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

The interplay between IQGAP1 and small GTPases in cancer metastasis

The metastatic spread of tumor cells to distant anatomical locations is a critical cause for disease progression and leads to more than 90 % of cancer-related deaths. IQ motif-containing GTPase-activating protein 1 (IQGAP1), a prominent regulator in the cancer metastasis process, is a scaffold protein that interacts with components of the cytoskeleton. As a critical node within the small GTPase network, IQGAP1 acts as a binding partner of several small GTPases, which in turn function as molecular switches to control most cellular processes, including cell migration and invasion. Given the significant interaction between IQGAP1 and small GTPases in cancer metastasis, we briefly elucidate the role of IQGAP1 in regulating cancer metastasis and the varied interactions existing between IQGAP1 and small GTPases. In addition, the potential regulators for IQGAP1 activity and its interaction with small GTPases are also incorporated in this review. Overall, we comprehensively summarize the role of IQGAP1 in cancer tumorigenicity and metastasis, which may be a potential anti-tumor target to restrain cancer progression.

Evaluation of epidermal growth factor receptor signaling effects in gastric cancer cell lines by detailed motility-focused phenotypic characterization linked with molecular analysis

Background

Gastric cancers frequently overexpress the epidermal growth factor receptor (EGFR), which has been implicated in pathological processes including tumor cell motility, invasion and metastasis. Targeting EGFR with the inhibitory antibody cetuximab may affect the motile and invasive behavior of tumor cells. Here, we evaluated the effects of EGFR signaling in gastric cancer cell lines to link the phenotypic behavior of the cells with their molecular characteristics.

Methods

Phenotypic effects were analyzed in four gastric cancer cell lines (AGS, Hs746T, LMSU and MKN1) by time-lapse microscopy and transwell invasion assay. Effects on EGFR signaling were detected using Western blot and proteome profiler analyses. A network was constructed linking EGFR signaling to the regulation of cellular motility.

Results

The analysis of the effects of treatment with epidermal growth factor (EGF) and cetuximab revealed that only one cell line (MKN1) was sensitive to cetuximab treatment in all phenotypic assays, whereas the other cell lines were either not responsive (Hs746T, LMSU) or sensitive only in certain tests (AGS). Cetuximab inhibited EGFR, MAPK and AKT activity and associated components of the EGFR signaling pathway to different degrees in cetuximab-sensitive MKN1 cells. In contrast, no such changes were observed in Hs746T cells. Thus, the different phenotypic behaviors of the cells were linked to their molecular response to treatment. Genetic alterations had different associations with response to treatment: while PIK3CA mutations and KRAS mutation or amplification were not obstructive, the MET mutation was associated with non-response.

Conclusion

These results identify components of the EGFR signaling network as important regulators of the phenotypic and molecular response to cetuximab treatment.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3822-3) contains supplementary material, which is available to authorized users.

A protein and mRNA expression-based classification of gastric cancer

The overall survival of gastric carcinoma patients remains poor despite improved control over known risk factors and surveillance. This highlights the need for new classifications, driven towards identification of potential therapeutic targets. Using sophisticated molecular technologies and analysis, three groups recently provided genetic and epigenetic molecular classifications of gastric cancer (The Cancer Genome Atlas, 'Singapore-Duke' study, and Asian Cancer Research Group). Suggested by these classifications, here, we examined the expression of 14 biomarkers in a cohort of 146 gastric adenocarcinomas and performed unsupervised hierarchical clustering analysis using less expensive and widely available immunohistochemistry and in situ hybridization. Ultimately, we identified five groups of gastric cancers based on Epstein-Barr virus (EBV) positivity, microsatellite instability, aberrant E-cadherin, and p53 expression; the remaining cases constituted a group characterized by normal p53 expression. In addition, the five categories correspond to the reported molecular subgroups by virtue of clinicopathologic features. Furthermore, evaluation between these clusters and survival using the Cox proportional hazards model showed a trend for superior survival in the EBV and microsatellite-instable related adenocarcinomas. In conclusion, we offer as a proposal a simplified algorithm that is able to reproduce the recently proposed molecular subgroups of gastric adenocarcinoma, using immunohistochemical and in situ hybridization techniques.

