Kinetics of v-src-induced epithelial-mesenchymal transition in developing glandular stomach

c-Met activation leads to the establishment of a TGFβ-receptor regulatory network in bladder cancer progression

Treatment of muscle-invasive bladder cancer remains a major clinical challenge. Aberrant HGF/c-MET upregulation and activation is frequently observed in bladder cancer correlating with cancer progression and invasion. However, the mechanisms underlying HGF/c-MET-mediated invasion in bladder cancer remains unknown. As part of a negative feedback loop SMAD7 binds to SMURF2 targeting the TGFβ receptor for degradation. Under these conditions, SMAD7 acts as a SMURF2 agonist by disrupting the intramolecular interactions within SMURF2. We demonstrate that HGF stimulates TGFβ signalling through c-SRC-mediated phosphorylation of SMURF2 resulting in loss of SMAD7 binding and enhanced SMURF2 C2-HECT interaction, inhibiting SMURF2 and enhancing TGFβ receptor stabilisation. This upregulation of the TGFβ pathway by HGF leads to TGFβ-mediated EMT and invasion. In vivo we show that TGFβ receptor inhibition prevents bladder cancer invasion. Furthermore, we make a rationale for the use of combinatorial TGFβ and MEK inhibitors for treatment of high-grade non-muscle-invasive bladder cancers.

Cytokinesis Failure Leading to Chromosome Instability in v-Src-Induced Oncogenesis

v-Src, an oncogene found in Rous sarcoma virus, is a constitutively active variant of c-Src. Activation of Src is observed frequently in colorectal and breast cancers, and is critical in tumor progression through multiple processes. However, in some experimental conditions, v-Src causes growth suppression and apoptosis. In this review, we highlight recent progress in our understanding of cytokinesis failure and the attenuation of the tetraploidy checkpoint in v-Src-expressing cells. v-Src induces cell cycle changes—such as the accumulation of the 4N cell population—and increases the number of binucleated cells, which is accompanied by an excess number of centrosomes. Time-lapse analysis of v-Src-expressing cells showed that cytokinesis failure is caused by cleavage furrow regression. Microscopic analysis revealed that v-Src induces delocalization of cytokinesis regulators including Aurora B and Mklp1. Tetraploid cell formation is one of the causes of chromosome instability; however, tetraploid cells can be eliminated at the tetraploidy checkpoint. Interestingly, v-Src weakens the tetraploidy checkpoint by inhibiting the nuclear exclusion of the transcription coactivator YAP, which is downstream of the Hippo pathway and its nuclear exclusion is critical in the tetraploidy checkpoint. We also discuss the relationship between v-Src-induced chromosome instability and growth suppression in v-Src-induced oncogenesis.

Characterization and Endocytic Internalization of Epith-2 Cell Surface Glycoprotein during the Epithelial-to-Mesenchymal Transition in Sea Urchin Embryos

The epithelial cells of the sea urchin Hemicentrotus pulcherrimus embryo express an Epith-2, uncharacterized glycoprotein, on the lateral surface. Here, we describe internalization of Epith-2 during mesenchyme formation through the epithelial-to-mesenchymal transition (EMT). Epith-2 was first expressed on the entire egg surface soon after fertilization and on the blastomeres until the 4-cell stage, but was localized to the lateral surface of epithelial cells at and after the 16-cell stage throughout the later developmental period. However, primary mesenchyme cells (PMC) and secondary mesenchyme cells (SMC) that ingress by EMT lost Epith-2 from their cell surface by endocytosis during dissociation from the epithelium, which was associated with the appearance of cytoplasmic Epith-2 dots. The cytoplasmic Epith-2 retained a similar relative molecular mass to that of the cell surface immediately after ingression through the early period of the spreading to single cells. Then, Epith-2 was completely lost from the cytoplasm. Tyrosine residues of Epith-2 were phosphorylated. The endocytic retraction of Epith-2 was inhibited by herbimycin A (HA), a protein tyrosine kinase (PTK) inhibitor, and suramin, a growth factor receptor (GFR) inhibitor, suggesting the involvement of the GFR/PTK (GP) signaling pathway. These two GP inhibitors also inhibited PMC and SMC spreading to individual cells after ingression, but the dissociation of PMC and SMC from the epithelium was not inhibited. In suramin-treated embryos, dissociated mesenchyme cells migrated partially by retaining their epithelial morphology. In HA-treated embryos, no mesenchyme cells migrated. Thus, the EMT occurs in relation to internalization of Epith-2 from presumptive PMC and SMC.

