Src SH3/2 domain-mediated peripheral accumulation of Src and phospho-myosin is linked to deregulation of E-cadherin and the epithelial-mesenchymal transition

The Protective Potential of Butyrate against Colon Cancer Cell Migration and Invasion Is Critically Dependent on Cell Type

SCOPE

Short-chain fatty acids such as butyrate are produced through the fermentation of dietary fiber by colonic bacteria. Preclinical studies indicate an anticancer potential of butyrate, but clinical evidence shows greater variability. The study hypothesizes the effectiveness of butyrate on reducing colon cancer cell migration and invasion may vary due to the cell-type.

METHODS AND RESULTS

The study determines the efficacy of butyrate (0-4 mM) to inhibit cancer cell migration, invasion, and related signaling proteins in three distinct human colorectal cancer (CRC) cell lines: HCT116, HT-29, and Caco-2. Butyrate exhibits a dose-dependent inhibitory effect on cancer cell migration and invasion. This inhibitory potential on oncogenic focal adhesion kinase (FAK) and sarcoma (Src) proteins is greater in HCT116 cells (1.1 and 0.8-fold) and HT-29 cells (0.9 and 0.4-fold) compared to Caco-2 cells, respectively. Conversely, E-cadherin protein, a classical epithelial cell marker and potential tumor suppressor, is 2.3-fold greater in HCT116 cells than in HT-29 cells and Caco-2 cells. Moreover, survival analysis from a public cancer database demonstrates that CRC patients with high E-cadherin expression have a 13% greater 5-year survival rate than those with low expression.

CONCLUSION

Collectively, butyrate's anti-cancer efficacy on CRC cells varies depending on cell-type and is linked to the FAK/Src/E-cadherin pathway.

A TGF-β-responsive enhancer regulates SRC expression and epithelial-mesenchymal transition-associated cell migration

The non-receptor tyrosine kinase SRC is overexpressed and/or hyperactivated in various human cancers, and facilitates cancer progression by promoting invasion and metastasis. However, the mechanisms underlying SRC upregulation are poorly understood. In this study, we demonstrate that transforming growth factor-β (TGF-β) induces SRC expression at the transcriptional level by activating an intragenic the SRC enhancer. In the human breast epithelial cell line MCF10A, TGF-β1 stimulation upregulated one of the SRC promotors, the 1A promoter, resulting in increased SRC mRNA and protein levels. Chromatin immunoprecipitation (ChIP)-sequencing analysis revealed that the SMAD complex is recruited to three enhancer regions ∼15 kb upstream and downstream of the SRC promoter, and one of them is capable of activating the SRC promoter in response to TGF-β. JUN, a member of the activator protein (AP)-1 family, localises to the enhancer and regulates TGF-β-induced SRC expression. Furthermore, TGF-β-induced SRC upregulation plays a crucial role in epithelial-mesenchymal transition (EMT)-associated cell migration by activating the SRC-focal adhesion kinase (FAK) circuit. Overall, these results suggest that TGF-β-induced SRC upregulation promotes cancer cell invasion and metastasis in a subset of human malignancies.

Adherens junctions stimulate and spatially guide integrin activation and extracellular matrix deposition

Cadherins and integrins are intrinsically linked through the actin cytoskeleton and are largely responsible for the mechanical integrity and organization of tissues. We show that cadherin clustering stimulates and spatially guides integrin activation. Adherens junction (AJ)-associated integrin activation depends on locally generated tension and does not require extracellular matrix ligands. It leads to the creation of primed integrin clusters, which spatially determine where focal adhesions will form if ligands are present and where ligands will be deposited. AJs that display integrin activation are targeted by microtubules facilitating their disassembly via caveolin-based endocytosis, showing that integrin activation impacts the stability of the core cadherin complex. Thus, the interplay between cadherins and integrins is more intimate than what was once believed and is rooted in the capacity of active integrins to be stabilized via AJ-generated tension. Altogether, our data establish a mechanism of cross-regulation between cadherins and integrins.

Platelet Activation in High D-Dimer Plasma Plays a Role in Acquired Resistance to Epidermal Growth Factor Receptor Tyrosine Kinase Inhibitors in Patients with Mutant Lung Adenocarcinoma

Objective

Platelet activation and adhesion to cancer cells increase the release of multiple factors that contribute to EMT and chemoresistance. Elevated levels of D-dimer have been associated with poor clinical outcomes in lung cancer. Platelets in high D-dimer plasma may be activated and implicated in acquired resistance to EGFR TKI in advanced lung adenocarcinoma with mutant EGFR.

Materials and Methods

Clinical responsive rate (RR), progression-free survival (PFS), and overall survival (OS) were prospectively measured in treatment-naïve lung adenocarcinoma patients with activation mutation. Plasma or platelets from patients with high or low D-dimer level were obtained to investigate the cytotoxic effects of TKIs on mutant cancer cells, and the mechanistic pathways were also explored.

Results

Patients with high D-dimer had worse RR, PFS, and OS. High D-dimer plasma induced resistance to gefitinib, erlotinib, afatinib, or osimertinib in EGFR mutant lung cancer cells. Depletion of platelets in high D-dimer plasma reversed the resistance to TKI. Platelets of high D-dimer plasma had higher adherence capacity to cancer cells, and induced EGFR and Akt activation as well as EMT through Src activation. Inhibition of platelet adherence or activation of Src or Akt conquered the resistance to TKI. The acquired resistance to TKI by high D-dimer plasma was less attributed to secondary gene mutation.

Conclusion

Increased platelet activation in the high D-dimer plasma may contribute to first-line acquired EGFR TKI resistance. Thus, therapeutic strategy against platelet activation in patients with high D-dimer levels may improve the efficacy of first-line treatment with EGFR TKI.

An Improved Scalable Hydrogel Dish for Spheroid Culture

Research in fields studying cellular response to surface tension and mechanical forces necessitate cell culture tools with tunability of substrate stiffness. We created a scalable hydrogel dish design to facilitate scaffold-free formation of multiple spheroids in a single dish. Our novel design features inner and outer walls, allowing efficient media changes and downstream experiments. The design is easily scalable, accommodating varying numbers of microwells per plate. We report that non-adherent hydrogel stiffness affects spheroid morphology and compaction. We found that spheroid morphology and viability in our hydrogel dishes were comparable to commercially available Aggrewell™800 plates, with improved tunability of surface stiffness and imaging area. Device function was demonstrated with a migration assay using two investigational inhibitors against EMT. We successfully maintained primary-derived spheroids from murine and porcine lungs in the hydrogel dish. These features increase the ability to produce highly consistent cell aggregates for biological research.

The Relevance of the SH2 Domain for c-Src Functionality in Triple-Negative Breast Cancer Cells

The role of Src family kinases (SFKs) in human tumors has been always associated with tyrosine kinase activity and much less attention has been given to the SH2 and SH3 adapter domains. Here, we studied the role of the c-Src-SH2 domain in triple-negative breast cancer (TNBC). To this end, SUM159PT and MDA-MB-231 human cell lines were employed as model systems. These cells conditionally expressed, under tetracycline control (Tet-On system), a c-Src variant with point-inactivating mutation of the SH2 adapter domain (R175L). The expression of this mutant reduced the self-renewal capability of the enriched population of breast cancer stem cells (BCSCs), demonstrating the importance of the SH2 adapter domain of c-Src in the mammary gland carcinogenesis. In addition, the analysis of anchorage-independent growth, proliferation, migration, and invasiveness, all processes associated with tumorigenesis, showed that the SH2 domain of c-Src plays a very relevant role in their regulation. Furthermore, the transfection of two different aptamers directed to SH2-c-Src in both SUM159PT and MDA-MB-231 cells induced inhibition of their proliferation, migration, and invasiveness, strengthening the hypothesis that this domain is highly involved in TNBC tumorigenesis. Therefore, the SH2 domain of c-Src could be a promising therapeutic target and combined treatments with inhibitors of c-Src kinase enzymatic activity may represent a new therapeutic strategy for patients with TNBC, whose prognosis is currently very negative.

