p120 Catenin is required for growth factor-dependent cell motility and scattering in epithelial cells

Resolving the role of podoplanin in the motility of papillary thyroid carcinoma-derived cells using RNA sequencing

The intracellular level of podoplanin (PDPN), a transmembrane protein of still unclear function, is frequently altered in metastatic tumors. High expression of PDPN is frequently observed in papillary thyroid cancer (PTC) specimens. Similarly, PTC-derived cell lines (BCPAP and TPC1, harboring the BRAF V600E mutation and RET/PTC1 fusion, respectively), also present enhanced PDPN yield. We previously reported that depletion of PDPN impairs migration of TPC1 cells, but augments metastasis of BCPAP cells. Interestingly, this phenomenon stays in contrast to the migratory pattern observed for wild-type cells, where TPC1 exhibited higher motility than BCPAP cells. Here, we aimed to elucidate the potential role of PDPN in regulation of molecular mechanisms leading to the diverse metastatic features of the studied PTC-derived cells. We consider that this phenomenon may be caused by alternative regulation of signaling pathways due to the presence of the mutated BRAF allele or RET/PTC1 fusion. The high-throughput RNA sequencing (RNA-seq) technique was used to uncover the genes and signaling pathways affected in wild-type and PDPN-depleted TPC1 and BCPAP cells. We found that changes in the expression of various factors of signaling pathways, like RHOA and RAC1 GTPases and their regulators, are linked with both high PDPN levels and presence of the BRAF V600E mutation. We imply that the suppressed motility of wild-type BCPAP cells results from overactivation of RHOA through natively high PDPN expression. This process is accompanied by inhibition of the PI3K kinase and consequently RAC1, due to overactivation of RAS-mediated signaling and the PTEN regulator.

Cadherins and catenins in cancer: connecting cancer pathways and tumor microenvironment

Cadherin-catenin complexes are integral components of the adherens junctions crucial for cell-cell adhesion and tissue homeostasis. Dysregulation of these complexes is linked to cancer development via alteration of cell-autonomous oncogenic signaling pathways and extrinsic tumor microenvironment. Advances in multiomics have uncovered key signaling events in multiple cancer types, creating a need for a better understanding of the crosstalk between cadherin-catenin complexes and oncogenic pathways. In this review, we focus on the biological functions of classical cadherins and associated catenins, describe how their dysregulation influences major cancer pathways, and discuss feedback regulation mechanisms between cadherin complexes and cellular signaling. We discuss evidence of cross regulation in the following contexts: Hippo-Yap/Taz and receptor tyrosine kinase signaling, key pathways involved in cell proliferation and growth; Wnt, Notch, and hedgehog signaling, key developmental pathways involved in human cancer; as well as TGFβ and the epithelial-to-mesenchymal transition program, an important process for cancer cell plasticity. Moreover, we briefly explore the role of cadherins and catenins in mechanotransduction and the immune tumor microenvironment.

The Cross-Talk Between EGFR and E-Cadherin

Epidermal growth factor receptor (EGFR) and adhesion protein E-cadherin are major regulators of proliferation and differentiation in epithelial cells. Consistently, defects in both EGFR and E-cadherin-mediated intercellular adhesion are linked to various malignancies. These defects in either are further exacerbated by the reciprocal interactions between the two transmembrane proteins. On the one hand, EGFR can destabilize E-cadherin adhesion by increasing E-cadherin endocytosis, modifying its interactions with cytoskeleton and decreasing its expression, thus promoting tumorigenesis. On the other hand, E-cadherin regulates EGFR localization and tunes its activity. As a result, loss and mutations of E-cadherin promote cancer cell invasion due to uncontrolled activation of EGFR, which displays enhanced surface motility and changes in endocytosis. In this minireview, we discuss the molecular and cellular mechanisms of the cross-talk between E-cadherin and EGFR, highlighting emerging evidence for the role of endocytosis in this feedback, as well as its relevance to tissue morphogenesis, homeostasis and cancer progression.

Helicobacter pylori-activated gastric fibroblasts induce epithelial-mesenchymal transition of gastric epithelial cells in vitro in a TGF-β-dependent manner

BACKGROUND

Colonization of the gastric mucosa with Helicobacter pylori (Hp) leads to the cascade of pathologic events including local inflammation, gastric ulceration, and adenocarcinoma formation. Paracrine loops between tissue cells and Hp contribute to the formation of gastric cancerous loci; however, the specific mechanisms underlying existence of these loops remain unknown. We determined the phenotypic properties of gastric fibroblasts exposed to Hp (cagA+vacA+) infection and their influence on normal epithelial RGM-1 cells.

MATERIALS AND METHODS

RGM-1 cells were cultured in the media conditioned with Hp-activated gastric fibroblasts. Their morphology and phenotypical changes associated with epithelial-mesenchymal transition (EMT) were assessed by Nomarski and fluorescence microscopy and Western blot analysis. Motility pattern of RGM-1 cells was examined by time-lapse video microscopy and transwell migration assay. The content of TGF-β in Hp-activated fibroblast-conditioned media was determined by ELISA.

RESULTS

The supernatant from Hp-activated gastric fibroblasts caused the EMT-like phenotypic diversification of RGM-1 cells. The formation of fibroblastoid cell sub-populations, the disappearance of their collective migration, an increase in transmigration potential with downregulation of E-cadherin and upregulation of N-cadherin proteins, prominent stress fibers, and decreased proliferation were observed. The fibroblast (CAF)-like transition was manifested by increased secretome TGF-β level, α-SMA protein expression, and its incorporation into stress fibers, and the TGF-βR1 kinase inhibitor reduced the rise in Snail, Twist, and E-cadherin mRNA and increased E-cadherin expression induced by CAFs.

CONCLUSION

Gastric fibroblasts which are one of the main targets for Hp infection contribute to the paracrine interactions between Hp, gastric fibroblasts, and epithelial cells. TGF-β secreted by Hp-activated gastric fibroblasts prompting their differentiation toward CAF-like phenotype promotes the EMT-related phenotypic shifts in normal gastric epithelial cell populations. This mechanism may serve as the prerequisite for GC development.

Phosphoproteome Profiling Reveals Molecular Mechanisms of Growth-Factor-Mediated Kinase Inhibitor Resistance in EGFR-Overexpressing Cancer Cells

Although substantial progress has been made regarding the use of molecularly targeted cancer therapies, resistance almost invariably develops and presents a major clinical challenge. The tumor microenvironment can rescue cancer cells from kinase inhibitors by growth-factor-mediated induction of pro-survival pathways. Here we show that epidermal growth factor receptor (EGFR) inhibition by Gefitinib is counteracted by growth factors, notably FGF2, and we assessed the global molecular consequences of this resistance at the proteome and phosphoproteome level in A431 cells. Tandem mass tag peptide labeling and quantitative mass spectrometry allowed the identification and quantification of 22 000 phosphopeptides and 8800 proteins in biological triplicates without missing values. The data show that FGF2 protects the cells from the antiproliferative effect of Gefitinib and largely prevents reprogramming of the proteome and phosphoproteome. Simultaneous EGFR/FGFR or EGFR/GSG2 (Haspin) inhibition overcomes this resistance, and the phosphoproteomic experiments further prioritized the RAS/MEK/ERK as well as the PI3K/mTOR axis for combination treatment. Consequently, the MEK inhibitor Trametinib prevented FGF2-mediated survival of EGFR inhibitor-resistant cells when used in combination with Gefitinib. Surprisingly, the PI3K/mTOR inhibitor Omipalisib reversed resistance mediated by all four growth factors tested, making it an interesting candidate for mitigating the effects of the tumor microenvironment.

