Tumor-derived mutated E-cadherin influences beta-catenin localization and increases susceptibility to actin cytoskeletal changes induced by pervanadate

Comparative proteomic analysis for the insoluble fractions of colorectal cancer patients

We used label-free quantitative proteomics with the insoluble fractions from colorectal cancer (CRC) patients to gain further insight into the utility of profiling altered protein expression as a potential biomarker for cancer. The insoluble fractions were prepared from paired tumor/normal biopsies from 13 patients diagnosed with CRC (stages I to IV). Fifty-six proteins identified in data pooled from the 13 cases were differentially expressed between the tumor and adjacent normal tissue. The connections between these proteins are involved in reciprocal networks related to tumorigenesis, cancer incidence based on genetic disorder, and skeletal and muscular disorders. To assess their potential utility as biomarkers, the relative expression levels of the proteins were validated using personal proteomics and a heat map to compare five individual CRC samples with five normal tissue samples. Further validation of a panel of proteins (KRT5, JUP, TUBB, and COL6A1) using western blotting confirmed the differential expression. These proteins gave specific network information for CRC, and yielded a panel of novel markers and potential targets for treatment. It is anticipated that the experimental approach described here will increase our understanding of the membrane environment in CRC, which may provide direction for making diagnoses and prognoses through molecular biomarker targeting.

Biophysics of cadherin adhesion

Since the identification of cadherins and the publication of the first crystal structures, the mechanism of cadherin adhesion, and the underlying structural basis have been studied with a number of different experimental techniques, different classical cadherin subtypes, and cadherin fragments. Earlier studies based on biophysical measurements and structure determinations resulted in seemingly contradictory findings regarding cadherin adhesion. However, recent experimental data increasingly reveal parallels between structures, solution binding data, and adhesion-based biophysical measurements that are beginning to both reconcile apparent differences and generate a more comprehensive model of cadherin-mediated cell adhesion. This chapter summarizes the functional, structural, and biophysical findings relevant to cadherin junction assembly and adhesion. We emphasize emerging parallels between findings obtained with different experimental approaches. Although none of the current models accounts for all of the available experimental and structural data, this chapter discusses possible origins of apparent discrepancies, highlights remaining gaps in current knowledge, and proposes challenges for further study.

Cyto- and genotoxicity of a vanadyl(IV) complex with oxodiacetate in human colon adenocarcinoma (Caco-2) cells: potential use in cancer therapy

The complex of vanadyl(IV) cation with oxodiacetate, VO(oda) caused an inhibitory effect on the proliferation of the human colon adenocarcinoma cell line Caco-2 in the range of 25-100 μM (P < 0.001). This inhibition was partially reversed by scavengers of free radicals. The difference in cell proliferation in the presence and the absence of scavengers was statistically significant in the range of 50-100 μM (P < 0.05). VO(oda) altered lysosomal and mitochondria metabolisms (neutral red and MTT bioassays) in a dose-response manner from 10 μM (P < 0.001). Morphological studies showed important transformations that correlated with the disassembly of actin filaments and a decrease in the number of cells in a dose response manner. Moreover, VO(oda) caused statistically significant genotoxic effects on Caco-2 cells in the low range of concentration (5-25 μM) (Comet assay). Increment in the oxidative stress and a decrease in the GSH level are the main cytotoxic mechanisms of VO(oda). These effects were partially reversed by scavengers of free radicals in the range of 50-100 μM (P < 0.05). Besides, VO(oda) interacted with plasmidic DNA causing single and double strand cleavage, probably through the action of free radical species. Altogether, these results suggest that VO(oda) is a good candidate to be evaluated for alternative therapeutics in cancer treatment.

Signalling to actin: role of C3G, a multitasking guanine-nucleotide-exchange factor

C3G (Crk SH3-domain-binding guanine-nucleotide-releasing factor) is a ubiquitously expressed member of a class of molecules called GEFs (guanine-nucleotide-exchange factor) that activate small GTPases and is involved in pathways triggered by a variety of signals. It is essential for mammalian embryonic development and many cellular functions in adult tissues. C3G participates in regulating functions that require cytoskeletal remodelling such as adhesion, migration, maintenance of cell junctions, neurite growth and vesicle traffic. C3G is spatially and temporally regulated to act on Ras family GTPases Rap1, Rap2, R-Ras, TC21 and Rho family member TC10. Increased C3G protein levels are associated with differentiation of various cell types, indicating an important role for C3G in cellular differentiation. In signalling pathways, C3G serves functions dependent on catalytic activity as well as protein interaction and can therefore integrate signals necessary for the execution of more than one cellular function. This review summarizes our current knowledge of the biology of C3G with emphasis on its role as a transducer of signals to the actin cytoskeleton. Deregulated C3G may also contribute to pathogenesis of human disorders and therefore could be a potential therapeutic target.