SRC Signaling in Cancer and Tumor Microenvironment

Pioneering experiments performed by Harold Varmus and Mike Bishop in 1976 led to one of the most influential discoveries in cancer research and identified the first cancer-causing oncogene called Src. Later experimental and clinical evidence suggested that Src kinase plays a significant role in promoting tumor growth and progression and its activity is associated with poor patient survival. Thus, several Src inhibitors were developed and approved by FDA for treatment of cancer patients. Tumor microenvironment (TME) is a highly complex and dynamic milieu where significant cross-talk occurs between cancer cells and TME components, which consist of tumor-associated macrophages, fibroblasts, and other immune and vascular cells. Growth factors and chemokines activate multiple signaling cascades in TME and induce multiple kinases and pathways, including Src, leading to tumor growth, invasion/metastasis, angiogenesis, drug resistance, and progression. Here, we will systemically evaluate recent findings regarding regulation of Src and significance of targeting Src in cancer therapy.

EPS8 phosphorylation by Src modulates its oncogenic functions

Background

EPS8 is a scaffolding protein that regulates proliferation, actin dynamics and receptor trafficking. Its expression is increased in cancer, enhancing mitogenesis, migration and tumorigenesis. Src phosphorylates EPS8 at four tyrosine residues, although the function is unknown. Here we investigated the pro-oncogenic role of EPS8 tyrosine phosphorylation at Src target sites in HNSCC.

Methods

Plasmids expressing EPS8 Src-mediated phosphorylation site mutants (Y485F, Y525F, Y602F, Y774F and all four combined [FFFF]) were expressed in cells containing a normal endogenous level of EPS8. In addition, cells were treated with dasatinib to inhibit Src activity. EPS8 downstream targets were evaluated by western blotting. Wound closure, proliferation, immunofluorescence and tumorgenicity assays were used to investigate the impact of phenylalanine mutations on EPS8 biological functions.

Results

FOXM1, AURKA, and AURKB were decreased in cells expressing FFFF- and Y602F-EPS8 mutants, while cells harbouring the Y485F-, Y525F- and Y774F-EPS8 mutants showed no differences compared to controls. Consistent with this, dasatinib decreased the expression of EPS8 targets. Moreover, Y602F- and FFFF-EPS8 mutants reduced mitogenesis and motility. Strikingly though, FFFF- or Y602F-EPS8 mutants actually promoted tumorigenicity compared with control cells.

Conclusions

Phosphorylation of EPS8 at Y602 is crucial for signalling to the cell cycle and may provide insight to explain reduced efficacy of dasatinib treatment.

Regulation of Src Family Kinases during Colorectal Cancer Development and Its Clinical Implications

Src family kinases (SFKs) are non-receptor kinases that play a critical role in the pathogenesis of colorectal cancer (CRC). The expression and activity of SFKs are upregulated in patients with CRC. Activation of SFKs promotes CRC cell proliferation, metastases to other organs and chemoresistance, as well as the formation of cancer stem cells (CSCs). The enhanced expression level of Src is associated with decreased survival in patients with CRC. Src-mediated regulation of CRC progression involves various membrane receptors, modulators, and suppressors, which regulate Src activation and its downstream targets through various mechanisms. This review provides an overview of the current understanding of the correlations between Src and CRC progression, with a special focus on cancer cell proliferation, invasion, metastasis and chemoresistance, and formation of CSCs. Additionally, this review discusses preclinical and clinical strategies to improve the therapeutic efficacy of drugs targeting Src for treating patients with CRC.

The Regulation of Intestinal Mucosal Barrier by Myosin Light Chain Kinase/Rho Kinases

The intestinal epithelial apical junctional complex, which includes tight and adherens junctions, contributes to the intestinal barrier function via their role in regulating paracellular permeability. Myosin light chain II (MLC-2), has been shown to be a critical regulatory protein in altering paracellular permeability during gastrointestinal disorders. Previous studies have demonstrated that phosphorylation of MLC-2 is a biochemical marker for perijunctional actomyosin ring contraction, which increases paracellular permeability by regulating the apical junctional complex. The phosphorylation of MLC-2 is dominantly regulated by myosin light chain kinase- (MLCK-) and Rho-associated coiled-coil containing protein kinase- (ROCK-) mediated pathways. In this review, we aim to summarize the current state of knowledge regarding the role of MLCK- and ROCK-mediated pathways in the regulation of the intestinal barrier during normal homeostasis and digestive diseases. Additionally, we will also suggest potential therapeutic targeting of MLCK- and ROCK-associated pathways in gastrointestinal disorders that compromise the intestinal barrier.

MicroRNA-200 family governs ovarian inclusion cyst formation and mode of ovarian cancer spread

Epidemiologic and histopathologic findings and the laying hen model support the long-standing incessant ovulation hypothesis and cortical inclusion cyst involvement in sporadic ovarian cancer development. MicroRNA-200 (miR-200) family is highly expressed in ovarian cancer. Herewith, we show that ovarian surface epithelial (OSE) cells with ectopic miR-200 expression formed stabilized cysts in three-dimensional (3D) organotypic culture with E-cadherin fragment expression and steroid hormone pathway activation, whereas ovarian cancer 3D cultures with miR-200 knockdown showed elevated TGF-β expression, mitotic spindle disorientation, increased lumenization, disruption of ROCK-mediated myosin II phosphorylation, and SRC signaling, which led to histotype-dependent loss of collective movement in tumor spread. Gene expression profiling revealed that epithelial-mesenchymal transition and hypoxia were the top enriched gene sets regulated by miR-200 in both OSE and ovarian cancer cells. The molecular changes uncovered by the in vitro studies were verified in both human and laying hen ovarian cysts and tumor specimens. As miR-200 is also essential for ovulation, our results of estrogen pathway activation in miR-200-expressing OSE cells add another intriguing link between incessant ovulation and ovarian carcinogenesis.

The effects of c-Src kinase on EMT signaling pathway in human lens epithelial cells associated with lens diseases

Background

The signaling pathway of epithelial to mesenchymal transition (EMT) is regulated by c-Src kinase in many cells. The purpose of this study was to investigate the effects of c-Src kinase on EMT of human lens epithelial cells in vivo stimulated by different factors.

Methods

Human lens epithelial cells, HLE-B3, were exposed to either an inflammatory factor, specifically IL-1α, IL-6, TNF-α or IL-1β, at 10 ng/mL or high glucose (35.5 mM) for 30 mins. Activity of c-Src kinase was evaluated by the expression of p-Src⁴¹⁸ with western blot assay. To investigate the effects of activation of c-Src on EMT, HLE-B3 cells were transfected with pCDNA3.1-Src^Y530F to upregulate activity of c-Src kinase, and pSlience4.1-ShSrc to knock it down. The expressions of c-Src kinase and molecular markers of EMT such as E-cadherin, ZO-1, α-SMA, and Vimentin were examined at 48 h by RT-PCR and western blot. At 48 h and 72 h of transfection, cell proliferation was detected by MTT, and cell mobility and migration were determined by scratch and transwell assays.

Results

Activity of c-Src kinase, which causes the expression of p-Src⁴¹⁸, was upregulated by different inflammatory factors and high glucose in HLE-B3 cells. When HLE-B3 cells were transfected with pCDNA3.1-Src^Y530F, the expression of c-Src kinase was upregulated on both mRNA and protein levels, and activity of c-Src kinase, expression of p-Src⁴¹⁸ increased. The expressions of both E-cadherin and ZO-1 were suppressed, while the expressions of vimentin and α-SMA were elevated on both mRNA and protein levels at the same time. Cell proliferation, mobility and migration increased along with activation of c-Src kinase. Conversely, when HLE-B3 cells were transfected with pSlience4.1-ShSrc, both c-Src kinase and p-Src⁴¹⁸ expressions were knocked down. The expressions of E-cadherin and ZO-1 increased, but the expressions of Vimentin and α-SMA decreased; meanwhile, cell proliferation, mobility and migration reduced.

