The intracellular E-cadherin germline mutation V832 M lacks the ability to mediate cell-cell adhesion and to suppress invasion

Lifestyles, genetics, and future perspectives on gastric cancer in east Asian populations

The prevalence of gastric cancer (GC) differs among regions worldwide, with the highest occurrence in east Asia. Thus, its etiology, with respect to ethnic background, environmental factors, and lifestyles, is also thought to differ essentially. In addition, etiology of GC is speculated to be changing due to the recent decrease in the Helicobacter pylori (H. pylori) infection in Japan. State-of-the-art somatic/germline cancer genomics has clarified the etiologies of gastric carcinogenesis. In this review article, we summarize past and present milestones in our understanding of GC achieved through genomic approaches, including a recent report that revealed higher-than-expected frequencies of GCs attributed to east Asian-specific germline variants in ALDH2 or CDH1 in combination with lifestyles. Based on this updated knowledge, we also discuss the possible impact of and high-risk approaches for GCs in the upcoming "H. pylori-negative era."

Hereditary Gastric and Breast Cancer Syndromes Related to CDH1 Germline Mutation: A Multidisciplinary Clinical Review

E-cadherin (CDH1 gene) germline mutations are associated with the development of diffuse gastric cancer in the context of the so-called hereditary diffuse gastric syndrome, and with an inherited predisposition of lobular breast carcinoma. In 2019, the international gastric cancer linkage consortium revised the clinical criteria and established guidelines for the genetic screening of CDH1 germline syndromes. Nevertheless, the introduction of multigene panel testing in clinical practice has led to an increased identification of E-cadherin mutations in individuals without a positive family history of gastric or breast cancers. This observation motivated us to review and present a novel multidisciplinary clinical approach (nutritional, surgical, and image screening) for single subjects who present germline CDH1 mutations but do not fulfil the classic clinical criteria, namely those identified as-(1) incidental finding and (2) individuals with lobular breast cancer without family history of gastric cancer (GC).

Defined lifestyle and germline factors predispose Asian populations to gastric cancer

Germline and environmental effects on the development of gastric cancers (GC) and their ethnic differences have been poorly understood. Here, we performed genomic-scale trans-ethnic analysis of 531 GCs (319 Asian and 212 non-Asians). There was one distinct GC subclass with clear alcohol-associated mutation signature and strong Asian specificity, almost all of which were attributable to alcohol intake behavior, smoking habit, and Asian-specific defective ALDH2 allele. Alcohol-related GCs have low mutation burden and characteristic immunological profiles. In addition, we found frequent (7.4%) germline CDH1 variants among Japanese GCs, most of which were attributed to a few recurrent single-nucleotide variants shared by Japanese and Koreans, suggesting the existence of common ancestral events among East Asians. Specifically, approximately one-fifth of diffuse-type GCs were attributable to the combination of alcohol intake and defective ALDH2 allele or to CDH1 variants. These results revealed uncharacterized impacts of germline variants and lifestyles in the high incidence areas.

Frequency and Clinical Characteristics of Unselected Korean Gastric Cancer Patients with a Germline CDH1 V832M Mutation

Background: Germline mutations in CDH1 are associated with hereditary and early onset- diffuse gastric cancer. However, the frequency of CDH1 germline mutation in unselected gastric cancer cases is not well established.

Aim: The aim of this study was to investigate the frequency and clinical characteristics of germline CDH1 V832M mutation carriers in unselected Korean gastric cancer cases.

Methods: Direct sequencing was performed to determine the presence of CDH1 V832M in 305 unselected Korean gastric cancer patients. Lauren's histologic type, family history of gastric cancer, and age of cancer diagnosis were compared between V832M carriers and non-carriers.

Results: In the study population, seven gastric cancer patients (7/305, 2.29%) were found to have the CDH1 V832M mutation. The CDH1 V832M mutation carrier state was not significantly associated with phenotypes including Lauren's histologic type, family history of gastric cancer, age of cancer diagnosis, and other cancer history in a patient.

Conclusion: This study demonstrates that the germline CDH1 V832M mutation is common in sporadic, late onset, and intestinal type gastric cancer as well as familial, early onset, and diffuse type gastric cancer. Our finding suggests that guidelines for managing CDH1 mutation carriers should be refined through additional data on penetration according to CDH1 mutation type in sporadic cases.

Frequency of CDH1 germline variants and contribution of dietary habits in early age onset gastric cancer patients in Brazil

INTRODUCTION

The contribution of CDH1 germline variants to gastric cancer burden among young adults is unknown in Brazil. We aimed to evaluate the frequency of CDH1 germline variants and the diet/lifestyle habits in early age onset gastric cancer (EOGC, ≤ 55 years old) patients.

METHODOLOGY

From 2013 to 2015, a total of 88 unrelated and consecutive patients diagnosed with EOGC were enrolled. All CDH1 exons and intronic boundaries were sequenced, and large genomic rearrangements were screened by MLPA. CDH1 transcription analysis was performed for variants that could potentially induce an effect on splicing. The diet and lifestyle habits of EOGC patients were compared to Brazilian population diet and lifestyle, obtained from governmental databases.

RESULTS

Of 88 patients, the mean age at EOGC diagnosis was 39 years and 55% fulfilled the criteria for hereditary diffuse gastric cancer. The majority of the tumors were diffuse (74%) and poorly differentiated (80%). In total, 4 novel missense variants of uncertain significance (VUS) were identified: c.313T>A, c.387G>T, c.1676G>A, and c.1806C>A. The MLPA results revealed no rearrangements and CDH1 transcription analysis for variants of interest were inconclusive. EOGC patients had a higher red (OR:2.6, 95%CI:1.4-4.9) and processed (OR:3.1, 95%CI:1.6-6.0) meat intake and higher fruit consumption (OR:0.4, 95%IC:0.3-0.7) compared to eating habits of the Brazilian population.

CONCLUSIONS

No unequivocal pathogenic germline CDH1 variants were identified in Brazilian EOGC patients. Dietary habits may be associated with the EOGC development.

Specifications of the ACMG/AMP variant curation guidelines for the analysis of germline CDH1 sequence variants

The variant curation guidelines published in 2015 by the American College of Medical Genetics and Genomics and the Association for Molecular Pathology (ACMG/AMP) provided the genetics community with a framework to assess variant pathogenicity; however, these rules are not gene specific. Germline pathogenic variants in the CDH1 gene cause hereditary diffuse gastric cancer and lobular breast cancer, a clinically challenging cancer predisposition syndrome that often requires a multidisciplinary team of experts to be properly managed. Given this challenge, the Clinical Genome Resource (ClinGen) Hereditary Cancer Domain prioritized the development of the CDH1 variant curation expert panel (VCEP) to develop and implement rules for CDH1 variant classifications. Here, we describe the CDH1 specifications of the ACMG/AMP guidelines, which were developed and validated after a systematic evaluation of variants obtained from a cohort of clinical laboratory data encompassing ∼827,000 CDH1 sequenced alleles. Comparing previously reported germline variants that were classified using the 2015 ACMG/AMP guidelines to the CDH1 VCEP recommendations resulted in reduced variants of uncertain significance and facilitated resolution of variants with conflicted assertions in ClinVar. The ClinGen CDH1 VCEP recommends the use of these CDH1-specific guidelines for the assessment and classification of variants identified in this clinically actionable gene.