Tissue organization by cadherin adhesion molecules: dynamic molecular and cellular mechanisms of morphogenetic regulation

This review addresses the cellular and molecular mechanisms of cadherin-based tissue morphogenesis. Tissue physiology is profoundly influenced by the distinctive organizations of cells in organs and tissues. In metazoa, adhesion receptors of the classical cadherin family play important roles in establishing and maintaining such tissue organization. Indeed, it is apparent that cadherins participate in a range of morphogenetic events that range from support of tissue integrity to dynamic cellular rearrangements. A comprehensive understanding of cadherin-based morphogenesis must then define the molecular and cellular mechanisms that support these distinct cadherin biologies. Here we focus on four key mechanistic elements: the molecular basis for adhesion through cadherin ectodomains, the regulation of cadherin expression at the cell surface, cooperation between cadherins and the actin cytoskeleton, and regulation by cell signaling. We discuss current progress and outline issues for further research in these fields.

Rac1 and Rho contribute to the migratory and invasive phenotype associated with somatic E-cadherin mutation

Recent evidence suggests a close association between extracellular E-cadherin mutation in diffuse-type gastric carcinoma and the acquisition of a migratory phenotype of tumour cells. To characterize the cellular machinery that mediates the gain of motility of tumour cells with mutant E-cadherin, we turned to the small Rho GTPases Rac1 and Rho because they have been implicated in pathological processes including tumour cell migration and invasion. In the present study, we analyse the activity of Rac1 and Rho in relation to E-cadherin harbouring an in-frame deletion of exon 8 and prove for the first time that the mutation reduces the ability of E-cadherin to activate Rac1 and to inhibit Rho. We provide evidence that the lack of Rac1 activation observed in response to mutant E-cadherin influences the downstream signalling of Rac1, as is shown by the decrease in the binding of the Rac1 effector protein IQGAP1 to Rac1-GTP. Moreover, reduced membranous localization of p120-catenin in mutant E-cadherin expressing cells provides an explanation for the lack of negative regulation of Rho by mutant E-cadherin. Further, we show by time-lapse laser scanning microscopy and invasion assay that the enhanced motility and invasion associated with mutant E-cadherin is sensitive to the inhibition of Rac1 and Rho. Together, these findings present evidence that the mutation of E-cadherin influences Rac1 and Rho activation in opposite directions and that Rac1 and Rho are involved in the establishment of the migratory and invasive phenotype of tumour cells that have an E-cadherin mutation.

Atypical E-cadherin expression in cell clusters overlying focally disrupted mammary myoepithelial cell layers: implications for tumor cell motility and invasion

Our recent studies showed that cell clusters overlying focal myoepithelial cell layer disruptions (FMCLD) had a significantly higher rate of ER negativity, genetic instabilities, and expression of invasion-related genes than adjacent cells within the same duct. This study attempted to determine if these cells would show aberrant E-cadherin expression, which imparts greater propensity for cell motility and invasion. Consecutive sections from breast tumors with a high frequency of FMCLD were double-immunostained for E-cadherin and a panel of related markers. The E-cadherin mRNA levels in cells overlying FMCLD and adjacent cells within the same duct were compared using real-time PCR. Nearly all the cell clusters overlying FMCLD were strongly immunoreactive for E-cadherin, whereas their adjacent counterparts within the same duct were largely negative. Cell clusters overlying FMCLD were generally arranged as tongue-like projections, "puncturing" deep into the stroma or tube-like structures that often contained red blood cells. The sub-cellular localization of E-cadherin in the above structures, however, was primarily cytoplasmic. The mRNA level of E-cadherin in cell clusters overlying FMCLD was significantly higher than that in adjacent cells within the same duct. These findings suggest that aberrant expression of E-cadherin may contribute to cell motility and invasion.