Conclusions

The c-Src kinase in lens epithelial cells is easily activated by external stimuli, resulting in the induction of cell proliferation, mobility, migration and EMT.

LIN28B increases neural crest cell migration and leads to transformation of trunk sympathoadrenal precursors

The RNA-binding protein LIN28B regulates developmental timing and determines stem cell identity by suppressing the let-7 family of microRNAs. Postembryonic reactivation of LIN28B impairs cell commitment to differentiation, prompting their transformation. In this study, we assessed the extent to which ectopic lin28b expression modulates the physiological behavior of neural crest cells (NCC) and governs their transformation in the trunk region of developing embryos. We provide evidence that the overexpression of lin28b inhibits sympathoadrenal cell differentiation and accelerates NCC migration in two vertebrate models, Xenopus leavis and Danio rerio. Our results highlight the relevance of ITGA5 and ITGA6 in the LIN28B-dependent regulation of the invasive motility of tumor cells. The results also establish that LIN28B overexpression supports neuroblastoma onset and the metastatic potential of malignant cells through let-7a-dependent and let-7a-independent mechanisms.

Dichotomy of the function of DDR1 in cells and disease progression

Discoidin domain receptors DDR1 and DDR2 are collagen receptor tyrosine kinases that have many roles in tissue development and disease progression. Under physiological conditions, DDR1 is predominantly expressed in epithelial cells and functions to maintain cell differentiation and tissue homeostasis. A switch in expression from DDR1 to DDR2 occurs during epithelial-to-mesenchymal transition. However, opposite effects of DDR1 are reported to be involved in the progression of cancer and fibrotic diseases. Accumulating evidence suggests that DDR1 is involved in pro-metastasis and pro-survival signals. This review summarizes the roles of DDR1 in epithelial cell differentiation, cell migration, cancer progression and tissues fibrosis and highlights how the dichotomous functions of DDR1 may relevant to different cell types and statues. Elucidation of the underlying mechanism of the dichotomous functions of DDR1 will help to develop DDR1 as a therapeutic target.

Distinct contributions of tensile and shear stress on E-cadherin levels during morphogenesis

During epithelial morphogenesis, cell contacts (junctions) are constantly remodeled by mechanical forces that work against adhesive forces. E-cadherin complexes play a pivotal role in this process by providing persistent cell adhesion and by transmitting mechanical tension. In this context, it is unclear how mechanical forces affect E-cadherin adhesion and junction dynamics. During Drosophila embryo axis elongation, Myosin-II activity in the apico-medial and junctional cortex generates mechanical forces to drive junction remodeling. Here we report that the ratio between Vinculin and E-cadherin intensities acts as a ratiometric readout for these mechanical forces (load) at E-cadherin complexes. Medial Myosin-II loads E-cadherin complexes on all junctions, exerts tensile forces, and increases levels of E-cadherin. Junctional Myosin-II, on the other hand, biases the distribution of load between junctions of the same cell, exerts shear forces, and decreases the levels of E-cadherin. This work suggests distinct effects of tensile versus shear stresses on E-cadherin adhesion.

Trafficking of Adhesion and Growth Factor Receptors and Their Effector Kinases

Cell adhesion to macromolecules in the microenvironment is essential for the development and maintenance of tissues, and its dysregulation can lead to a range of disease states, including inflammation, fibrosis, and cancer. The biomechanical and biochemical mechanisms that mediate cell adhesion rely on signaling by a range of effector proteins, including kinases and associated scaffolding proteins. The intracellular trafficking of these must be tightly controlled in space and time to enable effective cell adhesion and microenvironmental sensing and to integrate cell adhesion with, and compartmentalize it from, other cellular processes, such as gene transcription, protein degradation, and cell division. Delivery of adhesion receptors and signaling proteins from the plasma membrane to unanticipated subcellular locales is revealing novel biological functions. Here, we review the expected and unexpected trafficking, and sites of activity, of adhesion and growth factor receptors and intracellular kinase partners as we begin to appreciate the complexity and diversity of their spatial regulation.

c-CBL regulates melanoma proliferation, migration, invasion and the FAK-SRC-GRB2 nexus

Melanoma is one of the most aggressive and lethal forms of skin cancer. Despite recent improvements in targeted therapies, many patients with advanced disease fail to achieve lasting tumor regression. Therefore, it is important to develop novel druggable targets that can be exploited to improve clinical outcome. Here, we studied the role of Casitas B-lineage lymphoma (c-CBL), an E3 ubiquitin ligase, in human melanoma. Employing quantitative real-time PCR and Western blot analysis in a panel of human melanoma cell lines (A375, G361, Hs-294T, SK-Mel-2, SK-Mel-28 and 451Lu), we found that c-CBL is strongly expressed in human melanoma cells at the mRNA and protein levels. Further, we determined c-CBL levels in clinical samples of melanomas and benign melanocytic nevi, using quantitative Nuance multispectral imaging. Compared to benign nevi, melanomas showed an overlapping range of c-CBL immunoreactivity. Small interfering RNA (siRNA)-mediated knockdown of c-CBL resulted in decreased proliferation, clonogenic survival and migration of melanoma cells. Furthermore, it also resulted in decreased cellular invasion in a 3D spheroid assay system. C-CBL and FAK are regulated by SRC, and FAK binds SRC and GRB2. C-CBL E3 ligase domain regulates receptor tyrosine kinase internalization through ubiquitination and its ring finger domain stabilizes the FAK-SRC-actin cytoskeleton thereby promoting cellular motility. C-CBL knockdown was associated with decreased protein and/or mRNA levels of SRC, FAK and GRB2. Taken together, we have provided evidence that c-CBL plays a role in melanoma cell proliferation, migration and invasion as well as inhibition of the FAK-GRB2-SRC nexus. Our findings indicate that additional studies are warranted to further dissect the role of c-CBL in melanoma and determine the therapeutic potential of its inhibition.

Regulation of E-cadherin localization by microtubule targeting agents: rapid promotion of cortical E-cadherin through p130Cas/Src inhibition by eribulin

Microtubule targeting agents (MTAs) are some of the most effective anticancer drugs used to treat a wide variety of adult and pediatric cancers. Building evidence suggests that these drugs inhibit interphase signaling events and that this contributes to their anticancer actions. The effects of diverse MTAs were evaluated following a 2 hour incubation with clinically relevant concentrations to test the hypothesis that these drugs rapidly and differentially disrupt epithelial-to-mesenchymal transition (EMT)-related signaling. The MTAs rapidly promoted the cortical localization of internal pools of E-cadherin in HCC1937 breast cancer cells, with the most robust effects observed with the microtubule destabilizers eribulin and vinorelbine. Cortical E-cadherin localization was also promoted by the Src kinase inhibitor dasatinib or by siRNA-mediated depletion of the p130Cas scaffold. Mechanistic studies demonstrate that eribulin disrupts the interaction between p130Cas and Src, leading to decreased cortical Src phosphorylation that precedes the accumulation of cortical E-cadherin. These results suggest that microtubules can be actively co-opted by cancer cells to inhibit cortical E-cadherin localization, a hallmark of EMT, and provide a direct link between the initial disruption of the microtubule network and reversal of EMT phenotypes demonstrated by eribulin in long-term studies.

c-Src activation promotes nasopharyngeal carcinoma metastasis by inducing the epithelial-mesenchymal transition via PI3K/Akt signaling pathway: a new and promising target for NPC

Aberrant activation of cellular Src (c-Src), a non-receptor tyrosine kinase, could promote cancer progression through activating its downstream signaling pathways. However, the roles of c-Src and phosphorylated-Src (p-Src) in nasopharyngeal carcinoma (NPC) progression are rarely investigated. Herein, we have identified high c-Src concentrations in the serum of NPC patients with distant metastasis using high-throughput protein microarrays. Levels of c-Src in serum and p-Src in human primary NPC samples were unfavorable independent prognostic factors for cancer-specific survival, disease-free survival, and distant metastasis-free survival. Depletion or inactivation of c-Src in NPC cells using sgRNA with CRISPR/Cas9 system or PP2 decreased cell viability, colony formation, migration and invasion in vitro and metastasis in vivo. In contrast, these malignancies could be up-regulated by overexpressed c-Src in a NPC cell line with low-metastasis potential. Furthermore, p-Src was involved in promoting NPC cell metastasis by inducing the epithelial-mesenchymal transition (EMT) process via activating the PI3K/Akt pathway and cytoskeleton remodeling. The p-Src-induced EMT process could be retarded by PP2, which mediated by down-regulating the PI3K/Akt pathway. In conclusion, elevated levels of c-Src in serum and p-Src in primary NPC tissue correlated with poor outcomes of NPC patients. And aberrant activation of c-Src facilitated NPC cells with malignant potential, especially metastasis ability, which mediated by the PI3K/Akt pathway activation and sequentially induced the EMT process. These findings unveiled a promising approach for targeted therapy of advanced NPC.