Negative pressure induces p120-catenin-dependent adherens junction disassembly in keratinocytes during wound healing

A negative-pressure of 125mmHg (NP) has been widely used to treat chronic wounds in modern medicine. Keratinocytes under NP treatment have shown accelerated cell movement and decreased E-cadherin expression. However, the molecular mechanism of E-cadherin regulation under NP remains incompletely understood. Therefore, we investigated the E-cadherin regulation in keratinocytes (HaCaT cells) under NP. HaCaT cells were treated at ambient pressure (AP) and NP for 12h. Cell movement was measured by traditional and electric wound healing assays at the 2 different pressures. Mutants with overexpression of p120-catenin (p120(ctn)) were used to observe the effect of NP on p120(ctn) and E-cadherin expression during wound healing. Cell fractionation and immunoblotting data showed that NP increased Y228-phosphorylated p120(ctn) level and resulted in the translocation of p120(ctn) from the plasma membrane to cytoplasm. Immunofluorescence images revealed that NP decreased the co-localization of p120(ctn) and E-cadherin on the plasma membrane. Knockdown of p120(ctn) reduced E-cadherin expression and accelerated cell movement under AP. Overexpression of the Y228-phosphorylation-mimic p120(ctn) decreased E-cadherin membrane expression under both AP and NP. Phosphorylation-deficient mutants conferred restored adherens junctions (AJs) under NP. The Src inhibitor blocked the phosphorylation of p120(ctn) and impeded cell migration under NP. In conclusion, Src-dependent phosphorylation of p120(ctn) can respond rapidly to NP and contribute to E-cadherin downregulation. The NP-induced disassembly of the AJ further accelerates wound healing.

Identification of mRNA isoform switching in breast cancer

BACKGROUND

Alternative splicing provides a major mechanism to generate protein diversity. Increasing evidence suggests a link of dysregulation of splicing associated with cancer. While previous genomic-based studies demonstrated the expression of a handful of tumor-specific isoforms, genome-wide alterations in the balance between isoforms and cancer subtypes is understudied.

RESULT

We systematically analyzed the isoform-level expression patterns and isoform switching events of 819 breast tumor and normal samples assayed by mRNA-seq from TCGA project. On average, 2.2 isoforms per gene were detected and 67.5 % of detected genes (i.e. expressed) showed 1-2 isoforms only. While the majority of isoforms for a given gene were positively correlated with each other and the overall gene level, 470 pairs of isoforms displayed an inverse correlation suggesting a switching event. Most of the isoform switching events were associated with molecular subtypes, including a Basal-like-associated switching in CTNND1. 88 genes showed switching independent of subtypes, among which the isoform pattern of PRICKLE1 was associated with a large genomic signature of biological significance.

CONCLUSION

Our results reveal that the majority of genes do not undergo complex mRNA splicing within breast cancers, and that there is a general concordance in isoform and gene expression levels in breast tumors. We identified hundreds of isoform switching events across breast tumors, most of which were associated with differences in tumor subtypes. As exemplified by the detailed analysis of CTNND1 and PRICKLE1, these isoform switching events potentially provide new insights into the post-transcriptional regulatory mechanisms of tumor subtypes and cancer biology.

The bipartite rac1 Guanine nucleotide exchange factor engulfment and cell motility 1/dedicator of cytokinesis 180 (elmo1/dock180) protects endothelial cells from apoptosis in blood vessel development

Engulfment and cell motility 1/dedicator of cytokinesis 180 (Elmo1/Dock180) is a bipartite guanine nucleotide exchange factor for the monomeric GTPase Ras-related C3 botulinum toxin substrate 1 (Rac1). Elmo1/Dock180 regulates Rac1 activity in a specific spatiotemporal manner in endothelial cells (ECs) during zebrafish development and acts downstream of the Netrin-1/Unc5-homolog B (Unc5B) signaling cascade. However, mechanistic details on the pathways by which Elmo1/Dock180 regulates endothelial function and vascular development remained elusive. In this study, we aimed to analyze the vascular function of Elmo1 and Dock180 in human ECs and during vascular development in zebrafish embryos. In vitro overexpression of Elmo1 and Dock180 in ECs reduced caspase-3/7 activity and annexin V-positive cell number upon induction of apoptosis. This protective effect of Elmo1 and Dock180 is mediated by activation of Rac1, p21-activated kinase (PAK) and AKT/protein kinase B (AKT) signaling. In zebrafish, Elmo1 and Dock180 overexpression reduced the total apoptotic cell and apoptotic EC number and promoted the formation of blood vessels during embryogenesis. In conclusion, Elmo1 and Dock180 protect ECs from apoptosis by the activation of the Rac1/PAK/AKT signaling cascade in vitro and in vivo. Thus, Elmo1 and Dock180 facilitate blood vessel formation by stabilization of the endothelium during angiogenesis.

Physiological Signaling and Structure of the HGF Receptor MET

The "hepatocyte growth factor" also known as "scatter factor", is a multifunctional cytokine with the peculiar ability of simultaneously triggering epithelial cell proliferation, movement and survival. The combination of those proprieties results in the induction of an epithelial to mesenchymal transition in target cells, fundamental for embryogenesis but also exploited by tumor cells during metastatization. The hepatocyte growth factor receptor, MET, is a proto-oncogene and a prototypical transmembrane tyrosine kinase receptor. Inhere we discuss the MET molecular structure and the hepatocyte growth factor driven physiological signaling which coordinates epithelial proliferation, motility and morphogenesis.

Protection after stroke: cellular effectors of neurovascular unit integrity

Neurological disorders are prevalent worldwide. Cerebrovascular diseases (CVDs), which account for 55% of all neurological diseases, are the leading cause of permanent disability, cognitive and motor disorders and dementia. Stroke affects the function and structure of blood-brain barrier, the loss of cerebral blood flow regulation, oxidative stress, inflammation and the loss of neural connections. Currently, no gold standard treatments are available outside the acute therapeutic window to improve outcome in stroke patients. Some promising candidate targets have been identified for the improvement of long-term recovery after stroke, such as Rho GTPases, cell adhesion proteins, kinases, and phosphatases. Previous studies by our lab indicated that Rho GTPases (Rac and RhoA) are involved in both tissue damage and survival, as these proteins are essential for the morphology and movement of neurons, astrocytes and endothelial cells, thus playing a critical role in the balance between cell survival and death. Treatment with a pharmacological inhibitor of RhoA/ROCK blocks the activation of the neurodegeneration cascade. In addition, Rac and synaptic adhesion proteins (p120 catenin and N-catenin) play critical roles in protection against cerebral infarction and in recovery by supporting the neurovascular unit and cytoskeletal remodeling activity to maintain the integrity of the brain parenchyma. Interestingly, neuroprotective agents, such as atorvastatin, and CDK5 silencing after cerebral ischemia and in a glutamate-induced excitotoxicity model may act on the same cellular effectors to recover neurovascular unit integrity. Therefore, future efforts must focus on individually targeting the structural and functional roles of each effector of neurovascular unit and the interactions in neural and non-neural cells in the post-ischemic brain and address how to promote the recovery or prevent the loss of homeostasis in the short, medium and long term.

