Transformation Of Intestinal Epithelial Cells Research Articles

Arachidonic acid released by PIK3CA mutant tumor cells triggers malignant transformation of colonic epithelium by inducing chromatin remodeling

Key gene mutations are essential for colorectal cancer (CRC) development; however, how the mutated tumor cells impact the surrounding normal cells to promote tumor progression has not been well defined. Here, we report that PIK3CA mutant tumor cells transmit oncogenic signals and result in malignant transformation of intestinal epithelial cells (IECs) via paracrine exosomal arachidonic acid (AA)-induced H3K4 trimethylation. Mechanistically, PIK3CA mutations sustain SGK3-FBW7-mediated stability of the cPLA2 protein, leading to the synthetic increase in AA, which is transported through exosome and accumulated in IECs. Transferred AA directly binds Menin and strengthens the interactions of Menin and MLL1/2 methyltransferase. Finally, the combination of VTP50469, an inhibitor of the Menin-MLL interaction, and alpelisib synergistically represses PDX tumors harboring PIK3CA mutations. Together, these findings unveil the metabolic link between PIK3CA mutant tumor cells and the IECs, highlighting AA as the potential target for the treatment of patients with CRC harboring PIK3CA mutations.

Intestinal Fibrogenesis in Inflammatory Bowel Diseases: Exploring the Potential Role of Gut Microbiota Metabolites as Modulators.

Fibrosis, sustained by the transformation of intestinal epithelial cells into fibroblasts (epithelial-to-mesenchymal transition, EMT), has been extensively studied in recent decades, with the molecular basis well-documented in various diseases, including inflammatory bowel diseases (IBDs). However, the factors influencing these pathways remain unclear. In recent years, the role of the gut microbiota in health and disease has garnered significant attention. Evidence suggests that an imbalanced or dysregulated microbiota, along with environmental and genetic factors, may contribute to the development of IBDs. Notably, microbes produce various metabolites that interact with host receptors and associated signaling pathways, influencing physiological and pathological changes. This review aims to present recent evidence highlighting the emerging role of the most studied metabolites as potential modulators of molecular pathways implicated in intestinal fibrosis and EMT in IBDs. These studies provide a deeper understanding of intestinal inflammation and fibrosis, elucidating the molecular basis of the microbiota role in IBDs, paving the way for future treatments.

Microbiota-associated mechanisms in colorectal cancer.

Colorectal cancer (CRC) is one of the most common cancers worldwide, ranking third in terms of incidence and second as a cause of cancer-related death. There is growing scientific evidence that the gut microbiota plays a key role in the initiation and development of CRC. Specific bacterial species and complex microbial communities contribute directly to CRC pathogenesis by promoting the neoplastic transformation of intestinal epithelial cells or indirectly through their interaction with the host immune system. As a result, a protumoural and immunosuppressive environment is created conducive to CRC development. On the other hand, certain bacteria in the gut microbiota contribute to protection against CRC. In this chapter, we analysed the relationship of the gut microbiota to CRC and the associations identified with specific bacteria. Microbiota plays a key role in CRC through various mechanisms, such as increased intestinal permeability, inflammation and immune system dysregulation, biofilm formation, genotoxin production, virulence factors and oxidative stress. Exploring the interaction between gut microbiota and tumourigenesis is essential for developing innovative therapeutic approaches in the fight against CRC.

Influence on proliferation and apoptosis of intestinal epithelial cells and expression of ACVR1 by Helicobacter pylori

To discuss the influence on proliferation and apoptosis of human intestinal epithelial cells by Helicobacter pylori (Hp). CCK-8 method and flow cytometry to test the influence on proliferation and apoptosis of intestinal epithelial cells by Hp and cell cycle distribution. Immunocytochemistry, qRT-PCR, and WB to analyze the expression and activation of ACVR1. Functional studies of TNBS-induced IBD on mice and DSS-induced IBD on C57BL/6J mice with HP used for intervention were also performed. Hp facilitated the proliferation of intestinal epithelial cells with the breeding ratios on the first and third day are 5.24% ± 3.26% and 34.18% ± 6.68% respectively. ACVR1 is activated and the expression of anti-apoptosis protein Bcl-2 and Bcl-XL is up-regulated. In vivo, TNBS-induced and Hp-induced exhibited inflammatory lesions of intestine, ACVR1 and Bcl-2 higher expressions as compared to wild-type mice. Hp is likely to play a very important role in the proliferation, apoptosis, and malignant transformation of intestinal epithelial cells through ACVR1 pathway.