Redox regulation in tumor cell epithelial-mesenchymal transition: molecular basis and therapeutic strategy

Epithelial–mesenchymal transition (EMT) is recognized as a driving force of cancer cell metastasis and drug resistance, two leading causes of cancer recurrence and cancer-related death. It is, therefore, logical in cancer therapy to target the EMT switch to prevent such cancer metastasis and recurrence. Previous reports have indicated that growth factors (such as epidermal growth factor and fibroblast growth factor) and cytokines (such as the transforming growth factor beta (TGF-β) family) are major stimulators of EMT. However, the mechanisms underlying EMT initiation and progression remain unclear. Recently, emerging evidence has suggested that reactive oxygen species (ROS), important cellular secondary messengers involved in diverse biological events in cancer cells, play essential roles in the EMT process in cancer cells by regulating extracellular matrix (ECM) remodeling, cytoskeleton remodeling, cell–cell junctions, and cell mobility. Thus, targeting EMT by manipulating the intracellular redox status may hold promise for cancer therapy. Herein, we will address recent advances in redox biology involved in the EMT process in cancer cells, which will contribute to the development of novel therapeutic strategies by targeting redox-regulated EMT for cancer treatment.

IGF-I Induces Epithelial-to-Mesenchymal Transition via the IGF-IR-Src-MicroRNA-30a-E-Cadherin Pathway in Nasopharyngeal Carcinoma Cells

Recurrence and distant metastasis are the most common cause of therapeutic failure in nasopharyngeal carcinoma (NPC) patients. Insulin-like growth factor I (IGF-I) can induce epithelial-to-mesenchymal transition (EMT) in many epithelial tumors; however, whether IGF-I can enhance NPC metastasis by EMT and the mechanisms remain unclear. Herein, we have identified that IGF-I could induce EMT and enhance migration ability in NPC cell lines. Furthermore, both Src inhibitor and microRNA-30a (miR-30a) inhibitor reversed IGF-I-induced EMT, suggesting the involvement of an IGF-IR-Src-miR-30a-E-cadherin pathway in IGF-I-induced EMT in NPC cell lines. Overall, the results of the present study may provide more useful information regarding the mechanisms of the IGF-IR signaling pathway in the regulation of NPC metastasis. Both Src kinase and miR-30a can be potential biomarkers for selecting high risk of metastasis in NPC patients.

DDR1 promotes E-cadherin stability via inhibition of integrin-β1-Src activation-mediated E-cadherin endocytosis

Discoidin domain receptor 1 (DDR1), a receptor tyrosine kinase of collagen, is primarily expressed in epithelial cells. Activation of DDR1 stabilises E-cadherin located on the cell membrane; however, the detailed mechanism of DDR1-stabilised E-cadherin remains unclear. We performed DDR1 knockdown (Sh-DDR1) on Mardin-Darby canine kidney cells to investigate the mechanism of DDR1-stabilised E-cadherin. Sh-DDR1 decreased junctional localisation, increased endocytosis of E-cadherin, and increased physical interactions between E-cadherin and clathrin. Treatment of the dynamin inhibitor Dyngo 4a suppressed Sh-DDR1-induced E-cadherin endocytosis. In addition, the phosphorylation level of Src tyrosine 418 was increased in Sh-DDR1 cell junctions, and inhibition of Src activity decreased Sh-DDR1-induced E-cadherin endocytosis. To characterise the molecular mechanisms, blocking integrin β1 decreased Src activity and E-cadherin junctional localisation in Sh-DDR1 cells. Photoconversion results showed that inhibition of Src activity rescued E-cadherin membrane stability and that inhibition of integrin β1-Src signalling decreased stress fibres and rescued E-cadherin membrane stability in Sh-DDR1 cells. Taken together, DDR1 stabilised membrane localisation of E-cadherin by inhibiting the integrin β1-Src-mediated clathrin-dependent endocytosis pathway.

The molecular effect of metastasis suppressors on Src signaling and tumorigenesis: new therapeutic targets

A major problem for cancer patients is the metastasis of cancer cells from the primary tumor. This involves: (1) migration through the basement membrane; (2) dissemination via the circulatory system; and (3) invasion into a secondary site. Metastasis suppressors, by definition, inhibit metastasis at any step of the metastatic cascade. Notably, Src is a non-receptor, cytoplasmic, tyrosine kinase, which becomes aberrantly activated in many cancer-types following stimulation of plasma membrane receptors (e.g., receptor tyrosine kinases and integrins). There is evidence of a prominent role of Src in tumor progression-related events such as the epithelial–mesenchymal transition (EMT) and the development of metastasis. However, the precise molecular interactions of Src with metastasis suppressors remain unclear. Herein, we review known metastasis suppressors and summarize recent advances in understanding the mechanisms of how these proteins inhibit metastasis through modulation of Src. Particular emphasis is bestowed on the potent metastasis suppressor, N-myc downstream regulated gene 1 (NDRG1) and its interactions with the Src signaling cascade. Recent studies demonstrated a novel mechanism through which NDRG1 plays a significant role in regulating cancer cell migration by inhibiting Src activity. Moreover, we discuss the rationale for targeting metastasis suppressor genes as a sound therapeutic modality, and we review several examples from the literature where such strategies show promise. Collectively, this review summarizes the essential interactions of metastasis suppressors with Src and their effects on progression of cancer metastasis. Moreover, interesting unresolved issues regarding these proteins as well as their potential as therapeutic targets are also discussed.

Extracellularly Extruded Syntaxin-4 Binds to Laminin and Syndecan-1 to Regulate Mammary Epithelial Morphogenesis

Epithelial morphogenesis in the mammary gland proceeds as a consequence of complex cell behaviors including apoptotic cell death and epithelial-mesenchymal transition (EMT); the extracellular matrix (ECM) protein laminin is crucially involved. Syntaxins mediate intracellular vesicular fusion, yet certain plasmalemmal members have been shown to possess latent extracellular functions. In this study, the extracellular subpopulation of syntaxin-4, extruded in response to the induction of differentiation or apoptosis in mammary epithelial cells, was detected. Using a tetracycline-repressive transcriptional system and clonal mammary epithelial cells, SCp2, we found that the expression of cell surface syntaxin-4 elicits EMT-like cell behaviors. Intriguingly, these cells did not up-regulate key transcription factors associated with the canonical EMT such as snail, slug, or twist, and repressed translation of E-cadherin. Concurrently, the cells completely evaded the cellular aggregation/rounding triggered by a potent EMT blocker laminin-111. We found that the recombinant form of syntaxin-4 not only bound to laminin but also latched onto the glycosaminoglycan (GAG) side chains of syndecan-1, a laminin receptor that mediates epithelial morphogenesis. Thus, temporal extracellular extrusion of syntaxin-4 emerged as a novel regulatory element for laminin-induced mammary epithelial cell behaviors. J. Cell. Biochem. 118: 686-698, 2017. © 2016 Wiley Periodicals, Inc.

