Reduced E-cadherin expression contributes to the loss of p27kip1-mediated mechanism of contact inhibition in thyroid anaplastic carcinomas

Mechanical feedback links cell division and dynamics in growing cell collectives

Local stresses in a tissue, a collective property, regulate cell division and apoptosis. In turn, cell growth and division induce active stresses in the tissue. As a consequence, there is a feedback between cell growth and local stresses. However, how the cell dynamics depend on local stress-dependent cell division and the feedback strength is not understood. Here, we probe the consequences of stress-mediated growth and cell division on cell dynamics using agent-based simulations of a two-dimensional growing tissue. We discover a rich dynamical behavior of individual cells, ranging from jamming (mean square displacement, Δ(t) ∼ tα with α less than unity), to hyperdiffusion (α > 2) depending on cell division rate and the strength of the mechanical feedback. Strikingly, Δ(t) is determined by the tissue growth law, which quantifies cell proliferation, measuring the number of cells N(t) as a function of time. The growth law (N(t) ∼ tλ at long times) is regulated by the critical pressure that controls the strength of the mechanical feedback and the ratio between cell division-apoptosis rates. We show that λ ∼ α, which implies that higher growth rate leads to a greater degree of cell migration. The variations in cell motility are linked to the emergence of highly persistent forces extending over several cell cycle times. Our predictions are testable using cell-tracking imaging techniques.

Cadherins and catenins in cancer: connecting cancer pathways and tumor microenvironment

Cadherin-catenin complexes are integral components of the adherens junctions crucial for cell-cell adhesion and tissue homeostasis. Dysregulation of these complexes is linked to cancer development via alteration of cell-autonomous oncogenic signaling pathways and extrinsic tumor microenvironment. Advances in multiomics have uncovered key signaling events in multiple cancer types, creating a need for a better understanding of the crosstalk between cadherin-catenin complexes and oncogenic pathways. In this review, we focus on the biological functions of classical cadherins and associated catenins, describe how their dysregulation influences major cancer pathways, and discuss feedback regulation mechanisms between cadherin complexes and cellular signaling. We discuss evidence of cross regulation in the following contexts: Hippo-Yap/Taz and receptor tyrosine kinase signaling, key pathways involved in cell proliferation and growth; Wnt, Notch, and hedgehog signaling, key developmental pathways involved in human cancer; as well as TGFβ and the epithelial-to-mesenchymal transition program, an important process for cancer cell plasticity. Moreover, we briefly explore the role of cadherins and catenins in mechanotransduction and the immune tumor microenvironment.

FAM83B is involved in thyroid cancer cell differentiation and migration

FAM83B has been recently identified as an oncogene, but its role in thyroid cancers (TC) is still unclear. We examined the expression of FAM83B and its possible involvement in cell migration and differentiation, in neoplastic/normal thyroid tissues and in TC human cell lines. FAM83B expression in TC varies according to the tumor histotype, being significantly downregulated in more aggressive and metastatic tissues. FAM83B levels in cell lines recapitulate patients’ samples variations, and its total and cytoplasmic levels decrease upon the induction of migration, together with an increase in its nuclear localization. Similar variations were detected in the primary tumor and in the metastatic tissues from a follicular TC. FAM83B knock down experiments confirmed its role in thyroid differentiation and cell migration, as demonstrated by the reduction of markers of thyroid differentiation and the increase of the mesenchymal marker vimentin. Moreover, the silencing of FAM83B significantly increased cells migration abilities, while not affecting the oncogenic RAS/MAPK/PI3K pathways. Our data indicate for the first time a role for FAM83B in TC cell differentiation and migration. Its expression is reduced in dedifferentiated tumors and its nuclear re-localization could favour distant migration, suggesting that FAM83B should be considered a possible diagnostic and prognostic biomarker.

Role of Cadherins in Cancer-A Review

Cadherins play an important role in tissue homeostasis, as they are responsible for cell-cell adhesion during embryogenesis, tissue morphogenesis, differentiation and carcinogenesis. Cadherins are inseparably connected with catenins, forming cadherin-catenin complexes, which are crucial for cell-to-cell adherence. Any dysfunction or destabilization of cadherin-catenin complex may result in tumor progression. Epithelial mesenchymal transition (EMT) is a mechanism in which epithelial cadherin (E-cadherin) expression is lost during tumor progression. However, during tumorigenesis, many processes take place, and downregulation of E-cadherin, nuclear β-catenin and p120 catenin (p120) signaling are among the most critical. Additional signaling pathways, such as Receptor tyrosine kinase (RTK), Rho GTPases, phosphoinositide 3-kinase (PI3K) and Hippo affect cadherin cell-cell adhesion and also contribute to tumor progression and metastasis. Many signaling pathways may be activated during tumorigenesis; thus, cadherin-targeting drugs seem to limit the progression of malignant tumor. This review discusses the role of cadherins in selected signaling mechanisms involved in tumor growth. The clinical importance of cadherin will be discussed in cases of human and animal cancers.

The Many Faces of Matrix Metalloproteinase-7 in Kidney Diseases

Matrix metalloproteinase-7 (MMP-7) is a secreted zinc-dependent endopeptidase that is implicated in regulating kidney homeostasis and diseases. MMP-7 is produced as an inactive zymogen, and proteolytic cleavage is required for its activation. MMP-7 is barely expressed in normal adult kidney but upregulated in acute kidney injury (AKI) and chronic kidney disease (CKD). The expression of MMP-7 is transcriptionally regulated by Wnt/β-catenin and other cues. As a secreted protein, MMP-7 is present and increased in the urine of patients, and its levels serve as a noninvasive biomarker for predicting AKI prognosis and monitoring CKD progression. Apart from degrading components of the extracellular matrix, MMP-7 also cleaves a wide range of substrates, such as E-cadherin, Fas ligand, and nephrin. As such, it plays an essential role in regulating many cellular processes, such as cell proliferation, apoptosis, epithelial-mesenchymal transition, and podocyte injury. The function of MMP-7 in kidney diseases is complex and context-dependent. It protects against AKI by priming tubular cells for survival and regeneration but promotes kidney fibrosis and CKD progression. MMP-7 also impairs podocyte integrity and induces proteinuria. In this review, we summarized recent advances in our understanding of the regulation, role, and mechanisms of MMP-7 in the pathogenesis of kidney diseases. We also discussed the potential of MMP-7 as a biomarker and therapeutic target in a clinical setting.