Targeting Fyn in Ras-transformed cells induces F-actin to promote adherens junction-mediated cell-cell adhesion

Fyn, a member of the Src family kinases (SFK), is an oncogene in murine epidermis and is associated with cell-cell adhesion turnover and induction of cell migration. Additionally, Fyn upregulation has been reported in multiple tumor types, including cutaneous squamous cell carcinoma (cSCC). Introduction of active H-Ras(G12V) into the HaCaT human keratinocyte cell line resulted in upregulation of Fyn mRNA (200-fold) and protein, while expression of other SFKs remained unaltered. Transduction of active Ras or Fyn was sufficient to induce an epithelial-to-mesenchymal transition in HaCaT cells. Inhibition of Fyn activity, using siRNA or the clinical SFK inhibitor Dasatinib, increased cell-cell adhesion and rapidly (5-60 min) increased levels of cortical F-actin. Fyn inhibition with siRNA or Dasatinib also induced F-actin in MDA-MB-231 breast cancer cells, which have elevated Fyn. F-actin co-localized with adherens junction proteins, and Dasatinib-induced cell-cell adhesion could be blocked by Cytochalasin D, indicating that F-actin polymerization was a key initiator of cell-cell adhesion through the adherens junction. Conversely, inhibiting cell-cell adhesion with low Ca(2+) media did not block Dasatinib-induced F-actin polymerization. Inhibition of the Rho effector kinase ROCK blocked Dasatinib-induced F-actin and cell-cell adhesion, implicating relief of Rho GTPase inhibition as a mechanism of Dasatinib-induced cell-cell adhesion. Finally, topical Dasatinib treatment significantly reduced total tumor burden in the SKH1 mouse model of UV-induced skin carcinogenesis. Together these results identify the promotion of actin-based cell-cell adhesion as a newly described mechanism of action for Dasatinib and suggest that Fyn inhibition may be an effective therapeutic approach in treating cSCC.

p120-catenin in cancer - mechanisms, models and opportunities for intervention

The epithelial adherens junction is an E-cadherin-based complex that controls tissue integrity and is stabilized at the plasma membrane by p120-catenin (p120, also known as CTNND1). Mutational and epigenetic inactivation of E-cadherin has been strongly implicated in the development and progression of cancer. In this setting, p120 translocates to the cytosol where it exerts oncogenic properties through aberrant regulation of Rho GTPases, growth factor receptor signaling and derepression of Kaiso (also known as ZBTB33) target genes. In contrast, indirect inactivation of the adherens junction through conditional knockout of p120 in mice was recently linked to tumor formation, indicating that p120 can also function as a tumor suppressor. Supporting these opposing functions are findings in human cancer, which show that either loss or cytoplasmic localization of p120 is a common feature in the progression of several types of carcinoma. Underlying this dual biological phenomenon might be the context-dependent regulation of Rho GTPases in the cytosol and the derepression of Kaiso target genes. Here, we discuss past and present findings that implicate p120 in the regulation of cancer progression and highlight opportunities for clinical intervention.

p120 catenin: an essential regulator of cadherin stability, adhesion-induced signaling, and cancer progression

p120 catenin is the best studied member of a subfamily of proteins that associate with the cadherin juxtamembrane domain to suppress cadherin endocytosis. p120 also recruits the minus ends of microtubules to the cadherin complex, leading to junction maturation. In addition, p120 regulates the activity of Rho family GTPases through multiple interactions with Rho GEFs, GAPs, Rho GTPases, and their effectors. Nuclear signaling is affected by the interaction of p120 with Kaiso, a transcription factor regulating Wnt-responsive genes as well as transcriptionally repressing methylated promoters. Multiple alternatively spliced p120 isoforms and complex phosphorylation events affect these p120 functions. In cancer, reduced p120 expression correlates with reduced E-cadherin function and with tumor progression. In contrast, in tumor cells that have lost E-cadherin expression, p120 promotes cell invasion and anchorage-independent growth. Furthermore, p120 is required for Src-induced oncogenic transformation and provides a potential target for future therapeutic interventions.

p120catenin alteration in cancer and its role in tumour invasion

Since its discovery in 1989 as a substrate of the Src oncogene, p120catenin has been revealed as an important player in cancer initiation and tumour dissemination. p120catenin regulates a wide range of cellular processes such as cell-cell adhesion, cell polarity and cell proliferation and plays a pivotal role in morphogenesis, inflammation and innate immunity. The pleiotropic effects of p120catenin rely on its interactions with numerous partners such as classical cadherins at the plasma membrane, Rho-GTPases and microtubules in the cytosol and transcriptional modulators in the nucleus. Alterations of p120catenin in cancer not only concern its expression level but also its intracellular localization and can lead to both pro-invasive and anti-invasive effects. This review focuses on the p120catenin-mediated pathways involved in cell migration and invasion and discusses the potential consequences of major cancer-related p120catenin alterations with respect to tumour spread.

Drosophila actin-Capping Protein limits JNK activation by the Src proto-oncogene

The Src family kinases c-Src, and its downstream effectors, the Rho family of small GTPases RhoA and Jun N-terminal kinase (JNK) have a significant role in tumorigenesis. In this report, using the Drosophila wing disc epithelium as a model system, we demonstrate that the actin-Capping Protein (CP) αβ heterodimer, which regulates actin filament (F-actin) polymerization, limits Src-induced apoptosis or tissue overgrowth by restricting JNK activation. We show that overexpressing Src64B drives JNK-independent loss of epithelial integrity and JNK-dependent apoptosis via Btk29A, p120ctn and Rho1. However, when cells are kept alive with the Caspase inhibitor P35, JNK acts as a potent inducer of proliferation via activation of the Yorkie oncogene. Reducing CP levels direct apoptosis of overgrowing Src64B-overexpressing tissues. Conversely, overexpressing capping protein inhibits Src64B and Rho1, but not Rac1-induced JNK signaling. CP requires the actin-binding domain of the α-subunit to limit Src64B-induced apoptosis, arguing that the control of F-actin mediates this effect. In turn, JNK directs F-actin accumulation. Moreover, overexpressing capping protein also prevents apoptosis induced by ectopic JNK expression. Our data are consistent with a model in which the control of F-actin by CP limits Src-induced apoptosis or tissue overgrowth by acting downstream of Btk29A, p120ctn and Rho1, but upstream of JNK. In turn, JNK may counteract the effect of CP on F-actin, providing a positive feedback, which amplifies JNK activation. We propose that cytoskeletal changes triggered by misregulation of F-actin modulators may have a significant role in Src-mediated malignant phenotypes during the early stages of cellular transformation.