Hereditary lobular breast cancer with an emphasis on E-cadherin genetic defect

Recent studies have reported germline CDH1 mutations in cases of lobular breast cancer (LBC) not associated with the classical hereditary diffuse gastric cancer syndrome. A multidisciplinary workgroup discussed genetic susceptibility, pathophysiology and clinical management of hereditary LBC (HLBC). The team has established the clinical criteria for CDH1 screening and results' interpretation, and created consensus guidelines regarding genetic counselling, breast surveillance and imaging techniques, clinicopathological findings, psychological and decisional support, as well as prophylactic surgery and plastic reconstruction. Based on a review of current evidence for the identification of HLBC cases/families, CDH1 genetic testing is recommended in patients fulfilling the following criteria: (A) bilateral LBC with or without family history of LBC, with age at onset <50 years, and (B) unilateral LBC with family history of LBC, with age at onset <45 years. In CDH1 asymptomatic mutant carriers, breast surveillance with clinical examination, yearly mammography, contrast-enhanced breast MRI and breast ultrasonography (US) with 6-month interval between the US and the MRI should be implemented as a first approach. In selected cases with personal history, family history of LBC and CDH1 mutations, prophylactic mastectomy could be discussed with an integrative group of clinical experts. Psychodecisional support also plays a pivotal role in the management of individuals with or without CDH1 germline alterations. Ultimately, the definition of a specific protocol for CDH1 genetic screening and ongoing coordinated management of patients with HLBC is crucial for the effective surveillance and early detection of LBC.

Predicting the Functional Impact of CDH1 Missense Mutations in Hereditary Diffuse Gastric Cancer

The role of E-cadherin in Hereditary Diffuse Gastric Cancer (HDGC) is unequivocal. Germline alterations in its encoding gene (CDH1) are causative of HDGC and occur in about 40% of patients. Importantly, while in most cases CDH1 alterations result in the complete loss of E-cadherin associated with a well-established clinical impact, in about 20% of cases the mutations are of the missense type. The latter are of particular concern in terms of genetic counselling and clinical management, as the effect of the sequence variants in E-cadherin function is not predictable. If a deleterious variant is identified, prophylactic surgery could be recommended. Therefore, over the last few years, intensive research has focused on evaluating the functional consequences of CDH1 missense variants and in assessing E-cadherin pathogenicity. In that context, our group has contributed to better characterize CDH1 germline missense variants and is now considered a worldwide reference centre. In this review, we highlight the state of the art methodologies to categorize CDH1 variants, as neutral or deleterious. This information is subsequently integrated with clinical data for genetic counseling and management of CDH1 variant carriers.

Profiling cancer-associated genetic alterations and molecular classification of cancer in Korean gastric cancer patients

Recently, the Cancer Genome Atlas (TCGA) Research Network and Asian Cancer Research Group provided a new classification of gastric cancer (GC) to aid the development of biomarkers for targeted therapy and predict prognosis. We studied associations between genetically aberrant profiles of cancer-related genes, environmental factors, and histopathological features in 107 paired gastric tumor-non-tumor tissue GC samples. 6.5% of our GC cases were classified as the EBV subtype, 17.8% as the MSI subtype, 43.0% as the CIN subtype, and 32.7% as the GS subtype. The distribution of four GC subgroups based on the TCGA and our dataset were similar. The MSI subtype showed a hyper-mutated status and the best prognosis among molecular subtype. However, molecular classification based on the four GC subtypes showed no significant survival differences in terms of overall survival (p= 0.548) or relapse-free survival (RFS, p=0.518). The P619fs*43 in ZBTB20 was limited to MSI group (n= 5/19, 26.3%), showing similar trends observed in TCGA dataset.

Genetic alterations of the RTK/RAS/MAPK and PI3K/AKT/mTOR pathways were detected in 34.6% of GC cases (37 individual cases). We also found two cases with likely pathogenic variants (NM_004360.4: c. 2494 G>A, p.V832M) in the CDH1 gene.

Here, we classified molecular subtypes of GC according to the TCGA system and provide a critical starting point for the design of more appropriate clinical trials based on a comprehensive analysis of genetic alterations in Korean GC patients.

Quantification of topological features in cell meshes to explore E-cadherin dysfunction

In cancer, defective E-cadherin leads to cell detachment, migration and metastization. Further, alterations mediated by E-cadherin dysfunction affect cell topology and tissue organization. Herein, we propose a novel quantitative approach, based on microscopy images, to analyse abnormal cellular distribution patterns. We generated undirected graphs composed by sets of triangles which accurately reproduce cell positioning and structural organization within each image. Network analysis was developed by exploring triangle geometric features, namely area, edges length and formed angles, as well as their variance, when compared with the respective equilateral triangles. We generated synthetic networks, mimicking the diversity of cell-cell interaction patterns, and evaluated the applicability of the selected metrics to study topological features. Cells expressing wild-type E-cadherin and cancer-related mutants were used to validate our strategy. Specifically, A634V, R749W and P799R cancer-causing mutants present more disorganized spatial distribution when compared with wild-type cells. Moreover, P799R exhibited higher length and angle distortions and abnormal cytoskeletal organization, suggesting the formation of very dynamic and plastic cellular interactions. Hence, topological analysis of cell network diagrams is an effective tool to quantify changes in cell-cell interactions and, importantly, it can be applied to a myriad of processes, namely tissue morphogenesis and cancer.

[Role of cadherins in health and in developing breast cancer]

The review gives data on the structure of cadherin cell adhesion molecules, their role in the body's development and malignant tumor progression. It describes cadherins that are considered to play the most important role in the development of a tumor process: E-, P-, and N-cadherins that belong to type I classical cadhedrins and VE-cadhedrin that does to type II cadherins. Particular emphasis is placed on the signal mechanisms with involvement of cadherins and cadherin-related molecules, which are realized in the body in health and in tumor transformation of cells.

E-cadherin germline mutation carriers: clinical management and genetic implications

Hereditary diffuse gastric cancer is an autosomic dominant syndrome associated with E-cadherin protein (CDH1) gene germline mutations. Clinical criteria for genetic screening were revised in 2010 by the International Gastric Cancer Linkage Consortium at the Cambridge meeting. About 40 % of families fulfilling clinical criteria for this inherited disease present deleterious CDH1 germline mutations. Lobular breast cancer is a neoplastic condition associated with hereditary diffuse gastric cancer syndrome. E-cadherin constitutional mutations have been described in both settings, in gastric and breast cancers. The management of CDH1 asymptomatic mutation carriers requires a multidisciplinary approach; the only life-saving procedure is the prophylactic total gastrectomy after thorough genetic counselling. Several prophylactic gastrectomies have been performed to date; conversely, no prophylactic mastectomies have been described in CDH1 mutant carriers. However, the recent discovery of novel germline alterations in pedigree clustering only for lobular breast cancer opens up a new debate in the management of these individuals. In this critical review, we describe the clinical management of CDH1 germline mutant carriers providing specific recommendations for genetic counselling, clinical criteria, surveillance and/ or prophylactic surgery.

