The integration of cell adhesion with gene expression: the role of beta-catenin

WNT ligands in non-small cell lung cancer: from pathogenesis to clinical practice

Non-small cell lung cancer (NSCLC) is the malignant tumor with the highest morbidity and leading cause of death worldwide, whereas its pathogenesis has not been fully elucidated. Although mutations in some crucial genes in WNT pathways such as β-catenin and APC are not common in NSCLC, the abnormal signal transduction of WNT pathways is still closely related to the occurrence and progression of NSCLC. WNT ligands (WNTs) are a class of secreted glycoproteins that activate WNT pathways through binding to their receptors and play important regulatory roles in embryonic development, cell differentiation, and tissue regeneration. Therefore, the abnormal expression or dysfunction of WNTs undoubtedly affects WNT pathways and thus participates in the pathogenesis of diseases. There are 19 members of human WNTs, WNT1, WNT2, WNT2b, WNT3, WNT3a, WNT4, WNT5a, WNT5b, WNT6, WNT7a, WNT7b, WNT8a, WNT8b, WNT9a, WNT9b, WNT10a, WNT10b, WNT11 and WNT16. The expression levels of WNTs, binding receptors, and activated WNT pathways are diverse in different tissue types, which endows the complexity of WNT pathways and multifarious biological effects. Although abundant studies have reported the role of WNTs in the pathogenesis of NSCLC, it still needs further study as therapeutic targets for lung cancer. This review will systematically summarize current research on human WNTs in NSCLC, from molecular pathogenesis to potential clinical practice.

miR106a Promotes the Growth of Transplanted Breast Cancer and Decreases the Sensitivity of Transplanted Tumors to Cisplatin

Objective

To explore the effect of miR106a on the growth of breast cancer xenografts and the sensitivity of chemotherapeutic agents.

Methods

Breast cancer cell lines (MDA-MB231 and MCF7) were transfected with an miR106 mimic and miR106a inhibitor. BALB/c female nude mice were selected to construct a transplanted-tumor model. Cisplatin treatment was performed 2 weeks after inoculation. After 5 weeks, tumor tissue was weighed. Apoptosis of tumor cells was detected by TUNEL staining. The expression of these proteins (Ki67, β-catenin, cyclin D1 and cMyc) was detected by immunohistochemistry. The contents of P53, RUNX3, ABCG2, β-catenin, BAX, and BCL2 mRNA were detected by qRT-PCR.

Results

The miR106a mimic (MM) group’s tumor volume and weight were significantly bigger than those of the model group. miR106a mRNA content was higher than the blank control group, and β-catenin and Ki67 protein were strongly positive. β-catenin, BCL2, and ABCG2 mRNA content was were increased. P53, BAX, and RUNX3 mRNA content was decreased. The number of positive cells on TUNEL staining was significantly lower in the miR106a inhibitor (MI) group. After cisplatin treatment, inhibition of tumor growth was most obvious in the MI+DDP (cisplatin) group. Compared with the MM group, tumor growth in the MM+FH535 (Wnt-pathway inhibitor) group was significantly lower, and Wnt-pathway activity was decreased.

Conclusion

Overexpression of miR106a can promote the growth of transplanted breast cancer and decrease the sensitivity of transplanted tumors to cisplatin. The mechanism may be related to abnormal activation of the Wnt-signaling pathway.

miR-193a-3p inhibition of the Slug activator PAK4 suppresses non-small cell lung cancer aggressiveness via the p53/Slug/L1CAM pathway

L1 cell adhesion molecule (L1CAM) promotes invasiveness and metastasis in non-small cell lung cancer (NSCLC) cells and is upregulated by the p53-regulated transcription factor Slug. p21-activated kinase 4 (PAK4) directly phosphorylates Slug, resulting in pro-malignant Slug stabilization. We hypothesized that microRNA-based negative regulation of PAK4 would reduce L1CAM-induced NSCLC aggressiveness via destabilizing Slug. We found that elevated L1CAM expression was tightly correlated with p53 loss-of-function and reduced NSCLC patient survival. L1CAM suppression reduced NSCLC cell migration and invasiveness in vitro as well as tumor formation and distal metastasis in vivo. Mechanistically, p53 restricts L1CAM expression through the β-catenin/Slug pathway, with levels of β-catenin and Slug positively correlating with L1CAM expression in NSCLC tumors. The microRNA miR-193a-3p directly targets PAK4 and suppresses downstream p-Slug and L1CAM expression. Silencing PAK4, Slug, and L1CAM mirrored miR-193a-3p's effects upon the migration and invasiveness of NSCLC cells in vitro. Decreased miR-193a-3p levels correlated with elevated PAK4, p-Slug, and L1CAM levels in NSCLC tumors. Our findings support a model of miR-193a-3p as a suppressor of metastatic disease progression in NSCLC via modulation of the p53/Slug/L1CAM pathway.

PCDHGA9 acts as a tumor suppressor to induce tumor cell apoptosis and autophagy and inhibit the EMT process in human gastric cancer

The results of a cDNA  array revealed that protocadherin gamma subfamily A, 9 (PCDHGA9) was significantly decreased in SGC-7901 gastric cancer (GC) cells compared with GES-1 normal gastric cells and was strongly associated with the Wnt/β-catenin and transforming growth factor-β (TGF-β)/Smad2/3 signaling pathway. As a member of the cadherin family, PCDHGA9 functions in both cell-cell adhesion and nuclear signaling. However, its role in tumorigenicity or metastasis has not been reported. In the present study, we found that PCDHGA9 was decreased in GC tissues compared with corresponding normal mucosae and its expression was correlated with the GC TNM stage, the UICC stage, differentiation, relapse, and metastasis (p < 0.01). Multivariate Cox analysis revealed that PCDHGA9 was an independent prognostic indicator for overall survival (OS) and disease-free survival (DFS) (p < 0.01). The effects of PCDHGA9 on GC tumor growth and metastasis were examined both in vivo and in vitro. PCDHGA9 knockdown promoted GC cell proliferation, migration, and invasion, whereas PCDHGA9 overexpression inhibited GC tumor growth and metastasis but induced apoptosis, autophagy, and G1 cell cycle arrest. Furthermore, PCDHGA9 suppressed epithelial-mesenchymal transition (EMT) induced by TGF-β, decreased the phosphorylation of Smad2/3, and inhibited the nuclear translocation of pSmad2/3. Our results suggest that PCDHGA9 might interact with β-catenin to prevent β-catenin from dissociating in the cytoplasm and translocating to the nucleus. Moreover, PCDHGA9 overexpression restrained cell proliferation and reduced the nuclear β-catenin, an indicator of Wnt/β-catenin pathway activation, suggesting that PCDHGA9 negatively regulates Wnt signaling. Together, these data indicate that PCDHGA9 acts as a tumor suppressor with anti-proliferative activity and anti-invasive ability, and the reduction of PCDHGA9 could serve as an independent prognostic biomarker in GC.

Wnt/β-catenin pathway in arrhythmogenic cardiomyopathy

Wnt/β-catenin signaling pathway plays essential roles in heart development as well as cardiac tissue homoeostasis in adults. Abnormal regulation of this signaling pathway is linked to a variety of cardiac disease conditions, including hypertrophy, fibrosis, arrhythmias, and infarction. Recent studies on genetically modified cellular and animal models document a crucial role of Wnt/β-catenin signaling in the molecular pathogenesis of arrhythmogenic cardiomyopathy (AC), an inherited disease of intercalated discs, typically characterized by ventricular arrhythmias and progressive substitution of the myocardium with fibrofatty tissue. In this review, we summarize the conflicting published data regarding the Wnt/β-catenin signaling contribution to AC pathogenesis and we report the identification of a new potential therapeutic molecule that prevents myocyte injury and cardiac dysfunction due to desmosome mutations in vitro and in vivo by interfering in this signaling pathway. Finally, we underline the potential function of microRNAs, epigenetic regulatory RNA factors reported to participate in several pathological responses in heart tissue and in the Wnt signaling network, as important modulators of Wnt/β-catenin signaling transduction in AC.

