Dysregulation of E-cadherin by oncogenic ras in intestinal epithelial cells is blocked by inhibiting MAP kinase

Ras-transfected human mammary tumour cells are resistant to photodynamic therapy by mechanisms related to cell adhesion

AIMS

Photodynamic therapy (PDT) is a treatment modality for several cancers involving the administration of a tumour-localising photosensitiser (PS) and its subsequent activation by light, resulting in tumour damage. Ras oncogenes have been strongly associated with chemo- and radio-resistance. Based on the described roles of adhesion and cell morphology on drug resistance, we studied if the differences in shape, cell-extracellular matrix and cell-cell adhesion induced by Ras transfection, play a role in the resistance to PDT.

MATERIALS AND METHODS

We employed the human normal breast HB4a cells transfected with H-RAS and a panel of five PSs.

KEY FINDINGS

We found that resistance to PDT of the HB4a-Ras cells employing all the PSs, increased between 1.3 and 2.5-fold as compared to the parental cells. There was no correlation between resistance and intracellular PS levels or PS intracellular localisation. Even when Ras-transfected cells present lower adherence to the ECM proteins, this does not make them more sensitive to PDT or chemotherapy. On the contrary, a marked gain of resistance to PDT was observed in floating cells as compared to adhesive cells, accounting for the higher ability conferred by Ras to survive in conditions of decreased cell-extracellular matrix interactions. HB4a-Ras cells displayed disorganisation of actin fibres, mislocalised E-cadherin and vinculin and lower expression of E-cadherin and β1-integrin as compared to HB4a cells.

SIGNIFICANCE

Knowledge of the mechanisms of resistance to photodamage in Ras-overexpressing cells may lead to the optimization of the combination of PDT with other treatments.

Oncogenic RAS instructs morphological transformation of human epithelia via differential tissue mechanics

The loss of epithelial homeostasis and the disruption of normal tissue morphology are hallmarks of tumor development. Here, we ask how the uniform activation oncogene RAS affects the morphology and tissue mechanics in a normal epithelium. We found that inducible induction of HRAS in confined epithelial monolayers on soft substrates drives a morphological transformation of a 2D monolayer into a compact 3D cell aggregate. This transformation was initiated by the loss of monolayer integrity and formation of two distinct cell layers with differential cell-cell junctions, cell-substrate adhesion, and tensional states. Computational modeling revealed how adhesion and active peripheral tension induces inherent mechanical instability in the system, which drives the 2D-to-3D morphological transformation. Consistent with this, removal of epithelial tension through the inhibition of actomyosin contractility halted the process. These findings reveal the mechanisms by which oncogene activation within an epithelium can induce mechanical instability to drive morphological tissue transformation.

KGF inhibits hypoxia-induced intestinal epithelial cell apoptosis by upregulating AKT/ERK pathway-dependent E-cadherin expression

OBJECTIVE

Intestinal ischemia-reperfusion (I/R) causes direct cellular damage, and the potential injury to the mucosal structure and barrier function. Keratinocyte growth factor (KGF) is highly expressed in gastrointestinal tract and exerts beneficial effects for intestinal epithelial growth and maintenance. E-cadherin plays an important role in intestinal epithelium renewal. However, the regulatory role of KGF on E-cadherin levels and I/R-induced apoptosis remain to be explored. The present study aimed to identify the effect of KGF on E-cadherin expression and I/R-induced intestinal epithelial cell apoptosis.

METHODS

Caco2 cells were treated with KGF (100 ng/ml) for 0, 4, 8, 12, and 24 h under hypoxia or normoxia. An E-cadherin-knockdown model was successfully established by treatment with E-cadherin RNAi. Western blotting and immunofluorescence labeling were performed to assess E-cadherin expression. Levels of PI3K|[sol]|Akt/mitogen-activated protein kinases (MAPKs), phosphoinositide 3-kinase (PI3K|[sol]|Akt)/PI3K|[sol]|Akt pathway-related proteins, and apoptosis-related proteins were also detected by western blot. Finally, a rat model of acute intestinal I/R was established and treated with KGF. Hematoxylin-eosin (HE), terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL), and immunofluorescence staining were performed to detect morphological changes in intestinal mucosal epithelium and Caco2 cell apoptosis.

RESULTS

KGF enhanced E-cadherin expression in differentiated intestinal epithelial cells under hypoxia via AKT/extracellular-regulated kinase (ERK) pathway regulation. In vitro, E-cadherin downregulation aggravates hypoxia-induced intestinal epithelial cell apoptosis. In the rat model, KGF increased E-cadherin expression, which was associated with the reduced apoptosis.

CONCLUSIONS

KGF exerts protective effects on intestinal epithelial cells under hypoxia by elevating E-cadherin levels or activating AKT/ERK signaling.