Quantification of mutant E-cadherin using bioimaging analysis of in situ fluorescence microscopy. A new approach to CDH1 missense variants

Missense mutations result in full-length proteins containing an amino acid substitution that can be neutral or deleterious, interfering with the normal conformation, localization, and function of a protein. A striking example is the presence of CDH1 (E-cadherin gene) germline missense variants in hereditary diffuse gastric cancer (HDGC), which represent a clinical burden for genetic counseling and surveillance of mutation carriers and their families. CDH1 missense variants can compromise not only the function of E-cadherin but also its expression pattern. Here, we propose a novel method to characterize E-cadherin signature in order to identify cases with E-cadherin deregulation and functional impairment. The strategy includes a bioimaging pipeline to quantify the expression level and characterize the distribution of the protein from in situ immunofluorescence images. The algorithm computes 1D (dimension intensity) radial and internuclear fluorescence profiles to generate expression outlines and 2D virtual cells representing a typical cell within the populations analyzed. Using this new approach, we verify that cells expressing mutant forms of E-cadherin display fluorescence profiles distinct from those of the wild-type cells. Mutant proteins showed a significantly decrease of fluorescence intensity at the membrane and often abnormal expression peaks in the cytoplasm, reflecting the underlying molecular mechanism of trafficking deregulation. Our results suggest employing this methodology as a complementary approach to evaluate the pathogenicity of E-cadherin missense variants. Moreover, it can be applied to a wide range of proteins and, more importantly, to diseases characterized by aberrant protein expression or trafficking deregulation.

Genomic profile analysis of diffuse-type gastric cancers

BACKGROUND

Stomach cancer is the third deadliest among all cancers worldwide. Although incidence of the intestinal-type gastric cancer has decreased, the incidence of diffuse-type is still increasing and its progression is notoriously aggressive. There is insufficient information on genome variations of diffuse-type gastric cancer because its cells are usually mixed with normal cells, and this low cellularity has made it difficult to analyze the genome.

RESULTS

We analyze whole genomes and corresponding exomes of diffuse-type gastric cancer, using matched tumor and normal samples from 14 diffuse-type and five intestinal-type gastric cancer patients. Somatic variations found in the diffuse-type gastric cancer are compared to those of the intestinal-type and to previously reported variants. We determine the average exonic somatic mutation rate of the two types. We find associated candidate driver genes, and identify seven novel somatic mutations in CDH1, which is a well-known gastric cancer-associated gene. Three-dimensional structure analysis of the mutated E-cadherin protein suggests that these new somatic mutations could cause significant functional perturbations of critical calcium-binding sites in the EC1-2 junction. Chromosomal instability analysis shows that the MDM2 gene is amplified. After thorough structural analysis, a novel fusion gene TSC2-RNF216 is identified, which may simultaneously disrupt tumor-suppressive pathways and activate tumorigenesis.

CONCLUSIONS

We report the genomic profile of diffuse-type gastric cancers including new somatic variations, a novel fusion gene, and amplification and deletion of certain chromosomal regions that contain oncogenes and tumor suppressors.

Identification and characterization of CDH1 germline variants in sporadic gastric cancer patients and in individuals at risk of gastric cancer

Objective

To screen and characterize germline variants for E-cadherin (CDH1) in non-hereditary gastric cancer (GC) patients and in subjects at risk of GC.

Methods

59 GCs, 59 first degree relatives (FDRs) of GC, 20 autoimmune metaplastic atrophic gastritis (AMAGs) and 52 blood donors (BDs) were analyzed for CDH1 by direct sequencing, structural modelling and bioinformatics. Functional impact on splicing was assessed for intronic mutations. E-cadherin/β-catenin immunohistochemical staining and E-cadherin mRNA quantification using RT-PCR were performed.

Results

In GCs, 4 missense variants (p.G274S; p.A298T; p.T470I; p.A592T), 1 mutation in the 5′UTR (−71C>G) and 1 mutation in the intronic IVS12 (c.1937-13T>C) region were found. First pathogenic effect of p.A298T mutation was predicted by protein 3D modelling. The novel p.G274S mutation showed a no clear functional significance. Moreover, first, intronic IVS12 (c.1937-13T>C) mutation was demonstrated to lead to an aberrant CDH1 transcript with exon 11 deletion. This mutation was found in 2 GCs and in 1 BD. In FDRs, we identified 4 variants: the polymorphic (p.A592T) and 3 mutations in untranslated regions with unidentified functional role except for the 5′UTR (−54G>C) that had been found to decrease CDH1 transcription. In AMAGs, we detected 2 alterations: 1 missense (p.A592T) and 1 novel variant (IVS1 (c.48+7C>T)) without effect on CDH1 splicing. Several silent and polymorphic substitutions were found in all the groups studied.

Conclusions

Overall our study improves upon the current characterization of CDH1 mutations and their functional role in GC and in individuals at risk of GC. Mutations found in untranslated regions and data on splicing effects deserve a particular attention like associated with a reduced E-cadherin amount. The utility of CDH1 screening, in addition to the identification of other risk factors, could be useful for the early detection of GC in subjects at risk (i.e. FDRs and AMAGs), and warrants further study.

Identification of germline mutations in the cancer predisposing gene CDH1 in patients with orofacial clefts

Orofacial clefts (OFC) are among the most common birth defects worldwide. The etiology of non-syndromic OFC is still largely unknown. During embryonic development, the cell adhesion molecule E-cadherin, encoded by CDH1, is highly expressed in the median edge epithelium of the palate. Furthermore, in multiple families with CDH1 mutations, OFC cases are observed. To determine whether CDH1 is a causative gene for non-syndromic OFC and to assess whether CDH1 mutation screening in non-syndromic OFC patients enables identification of families at risk of cancer, direct sequencing of the full coding sequence of CDH1 was performed in a cohort of 81 children with non-syndromic OFC. Eleven children had heterozygous CDH1 sequence variants, 5 cases with 4 distinct missense mutations and 8 cases with 4 intronic variants. Using a combination of in silico predictions and in vitro functional assays, three missense mutations in four non-syndromic OFC patients were predicted to be damaging to E-cadherin protein function. The intronic variants including one tested in an in vitro assay appeared to be benign, showing no influence on splicing. Functionally relevant heterozygous CDH1 missense mutations were found in 4 out of 81 (5%) patients with non-syndromic OFC. This finding opens a new pathway to reveal the molecular basis of non-syndromic OFC. Cancer risk among carriers of these mutations needs to be defined.

The importance of E-cadherin binding partners to evaluate the pathogenicity of E-cadherin missense mutations associated to HDGC

In hereditary diffuse gastric cancer (HDGC), CDH1 germline gene alterations are causative events in 30% of the cases. In 20% of HDGC families, CDH1 germline mutations are of the missense type and the mutation carriers constitute a problem in terms of genetic counseling and surveillance. To access the pathogenic relevance of missense mutations, we have previously developed an in vitro method to functionally characterize them. Pathogenic E-cadherin missense mutants fail to aggregate and become more invasive, in comparison with cells expressing the wild-type (WT) protein. Herein, our aim was to develop a complementary method to unravel the pathogenic significance of E-cadherin missense mutations. We used cells stably expressing WT E-cadherin and seven HDGC-associated mutations (five intracellular and two extracellular) and studied by proximity ligation assays (PLA) how these mutants bind to fundamental regulators of E-cadherin function and trafficking. We focused our attention on the interaction with: p120, β-catenin, PIPKIγ and Hakai. We showed that cytoplasmic E-cadherin mutations affect the interaction of one or more binding partners, compromising the E-cadherin stability at the plasma membrane and likely affecting the adhesion complex competence. In the present work, we demonstrated that the study of the interplay between E-cadherin and its binding partners, using PLA, is an easy, rapid, quantitative and highly reproducible technique that can be applied in routine labs to verify the pathogenicity of E-cadherin missense mutants for HDGC diagnosis, especially those located in the intracellular domain of the protein.