Enhanced activation of epidermal growth factor receptor caused by tumor-derived E-cadherin mutations

Mutations of the tumor suppressor E-cadherin and overexpression of the receptor tyrosine kinase epidermal growth factor receptor (EGFR) are among the most frequent genetic alterations associated with diffuse-type gastric carcinoma. Accumulating evidence suggests a functional relationship between E-cadherin and EGFR that regulates both proteins. We report that somatic mutation of E-cadherin is associated with increased activation of EGFR followed by enhanced recruitment of the downstream acting signaling components growth factor receptor binding protein 2 and Shc, and activation of Ras. Reduced complex formation of mutant E-cadherin - with an in frame deletion of exon 8 in the extracellular domain resulting in reduced adhesion and increased motility - with EGFR was observed compared with wild-type E-cadherin. We conclude that reduced binding of mutant E-cadherin to EGFR in a multicomponent complex or reduced stability of the complex may enhance EGFR surface motility, thereby facilitating EGFR dimerization and activation. Furthermore, reduced surface localization due to enhanced internalization of mutant E-cadherin compared with the wild-type protein was observed. The internalization of EGFR was decreased in response to epidermal growth factor stimulation in cells expressing mutant E-cadherin, suggesting that mutation of E-cadherin also influences the endocytosis of EGFR. Moreover, we show increased activation of EGFR in gastric carcinoma samples with mutant E-cadherin lacking exons 8 or 9. In summary, we describe activation of EGFR by mutant E-cadherin as a novel mechanism in tumor cells that explains the enhanced motility of tumor cells in the presence of an extracellular mutation of E-cadherin.

Deletion of exon 8 increases cisplatin-induced E-cadherin cleavage

E-Cadherin-mediated cell-cell adhesion plays a key role in epithelial cell survival and loss of E-cadherin or beta-catenin expression is associated with invasive tumor growth. Somatic E-cadherin mutations have been identified in sporadic diffuse-type gastric carcinoma. Here, we analysed the fate of E-cadherin with an in frame deletion of exon 8 compared to wild-type E-cadherin and the involved signalling events during cisplatin-induced apoptosis. We report that mutant E-cadherin was more readily cleaved during apoptosis than the wild-type form. Also beta-catenin, an important binding partner of E-cadherin, was processed. E-cadherin cleavage resulted in disconnection of the actin cytoskeleton and accumulation of E-cadherin and beta-catenin in the cytoplasm. Inhibitor studies demonstrated that E-cadherin cleavage was caused by a caspase-3-mediated mechanism. We identified the Akt/PKB and the ERK1/2 signalling pathways as important regulators since inhibition resulted in increased E-cadherin cleavage and apoptosis. In summary, we clearly demonstrate that somatic E-cadherin mutations affect apoptosis regulation in that way that they can facilitate the disruption of adherens junctions thereby possibly influencing the response to cisplatin-based chemotherapy. Elucidating the mechanisms that regulate the apoptotic program of tumor cells can contribute to a better understanding of tumor development and potentially be relevant for therapeutic drug design.

Protein-Tyrosine Phosphatase Sigma Is Associated with Ulcerative Colitis

Inflammatory bowel disease (IBD), a relatively common chronic debilitating intestinal illness, is composed of two broadly defined groups, Crohn's disease (CD) and ulcerative colitis (UC). Although several susceptibility genes for CD have been recently described, susceptibility genes exclusive for UC have not been forthcoming. Here, we show that receptor protein-tyrosine phosphatase sigma (PTPRS-encoding PTPsigma) knockout mice spontaneously develop mild colitis that becomes severe when challenged with two known inducers of colitis. We also demonstrate that E-cadherin and beta-catenin, two important adherens junction proteins involved in maintenance of barrier defense in the colon, act as colonic substrates for PTPsigma. Furthermore, we show that three SNPs (rs886936, rs17130, and rs8100586) that flank exon 8 in the human PTPRS gene are associated with UC. The presence of these SNPs is associated with novel splicing that removes the third immunoglobulin-like domain (exon 9) from the extracellular portion of PTPsigma, possibly altering dimerization or ligand recognition. We propose that polymorphisms in the human PTPRS gene lead to ulcerative colitis.

A subset of cell clusters with malignant features in morphologically normal-appearing and hyperplastic tissues

BACKGROUND

The development of human breast cancer may be a multistep process, sequentially undergoing normal, hyperplastic, in situ, invasive, and metastatic stages.