Herbs-Partitioned Moxibustion Combined with Acupuncture Inhibits TGF-β1-Smad-Snail-Induced Intestinal Epithelial Mesenchymal Transition in Crohn's Disease Model Rats.

Crohn's disease may cause excessive damage and repair in the intestinal epithelium due to its chronic relapsing intestinal inflammation. These factors may initiate the TGF-β 1-Smad pathway to activate the transcription factor of Snail, and the Snail-mediated pathway promotes the transformation of intestinal epithelial cells to mesenchymal cells, leading to intestinal fibrosis. Acupuncture and moxibustion have been demonstrated to prevent intestinal fibrosis in Crohn's disease. However, it is not clear whether acupuncture and moxibustion can inhibit intestinal epithelial mesenchymal transformation in Crohn's disease by affecting the TGF-β 1-Smad-Snail pathway. This study indicated that abnormal increased expressions of TGFβ1, TβR2, Smad3, and Snail were significantly downregulated by herbs-partitioned moxibustion at Tianshu (ST25) and Qihai (RN6) and acupuncture at Zusanli (ST36) and Shangjuxu (ST37). In addition, protein and mRNA levels of E-cadherin, the epithelial cell marker, were significantly increased. Protein and mRNA levels of fibronectin, the mesenchymal cell marker, were decreased in the intestinal tissue. Moreover, the number of mesenchymal cells in the intestinal mucosa can be reversely transformed to intestinal epithelial cells. Therefore, herbs-partitioned moxibustion combined with acupuncture can prevent intestinal epithelial mesenchymal transition by inhibiting abnormal expression of TGFβ1, TβR2, Smad3, and Snail in the TGF-β1-Smad-Snail pathway in Crohn's disease.

Abstract A41: The RNA binding protein HuR enhances exosome secretion in colorectal cancer

Abstract Enhanced secretion of extracellular vesicles such as microvesicles and exosomes by cancer cells has been recently recognized as a new means of transferring oncogenic information within the tumor microenvironment. Through their ability to carry specific RNA and protein cargo, tumor-derived exosomes can directly impact neighboring cells to support tumor progression. However, it remains unclear what regulates exosome production in tumor cells and the factors influencing loading of tumor-promoting RNA cargo. Our prior work has established that colorectal cells (CRC) and tumors overexpress the key RNA-binding protein HuR early in GI tumor development. When overexpressed and present in the cytoplasm, HuR can promote mRNA stabilization of tumor-promoting genes through binding of 3'UTR AU-rich elements (ARE). While the ability of HuR overexpression to promote gene expression is well recognized, our understanding of how HuR communicates this information within the tumor microenvironment is limited. To test if HuR overexpression could impact exosomes, Tet-regulated HuR-inducible HeLa cells were used to demonstrate that cytoplasmic HuR overexpression promoted a 4-fold increase in exosomes produced. Furthermore, HuR was detected in exosomes produced only from HuR-overexpressing cells. The presence of HuR in exosomes directly impacted mRNA cargo, as selective uptake of ARE-containing mRNAs were observed in exosomes derived from HuR overexpressing cells. To test if these effects were seen in CRC cells that endogenously overexpress HuR, exosome levels from CRC cells were compared to normal primary human intestinal epithelial and myofibroblast cells. When normalized to total cell numbers, CRC cells secrete ~3-fold greater exosome levels than normal cells and enhanced exosome production was dependent upon HuR. Knockdown of HuR in CRC cells directly impacted exosome secretion to levels observed in normal cells. HuR was also only detected in exosomes produced from CRC cells. Using an inducible model of RasV12-mediated transformation of intestinal epithelial cells, endogenous HuR overexpression was observed concomitant with 4-fold greater levels of exosomes containing HuR as cargo. These findings were reflected in vivo where GI-tumor bearing APCMin/+ mice produced ~3-fold more serum exosomes, with HuR as exosomal cargo in APCMin/+ mice whereas no expression of exosomal HuR was detected in wild-type mice. This work has identified a novel connection between HuR-mediated post-transcriptional regulation and tumor-derived exosome production, along with providing the first evidence indicating the presence of exosomal HuR as a serum-based CRC biomarker. Citation Format: Ranjan Preet, Shufei Zhuang, Wei-Ting Hung, Lane K. Christenson, Dan A. Dixon. The RNA binding protein HuR enhances exosome secretion in colorectal cancer. [abstract]. In: Proceedings of the AACR Special Conference: Function of Tumor Microenvironment in Cancer Progression; 2016 Jan 7–10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2016;76(15 Suppl):Abstract nr A41.