E-cadherin dysfunction in gastric cancer--cellular consequences, clinical applications and open questions

E-cadherin plays a major role in cell-cell adhesion and inactivating germline mutations in its encoding gene predispose to hereditary diffuse gastric cancer. Evidence indicates that aside from its recognized role in early tumourigenesis, E-cadherin is also pivotal for tumour progression, including invasion and metastization. Herein, we discuss E-cadherin alterations found in a cancer context, associated cellular effects and signalling pathways, and we raise new key questions that will impact in the management of GC patients and families.

Epithelial E- and P-cadherins: role and clinical significance in cancer

E-cadherin and P-cadherin are major contributors to cell-cell adhesion in epithelial tissues, playing pivotal roles in important morphogenetic and differentiation processes during development, and in maintaining integrity and homeostasis in adult tissues. It is now generally accepted that alterations in these two molecules are observed during tumour progression of most carcinomas. Genetic or epigenetic alterations in E- and P-cadherin-encoding genes (CDH1 and CDH3, respectively), or alterations in their proteins expression, often result in tissue disorder, cellular de-differentiation, increased invasiveness of tumour cells and ultimately in metastasis. In this review, we will discuss the major properties of E- and P-cadherin molecules, its regulation in normal tissue, and their alterations and role in cancer, with a specific focus on gastric and breast cancer models.

E-cadherin destabilization accounts for the pathogenicity of missense mutations in hereditary diffuse gastric cancer

E-cadherin is critical for the maintenance of tissue architecture due to its role in cell-cell adhesion. E-cadherin mutations are the genetic cause of Hereditary Diffuse Gastric Cancer (HDGC) and missense mutations represent a clinical burden, due to the uncertainty of their pathogenic role. In vitro and in vivo, most mutations lead to loss-of-function, although the causal factor is unknown for the majority. We hypothesized that destabilization could account for the pathogenicity of E-cadherin missense mutations in HDGC, and tested our hypothesis using in silico and in vitro tools. FoldX algorithm was used to calculate the impact of each mutation in E-cadherin native-state stability, and the analysis was complemented with evolutionary conservation, by SIFT. Interestingly, HDGC patients harbouring germline E-cadherin destabilizing mutants present a younger age at diagnosis or death, suggesting that the loss of native-state stability of E-cadherin accounts for the disease phenotype. To elucidate the biological relevance of E-cadherin destabilization in HDGC, we investigated a group of newly identified HDGC-associated mutations (E185V, S232C and L583R), of which L583R is predicted to be destabilizing. We show that this mutation is not functional in vitro, exhibits shorter half-life and is unable to mature, due to premature proteasome-dependent degradation, a phenotype reverted by stabilization with the artificial mutation L583I (structurally tolerated). Herein we report E-cadherin structural models suitable to predict the impact of the majority of cancer-associated missense mutations and we show that E-cadherin destabilization leads to loss-of-function in vitro and increased pathogenicity in vivo.

PIP kinases from the cell membrane to the nucleus

Phosphatidylinositol 4,5-bisphosphate (PIP(2)) is a membrane bound lipid molecule with capabilities to affect a wide array of signaling pathways to regulate very different cellular processes. PIP(2) is used as a precursor to generate the second messengers PIP(3), DAG and IP(3), indispensable molecules for signaling events generated by membrane receptors. However, PIP(2) can also directly regulate a vast array of proteins and is emerging as a crucial messenger with the potential to distinctly modulate biological processes critical for both normal and pathogenic cell physiology. PIP(2) directly associates with effector proteins via unique phosphoinositide binding domains, altering their localization and/or enzymatic activity. The spatial and temporal generation of PIP(2) synthesized by the phosphatidylinositol phosphate kinases (PIPKs) tightly regulates the activation of receptor signaling pathways, endocytosis and vesicle trafficking, cell polarity, focal adhesion dynamics, actin assembly and 3' mRNA processing. Here we discuss our current understanding of PIPKs in the regulation of cellular processes from the plasma membrane to the nucleus.

The tumor ecosystem regulates the roads for invasion and metastasis

Invasive cancer cells traffic from the primary tumor ecosystem to distant metastatic sites. Experimental data are reviewed with a focus on cross-signaling between cancer cells and host cells such as myofibroblasts and mesenchymal stem cells. Invasion-associated cellular activities, namely vesicle exocytosis and epithelial to mesenchymal transition, depend on complex networks of signal transduction pathways including activation of tyrosine kinases, the Rab, Rac and Rho family of small GTPases and cadherin signaling. As clinical validation, some cell types or molecules implicated in invasion-associated activities may serve as prognostic/predictive biomarker or as target for patient-tailored therapy.

ADP-ribosylation factor 6 mediates E-cadherin recovery by chemical chaperones

E-cadherin plays a powerful tumor suppressor role. Germline E-cadherin mutations justify 30% of Hereditary Diffuse Gastric Cancer (HDGC) and missense mutations are found in 30% of these families. We found possible to restore in vitro mutant E-cadherin associated to HDGC syndrome by using Chemical Chaperones (CCs). Herein, our aim was to disclose the molecular mechanisms underlying the CCs effects in E-cadherin regulation. Using cells stably expressing WT E-cadherin or two HDGC-associated missense mutations, we show that upon DMSO treatment, not only mutant E-cadherin is restored and stabilized at the plasma membrane (PM), but also Arf6 and PIPKIγ expressions are altered. We show that modulation of Arf6 expression partially mimics the effect of CCs, suggesting that the cellular effects observed upon CCs treatment are mediated by Arf6. Further, we show that E-cadherin expression recovery is specifically linked to Arf6 due to its role on endocytosis and recycling pathways. Finally, we demonstrated that, as DMSO, several others CCs are able to modulate the trafficking machinery through an Arf6 dependent mechanism. Interestingly, the more effective compounds in E-cadherin recovery to PM are those that simultaneously inhibit Arf6 and stimulate PIPKIγ expression and binding to E-cadherin. Here, we present the first evidence of a direct influence of CCs in cellular trafficking machinery and we show that this effect is of crucial importance in the context of juxtamembrane E-cadherin missense mutations associated to HDGC. We propose that this influence should be taken into account when exploring the therapeutic potential of this type of chemicals in genetic diseases associated to protein-misfolding.

PIPKIγ regulates β-catenin transcriptional activity downstream of growth factor receptor signaling

Increased β-catenin transcriptional activity downstream of the Wnt/Wingless signaling pathway has been observed in many human tumors, most notably colorectal carcinomas. However, β-catenin activation is also observed in many human malignancies with no observable Wnt activity. Wnt-independent pathways that activate β-catenin remain undefined, yet have the potential to play a significant role during tumorigenesis. Here, we report that phosphotidylinositol phosphate kinase Iγ (PIPKIγ), an enzyme that generates phosphoinositide messengers in vivo, directly associates with β-catenin and increases β-catenin activity downstream of growth factor stimulation. PIPKIγ expression and kinase activity enhance β-catenin phosphorylation on residues that promote nuclear importation and transcriptional activity. Lastly, we show that β-catenin is required for PIPKIγ-dependent increased cell proliferation. These results reveal a novel mechanism in which PIPKIγ expression and catalytic activity enhance β-catenin nuclear translocation and expression of its target genes to promote tumorigenic phenotypes.