METHODS

Our previous and current studies have revealed that a subset of morphologically normal-appearing and hyperplastic breast tissues adjacent to or distant from malignant breast lesions contained cell clusters that showed malignancy-associated immunohistochemical and cytological alterations.

RESULTS

Compared to their morphologically similar counterparts within the same lesion, these cell clusters exhibited several unique features: (1) a significantly increased frequency of focal disruptions in surrounding myoepithelial cell layers and the loss of estrogen receptor expression, (2) signs of stromal and vascular invasion, (3) distinct alterations in the cytoplasmic-nuclear ratio and nuclear shape, size, and polarity, (4) the expression of multiple malignancy-associated biomarkers, and (5) malignancy-associated nuclear changes in benign-appearing cells.

CONCLUSIONS

These changes are likely to reflect DNA structural abnormalities resulting from the disposition of DNA and RNA structural defects or cancer susceptibility genes that facilitate progression and invasion, or to suggest that breast tumor progression and invasion may not always follow the hypothesized sequences. Thus, an integrated immunohistochemical and cytological assessment might facilitate the differential diagnosis, early detection and prevention of malignant breast lesions.

A subset of prostate basal cells lacks the expression of corresponding phenotypic markers

Immunohistochemical staining for cytokeratin (CK) 34ssE12 has been routinely used to elucidate prostate basal cells for differentiation between non-invasive and invasive lesions. Our previous studies, however, revealed that some morphologically distinct basal cells observed on H&E-stained sections completely lacked CK34ssE12 expression. Our current study attempted to assess whether these basal cells would also lack the expression of other phenotypic markers, and whether basal cell alterations would affect the proliferation status of the associated tumor cells. Consecutive sections from prostate tumors with large basal cell clusters that were morphologically distinct in H&E sections but were completely negative for CK 34ssE12 were morphologically and immunohistochemically assessed with a panel of basal cell phenotypic and other markers. In addition to CK 34ssE12, these basal cells also completely lacked the expression of other phenotypic markers, including CK5, CK14, p63, and maspin, in contrast to adjacent basal cells, which were strongly positive for these markers. Tumors surrounded by basal cell layers that lack the expression of basal cell phenotypic markers showed a significantly higher rate of cell proliferation and mast cell infiltration than their counterparts. These findings suggest that basal cells might be targets of a variety of pathological alterations, which could significantly impact biological presentations of associated tumor cells.

A subset of in situ breast tumor cell clusters lacks expression of proliferation and progression related markers but shows signs of stromal and vascular invasion

BACKGROUND

Our previous studies in pre-invasive mammary tumors revealed that estrogen receptor negative cell clusters (ER NCC) overlying focally disrupted myoepithelial (ME) cell layers showed a significantly higher rate of genetic abnormalities and cell proliferation than adjacent cells without ME cell layer disruptions. A subset of these ER NCC, however, completely lacked expression of Ki-67, a most commonly used marker for cell proliferation. The purpose of this study was to further elucidate the immunohistochemical and morphological profiles of these ER NCC.

METHODS

Fifteen cases with such ER NCC were selected from our previous studies and assessed with a panel of commonly used biomarkers for cell proliferation, tumor progression, and normal stem cells.

RESULTS

Immunohistochemically, in addition to Ki-67 and ER, these ER NCC completely lacked expression of all other proliferation and progression related markers that were distinctly expressed in adjacent cells within the same duct but overlying the non-disrupted ME cell layer. These ER NCC also lacked expression of all normal stem cell-related markers tested. These cell clusters, however, showed a higher and atypical expression of c-erb-B2, compared to their adjacent counterparts. Morphologically, these ER NCC were generally arranged as triangle shaped structures penetrating into the stroma, similar to micro-invasive lesions. About 15% of these ER NCC appeared to directly spread into blood vessel-like structures. These ER NCC and their possible derivatives within the stroma and blood vessels-like structures shared the same morphologic and immunohistochemical features. No comparable ER positive cell clusters were identified in any of the cases.

CONCLUSIONS

These findings suggest that these ER NCC and their possible derivatives are likely regulated by yet to be defined molecules and mechanisms, and they are unlikely to respond to currently available anti-mitotic agents.