Barriers to horizontal cell transformation by extracellular vesicles containing oncogenic H-ras

Extracellular vesicles (EVs) enable the exit of regulatory, mutant and oncogenic macromolecules (proteins, RNA and DNA) from their parental tumor cells and uptake of this material by unrelated cellular populations. Among the resulting biological effects of interest is the notion that cancer-derived EVs may mediate horizontal transformation of normal cells through transfer of mutant genes, including mutant ras. Here, we report that H-ras-mediated transformation of intestinal epithelial cells (IEC-18) results in the emission of exosome-like EVs containing genomic DNA, HRAS oncoprotein and transcript. However, EV-mediated horizontal transformation of non-transformed cells (epithelial, astrocytic, fibroblastic and endothelial) is transient, limited or absent due to barrier mechanisms that curtail the uptake, retention and function of oncogenic H-ras in recipient cells. Thus, epithelial cells and astrocytes are resistant to EV uptake, unless they undergo malignant transformation. In contrast, primary and immortalized fibroblasts are susceptible to the EV uptake, retention of H-ras DNA and phenotypic transformation, but these effects are transient and fail to produce a permanent tumorigenic conversion of these cells in vitro and in vivo, even after several months of observation. Increased exposure to EVs isolated from H-ras-transformed cancer cells, but not to those from their indolent counterparts, triggers demise of recipient fibroblasts. Uptake of H-ras-containing EVs stimulates but fails to transform primary endothelial cells. Thus, we suggest that intercellular transfer of oncogenes exerts regulatory rather than transforming influence on recipient cells, while cancer cells may often act as preferential EV recipients.

Abstract 5104: The RNA binding protein HuR enhances exosome secretion in colorectal cancer

Abstract Enhanced secretion of extracellular vesicles such as microvesicles and exosomes by cancer cells has been recently recognized as a new means of transferring oncogenic information within the tumor microenvironment. Through their ability to carry specific RNA and protein cargo, tumor-derived exosomes can directly impact neighboring cells to support tumor progression. However, it remains unclear what regulates exosome production in tumor cells and the factors influencing loading of tumor-promoting RNA cargo. Our prior work has established that colorectal cancer (CRC) cells and tumors overexpress the key RNA-binding protein HuR early in GI tumor development. When overexpressed and present in the cytoplasm, HuR can promote mRNA stabilization of tumor-promoting genes through binding of 3’UTR AU-rich elements (ARE). While the ability of HuR overexpression to promote gene expression is well recognized, our understanding of how HuR communicates this information within the tumor microenvironment is limited. To test if HuR overexpression could impact secreted exosomes, Tet-regulated HuR-inducible HeLa cells were used to demonstrate that cytoplasmic HuR overexpression promoted a 4-fold increase in exosomes produced. Furthermore, HuR was detected in exosomes produced only from HuR-overexpressing cells. The presence of HuR in exosomes directly impacted mRNA cargo, as selective uptake of ARE-containing mRNAs was observed in exosomes derived from HuR overexpressing cells. To test if these effects were seen in CRC cells that endogenously overexpress HuR, exosome levels from CRC cells were compared to normal primary human intestinal epithelial and myofibroblast cells. When normalized to total cell numbers, CRC cells secrete ∼3-fold greater exosome levels than normal cells and enhanced exosome production was dependent upon HuR. Knockdown of HuR in CRC cells directly impacted exosome secretion to levels observed in normal cells. HuR was also only detected in exosomes produced from CRC cells. Using an inducible model of RasV12-mediated transformation of intestinal epithelial cells, endogenous HuR overexpression was observed associated with 4-fold greater levels of exosomes containing HuR as cargo. These findings were reflected in vivo where GI-tumor bearing APCMin/+ mice produced ∼3-fold more serum exosomes, with HuR as exosomal cargo in APCMin/+ mice where as no expression of exosomal HuR was detected in wild-type mice. This work has identified a novel connection between HuR-mediated post-transcriptional regulation and tumor-derived exosome production, along with providing the first evidence indicating the presence of exosomal HuR as a serum-based CRC biomarker. Citation Format: Ranjan Preet, Shufei Zhuang, Wei-ting Hung, Lane K. Christenson, Dan A. Dixon. The RNA binding protein HuR enhances exosome secretion in colorectal cancer. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 5104.