YAP-Mediated Recruitment of YY1 and EZH2 Represses Transcription of Key Cell-Cycle Regulators

The Hippo pathway regulates cell proliferation and organ size through control of the transcriptional regulators YAP (yes-associated protein) and TAZ. Upon extracellular stimuli such as cell-cell contact, the pathway negatively regulates YAP through cytoplasmic sequestration. Under conditions of low cell density, YAP is nuclear and associates with enhancer regions and gene promoters. YAP is mainly described as a transcriptional activator of genes involved in cell proliferation and survival. Using a genome-wide approach, we show here that, in addition to its known function as a transcriptional activator, YAP functions as a transcriptional repressor by interacting with the multifunctional transcription factor Yin Yang 1 (YY1) and Polycomb repressive complex member enhancer of zeste homologue 2 (EZH2). YAP colocalized with YY1 and EZH2 on the genome to transcriptionally repress a broad network of genes mediating a host of cellular functions, including repression of the cell-cycle kinase inhibitor p27, whose role is to functionally promote contact inhibition. This work unveils a broad and underappreciated aspect of YAP nuclear function as a transcriptional repressor and highlights how loss of contact inhibition in cancer is mediated in part through YAP repressive function. SIGNIFICANCE: This study provides new insights into YAP as a broad transcriptional repressor of key regulators of the cell cycle, in turn influencing contact inhibition and tumorigenesis.

Relationship between apical junction proteins, gene expression and cancer

The apical junctional complex (AJC) is a cell-cell adhesion system present at the upper portion of the lateral membrane of epithelial cells integrated by the tight junction (TJ) and the adherens junction (AJ). This complex is crucial to initiate and stabilize cell-cell adhesion, to regulate the paracellular transit of ions and molecules and to maintain cell polarity. Moreover, we now consider the AJC as a hub of signal transduction that regulates cell-cell adhesion, gene transcription and cell proliferation and differentiation. The molecular components of the AJC are multiple and diverse and depending on the cellular context some of the proteins in this complex act as tumor suppressors or as promoters of cell transformation, migration and metastasis outgrowth. Here, we describe these new roles played by TJ and AJ proteins and their potential use in cancer diagnostics and as targets for therapeutic intervention.

CDC25A Facilitates Chemo-resistance in Ovarian Cancer Multicellular Spheroids by Promoting E-cadherin Expression and Arresting Cell Cycles

Peritoneal metastasis is the most common pathway for the spread of ovarian cancer and one of the major causes of cancer death. Ovarian cancer cells in ascites prefer to aggregate into the multicellular spheroids (MCS) with an inadequate response to chemotherapy. In this study, gene expression analysis implicated that ovarian cancer MCS had its unique expression pattern and the cell cycle-related pathways were prominently altered in MCS cells compared to the monolayer adherent cells. Flow cytometry and western blots confirmed the cell cycle stagnancy in MCS. Among the cell cycle-related proteins, we found that expression of CDC25A was upregulated in MCS and displayed a time-dependent decrease during the transition from MCS to monolayer adherent cells. Loss-of-function studies showed that CDC25A promoted cisplatin-resistance and paclitaxel-resistance and inhibited the drug-induced apoptosis in ovarian cancer MCS. Mechanically, CDC25A impeded cell cycle progression in MCS cells, enhanced their structure integrity, and maintained upregulation of E-cadherin in MCS cells. Accordingly, addition of NSC95397, a small molecular inhibitor of CDC25A, sensitized the ovarian cancer MCS to chemotherapeutic agents. This provides us a novel strategy for the treatment of ovarian cancer peritoneal metastasis and may help improve the overall survival of ovarian cancer patients.

Single-nucleotide polymorphisms of the adherent junction component cadherin gene are associated with leukoaraiosis

BACKGROUND

Leukoaraiosis (LA) is one of the manifestations of cerebral small vessel disease. Blood-brain barrier (BBB) disruption plays a key role in LA. Cadherin is a component of adherent junctions (AJ), which play a crucial role in cell-cell adhesion, cell-cell recognition and homeostasis in BBB development. We hypothesized that alterations in cadherin genes might be a potential cause of BBB abnormalities that result in LA.

METHODS

A total of 339 LA individuals (LA-PVWM, 183; LA-DWM 156) were enrolled, who underwent brain magnetic resonance imaging with obtainable vascular risk factors. Genotyping of cadherin single-nucleotide polymorphisms (SNPs) (rs5030625, rs1801026, and rs16260) was performed by real-time polymerase chain reaction with LightSNiP reagents (coupled primer and probe) and FastStart DNAMaster HybProbe (Roche Diagnostic, GmBH, Mannheim, Germany) on a LightCycler 2.0 instrument.

RESULTS

Two SNPs, rs1801026 and rs16260, were significantly different between the control and LA groups. The combinatorial effects of the three SNPs were also significant. The haplotypes G-T-C and GA-T-A increased the development of LA-PVWM (OR = 1.76 and OR = 40.7, respectively). The haplotypes G-T-A and GA-T-A increased the development of LA-DWM (OR = 2.56 and OR = 10.48, respectively), but G-C-C decreased the development of LA-DWM (OR = 17.57).

CONCLUSION

This study provides evidence for genetic polymorphisms of the AJ component cadherin gene and the association of its haplotypes with LA.

E-cadherin in contact inhibition and cancer

E-cadherin is a key component of the adherens junctions that are integral in cell adhesion and maintaining epithelial phenotype of cells. Homophilic E-cadherin binding between cells is important in mediating contact inhibition of proliferation when cells reach confluence. Loss of E-cadherin expression results in loss of contact inhibition and is associated with increased cell motility and advanced stages of cancer. In this review we discuss the role of E-cadherin and its downstream signaling in regulation of contact inhibition and the development and progression of cancer.

E-cadherin: Its dysregulation in carcinogenesis and clinical implications

E-cadherin is a transmembrane glycoprotein which connects epithelial cells together at adherens junctions. In normal cells, E-cadherin exerts its tumour suppressing role mainly by sequestering β-catenin from its binding to LEF (Lymphoid enhancer factor)/TCF (T cell factor) which serves the function of transcribing genes of the proliferative Wnt signaling pathway. Despite the ongoing debate on whether the loss of E-cadherin is the cause or effect of epithelial-mesenchymal transition (EMT), E-cadherin functional loss has frequently been associated with poor prognosis and survival in patients of various cancers. The dysregulation of E-cadherin expression that leads to carcinogenesis happens mostly at the epigenetic level but there are cases of genetic alterations as well. E-cadherin expression has been linked to the cellular functions of invasiveness reduction, growth inhibition, apoptosis, cell cycle arrest and differentiation. Studies on various cancers have shown that these different cellular functions are also interdependent. Recent studies have reported a rapid expansion of E-cadherin clinical relevance in various cancers. This review article summarises the multifaceted effect E-cadherin expression has on cellular functions in the context of carcinogenesis as well as its clinical implications in diagnosis, prognosis and therapeutics.