Elucidation of the precise regulatory mechanism of Wnt/β-catenin signaling in AC molecular pathogenesis could provide fundamental insights for new mechanism-based therapeutic strategy to delay the onset or progression of this cardiac disease.

Epithelial-mesenchymal transition and clinicopathological correlation in craniopharyngioma

AIMS

To assess the immunophenotypic changes associated with epithelial-mesenchymal transition (EMT) in craniopharyngioma, especially at the tumour invasive front, and to correlate the findings with clinicopathological features and patient outcomes.

METHODS AND RESULTS

Forty-two craniopharyngiomas were investigated for the presence of EMT markers (vimentin, E-cadherin and β-catenin) by immunohistochemistry and western blot. The relationships between expression of these markers and various clinicopathological indicators and clinical outcomes of the tumours were analysed. There were statistically significant differences in the expression of vimentin and E-cadherin-β-catenin between adamantinomatous and papillary variants. The expression of vimentin and E-cadherin (but not that of β-catenin) in whole tumour sections was associated with tumour recurrence, and with postoperative weight and hypothalamic disturbances; the expression of vimentin and E-cadherin-β-catenin at the tumour invasive front was also associated with tumour recurrence, postoperative weight, and hypothalamic disturbances. The results from western blotting closely matched those of immunohistochemistry.

CONCLUSION

Our study demonstrates, for the first time, the potential prognostic implications of vimentin, E-cadherin and β-catenin expression in craniopharyngiomas. EMT may represent a crucial mechanism in the progression of craniopharyngiomas.

HN1 negatively influences the β-catenin/E-cadherin interaction, and contributes to migration in prostate cells

Previously, it has been reported that HN1 is involved in cytoplasmic retention and degradation of androgen receptor in an AKT dependent manner. As HN1 is a hormone inducible gene, and has been shown that it is upregulated in various cancers, we studied the importance of HN1 function in β-catenin signaling in prostate cancer cell line, PC-3 and mammary cancer cell line MDA-MB231. Here, we demonstrated that HN1 physically associates with GSK3β/β-catenin destruction complex and abundantly localizes to cytoplasm, especially when the GSK3β is phosphorylated on S9 residue. Further, ectopic HN1 expression results an increase in the β-catenin degradation leading to loss of E-cadherin interaction, concurrently contributing to actin re-organization, colony formation and migration in cancer cell lines. Thus, we report that HN1 is an essential factor for β-catenin turnover and signaling, augments cell growth and migration in prostate cancer cells.

Upper-body resistance exercise augments vastus lateralis androgen receptor-DNA binding and canonical Wnt/β-catenin signaling compared to lower-body resistance exercise in resistance-trained men without an acute increase in serum testosterone

The purpose of the study was to determine the effect of single bouts of lower-body (LB) and upper- and lower-body (ULB) resistance exercise on serum testosterone concentrations and the effects on muscle testosterone, dihydrotestosterone (DHT), androgen receptor (AR) protein content, and AR-DNA binding. A secondary purpose was to determine the effects on serum wingless-type MMTV integration site (Wnt4) levels and skeletal muscle β-catenin content. In a randomized cross-over design, exercise bouts consisted of a LB and ULB protocol, and each bout was separated by 1 week. Blood and muscle samples were obtained before exercise and 3 and 24h post-exercise; blood samples were also obtained at 0.5, 1, and 2 h post-exercise. Statistical analyses were performed by separate two-way factorial analyses of variance (ANOVA) with repeated measures. No significant differences from baseline were observed in serum total and free testosterone and skeletal muscle testosterone and DHT with either protocol (p>0.05). AR protein was significantly increased at 3 h post-exercise and decreased at 24 h post-exercise for ULB, whereas AR-DNA binding was significantly increased at 3 and 24h post-exercise (p<0.05). In response to ULB, serum Wnt4 was significantly increased at 0.5, 1, and 2 h post-exercise (p<0.05) and β-catenin was significantly increased at 3 and 24 h post-exercise (p<0.05). It was concluded that, despite a lack of increase in serum testosterone and muscle androgen concentrations from either mode of resistance exercise, ULB resistance exercise increased Wnt4/β-catenin signaling and AR-DNA binding.

Nuclear signaling from cadherin adhesion complexes

The arrival of multicellularity in evolution facilitated cell-cell signaling in conjunction with adhesion. As the ectodomains of cadherins interact with each other directly in trans (as well as in cis), spanning the plasma membrane and associating with multiple other entities, cadherins enable the transduction of "outside-in" or "inside-out" signals. We focus this review on signals that originate from the larger family of cadherins that are inwardly directed to the nucleus, and thus have roles in gene control or nuclear structure-function. The nature of cadherin complexes varies considerably depending on the type of cadherin and its context, and we will address some of these variables for classical cadherins versus other family members. Substantial but still fragmentary progress has been made in understanding the signaling mediators used by varied cadherin complexes to coordinate the state of cell-cell adhesion with gene expression. Evidence that cadherin intracellular binding partners also localize to the nucleus is a major point of interest. In some models, catenins show reduced binding to cadherin cytoplasmic tails favoring their engagement in gene control. When bound, cadherins may serve as stoichiometric competitors of nuclear signals. Cadherins also directly or indirectly affect numerous signaling pathways (e.g., Wnt, receptor tyrosine kinase, Hippo, NFκB, and JAK/STAT), enabling cell-cell contacts to touch upon multiple biological outcomes in embryonic development and tissue homeostasis.

Ribosome biogenesis: emerging evidence for a central role in the regulation of skeletal muscle mass

The ribosome is a supramolecular ribonucleoprotein complex that functions at the heart of the translation machinery to convert mRNA into protein. Ribosome biogenesis is the primary determinant of translational capacity of the cell and accordingly has an essential role in the control of cell growth in eukaryotes. Cumulative evidence supports the hypothesis that ribosome biogenesis has an important role in the regulation of skeletal muscle mass. The purpose of this review is to, first, summarize the main mechanisms known to regulate ribosome biogenesis and, second, put forth the hypothesis that ribosome biogenesis is a central mechanism used by skeletal muscle to regulate protein synthesis and control skeletal muscle mass in response to anabolic and catabolic stimuli. The mTORC1 and Wnt/β-catenin/c-myc signaling pathways are discussed as the major pathways that work in concert with each of the three RNA polymerases (RNA Pol I, II, and III) in regulating ribosome biogenesis. Consistent with our hypothesis, activation of these two pathways has been shown to be associated with ribosome biogenesis during skeletal muscle hypertrophy. Although further study is required, the finding that ribosome biogenesis is altered under catabolic states, in particular during disuse atrophy, suggests that its activation represents a novel therapeutic target to reduce or prevent muscle atrophy. Lastly, the emerging field of ribosome specialization is discussed and its potential role in the regulation of gene expression during periods of skeletal muscle plasticity.

Cytoskeletal dynamics and lung fluid balance

This article examines the role of the endothelial cytoskeleton in the lung's ability to restrict fluid and protein to vascular space at normal vascular pressures and thereby to protect lung alveoli from lethal flooding. The barrier properties of microvascular endothelium are dependent on endothelial cell contact with other vessel-wall lining cells and with the underlying extracellular matrix (ECM). Focal adhesion complexes are essential for attachment of endothelium to ECM. In quiescent endothelial cells, the thick cortical actin rim helps determine cell shape and stabilize endothelial adherens junctions and focal adhesions through protein bridges to actin cytoskeleton. Permeability-increasing agonists signal activation of "small GTPases" of the Rho family to reorganize the actin cytoskeleton, leading to endothelial cell shape change, disassembly of cortical actin rim, and redistribution of actin into cytoplasmic stress fibers. In association with calcium- and Src-regulated myosin light chain kinase (MLCK), stress fibers become actinomyosin-mediated contractile units. Permeability-increasing agonists stimulate calcium entry and induce tyrosine phosphorylation of VE-cadherin (vascular endothelial cadherin) and β-catenins to weaken or pull apart endothelial adherens junctions. Some permeability agonists cause latent activation of the small GTPases, Cdc42 and Rac1, which facilitate endothelial barrier recovery and eliminate interendothelial gaps. Under the influence of Cdc42 and Rac1, filopodia and lamellipodia are generated by rearrangements of actin cytoskeleton. These motile evaginations extend endothelial cell borders across interendothelial gaps, and may initiate reannealing of endothelial junctions. Endogenous barrier protective substances, such as sphingosine-1-phosphate, play an important role in maintaining a restrictive endothelial barrier and counteracting the effects of permeability-increasing agonists.