Difference in F-actin depolymerization induced by toxin B from the Clostridium difficile strain VPI 10463 and toxin B from the variant Clostridium difficile serotype F strain 1470

Clostridium difficile toxin A (TcdA) and toxin B (TcdB) are the causative agent of the C. difficile-associated diarrhea (CDAD) and its severe form, the pseudomembranous colitis (PMC). TcdB from the C. difficile strain VPI10463 mono-glucosylates (thereby inactivates) the small GTPases Rho, Rac, and Cdc42, while Toxin B from the variant C. difficile strain serotype F 1470 (TcdBF) specifically mono-glucosylates Rac but not Rho(A/B/C). TcdBF is related to lethal toxin from C. sordellii (TcsL) that glucosylates Rac1 but not Rho(A/B/C). In this study, the effects of Rho-inactivating toxins on the concentrations of cellular F-actin were investigated using the rhodamine-phalloidin-based F-actin ELISA. TcdB induces F-actin depolymerization comparable to the RhoA-inactivating exoenzyme C3 from C. limosum (C3-lim). In contrast, the Rac-glucosylating toxins TcdBF and TcsL did not cause F-actin depolymerization. These observations led to the conclusion that F-actin depolymerization depends on the toxin’s capability of glucosylating RhoA. Furthermore, the integrity of focal adhesions (FAs) was analyzed using paxillin and p21-activated kinase (PAK) as FA marker proteins. Paxillin dephosphorylation was observed upon treatment of cells with TcdB, TcdBF, or C3-lim. In conclusion, the Rho-inactivating toxins induce loss of cell shape by either F-actin depolymerization (upon RhoA inactivation) or the disassembly of FAs (upon Rac1 inactivation).

Cdc42 GTPase and Rac1 GTPase act downstream of p120 catenin and require GTP exchange during gastrulation of zebrafish mesoderm

BACKGROUND

We investigated the roles of p120 catenin, Cdc42, Rac1, and RhoA GTPases in regulating migration of presomitic mesoderm cells in zebrafish embryos. p120 catenin has dual roles: It binds the intracellular and juxtamembrane region of cadherins to stabilize cadherin-mediated adhesion with the aid of RhoA GTPase, and it activates Cdc42 GTPase and Rac1 GTPase in the cytosol to initiate cell motility.

RESULTS

During gastrulation of zebrafish embryos, knockdown of the synthesis of zygotic p120 catenin δ1 mRNAs with a splice-site morpholino caused lateral widening and anterior-posterior shortening of the presomitic mesoderm and somites and a shortened anterior-posterior axis. These phenotypes indicate a cell-migration effect. Co-injection of low amounts of wild-type Cdc42 or wild-type Rac1 or dominant-negative RhoA mRNAs, but not constitutively-active Cdc42 mRNA, rescued these p120 catenin δ1-depleted embryos.

CONCLUSIONS

These downstream small GTPases require appropriate spatiotemporal stimulation or cycling of GTP to guide mesodermal cell migration. A delicate balance of Rho GTPases and p120 catenin underlies normal development.

Cadherin point mutations alter cell sorting and modulate GTPase signaling

This study investigated the impact of cadherin binding differences on both cell sorting and GTPase activation. The use of N-terminal domain point mutants of Xenopus C-cadherin enabled us to quantify binding differences and determine their effects on cadherin-dependent functions without any potential complications arising as a result of differences in cytodomain interactions. Dynamic cell-cell binding measurements carried out with the micropipette manipulation technique quantified the impact of these mutations on the two-dimensional binding affinities and dissociation rates of cadherins in the native context of the cell membrane. Pairwise binding affinities were compared with in vitro cell-sorting specificity and ligation-dependent GTPase signaling. Two-dimensional affinity differences greater than five-fold correlated with cadherin-dependent in vitro cell segregation, but smaller differences failed to induce cell sorting. Comparison of the binding affinities with GTPase signaling amplitudes further demonstrated that differential binding also proportionally modulates intracellular signaling. These results show that differential cadherin affinities have broader functional consequences than merely controlling cell-cell cohesion.