MiR-650 represses high-risk non-metastatic colorectal cancer progression via inhibition of AKT2/GSK3β/E-cadherin pathway

Although 5-year survival rate of non-metastatic colorectal cancer (CRC) is high, about 10% of patients in stage I and II still develop into metastatic CRC and eventually die after resection. Currently, there is no effective biomarker for predicting the prognosis of non-metastatic CRC in clinical practice. In this study, we identified miR-650 as a biomarker for prognosis prediction. We observed that the expression of miR-650 in tumor tissues had a positive association with overall survival. MiR-650 inhibited cell growth and invasion in vitro and in vivo. Furthermore, miR-650 targeted AKT2 and repressed the activation of the AKT pathway (AKT2/GSK3β/E-cadherin). Thus it induced the translocation of E-cadherin and β-catenin in cancer cells. Our results highlight the potential of miR-650 as a prognostic prediction biomarker and therapeutic target in non-metastatic CRC via inhibition of the AKT2/GSK3β/E-cadherin pathway.

CDH1 (E-cadherin) expression independently affects clinical outcome in acute myeloid leukemia with normal cytogenetics

BACKGROUND

Epithelial-mesenchymal transition (EMT) is a critical process which involves in tumor metastasis. As an important EMT marker gene, CDH1 (E-cadherin) expression and its clinical implication in acute myeloid leukemia (AML) remain largely elusive.

METHODS

Real-time quantitative PCR (RQ-PCR) was carried out to examine CDH1 transcript level in 123 de novo AML patients and 34 controls.

RESULTS

Compared with controls, CDH1 was significantly downregulated in AML (p<0.001). The median level of CDH1 expression divided total AML patients into CDH1 low-expressed (CDH11ow) and CDH1 high-expressed (CDH1high) groups. There were no significant differences between the two groups in age, peripheral blood cell counts, complete remission (CR) rate, and the distribution of FAB/WHO subtypes as well as karyotypes/karyotypic classifications (p>0.05). However, CDH11ow group tended to have a higher bone marrow (BM) blasts (p=0.093). The spearman correlation analysis further illustrated a trend towards a negative correlation between CDH1 expression level and BM blasts (r=-0.214, p=0.052). CDH1low group had a tendency towards a lower frequency of N/K-RAS mutations (p=0.094). Furthermore, CDH1low patients had markedly shorter overall survival (OS) time in cytogenetic normal AML (CN-AML) (p=0.019). Both univariate and multivariate analyses confirmed the prognostic value of CDH1 expression in CN-AML patients (p=0.027 and 0.033, respectively).

CONCLUSIONS

CDH1 downregulation acted as an independent prognostic biomarker in CN-AML patients.

WT1/EGR1-mediated control of STIM1 expression and function in cancer cells

There have been numerous publications linking Ca(2+) signaling and cancer, however, a clear explanation for this link has remained elusive. We recently identified the oncogenes/tumor suppressors Wilms Tumor Suppressor 1 (WT1) and Early Growth Response 1 (EGR1) as regulators of the expression of STIM1, an essential regulator of Ca(2+) entry in non-excitable cells. The current review focuses on the literature defining both differential Ca(2+) signaling and WT1/EGR1 expression patterns in 6 specific cancer subtypes: Acute Myeloid Leukemia, Wilms Tumor, breast cancer, ovarian cancer, glioblastoma and prostate cancer. For each tumor-type, we have assessed how specific changes in WT1 and EGR1 expression might contribute to aberrant Ca(2+) homeostasis as well as the therapeutic potential of these observations.

Restoration of E-cadherin cell-cell junctions requires both expression of E-cadherin and suppression of ERK MAP kinase activation in Ras-transformed breast epithelial cells

E-cadherin is a main component of the cell-cell adhesion junctions that play a principal role in maintaining normal breast epithelial cell morphology. Breast and other cancers that have up-regulated activity of Ras are often found to have down-regulated or mislocalized E-cadherin expression. Disruption of E-cadherin junctions and consequent gain of cell motility contribute to the process known as epithelial-to-mesenchymal transition (EMT). Enforced expression of E-cadherin or inhibition of Ras-signal transduction pathway has been shown to be effective in causing reversion of EMT in several oncogene-transformed and cancer-derived cell lines. In this study, we investigated MCF10A human breast epithelial cells and derivatives that were transformed with either activated H-Ras or N-Ras to test for the reversion of EMT by inhibition of Ras-driven signaling pathways. Our results demonstrated that inhibition of mitogen-activated protein kinase (MAPK) kinase, but not PI3-kinase, Rac, or myosin light chain kinase, was able to completely restore E-cadherin cell-cell junctions and epithelial morphology in cell lines with moderate H-Ras expression. In MCF10A cells transformed by a high-level expression of activated H-Ras or N-Ras, restoration of E-cadherin junction required both the enforced reexpression of E-cadherin and suppression of MAPK kinase. Enforced expression of E-cadherin alone did not induce reversion from the mesenchymal phenotype. Our results suggest that Ras transformation has at least two independent actions to disrupt E-cadherin junctions, with effects to cause both mislocalization of E-cadherin away from the cell surface and profound decrease in the expression of E-cadherin.