Germline mutations in CDH1 are infrequent in women with early-onset or familial lobular breast cancers

BACKGROUND

Germline mutations in CDH1 are associated with hereditary diffuse gastric cancer; lobular breast cancer also occurs excessively in families with such condition.

METHOD

To determine if CDH1 is a susceptibility gene for lobular breast cancer in women without a family history of diffuse gastric cancer, germline DNA was analysed for the presence of CDH1 mutations in 318 women with lobular breast cancer who were diagnosed before the age of 45 years or had a family history of breast cancer and were not known, or known not, to be carriers of germline mutations in BRCA1 or BRCA2. Cases were ascertained through breast cancer registries and high-risk cancer genetic clinics (Breast Cancer Family Registry, the kConFab and a consortium of breast cancer genetics clinics in the United States and Spain). Additionally, Multiplex Ligation-dependent Probe Amplification was performed for 134 cases to detect large deletions.

RESULTS

No truncating mutations and no large deletions were detected. Six non-synonymous variants were found in seven families. Four (4/318 or 1.3%) are considered to be potentially pathogenic through in vitro and in silico analysis.

CONCLUSION

Potentially pathogenic germline CDH1 mutations in women with early-onset or familial lobular breast cancer are at most infrequent.

De novo expression of CD44 variants in sporadic and hereditary gastric cancer

CD44 is the major ubiquitously expressed cell surface receptor for hyaluronate. The CD44 gene encodes several protein isoforms due to extensive alternative splicing and post-translational modifications. Some of these CD44 variable isoforms have been foreseen as key players in malignant transformation and their expression is highly restricted and highly specific, unlike the canonical CD44 standard isoform. In this study, we aimed at dissecting the mRNA splicing pattern of CD44 in normal stomach and gastric cancer (GC) cell lines (n=9) using cloning and quantitative mRNA amplification assays. Moreover, we assessed the RNA levels and protein expression pattern of relevant splicing forms in distinct premalignant and malignant gastric lesions (sporadic (n=43) and hereditary (n=3) forms) using real-time RT-PCR and immunohistochemistry. We also explored the association of CD44 and E-cadherin expression by immunohistochemistry, as E-cadherin has a pivotal functional role in GC. We established the pattern of CD44 variant forms in normal stomach and gastric malignancy. We observed that although exon v6-containing isoforms were rarely expressed in normal gastric mucosa, they became increasingly expressed both in gastric premalignant (hyperplastic polyps, complete and incomplete intestinal metaplasia, low- and high-grade dysplasia) and malignant lesions (cell lines derived from GCs, primary sporadic GCs and hereditary diffuse GCs (HDGCs)). Moreover, we verified that whenever E-cadherin expression was absent, exon v6-containing CD44 isoforms were overexpressed. The lack of expression of CD44 isoforms containing exon v6 in the surface and foveolar epithelia of normal stomach and, its de novo expression in premalignant, as well as in sporadic and hereditary malignant lesions of the stomach, pinpoint CD44 v6-containing isoforms as potential biomarkers for early transformation of the gastric mucosa. Further, our results raise the hypothesis of using CD44v6 as a marker of early invasive intramucosal carcinoma in HDGC CDH1 mutation carriers that lack CDH1 expression in their tumors.

Phosphoinositide signalling in cancer: beyond PI3K and PTEN

There are numerous studies that suggest multiple links between the cellular phosphoinositide system and cancer. As key roles in cancer have been established for PI3K and PTEN - enzymes that regulate the levels of phosphatidylinositol-3,4,5-trisphosphate - compounds targeting this pathway are entering the clinic at a rapid pace. Several other phosphoinositide-modifying enzymes, including phosphoinositide kinases, phosphatases and phospholipase C enzymes, have been implicated in the generation and progression of tumours. Studies of these enzymes are providing new insights into the mechanisms and the extent of their involvement in cancer, highlighting new potential targets for therapeutic intervention.

Advanced gastric cancer--slow but steady progress

Progress in gastric cancer has been slow, but steady. Historically, patients commonly presented with significant disease related co-morbidity and received treatment of marginal benefit but unfortunately associated with significant toxicity. Today there is no universally accepted reference standard chemotherapy for this disease. However, there is reason for optimism. Meta-analyses of randomized trials have shown a benefit for first-line combination chemotherapy. Current three drug chemotherapy regimens remain toxic, though perhaps less so than previously, and can result in a small but significant survival advantage in carefully chosen patients. Incremental improvements have been observed in both treatment-related toxicity and survival after first-line therapy. More patients are candidates for chemotherapy beyond progression with first-line therapy and response rates with second-line regimens are similar to those seen in other solid tumor malignancies. Although there is no randomized data to support its use second-line treatment should be considered in appropriate patients. Even before the integration of targeted therapies in the treatment of gastric cancer, it was evident that survival for more than 2 years is possible in a subset of patients and large retrospective studies have highlighted clinicopathologic factors associated with improved survival. Presently, with the addition of targeted therapy, especially anti-angiogenic and anti-Her2 therapy, and a better understanding of the biology of the disease, perhaps a sense of optimism should indeed suppress the nihilism commonly associated with this disease.

Schistosoma haematobium total antigen induces increased proliferation, migration and invasion, and decreases apoptosis of normal epithelial cells

Schistosome worms are blood-dwelling flukes that cause chronic infection in more than 200 million people and are thought to be responsible for 500,000 deaths annually. During infection with Schistosoma haematobium, eggs are deposited in the mucosa and submucosa of the bladder and lower ureters. Squamous cell carcinoma (SCC) of the bladder is a long-term sequela of chronic infection. The mechanisms underlying the association between S. haematobium and SCC of the bladder are largely unknown, with all reports to date exclusively demonstrating epidemiological evidence linking S. haematobium infection with SCC of the bladder. We hypothesised that the parasite antigens might induce alterations in epithelial cells towards cancer. For this we used Chinese Hamster Ovary (CHO) cells and treated the cells in culture with S. haematobium total antigen (Sh). Our results showed increased proliferation, increased S-phase and decreased apoptosis, as well as down-regulation of tumour suppressor p27 and up-regulation of anti-apoptotic molecule Bcl-2 in Sh-treated cells compared with controls. We also found increased migration and invasion. To our knowledge, this is the first report demonstrating alterations of normal epithelial cells as a direct effect of S. haematobium antigens.

E-cadherin mutations and cell motility: a genotype-phenotype correlation

E-cadherin has a determinant role in tumour progression, acting as an invasion and metastasis suppressor. Germline mutations of E-cadherin gene (CDH1) occur in 30% of families with Hereditary Diffuse Gastric Cancer (HDGC); of these 23% are missense mutations. The CDH1 missense mutations described to date span the entire gene and some lead to significant functional consequences. In this study, we explored the hypothesis that mutations affecting different E-cadherin protein domains have distinct effects on cell motility. To accomplish our objective we characterized the effect of eleven HDGC CDH1 germline missense mutations (T118R, L214P, G239R, A298T, T340A, P373L, R749W, E757K, E781D, P799R and V832M) on cell motility. Further, we studied their effect on the activation of signalling pathways known to be relevant for cell motility such as the EGFR, Src kinase and MAPKs. CDH1 mutations localized on the extracellular and juxtamembrane domains, both affecting the integrity of the extracellular domain, led to increased cell motility accompanied by increased EGFR activation. Moreover, we observed that cells expressing extracellular mutants exhibit increased activation of Src kinase and p38 MAPK. Our results allowed the identification of the E-cadherin domains pivotal for cell motility, further demonstrated a genotype-phenotype correlation, and defined a subset of HDGC cases which may benefit from EGFR inhibitors.