Dynamics of cell adhesion and motility in living cells is altered by a single amino acid change in E-cadherin fused to enhanced green fluorescent protein

E-Cadherin regulates epithelial cell adhesion and is critical for the maintenance of tissue integrity. In sporadic diffuse-type gastric carcinoma, mutations of the E-cadherin gene are frequently observed that predominantly affect putative calcium binding motifs located in the linker region between the second and third extracellular domains. A single amino acid change (D370A) as found in a gastric carcinoma patient reduces cell adhesion and up-regulates cell motility. To study the effect of this mutation on the dynamics of cell adhesion and motility in living cells, enhanced green fluorescent protein (EGFP) was C-terminally fused to E-cadherin. The resulting mutant E-cadherin-EGFP fusion protein with a point mutation in exon 8 (p8-EcadEGFP) and a wild-type E-cadherin-EGFP fusion construct (wt-EcadEGFP) were expressed in human MDA-MB-435S cells. Fluorescent images were acquired by time-lapse laser scanning microscopy and E-cadherin was visualized during contact formation and in moving cells. Spatial and temporal localization of p8- and wt-EcadEGFP differed significantly. While wt-EcadEGFP was mainly localized at lateral membranes of contacting cells and formed E-cadherin puncta and plaques, p8-EcadEGFP-expressing cells frequently formed transient cell-cell contacts. During random cell migration, p8-EcadEGFP was found in lamellipodia. In contrast, wt-EcadEGFP localized at lateral cell-cell contact sites in low or non-motile cells. Inhibition of the epidermal growth factor (EGF) receptor, which plays a major role in lamellipodia formation and cell migration, reduced the motility of p8-EcadEGFP-expressing cells and caused lateral membrane staining of p8-EcadEGFP. Conversely, EGF induced cell motility and caused formation of lamellipodia that were E-cadherin positive. In conclusion, our data show that mutant E-cadherin significantly alters the dynamics of cell adhesion and motility in living cells and interferes with the formation of stable cell-cell contacts.

Mutated E-cadherin: genomic and functional characterization in thyroid cells from the KAT family

Members of a family of thyroid cell lines (KAT) were analyzed because they expressed a higher molecular weight (135 kd) form of E-cadherin at their surface. We found that this aberrant E-cadherin is the result of a point mutation in the exon 9 donor splice site causing a skipping of exon 9 with consequent deletion of the corresponding aminoacids on E-cadherin protein. As a spin-off, we report that the various members of the KAT family share this mutation as well as the genetic background. Furthermore we found that this mutated protein leads to disturbed cell-cell adhesion although E-cadherin is still able to mediate the formation of the cadherin/ catenin complex. We also demonstrate the presence of another cell-cell adhesion complex, formed by Pcadherin and the catenins. The latter is also not able to mediate cell-cell adhesion. Although these cells lack cell-cell adhesion they are not invasive without exogenous stimulus.

Tumor-associated E-cadherin mutations do not induce Wnt target gene expression, but affect E-cadherin repressors

E-cadherin is a cell-cell adhesion molecule and tumor invasion suppressor gene that is frequently altered in human cancers. It interacts through its cytoplasmic domain with beta-catenin which in turn interacts with the Wnt (wingless) signaling pathway. We have compared the effects of different tumor-derived E-cadherin variants with those of normal E-cadherin on Wnt signaling and on genes involved in epithelial mesenchymal transition. We established an in-house cDNA microarray composed of 1105 different, sequence verified cDNA probes corresponding to 899 unique genes that represent the majority of genes known to be involved in cadherin-dependent cell adhesion and signaling ('Adhesion/Signaling Array'). The expression signatures of E-cadherin-negative MDA-MB-435S cancer cells transfected with E-cadherin variants (in frame deletions of exon 8 or 9, D8 or D9, respectively, or a point mutation in exon 8 (D370A)) were compared to that of wild-type E-cadherin (WT) transfected cells. From the differentially expressed genes, we selected 38 that we subsequently analyzed by quantitative real-time RT-PCR and/or Northern Blot. A total of 92% of these were confirmed as differentially expressed. Most of these genes encode proteins of the cytoskeleton, cadherins/integrins, oncogenes and matrix metalloproteases. No significant expression differences of genes downstream of the Wnt-pathway were found, except in E-cadherin D8 transfected cells where upregulation of three Tcf/Lef-transcribed genes was seen. One possible reason for the lack of expression differences of the Tcf/Lef-regulated genes is upregulation of SFRP1 and SFRP3; both of which are competitive inhibitors of the Wnt proteins. Interestingly, known E-cadherin transcriptional repressors, such as SLUG (SNAI2), SIP1 (ZEB2), TWIST1, SNAIL (SNAI1) and ZEB1 (TCF8), but not E12/E47 (TCF3), had a lack of upregulation in cells expressing mutated E-cadherin compared to WT. In conclusion, E-cadherin mutations have no influence on expression of genes involved in Wnt-signaling, but they may promote their own expression by blocking upregulation of E-cadherin repressors.