Bench to bedside and back again: molecular mechanisms of alpha-catenin function and roles in tumorigenesis

The cadherin/catenin complex, comprised of E-cadherin, beta-catenin and alpha-catenin, is essential for initiating cell-cell adhesion, establishing cellular polarity and maintaining tissue organization. Disruption or loss of the cadherin/catenin complex is common in cancer. As the primary cell-cell adhesion protein in epithelial cells, E-cadherin has long been studied in cancer progression. Similarly, additional roles for beta-catenin in the Wnt signaling pathway has led to many studies of the role of beta-catenin in cancer. Alpha-catenin, in contrast, has received less attention. However, recent data demonstrate novel functions for alpha-catenin in regulating the actin cytoskeleton and cell-cell adhesion, which when perturbed could contribute to cancer progression. In this review, we use cancer data to evaluate molecular models of alpha-catenin function, from the canonical role of alpha-catenin in cell-cell adhesion to non-canonical roles identified following conditional alpha-catenin deletion. This analysis identifies alpha-catenin as a prognostic factor in cancer progression.

Silencing of the metastasis suppressor RECK by RAS oncogene is mediated by DNA methyltransferase 3b-induced promoter methylation

RECK is a membrane-anchored glycoprotein that may negatively regulate matrix metalloproteinase activity to suppress tumor invasion and metastasis. Our previous study indicated that oncogenic RAS inhibited RECK expression via a histone deacetylation mechanism. In this study, we address whether DNA methyltransferases (DNMT) participate in the inhibition of RECK by RAS. Induction of Ha-RAS(Val12) oncogene increased DNMT3b, but not DNMT1 and DNMT3a, expression in 2-12 cells. In addition, induction of DNMT3b by RAS was through the extracellular signal-regulated kinase signaling pathway. Oncogenic RAS increased the binding of DNMT3b to the promoter of RECK gene and this binding induced promoter methylation, which could be reversed by 5'-azacytidine and DNMT3b small interfering RNA (siRNA). The MEK inhibitor U0126 also reversed RAS-induced DNMT3b binding and RECK promoter methylation. Treatment of 5'-azacytidine and DNMT3b siRNA restored RECK expression in 2-12 cells and potently suppressed RAS-stimulated cell invasion. In addition, the inhibitory effect of 5'-azacytidine on RAS-induced cell invasion was attenuated after knockdown of RECK by siRNA. Interestingly, human lung cancer cells harboring constitutively activated RAS exhibited lower RECK expression and higher promoter methylation of RECK gene. 5'-Azacytidine and DNMT3b siRNA restored RECK expression in these cells and effectively suppressed invasiveness. Collectively, our results suggest that RAS oncogene induces RECK gene silencing through DNMT3b-mediated promoter methylation, and DNMT inhibitors may be useful for the treatment of RAS-induced metastasis.

E-cadherin is regulated by the transcriptional repressor SLUG during Ras-mediated transformation of intestinal epithelial cells

BACKGROUND

Loss of the cell membrane protein E-cadherin is a critical event during Ras-mediated transformation of intestinal epithelial cells. The purpose of our study is to determine if activation of the transcriptional repressor SLUG is an important component of the mechanism of Ras-induced loss of E-cadherin.

METHODS

Rat intestinal epithelial (RIE) cells were engineered to express mutated human Ha-Ras(Val12) complementary DNA (H-Ras cells). Cell morphology was examined by light microscopy. RNA and protein expression were measured by semiquantitative polymerase chain reaction and Western blot analyses, respectively. Short interfering RNA with 2 different oligos was used to knock down the expression of SLUG.

RESULTS

Oncogenic ras induces upregulation of the transcriptional repressor SLUG and subsequent downregulation of the junctional protein E-cadherin. Gene silencing of SLUG by short interfering RNA allows E-cadherin to be reexpressed. E-cadherin protein reexpression allows partial rescue of the transformed phenotype.

CONCLUSION

These data suggest a mechanism whereby Ras signaling causes an upregulation of transcriptional repressors and subsequent downregulation of E-cadherin as a malignant phenotype is propagated.