Dynamic interplay between adhesion surfaces in carcinomas: Cell-cell and cell-matrix crosstalk

Cell-cell and cell-matrix signaling and communication between adhesion sites involve mechanisms which are required for cellular functions during normal development and homeostasis; however these cellular functions and mechanisms are often deregulated in cancer. Aberrant signaling at cell-cell and cell-matrix adhesion sites often involves downstream mediators including Rho GTPases and tyrosine kinases. This review discusses these molecules as putative mediators of cellular crosstalk between cell-cell and cell-matrix adhesion sites, in addition to their attractiveness as therapeutic targets in cancer. Interestingly, inter-junctional crosstalk mechanisms are frequently typified by the way in which bacterial and viral pathogens opportunistically infect or intoxicate mammalian cells. This review therefore also discusses the concept of learning from pathogen-host interaction studies to better understand coordinated communication between cell-cell and cell-matrix adhesion sites, in addition to highlighting the potential therapeutic usefulness of exploiting pathogens or their products to tap into inter-junctional crosstalk. Taken together, we feel that increased knowledge around mechanisms of cell-cell and cell-matrix adhesion site crosstalk and consequently a greater understanding of their therapeutic targeting offers a unique opportunity to contribute to the emerging molecular revolution in cancer biology.

Src promotes cutaneous wound healing by regulating MMP-2 through the ERK pathway

Wound healing is a highly orchestrated, multistep process, and delayed wound healing is a significant symptomatic clinical problem. Keratinocyte migration and re-epithelialization play the most important roles in wound healing, as they determine the rate of wound healing. In our previous study, we found that Src, one of the oldest proto-oncogenes encoding a membrane-associated, non-receptor protein tyrosine kinase, promotes keratinocyte migration. We therefore hypothesized that Src promotes wound healing through enhanced keratinocyte migration. In order to test this hypothesis, vectors for overexpressing Src and small interfering RNAs (siRNAs) for silencing of Src were used in the present study. We found that the overexpression of Src accelerated keratinocyte migration in vitro and promoted wound healing in vivo without exerting a marked effect on cell proliferation. The extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) signaling pathways play important roles in Src-accelerated keratinocyte migration. Further experiments demonstrated that Src induced the protein expression of matrix metallopro-teinase-2 (MMP-2) and decreased the protein expression of E-cadherin. We suggest that ERK signaling is involved in the Src-mediated regulation of MMP-2 expression. The present study provided evidence that Src promotes keratinocyte migration and cutaneous wound healing, in which the regulation of MMP-2 through the ERK pathway plays an important role, and thus we also demonstrated a potential therapeutic role for Src in cutaneous wound healing.

Protrusive activity guides changes in cell-cell tension during epithelial cell scattering

Knowing how epithelial cells regulate cell-matrix and cell-cell adhesions is essential to understand key events in morphogenesis as well as pathological events such as metastasis. During epithelial cell scattering, epithelial cell islands rupture their cell-cell contacts and migrate away as single cells on the extracellular matrix (ECM) within hours of growth factor stimulation, even as adhesion molecules such as E-cadherin are present at the cell-cell contact. How the stability of cell-cell contacts is modulated to effect such morphological transitions is still unclear. Here, we report that in the absence of ECM, E-cadherin adhesions continue to sustain substantial cell-generated forces upon hepatocyte growth factor (HGF) stimulation, consistent with undiminished adhesion strength. In the presence of focal adhesions, constraints that preclude the spreading and movement of cells at free island edges also prevent HGF-mediated contact rupture. To explore the role of cell motion and cell-cell contact rupture, we examine the biophysical changes that occur during the scattering of cell pairs. We show that the direction of cell movement with respect to the cell-cell contact is correlated with changes in the average intercellular force as well as the initial direction of cell-cell contact rupture. Our results suggest an important role for protrusive activity resulting in cell displacement and force redistribution in guiding cell-cell contact rupture during scattering.

Signaling pathways in anchoring junctions of epithelial cells: cell-to-cell and cell-to-extracellular matrix interactions

Epithelial cells form the epithelium, one of the basic tissues of the human body. These cells present specializations from tissue to tissue, determining different structures and functions. Tissues formed by epithelial cells are characterized by the few extracellular matrix found between adjacent cells. In this way, to preserve tissue integrity, cells have to stick to each other and have to maintain a strict communication with the environment via cell junctions. Signal transduction is the main way of cell communication, being vital for the regulation of cell survival and proliferation. In cell junctions, this communication occurs through cell adhesion molecules that promote cell-to-cell and cell-to-extracellular matrix adhesion, as well as, enable the flow of information to the inside and to the outside of the cell. These molecules include integrins and cadherins, among others. The impairment of cell signaling in epithelial junctions has been involved in several pathological processes that underlie the development of, for example, colorectal cancer. Thus, epithelial cell signaling mediators have been explored as potential therapeutic targets and efforts have been made to achieve a deeper understanding of molecular events that occur at cell junctions. In this review, we address the current knowledge on the main signaling events that take place in anchoring junctions of epithelial cells, focusing both on cell-to-cell and cell-to-matrix interactions. To conclude, we explore some relevant consequences from epithelial cell signaling impairment and demonstrate that the molecular mediators of the pathways analyzed may be putative therapeutic targets.

Natural history of hepatic metastases from colorectal cancer - pathobiological pathways with clinical significance

Colorectal cancer hepatic metastases represent the final stage of a multi-step biological process. This process starts with a series of mutations in colonic epithelial cells, continues with their detachment from the large intestine, dissemination through the blood and/or lymphatic circulation, attachment to the hepatic sinusoids and interactions with the sinusoidal cells, such as sinusoidal endothelial cells, Kupffer cells, stellate cells and pit cells. The metastatic sequence terminates with colorectal cancer cell invasion, adaptation and colonisation of the hepatic parenchyma. All these events, termed the colorectal cancer invasion-metastasis cascade, include multiple molecular pathways, intercellular interactions and expression of a plethora of chemokines and growth factors, and adhesion molecules, such as the selectins, the integrins or the cadherins, as well as enzymes including matrix metalloproteinases. This review aims to present recent advances that provide insights into these cell-biological events and emphasizes those that may be amenable to therapeutic targeting.

Sphingosine-1-phosphate induces differentiation of cultured renal tubular epithelial cells under Rho kinase activation via the S1P2 receptor

BACKGROUND

Sphingosine-1-phosphate (S1P) is reportedly involved in the pathogenesis of kidney disease; however, the precise role played by S1P in renal disorders still remains controversial. Rho kinase plays an important role in the development of diabetic nephropathy by inducing glomerular and tubulointerstitial fibrosis. Rho kinase is known to be stimulated by S1P through its specific receptor, S1P2 receptor (S1P2). Hence, we investigated whether S1P-S1P2 signaling plays a role in the epithelial-mesenchymal transition (EMT) through Rho kinase activation in renal tubules.

METHOD

To characterize the distribution of the S1P2, an immunohistochemical examination of the receptor was performed in the kidney of the non-diabetic and diabetic mice. Next, we examined Rho kinase activity as well as E-cadherin and alpha-smooth muscle actin (α-SMA) expression by real-time RT-PCR and western blotting in cultured rat tubular epithelial cells under S1P stimulation with and without a Rho kinase inhibitor and an S1P2 blocker. In addition, the distribution of E-cadherin and α-SMA was examined by immunocytochemistry.

RESULT

S1P2 was expressed mainly in the renal tubules; expression was intense in collecting ducts and distal tubules compared to other segments. S1P induced activation of Rho kinase through the S1P2, which changed the distribution of E-cadherin and increased the expression of α-SMA.

CONCLUSION

Rho kinase activation by S1P via S1P2 initiated EMT changes in cultured renal tubular cells. Our results suggest that excessive stimulation of S1P might facilitate renal fibrosis via activation of Rho kinase through S1P2.