A central role for cadherin signaling in cancer

Cadherins are homophilic adhesion molecules with important functions in cell-cell adhesion, tissue morphogenesis, and cancer. In epithelial cells, E-cadherin accumulates at areas of cell-cell contact, coalesces into macromolecular complexes to form the adherens junctions (AJs), and associates via accessory partners with a subcortical ring of actin to form the apical zonula adherens (ZA). As a master regulator of the epithelial phenotype, E-cadherin is essential for the overall maintenance and homeostasis of polarized epithelial monolayers. Its expression is regulated by a host of genetic and epigenetic mechanisms related to cancer, and its function is modulated by mechanical forces at the junctions, by direct binding and phosphorylation of accessory proteins collectively termed catenins, by endocytosis, recycling and degradation, as well as, by multiple signaling pathways and developmental processes, like the epithelial to mesenchymal transition (EMT). Nuclear signaling mediated by the cadherin associated proteins β-catenin and p120 promotes growth, migration and pluripotency. Receptor tyrosine kinase, PI3K/AKT, Rho GTPase, and HIPPO signaling, are all regulated by E-cadherin mediated cell-cell adhesion. Finally, the recruitment of the microprocessor complex to the ZA by PLEKHA7, and the subsequent regulation of a small subset of miRNAs provide an additional mechanism by which the state of epithelial cell-cell adhesion affects translation of target genes to maintain the homeostasis of polarized epithelial monolayers. Collectively, the data indicate that loss of E-cadherin function, especially at the ZA, is a common and crucial step in cancer progression.

c‑Myc promotes cholangiocarcinoma cells to overcome contact inhibition via the mTOR pathway

The loss of contact inhibition is a hallmark of a wide range of human cancer cells. Yet, the precise mechanism behind this process is not fully understood. c‑Myc plays a pivotal role in carcinogenesis, but its involvement in regulating contact inhibition has not been explored to date. Here, we report that c‑Myc plays an important role in abrogating contact inhibition in human cholangiocarcinoma (CCA) cells. Our data show that the protein level of c‑Myc obviously decreased in contact-inhibited normal biliary epithelial cells. However, CCA cells sustain high protein levels of c‑Myc and keep strong proliferation ability in confluent conditions. Importantly, the suppression of c‑Myc by inhibitor or siRNA induced G0/G1 phase cell cycle arrest in confluent CCA cells. We demonstrate that the inhibition of c‑Myc suppressed the activity of mammalian target of rapamycin (mTOR) in confluent CCA cells, and mTOR inhibition induced G0/G1 phase cell cycle arrest in confluent CCA cells. In confluent CCA cells, the activity of Merlin is downregulated, and Yes-associated protein (YAP) sustains high levels of activity. Furthermore, YAP inhibition not only induced G0/G1 phase cell cycle arrest, but also decreased c‑Myc expression in confluent CCA cells. These results indicate that Merlin/YAP/c‑Myc/mTOR signaling axis promotes human CCA cell proliferation by overriding contact inhibition. We propose that overriding c‑Myc‑mediated contact inhibition is implicated in the development of CCA.

Dual Inhibition of HDAC and Tyrosine Kinase Signaling Pathways with CUDC-907 Inhibits Thyroid Cancer Growth and Metastases

Purpose: There is currently no standard therapy for anaplastic thyroid cancer (ATC) and poorly differentiated thyroid cancer (PDTC), which account for two-thirds of thyroid cancer-related deaths. Driver mutations in the PI3K/AKT and RAF/RAS/MEK/ERK pathways are common in ATC and PDTC. Histone deacetylases (HDAC) regulate cancer initiation and progression. Our aim was to determine the therapeutic efficacy of simultaneously targeting these pathways in thyroid cancer with a single agent and to evaluate biomarkers of treatment response.Experimental Design: CUDC-907 is a first-in-class compound, functioning as a dual inhibitor of HDACs and the PI3K/AKT pathway. We investigated its antiproliferative effect in vitro and in vivoResults: CUDC-907 significantly inhibited cellular proliferation in thyroid cancer cell lines, induced G₂-M arrest with decreased levels of the checkpoint regulators cyclin B1, AURKA, AURKB, PLK1, and increased p21 and p27. Treatment induced apoptosis with increased caspase-3/7 activity and decreased survivin levels and decreased cellular migration and invasion. CUDC-907 treatment caused H3 hyperacetylation and decreased HDAC2 expression. HDAC2 was upregulated in ATC and other thyroid cancer histologic subtypes. CUDC-907 treatment reduced both p-AKT and p-ERK1/2 levels. Finally, CUDC-907 treatment, in a metastatic mouse model of thyroid cancer, showed significant inhibition of growth and metastases, and tumors from treated mice had decreased HDAC2 expression, suggesting that this may be a useful biomarker of response.Conclusions: Dual inhibition of HDAC and the tyrosine kinase signaling pathways with CUDC-907 is a promising treatment strategy for advanced, metastatic thyroid cancer. Clin Cancer Res; 23(17); 5044-54. ©2017 AACR.

Clinicopathological significance of loss of p27kip1 expression in papillary thyroid carcinoma

INTRODUCTION

A meta-analysis was done to investigate the clinicopathological significance of the loss of p27kip1 expression in papillary thyroid carcinoma (PTC).

METHODS

The meta-analysis involving 17 studies included 1,652 PTC and 328 benign cases. The rate of p27kip1 expression loss in PTC and benign lesions, and the correlations between p27kip1 expression loss and clinicopathological characteristics of PTC were determined.

RESULTS

The estimated rate of p27kip1 expression loss was 0.557 (95% confidence interval [CI] 0.443-0.665) and 0.139 (95% CI 0.062-0.283) in PTC and benign lesions, respectively. In subgroup analysis, the rates of p27kip1 expression loss were 0.683, 0.393, and 0.414 in the classical variant, follicular variant, and papillary thyroid microcarcinoma, respectively. Loss of p27kip1 expression was significantly correlated with lymph node metastasis and distant metastasis (odds ratio 3.559, 95% CI 1.146-11.056 and 4.735, 95% CI 1.322-16.960, respectively). Extrathyroidal extension was correlated with loss of p27kip1 expression, but not in a statistically significant way (p = 0.051). There were no significant correlations between loss of p27kip1 expression and sex, tumor size, BRAFV600E mutation, and tumor multifocality.

CONCLUSIONS

Loss of p27kip1 expression is frequently found in PTC compared with benign lesions and normal thyroid tissue. When present in PTC, it is correlated with aggressive tumor behavior.

Actomyosin contractility provokes contact inhibition in E-cadherin-ligated keratinocytes

Confluence-dependent inhibition of epithelial cell proliferation, termed contact inhibition, is crucial for epithelial homeostasis and organ size control. Here we report that among epithelial cells, keratinocytes, which compose the stratified epithelium in the skin, possess a unique, actomyosin-dependent mechanism for contact inhibition. We have observed that under actomyosin-inhibited conditions, cell-cell contact itself through E-cadherin promotes proliferation of keratinocytes. Actomyosin activity in confluent keratinocytes, however, inhibits nuclear localization of β-catenin and YAP, and causes attenuation of β-catenin- and YAP-driven cell proliferation. Confluent keratinocytes develop E-cadherin-mediated punctate adhesion complexes, to which radial actin cables are connected. Eliminating the actin-to-E-cadherin linkage by depleting α-catenin increases proliferation of confluent keratinocytes. By contrast, enforced activation of RhoA-regulated actomyosin or external application of pulling force to ligated E-cadherin attenuates their proliferation, suggesting that tensile stress at E-cadherin-mediated adhesion complexes inhibits proliferation of confluent keratinocytes. Our results highlight actomyosin contractility as a crucial factor that provokes confluence-dependent inhibition of keratinocyte proliferation.