Met receptor-induced Grb2 or Shc signals both promote transformation of intestinal epithelial cells, albeit they are required for distinct oncogenic functions

BackgroundDeregulation of receptor tyrosine kinases (RTK) contributes to the initiation and progression of intestinal-derived epithelial cancers, including colorectal cancer (CRC). However, the roles of the proximal signaling molecules engaged by RTKs in different oncogenic functions of CRC remain unclear.MethodsHerein, the functional impact of expressing variant forms of the oncogenic Met receptor (Tpr-Met) that selectively recruit the adaptor proteins Grb2 or Shc was investigated in a model derived from normal intestinal epithelial cells (IEC-6). An RNA interference (RNAi) approach was used to define the requirement of Grb2 or Shc in Tpr-Met-transformed IEC-6 cells. Since Grb2 and Shc couple RTKs to the activation of the Ras/MEK/Erk and PI3K/Akt pathways, Erk and Akt phosphorylation/activation states were monitored in transformed IEC-6 cells, and a pharmacological approach was employed to provide insights into the roles of these pathways in oncogenic processes evoked by activated Met, and downstream of Grb2 and Shc.ResultsWe show, for the first time, that constitutive activation of either Grb2 or Shc signals in IEC-6 cells, promotes morphological transformation associated with down-regulation of E-cadherin, as well as increased cell growth, loss of growth contact inhibition, anchorage-independent growth, and resistance to serum deprivation and anoikis. Oncogenic activation of Met was revealed to induce morphological transformation, E-cadherin down-regulation, and protection against anoikis by mechanisms dependent on Grb2, while Shc was shown to be partly required for enhanced cell growth. The coupling of activated Met to the Ras/MEK/Erk and PI3K/Akt pathways, and the sustained engagement of Grb2 or Shc in IECs, was shown to trigger negative feedback, limiting the extent of activation of these pathways. Nonetheless, morphological alterations and E-cadherin down-regulation induced by the oncogenic Tpr-Met, and by Grb2 or Shc signals, were blocked by MEK, but not PI3K, inhibitors while the enhanced growth and resistance to anoikis induced by Tpr-Met were nearly abolished by co-treatment with both inhibitors.ConclusionOverall, these results identify Grb2 and Shc as central signaling effectors of Met-driven progression of intestinal epithelial-derived cancers. Notably, they suggest that Grb2 may represent a promising target for the design of novel CRC therapies.

Ras-induced Up-regulation of CTP:Phosphocholine Cytidylyltransferase α Contributes to Malignant Transformation of Intestinal Epithelial Cells

Cancer cells have enhanced lipogenic capacity characterized by increased synthesis of fatty acids and complex lipids, including phosphatidylcholine (PC). As the rate-limiting enzyme in the CDP-choline pathway for PC synthesis, CTP:phosphocholine cytidylyltransferase α (CCTα) is implicated in the provision of membranes and bioactive lipids necessary of cell proliferation. In this study, we assessed the role of CCTα in malignant intestinal epithelial cells transformed with activated H-ras (IEC-ras). Three IEC-ras clones had significant up-regulation CCTα expression, but PC synthesis and in vitro activity of CCTα were similar to control IEC. RNA interference of CCTα in adherent IEC-ras did not affect PC synthesis, confirming that the enzyme was relatively inactive. However, CCTα silencing in ras-transformed IEC reduced anchorage-independent growth, a criterion for malignant transformation, as well as tumorigenicity in mice. Relative to their adherent counterparts, detached IEC-ras had increased PC synthesis that was attenuated by inducible CCTα silencing. Detachment of IEC-ras was accompanied by increased CCTα phosphorylation and cytosolic enzyme activity. We conclude that the expanded pool of CCTα in IEC-ras is activated by detachment. This provides the increased PC biosynthetic capacity that contributes to malignant transformation of intestinal epithelial cells when detached from the extracellular matrix.