Single-cell imaging of mechanotransduction in endothelial cells

Endothelial cells (ECs) are constantly exposed to chemical and mechanical microenvironment in vivo. In mechanotransduction, cells can sense and translate the extracellular mechanical cues into intracellular biochemical signals, to regulate cellular processes. This regulation is crucial for many physiological functions, such as cell adhesion, migration, proliferation, and survival, as well as the progression of disease such as atherosclerosis. Here, we overview the current molecular understanding of mechanotransduction in ECs associated with atherosclerosis, especially those in response to physiological shear stress. The enabling technology of live-cell imaging has allowed the study of spatiotemporal molecular events and unprecedented understanding of intracellular signaling responses in mechanotransduction. Hence, we also introduce recent studies on mechanotransduction using single-cell imaging technologies.

The molecular basis for the pharmacokinetics and pharmacodynamics of curcumin and its metabolites in relation to cancer

This review addresses the oncopharmacological properties of curcumin at the molecular level. First, the interactions between curcumin and its molecular targets are addressed on the basis of curcumin's distinct chemical properties, which include H-bond donating and accepting capacity of the β-dicarbonyl moiety and the phenylic hydroxyl groups, H-bond accepting capacity of the methoxy ethers, multivalent metal and nonmetal cation binding properties, high partition coefficient, rotamerization around multiple C-C bonds, and the ability to act as a Michael acceptor. Next, the in vitro chemical stability of curcumin is elaborated in the context of its susceptibility to photochemical and chemical modification and degradation (e.g., alkaline hydrolysis). Specific modification and degradatory pathways are provided, which mainly entail radical-based intermediates, and the in vitro catabolites are identified. The implications of curcumin's (photo)chemical instability are addressed in light of pharmaceutical curcumin preparations, the use of curcumin analogues, and implementation of nanoparticulate drug delivery systems. Furthermore, the pharmacokinetics of curcumin and its most important degradation products are detailed in light of curcumin's poor bioavailability. Particular emphasis is placed on xenobiotic phase I and II metabolism as well as excretion of curcumin in the intestines (first pass), the liver (second pass), and other organs in addition to the pharmacokinetics of curcumin metabolites and their systemic clearance. Lastly, a summary is provided of the clinical pharmacodynamics of curcumin followed by a detailed account of curcumin's direct molecular targets, whereby the phenotypical/biological changes induced in cancer cells upon completion of the curcumin-triggered signaling cascade(s) are addressed in the framework of the hallmarks of cancer. The direct molecular targets include the ErbB family of receptors, protein kinase C, enzymes involved in prostaglandin synthesis, vitamin D receptor, and DNA.

Ocular hypotensive efficacy of Src-family tyrosine kinase inhibitors via different cellular actions from Rock inhibitors

We investigated the effects of Src-family tyrosine kinase (SFK) inhibitors on intraocular pressure (IOP) and trabecular meshwork (TM) cells. The SFK inhibitors, PP2, PP1, and damnacanthal, significantly lowered IOP from baseline following intracameral injection in ocular normotensive rabbits, and PP2 decreased trans-epithelial electrical resistance (TEER) of TM cell layers in a dose-dependent manner ranging from 0.1 μM to 100 μM. The maximal efficacy of PP2 on TEER was a reduction to 71.7% relative to the vehicle-treated group at 100 μM. PP2 decreased the adhesion of TM cells to culture surfaces either uncoated with specific ECM proteins dose-dependently or coated with extracellular matrix proteins such as laminin I, fibronectin, collagen type I and basement membrane extraction. Tyrosine phosphorylation of focal adhesion kinase and p130(cas) was decreased by PP2. On the other hand, major changes in actin staining of TM cells were not able to be detected after PP2 treatment, although quantitative analysis showed that PP2 induced some morphological changes which were in the different direction to those caused by Y-27632, a Rock inhibitor. Y-27632 at 10 μM increased the permeability of TM cell layers, but did not induce changes in the adhesion of TM cells. These results suggest that SFK inhibitors lower IOP, at least partly, by acting on TM cells in a manner that is distinct from Rock inhibitors.

PTK6 activation at the membrane regulates epithelial-mesenchymal transition in prostate cancer

The intracellular tyrosine kinase protein tyrosine kinase 6 (PTK6) lacks a membrane-targeting SH4 domain and localizes to the nuclei of normal prostate epithelial cells. However, PTK6 translocates from the nucleus to the cytoplasm in human prostate tumor cells. Here, we show that while PTK6 is located primarily within the cytoplasm, the pool of active PTK6 in prostate cancer cells localizes to membranes. Ectopic expression of membrane-targeted active PTK6 promoted epithelial-mesenchymal transition in part by enhancing activation of AKT, thereby stimulating cancer cell migration and metastases in xenograft models of prostate cancer. Conversely, siRNA-mediated silencing of endogenous PTK6 promoted an epithelial phenotype and impaired tumor xenograft growth. In mice, PTEN deficiency caused endogenous active PTK6 to localize at membranes in association with decreased E-cadherin expression. Active PTK6 was detected at membranes in some high-grade human prostate tumors, and PTK6 and E-cadherin expression levels were inversely correlated in human prostate cancers. In addition, high levels of PTK6 expression predicted poor prognosis in patients with prostate cancer. Our findings reveal novel functions for PTK6 in the pathophysiology of prostate cancer, and they define this kinase as a candidate therapeutic target. Cancer Res; 73(17); 5426-37. ©2013 AACR.

Complex temporal changes in TGFβ oncogenic signaling drive thyroid carcinogenesis in a mouse model

Despite recent advances, understanding of molecular genetic alterations underlying thyroid carcinogenesis remains unclear. One key question is how dynamic temporal changes in global genomic expression affect carcinogenesis as the disease progresses. To address this question, we used a mouse model that spontaneously develops follicular thyroid cancer similar to human cancer (Thrb (PV/PV) mice). Using complementary DNA microarrays, we compared global gene expression profiles of thyroid tumors of Thrb (PV/PV) mice with the age- and gender-matched thyroids of wild-type mice at 3 weeks and at 2, 4, 6 and 14 months. These time points covered the pathological progression from early hyperplasia to capsular invasion, vascular invasion and eventual metastasis. Microarray data indicated that 462 genes were upregulated (Up-cluster genes) and 110 genes were downregulated (Down-cluster genes). Three major expression patterns (trending up, cyclical and spiking up and then down) and two (trending down and cyclical) were apparent in the Up-cluster and Down-cluster genes, respectively. Functional clustering of tumor-related genes followed by Ingenuity Pathways Analysis identified the transforming growth factor β (TGF β)-mediated network as key signaling pathways. Further functional analyses showed sustained activation of TGFβ receptor-pSMAD2/3 signaling, leading to decreased expression of E-cadherin and increased expression of fibronectin, vimentin, collagens and laminins. These TGFβ-induced changes facilitated epithelial-to-mesenchymal transition, which promotes cancer invasion and migration. Thus, complex temporal changes in gene expression patterns drive thyroid cancer progression, and persistent activation of TGFβ-TGFRβII-pSMAD2/3 signaling leads to EMT, thus promoting metastasis. This study provides new understanding of progression and metastatic spread of human thyroid cancer.

E-cadherin-integrin crosstalk in cancer invasion and metastasis

E-cadherin is a single-pass transmembrane protein that mediates homophilic cell-cell interactions. Tumour progression is often associated with the loss of E-cadherin function and the transition to a more motile and invasive phenotype. This requires the coordinated regulation of both E-cadherin-mediated cell-cell adhesions and integrin-mediated adhesions that contact the surrounding extracellular matrix (ECM). Regulation of both types of adhesion is dynamic as cells respond to external cues from the tumour microenvironment that regulate polarity, directional migration and invasion. Here, we review the mechanisms by which tumour cells control the cross-regulation between dynamic E-cadherin-mediated cell-cell adhesions and integrin-mediated cell-matrix contacts, which govern the invasive and metastatic potential of tumours. In particular, we will discuss the role of the adhesion-linked kinases Src, focal adhesion kinase (FAK) and integrin-linked kinase (ILK), and the Rho family of GTPases.