Expression profile of biomarkers altered in papillary and anaplastic thyroid carcinoma: Contribution of Tunisian patients

AIMS

The objective of this study was to compare the protein expression profile between well-differentiated (papillary) and undifferentiated (anaplastic) thyroid carcinoma in Tunisian patients.

METHODS

This first Tunisian retrospective study concerned data of 38 thyroid cancer cases (19 papillary carcinoma PTC and 19 anaplastic carcinoma ATC) collected at Salah Azaiez Institute of Tunisia. Immunohistochemistry was used to evaluate tumor expression of different molecular markers (p53, Ki67, E-cadherin, cyclin D1, bcl2, S100 and Her-2). The molecular expression was correlated with the clinicopathological characteristics of the tumors.

RESULTS

There were 6 differentially expressed markers when comparing anaplastic thyroid carcinoma ATC with papillary thyroid carcinoma PTC. Expression of p53 and Ki67 were significantly increased in 16 and 18 ATC cases respectively, the Ki67 expression was lost in PTC. Cyclin D1, E-cadherin, bcl2 and S100 were overexpressed in PTC tumors; however, they were significantly decreased in ATC. The last marker, Her-2 was expressed in one case of PTC only.

CONCLUSION

Our results, similar with findings of other ethnic groups, showed alteration in expression of molecular markers associated with tumor dedifferentiation, indicating loss of cell cycle control with increased proliferative activity in ATC carcinoma. These data support the hypothesis that ATC may derive from dedifferentiation of preexisting PTC tumor.

RhoE is required for contact inhibition and negatively regulates tumor initiation and progression

RhoE is a small GTPase involved in the regulation of actin cytoskeleton dynamics, cell cycle and apoptosis. The role of RhoE in cancer is currently controversial, with reports of both oncogenic and tumor-suppressive functions for RhoE. Using RhoE-deficient mice, we show here that the absence of RhoE blunts contact-inhibition of growth by inhibiting p27Kip1 nuclear translocation and cooperates in oncogenic transformation of mouse primary fibroblasts. Heterozygous RhoE+/gt mice are more susceptible to chemically induced skin tumors and RhoE knock-down results in increased metastatic potential of cancer cells. These results indicate that RhoE plays a role in suppressing tumor initiation and progression.

Upregulation of TPX2 by STAT3: identification of a novel STAT3 binding site

TPX2, a protein involved in mitosis, is considered a good marker for actively proliferating tissues, highly expressed in a number of cancer cells. We show the presence of high-affinity binding site for STAT3 in the 5'-flanking region of the Tpx2 gene, which is in vivo bound by activated STAT3. A specific STAT3 peptide inhibitor represses the expression of the Tpx2 gene and inhibits the binding of STAT3 to its consensus sequence in human cell lines where STAT3 is activated. These results indicate that activated STAT3 contributes to the over-expression of Tpx2 through the binding to an enhancer site.

Toxicity of functional nano-micro zinc oxide tetrapods: impact of cell culture conditions, cellular age and material properties

With increasing production and applications of nanostructured zinc oxide, e.g., for biomedical and consumer products, the question of safety is getting more and more important. Different morphologies of zinc oxide structures have been synthesized and accordingly investigated. In this study, we have particularly focused on nano-micro ZnO tetrapods (ZnO-T), because their large scale fabrication has been made possible by a newly introduced flame transport synthesis approach which will probably lead to several new applications. Moreover, ZnO-T provide a completely different morphology then classical spherical ZnO nanoparticles. To get a better understanding of parameters that affect the interactions between ZnO-T and mammalian cells, and thus their biocompatibility, we have examined the impact of cell culture conditions as well as of material properties on cytotoxicity. Our results demonstrate that the cell density of fibroblasts in culture along with their age, i.e., the number of preceding cell divisions, strongly affect the cytotoxic potency of ZnO-T. Concerning the material properties, the toxic potency of ZnO-T is found to be significantly lower than that of spherical ZnO nanoparticles. Furthermore, the morphology of the ZnO-T influenced cellular toxicity in contrast to surface charges modified by UV illumination or O₂ treatment and to the material age. Finally, we have observed that direct contact between tetrapods and cells increases their toxicity compared to transwell culture models which allow only an indirect effect via released zinc ions. The results reveal several parameters that can be of importance for the assessment of ZnO-T toxicity in cell cultures and for particle development.

p120 catenin: an essential regulator of cadherin stability, adhesion-induced signaling, and cancer progression

p120 catenin is the best studied member of a subfamily of proteins that associate with the cadherin juxtamembrane domain to suppress cadherin endocytosis. p120 also recruits the minus ends of microtubules to the cadherin complex, leading to junction maturation. In addition, p120 regulates the activity of Rho family GTPases through multiple interactions with Rho GEFs, GAPs, Rho GTPases, and their effectors. Nuclear signaling is affected by the interaction of p120 with Kaiso, a transcription factor regulating Wnt-responsive genes as well as transcriptionally repressing methylated promoters. Multiple alternatively spliced p120 isoforms and complex phosphorylation events affect these p120 functions. In cancer, reduced p120 expression correlates with reduced E-cadherin function and with tumor progression. In contrast, in tumor cells that have lost E-cadherin expression, p120 promotes cell invasion and anchorage-independent growth. Furthermore, p120 is required for Src-induced oncogenic transformation and provides a potential target for future therapeutic interventions.

Signaling pathways in follicular cell-derived thyroid carcinomas (review)

Thyroid carcinoma is the most common malignant endocrine neoplasia. Differentiated thyroid carcinomas (DTCs) represent more than 90% of all thyroid carcinomas and comprise the papillary and follicular thyroid carcinoma subtypes. Anaplastic thyroid carcinomas correspond to less than 1% of all thyroid tumors and can arise de novo or by dedifferentiation of a differentiated tumor. The etiology of DTCs is not fully understood. Several genetic events have been implicated in thyroid tumorigenesis. Point mutations in the BRAF or RAS genes or rearranged in transformation (RET)/papillary thyroid carcinoma (PTC) gene rearrangements are observed in approximately 70% of papillary cancer cases. Follicular carcinomas commonly harbor RAS mutations and paired box gene 8 (PAX8)-peroxisome proliferator-activated receptor γ (PPARγ) rearrangements. Anaplastic carcinomas may have a wide set of genetic alterations, that include gene effectors in the mitogen-activated protein kinase (MAPK), phosphatidylinositol 3-kinase (PI3K) and/or β-catenin signaling pathways. These distinct genetic alterations constitutively activate the MAPK, PI3K and β-catenin signaling pathways, which have been implicated in thyroid cancer development and progression. In this context, the evaluation of specific genes, as well as the knowledge of their effects on thyroid carcinogenesis may provide important information on disease presentation, prognosis and therapy, through the development of specific tyrosine kinase targets. In this review, we aimed to present an updated and comprehensive review of the recent advances in the understanding of the genetic basis of follicular cell-derived thyroid carcinomas, as well as the molecular mechanisms involved in tumor development and progression.