Fibrous stroma is associated with poorer prognosis in lung squamous cell carcinoma patients

INTRODUCTION

Cancer tissue is composed of various stromal cells forming cancer-specific microenvironments. Peritumoral stroma is reportedly composed of activated fibroblasts that can influence the biological properties of tumor cells, mainly their local aggressiveness and their ability. The aim of this study was to examine whether the histological properties of peritumoral stroma are correlated with squamous cell carcinoma (SqCC) aggressiveness and clinical outcome.

METHODS

A series of 220 pathological stage I lung SqCC were categorized into two types according to the histological properties of the peritumoral stroma, "fibrous stroma type" (n = 85), and "thin stroma type" (n = 135), and compared the prognostic significance. Furthermore, we compared the immunohistochemical properties of the SqCC cells surrounded by "fibrous stroma" with those of the SqCC cells surrounded by "thin stroma."

RESULTS

The prognosis of the patients with fibrous stroma-type tumors was significantly poorer than that of the thin stroma type with regard to both recurrence-free survival (p = 0.005) and overall survival (p = 0.008). A multivariate analysis showed that the presence of a fibrous stroma was an independent prognostic factor (p = 0.030). Compared with the SqCC cells with a thin stroma, the SqCC cells with a fibrous stroma exhibited reduced expression of E-cadherin (55.9 versus 126.0, p < 0.001) and an increased expression of laminin-5γ2 (94.6 versus 25.0, p = 0.001), matrix metalloproteinase-7 (26.0 versus 3.50, p = 0.009), and c-Met (64.0 versus 36.5, p = 0.033).

CONCLUSION

SqCC with a fibrous stroma displayed higher invasive phenotype and were associated with a significantly poor prognosis. The current results suggest that the microenvironment created by both SqCC cells and the peritumoral fibroblasts may facilitate cancer aggressiveness.

Slit-Robo signaling induces malignant transformation through Hakai-mediated E-cadherin degradation during colorectal epithelial cell carcinogenesis

The Slit family of guidance cues binds to Roundabout (Robo) receptors and modulates cell migration. We report here that ectopic expression of Slit2 and Robo1 or recombinant Slit2 treatment of Robo1-expressing colorectal epithelial carcinoma cells recruited an ubiquitin ligase Hakai for E-cadherin (E-cad) ubiquitination and lysosomal degradation, epithelial-mesenchymal transition (EMT), and tumor growth and liver metastasis, which were rescued by knockdown of Hakai. In contrast, knockdown of endogenous Robo1 or specific blockade of Slit2 binding to Robo1 prevented E-cad degradation and reversed EMT, resulting in diminished tumor growth and liver metastasis. Ectopic expression of Robo1 also triggered a malignant transformation in Slit2-positive human embryonic kidney 293 cells. Importantly, the expression of Slit2 and Robo1 was significantly associated with an increased metastatic risk and poorer overall survival in colorectal carcinoma patients. We conclude that engagement of Robo1 by Slit2 induces malignant transformation through Hakai-mediated E-cad ubiquitination and lysosomal degradation during colorectal epithelial cell carcinogenesis.

Src signaling in cancer invasion

Src is a non-receptor cytoplasmic tyrosine kinase which becomes activated following the stimulation of plasma membrane receptors including receptor tyrosine kinases and integrins, and is an indispensable player of multiple physiological homeostatic pathways. Once activated, Src is the starting point for several biochemical cascades that thereby propagate signals generated extracellularly along intracellular interconnected transduction pathways. Src transmits signals promoting cell survival and mitogenesis and, in addition, exerts a profound effect on the reorganization of the cytoskeleton and the adhesion systems that underpin cell migration and invasion. Because increased activity of Src is a frequent occurrence in many types of human cancer, and because there is evidence of a prominent role of Src in invasion and in other tumor progression-related events such as epithelial-mesenchymal transition (EMT) and development of metastasis, inhibitors targeting Src are being viewed as promising drugs for cancer therapy.