Out, in and back again: PtdIns(4,5)P(2) regulates cadherin trafficking in epithelial morphogenesis

The morphogenesis of epithelial cells in the tissue microenvironment depends on the regulation of the forces and structures that keep cells in contact with their neighbours. The formation of cell-cell contacts is integral to the establishment and maintenance of epithelial morphogenesis. In epithelial tissues, the misregulation of the signalling pathways that control epithelial polarization induces migratory and invasive cellular phenotypes. Many cellular processes influence cadherin targeting and function, including exocytosis, endocytosis and recycling. However, the localized generation of the lipid messenger PtdIns(4,5)P(2) is emerging as a fundamental signal controlling all of these processes. The PtdIns(4,5)P(2)-generating enzymes, PIPKs (phosphatidylinositol phosphate kinases) are therefore integral to these pathways. By the spatial and temporal targeting of PIPKs via the actions of its functional protein associates, PtdIns(4,5)P(2) is generated at discrete cellular locales to provide the cadherin-trafficking machinery with its required lipid messenger. In the present review, we discuss the involvement of PtdIns(4,5)P(2) and the PIPKs in the regulation of the E-cadherin (epithelial cadherin) exocytic and endocytic machinery, the modulation of actin structures at sites of adhesion, and the direction of cellular pathways which determine the fate of E-cadherin and cell-cell junctions. Recent work is also described that has defined phosphoinositide-mediated E-cadherin regulatory pathways by the use of organismal models.

Cadherin-catenin adhesion system and mucin expression: a comparison between young and older patients with gastric carcinoma

BACKGROUND

Young patients are thought to develop gastric carcinomas with a molecular genetic profile that is distinct from that of gastric carcinomas occurring at a later age. The aim of this study was to compare the clinicopathological features and expression patterns of the markers E-cadherin and beta-catenin, and mucins (MUC1, MUC2, MUC5AC, and MUC6) in young and older patients.

METHODS

The clinicopathological features and overall survival data of 62 young patients (age <or=40 years) with gastric cancer were retrospectively reviewed from hospital records and compared with the data for 453 older patients (age >40 years). A tissue microarray method and immunohistochemistry were used in order to analyze marker expression in paraffin-embedded tissue blocks obtained from both groups.

RESULTS

The young group presented a higher percentage of diffuse-type tumors in comparison to the older group (P<0.01). The rates of positivity for E-cadherin and beta-catenin membranous expression patterns and mucin (MUC2, MUC5AC and MUC6) positivity were higher in the young group (P<0.01). Although young patients showed a lower frequency of alterations in marker expression and had significantly better survival rates than the older patients, neither age nor the marker expression pattern were found to be independent prognostic factors of survival. Only stage, tumor size, and tumor location persisted as prognostic factors for patients with gastric cancer.

CONCLUSION

Biological markers of cellular adhesion and gastric differentiation were differently expressed in young and older patients. Our findings support the hypothesis that young patients develop carcinomas with a different genetic pathway compared to the pathway of tumors occurring at a later age, and we suggest further investigations to assess the prognostic relevance of the markers to specific subgroups.

{alpha}-Catenin mediates initial E-cadherin-dependent cell-cell recognition and subsequent bond strengthening

alpha-Catenin is essential in cadherin-mediated epithelium development and maintenance of tissues and in cancer progression and metastasis. However, recent studies question the conventional wisdom that alpha-catenin directly bridges the cadherin adhesion complex to the actin cytoskeleton. Therefore, whether alpha-catenin plays a direct role in cadherin-dependent cell adhesion is unknown. Here, single-molecule force spectroscopy measurements in cells depleted of alpha-catenin or expressing the hereditary diffuse gastric cancer associated V832M E-cadherin germ-line missense mutation show that alpha-catenin plays a critical role in cadherin-mediated intercellular recognition and subsequent multibond formation within the first 300 ms of cell contact. At short contact times, alpha-catenin mediates a 30% stronger interaction between apposing E-cadherin molecules than when it cannot bind the E-cadherin-beta-catenin complex. As contact time between cells increases, alpha-catenin is essential for the strengthening of the first intercellular cadherin bond and for the ensuing formation of additional bonds between the cells, all without the intervention of actin. These results suggest that a critical decision to form an adhesion complex between 2 cells occurs within an extremely short time span and at a single-molecule level and identify a previously unappreciated role for alpha-catenin in these processes.

Frequent accumulation of nuclear E-cadherin and alterations in the Wnt signaling pathway in esophageal squamous cell carcinomas

Esophageal squamous cell carcinoma is frequently associated with poor prognosis, as a result of high levels of lymph node metastasis. So far, very few genetic abnormalities have been associated with this disease, and its molecular etiology remains largely unknown. To assess whether the Wnt pathway contributes to esophageal squamous cell carcinoma, we characterized the expression and subcellular localization of the key Wnt signaling components in all 30 cases of esophageal squamous cell carcinomas analyzed. We found abnormal expression and/or localization in glycogen synthase kinase-3 alpha/beta (34%), Axin2 (48%), alpha-catenin (31%), MYC (73%) and cyclin D1 in 46% of cases. Only 13% of tumors showed nuclear accumulation of beta-catenin. By contrast, 60% showed nuclear expression of E-cadherin using an antibody that recognizes the cytoplasmic domain of E-cadherin. When the same tumors were stained with antibody raised against the extracellular domain of E-cadherin, the expression was lost. A direct correlation was found between nuclear E-cadherin and the increased nuclear cyclin D1, one of the AP-1 target genes in these tumors. By transfection experiments, the cytoplasmic portion of E-cadherin was found to activate the AP-1 transcription factor pathway and induced cyclin D1 promoter activity, but beta-catenin/Tcf transcription activity was unaffected. Nuclear expression of E-cadherin was also detected in tumors other than squamous cell carcinoma, including pancreatic and colon cancers, albeit at lower frequency. Nuclear accumulation of a portion of E-cadherin in esophageal squamous cell carcinoma and the other types of tumors indicates that, in addition to the previously implicated tumor suppressor activity of E-cadherin, modified forms of this glycoprotein might also play a role in growth promotion.

Evidence that the V832M E-cadherin germ-line missense mutation does not influence the affinity of alpha -catenin for the cadherin/catenin complex

Mutations in E-cadherin are associated with a number of diseases, and have been shown to contribute to disease progression. In particular, 50% of hereditary diffuse gastric cancer cases have inactivating mutations in the E-cadherin gene. An interesting mutation near the beta-catenin-binding site on the cytoplasmic domain of E-cadherin (V832M) was recently reported that produces full-length protein, but exhibits decreased binding of alpha -catenin to the cadherin/catenin complex. The study was done by transfecting mutant E-cadherin into Chinese hamster ovary fibroblast cells. Here we show that the previously reported characteristics of this mutation do not apply to human epithelial cells expressing this mutant protein and suggest that the mechanism whereby the V832M mutation in human E-cadherin promotes gastric cancer is not yet understood.