A tale of two collagen receptors, integrin β1 and discoidin domain receptor 1, in epithelial cell differentiation

As increase in collagen deposition is no longer taken as simply a consequence but, rather, an inducer of disease progression; therefore, the understanding of collagen signal transduction is fundamentally important. Cells contain at least two types of collagen receptors: integrins and discoidin domain receptors (DDRs). The integrin heterodimers α1β1, α2β1, α10β1, and α11β1 are recognized as the non-tyrosine kinase collagen receptors. DDR1 and 2, the tyrosine kinase receptors of collagen, are specifically expressed in epithelium and mesenchyme, respectively. While integrin β1 and DDR1 are both required for cell adhesion on collagen, their roles in epithelial cell differentiation during development and disease progression seem to counteract each other, with integrin β1 favoring epithelium mesenchyme transition (EMT) and DDR1 inducing epithelial cell differentiation. The in vitro evidence shows that the integrin β1 and DDR1 exert opposing actions in regulation of membrane stability of E-cadherin, which itself is a critical regulator of epithelial cell differentiation. Here, we review the functional roles of integrin β1 and DDR1 in regulation of epithelial cell differentiation during development and disease progression, and explore the underlining mechanisms regarding to the regulation of membrane stability of E-cadherin.

[Regulation of intercellular adhesion during epithelial morphogenesis]

The epithelium is one of the most abundant tissues in metazoans. It is required to generate stable chemical and mechanical barriers between physiological compartments (fluid matrix/external environment). This function is based on multiple intercellular junctions, which insulate and stabilize cell-cell contacts in the tissue. Despite this apparent robustness, epithelia can be extensively remodeled during wound healing, embryogenesis and tumor progression. The capacity to be remodeled while keeping tissue cohesion requires a perfect balance between stability and plasticity of intercellular junctions. The balance is partially regulated by intercellular adhesion, which is mostly based on adherens junctions and the transmembrane protein E-cadherin. The aim of this review is to report the molecular basis of the balance between plasticity and robustness in the epithelium. We will first present the minimal physical framework used to describe epithelial cell shape. We will then describe the main processes involved in intercellular adhesion regulation and their functions during epithelial morphogenesis. Eventually, we will analyze the relationship and the coupling between adhesive forces and cortical tension.

EMT and oxidative stress: a bidirectional interplay affecting tumor malignancy

SIGNIFICANCE

Epithelial-mesenchymal transition (EMT) is emerging as a driving force in tumor progression, enabling cancer cells to evade their "homeland" and to colonize remote locations. In this review, we focus on the emerging views dealing with a redox control of EMT and with the importance of a pro-oxidant environment, both in cancer and stromal cells, to attain an improvement in tumor malignancy.

RECENT ADVANCES

The variety of signals able to promote EMT is large and continuously growing, ranging from soluble factors to components of the extracellular matrix. Compelling evidence highlights reactive oxygen species (ROS) as crucial conspirators in EMT engagement.

CRITICAL ISSUES

Tumor microenvironment exploits a fascinating role in ensuring EMT outcome within the primary tumor, granting for the achievement of an essential selective advantage for cancer cells. Cancer-associated fibroblasts, macrophages, and hypoxia are major players in this scenario, exerting a propelling role for EMT, as well as for invasiveness, stemness, and dissemination of metastatic cells.

FUTURE DIRECTIONS

Future research focused on EMT should address some key points that are still unclear. They include: i) the role of the reverse phenomenon (i.e., mesenchymal-epithelial transition) that is likely regulated in the final stages of tumor progression, or that of mesenchymal-amoeboid transition, a plasticity program of cancer cells, which often follows EMT and offers a further metastatic advantage, and ii) the molecular basis of the correlation between stemness, EMT and ROS content.

Crossroads of integrins and cadherins in epithelia and stroma remodeling

Adhesion events mediated by cadherin and integrin adhesion receptors have fundamental roles in the maintenance of the physiological balance of epithelial tissues, and it is well established that perturbations in their normal functional activity and/or changes in their expression are associated with tumorigenesis. Over the last decades, increasing evidence of a dynamic collaborative interaction between these complexes through their shared interactions with cytoskeletal proteins and common signaling pathways has emerged not only as an important regulator of several aspects of epithelial cell behavior, but also as a coordinated adhesion module that senses and transmits signals from and to the epithelia surrounding microenvironment. The tight regulation of their crosstalk is particularly important during epithelial remodeling events that normally take place during morphogenesis and tissue repair, and when defective it leads to cell transformation and aggravated responses of the tumor microenvironment that contribute to tumorigenesis. In this review we highlight some of the interactions that regulate their crosstalk and how this could be implicated in regulating signals across epithelial tissues to sustain homeostasis.

Rac1 and RhoA GTPases have antagonistic functions during N-cadherin-dependent cell-cell contact formation in C2C12 myoblasts

BACKGROUND INFORMATION

N-cadherin, a member of the Ca(2+)-dependent cell-cell adhesion molecule family, plays an essential role in the induction of the skeletal muscle differentiation programme. However, the molecular mechanisms which govern the formation of N-cadherin-dependent cell-cell contacts in myoblasts remain unexplored.

RESULTS

In the present study, we show that N-cadherin-dependent cell contact formation in myoblasts is defined by two stages. In the first phase, N-cadherin is highly mobile in the lamellipodia extensions between the contacting cells. The second stage corresponds to the formation of mature N-cadherin-dependent cell contacts, characterized by the immobilization of a pool of N-cadherin which appears to be clustered in the interdigitated membrane structures that are also membrane attachment sites for F-actin filaments. We also demonstrated that the formation of N-cadherin-dependent cell-cell contacts requires a co-ordinated and sequential activity of Rac1 and RhoA. Rac1 is involved in the first stage and facilitates N-cadherin-dependent cell-cell contact formation, but it is not absolutely required. Conversely, RhoA is necessary for N-cadherin-dependent cell contact formation, since, via ROCK (Rho-associated kinase) signalling and myosin 2 activation, it allows the stabilization of N-cadherin at the cell-cell contact sites.

CONCLUSIONS

We have shown that Rac1 and RhoA have opposite effects on N-cadherin-dependent cell-cell contact formation in C2C12 myoblasts and act sequentially to allow its formation.

Protein-tyrosine kinase 6 promotes peripheral adhesion complex formation and cell migration by phosphorylating p130 CRK-associated substrate

Protein-tyrosine kinase 6 (PTK6) is a non-myristoylated intracellular tyrosine kinase evolutionarily related to Src kinases. Aberrant PTK6 expression and intracellular localization have been detected in human prostate tumors. In the PC3 prostate cancer cell line, the pool of endogenous activated PTK6, which is phosphorylated on tyrosine residue 342, is localized at the membrane. Expression of ectopic membrane-targeted PTK6 led to dramatic morphology changes and formation of peripheral adhesion complexes in PC3 cells. Peripheral adhesion complex formation was dependent upon PTK6 kinase activity. We demonstrated that p130 CRK-associated substrate (p130CAS) is a novel direct substrate of PTK6, and it works as a crucial adapter protein in inducing peripheral adhesion complexes. Activation of ERK5 downstream of p130CAS was indispensable for this process. Knockdown of endogenous PTK6 led to reduced cell migration and p130CAS phosphorylation, whereas knockdown of p130CAS attenuated oncogenic signaling induced by membrane-targeted PTK6, including ERK5 and AKT activation. Expression of membrane-targeted PTK6 promoted cell migration, which could be impaired by knockdown of p130CAS or ERK5. Our study reveals a novel function for PTK6 at the plasma membrane and suggests that the PTK6-p130CAS-ERK5 signaling cascade plays an important role in cancer cell migration and invasion.