Destabilized adhesion in the gastric proliferative zone and c-Src kinase activation mark the development of early diffuse gastric cancer

The initial development of diffuse gastric cancer (DGC) is poorly understood. The study of E-cadherin (CDH1) germ line mutation carriers predisposed to DGC provides a rare opportunity to elucidate the genetic and biological events surrounding disease initiation. Samples from various stages of hereditary and sporadic DGC were investigated to determine general mechanisms underlying early DGC development. Paraffin-embedded tissues from 13 CDH1 mutation carriers and from 10 sporadic early DGC cases were analyzed. Immunofluorescence and immunohistochemistry using differentiation, proliferation, and adhesion markers showed that DGC initiation seems to occur at the proliferative zone (the upper neck) of the gastric epithelium and correlates with absent or reduced expression of junctional proteins (beta-actin, p120, Lin-7). Slow proliferation of neoplastic cells at the upper gastric neck leads to the formation of intramucosal signet-ring cell carcinoma (SRCC) displaying differentiated features. As shown by immunolabeling, invasion from SRCC lesions beyond the gastric mucosa is associated with poor differentiation, increased proliferation, activation of the c-Src system, and an epithelial-mesenchymal transition. Our results provide a molecular description of the early development of DGC and explain the relationship between the two main DGC types, poorly differentiated carcinoma and SRCC: both share their origin, but SRCC develops following cancer cell differentiation and seems relatively indolent in its intramucosal stage.

Wnt signalling in lung development and diseases

There are several signalling pathways involved in lung organogenesis including Notch, TGFbeta/BMP, Sonic hedgehog (Shh), FGF, EGF, and Wnt. Despite the widely acknowledged significance of Wnt signalling in embryonic lung development, the role of different Wnt pathways in lung pathologies has been slow to emerge. In this review, we will present a synopsis of current Wnt research with particular attention paid to the role of Wnt signals in lung development and in pulmonary diseases.

Disassembling adherens junctions: breaking up is hard to do

Epithelial cells regulate their contacts with neighboring cells during embryonic development and in disease states such as tumor metastasis. The intercellular adherens junctions (AJs) are specialized subapical structures that function as principle mediators of cell-cell adhesion. Their disassembly correlates with a loss of cell-cell contact and an acquisition of migratory potential. Regulation of the expression of AJ components by gene transcription can dictate the stability of intercellular adhesive contacts, and accruing evidence indicates that the coordinated regulation of cellular processes such as membrane trafficking and cytoskeletal remodeling can also result in the effective dissolution of AJs. Studies of the posttranscriptional mechanisms by which adhesive interactions are regulated in response to growth factors and/or developmental cues have opened new avenues for investigating cell-cell adhesion during development and in disease.

Lysosomal targeting of E-cadherin: a unique mechanism for the down-regulation of cell-cell adhesion during epithelial to mesenchymal transitions

A hallmark characteristic of epithelial tumor progression as well as some processes of normal development is the loss of the epithelial phenotype and acquisition of a motile or mesenchymal phenotype. Such epithelial to mesenchymal transitions are accompanied by the loss of E-cadherin function by either transcriptional or posttranscriptional mechanisms. Here we demonstrate that, upon v-Src expression, a potent trigger of epithelial to mesenchymal transitions, E-cadherin is internalized and then shuttled to the lysosome instead of being recycled back to the lateral membrane. Thus, while E-cadherin internalization facilitates the dissolution of adherens junctions, its subsequent traffic to the lysosome serves as a means to ensure that cells do not reform their cell-cell contacts and remain motile. We also show that ubiquitin tagging of E-cadherin is essential for its sorting to the lysosome. The lysosomal targeting of E-cadherin is mediated by hepatocyte growth factor-regulated tyrosine kinase substrate (Hrs) and v-Src-induced activation of the Rab5 and Rab7 GTPases. Our studies reveal that the lysosomal targeting of E-cadherin is an important posttranscriptional mechanism to deplete cellular E-cadherin during Src-induced epithelial to mesenchymal transitions.