Alteration of the E-Cadherin/β-Catenin Complex Is an Independent Poor Prognostic Factor in Lung Adenocarcinoma

Background

Epithelial-mesenchymal transition (EMT) is an important step in the invasion and progression of cancer and in the development of chemoresistance by cancer cells.

Methods

To address the clinical significance of the EMT pathway in lung adenocarcinoma and the association of the pathway with histological subtype, we examined 193 surgically resected lung adenocarcinoma samples for the expression of representative EMT-related proteins (E-cadherin, β-catenin, and vimentin) by immunohistochemistry. Histological subtypes were classified according to the 2011 International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society classification. The results for EMT-related protein expression were analyzed for correlation with clinicopathological features and with survival.

Results

The loss of E-cadherin expression and aberrant β-catenin expression were significantly associated with larger tumor size, pleural invasion, lymphatic/vascular invasion, and advanced pathological stage (p<0.05). The alteration of the E-cadherin/β-catenin complex was least frequently observed in the lepidic-predominant group, but these associations were not statistically significant. In the multivariate analysis, altered E-cadherin/β-catenin complex expression was found to be an independent poor prognostic factor (p=0.017; hazard ratio, 1.926; 95% confidence interval, 1.119 to 3.314).

Conclusions

The alteration of the expression of the E-cadherin/β-catenin complex was associated with aggressive tumor behavior in lung adenocarcinoma.

A novel function of YWHAZ/β-catenin axis in promoting epithelial-mesenchymal transition and lung cancer metastasis

YWHAZ, also known as 14-3-3zeta, has been reportedly elevated in many human tumors, including non-small cell lung carcinoma (NSCLC) but little is known about its specific contribution to lung cancer malignancy. Through a combined array-based comparative genomic hybridization and expression microarray analysis, we identified YWHAZ as a potential metastasis enhancer in lung cancer. Ectopic expression of YWHAZ on low invasive cancer cells showed enhanced cell invasion, migration in vitro, and both the tumorigenic and metastatic potentials in vivo. Gene array analysis has indicated these changes associated with an elevation of pathways relevant to epithelial-mesenchymal transition (EMT), with an increase of cell protrusions and branchings. Conversely, knockdown of YWHAZ levels with siRNA or short hairpin RNA (shRNA) in invasive cancer cells led to a reversal of EMT. We observed that high levels of YWHAZ protein are capable of activating β-catenin-mediated transcription by facilitating the accumulation of β-catenin in cytosol and nucleus. Coimmunoprecipitation assays showed a decrease of ubiquitinated β-catenin in presence of the interaction between YWHAZ and β-catenin. This interaction resulted in disassociating β-catenin from the binding of β-TrCP leading to increase β-catenin stability. Using enforced expression of dominant-negative and -positive β-catenin mutants, we confirmed that S552 phosphorylation of β-catenin increases the β-catenin/YWHAZ complex formation, which is important in promoting cell invasiveness and the suppression of ubiquitnated β-catenin. This is the first demonstration showing YWHAZ through its complex with β-catenin in mediating lung cancer malignancy and β-catenin protein stability.

The skeletal muscle Wnt pathway may modulate insulin resistance and muscle development in a diet-induced obese rat model

The Wnt signaling pathway is involved in lipid metabolism and obesity development. Skeletal muscle, a pivotal tissue for metabolism, is regulated by the Wnt signaling. However, little is known of this pathway's involvement in insulin sensitivity and myogenesis in animals. The current study focused on the potential role of Wnt signaling in insulin sensitivity and myogenic events and its further impact on intramuscular fat accumulation. Obesity resistant (OR) and obesity prone (OP) rats were fed a high-fat (HF, 45% kcal fat) diet for 13 weeks. Body weight and circulating triglyceride (TG) were measured and gastrocnemius muscle was collected for analysis of gene expression and protein amount. OP rats had higher body weight and blood TG than OR, and our study demonstrated that the skeletal muscle of OR and OP rats had different levels of β-catenin, which also corresponded to the expression of Wnt downstream genes. The expression of insulin receptor substrate (IRS) was significantly lower in OP than OR skeletal muscle, as was the protein amount of phosphorylated Akt, myocyte enhancer factor-2 (MEF2), and GLUT4. Expression of Myogenic regulatory factor (Myf) 5 and Myf3 (MyoD) were decreased significantly in OP skeletal muscle when compared to OR. Additionally, intramuscular fat was higher in OP than in OR rats. Thus, we propose that the differential Wnt signaling in the skeletal muscle of OR and OP rats is highly likely associated with the differences in insulin sensitivity and myogenic capability in these two strains.

Glycogen synthase kinase-3β/β-catenin signaling regulates neonatal lung mesenchymal stromal cell myofibroblastic differentiation

In bronchopulmonary dysplasia (BPD), alveolar septa are thickened with collagen and α-smooth muscle actin-, transforming growth factor (TGF)-β-positive myofibroblasts. We examined the biochemical mechanisms underlying myofibroblastic differentiation, focusing on the role of glycogen synthase kinase-3β (GSK-3β)/β-catenin signaling pathway. In the cytoplasm, β-catenin is phosphorylated on the NH(2) terminus by constitutively active GSK-3β, favoring its degradation. Upon TGF-β stimulation, GSK-3β is phosphorylated and inactivated, allowing β-catenin to translocate to the nucleus, where it activates transcription of genes involved in myofibroblastic differentiation. We examined the role of β-catenin in TGF-β1-induced myofibroblastic differentiation of neonatal lung mesenchymal stromal cells (MSCs) isolated from tracheal aspirates of premature infants with respiratory distress. TGF-β1 increased β-catenin expression and nuclear translocation. Transduction of cells with GSK-3β S9A, a nonphosphorylatable, constitutively active mutant that favors β-catenin degradation, blocked TGF-β1-induced myofibroblastic differentiation. Furthermore, transduction of MSCs with ΔN-catenin, a truncation mutant that cannot be phosphorylated on the NH(2) terminus by GSK-3β and is not degraded, was sufficient for myofibroblastic differentiation. In vivo, hyperoxic exposure of neonatal mice increases expression of β-catenin in α-smooth muscle actin-positive myofibroblasts. Similar changes were found in lungs of infants with BPD. Finally, low-passage unstimulated MSCs from infants developing BPD showed higher phospho-GSK-3β, β-catenin, and α-actin content compared with MSCs from infants not developing this disease, and phospho-GSK-3β and β-catenin each correlated with α-actin content. We conclude that phospho-GSK-3β/β-catenin signaling regulates α-smooth muscle actin expression, a marker of myofibroblast differentiation, in vitro and in vivo. This pathway appears to be activated in lung mesenchymal cells from patients with BPD.

Ethanol disrupts vascular endothelial barrier: implication in cancer metastasis

Both epidemiological and experimental studies indicate that ethanol exposure enhances tumor progression. Ethanol exposure promotes cancer cell invasion and is implicated in tumor metastasis. Metastasis consists of multiple processes involving intravasation and extravasation of cancer cells across the blood vessel walls. The integrity of the vascular endothelial barrier that lines the inner surface of blood vessels plays a critical role in cancer cell intravasation/extravasation. We examined the effects of ethanol on the endothelial integrity in vitro. Ethanol at physiologically relevant concentrations did not alter cell viability but disrupted the endothelial monolayer integrity, which was evident by a decrease in the electric resistance and the appearance of intercellular gaps in the endothelial monolayer. The effect of ethanol was reversible once ethanol was removed. The disruption of the endothelial monolayer integrity was associated with an increased invasion of cancer cells through the endothelial monolayer. Ethanol induced the formation of stress fibers; stabilization of actin filaments by jasplakinolide prevented ethanol-induced disruption of endothelial integrity and cancer cell invasion. VE-cadherin is a critical component of the adherens junctions, which regulates vascular endothelial integrity. Ethanol induced the endocytosis of VE-cadherin and the effect was blocked by jasplakinolide. Our results indicate that ethanol may facilitate cancer metastasis by disrupting the vascular endothelial barrier.