TGF-β1-dependent L1CAM expression has an essential role in macrophage-induced apoptosis resistance and cell migration of human intestinal epithelial cells

Patients with chronic inflammatory bowel disease (IBD) have an increased risk to develop colorectal cancer (CRC) particularly after long duration of the disease. Chronic inflammation of the intestinal mucosa is characterized by a marked enrichment of immune cells such as macrophages as well as by high expression of cytokines and growth factors including transforming growth factor-beta 1 (TGF-β1). The adhesion molecule L1CAM mediates chemoresistance and migration of tumor cells and is elevated in CRC tissues being associated with metastatic spread and poor prognosis for the patients. In this study, we examine the role of TGF-β1-induced L1CAM expression and macrophages in malignant transformation of intestinal epithelial cells. We demonstrate that TGF-β1 stimulation leads to a Slug-dependent upregulation of L1CAM expression already in the colonic intestinal epithelial cell line NCM460 thereby enhancing cell motility and apoptosis resistance. Accordingly, NCM460 cells acquired a migratory and apoptosis-resistant phenotype if transfected with L1CAM. Immunohistochemistry of colonic biopsies revealed considerable L1CAM expression in intestinal epithelial cells in tissues from IBD patients but not in normal colonic tissues. Moreover, L1CAM expression increased with duration of disease being associated with the presence of CD33+ macrophages. Coculture with macrophages generated from monocyte colony-stimulating factor (MCSF)-treated monocytes led to the upregulation of Slug and L1CAM in NCM460 cells thereby elevating cell motility and apoptosis resistance. Pharmacological inhibition of TGF-β1 signalling abolished expression of Slug and L1CAM in cocultured NCM460 cells resulting in decreased cell migration and apoptosis resistance. In conclusion, these data provide new insights into the mechanisms by which IBD promotes malignant transformation of intestinal epithelial cells and underscore the role of L1CAM and macrophages in this scenario.

Involvement of Autophagy in Oncogenic K-Ras-induced Malignant Cell Transformation

Autophagy has recently been implicated in both the prevention and progression of cancer. However, the molecular basis for the relationship between autophagy induction and the initial acquisition of malignancy is currently unknown. Here, we provide the first evidence that autophagy is essential for oncogenic K-Ras (K-RasV12)-induced malignant cell transformation. Retroviral expression of K-RasV12 induced autophagic vacuole formation and malignant transformation in human breast epithelial cells. Interestingly, pharmacological inhibition of autophagy completely blocked K-RasV12-induced, anchorage-independent cell growth on soft agar. Both mRNA and protein levels of ATG5 and ATG7 (autophagy-specific genes 5 and 7, respectively) were increased in cells overexpressing K-RasV12. Targeted suppression of ATG5 or ATG7 expression by short hairpin (sh) RNA inhibited cell growth on soft agar and tumor formation in nude mice. Moreover, inhibition of reactive oxygen species (ROS) with antioxidants clearly attenuated K-RasV12-induced ATG5 and ATG7 induction, autophagy, and malignant cell transformation. MAPK pathway components were activated in cells overexpressing K-RasV12, and inhibition of JNK blunted induction of ATG5 and ATG7 and subsequent autophagy. In addition, pretreatment with antioxidants completely inhibited K-RasV12-induced JNK activation. Our results provide novel evidence that autophagy is critically involved in malignant transformation by oncogenic K-Ras and show that reactive oxygen species-mediated JNK activation plays a causal role in autophagy induction through up-regulation of ATG5 and ATG7.