Multiple factors influencing the release of hTERT mRNA from pancreatic cancer cell lines in in vitro culture

Since telomerase expression is highly prevalent in human cancers, the quantitation of serum/plasma hTERT (human telomerase reverse transcriptase) mRNA levels may be useful for early detection of PCa (pancreatic cancer). To analyse the correspondence between exhTERT (extracellular hTERT) mRNA levels and hTERT expression, we designed a cell culture system to investigate factors modulating the extracellular levels of hTERT mRNA in media conditioned by eight PCa cell lines. We found that the level of exhTERT mRNA was dependent on cell growth rate. MIAPaCa-2, PANC-1, KLM-1 and PK-9 cells expressed high levels of exhTERT mRNA, independent of cell density, whereas proliferating PK-59, BxPC-3 and PK-45H cells released low levels of exhTERT mRNA. The augmented release of mRNA by spontaneous dead MIAPaCa-2 cells was further increased at postconfluence. In Capan-1 cells, low correspondence of marker was also due to RNase secretion. Upon reaching confluence, some PCa cell lines showed down-regulation of hTERT expression. Following cell-cell adhesion, as shown by E-cadherin engagement, PK-59 cells showed levels of extracellular message below the limits of detection, a loss not due to an increase in message degradation. These results suggest that the levels of exhTERT mRNA in the medium of PCa cell lines are altered not only in response to cell growth rate and cell destruction, but are responsive to extracellular cues such as RNases and cell density. A cell-free assay for exhTERT mRNA may therefore not be useful for early detection of PCa.

Arecoline downregulates levels of p21 and p27 through the reactive oxygen species/mTOR complex 1 pathway and may contribute to oral squamous cell carcinoma

Arecoline, the major alkaloid of areca nut, has been shown to cause strong genotoxicity and is considered a potential carcinogen. However, the detailed mechanism for arecoline-induced carcinogenesis remains obscure. In this study, we noticed that the levels of p21 and p27 increased in two oral squamous cell carcinoma cell lines with high confluence. Furthermore, when treated with arecoline, elevated levels of p21 and p27 could be downregulated through the reactive oxygen species/mTOR complex 1 (ROS/mTORC1) pathway. Although arecoline decreased the activity of mTORC1, the amounts of autophagosome-like vacuoles or type II LC3 remained unchanged, suggesting that the downregulation of p21 and p27 was independent of autophagy-mediated protein destruction. Arecoline also caused DNA damage through ROS, indicating that the reduced levels of p21 and p27 might facilitate G (1) /S transition of the cell cycle and subsequently lead to error-prone DNA replication. In conclusion, these data have provided a possible mechanism for arecoline-induced carcinogenesis in subcytolytic doses in vivo.

Regulation of p27 (Kip1) by mitogen-induced tyrosine phosphorylation

Extracellular mitogen signal transduction is initiated by ligand binding to specific receptors of target cells. This causes a cellular response that frequently triggers the activation of tyrosine kinases. Non-receptor kinases like Src and Lyn can directly phosphorylate the Cdk inhibitor protein p27 (Kip1) . Tyrosine phosphorylation can cause impaired Cdk-inhibitory activity and decreased stability of p27. In addition to these non-receptor tyrosine kinases, the receptor-associated tyrosine kinase Janus kinase 2 (JAK2) was recently identified to phosphorylate p27. JAK2 becomes activated through binding of various cytokines and growth factors to their corresponding receptors and can directly bind and selectively phosphorylate tyrosine residue 88 (Y88) of the Cdk inhibitor p27. This impairs Cdk inhibition by p27 and promotes its ubiquitin-dependent proteasomal degradation. Via this mechanism, JAK2 can link cytokine and growth factor initiated signal transduction to p27 regulation, whereas oncogenes like JAK2V617F or BCR-Abl can use this mechanism to inactivate the Cdk inhibitor.

Pivotal role of epithelial cell adhesion molecule in the survival of lung cancer cells

Epithelial cell adhesion molecule (EpCAM) is overexpressed in a wide variety of human cancers including lung cancer, and its contribution to increased proliferation through upregulation of cell cycle accelerators such as cyclins A and E has been well established in breast and gastric cancers. Nevertheless, very little is known about its role in supporting the survival of cancer cells. In addition, the functional role of EpCAM in the pathogenesis of lung cancer remains to be explored. In this study, we show that RNAi-mediated knockdown of EpCAM suppresses proliferation and clonogenic growth of three EpCAM-expressing lung cancer cell lines (H3255, H358, and HCC827), but does not induce cell cycle arrest in any of these. In addition, EpCAM knockdown inhibits invasion in the highly invasive H358 but not in less invasive H3255 cells in a Transwell assay. Of note, the EpCAM knockdown induces massive apoptosis in the three cell lines as well as in another EpCAM-expressing lung cancer cell line, HCC2279, but to a much lesser extent in a cdk4/hTERT immortalized normal human bronchial epithelial cell line, HBEC4, suggesting that EpCAM could be a therapeutic target for lung cancer. Finally, EpCAM knockdown partially restores contact inhibition in HCC827, in association with p27(Kip1) upregulation. These results indicate that EpCAM could contribute substantially to the pathogenesis of lung cancer, especially cancer cell survival, and suggest that EpCAM targeted therapy for lung cancer may have potential.

RNAi-mediated knock-down of arylamine N-acetyltransferase-1 expression induces E-cadherin up-regulation and cell-cell contact growth inhibition

Arylamine N-acetyltransferase-1 (NAT1) is an enzyme that catalyzes the biotransformation of arylamine and hydrazine substrates. It also has a role in the catabolism of the folate metabolite p-aminobenzoyl glutamate. Recent bioinformatics studies have correlated NAT1 expression with various cancer subtypes. However, a direct role for NAT1 in cell biology has not been established. In this study, we have knocked down NAT1 in the colon adenocarcinoma cell-line HT-29 and found a marked change in cell morphology that was accompanied by an increase in cell-cell contact growth inhibition and a loss of cell viability at confluence. NAT1 knock-down also led to attenuation in anchorage independent growth in soft agar. Loss of NAT1 led to the up-regulation of E-cadherin mRNA and protein levels. This change in E-cadherin was not attributed to RNAi off-target effects and was also observed in the prostate cancer cell-line 22Rv1. In vivo, NAT1 knock-down cells grew with a longer doubling time compared to cells stably transfected with a scrambled RNAi or to parental HT-29 cells. This study has shown that NAT1 affects cell growth and morphology. In addition, it suggests that NAT1 may be a novel drug target for cancer therapeutics.