Canonical Wnt signaling negatively regulates platelet function

Wnts regulate important intracellular signaling events, and dysregulation of the Wnt pathway has been linked to human disease. Here, we uncover numerous Wnt canonical effectors in human platelets where Wnts, their receptors, and downstream signaling components have not been previously described. We demonstrate that the Wnt3a ligand inhibits platelet adhesion, activation, dense granule secretion, and aggregation. Wnt3a also altered platelet shape change and inhibited the activation of the small GTPase RhoA. In addition, we found the Wnt-beta-catenin signaling pathway to be functional in platelets. Finally, disruption of the Wnt Frizzled 6 receptor in the mouse resulted in a hyperactivatory platelet phenotype and a reduced sensitivity to Wnt3a. Taken together our studies reveal a novel functional role for Wnt signaling in regulating anucleate platelet function and may provide a tractable target for future antiplatelet therapy.

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.

Cell adhesion and spreading behavior on vertically aligned silicon nanowire arrays

In this report, we studied the interactions between biological cells and vertically aligned silicon nanowire (SiNW) arrays and focused on how SiNW arrays affected cellular behaviors such as cell adhesion and spreading. We observed that SiNW arrays could support cell adhesion and growth and guide cell adhesion and spreading behaviors. The results also showed that SiNW arrays could not only enhance the cell-substrate adhesion force but also restrict cell spreading. Combining the results from scanning electron microscopy images of cell morphology and the expression analysis of genes and proteins related to cell adhesion and spreading process, we proposed a mechanism on how cell adhesion and spreading was controlled by arrayed SiNWs. The effects of SiNW arrays in guiding cell adhesion and spreading behavior might be useful in the development of cell microarrays, tissue engineering scaffolds, and molecule delivery vehicles in which strong cell-substrate adhesion and reduced cell-cell communication were beneficial.

Wnt1 overexpression promotes tumour progression in non-small cell lung cancer

BACKGROUND

The Wnt gene family is involved in embryogenesis and tumourigenesis. We investigated the clinical significance of Wnt1 expression in non-small cell lung cancer (NSCLC).

METHOD

We studied 216 NSCLC patients. Immunohistochemistry was performed to investigate the Wnt1 expression in relation to the expression of beta-catenin and Wnt-targets, including c-Myc, Cyclin D1, VEGF-A and MMP-7. The Ki-67 proliferation index and the intratumoural microvessel density (IMD) were also evaluated.

RESULTS

The ratio of tumours with an aberrant beta-catenin expression was significantly higher in Wnt1-positive tumours than in Wnt1-negative tumours (p<0.0001). The Wnt1 expression significantly correlated with the expression of c-Myc (p<0.0001), Cyclin D1 (p<0.0001), VEGF-A (p=0.0160), MMP-7 (p<0.0001), the Ki-67 index (p=0.0048) and the IMD (p=0.0267). Furthermore, the Wnt1 status was a significant prognostic factor for NSCLC patients (p=0.0127).

CONCLUSIONS

The Wnt1 overexpression is associated with the expression of tumour-associated Wnt-targets, tumour proliferation, angiogenesis and a poor prognosis in NSCLCs.

Overexpression of matrix metalloproteinase-7 (MMP-7) correlates with tumor proliferation, and a poor prognosis in non-small cell lung cancer

BACKGROUND

Matrix metalloporteinase-7 (MMP-7) is a member of the MMP family, and it has been reported to play an important role in tumorigenesis, invasion and metastasis. We performed a retrospective study on the MMP-7 expression in non-small cell lung cancer (NSCLC) according to the clinical characteristics, biological markers and the Wnt1 expression.

PATIENTS AND METHODS

One hundred forty-seven postsurgical NSCLC patients were investigated. Immunohistochemistry was performed to evaluate the MMP-7 expression, the Ki-67 proliferation index, tumor angiogenesis and the Wnt1 expression. The TUNEL method was performed to investigate tumor apoptosis.

RESULTS

Seventy-six carcinomas (51.7%) were MMP-7-positive. The MMP-7 expression was significantly higher in squamous cell carcinomas than in adenocarcinomas (P<0.0001). The Ki-67 proliferation index was significantly higher in MMP-7-positvie tumors than in MMP-7-negative tumors (P=0.0003). However, there was no difference in the MMP-7 expression in relation to apoptosis or angiogenesis. Regarding its regulation, the MMP-7 expression significantly correlated with the Wnt1 expression (r=0.426, P<0.0001). The overall survival was significantly lower in patients with MMP-7-positive NSCLCs than in those with MMP-7-negative NSCLCs (P=0.0018). A Cox regression analyses also demonstrated MMP-7 status to be a significant prognostic factor (hazard ratio, 2.187; P=0.0023).

CONCLUSIONS

The overexpression of MMP-7 was associated with tumor proliferation, and a poor prognosis in NSCLCs. In addition, Wnt1 may play a critical role in regulating the intratumoral MMP-7 expression.

Cell adhesion molecules in chemically-induced renal injury

Cell adhesion molecules are integral cell-membrane proteins that maintain cell-cell and cell-substrate adhesion and in some cases act as regulators of intracellular signaling cascades. In the kidney, cell adhesion molecules, such as the cadherins, the catenins, the zonula occludens protein-1 (ZO-1), occludin and the claudins are essential for maintaining the epithelial polarity and barrier integrity that are necessary for the normal absorption/excretion of fluid and solutes. A growing volume of evidence indicates that these cell adhesion molecules are important early targets for a variety of nephrotoxic substances including metals, drugs, and venom components. In addition, it is now widely appreciated that molecules, such as intracellular adhesion molecule-1 (ICAM-1), integrins, and selectins play important roles in the recruitment of leukocytes and inflammatory responses that are associated with nephrotoxic injury. This review summarizes the results of recent in vitro and in vivo studies indicating that these cell adhesion molecules may be primary molecular targets in many types of chemically-induced renal injury. Some of the specific agents that are discussed include cadmium (Cd), mercury (Hg), bismuth (Bi), cisplatin, aminoglycoside antibiotics, S-(1,2-dichlorovinyl)-l-cysteine (DCVC), and various venom toxins. This review also includes a discussion of the various mechanisms, by which these substances can affect cell adhesion molecules in the kidney.

GSKIP is homologous to the Axin GSK3beta interaction domain and functions as a negative regulator of GSK3beta

Although prominent FRAT/GBP exhibits a limited degree of homology to Axin, the binding sites on GSK3 for FRAT/GBP and Axin may overlap to prevent the effect of FRAT/GBP in stabilizing beta-catenin in the Wnt pathway. Using a yeast two-hybrid screen, we identified a novel protein, GSK3beta interaction protein (GSKIP), which binds to GSK3beta. We have defined a 25-amino acid region in the C-terminus of GSKIP that is highly similar to the GSK3beta interaction domain (GID) of Axin. Using an in vitro kinase assay, our results indicate that GSKIP is a good GSK3beta substrate, and both the full-length protein and a C-terminal fragment of GSKIP can block phosphorylation of primed and nonprimed substrates in different fashions. Similar to Axin GID(381-405) and FRATtide, synthesized GSKIPtide is also shown to compete with and/or block the phosphorylation of Axin and beta-catenin by GSK3beta. Furthermore, our data indicate that overexpression of GSKIP induces beta-catenin accumulation in the cytoplasm and nucleus as visualized by immunofluorescence. A functional assay also demonstrates that GSKIP-transfected cells have a significant effect on the transactivity of Tcf-4. Collectively, we define GSKIP as a naturally occurring protein that is homologous with the GSK3beta interaction domain of Axin and is able to negatively regulate GSK3beta of the Wnt signaling pathway.