Effect of tumor-associated mutant E-cadherin variants with defects in exons 8 or 9 on matrix metalloproteinase 3

Tumor progression is characterized by loss of cell adhesion and increase of invasion and metastasis. The cell adhesion molecule E-cadherin is frequently down-regulated or mutated in tumors. In addition to down-regulation of cell adhesion, degradation of the extracellular matrix by matrix metalloproteinases is necessary for tumor cell spread. To investigate a possible link between E-cadherin and matrix metalloproteinase 3 (MMP-3), we examined expression of MMP-3 in human MDA-MB-435S cells transfected with wild-type (wt) or three different tumor-associated mutant E-cadherin variants with alterations in exons 8 or 9, originally identified in gastric carcinoma patients. In the presence of wt E-cadherin, the MMP-3 protein level was decreased in cellular lysates and in the supernatant where a secreted form of the protein is detectable. Down-regulation of MMP-3 was not found in MDA-MB-435S transfectants expressing mutant E-cadherin variants which indicates that E-cadherin mutations interfere with the MMP-3 suppressing function of E-cadherin. The mechanism of regulation of MMP-3 by E-cadherin is presently not clear. We have previously found that cell motility is enhanced by expression of the mutant E-cadherin variants used in this study. Here, we found that application of the synthetic inhibitor of MMP-3 NNGH and small interfering RNA (siRNA) directed against MMP-3 reduce mutant E-cadherin-enhanced cell motility. Taken together, our results point to a functional link between MMP-3 and E-cadherin. MMP-3 is differentially regulated by expression of wt or mutant E-cadherin. On the other hand, MMP-3 plays a role in the enhancement of cell motility by mutant E-cadherin. Both observations may be highly relevant for tumor progression since they concern degradation of the extracellular matrix and tumor cell spread.

Effect of P-selectin monoclonal antibody on metastasis of gastric cancer and immune function

AIM: To investigate the effect of cell adhesion molecule P-selectin monoclonal antibody (Mab) on metastasis and immune function of mice orthototopically implanted with human gastric cancer tissue.

METHODS: SCID mice were implanted orthotopically with SGC-7901 human gastric carcinoma tissue. Starting from day 3 after operation, animals were given intravenously PBS or P-selectin Mab (100 μg/injection) (for both normal mice and tumor-implanted mice with tumors), twice weekly for 3 wk. Two animals in each group were sacrificed randomly at the 1st, 2nd, 4th week and 6th week. While T cell and B cell transformation indices were determined with the ³H TdR infiltration method, the NK cell activity was detected by the LDH release method.

RESULTS: The metastatic rate in the P-selectin Mab treated group was lower than that in the PBS treated group (with tumors). The NK activity of normal mice increased over time. The immune functions (T, B cell function, NK activity) of the tumor group in the 6th week were significantly lower than those in the 4th week, but the change was attenuated by P-selectin Mab.

CONCLUSION: P-selectin Mab could suppress the metastasis of gastric cancer with no adverse effect on host immune function.

Relationship between E-cadherin gene mutation and p53 gene mutation, p53 accumulation, Bcl-2 expression and Ki-67 staining in diffuse-type gastric carcinoma

