proteins that were Ser/Thr phosphorylated in response to ITF stimulation were immunoprecipitated from human colon carcinoma cell lines and identified by mass spectrometry. We demonstrated that Van Gogh-like protein 1 (also designated Vang-like 1 or Vangl1), a protein with four transmembrane domains, was Ser/Thr phosphorylated in response to ITF stimulation. Vangl1 was present in normal human colon and all intestinal epithelial cell lines (IEC) tested. In transfected IEC, FLAG-Vangl1 was mostly present in the Nonidet P-40 soluble fraction as detected by Western blotting, corresponding to the localization of endogenous protein in cytoplasmic vesicular structures by confocal microscopy with rabbit polyclonal anti-human Vangl1 antibody (alpha-Vangl1). Vangl1 cell membrane association increased with differentiation, as demonstrated by co-localization with E-cadherin in differentiated IEC. Increased Vangl1 phosphorylation after stimulation with ITF corresponded to decreased cell membrane association with E-cadherin. Functionally, Vangl1 overexpression enhanced ITF unstimulated and stimulated wound closure of IEC, whereas siRNA directed against Vangl1 inhibited the migratory response to ITF. Vangl1 protein may serve as an effector mediating the ITF healing response of the intestinal mucosa.

Cdc42 and Par6-PKCzeta regulate the spatially localized association of Dlg1 and APC to control cell polarization

Cell polarization is essential in a wide range of biological processes such as morphogenesis, asymmetric division, and directed migration. In this study, we show that two tumor suppressor proteins, adenomatous polyposis coli (APC) and Dlg1-SAP97, are required for the polarization of migrating astrocytes. Activation of the Par6–PKCζ complex by Cdc42 at the leading edge of migrating cells promotes both the localized association of APC with microtubule plus ends and the assembly of Dlg-containing puncta in the plasma membrane. Biochemical analysis and total internal reflection fluorescence microscopy reveal that the subsequent physical interaction between APC and Dlg1 is required for polarization of the microtubule cytoskeleton.

Recent progress in histochemistry and cell biology: the state of the art 2005

Advances in the field of histochemistry, a multidisciplinary area including the detection, localization and functional characterization of molecules in single cells and complex tissues, often drives the attainment of new knowledge in the broadly defined discipline of cell biology. These two disciplines, histochemistry and cell biology, have been joined in this journal to facilitate the flow of information with celerity from technical advancement in histochemical procedures, to their utilization in experimental models. This review summarizes advancements in these fields during the past year.

Non-traditional roles for the Adenomatous Polyposis Coli (APC) tumor suppressor protein

The Adenomatous Polyposis Coli (APC) tumor suppressor is a multifunctional protein that is mutated in a majority of colon cancers. The role of APC as an antagonist of the Wnt signaling pathway is well known and it is widely accepted that inappropriate activation of this pathway through loss of APC function contributes to the progression of colon cancers. However, a body of evidence is growing to support the idea that APC plays non-traditional functions outside of the Wnt pathway with roles in cell migration, adhesion, chromosome segregation, spindle assembly, apoptosis, and neuronal differentiation. This review highlights the research into alternate functions for APC beyond its role in Wnt signaling and discusses the possible contributions for these non-traditional functions of APC in tumor formation.

Adenomatous polyposis coli (Apc) tumor suppressor gene as a multifunctional gene

The adenomatous polyposis coli (Apc) gene is mutated in familial adenomatous polyposis and in sporadic colorectal tumors. The Apc gene product (APC), basically a cytoplasmic protein, blocks cell cycle progression and plays crucial roles in development. The APC binds to beta-catenin, axin and glycogen synthase kinase 3beta to form a large protein complex, in which beta-catenin is phosphorylated and broken down, resulting in negative regulation of the Wnt signaling pathway. Most of the mutated Apc genes in colorectal tumors lack beta-catenin-binding regions and fail to inhibit Wnt signaling, leading to overproliferation of tumor cells. The APC, having some nuclear localizing signals in its molecule, can also be localized in the nucleus. The nuclear APC exports excess beta-catenin to the cytoplasm. Through its C-terminus, APC binds to post-synaptic density discs large zonula occludens domain-containing proteins, such as discs large (DLG) and post-synaptic density (PSD)-95, and may play important roles in epithelial morphogenesis, brain development and neuronal functions. In addition, APC is involved in cell motility through its association with microtubules and APC-stimulated guanine nucleotide exchange factor. Colocalization of APC and DLG is dependent on microtubules. The Apc gene is highly expressed in the embryonic and postnatal developing brain. Recently, we found that APC is required for the activity of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors by facilitating the clustering of PSD-95 and these receptors at the postsynapse. In addition, APC is present in astrocytes, although its role in astrocytes is, as yet, unknown.