The vascular endothelium as a target of cadmium toxicity

Cadmium (Cd) is an important industrial and environmental pollutant that can produce a wide variety of adverse effects in humans and animals. A growing volume of evidence indicates that the vascular endothelium may be one of the primary targets of Cd toxicity in vivo. Studies over the past 20 years have shown that Cd, at relatively low, sublethal concentrations, can target vascular endothelial cells at a variety of molecular levels, including cell adhesion molecules, metal ion transporters and protein kinase signaling pathways. The purpose of this review is to summarize the results of these recent studies and to discuss the implications of these findings with regard to the mechanisms of Cd toxicity in specific organs including the lung, liver, kidney, testis and heart. In addition the possible roles of the vascular endothelium in mediating the tumor promoting and anticarcinogenic effects of Cd are discussed.

Wnt5a expression is associated with the tumor proliferation and the stromal vascular endothelial growth factor--an expression in non-small-cell lung cancer

PURPOSE

The Wnt gene family encodes the multifunctional signaling glycoproteins. We performed the present study to investigate the clinical significance of Wnt5a expression in non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

One hundred twenty-three patients with NSCLC who had undergone resection were investigated. Real-time quantitative reverse transcriptase polymerase chain reaction was performed to evaluate the Wnt5a gene expression. Immunohistochemistry was performed to investigate the Wnt5a protein expression, the Ki-67 proliferation index, tumor angiogenesis, and the expression of beta-catenin and vascular endothelial growth factor-A (VEGF-A).

RESULTS

Wnt5a gene expression in squamous cell carcinoma was significantly higher than that in adenocarcinoma (P < .0001). There was a significant correlation between the normalized Wnt5a gene expression ratio and the intratumoral Wnt5a protein expression (r = 0.729; P < .0001). The intratumoral Wnt5a expression was significantly correlated with the Ki-67 proliferation index (r = 0.708; P < .0001). In contrast, no correlation was observed between the intratumoral Wnt5a expression and tumor angiogenesis. Furthermore, the intratumoral Wnt5a expression was significantly correlated with the stromal expression of beta-catenin (r = 0.729; P < .0001) and VEGF-A (r = 0.661; P < .0001). In addition, the stromal VEGF-A expression was also correlated with Ki-67 proliferation (r = 0.627; P < .0001). Cox regression analyses demonstrated Wnt5a status to be a significant prognostic factor for NSCLC patients (P = .0193), especially for patients with squamous cell carcinomas (P = .0491).

CONCLUSION

The present study revealed that an overexpression of Wnt5a could produce more aggressive NSCLC, especially in squamous cell carcinomas, during tumor progression.

Signaling Mechanisms Regulating Endothelial Permeability

The microvascular endothelial cell monolayer localized at the critical interface between the blood and vessel wall has the vital functions of regulating tissue fluid balance and supplying the essential nutrients needed for the survival of the organism. The endothelial cell is an exquisite “sensor” that responds to diverse signals generated in the blood, subendothelium, and interacting cells. The endothelial cell is able to dynamically regulate its paracellular and transcellular pathways for transport of plasma proteins, solutes, and liquid. The semipermeable characteristic of the endothelium (which distinguishes it from the epithelium) is crucial for establishing the transendothelial protein gradient (the colloid osmotic gradient) required for tissue fluid homeostasis. Interendothelial junctions comprise a complex array of proteins in series with the extracellular matrix constituents and serve to limit the transport of albumin and other plasma proteins by the paracellular pathway. This pathway is highly regulated by the activation of specific extrinsic and intrinsic signaling pathways. Recent evidence has also highlighted the importance of the heretofore enigmatic transcellular pathway in mediating albumin transport via transcytosis. Caveolae, the vesicular carriers filled with receptor-bound and unbound free solutes, have been shown to shuttle between the vascular and extravascular spaces depositing their contents outside the cell. This review summarizes and analyzes the recent data from genetic, physiological, cellular, and morphological studies that have addressed the signaling mechanisms involved in the regulation of both the paracellular and transcellular transport pathways.

P-cadherin promotes cell-cell adhesion and counteracts invasion in human melanoma

Malignant transformation of melanocytes frequently coincides with alterations in epithelial cadherin (E-cadherin) expression, switching on of neural cadherin (N-cadherin), and, when progressed to a metastatic stage, loss of membranous placental cadherin (P-cadherin). In vitro studies of melanoma cell lines have shown invasion suppressor and promoter roles for E-cadherin and N-cadherin, respectively. In the present study, we investigated the effect of P-cadherin on aggregation and invasion using melanoma cells retrovirally transduced with human P-cadherin. De novo expression of P-cadherin in P-cadherin-negative cell lines (BLM and HMB2) promoted cell-cell contacts and Ca2+-dependent cell-cell aggregation in two- and three-dimensional cultures, whereas it counteracted invasion. These effects were not observed following P-cadherin transduction of endogenously P-cadherin-positive MeWo cells. In addition, P-cadherin-transduced BLM cells coaggregated with keratinocytes and showed markedly reduced invasion in a reconstructed skin model. The proadhesive and anti-invasive effects of P-cadherin were abolished on targeted mutation of its intracellular juxtamembrane domain or its extracellular domain. For the latter mutation, we mimicked a known missense mutation in P-cadherin (R503H), which is associated with congenital hypotrichosis with juvenile macular dystrophy.

Inhibition of glycogen synthase kinase 3beta suppresses coxsackievirus-induced cytopathic effect and apoptosis via stabilization of beta-catenin

Coxsackievirus B3 (CVB3), a common human pathogen for viral myocarditis, induces a direct cytopathic effect (CPE) and apoptosis on infected cells. To elucidate the mechanisms that contribute to these processes, we studied the role of glycogen synthase kinase 3beta (GSK3beta). GSK3beta activity was significantly increased after CVB3 infection and addition of tyrosine kinase inhibitors blocked CVB3-triggered GSK3beta activation. Inhibition of caspase activity had no inhibitory effect on CVB3-induced CPE; however, blockage of GSK3beta activation attenuated both CVB3-induced CPE and apoptosis. We further showed that CVB3 infection resulted in reduced beta-catenin protein expression, and GSK3beta inhibition led to the accumulation and nuclear translocation of beta-catenin. Finally, we found that CVB3-induced CPE and apoptosis were significantly reduced in cells stably overexpressing beta-catenin. Taken together, our results demonstrate that CVB3 infection stimulates GSK3beta activity via a tyrosine kinase-dependent mechanism, which contributes to CVB3-induced CPE and apoptosis through dysregulation of beta-catenin.

Regulators of angiogenesis and strategies for their therapeutic manipulation

Angiogenesis provides a mechanism by which delivery of oxygen and nutrients is adapted to compliment changes in tissue mass or metabolic activity. However, maladaptive angiogenesis is integral to the process of several diseases common in Western countries, including tumor growth, vascular insufficiency, diabetic retinopathy and rheumatoid arthritis. Understanding the process of capillary growth, including the identification and functional analyses of key pro- and anti-angiogenic factors, provides knowledge that can be applied to improve/reverse these pathological states. Initially, angiogenesis research focused predominantly on vascular endothelial growth factor (VEGF) as a main player in the angiogenesis cascade. It is apparent now that participation of multiple angiogenic factors and signal pathways is critical to enable effective growth and maturation of nascent capillaries. The purpose of this review is to focus on recent progress in identifying angiogenesis signaling pathways that show promise as targets for successful induction or inhibition of capillary growth. The strategies applied to achieve these contradictory tasks are discussed within the framework of our existing fundamental knowledge of angiogenesis signaling cascades, with an emphasis on comparing the employment of distinctive tactics in modulation of these pathways. Innovative developments that are presented include: (1) inducing a pleiotropic response via activation or inhibition of angiogenic transcription factors; (2) modulation of nitric oxide tissue concentration; (3) manipulating the kallikrein-kinin system; (4) use of endothelial progenitor cells as a means to either directly contribute to capillary growth or to be used as a vehicle to deliver "suicide genes" to tumor tissue.