Integrins and cadherins join forces to form adhesive networks

Cell-cell and cell-extracellular-matrix (cell-ECM) adhesions have much in common, including shared cytoskeletal linkages, signaling molecules and adaptor proteins that serve to regulate multiple cellular functions. The term 'adhesive crosstalk' is widely used to indicate the presumed functional communication between distinct adhesive specializations in the cell. However, this distinction is largely a simplification on the basis of the non-overlapping subcellular distribution of molecules that are involved in adhesion and adhesion-dependent signaling at points of cell-cell and cell-substrate contact. The purpose of this Commentary is to highlight data that demonstrate the coordination and interdependence of cadherin and integrin adhesions. We describe the convergence of adhesive inputs on cell signaling pathways and cytoskeletal assemblies involved in regulating cell polarity, migration, proliferation and survival, differentiation and morphogenesis. Cell-cell and cell-ECM adhesions represent highly integrated networks of protein interactions that are crucial for tissue homeostasis and the responses of individual cells to their adhesive environments. We argue that the machinery of adhesion in multicellular tissues comprises an interdependent network of cell-cell and cell-ECM interactions and signaling responses, and not merely crosstalk between spatially and functionally distinct adhesive specializations within cells.

Src/FAK-mediated regulation of E-cadherin as a mechanism for controlling collective cell movement: insights from in vivo imaging

Recent advances in confocal and multi-photon microscopy, together with fluorescent probe development, have enabled cancer biology studies to go beyond the culture dish and interrogate cancer-associated processes in the complex in vivo environment. Regulation of the tumor suppressor protein E-cadherin plays an important role in cancer development and progression and may contribute to the decision between 'single cell' and 'collective invasion' in vivo. Mounting evidence from in vitro and in vivo experiments places the two non-receptor protein tyrosine kinases Src and Focal Adhesion Kinase, at the heart of E-cadherin regulation, and the crosstalk between integrins and cadherins. Here we discuss recent insights, attained using high resolution fluorescent in vivo imaging, into the regulation of E-cadherin and collective invasion. We focus on the regulatory crosstalk between the Src/FAK signaling axis and E-cadherin in vivo.

Rack1 promotes epithelial cell-cell adhesion by regulating E-cadherin endocytosis

E-cadherin and its cytoplasmic partners, catenins, mediate epithelial cell-cell adhesion. Disruption of this adhesion allows cancer cells to invade and metastasize. Aberrant activation of the Src tyrosine kinase disrupts cell-cell contacts through an E-cadherin/catenin-dependent mechanism. Previously we showed that Rack1 regulates the growth of colon cells by suppressing Src activity at G(1) and mitotic checkpoints, and in the intrinsic apoptotic and Akt cell survival pathways. Here we show that Rack1, partly by inhibiting Src, promotes cell-cell adhesion and reduces the invasive potential of colon cancer cells. Rack1 stabilizes E-cadherin and catenins at cell-cell contacts by inhibiting the Src phosphorylation of E-cadherin, the ubiquitination of E-cadherin by the E3 ligase Hakai and the endocytosis of E-cadherin. Upon depletion and restoration of extracellular calcium, Rack1 facilitates the re-assembly of E-cadherin-containing cell-cell contacts. Rack1 also blocks HGF-induced endocytosis of E-cadherin, disruption of cell-cell contacts and cell scatter. Our results uncover a novel function of Rack1 in maintaining the junctional homeostasis of intestinal epithelial cells by regulation of the Src- and growth factor-induced endocytosis of E-cadherin.

NUMB-ing down cancer by more than just a NOTCH

The protein Numb does not live up to its name. This passive-sounding protein is anything but spent. Originally identified as a cell-fate determinant in Drosophila development, Numb received a good deal of attention as an inhibitor of the Notch receptor signaling pathway. It turns out, however, that Numb does a lot more than simply regulate Notch. It has been implicated in a variety of biochemical pathways connected with signaling (it regulates Notch-, Hedgehog- and TP53-activated pathways), endocytosis (it is involved in cargo internalization and recycling), determination of polarity (it interacts with the PAR complex, and regulates adherens and tight junctions), and ubiquitination (it exploits this mechanism to regulate protein function and stability). This complex biochemical network lies at the heart of Numb's involvement in diverse cellular phenotypes, including cell fate developmental decisions, maintenance of stem cell compartments, regulation of cell polarity and adhesion, and migration. Considering its multifaceted role in cellular homeostasis, it is not surprising that Numb has been implicated in cancer as a tumor suppressor. Our major goal here is to explain the cancer-related role of Numb based on our understanding of its role in cell physiology. We will attempt to do this by reviewing the present knowledge of Numb at the biochemical and functional level, and by integrating its apparently heterogeneous functions into a unifying scenario, based on our recently proposed concept of the "endocytic matrix". Finally, we will discuss the role of Numb in the maintenance of the normal stem cell compartment, as a starting point to interpret the tumor suppressor function of Numb in the context of the cancer stem cell hypothesis.

Tumor budding as a strong prognostic indicator in invasive ampullary adenocarcinomas

Prognostication of invasive ampullary adenocarcinomas (AACs) and their stratification into appropriate management categories have been highly challenging owing to a lack of well-established predictive parameters. In colorectal cancers, recent studies have shown that tumor budding confers a worse prognosis and correlates significantly with nodal metastasis and recurrence; however, this has not been evaluated in AAC.To investigate the prevalence, significance, and clinical correlations of tumor budding in AAC, 244 surgically resected, stringently defined, invasive AAC were analyzed for tumor budding---defined as the presence of more than or equal to 5 isolated single cancer cells or clusters composed of fewer than 5 cancer cells per field measuring 0.785 mm using a 20× objective lens in the stroma of the invasive front. The extent of the budding was then further classified as "high" if there were greater than or equal to 3 budding foci and as "low" if there were <3 budding foci or no budding focus.One hundred ninety-four AACs (80%) were found to be high-budding and 50 (20%) were low-budding. When the clinicopathologic features and survival of the 2 groups were compared, the AACs with high-budding had larger invasion size (19 mm vs. 13 mm; P<0.001), an unrecognizable/absent preinvasive component (57% vs. 82%; P<0.005), infiltrative growth (51% vs. 2%; P<0.001), nonintestinal-type histology (72% vs. 46%; P<0.001), worse differentiation (58% vs. 10%; P<0.001), more lymphatic (74% vs. 10%; P<0.001), and perineural invasion (28% vs. 2%; P<0.001); more lymph node metastasis (44% vs. 17%; P<0.001), higher T-stage (T3 and T4) (42% vs. 10%; P<0.001), and more aggressive behavior (mean survival: 50 mo vs. 32 mo; 3-year and 5-year survival rates: 93% vs. 41% and 68% vs. 24%, respectively; P<0.001). Furthermore, using a multivariable Cox regression model, tumor budding was found to be an independent predictor of survival (P=0.01), which impacts prognosis (hazard ratio: 2.6) even more than T-stage and lymph node metastasis (hazard ratio: 1.9 and 1.8, respectively).In conclusion, tumor budding is frequently encountered in AAC. High-budding is a strong independent predictor of overall survival, with a prognostic correlation stronger than the 2 established parameters: T-stage and lymph node metastasis. Therefore, budding should be incorporated into surgical pathology reports for AAC.

Vinculin potentiates E-cadherin mechanosensing and is recruited to actin-anchored sites within adherens junctions in a myosin II-dependent manner

Vinculin localizes to tension-bearing cell–cell junctions to help transmit signals from E-cadherin to the actin cytoskeleton in response to mechanical stress.

Cell surface receptors integrate chemical and mechanical cues to regulate a wide range of biological processes. Integrin complexes are the mechanotransducers between the extracellular matrix and the actomyosin cytoskeleton. By analogy, cadherin complexes may function as mechanosensors at cell–cell junctions, but this capacity of cadherins has not been directly demonstrated. Furthermore, the molecular composition of the link between E-cadherin and actin, which is needed to sustain such a function, is unresolved. In this study, we describe nanomechanical measurements demonstrating that E-cadherin complexes are functional mechanosensors that transmit force between F-actin and E-cadherin. Imaging experiments reveal that intercellular forces coincide with vinculin accumulation at actin-anchored cadherin adhesions, and nanomechanical measurements show that vinculin potentiates the E-cadherin mechanosensory response. These investigations directly demonstrate the mechanosensory capacity of the E-cadherin complex and identify a novel function for vinculin at cell–cell junctions. These findings have implications for barrier function, morphogenesis, cell migration, and invasion and may extend to all soft tissues in which classical cadherins regulate cell–cell adhesion.