The NADPH oxidase pathway is dysregulated by the P2X7 receptor in the SOD1-G93A microglia model of amyotrophic lateral sclerosis

Inflammation and oxidative stress are thought to play determinant roles in the pathogenesis of amyotrophic lateral sclerosis (ALS). Degenerating motor neurons produce signals that activate microglia to release reactive oxygen species (ROS) and proinflammatory cytokines, resulting in a vicious cycle of neurodegeneration. The ALS-causing mutant protein Cu(+)/Zn(+) superoxide dismutase SOD1-G93A directly enhances the activity of the main ROS-producing enzyme in microglia, NADPH oxidase 2 (NOX2), a well-known player in the pathogenesis of ALS. Considering that extracellular ATP through P2X7 receptor constitutes a neuron-to-microglia alarm signal implicated in ALS pathology, we used primary microglial cells derived from transgenic SOD1-G93A mice and SOD1-G93A mice lacking the P2X7 receptor to investigate the effects of both pharmacological induction and genetic ablation of receptor activity on the NOX2 pathway. We observed that, in SOD1-G93A microglia, the stimulation of P2X7 receptor by 2'-3'-O-(benzoyl-benzoyl) ATP enhanced NOX2 activity in terms of translocation of p67(phox) to the membrane and ROS production; this effect was totally dependent on Rac1. We also found that, following P2X7 receptor stimulation, the phosphorylation of ERK1/2 was augmented in ALS microglia, and there was a mutual dependency between the NOX2 and ERK1/2 pathways. All of these microglia-mediated damaging mechanisms were prevented by knocking out P2X7 receptor and by the use of specific antagonists. These findings suggest a noxious mechanism by which P2X7 receptor leads to enhanced oxidative stress in ALS microglia and identify the P2X7 receptor as a promising target for the development of therapeutic strategies to slow down the progression of ALS.

Galectin-3 protein regulates mobility of N-cadherin and GM1 ganglioside at cell-cell junctions of mammary carcinoma cells

Galectin-3 binding to cell surface glycoproteins, including branched N-glycans generated by N-acetylglucosaminyltransferase V (Mgat5) activity, forms a multivalent, heterogeneous, and dynamic lattice. This lattice has been shown to regulate integrin and receptor tyrosine kinase signaling promoting tumor cell migration. N-cadherin is a homotypic cell-cell adhesion receptor commonly overexpressed in tumor cells that contributes to cell motility. Here we show that galectin-3 and N-cadherin interact and colocalize with the lipid raft marker GM1 ganglioside in cell-cell junctions of mammary epithelial cancer cells. Disruption of the lattice by deletion of Mgat5, siRNA depletion of galectin-3, or competitive inhibition with lactose stabilizes cell-cell junctions. It also reduces, in a p120-catenin-dependent manner, the dynamic pool of junctional N-cadherin. Proteomic analysis of detergent-resistant membranes (DRMs) revealed that the galectin lattice opposes entry of many proteins into DRM rafts. N-cadherin and catenins are present in DRMs; however, their DRM distribution is not significantly affected by lattice disruption. Galectin lattice integrity increases the mobile fraction of the raft marker, GM1 ganglioside binding cholera toxin B subunit Ctb, at cell-cell contacts in a p120-catenin-independent manner, but does not affect the mobility of either Ctb-labeled GM1 or GFP-coupled N-cadherin in nonjunctional regions. Our results suggest that the galectin lattice independently enhances lateral molecular diffusion by direct interaction with specific glycoconjugates within the adherens junction. By promoting exchange between raft and non-raft microdomains as well as molecular dynamics within junction-specific raft microdomains, the lattice may enhance turnover of N-cadherin and other glycoconjugates that determine junctional stability and rates of cell migration.

Synthetic immunomodulatory peptide IDR-1002 enhances monocyte migration and adhesion on fibronectin

Regulation of the immune system by immunomodulatory agents, such as the synthetic innate defense regulator (IDR) peptides, has been proposed as a potential strategy to strengthen host immune responses against infection. IDR peptides confer protection in vivo against a range of bacterial infections and have been developed as components of single-dose vaccine adjuvants due to their ability to modulate innate immunity, correlating with an increased recruitment of monocytes to sites of infection or immunization. However, the mechanisms by which IDR peptides augment monocyte recruitment remain poorly defined. Anti-infective peptide IDR-1002 was demonstrated here to lack direct monocyte chemoattractive activity yet enhance, by up to 5-fold, the ability of human monocytes to migrate on fibronectin towards chemokines. This effect correlated with an increased adhesion of monocytes and THP-1 cells to fibronectin by IDR-1002 and other IDR peptides and the adhesion of THP-1 cells to fibronectin occurred in a β(1)-integrin-dependent manner, corresponding with an increased activation of β(1)-integrins and the phosphoinositide 3-kinase (PI3K)-Akt pathway. PI3K- and Akt-specific inhibitors abrogated IDR-1002-induced adhesion and activation of β(1)-integrins, whereas p38 and MEK1 inhibitors did not affect, or moderately inhibited, adhesion, respectively. Furthermore, IDR-1002 enhancement of monocyte migration towards chemokines and activation of β(1)-integrins was abrogated in the presence of PI3K- and Akt-specific inhibitors. In summary, IDR-1002 enhanced monocyte migration on fibronectin through promotion of β(1)-integrin-mediated interactions regulated by the PI3K-Akt pathway, revealing a mechanism by which IDR-1002 promotes monocyte recruitment.

Mitochondrial redox signalling by p66Shc mediates ALS-like disease through Rac1 inactivation

Increased oxidative stress and mitochondrial damage are among the mechanisms whereby mutant SOD1 (mutSOD1) associated with familial forms of amyotrophic lateral sclerosis (ALS) induces motoneuronal death. The 66 kDa isoform of the growth factor adapter Shc (p66Shc) is known to be central in the control of mitochondria-dependent oxidative balance. Here we report that expression of mutSOD1s induces the activation of p66Shc in neuronal cells and that the overexpression of inactive p66Shc mutants protects cells from mutSOD1-induced mitochondrial damage. Most importantly, deletion of p66Shc ameliorates mitochondrial function, delays onset, improves motor performance and prolongs survival in transgenic mice modelling ALS. We also show that p66Shc activation by mutSOD1 causes a strong decrease in the activity of the small GTPase Rac1 through a redox-sensitive regulation. Our results provide new insight into the potential mechanisms of mutSOD1-mediated mitochondrial dysfunction.