G1 checkpoint failure and increased tumor susceptibility in mice lacking the novel p53 target Ptprv

In response to DNA damage, p53 activates a G1 cell cycle checkpoint, in part through induction of the cyclin-dependent kinase inhibitor p21(Waf1/Cip1). Here we report the identification of a new direct p53 target, Ptprv (or ESP), encoding a transmembrane tyrosine phosphatase. Ptprv transcription is dramatically and preferentially increased in cultured cells undergoing p53-dependent cell cycle arrest, but not in cells undergoing p53-mediated apoptosis. This observation was further confirmed in vivo using a Ptprv null-reporter mouse line. A p53-responsive element is present in the Ptprv promoter and p53 is recruited to this site in vivo. Importantly, while p53-dependent apoptosis is intact in mice lacking Ptprv, Ptprv-null fibroblasts and epithelial cells of the small intestine are defective in G1 checkpoint control. Thus, Ptprv is a new direct p53 target and a key mediator of p53-induced cell cycle arrest. Finally, Ptprv loss enhances the formation of epidermal papillomas after exposure to chemical carcinogens, suggesting that Ptprv acts to suppress tumor formation in vivo.

Wnt/beta-catenin signaling activates growth-control genes during overload-induced skeletal muscle hypertrophy

Beta-catenin is a transcriptional activator shown to regulate the embryonic, postnatal, and oncogenic growth of many tissues. In most research to date, beta-catenin activation has been the unique downstream function of the Wnt signaling pathway. However, in the heart, a Wnt-independent mechanism involving Akt-mediated phosphorylation of glycogen synthase kinase (GSK)-3beta was recently shown to activate beta-catenin and regulate cardiomyocyte growth. In this study, results have identified the activation of the Wnt/beta-catenin pathway during hypertrophy of mechanically overloaded skeletal muscle. Significant increases in beta-catenin were determined during skeletal muscle hypertrophy. In addition, the Wnt receptor, mFrizzled (mFzd)-1, the signaling mediator disheveled-1, and the transcriptional co-activator, lymphocyte enhancement factor (Lef)-1, are all increased during hypertrophy of the overloaded mouse plantaris muscle. Experiments also determined an increased association between GSK-3beta and the inhibitory frequently rearranged in advanced T cell-1 protein with no increase in GSK-3beta phosphorylation (Ser9). Finally, skeletal muscle overload resulted in increased nuclear beta-catenin/Lef-1 expression and induction of the transcriptional targets c-Myc, cyclin D1, and paired-like homeodomain transcription factor 2. Thus this study provides the first evidence that the Wnt signaling pathway induces beta-catenin/Lef-1 activation of growth-control genes during overload induced skeletal muscle hypertrophy.

Enteropathogenic Escherichia coli outer membrane proteins induce changes in cadherin junctions of Caco-2 cells through activation of PKCalpha

Enteropathogenic Escherichia coli (EPEC) is a Gram-negative bacterial pathogen that adheres to human intestinal epithelial cells, resulting in watery, persistent diarrhoea. Despite the advances made in understanding EPEC-host cell interactions, the molecular mechanisms underlying watery diarrhoea have not been understood fully. Loss of transepithelial resistance and increased monolayer permeability by disruption of tight junctions has been implicated in this process. Apart from disruption of tight junctions, an important factor known to regulate monolayer permeability is E-cadherin and its interaction with beta-catenin, both of which constitute the adherens junctions. Our previous studies using HEp-2 cells demonstrated the morphological and cytoskeletal changes caused by cell-free outer membrane preparations (OMPs) of EPEC. In this study, we have shown that EPEC and its OMP induce significant changes in the adherens junctions of Caco-2 monolayers. We also observed significant phosphorylation of protein kinase Calpha (PKCalpha) in cells treated with either whole EPEC or its OMP. Immunoprecipitation of cell lysates with anti-E-cadherin and probing with phospho-PKCalpha monoclonal antibodies and anti-beta-catenins revealed that in these cells, phosphorylated PKCalpha is associated with cadherins, leading to the dissociation of the cadherin/beta-catenin complex. Immunofluorescence showed beta-catenins dissociated from the membrane-bound cadherins and redistributed into the cytoplasm. Expression of dominant negative PKCalpha reversed these effects caused by either whole EPEC or its OMP and also reduced the associated increase in monolayer permeability. It is possible that this mechanism may complement the earlier known pathways for loss of barrier function involving myosin light chain kinase activation and also may play a role in causing host cell death by apoptosis.

TNFalpha-mediated extracellular matrix remodeling is required for multiple division cycles in rat hepatocytes

During liver regeneration, hepatocytes proliferate under the control of both proinflammatory cytokines such as tumor necrosis factor alpha (TNFalpha) and growth factors, in parallel to extracellular matrix remodeling. This study investigated mechanisms by which mitogen and extracellular matrix signals are linked for inducing proliferation of differentiated hepatocytes. The authors used adult rat hepatocytes in coculture with liver biliary cells, because cells are stably differentiated for several weeks, capable of extracellular matrix deposition, and unable to divide in response to growth factor alone. This work demonstrated that hepatocytes could undergo several proliferation waves without loss of differentiation by using alternating periods of TNFalpha/growth factor stimulation and deprivation. Three days after stimulation with TNFalpha and epidermal growth factor (EGF), up to 35% of hepatocytes divided. Demonstration was also provided that EGF alone only promoted cell progression up to late G(1), whereas TNFalpha was necessary for G(1)/S transition and Cdk1 induction. TNFalpha promoted an extracellular matrix (ECM) degradation that involved the matrix metalloproteinase MMP-9 induction through activation of NF-kappaB pathway. Finally, the authors showed that ECM remodeling signal was required for initiating any new hepatocyte division wave, in presence of mitogen. In conclusion, these results highlight that hepatocyte division is dependent on ECM deposition associated with differentiation status, and that ECM degradation signal is critical in controlling G(1)/S transition and Cdk1 induction. These results provide new insights for understanding the unique hepatocyte proliferation control and improving regeneration in patients suffering from liver damage.

Nuclear translocation of integrin cytoplasmic domain-associated protein 1 stimulates cellular proliferation

Integrin cytoplasmic domain-associated protein 1 (ICAP-1) has been shown to interact specifically with the beta1 integrin cytoplasmic domain and to control cell spreading on fibronectin. Interestingly, ICAP-1 also is observed in the nucleus, by immunocytochemical staining, and after biochemical cell fractionation, suggesting that it has additional roles that have yet to be determined. We show that the nucleocytoplasmic shuttling capability of ICAP-1 is dependent on a functional nuclear localization signal. In addition, overexpression of beta1 integrin strongly reduced this nuclear localization, suggesting that integrin activity could modulate ICAP-1 shuttling by sequestering it in the cytoplasm. Indeed, the nuclear localization of ICAP-1 is dependent on the stage of cell spreading on fibronectin, and we also show that ICAP-1 expression stimulates cellular proliferation in a fibronectin-dependent manner. This function is dependent on its nuclear localization. Moreover, ICAP-1 is able to activate the c-myc promoter in vitro. Together, these results demonstrate that ICAP-1 shuttles between the nucleus and cytoplasm in a beta1 integrin-dependent manner. It could act as a messenger that relays information from sites of integrin-dependent cell adhesion to the nucleus for controlling gene expression and cell proliferation.

Repressed E-cadherin expression in the lower crypt of human small intestine: a cell marker of functional relevance

In epithelia, abnormal expression of E-cadherin is related to pathologies involving a loss of cell polarization and/or differentiation. However, recent observations suggest that E-cadherin could also be repressed under physiological conditions, such as in some epithelial stem cell lineages. In the present work, we have analyzed E-cadherin expression in human intestinal epithelial cell progenitors and investigated its potential role. E-cadherin expression was analyzed along the crypt-villus axis by immunofluorescence on cryosections of small intestine. E-cadherin was found to be differentially expressed, being significantly weaker in the cells located at the bottom of the crypts. Surprisingly, neither the E-cadherin protein nor transcript were detected in a normal human intestinal epithelial (HIEC) crypt cell model isolated in our laboratory, whereas other E-cadherin-related components such as catenins and APC were present. Forced expression of E-cadherin in HIEC cells increased membrane-associated beta-catenin and was accompanied by the appearance of junction-like structures at the cell-cell interface. Functionally, cell kinetics and p21Cip levels were found to be altered in the E-cadherin expressing HIEC cells as compared to controls. Furthermore, a significant reduction of the migration abilities and an increase in sensitivity to anoikis were also observed. These results suggest that down-regulated expression of E-cadherin is a human intestinal crypt base cell-related feature that appears to be of functional relevance for the maintenance of the progenitor cell population.