Dentin matrix protein 1 induces membrane expression of VE-cadherin on endothelial cells and inhibits VEGF-induced angiogenesis by blocking VEGFR-2 phosphorylation

Dentin matrix protein 1 (DMP1) is a member of the small integrin-binding ligand N-linked glycoprotein (SIBLING) family, a group of proteins initially described as mineralized extracellular matrices components. More recently, SIBLINGs have been implicated in several key steps of cancer progression, including angiogenesis. Although proangiogenic activities have been demonstrated for 2 SIBLINGs, the role of DMP1 in angiogenesis has not yet been addressed. We demonstrate that this extracellular matrix protein induced the expression of vascular endothelial cadherin (VE-cadherin), a key regulator of intercellular junctions and contact inhibition of growth of endothelial cells that is also known to modulate vascular endothelial growth factor receptor 2 (VEGFR-2) activity, the major high-affinity receptor for VEGF. DMP1 induced VE-cadherin and p27(Kip1) expression followed by cell-cycle arrest in human umbilical vein endothelial cells (HUVECs) in a CD44-dependent manner. VEGF-induced proliferation, migration, and tubulogenesis responses were specifically blocked on DMP1 pretreatment of HUVECs. Indeed, after VE-cadherin induction, DMP1 inhibited VEGFR-2 phosphorylation and Src-mediated signaling. However, DMP1 did not interfere with basic fibroblast growth factor-induced angiogenesis. In vivo, DMP1 significantly reduced laser-induced choroidal neovascularization lesions and tumor-associated angiogenesis. These data enable us to put DMP1 on the angiogenic chessboard for the first time and to identify this protein as a new specific inhibitor of VEGF-induced angiogenesis.

Profilin-1 overexpression inhibits proliferation of MDA-MB-231 breast cancer cells partly through p27kip1 upregulation

Profilin-1 (Pfn1), a ubiquitously expressed actin-binding protein, has gained interest in epithelial-derived cancer because of its downregulation in expression in various adenocarcinoma. Pfn1 overexpression impairs tumorigenic ability of human breast cancer xenografts thus suggesting that Pfn1 could be a tumor-suppressor protein. The objective of the present study was to determine how Pfn1 overexpression affects cell-cycle progression of breast cancer cells. We show that Pfn1 overexpression in MDA-MB-231 breast cancer cells causes cell-cycle arrest in G1 phase and dramatically reduced proliferation in culture. Pfn1 overexpression results in increased protein stability of p27(kip1) (p27-a major cyclin-dependent kinase inhibitor) and marked elevation in the overall cellular level of p27. Proliferation defect of Pfn1 overexpressers can be partly rescued by silencing p27 expression thus suggesting a critical role of p27 in Pfn1-induced growth inhibition of MDA-MB-231 cells. Finally, Pfn1 overexpression was found to sensitize MDA-MB-231 cells to apoptosis in response to cytotoxic stimulus thus suggesting for the first time that survival of breast cancer cells can also be negatively influenced by Pfn1 upregulation. These findings may provide novel insights underlying Pfn1's tumor-suppressive action.

Cadherins and Pak1 control contact inhibition of proliferation by Pak1-betaPIX-GIT complex-dependent regulation of cell-matrix signaling

It is crucial for organ homeostasis that epithelia have effective mechanisms to restrict motility and cell proliferation in order to maintain tissue architecture. On the other hand, epithelial cells need to rapidly and transiently acquire a more mesenchymal phenotype, with high levels of cell motility and proliferation, in order to repair epithelia upon injury. Cross talk between cell-cell and cell-matrix signaling is crucial for regulating these transitions. The Pak1-betaPIX-GIT complex is an effector complex downstream of the small GTPase Rac1. We previously showed that translocation of this complex from cell-matrix to cell-cell adhesion sites was required for the establishment of contact inhibition of proliferation. In this study, we provide evidence that this translocation depends on cadherin function. Cadherins do not recruit the complex by direct interaction. Rather, we found that inhibition of the normal function of cadherin or Pak1 leads to defects in focal adhesion turnover and to increased signaling by phosphatidylinositol 3-kinase. We propose that cadherins are involved in regulation of contact inhibition by controlling the function of the Pak1-betaPIX-GIT complex at focal contacts.

Reduced expression of a gene proliferation signature is associated with enhanced malignancy in colon cancer

The association between cell proliferation and the malignant potential of colon cancer is not well understood. Here, we evaluated this association using a colon-specific gene proliferation signature (GPS). The GPS was derived by combining gene expression data obtained from the analysis of a cancer cell line model and a published colon crypt profile. The GPS was overexpressed in both actively cycling cells in vitro and the proliferate compartment of colon crypts. K-means clustering was used to independantly stratify two cohorts of colon tumours into two groups with high and low GPS expression. Notably, we observed a significant association between reduced GPS expression and an increased likelihood of recurrence (P<0.05), leading to shorter disease-free survival in both cohorts. This finding was not a result of methodological bias as we verified the well-established association between breast cancer malignancy and increased proliferation, by applying our GPS to public breast cancer data. In this study, we show that reduced proliferation is a biological feature characterizing the majority of aggressive colon cancers. This contrasts with many other carcinomas such as breast cancer. Investigating the reasons underlying this unusual observation may provide important insight into the biology of colon cancer progression and putative novel therapy options.

Anaplastic thyroid cancer: molecular pathogenesis and emerging therapies

Anaplastic thyroid cancer (ATC) is a rare malignancy. While external beam radiation therapy has improved locoregional control, the median survival of approximately 4 months has not changed in more than half a century due to uncontrolled systemic metastases. The objective of this study was to review the literature in order to identify potential new strategies for treating this highly lethal cancer. PubMed searches were the principal source of articles reviewed. The molecular pathogenesis of ATC includes mutations in BRAF, RAS, catenin (cadherin-associated protein), beta 1, PIK3CA, TP53, AXIN1, PTEN, and APC genes, and chromosomal abnormalities are common. Several microarray studies have identified genes and pathways preferentially affected, and dysregulated microRNA profiles differ from differentiated thyroid cancers. Numerous proteins involving transcription factors, signaling pathways, mitosis, proliferation, cell cycle, apoptosis, adhesion, migration, epigenetics, and protein degradation are affected. A variety of agents have been successful in controlling ATC cell growth both in vitro and in nude mice xenografts. While many of these new compounds are in cancer clinical trials, there are few studies being conducted in ATC. With the recent increased knowledge of the many critical genes and proteins affected in ATC, and the extensive array of targeted therapies being developed for cancer patients, there are new opportunities to design clinical trials based upon tumor molecular profiling and preclinical studies of potentially synergistic combinatorial novel therapies.

Hypoxia-induced Abrogation of Contact-dependent Inhibition of Rheumatoid Arthritis Synovial Fibroblast Proliferation

Objective.

Uncontrolled proliferation of synovial fibroblasts is characteristic of the pathology of rheumatoid arthritis (RA). Since synovial tissues in the rheumatoid joints are hypoxic, we investigated how hypoxia affects RA synovial fibroblast (RASF) proliferation.

Methods.