P-cadherin cooperates with insulin-like growth factor-1 receptor to promote metastatic signaling of gonadotropin-releasing hormone in ovarian cancer via p120 catenin

Gonadotropin-releasing hormone (GnRH) is a potent prometastatic factor in ovarian cancer, but the intracellular signaling events are not well understood. The classical Gα(q)-phospholipase C signal transduction pathway known to operate in the pituitary is not involved in GnRH actions at non-pituitary targets. Here we showed that GnRH treatment of ovarian cancer cells led to a rapid and remarkable tyrosine phosphorylation of p120 catenin (p120(ctn)), which was mediated by P-cadherin. The use of P-cadherin small interfering RNA or neutralizing antibodies to inhibit P-cadherin expression and function resulted in diminished p120(ctn) activation, confirming that the effect was P-cadherin specific. On exploring how P-cadherin, which lacks intrinsic kinase activity, might regulate the activation of p120(ctn), we found that P-cadherin could induce the ligand-independent activation of insulin-like growth factor-1 receptor (IGF-1R). Inhibition of IGF-1R expression or its activity significantly inhibited GnRH-induced p120(ctn) activation, and the subsequent cell migration and invasion. In addition, we showed that IGF-1R regulation by P-cadherin was associated with complex formation between IGF-1R and P-cadherin, and this regulation was also observed to be in vivo correlated with metastasis. Furthermore, using a mouse model of ovarian cancer metastasis, GnRH receptor knockdown was shown to diminish peritoneal dissemination of tumors and ascites formation. These findings suggest for the first time that GnRH can initiate an outside-in p120(ctn) signal transduction through the cross-talk between P-cadherin and IGF-1R, thus providing a novel molecular mechanism by which GnRH may control the high level of aggressiveness and invasion and metastasis potential that are characteristic of ovarian cancer.

p120 regulates endothelial permeability independently of its NH2 terminus and Rho binding

The association of p120-catenin (p120) with the juxtamembrane domain (JMD) of vascular endothelial (VE)-cadherin is required to maintain VE-cadherin levels and transendothelial resistance (TEER) of endothelial cell monolayers. To distinguish whether decreased TEER was due to a loss of p120 and not to the decrease in VE-cadherin, we established a system in which p120 was depleted by short hairpin RNA delivered by lentivirus and VE-cadherin was restored via expression of VE-cadherin fused to green fluorescent protein (GFP). Loss of p120 resulted in decreased TEER, which was associated with decreased expression of VE-cadherin, β-catenin, plakoglobin, and α-catenin. Decreased TEER was rescued by restoration of p120 but not by the expression of VE-cadherin-GFP, despite localization of VE-cadherin-GFP at cell-cell borders. Expression of VE-cadherin-GFP restored levels of β-catenin and α-catenin but not plakoglobin, indicating that p120 may be important for recruitment of plakoglobin to the VE-cadherin complex. To evaluate the role of p120 interaction with Rho GTPase in regulating endothelial permeability, we expressed a recombinant form of p120, lacking the NH(2) terminus and containing alanine substitutions, that eliminates binding of Rho to p120. Expression of this isoform restored expression of the adherens junction complex and rescued permeability as measured by TEER. These results demonstrate that p120 is required for maintaining VE-cadherin expression and TEER independently of its NH(2) terminus and its role in regulating Rho.

Epiplakin accelerates the lateral organization of keratin filaments during wound healing

BACKGROUND

Epiplakin (EPPK) belongs to the plakin family of cytolinker proteins and, resembling other members of the plakin family such as BPAG1 (an autoantigen of bullous pemphigoid) and plectin, EPPK has plakin repeat domains (PRDs) that bind to intermediate filaments. Elimination of EPPK by gene targeting in mice resulted in the acceleration of keratinocyte migration during wound healing. EPPK is expressed in proliferating keratinocytes at wound edges and, in view of its putative function in binding to keratin, we postulated that the keratin network in EPPK-null (EPPK(-/-)) mice might be disrupted during wound healing.

OBJECTIVE

To examine this hypothesis and to determine the precise localization of EPPK in relation to keratin filaments, we compared the non-wounded and wounded epidermis of wild-type and EPPK(-/-) mice.

METHODS

Non-wounded epidermis and wounded epidermis from wild-type and EPPK(-/-) mice were examined by immunofluorescence staining and electron microscopy before and after double immunostaining.

RESULTS

EPPK was colocalized with keratin 17 (K17) more extensively than with other keratins examined in wounded epidermis. The expression of K5, K10, K6, and K17 was the same in EPPK(-/-) mice after wounding as in normal mice, but diameters of keratin filaments were reduced in EPPK(-/-) keratinocytes. Electron microscopy after immunostaining revealed that EPPK colocalized with K5, K10 and K6 after wounding in wild-type mice.

CONCLUSION

Our data indicate that EPPK accelerates keratin bundling in proliferating keratinocytes during wound healing and suggest that EPPK might contribute to reinforcement of keratin networks under mechanical stress.

Hepatocyte Growth Factor stimulated cell scattering requires ERK and Cdc42-dependent tight junction disassembly

The mechanism by which Hepatocyte Growth Factor (HGF) induces tight junction disassembly prior to cell scattering is largely unknown. Here, we show that HGF stimulates rapid loss of the TJ assembly protein Par6 from the TJ in an Erk-dependent manner. Erk activation by HGF is found to mediate the interaction of Par6 with GTP-loaded Cdc42. The Cdc42 GTPase activating protein cdGAP is shown to interact with Pkcζ at baseline and prevent Par6-Cdc42 association. Erk, by phosphorylating cdGAP at threonine776, can inhibit the GAP activity, thereby increasing Par6-Cdc42 association and TJ disassembly. Our findings reveal a novel pathway for regulating HGF signaling to the Par proteins through Erk-cdGAP, resulting in TJ disassembly and cell scattering.

Keeping in touch with contact inhibition of locomotion

Contact inhibition of locomotion (CIL) is the process by which cells in vitro change their direction of migration upon contact with another cell. Here, we revisit the concept that CIL plays a central role in the migration of single cells and in collective migration, during both health and disease. Importantly, malignant cells exhibit a diminished CIL behaviour which allows them to invade healthy tissues. Accumulating evidence indicates that CIL occurs in vivo and that regulation of small Rho GTPases is important in the collapse of cell protrusions upon cell contact, the first step of CIL. Finally, we propose possible cell surface proteins that could be involved in the initial contact that regulates Rho GTPases during CIL.

p120ctn and P-cadherin but not E-cadherin regulate cell motility and invasion of DU145 prostate cancer cells

Background

Adherens junctions consist of transmembrane cadherins, which interact intracellularly with p120ctn, ß-catenin and α-catenin. p120ctn is known to regulate cell-cell adhesion by increasing cadherin stability, but the effects of other adherens junction components on cell-cell adhesion have not been compared with that of p120ctn.