Involvement of JAK2 upstream of the PI 3-kinase in cell-cell adhesion regulation by gastrin

The Janus kinase/signal transducers and activators of transcription (JAK/STAT) signaling pathway has been implicated in cell transformation and proliferation. Besides aberrant cell proliferation, loss of cell-cell adhesion during epithelial-mesenchymal transition (EMT) is an important event which occurs during development of epithelial cancers. However, the role of JAK-dependent pathways in this process is not known. We analyzed the involvement of these pathways in the regulation of E-cadherin-dependent cell-cell adhesion by gastrin, a mitogenic factor for gastrointestinal (GI) tract. We identified JAK2/STAT3 as a new pathway in gastrin signaling. We demonstrated that JAK2 functions as an upstream mediator of the phosphatidylinositol 3 (PI 3)-kinase activity in gastrin signaling. Indeed, we observed a coprecipitation of both kinases and an inhibition of gastrin-induced PI 3-kinase activation when JAK2 activity is blocked. We also demonstrated that loss of cell-cell adhesion and the increase in cell motility induced by gastrin required the activation of JAK2 and the PI 3-kinase. Indeed, the modifications in localization of adherens junctions proteins and the migration, observed in gastrin-stimulated cells, were reversed by inhibition of both kinases. These results described the involvement of JAK2 in the modulation of cell-cell adhesion in epithelial cells. They support a possible role of JAK2 in the epithelial-mesenchymal transition which occurs during malignant development.

The expression pattern of β-catenin in mesothelial proliferative lesions and its diagnostic utilities

beta-Catenin is a component of the E-cadherin-catenin cell adhesion complex. It plays an important role in the Wnt/wg pathway, which conveys critical signals for cell proliferation and transformation. The beta-catenin mutation is an important event in the progression of a number of malignancies. In this study, we evaluated the immunohistochemical (IHC) pattern of beta-catenin in a spectrum of mesothelial lesions. Sixty-five formalin-fixed, paraffin-embedded blocks from 54 serous effusions and 11 pleural biopsies were examined. These cases consisted of 33 invasive mesotheliomas, 9 early mesotheliomas (with negative radiologic finding), so-called mesotheliomas in situ, and 23 reactive mesothelial proliferations. A distinct membranous and/or submembranous staining pattern was seen in 23 cases with normal and reactive mesothelium. In contrast, reduced membranous and/or submembranous antibody staining and markedly increased ectopic cytoplasmic and nuclear staining was seen in 26 cases of 33 mesotheliomas. Seven of 9 early mesotheliomas showed increased ectopic cytoplasmic and/or nuclear stain. On the basis of our findings, identification of beta-catenin staining pattern offers a useful marker in the diagnosis of mesothelial lesions and may help identify neoplastic change.

Early enterocytic differentiation of HT-29 cells: biochemical changes and strength increases of adherens junctions

We have characterized the modulation of cell-cell adhesion and the structure of adherens junctions in the human colon adenocarcinoma HT-29 cell line that differentiates into enterocytes after glucose substitution for galactose in the medium. We demonstrate that differentiated cells (HT-29 Gal) rapidly established E-cadherin-mediated interactions in aggregation assays. This effect is not due to an increase in E-cadherin expression during this early stage of cell differentiation, but rather results from the maturation of preexisting adherens junctions. These junctions are characterized by the redistribution of E-cadherin to the basolateral membrane and its co-localization with the actin cytoskeleton. Subcellular fractionation studies indicate that actin-associated E-cadherins bind beta-catenin and p120ctn. Furthermore, the p120ctn/E-cadherin association is upregulated. These data reveal a cooperative interaction between p120ctn and E-cadherin that corresponds to mature functional adherens junctions able to initiate tight cell-cell adhesion required for epithelium architecture and further affirm the gatekeeper role of p120ctn.

Wnt-4 activates the canonical beta-catenin-mediated Wnt pathway and binds Frizzled-6 CRD: functional implications of Wnt/beta-catenin activity in kidney epithelial cells

The Wnt signaling pathway is central to the development of all animals and to cancer progression, yet largely unknown are the pairings of secreted Wnt ligands to their respective Frizzled transmembrane receptors or, in many cases, the relative contributions of canonical (beta-catenin/LEF/TCF) versus noncanonical Wnt signals. Specifically, in the kidney where Wnt-4 is essential for the mesenchymal to epithelial transition that generates the tissue's collecting tubules, the corresponding Frizzled receptor(s) and downstream signaling mechanism(s) are unclear. In this report, we addressed these issues using Madin-Darby Canine Kidney (MDCK) cells, which are competent to form tubules in vitro. Employing established reporter constructs of canonical Wnt/beta-catenin pathway activity, we have determined that MDCK cells are highly responsive to Wnt-4, -1, and -3A, but not to Wnt-5A and control conditions, precisely reflecting functional findings from Wnt-4 null kidney mesenchyme ex vivo rescue studies. We have confirmed that Wnt-4's canonical signaling activity in MDCK cells is mediated by downstream effectors of the Wnt/beta-catenin pathway using beta-Engrailed and dnTCF-4 constructs that suppress this pathway. We have further found that MDCK cells express the Frizzled-6 receptor and that Wnt-4 forms a biochemical complex with the Frizzled-6 CRD. Since Frizzled-6 did not appear to transduce Wnt-4's canonical signal, data supported recently by Golan et al., there presumably exists another as yet unknown Frizzled receptor(s) mediating Wnt-4 activation of beta-catenin/LEF/TCF. Finally, we report that canonical Wnt/beta-catenin signals cells help maintain cell growth and survival in MDCK cells but do not contribute to standard HGF-induced (nonphysiologic) tubule formation. Our results in combination with work from Xenopus laevis (not shown) lead us to believe that Wnt-4 binds both canonical and noncanonical Frizzled receptors, thereby activating Wnt signaling pathways that may each contribute to kidney tubulogenesis.

The role of Xenopus frizzled-8 in pronephric development

Vertebrates use two or three forms of kidney successively during development and the nephric duct is essential for this succession of kidney induction. While transcripts of many Wnt ligands and Wnt receptor Frizzled genes have been localized in developing kidney, the relationship between Wnt signaling and nephric duct development remains unknown. This study investigated the role of Xenopus frizzled-8 (Xfz8) in pronephros development. Translational inhibition of Xfz8 caused a significant reduction in the staining of a duct-specific antibody, but did not affect the expression of early pronephric maker genes in the duct region. Defects in pronephric tubule branching were also observed following inhibition of Xfz8. Histological analysis revealed that the Xfz8-inhibited cells failed to form a normal epithelium structure. These results suggest that Xfz8 is involved in the process of normal epithelium formation in the developing pronephric duct and tubules after specification.

Differential expression of E-cadherin, N-cadherin and beta-catenin in proximal and distal segments of the rat nephron

BACKGROUND

The classical cadherins such as E- and N-cadherin are Ca2+-dependent cell adhesion molecules that play important roles in the development and maintenance of renal epithelial polarity. Recent studies have shown that a variety of cadherins are present in the kidney and are differentially expressed in various segments of the nephron. However, the interpretation of these findings has been complicated by the fact that the various studies focused on different panels of cadherins and utilized different species. Moreover, since only a few of the previous studies focused on the rat, information regarding the expression and localization of renal cadherins in this important species is lacking. In the present study, we have employed dual immunofluorescent labeling procedures that utilized specific antibodies against either E- or N-cadherin, along with antibodies that target markers for specific nephron segments, to characterize the patterns of cadherin expression in frozen sections of adult rat kidney.

RESULTS

The results showed that N-cadherin is the predominant cadherin in the proximal tubule, but is essentially absent in other nephron segments. By contrast, E-cadherin is abundant in the distal tubule, collecting duct and most medullary segments, but is present only at very low levels in the proximal tubule. Additional results revealed different patterns of N-cadherin labeling along various segments of the proximal tubule. The S1 and S2 segments exhibit a fine threadlike pattern of labeling at the apical cell surface, whereas the S3 segment show intense labeling at the lateral cell-cell contacts.