Gastric cancer: an update

Gastric cancer is an aggressive malignancy, which, if metastatic or unresectable, is incurable. However, with metastatic or unresectable disease, patients receive a palliative benefit from chemotherapy. Although the understanding of the biology of this disease is increasing, the development of biologically targeted therapies for gastric cancer has been limited. Cytotoxic therapy remains the standard approach, and although there is agreement on the active agents and active combination chemotherapy regimens, consensus on the standard or reference regimen is lacking. This article reviews the pathophysiology of this disease, placing it in the context of its epidemiology, and the current advances in the treatment of this disease.

Type I gamma phosphatidylinositol phosphate kinase modulates adherens junction and E-cadherin trafficking via a direct interaction with mu 1B adaptin

Assembly of E-cadherin–based adherens junctions (AJ) is obligatory for establishment of polarized epithelia and plays a key role in repressing the invasiveness of many carcinomas. Here we show that type Iγ phosphatidylinositol phosphate kinase (PIPKIγ) directly binds to E-cadherin and modulates E-cadherin trafficking. PIPKIγ also interacts with the μ subunits of clathrin adaptor protein (AP) complexes and acts as a signalling scaffold that links AP complexes to E-cadherin. Depletion of PIPKIγ or disruption of PIPKIγ binding to either E-cadherin or AP complexes results in defects in E-cadherin transport and blocks AJ assembly. An E-cadherin germline mutation that loses PIPKIγ binding and shows disrupted basolateral membrane targeting no longer forms AJs and leads to hereditary gastric cancers. These combined results reveal a novel mechanism where PIPKIγ serves as both a scaffold, which links E-cadherin to AP complexes and the trafficking machinery, and a regulator of trafficking events via the spatial generation of phosphatidylinositol-4,5-bisphosphate.

EGFR regulates RhoA-GTP dependent cell motility in E-cadherin mutant cells

Gastric cancer associated E-cadherin germline missense mutations lead to significant functional consequences, in both the structural and signalling properties of the protein. In this study, we have characterized the effect of four E-cadherin germline missense mutations (T340A, A634V, P799R and V832M) in the interaction with the epidermal growth factor receptor (EGFR). We challenged the hypothesis that E-cadherin mutations perturb its ability to bind to EGFR, leading to constitutional activation of the EGFR, triggering activation of downstream effectors. We verified that missense mutations localized in the extracellular domain of the protein (T340A and A634V) exhibited reduced stability of the EGFR/E-cadherin heterodimers in contrast to germline mutations localized at the cytoplasmatic domain of the protein (P799R and V832M). We observed that cells expressing E-cadherin extracellular mutants displayed increased levels of phosphorylated EGFR upon ligand stimulation, when compared with cells expressing wild-type E-cadherin or intracellular mutants. We showed that upon treatment of E-cadherin extracellular mutant cells with the EGFR inhibitor, the increase of RhoA activation is abrogated and accompanied by decreased migratory behaviour, supporting the idea that Rho-like proteins are EGFR downstream effectors. Our results bring new insights into the understanding of the distinct in vitro behaviours observed for E-cadherin missense mutations localized in different domains of the protein. Furthermore, we demonstrate that E-cadherin-dependent EGFR activation contributes to enhanced cell motility, in a mechanism involving RhoA activation.

Characterization of the P373L E-cadherin germline missense mutation and implication for clinical management

AIM

Hereditary diffuse gastric cancer (HDGC) is a cancer susceptibility syndrome caused by E-cadherin germline mutations. One-third of these mutations are of the missense type, representing a burden in genetic counselling. A new germline missense mutation (P373L) was recently identified in a HDGC Italian family. The present work aimed at addressing the disease-causative nature of the P373L mutant.

METHODS

Assessment of the P373L mutation effect was based on cell aggregation and invasion assays. LOH analysis at the E-cadherin locus, search for somatic E-cadherin mutations and for promoter hypermethylation were performed to identify the mechanism of inactivation of the E-cadherin wild-type allele in the tumour.

RESULTS

In vitro the P373L germline mutation impaired the E-cadherin functions. E-cadherin promoter hypermethylation was observed in the tumour of the P373L mutation carrier.

CONCLUSION

We conclude that the combination of clinical, in vitro and molecular genetic data is helpful for establishing an accurate analysis of HDGC-associated CDH1 germline missense mutations and subsequently for appropriate clinical management of asymptomatic mutation carriers.

Hereditary diffuse gastric cancer and E-cadherin: description of the first germline mutation in an Italian family

AIMS

Germline mutation of the E-cadherin gene (CDH1) accounts for the Hereditary Diffuse Gastric Cancer (HDGC) syndrome. Fourteen pedigrees with Diffuse Gastric Cancer that fulfilled the International Gastric Cancer Linkage Consortium (IGCLC) criteria were selected and screened for CDH1 germline mutations.

METHODS

The entire coding region of the CDH1 gene and all intron-exon boundaries were analyzed by direct sequencing in the 14 families fulfilling the IGCLC criteria. E-cadherin immunohistochemical expression was evaluated on tumour as well as normal formalin-fixed paraffin embedded tissues.

RESULTS

A novel germline missense mutation was found. It was a single C-->T substitution in exon 8, resulting in a transition of CCG-->CTG (C1118T; Pro373Leu) demonstrated in the proband and her brother. At immunohistochemical analysis, the staining intensity was reduced and considered weakly positive (15%).

CONCLUSIONS

The first CDH1 germline mutation of an Italian family is herein reported. The present missense mutation has never been described so far.

Helicobacter pylori induces gastric epithelial cell invasion in a c-Met and type IV secretion system-dependent manner

Helicobacter pylori interacts with gastric epithelial cells, activating signaling pathways important for carcinogenesis. In this study we examined the role of H. pylori on cell invasion and the molecular mechanisms underlying this process. The relevance of H. pylori cag pathogenicity island-encoded type IV secretion system (T4SS), CagA, and VacA for cell invasion was also investigated. We found that H. pylori induces AGS cell invasion in collagen type I and in Matrigel invasion assays. H. pylori-induced cell invasion requires the direct contact between bacteria and cancer cells. H. pylori-mediated cell invasion was dependent on the activation of the c-Met receptor and on increased MMP-2 and MMP-9 activity. The abrogation of the c-Met receptor using the specific NK4 inhibitor or the silencing of c-Met expression with small interference RNA suppressed both cell invasion and MMP activity. Studies with different H. pylori strains revealed that cell invasion, c-Met tyrosine phosphorylation, and increased MMP-2 and MMP-9 activity were all dependent on the presence of a functional bacterial T4SS, but not on VacA cytotoxicity. Our findings demonstrate that H. pylori strains with a functional T4SS stimulate gastric epithelial cell invasion through a c-Met-dependent signaling pathway that comprises an increase in MMP-2 and MMP-9 activity.