Methodology/Principal Findings

We show that depletion of p120ctn by small interfering RNA (siRNA) in DU145 prostate cancer and MCF10A breast epithelial cells reduces the expression levels of the adherens junction proteins, E-cadherin, P-cadherin, ß-catenin and α-catenin, and induces loss of cell-cell adhesion. p120ctn-depleted cells also have increased migration speed and invasion, which correlates with increased Rap1 but not Rac1 or RhoA activity. Downregulation of P-cadherin, β-catenin and α-catenin but not E-cadherin induces a loss of cell-cell adhesion, increased migration and enhanced invasion similar to p120ctn depletion. However, only p120ctn depletion leads to a decrease in the levels of other adherens junction proteins.

Conclusions/Significance

Our data indicate that P-cadherin but not E-cadherin is important for maintaining adherens junctions in DU145 and MCF10A cells, and that depletion of any of the cadherin-associated proteins, p120ctn, ß-catenin or α-catenin, is sufficient to disrupt adherens junctions in DU145 cells and increase migration and cancer cell invasion.

The 19-amino acid insertion in the tumor-associated splice isoform Rac1b confers specific binding to p120 catenin

The Rac1b splice isoform contains a 19-amino acid insertion not found in Rac1; this insertion leads to decreased GTPase activity and reduced affinity for GDP, resulting in the intracellular predominance of GTP-bound Rac1b. Here, using co-precipitation and proteomic methods, we find that Rac1b does not bind to many common regulators of Rho family GTPases but that it does display enhanced binding to SmgGDS, RACK1, and p120 catenin (p120(ctn)), proteins involved in cell-cell adhesion, motility, and transcriptional regulation. We use molecular modeling and structure analysis approaches to determine that the interaction between Rac1b and p120(ctn) is dependent upon protein regions that are predicted to be unstructured in the absence of molecular complex formation, suggesting that the interaction between these two proteins involves coupled folding and binding. We also find that directed cell movement initiated by Rac1b is dependent upon p120. These results define a distinct binding functionality of Rac1b and provide insight into how the distinct phenotypic program activated by this protein may be implemented through molecular recognition of effectors distinct from those of Rac1.

Role of RAS in the regulation of PI 3-kinase

Ras proteins are key regulators of signalling cascades, controlling many processes such as proliferation, differentiation and apoptosis. Mutations in these proteins or in their effectors, activators and regulators are associated with pathological conditions, particularly the development of various forms of human cancer. RAS proteins signal through direct interaction with a number of effector enzymes, one of the best characterized being type I phosphatidylinositol (PI) 3-kinases. Although the ability of RAS to control PI 3-kinase has long been well established in cultured cells, evidence for a role of the interaction of endogenous RAS with PI 3-kinase in normal and malignant cell growth in vivo has only been obtained recently. Mice with mutations in the PI 3-kinase catalytic p110a isoform that block its ability to interact with RAS are highly resistant to endogenous KRAS oncogene induced lung tumourigenesis and HRAS oncogene induced skin carcinogenesis. Cells from these mice show proliferative defects and selective disruption of signalling from certain growth factors to PI 3-kinase, while the mice also display delayed development of the lymphatic vasculature. The interaction of RAS with p110a is thus required in vivo for some normal growth factor signalling and also for RAS-driven tumour formation. RAS family members were among the first oncogenes identified over 40 years ago. In the late 1960s, the rat-derived Harvey and Kirsten murine sarcoma retroviruses were discovered and subsequently shown to promote cancer formation through related oncogenes, termed RAS (from rat sarcoma virus). The central role of RAS proteins in human cancer is highlighted by the large number of tumours in which they are activated by mutation: approximately 20% of human cancers carry a mutation in RAS proteins. Because of the complex signalling network in which RAS operates, with multiple activators and effectors, each with a different pattern of tissue-specific expression and a distinct set of intracellular functions, one of the critical issues concerns the specific role of each effector in RAS-driven oncogenesis. In this chapter, we summarize current knowledge about how RAS regulates one of its best-known effectors, phosphoinositide 3-kinase (PI3K).

Expression and clinical significance of p120 catenin mRNA and protein in pancreatic carcinoma

The aim of this work was investigate the association of P120 catenin expression with the clinicopathologic features and prognosis of pancreatic carcinoma. RT-PCR was performed to investigate the expression of P120 catenin mRNA and western blotting were performed to investigate the expression of P120 catenin protein in 52 patients with pancreatic carcinoma. The relationships between P120 catenin expression and clinicopathological characteristics and prognosis were analyzed. The mRNA and protein expression of P120 catenin detected by RT-PCR and western blotting in pancreatic carcinoma was significantly lower than that in normal pancreatic tissues (0.227+/-0.067 vs 0.793+/-0.162, t=9.157, P =0.000; 0.665+/-0.192 vs 0.936+/-0.251, t=3.857, P=0.002). Reduced expression of P120 catenin mRNA and protein was significantly correlated with lymph node metastasis (P =0.004, P =0.006), vascular invasion (P =0.022, P =0.039 ), distant metastasis (P =0.037 , P =0.025), differentiated (P =0.033, P =0.013) and pTNM stage (P =0.003, P =0.022) of tumours. Additionally, reduced expression of P120 catenin mRNA and protein in tumour correlated with a worse prognosis and normal expression with a better survival rate (P=0.022, P=0.007). The reduced expression of both P120 catenin mRNA and protein in pancreatic carcinoma suggest that low expressions relate to pancreatic carcinoma development. P120 catenin may be related to pancreatic carcinoma behaviour and be a potential prognostic molecule.

EMT, the cytoskeleton, and cancer cell invasion

The metastatic process, i.e. the dissemination of cancer cells throughout the body to seed secondary tumors at distant sites, requires cancer cells to leave the primary tumor and to acquire migratory and invasive capabilities. In a process of epithelial-mesenchymal transition (EMT), besides changing their adhesive repertoire, cancer cells employ developmental processes to gain migratory and invasive properties that involve a dramatic reorganization of the actin cytoskeleton and the concomitant formation of membrane protrusions required for invasive growth. The molecular processes underlying such cellular changes are still only poorly understood, and the various migratory organelles, including lamellipodia, filopodia, invadopodia and podosomes, still require a better functional and molecular characterization. Notably, direct experimental evidence linking the formation of migratory membrane protrusions and the process of EMT and tumor metastasis is still lacking. In this review, we have summarized recent novel insights into the molecular processes and players underlying EMT on one side and the formation of invasive membrane protrusions on the other side.