CONCLUSIONS

These results indicate that E- and N-cadherin are differentially expressed in the proximal and distal tubules of rat kidney and they raise the possibility that differences in cadherin expression and localization may contribute to the differences in the susceptibility of various nephron segments to renal pathology or nephrotoxic injury.

IFN-gamma gene expression in epithelial trophectoderm cells is linked to downregulation of the p44/p42 MAP kinase pathway

We previously stated that interferon-gamma (IFN-gamma) is highly expressed in a transient and developmentally regulated manner by the trophectoderm of the pig blastocyst, which represents a monolayer of polarized epithelial cells, during early pregnancy. In order to study the molecular mechanisms of this atypical IFN-gamma gene expression, we established the pig trophectoderm cell line TBA B4-3. These cells develop a polarized phenotype with high transepithelial electrical resistance (TER) when grown on a microporous membrane. We previously showed that treatment of polarized TBA B4-3 cells with the strong protein kinase C (PKC) agonist phorbol 12-myristate-13-acetate (PMA) induced 3-4 days later a transient IFN-gamma mRNA expression and apical IFN-gamma protein secretion. In the present paper, we report that after PMA removal, a transient phase of p44/p42 mitogen-activated protein (MAP) kinase activation occurs, followed by a strong downregulation preceding the phase of IFN-gamma expression. Surprisingly, we found that inhibition of this surge of p44/p42 MAP kinase activation with MEK inhibitors (U0126 and PD98059) triggers earlier IFN-gamma mRNA and protein expression, correlated with earlier TER rising and restoration of epithelial phenotype. These results indicate that in the TBA B4-3 cell system, activation of this signaling pathway has a negative effect on IFN-gamma gene expression. These observations reinforce the hypothesis of a link between establishment of cell polarity and induction of IFN-gamma that could be mediated by signaling from intercellular junctions.

Contextual binding of p120ctn to E-cadherin at the basolateral plasma membrane in polarized epithelia

E-cadherin-catenin complexes mediate cell-cell adhesion on the basolateral membrane of epithelial cells. The cytoplasmic tail of E-cadherin supports multiple protein interactions, including binding of beta-catenin at the C terminus and of p120ctn to the juxtamembrane domain. The temporal assembly and polarized trafficking of the complex or its individual components to the basolateral membrane are not fully understood. In Madin-Darby canine kidney cells at steady state and after treatment with cycloheximide or temperature blocks, E-cadherin and beta-catenin localized to the Golgi complex, but p120ctn was found only at the basolateral plasma membrane. We previously identified a dileucine sorting motif (Leu586-Leu587, termed S1) in the juxtamembrane domain of E-cadherin and now show that it is required to target full-length E-cadherin to the basolateral membrane. Removal of S1 resulted in missorting of E-cadherin mutants (EcadDeltaS1) to the apical membrane; beta-catenin was simultaneously missorted and appeared at the apical membrane. p120ctn was not mistargeted with EcadDeltaS1, but could be recruited to the E-cadherin-catenin complex only at the basolateral membrane. These findings help define the temporal assembly and sorting of the E-cadherin-catenin complex and show that membrane recruitment of p120ctn in polarized cells is contextual and confined to the basolateral membrane.

Glucocorticoids control beta-catenin protein expression and localization through distinct pathways that can be uncoupled by disruption of signaling events required for tight junction formation in rat mammary epithelial tumor cells

In Con8 rat mammary epithelial tumor cells, the synthetic glucocorticoid dexamethasone stimulates the remodeling of tight junctions and adherens junctions before formation of highly sealed tight junctions. In this study, the expression and localization of key components of the apical junction were examined as potential targets of glucocorticoid signaling. Western blot and RT-PCR demonstrated that dexamethasone up-regulated beta-catenin protein and transcript expression and nearly ablated beta-catenin phosphorylation under conditions that led to a significant increase in monolayer transepithelial resistance. Indirect immunofluorescence revealed that dexamethasone treatment also caused beta-catenin to localize predominantly at the cell membrane rather than the nucleus. The glucocorticoid regulation of beta-catenin expression and localization was not a consequence of dexamethasone inhibition of cell growth, because both responses were unaltered in the presence of hydroxyurea. The steroid induction of beta-catenin expression and localization can be uncoupled by altering the function of signaling pathways needed for tight junction formation. Expression of dominant-negative RasN17 abolished dexamethasone up-regulation of beta-catenin protein expression without affecting its localization at the membrane. In contrast, exogenous treatment or constitutive production of TGFalpha abolished the dexamethasone-induced alteration of beta-catenin localization without affecting the dexamethasone stimulation of beta-catenin expression. Taken together, our results demonstrate that glucocorticoids control beta-catenin at two distinct levels of cellular regulation that differ in their cell signaling requirements for the glucocorticoid regulation of mammary epithelial junctional dynamics.

Redistribution of β-catenin in response to EGF and lithium signalling in human oesophageal squamous carcinoma cell lines

BACKGROUND

The β-catenin link between membrane-bound cadherins and the actin cytoskeleton regulates cell adhesion and consequently metastasis. Abnormal stabilisation of β-catenin enhances its transcriptional activities. Factors affecting β-catenin's functions are important in understanding metastatic diseases such as oesophageal squamous cell carcinoma (SCC).

RESULTS

In human oesophageal SCCs β-catenin localises predominantly to the plasma membrane. The presence of free β-catenin in the cytoplasm/nucleus was low. This indicates that β-catenin's activities are skewed towards cell-cell adhesion in these oesophageal SCCs. Exposure to EGF or Li alone, produced a slight increase in membrane concentrations but only Li induced β-catenin stabilisation in the cytoplasm. In combination, EGF and Li decreased membrane-associated β-catenin, concomitantly increasing cytoplasmic concentrations. Convergence of these signalling pathways appears to induce a β-catenin shift from the membrane into the cytoplasm.

CONCLUSION

Therefore, although the adhesive role of β-catenin appears to be intact, exogenous signals increase the stability of free β-catenin thereby reducing cell-cell adhesion in these tumours.

The latency-associated nuclear antigen of Kaposi's sarcoma-associated herpesvirus manipulates the activity of glycogen synthase kinase-3beta

The latency-associated nuclear antigen (LANA) of Kaposi's sarcoma-associated herpesvirus (KSHV) is expressed in all KSHV-associated malignancies. LANA is essential for replication and maintenance of the viral episomes during latent infection. However, LANA also has a transcriptional regulatory role and can affect gene expression both positively and negatively. A previously performed yeast two-hybrid screen identified glycogen synthase kinase 3 (GSK-3) as a LANA-interacting protein. Interaction with both GSK-3alpha and GSK-3beta was confirmed in transfected cells with coprecipitation assays. GSK-3beta also interacted with the herpesvirus saimiri homolog ORF73. GSK-3beta is an intermediate in the Wnt signaling pathway and a negative regulator of beta-catenin. In transfected cells, LANA was shown to overcome GSK-3beta-mediated degradation of beta-catenin. Examination of primary effusion lymphoma (PEL) cells found increased levels of beta-catenin relative to KSHV-negative B cells, and this translated into increased activity of a beta-catenin-responsive reporter containing Tcf/Lef binding sites. In tetradecanoyl phorbol acetate-treated PEL cells, loss of LANA expression correlated temporally with loss of detectable beta-catenin. LANA was found to alter the intracellular distribution of GSK-3beta so that nuclear GSK-3beta was more readily detectable in the presence of LANA. Mapping experiments with coimmunoprecipitation assays revealed that both N-terminal and C-terminal LANA sequences were required for efficient GSK-3beta interaction. LANA mutants that were defective for GSK-3beta interaction were unable to mediate GSK-3beta relocalization or activate a beta-catenin-responsive Tcf-luciferase reporter. This study identified manipulation of GSK-3beta activity as a mechanism by which LANA may modify transcriptional activity and contribute to the phenotype of primary effusion lymphoma.