Anti-proliferative effects of green tea polyphenol EGCG on Ha-Ras-induced transformation of intestinal epithelial cells

Oncogenic Ras mutations are frequently observed in colorectal cancer and participate in neoplastic transformation of intestinal epithelial cells. Accumulating evidence demonstrates the chemopreventive properties of green tea on colon carcinogenesis. Here we investigated the major green tea polyphenol, (-)-epigallocatechin-3-gallate (EGCG), to inhibit proliferation of intestinal epithelial cells (RIE-1) transfected with an inducible Ha-Ras(Val12) cDNA. EGCG inhibited cell proliferation induced by oncogenic Ras and blocked cell cycle transition at G1 phase via inhibition of cyclin D1 expression. The EGCG IC(50) was 42microM in transformed cells and 81microM in non-transformed cells. EGCG also promoted E-cadherin expression, which is downregulated by Ras transformation. This study demonstrates the potential of the natural compound EGCG as an effective adjuvant therapy for colon tumors bearing Ras mutations.

Control of colorectal metastasis formation by K-Ras

Mutational activation of the K-Ras proto-oncogene is frequently observed during the very early stages of colorectal cancer (CRC) development. The mutant alleles are preserved during the progression from pre-malignant lesions to invasive carcinomas and distant metastases. Activated K-Ras may therefore not only promote tumor initiation, but also tumor progression and metastasis formation. Metastasis formation is a very complex and inefficient process: Tumor cells have to disseminate from the primary tumor, invade the local stroma to gain access to the vasculature (intravasation), survive in the hostile environment of the circulation and the distant microvascular beds, gain access to the distant parenchyma (extravasation) and survive and grow out in this new environment. In this review, we discuss the potential influence of mutant K-Ras on each of these phases. Furthermore, we have evaluated the clinical evidence that suggests a role for K-Ras in the formation of colorectal metastases.

K-ras mutation influences macroscopic features of gastric carcinoma

INTRODUCTION

Gastric carcinoma is classified morphologically as type 1 to 4. Type 1 is defined as a polypoid tumor; types 2 and 3 are defined as ulcerated tumors with polypoid growth or gastric wall infiltration, respectively, and type 4 tumors are defined as flat. This morphological classification is important because biological characteristics differ between the four morphological types, but little is known about genetic differences between them.

MATERIALS AND METHODS

One hundred eight gastric tumors were classified macroscopically as type 1 to 4. Tumoral DNA was microdissected from paraffin-embedded tissue sections. PCR amplification of exon 1 of a K-ras containing codons 12 and 13 was performed. K-ras amplicons were dot-blotted onto nylon filters and hybridized with radiolabeled oligomer primers.

RESULTS

A K-ras mutation was found in 20 of 108 gastric cancers. A significant relationship of K-ras mutation with polypoid cancer was found. The frequency of K-ras mutation was 6/14 (43%), 8/29 (28%), 2/11 (18%), and 4/54 (7%) in type 1 to 4 tumors, respectively. K-ras mutation was correlated with well-differentiated tumors. Of various types of K-ras mutations, 12 Asp often was seen in type 1 and 2 gastric cancers (well-demarcated, elevated tumors), while 12 Val and 12 Ser were often seen in type 3 and 4 cases (infiltrating carcinomas).

CONCLUSION

K-ras mutations occur prominently in type 1 and type 2 gastric cancers.

Oncogenic Ras dominates overexpression of E-cadherin in malignant transformation of intestinal epithelial cells

BACKGROUND

Loss of the adherens junction protein E-cadherin is a critical event during Ras-mediated transformation of intestinal epithelial cells. The purpose of our study was to determine if overexpression of E-cadherin prevents Ras-induced malignant transformation and suppresses cell growth.

METHODS

Rat intestinal epithelial cells were constructed with a mutated human Ha-RasVal12 cDNA. In these cells, Ras is constitutively expressed or induced by addition of isopropyl-1-thio-B-D-galactopyranoside. Cells were transfected with a bicistronic retroviral system that expressed green fluorescent protein alone or this protein and human E-cadherin. E-cadherin expression was measured by Western blot analysis, and localization by immunofluorescence. Anchorage-independent growth in soft agar was examined as well as tumor growth in nude mice.

RESULTS

After Ras induction, endogenous E-cadherin was downregulated, whereas overexpression of human E-cadherin was sustained. Oncogenic Ras dominated overexpression of E-cadherin by causing malignant transformation and E-cadherin mislocalization. Ras also promoted growth in soft agar and tumors in nude mice despite E-cadherin overexpression.

CONCLUSIONS

Oncogenic Ras subverts the tumor suppressor activity of E-cadherin in Ras-transformed intestinal epithelial cells by downregulating endogenous E-cadherin and mislocalizing transfected E-cadherin. The role of E-cadherin as a tumor suppressor in intestinal malignancies may be restricted by mutated or overactive Ras.