Oncogenic engagement of the Met receptor is sufficient to evoke angiogenic, tumorigenic, and metastatic activities in rat intestinal epithelial cells

The deregulation of Met/hepatocyte growth factor (HGF) receptor tyrosine kinase signaling constitutes a common event in colorectal cancers. However, the physiopathological functions of such a deregulation remain poorly understood. In the present study, we investigated the role of the deregulation of Met receptor in the neoplastic transformation of intestinal epithelial cells. To do so, the normal, well-established and characterized rat intestinal epithelial IEC-6 cells were transduced with a retrovirus carrying the oncogenic constitutive active form of Met receptor, Tpr-Met. Herein, we show that compared with control IEC-6 cells, Tpr-Met-IEC-6 cells exhibit enhanced proliferation, loss of growth-contact inhibition, cell morphological alterations, actin cytoskeletal reorganization, loss of E-cadherin expression and anchorage-independent growth. Moreover, Tpr-Met-IEC-6 cells are conferred the capacity to produce the proangiogenic factor VEGF and to reduce the potent antiangiogenic factor thrombospondin-1. Of significance, Tpr-Met-IEC-6 cells are endowed with the ability to elicit angiogenic responses and to form tumors and metastases in vivo. Hence, our study demonstrates for the first time that the sole oncogenic engagement of Met receptor in normal intestinal epithelial cells is sufficient to induce a wide array of cancerous biological processes that are fundamental to the initiation and malignant progression of colorectal cancers.

S1650 Regulation and Function of Amphiregulin in RAS-Mediated Transformation of Intestinal Epithelial Cells

S1650 Regulation and Function of Amphiregulin in RAS-Mediated Transformation of Intestinal Epithelial Cells

The role of signal transducers and activators of transcription in colon cancer

A family of latent cytoplasmic transcription factors, Signal Transducers and Activators of Transcription (STATs), convey signals from numerous cytokines and growth factors to the nucleus. Their expression and their activity have been shown to be perturbed in a variety of malignancies, including colorectal cancer. Among the STAT family members, oncogenic STAT3 has been shown to be constitutively activated or overexpressed in colon cancers. In contrast, the expression levels of STAT1 have been found to be reduced in transformed intestinal epithelial cells, consistent with tumor suppressor properties of STAT1. We showed that transformation of intestinal epithelial cells with KRasV12 is sufficient to downregulate the expression of STAT1. Because both STAT1 and STAT3 are important regulators of genes that are involved in cell survival (BCL-x, survivin, caspases) and cell proliferation (c-Myc, p21, cyclin D1), their deregulation significantly impacts the homeostasis of intestinal tissues. The critical role of STATs in oncogenesis and in inflammation merits further investigation of targeted inhibitors of STATs activity that could be used alone or in combination with conventional chemotherapy.

Heterozygous disruption of the PTEN promotes intestinal neoplasia in APCmin/+ mouse: roles of osteopontin

The persistent activation of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway is oncogenic and involved in colorectal neoplasia. Mutations of both regulatory subunit and catalytic subunit of PI3K have been demonstrated in colon cancers. In the present study, we show that heterozygous disruption of the phosphatase and tensin homolog (PTEN) tumor suppressor gene promoted tumor progression in APC(min/+) mice. Number and size of intestinal tumors were significantly increased in mice bearing both adenomatous polyposis coli (APC) and PTEN mutations. While APC(min/+)PTEN(+/+) mice developed adenomas, invasive carcinomas developed in APC(min/+)PTEN(+/-) mice. Large tumors often resulted in intestinal intussusception and early death of APC(min/+)PTEN(+/-) mice. Targeted array revealed that osteopontin (OPN) was the leading gene whose expression was strongly induced by deficiency of PTEN. In colon cancer cells, gain-of-function mutation of PI3K robustly increased levels of OPN and treatment with OPN reduced growth factor deprivation-induced programmed cell death. Moreover, OPN expression was strongly increased in Ras-induced transformation of intestinal epithelial cells in a PI3K-dependent manner. Inhibition of OPN expression by specific small interfering RNA reduced uncontrolled growth and invasiveness of Ras-transformed intestinal epithelial cells. Thus, our results suggest that the PI3K pathway promotes the transformation of intestinal adenoma to adenocarcinoma. OPN, a downstream effector of PI3K, protects transformed intestinal epithelial cells from programmed cell death and stimulates their anchorage-independent growth.

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 42 μM in transformed cells and 81 μM 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.

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

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. 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. 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. 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.

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

BackgroundLoss 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. MethodsRat 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. ResultsAfter 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. ConclusionsOncogenic 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.

The zinc finger transcriptional repressors SLUG and SIP1 are upregulated during ras-induced malignant transformation of intestinal epithelial cells

The zinc finger transcriptional repressors SLUG and SIP1 are upregulated during ras-induced malignant transformation of intestinal epithelial cells