Cytokines as genetic modifiers in K5-/- mice and in human epidermolysis bullosa simplex

Epidermolysis bullosa simplex (EBS) is a skin disorder caused by fully-penetrant mutations in the keratin genes KRT5 and KRT14, leading to extensive cytolysis and cell fragility of basal keratinocytes. EBS is subject to environmental conditions and displays high intra- and interfamilial variability, suggesting modifying loci. Here, we demonstrate that upregulation of certain cytokines accompanies mutations in keratin 5 (K5) but not in keratin 14 (K14). We find for the first time that cytokines macrophage chemotactic protein (MCP)-1/[chemokine (C-C motif) ligand 2] (CCL2), macrophage inflammatory protein (MIP)-3beta/CCL19 and MIP-3alpha/CCL20, all regulated by nuclear factor kappa B (NFkappaB) and involved in the recruitment, maturation, and migration of Langerhans cells (LCs) in the epidermis, are upregulated in the skin of K5(-/-), but not of K14(-/-) mice. In neonatal K5(-/-) epidermis, the number of LCs was increased two-fold. At the same time, tumor necrosis factor alpha (TNFalpha) remained unaltered, demonstrating the specificity of that process. Most remarkably, enhanced LC recruitment within the epidermis was found in five EBS patients carrying mutations in the KRT5 gene but not in EBS patients with KRT14 gene mutations. In agreement with the NFkappaB-dependent regulation of these cytokines, we found a decrease in p120-catenin in the basal epidermis of K5(-/-) mice. These data provide the first explanation for distinct, keratin-type-specific genotype-phenotype correlations in EBS and represent a rationale to investigate gene loci affecting skin pathology in EBS.

Ablation of p120-catenin enhances invasion and metastasis of human lung cancer cells

p120-catenin, a member of the Armadillo gene family, has emerged as both a master regulator of cadherin stability and an important modulator of small GTPase activities. Therefore, it plays novel roles in tumor malignant phenotype, such as invasion and metastasis. We have reported previously that abnormal expression of p120-catenin is associated with lymph node metastasis in lung squamous cell carcinomas (SCC) and adenocarcinomas. To investigate the role and possible mechanism of p120-catenin in lung cancer, we knocked down p120-catenin using small interfering RNA (siRNA). We found that ablation of p120-catenin reduced the levels of E-cadherin and beta-catenin proteins, as well as the mRNA of beta-catenin. Furthermore, p120-catenin depletion inactivated RhoA, but increased the activity of Cdc42 and Rac1, and promoted proliferation and the invasive ability of lung cancer cells both in vitro and in vivo. Our data reveal that p120-catenin gene knockdown enhances the metastasis of lung cancer cells, probably by either depressing cell-cell adhesion due to lower levels of E-cadherin and beta-catenin, or altering the activity of small GTPase, such as inactivation of RhoA and activation of Cdc42/Rac1.

Abnormal expression of p120-catenin, E-cadherin, and small GTPases is significantly associated with malignant phenotype of human lung cancer

Studies on a variety of cell lines have shown that p120-catenin can directly regulate the stability of E-cadherin complexes and control the activity of small GTPases to influence cell adhesion. Despite this data, clinical studies of human solid tumors have not been reported to investigate these protein interactions. To explore the correlation between p120-catenin, E-cadherin, and small GTPases in human lung cancer, we examined the expression patterns of p120-catenin, E-cadherin, RhoA, Cdc42, and Rac1, and their prognostic significance in 138 patients with non-small cell lung cancer (NSCLC). While normal bronchial epithelium showed strong membrane expression of p120-catenin and E-cadherin, lung cancer tissues had reduced membrane expression and ectopic cytoplasmic expression of p120-catenin and E-cadherin. Expression of RhoA, Cdc42, and Rac1 was also found to be higher in tumor tissue than in normal lung tissue. A correlation between abnormal p120-catenin, E-cadherin expression, and overexpression of specific small GTPases was also associated with poor differentiation, high TNM stage, and lymph node metastasis in NSCLC patients. We also used an in vitro model to evaluate their expression, and to determine whether protein expression correlated with the invasive capacity of lung cancer cell lines. Consistent with our in vivo data, abnormal expression of p120-catenin and E-cadherin with overexpression of specific small GTPases were significantly associated with the high metastatic capacity of BE1 cells. Based on our results, we conclude that abnormal p120-catenin expression correlates with abnormal E-cadherin expression and specific small GTPase overexpression, which contribute to the malignancy-related to NSCLC.

P120-catenin isoforms 1A and 3A differently affect invasion and proliferation of lung cancer cells

Different isoforms of p120-catenin (p120ctn), a member of the Armadillo gene family, are variably expressed in different tissues as a result of alternative splicing and the use of multiple translation initiation codons. When expressed in cancer cells, these isoforms may confer different properties with respect to cell adhesion and invasion. We have previously reported that the p120ctn isoforms 1 and 3 were the most highly expressed isoforms in normal lung tissues, and their expression level was reduced in lung tumor cells. To precisely define their biological roles, we transfected p120ctn isoforms 1A and 3A into the lung cancer cell lines A549 and NCI-H460. Enhanced expression of p120ctn isoform 1A not only upregulated E-cadherin and beta-catenin, but also downregulated the Rac1 activity, and as a result, inhibited the ability of cells to invade. In contrast, overexpression of p120ctn isoform 3A led to the inactivation of Cdc42 and the activation of RhoA, and had a smaller influence on invasion. However, we found that isoform 3A had a greater ability than isoform 1A in both inhibiting the cell cycle and reducing tumor cell proliferation. The present study revealed that p120ctn isoforms 1A and 3A differently regulated the adhesive, proliferative, and invasive properties of lung cancer cells through distinct mechanisms.

PDGF receptor activation induces p120-catenin phosphorylation at serine 879 via a PKCalpha-dependent pathway

p120-catenin (p120) is required for cadherin stability and is thought to have a central role in modulating cell-cell adhesion. Several lines of evidence suggest that S/T phosphorylation may regulate p120 activity, but the upstream kinases involved have not been established, nor has a discreet measurable function been assigned to an individual site. To approach these issues, we have generated p120 phospho-specific monoclonal antibodies to several individual phosphorylation sites and are using them to pinpoint upstream kinases and signaling pathways that control p120 activity. Protein Kinase C (PKC) has been implicated as a signaling intermediate in several cadherin-associated cellular activities. Signaling events that activate PKC induce rapid phosphorylation at p120 Serine 879 (S879), suggesting that p120 activity is regulated, in part, by one or more PKC isoforms. Here, we find that physiologic activation of a G-protein coupled receptor (i.e., endothelin receptor), as well as several Receptor Tyrosine Kinases, induce rapid and robust p120 phosphorylation at S879, suggesting that these pathways crosstalk to cadherin complexes via p120. Using Va2 cells and PDGF stimulation, we show for the first time that PDGFR-mediated phosphorylation at this site is dependent on PKCalpha, a conventional PKC isoform implicated previously in disruption of adherens junctions.

A p120 catenin isoform switch affects Rho activity, induces tumor cell invasion, and predicts metastatic disease

p120 catenin is a cadherin-associated protein that regulates Rho GTPases and promotes the invasiveness of E-cadherin-deficient cancer cells. Multiple p120 isoforms are expressed in cells via alternative splicing, and all of them are essential for HGF signaling to Rac1. However, only full-length p120 (isoform 1) promotes invasiveness. This selective ability of p120 isoform 1 is mediated by reduced RhoA activity, both under basal conditions and following HGF treatment. All p120 isoforms can bind RhoA in vitro, via a central RhoA binding site. However, only the cooperative binding of RhoA to the central p120 domain and to the alternatively spliced p120 N terminus stabilizes RhoA binding and inhibits RhoA activity. Consistent with this, increased expression of p120 isoform 1, when compared with other p120 isoforms, is predictive of renal tumor micrometastasis and systemic progression, following nephrectomy. Furthermore, ectopic expression of the RhoA-binding, N-terminal domain of p120 is sufficient to block the ability of p120 isoform 1 to inhibit RhoA and to promote invasiveness. The data indicate that the increased expression of p120 isoform 1 during tumor progression contributes to the invasive phenotype of cadherin-deficient carcinomas and that the N-terminal domain of p120 is a valid therapeutic target.