RASF were cultured at 2000 cells (low density culture) or at 5000 cells (high density, growth-inhibitory confluent culture) per microtiter well under hypoxic (10%, 3%, or 1% O2) or normoxic (21% O2) conditions. Some RASF were treated with recombinant human interleukin 1 receptor antagonist (IL-1ra), anti-tumor necrosis factor-α (TNF-α)-neutralizing antibodies, anti-N-cadherin-blocking antibodies, or MG132. 3H-labeled thymidine incorporation was quantified to assess their proliferation. Total RNA and cell lysates were prepared for real-time polymerase chain reaction and Western blot analyses.

Results.

Hypoxia exerted no effect on proliferation of RASF cultured at low density. At high density, it abrogated contact-dependent growth inhibition of RASF, but not of human dermal fibroblasts. Addition of anti-TNF-α antibodies or IL-1ra did not affect the results. Upregulated expression of cyclin-dependent kinase inhibitor p27Kip1 was observed in the cells cultured at high density under normoxic conditions, but not under hypoxic conditions. Hypoxia decreased N-cadherin expression on RASF. Addition of anti-N-cadherin-blocking antibodies mimicked the effects of hypoxic culture; it promoted proliferation of RASF cultured at high density under normoxic conditions. This antibody treatment also downmodulated p27Kip1 expression.

Conclusion.

Hypoxia downregulates N-cadherin expression on RASF, and thus prevents p27Kip1 upregulation for their contact inhibition. It is likely that hypoxia in rheumatoid synovial tissues contributes to rheumatoid pathology by augmenting proliferation of synovial fibroblasts.

The beta-catenin axis integrates multiple signals downstream from RET/papillary thyroid carcinoma leading to cell proliferation

RET/papillary thyroid carcinoma (RET/PTC) oncoproteins result from the in-frame fusion of the RET receptor tyrosine kinase domain with protein dimerization motifs encoded by heterologous genes. Here, we show that RET/PTC stimulates the beta-catenin pathway. By stimulating PI3K/AKT and Ras/extracellular signal-regulated kinase (ERK), RET/PTC promotes glycogen synthase kinase 3beta (GSK3beta) phosphorylation, thereby reducing GSK3beta-mediated NH(2)-terminal beta-catenin (Ser33/Ser37/Thr41) phosphorylation. In addition, RET/PTC physically interacts with beta-catenin and increases its phosphotyrosine content. The increased free pool of S/T(nonphospho)/Y(phospho)beta-catenin is stabilized as a result of the reduced binding affinity for the Axin/GSK3beta complex and activates the transcription factor T-cell factor/lymphoid enhancer factor. Moreover, through the ERK pathway, RET/PTC stimulates cyclic AMP-responsive element binding protein (CREB) phosphorylation and promotes the formation of a beta-catenin-CREB-CREB-binding protein/p300 transcriptional complex. Transcriptional complexes containing beta-catenin are recruited to the cyclin D1 promoter and a cyclin D1 gene promoter reporter is active in RET/PTC-expressing cells. Silencing of beta-catenin by small interfering RNA inhibits proliferation of RET/PTC-transformed PC Cl3 thyrocytes, whereas a constitutively active form of beta-catenin stimulates autonomous proliferation of thyroid cells. Thus, multiple signaling events downstream from RET/PTC converge on beta-catenin to stimulate cell proliferation.

Cyclin D1 and p27 expression as prognostic factor in papillary carcinoma of thyroid: association with clinicopathological parameters

AIM

To determine the prognostic value of cell cycle regulators cyclin D1 and p27 for papillary thyroid carcinomas.

METHODS

Analysis included 180 patients with papillary thyroid carcinoma who underwent surgery at Split University Hospital Center between 1999 and 2001. Clinical data were obtained from clinical charts and histopathology reports. Immunohistochemistry was performed on formalin-fixed, paraffin-embedded tissue by antibody p27 and cyclin D1. Quantification was based on the intensity and distribution of nuclear staining.

RESULTS

Univariate analysis showed that sex (P=0.019) and capsular invasion (P=0.010) were significant predictors of lymph node metastases, whereas age (P=0.96), histopathological variant (P=0.075), size (P=0.556) and multifocality (P=0.131) were not. Univariate analysis also showed that overexpression of cyclin D1 (P<0.001) and underexpression of p27 (P<0.001) predicted lymph node metastases in papillary thyroid carcinomas. There was a significant correlation between cyclin D1 (P=0.024) and p27 (P=0.029) expression in two prognostic groups of low and high risk. Low risk group was cyclin D1 negative and p27 positive, while high risk group was cyclin D1 positive and p27 negative. Multivariate analysis confirmed that sex (P=0.041), capsular invasion (P=0.027), and p27 (P<0.001) were strong independent predictors of lymph node metastases in the high-risk group.

CONCLUSIONS

Immunohistochemical analysis of p27 expression may be a valuable tool for identifying risk of lymph node metastases and more aggressive behavior of papillary thyroid carcinoma.

p120 catenin induces opposing effects on tumor cell growth depending on E-cadherin expression

p120 catenin regulates the activity of the Rho family guanosine triphosphatases (including RhoA and Rac1) in an adhesion-dependent manner. Through this action, p120 promotes a sessile cellular phenotype when associated with epithelial cadherin (E-cadherin) or a motile phenotype when associated with mesenchymal cadherins. In this study, we show that p120 also exerts significant and diametrically opposing effects on tumor cell growth depending on E-cadherin expression. Endogenous p120 acts to stabilize E-cadherin complexes and to actively promote the tumor-suppressive function of E-cadherin, potently inhibiting Ras activation. Upon E-cadherin loss during tumor progression, the negative regulation of Ras is relieved; under these conditions, endogenous p120 promotes transformed cell growth both in vitro and in vivo by activating a Rac1-mitogen-activated protein kinase signaling pathway normally activated by the adhesion of cells to the extracellular matrix. These data indicate that both E-cadherin and p120 are important regulators of tumor cell growth and imply roles for both proteins in chemoresistance and targeted therapeutics.

Formation of E-cadherin/beta-catenin-based adherens junctions in hepatocytes requires serine-10 in p27(Kip1)

The adhesion between epithelial cells at adherens junctions is regulated by signaling pathways that mediate the intracellular trafficking and assembly of its core components. Insight into the molecular mechanisms of this is necessary to understand how adherens junctions contribute to the functional organization of epithelial tissues. Here, we demonstrate that in human hepatic HepG2 cells, oncostatin M-p42/44 mitogen-activated protein kinase signaling stimulates the phosphorylation of p27(Kip1) on Ser-10 and promotes cell-cell adhesion. The overexpression of wild-type p27 or a phospho-mimetic p27S10D mutant in HepG2 cells induces a hyper-adhesive phenotype. In contrast, the overexpression of a nonphosphorylatable p27S10A mutant prevents the mobilization of E-cadherin and beta-catenin at the cell surface, reduces basal cell-cell adhesion strength, and prevents the stimulatory effect of oncostatin M on cell-cell adhesion. As part of the underlying molecular mechanism, it is shown that in p27S10A-expressing cells beta-catenin interacts with p27 and is prevented from interacting with E-cadherin. The intracellular retention of E-cadherin and beta-catenin is also observed in hepatocytes from p27S10A knockin mice that express the p27S10A mutant instead of wild-type p27. Together, these data suggest that the formation of adherens junctions in hepatocytes requires Ser-10 in p27.