E-cadherin mutations are found in 50% of diffuse-type gastric carcinoma, but not in intestinal gastric carcinoma. Because cell-cell adhesion mediated by E-cadherin plays an important role in epithelial cell survival, E-cadherin mutations could alter the apoptotic behavior of tumor cells. p53 and Bcl-2 family members are also important regulators of cellular apoptosis. This is the first study that investigates the relationship between E-cadherin gene mutation and p53 gene mutation, p53 accumulation, Bcl-2 expression, and Ki-67 expression in diffuse-type gastric carcinoma (24 cases, E-cadherin mutation status: wild-type in 8 patients and mutant in 16 patients). The mutation status of exons 5-8 of p53 was analyzed by denaturing high pressure liquid chromatography (DHPLC) in formalin-fixed, paraffin-embedded tumor sections, followed by direct sequencing of cases with aberrant chromatographic patterns. p53 mutations were found in 1 of 8 tumors without E-cadherin mutation (12.5%) and in 1 of 16 tumors with E-cadherin mutation (6.3%), a difference that was not statistically significant (p = 1.00). p53 accumulation was found in 8 of 24 tumors (33.3%) by immunohistochemical staining. p53 accumulation was significantly more frequent in tumors without E-cadherin mutations (5 of 8 tumors, 62.5%) than in gastric carcinoma tissues with E-cadherin mutations (3 of 16 tumors, 18.8%, p = 0.03). Bcl-2 staining was not observed in gastric carcinoma cells without E-cadherin mutations, but was detectable in 5 of 16 tumors with E-cadherin mutations (31.3%), a difference that was not statistically significant (p = 0.13). No relationship was observed between Ki-67 staining and the E-cadherin mutation status (p = 1.00). These data suggest that the presence of E-cadherin mutations can significantly alter the accumulation of the apoptosis-regulating p53 protein, whereas no correlation with the p53 mutation status or with Ki-67 staining was observed.

Motility enhancement by tumor-derived mutant E-cadherin is sensitive to treatment with epidermal growth factor receptor and phosphatidylinositol 3-kinase inhibitors

Diffuse-type gastric and lobular breast cancers are characterized by frequent mutations in the cell adhesion molecule E-cadherin. Here we report that tumor-associated mutations of E-cadherin enhanced random cell movement of transfected MDA-MB-435S mammary carcinoma cells as compared to wild-type (wt) E-cadherin-expressing cells. The mutations included in frame deletions of exons 8 or 9 and a point mutation in exon 8 which all affect putative calcium-binding sites within the linker region of the second and third extracellular domain. Motility enhancement by mutant E-cadherin was investigated by time-lapse laser scanning microscopy. Increased cell motility stimulated by mutant E-cadherin was influenced by cell-matrix interactions. The motility-increasing activity of mutant E-cadherin was blocked by application of pharmacological inhibitors of epidermal growth factor receptor and phosphatidylinositol (PI) 3-kinase. Investigation of the activation status of PI 3-kinase and the downstream signaling molecules Akt/protein kinase B and MAP kinase p44/42 showed that these kinases are not more strongly activated in mutant E-cadherin-expressing cells than in wt E-cadherin-expressing cells. Instead, the basal level of PI 3-kinase is necessary for mutant E-cadherin-enhanced cell motility. Our data suggest a critical role of E-cadherin mutations for the fine tuning of tumor cell motility.

Vanadium in cancer treatment

Vanadium compounds exert preventive effects against chemical carcinogenesis on animals, by modifying, mainly, various xenobiotic enzymes, inhibiting, thus, carcinogen-derived active metabolites. Studies on various cell lines reveal that vanadium exerts its antitumor effects through inhibition of cellular tyrosine phosphatases and/or activation of tyrosine phosphorylases. Both effects activate signal transduction pathways leading either to apoptosis and/or to activation of tumor suppressor genes. Furthermore, vanadium compounds may induce cell-cycle arrest and/or cytotoxic effects through DNA cleavage and fragmentation and plasma membrane lipoperoxidation. Reactive oxygen species generated by Fenton-like reactions and/or during the intracellular reduction of V(V) to V(IV) by, mainly, NADPH, participate to the majority of the vanadium-induced intracellular events. Vanadium may also exert inhibitory effects on cancer cell metastatic potential through modulation of cellular adhesive molecules, and reverse antineoplastic drug resistance. It also possesses low toxicity that, in combination with the synthesis of new, more potent and better tolerated complexes, may establish vanadium as an effective non-platinum, metal antitumor agent.

Hereditary diffuse gastric cancer

Hereditary diffuse gastric cancer (HDGC) is a cancer predisposition syndrome caused by germline mutation of the gene for the cell-to-cell adhesion protein E-cadherin. The syndrome is dominated by predisposition to the histologically diffuse, poorly differentiated form of gastric cancer. It is not associated with intestinal-type gastric cancer, but families may have an elevated risk of lobular breast cancer. Here, we review the identified families, mutations, and proposed mechanisms by which E-cadherin loss promotes tumorigenesis.