Srcasm modulates EGF and Src-kinase signaling in keratinocytes

The Src-activating and signaling molecule (Srcasm) is a recently described activator and substrate of Src-family tyrosine kinases (SFKs). When phosphorylated at specific tyrosines, Srcasm associates with Grb2 and p85, the regulatory subunit of phosphoinositide 3-kinase; however, little is known about the role of Srcasm in cellular signaling. Data presented here demonstrate that epidermal growth factor (EGF) receptor ligands promote the tyrosine phosphorylation of endogenous and adenovirally transduced Srcasm in keratinocytes, and that increased levels of Srcasm activate endogenous SFKs, with a preference for Fyn and Src. In addition, Srcasm potentiates EGF-dependent signals transmitted by SFKs in keratinocytes. Tyrosine phosphorylation of Srcasm is dependent on growth factors and the activity of EGFR and SFKs. Increased Srcasm expression enhances p44/42 mitogen-activated protein kinase activity and Elk-1-dependent transcriptional events. Elevated Srcasm levels inhibit keratinocyte proliferation while promoting specific aspects of keratinocyte differentiation. Lastly, Srcasm levels are decreased in human cutaneous neoplasia. Collectively, these data demonstrate that Srcasm plays a role in linking EGF receptor- and SFK-dependent signaling to differentiation in keratinocytes.

Newest findings on the oldest oncogene; how activated src does it

Oncogenic forms of the non-receptor tyrosine kinase Src alter cell structure, in particular the actin cytoskeleton and the adhesion networks that control cell migration, and also transmit signals that regulate proliferation and cell survival. Recent work indicates that they do so by influencing the RhoA-ROCK pathway that controls contractile actin filament assembly, the STAT family of transcription factors needed for transformation, and the Cbl ubiquitin ligase that controls Src protein levels. These studies also shed light on the role of focal adhesion kinase (FAK) downstream of v-Src and other signalling pathways in controlling migration, invasion and survival of transformed cells. Src directly phosphorylates integrins and can also modulate R-Ras activity. Moreover, it stimulates the E-cadherin regulator Hakai, interacts with and phosphorylates the novel podosome-linked adaptor protein Fish, and progressively phosphorylates the gap junction component connexion 43. A recurring theme is the identification of novel and important Src substrates that mediate key biological events associated with transformation.

Histochemical, ultrastructural, and three-dimensional observation of smooth muscle cells in human gastric mucosa

The present study was undertaken to clarify the histochemical and ultrastructural properties and the three-dimensional distribution of the smooth muscle cells (SMCs) located in the lamina propria (LP) of the human gastric mucosa. Standard paraffin sections obtained from stomachs surgically resected for gastric cancer were immunostained for alpha-smooth muscle actin (alpha-SMA), vimentin, desmin, laminin, and type IV collagen. In addition, 100-microm-thick sections were fluorostained for alpha-SMA and CD34, while three-dimensional images were prepared by confocal laser scanning microscope. Ultrastructural studies were carried out using normal gastric biopsy specimens. The results indicated that SMCs in the LP differed between the upper and lower regions, SMCs in the lower LP being fairly typical SMCs, whereas those in the upper LP had apparently lost reactivity for desmin but gained that for vimentin. The basal lamina became sparser, but a fibronexus was occasionally seen in SMCs in the upper LP. Three-dimensional images revealed bundles of SMCs in the upper LP encircling several foveolae to form acinus-like structures and, in the upper LP, SMCs branching into fine fibrils with a brush-like (corpus) or besom-like (i.e., a twiggy "witch's broom") appearance (antrum).

Epithelial–mesenchymal transitions in development and pathologies

The epithelial-mesenchymal transition (EMT) is a fundamental process governing morphogenesis in multicellular organisms. This process is also reactivated in a variety of diseases including fibrosis and in the progression of carcinoma. The molecular mechanisms of EMT were primarily studied in epithelial cell lines, leading to the discovery of transduction pathways involved in the loss of epithelial cell polarity and the acquisition of a variety of mesenchymal phenotypic traits. Similar mechanisms have also been uncovered in vivo in different species, showing that EMT is controlled by remarkably well-conserved mechanisms. Current studies further emphasise the critical importance of EMT and provide a better molecular and functional definition of mesenchymal cells and how they emerged >500 million years ago as a key event in evolution.