Cadherin-dependent mechanotransduction depends on ligand identity but not affinity

This study investigates the relationship between classical cadherin binding affinities and mechanotransduction through cadherin-mediated adhesions. The mechanical properties of cadherin-dependent intercellular junctions are generally attributed to differences in the binding affinities of classical cadherin subtypes that contribute to cohesive energies between cells. However, cell mechanics and mechanotransduction may also regulate intercellular contacts. We used micropipette measurements to quantify the two-dimensional affinities of cadherins at the cell surface, and two complementary mechanical measurements to assess ligand-dependent mechanotransduction through cadherin adhesions. At the cell surface, the classical cadherins investigated in this study form both homophilic and heterophilic bonds with two-dimensional affinities that differ by less than threefold. In contrast, mechanotransduction through cadherin adhesions is strongly ligand dependent such that homophilic, but not heterophilic ligation mediates mechanotransduction, independent of the cadherin binding affinity. These findings suggest that ligand-selective mechanotransduction may supersede differences in cadherin binding affinities in regulating intercellular contacts.

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.

Regulation of adherens junctions by Rho GTPases and p120-catenin

The molecular mechanisms leading to tumor progression and acquisition of a metastatic phenotype are highly complex and only partially understood. The spatiotemporal regulation of E-cadherin-mediated adherens junctions is essential for normal epithelia function and tissue integrity. Perturbation of the E-cadherin complex assembly is a key event in epithelial-mesenchymal transition and is directed by a huge number of mechanisms that differ greatly with regard to cell types and tissues. The reduction in intercellular adhesion interferes with tissue integrity and allows cancer cells to disseminate from the primary tumor thereby initiating cancer metastasis. In the present review we will summarize the current findings about the influence of Rho GTPases on the formation and maintenance of adherens junction and will then proceed to discuss the involvement of p120-catenin on cell-cell adhesion and tumor cell migration.

Double strand RNA-guided endogeneous E-cadherin up-regulation induces the apoptosis and inhibits proliferation of breast carcinoma cells in vitro and in vivo

E-cadherin plays a crucial role in epithelial cell-cell adhesion and in the maintenance of tissue architecture. Down-regulation of E-cadherin expression correlates with a strong invasive potential, resulting in poor prognosis in many human carcinomas, including breast cancer. Restoration of E-cadherin can inhibit cell invasion and metastasis in many types of tumors. It has been demonstrated that promoter hypermethylation causes transcriptional down-regulation of E-cadherin. Here, using an RNAa technique specifically activating the expression of E-cadherin through transcriptional regulation, we assessed the phenotype changes of a breast carcinoma cell line with transfection of small-activating RNAs (saRNAs). We observed cell apoptosis, proliferation inhibition and reduction in human breast cancer migration in vitro. Animal experiment results showed that saRNA could inhibit tumor growth in vivo compared with scramble double-small RNA (dsRNA).This study provides a new potential strategy for breast cancer therapy, and also demonstrates the potential for saRNA as a therapeutic option for enhancing tumor suppressor gene expression in breast cancer. (Cancer Sci 2010).

Cleavage of E-Cadherin by Matrix Metalloproteinase-7 Promotes Cellular Proliferation in Nontransformed Cell Lines via Activation of RhoA

Perturbations in cell-cell contact machinery occur frequently in epithelial cancers and result in increased cancer cell migration and invasion. Previously, we demonstrated that MMP-7, a protease implicated in mammary and intestinal tumor growth, can process the adherens junction component E-cadherin. This observation leads us to test whether MMP-7 processing of E-cadherin could directly impact cell proliferation in nontransformed epithelial cell lines (MDCK and C57MG). Our goal was to investigate the possibility that MMP-7 produced by cancer cells may have effects on adjacent normal epithelium. Here, we show that MMP-7 processing of E-cadherin mediates, (1) loss of cell-cell contact, (2) increased cell migration, (3) a loss of epithelial cell polarization and (4) increased cell proliferation via RhoA activation. These data demonstrate that MMP-7 promotes epithelial cell proliferation via the processing of E-cadherin and provide insights into the molecular mechanisms that govern epithelial cell growth.