Incidence of gastric cancer and breast cancer in CDH1 (E-cadherin) mutation carriers from hereditary diffuse gastric cancer families

BACKGROUND & AIMS

Germline mutations in CDH1 are known to cause hereditary diffuse gastric cancer (HDGC). Breast and colorectal cancer have also been reported in CDH1-associated HDGC. The purpose of this study was to estimate the cumulative risk of gastric and breast cancer in CDH1 mutation carriers.

METHODS

Family data were collected by member groups of the International Gastric Cancer Linkage Consortium. Eligible families had at least 3 cases of diffuse gastric cancer, and at least 1 affected member had tested positive for a mutation in CDH1. Eleven families met these criteria. We used the pedigree information to estimate penetrance using the MENDEL program. The conditional likelihood of the pedigree was maximized given the phenotype of the pedigree and genotype of the index case at ascertainment. We parameterized the model in terms of log relative risks for mutation carriers compared with risks in the general population of the United Kingdom. Noncarriers of the gene were assumed to develop the disease at population incidence rates.

RESULTS

The estimated cumulative risk of gastric cancer by age 80 years was 67% for men (95% confidence interval [95% CI], 39-99) and 83% for women (95% CI, 58-99). For women, the cumulative risk of breast cancer was 39% (95% CI, 12-84). The combined risk of gastric cancer and breast cancer in women was 90% by age 80 years.

CONCLUSIONS

These penetrance estimates should be useful for genetic counseling in multiple-case families. However, they may not apply to individuals with a minimal family history, in whom the risks may be lower.

Single amino acid substitutions in conserved extracellular domains of E-cadherin differ in their functional consequences

The calcium-dependent homophilic cell adhesion molecule E-cadherin typically connects epithelial cells. The extracellular portion of the mature transmembrane protein consists of five homologous domains. The four sequences linking these domains contain the structural amino acid motif DXXD that is thought to be involved in direct calcium binding. In gastric cancer patients mutations affecting this motif between the second and third domain are frequently seen. In order to determine the functional significance of similar sequence alterations with regard to their location, we analyzed single amino acid substitutions changing the DXXD motif to DXXA in each linker region according to a mutation found in gastric cancer (D370A). The cDNA sequences coding for DQND, DVLD and DVND were changed (D257A, D479A, D590A, respectively) and stably expressed in E-cadherin negative MDA-MB-435S mammary carcinoma cells. We found that the D257A and D370A mutations result in abnormal protein localization, changes in the actin cytoskeleton, markedly reduced homophilic cell adhesion, and altered cell morphology. Unexpectedly, the tumor-associated D370A mutation but not the D257A mutation induced increased cell motility. The D479A mutation only had slight functional consequences whereas cells expressing the D590A mutant did not differ from cells expressing the wild-type molecule. Although the putative calcium binding motif DXXD is located at repetitive positions in the extracellular portion of E-cadherin, our results indicate that it has different functions depending on the location. Remarkably, tumor cells select for mutations in the most critical domains resulting both in loss of function (decreased cell adhesion) and in gain of function (increased cell motility). Since multiple DXXD motifs are typically seen in other cadherins, our structure-function study is relevant for this gene family in general.

E-cadherin gene (CDH1) promoter methylation as the second hit in sporadic diffuse gastric carcinoma

In diffuse gastric carcinoma, despite common E-cadherin gene (CDH1) mutations, tumors show absence of CDH1 loss of heterozigosity (LOH) in most cases. This observation challenges the classical two-hit model of tumor suppressor gene inactivation. In order to investigate whether or not CDH1 promoter methylation may function as the second hit we analysed a series of 23 sporadic gastric carcinomas for the presence of CDH1 mutations, CDH1 promoter methylation, LOH and E-cadherin expression. CDH1 mutations were detected in nine of the 16 (56.3%) diffuse gastric carcinomas and in none of the seven intestinal gastric carcinomas. In diffuse gastric carcinomas harboring CDH1 mutations, LOH was observed in a single case. Loss of plasma membrane E-cadherin expression was consistently found in all nine cases with CDH1 mutation, suggesting that tumors inactivated the remaining CDH1 allele via a different mechanism. CDH1 promoter methylation was observed in nine of the 16 (56.3%) diffuse-type gastric carcinoma cases, including six of the nine cases (66.7%) harboring CDH1 mutations. CDH1 promoter methylation was also seen in two (28.6%) intestinal-type cases. Our results show that CDH1 promoter methylation is the second hit in more than half of the sporadic diffuse gastric carcinoma cases harboring CDH1 mutations.