Molecular profiling related to poor prognosis in thyroid carcinoma. Combining gene expression data and biological information

Undifferentiated and poorly differentiated thyroid tumors are responsible for more than half of thyroid cancer patient deaths in spite of their low incidence. Conventional treatments do not obtain substantial benefits, and the lack of alternative approaches limits patient survival. Additionally, the absence of prognostic markers for well-differentiated tumors complicates patient-specific treatments and favors the progression of recurrent forms. In order to recognize the molecular basis involved in tumor dedifferentiation and identify potential markers for thyroid cancer prognosis prediction, we analysed the expression profile of 44 thyroid primary tumors with different degrees of dedifferentiation and aggressiveness using cDNA microarrays. Transcriptome comparison of dedifferentiated and well-differentiated thyroid tumors identified 1031 genes with >2-fold difference in absolute values and false discovery rate of <0.15. According to known molecular interaction and reaction networks, the products of these genes were mainly clustered in the MAPkinase signaling pathway, the TGF-beta signaling pathway, focal adhesion and cell motility, activation of actin polymerization and cell cycle. An exhaustive search in several databases allowed us to identify various members of the matrix metalloproteinase, melanoma antigen A and collagen gene families within the upregulated gene set. We also identified a prognosis classifier comprising just 30 transcripts with an overall accuracy of 95%. These findings may clarify the molecular mechanisms involved in thyroid tumor dedifferentiation and provide a potential prognosis predictor as well as targets for new therapies.

E-cadherin homophilic ligation inhibits cell growth and epidermal growth factor receptor signaling independently of other cell interactions

E-cadherin function leads to the density-dependent contact inhibition of cell growth. Because cadherins control the overall state of cell contact, cytoskeletal organization, and the establishment of many other kinds of cell interactions, it remains unknown whether E-cadherin directly transduces growth inhibitory signals. To address this question, we have selectively formed E-cadherin homophilic bonds at the cell surface of isolated epithelial cells by using functionally active recombinant E-cadherin protein attached to microspheres. We find that E-cadherin ligation alone reduces the frequency of cells entering the S phase, demonstrating that E-cadherin ligation directly transduces growth inhibitory signals. E-cadherin binding to beta-catenin is required for cell growth inhibition, but beta-catenin/T-cell factor transcriptional activity is not involved in growth inhibition resulting from homophilic binding. Neither E-cadherin binding to p120-catenin nor beta-catenin binding to alpha-catenin, and thereby the actin cytoskeleton, is required for growth inhibition. E-cadherin ligation also inhibits epidermal growth factor (EGF) receptor-mediated growth signaling by a beta-catenin-dependent mechanism. It does not affect EGF receptor autophosphorylation or activation of ERK, but it inhibits transphosphorylation of Tyr845 and activation of signal transducers and activators of transcription 5. Thus, E-cadherin homophilic binding independent of other cell contacts directly transduces growth inhibition by a beta-catenin-dependent mechanism that inhibits selective signaling functions of growth factor receptors.

Gene expression and functional evidence of epithelial-to-mesenchymal transition in papillary thyroid carcinoma invasion

Papillary thyroid carcinomas (PTCs) that invade into local structures are associated with a poor prognosis, but the mechanisms for PTC invasion are incompletely defined, limiting the development of new therapies. To characterize biological processes involved in PTC invasion, we analyzed the gene expression profiles of microscopically dissected intratumoral samples from central and invasive regions of seven widely invasive PTCs and normal thyroid tissue by oligonucleotide microarray and performed confirmatory expression and functional studies. In comparison with the central regions of primary PTCs, the invasive fronts overexpressed TGF beta, NFkappaB and integrin pathway members, and regulators of small G proteins and CDC42. Moreover, reduced levels of mRNAs encoding proteins involved in cell-cell adhesion and communication were identified, consistent with epithelial-to-mesenchymal transition (EMT). To confirm that aggressive PTCs were characterized by EMT, 34 additional PTCs were examined for expression of vimentin, a hallmark of EMT. Overexpression of vimentin was associated with PTC invasion and nodal metastasis. Functional, in vitro studies demonstrated that vimentin was required both for the development and maintenance of a mesenchymal morphology and invasiveness in thyroid cancer cells. We conclude that EMT is common in PTC invasion and that vimentin regulates thyroid cancer EMT in vitro.

Polymorphisms in the E-cadherin (CDH1) gene promoter and the risk of bladder cancer

AIM

E-cadherin plays a role in carcinogenesis. For two genetic polymorphisms in the gene (CDH1) promoter, a reduced transcription has been reported: a C/A single nucleotide polymorphism (SNP) and a G/GA SNP at -160 bp and -347 bp, respectively, upstream of the transcriptional start site. We studied the association between both polymorphisms and the risk of bladder cancer.

METHODS

One hundred and ninety-seven patients with bladder cancer and 344 population controls were genotyped and haplotyped for both SNPs.

RESULTS

A borderline significantly increased risk for bladder cancer was found for A allele carriers (OR 1.36; 95% CI: 0.96-1.94). We did not find any association between the -347 G/GA SNP and bladder cancer. Haplotype analyses did not yield much stronger associations with bladder cancer than the -160 C/A genotype analyses.

CONCLUSION

This study supports earlier suggestions that the -160 C/A SNP in the CDH1 promoter is a risk factor for bladder cancer.

Human mesenchymal stem cells exert potent antitumorigenic effects in a model of Kaposi's sarcoma

Emerging evidence suggests that both human stem cells and mature stromal cells can play an important role in the development and growth of human malignancies. In contrast to these tumor-promoting properties, we observed that in an in vivo model of Kaposi's sarcoma (KS), intravenously (i.v.) injected human mesenchymal stem cells (MSCs) home to sites of tumorigenesis and potently inhibit tumor growth. We further show that human MSCs can inhibit the in vitro activation of the Akt protein kinase within some but not all tumor and primary cell lines. The inhibition of Akt activity requires the MSCs to make direct cell-cell contact and can be inhibited by a neutralizing antibody against E-cadherin. We further demonstrate that in vivo, Akt activation within KS cells is potently down-regulated in areas adjacent to MSC infiltration. Finally, the in vivo tumor-suppressive effects of MSCs correlates with their ability to inhibit target cell Akt activity, and KS tumors engineered to express a constitutively activated Akt construct are no longer sensitive to i.v. MSC administration. These results suggest that in contrast to other stem cells or normal stromal cells, MSCs possess intrinsic antineoplastic properties and that this stem cell population might be of particular utility for treating those human malignancies characterized by dysregulated Akt.