A model to infer the pathogenic significance of CDH1 germline missense variants

Germline mutations of the E-cadherin gene (CDH1) are involved in the tumorigenesis of hereditary diffuse gastric cancer (HDGC). Recent studies have highlighted the lifesaving potential of total prophylactic gastrectomy for CDH1 germline mutation carriers. In this regard, CDH1 germline mutations of the missense type represent a clinical burden in genetic counseling, as their pathogenic relevance is not straightforward. In this work, we have outlined a possible multivariate approach to infer the significance of such variants. We reviewed all HDGC-associated E-cadherin germline missense mutations reported to date. The information collected included: co-segregation of the mutation within pedigrees, frequency in healthy population control, recurrence in independent families, and functional in vitro and in silico data. We used the neighbor-joining method to group mutations according to the collected information and assessed the robustness of mutation clusters with a bootstrap test. CDH1 germline missense variants were classified according to the parameters defined in the multivariate analysis. This analysis allowed the distribution of the variants into two distinct groups: neutral variants vs mutations. The model described in this study provides an important tool that can ultimately improve the genetic counseling offered to the carriers of the germline CDH1 missense variants.

Genetics of hereditary diffuse gastric cancer: progress and future challenges

Hereditary diffuse gastric cancer (HDGC) is a rare cancer susceptibility syndrome. One third of HDGC syndrome families carry germline mutations of the E-cadherin gene. Owing to the limitation of the current endoscopic screening techniques and since no chemoprevention is yet available, total prophylactic gastrectomy is the only option offered to carriers of inactivating mutations in genetic counseling. In this regard, 30% of the E-cadherin germline mutations reported to date are of the missense type, and since their pathogenic significance is not straightforward, the management of carriers of such mutations is suboptimal. In the absence of definitive clinical evidence, functional in vitro studies together with in silico analysis have been used to infer the pathogenic significance of germline missense mutations. Since most of the HDGC families reported to date are negative for E-cadherin germline mutations, the identification of alternative genes underlying the tumorigenesis of diffuse gastric has become an important target for research.

Genetics, pathology, and clinics of familial gastric cancer

Gastric cancer is relatively common worldwide, mainly in its sporadic form, but familial aggregation of the disease may be seen in approximately 10% of the cases. This suggests a genetic cause for the cancer in those families that has not been identified in most cases. Despite all efforts to determine its genetic basis, a single syndrome has been characterized-the hereditary diffuse gastric cancer (HDGC)-which is specifically associated with CDH1 (E-cadherin) germline mutations in one third of the families. The other two thirds and all the gastric cancer families not fulfilling the HDGC criteria remain without molecular diagnosis. In this article we review the state of the art of familial gastric cancer regarding the molecular aspects, the clinical criteria, the pathology features, and the management recommendations described so far to be associated with this cancer disease.

E-cadherin missense mutations, associated with hereditary diffuse gastric cancer (HDGC) syndrome, display distinct invasive behaviors and genetic interactions with the Wnt and Notch pathways in Drosophila epithelia

Germline mutations in the human E-cadherin (hEcad) gene, CDH1, are initiating events in cases of human hereditary diffuse gastric cancer (HDGC) indicating that hEcad is a tumor suppressor. Among the hEcad mutations identified so far, some are missense, but the pathological relevance of these missense mutants is still unclear. In vitro assays show that missense mutations result in full-length hEcad molecules that retain some distinct biological activity, but in vivo functional studies in animal models are still lacking. Here we verify the potential of a Drosophila model to in vivo characterize the functional consequences of HDGC-associated germline missense mutations and to identify signaling pathways affected by these mutations. To this end, we have generated transgenic fly strains expressing the wild-type hEcad gene or its missense mutations. Similar to the fly Ecad, expression of wild-type hEcad and missense forms in fly epithelia resulted in their localization to the subapical region. In addition, we verify a genotype-phenotype correlation associated to the specific domain affected by the mutations, because cells expressing normal or missense mutant hEcad display different migratory and invasive behaviors in fly epithelia. We show that some of these effects might be mediated through hEcad interacting with the endogenous fly ss-catenin, Armadillo, thus interfering with the Wnt signaling pathway. Therefore, the use of this simple in vivo system will contribute to characterize the effects that missense hEcad have on cell behavior in a tissue environment, and might help to understand their significance in gastric cancer onset.

Hereditary diffuse gastric cancer: diagnosis and management

Hereditary diffuse gastric cancer (HDGC) is a familial cancer syndrome defined by germline mutation of the E-cadherin gene (CDH-1). The cumulative risk for advanced gastric cancer in HDGC is 67% in men and 83% in women by 80 years of age. Early HDGC is characterized by multiple microscopic foci of intramucosal signet-ring cell carcinoma. The time to progression of these foci appears to be variable and currently is not predictable--the carcinoma foci may remain confined to the mucosa for many years. The management options for mutation carriers include prophylactic gastrectomy or surveillance gastroscopy. The only extensive published surveillance experience used chromogastroscopy, which detected early HDGC foci not visible on white-light endoscopy. The use of new techniques such as confocal microscopy, spectroscopy, or autofluorescence may prove useful, but have not been studied in HDGC. In patients up to 20 years of age, the risk for gastric cancer is less than 1%; this risk is outweighed by the mortality and morbidity associated with total gastrectomy. It is therefore recommended that genetic testing should occur at 16 years of age and that annual surveillance chromogastroscopy also should begin at age 16 in identified CDH-1 mutation carriers. After 20 years of age, delaying prophylactic gastrectomy carries significant risk, particularly if the alternative is surveillance by white-light gastroscopy. Surveillance chromogastroscopy (Congo red/methylene blue technique) should be considered for individuals younger than 20 years and patients unwilling to undergo prophylactic gastrectomy. Sufficient evidence for an increased risk for lobular breast cancer in CDH-1 carriers exists to justify breast screening in female carriers older than 35 years of age, however, evidence is insufficient to recommend prophylactic mastectomy.

Characterization of a recurrent germ line mutation of the E-cadherin gene: implications for genetic testing and clinical management

PURPOSE

To identify germ line CDH1 mutations in hereditary diffuse gastric cancer (HDGC) families and develop guidelines for management of at risk individuals.

EXPERIMENTAL DESIGN

We ascertained 31 HDGC previously unreported families, including 10 isolated early-onset diffuse gastric cancer (DGC) cases. Screening for CDH1 germ line mutations was done by denaturing high-performance liquid chromatography and automated DNA sequencing.

RESULTS

We identified eight inactivating and one missense CDH1 germ line mutation. The missense mutation conferred in vitro loss of protein function. Two families had the previously described 1003C>T nonsense mutation. Haplotype analysis revealed this to be a recurrent and not a founder mutation. Thirty-six percent (5 of 14) of the families with a documented DGC diagnosed before the age of 50 and other cases of gastric cancer carried CDH1 germ line mutations. Two of 10 isolated cases of DGC in individuals ages <35 years harbored CDH1 germ line mutations. One mutation positive family was ascertained through a family history of lobular breast cancer (LBC) and another through an individual with both DGC and LBC. Occult DGC was identified in five of six prophylactic gastrectomies done on asymptomatic, endoscopically negative 1003C>T mutation carriers.

CONCLUSIONS

In addition to families with a strong history of early-onset DGC, CDH1 mutation screening should be offered to isolated cases of DGC in individuals ages <35 years and for families with multiple cases of LBC, with any history of DGC or unspecified GI malignancies. Prophylactic gastrectomy is potentially a lifesaving procedure and clinical breast screening is recommended for asymptomatic mutation carriers.