Generation and characterization of a novel phospho-specific monoclonal antibody to p120-catenin serine 879

To better understand the mechanisms that regulate p120-catenin (p120) and E-cadherin function, we are systematically generating phospho-specific monoclonal antibodies (MAb) to the major p120 phosphorylation sites. p120 has emerged recently as a master regulator of E-cadherin stability and an important modulator of RhoGTPase activities. A number of phosphorylation sites have been identified, but none have as yet been linked to specific regulatory roles. Here, we describe a novel phospho-specific monoclonal antibody to the major PKC-induced p120 phosphorylation site, phospho-serine 879 (pS879). With a few exceptions, p120 MAb pS879 is remarkably specific for the phosphorylated S879 epitope and works effectively in common applications such as Western blot analysis, immunoprecipitation, and immunofluorescence. p120 MAb pS879 should facilitate efforts to identify the role of S879 phosphorylation and to map signaling pathways that modify p120 function through activation of PKC.

Prognostic significance of altered p120 ctn expression in bladder cancer

OBJECTIVE

To identify the frequency of change in the expression and localization of p120(ctn) in bladder tumours and its association with clinical outcomes, and to investigate the potential role of p120(ctn) in the migratory and invasive behaviour of bladder carcinoma cells.

MATERIALS AND METHODS

In all, 425 superficial tumour specimens (Ta, Tis and T1) and 305 invasive (T2-T4) tumour specimens from 534 patients were assembled in 10 tissue microarrays. P120(ctn) immunostaining was scored for intensity and cellular localization and correlated with clinical variables and survival analysis. Knockdown of p120(ctn) was achieved using small-interference RNA (siRNA) followed by the assessment of migration and invasion behaviour in standard in vitro assays.

RESULTS

The expression levels of p120 catenin inversely correlated with pathological tumour stage (P < 0.001), histological grade (P < 0.001), presence of lymphovascular invasion (P = 0.02) but not lymph node (LN) involvement (P = 0.17). Non-membranous localization of p120(ctn) correlated with stage (P < 0.001), grade (P < 0.001), lymphovascular invasion (P = 0.04) and LN-positive disease (P = 0.02). A low expression level of p120(ctn) was linked to a poor outcome in cancer-specific survival analysis. Knockdown of p120(ctn) using siRNA resulted in a significant reduction in the migration and invasive potential of bladder carcinoma cells.

CONCLUSIONS

Our findings suggest that p120(ctn) acts as a prognostic factor in bladder tumours and has a primary role to play in the migratory and invasive behaviour of bladder carcinoma cells.

p120-catenin regulates microtubule dynamics and cell migration in a cadherin-independent manner

p120-catenin (p120) has been shown to be essential for cadherin stability. Here, we show that p120 is capable of regulating microtubule (MT) dynamics in a cadherin-independent manner. When p120 was depleted in cadherin-deficient Neuro-2a (N2a) cells, MT stability was reduced, as assessed by the nocodazole sensitivity of MTs. On the contrary, over-expression of p120 caused MTs to become resistant to nocodazole. Time-lapse recording of GFP-tagged EB1, a protein which binds the growing plus-ends of MTs, introduced into these cells demonstrated that the plus ends underwent more frequent catastrophe in p120-depleted cells. In addition, p120 knockdown up-regulated the motility of isolated cells, whereas it down-regulated the directional migration of cells from wound edges; and these migratory behaviors of cells were mimicked by nocodazole-induced MT depolymerization. These results suggest that p120 has the ability to regulate MT dynamics and that this activity, in turn, affects cell motility independently of the cadherin adhesion system.

p120 catenin regulates lamellipodial dynamics and cell adhesion in cooperation with cortactin

The armadillo-family protein, p120 catenin (p120), binds to the juxtamembrane domain of classical cadherins and increases cell-cell junction stability. Overexpression of p120 modulates the activity of Rho family GTPases and augments cell migratory ability. Here we show that down-regulation of p120 in epithelial MCF-7 cells by siRNA leads to a striking decrease in lamellipodial persistence and focal adhesion formation. Similar alterations in lamellipodial activity were observed in MCF-7 cells treated with siRNA to cortactin, an activator of Arp2/3-dependent actin polymerization. We found that, in many cell types, p120 is colocalized with cortactin-containing actin structures not only at cell-cell junctions, but also at extrajunctional sites including membrane ruffles and actin-rich halos around endocytotic vesicles. p120 depletion led to dramatic loss of cortactin and its partner, Arp3, from the cell leading edges. Cortactin and p120 are shown to directly interact with each other via the cortactin N-terminal region. We propose that the mechanism underlying p120 functions at the leading edge involves its cooperation with cortactin.

Hic-5 contributes to epithelial-mesenchymal transformation through a RhoA/ROCK-dependent pathway

Epithelial-mesenchymal transformation (EMT) in response to TGFbeta1 is a coordinated process of tissue morphogenesis that occurs during embryonic development as well as during certain pathologic events including kidney tubulointerstitial fibrosis. It is characterized by the disassembly of cell-cell junctions and dramatic alterations in the actin cytoskeleton that facilitates cell-matrix adhesion and stimulates migration. The focal adhesion adapter protein, Hic-5, has previously been reported to be upregulated during TGFbeta1-induced EMT in mouse mammary epithelial cells and the current study recapitulates this result in both mouse kidney proximal tubule epithelial, MCT, cells and human mammary epithelial, MCF10A, cells. To evaluate a causative role for Hic-5 in EMT, Hic-5 RNA interference (siRNA) was used to prevent Hic-5 expression in response to TGFbeta1 stimulation and was shown to suppress cell migration and actin stress fiber formation. It also resulted in the retention of a robust epithelial cell morphology characterized by elevated E-cadherin protein expression and well-organized adherens junctions. In addition, Hic-5 siRNA treatment led to the suppression of TGFbeta1 induction of RhoA activation. In contrast, forced expression of Hic-5 led to the formation of ROCK-dependent actin stress fibers. Furthermore, the induction of Hic-5 expression in response to TGFbeta1 was shown to be a RhoA/ROCK I-dependent process. Together, these data implicate Hic-5 as a key regulator of EMT and suggest that RhoA stimulated Hic-5 expression in response to TGFbeta1 may be functioning in a feed forward mechanism whereby Hic-5 maintains the mesenchymal phenotype through sustained RhoA activation and signaling.

Interplay of distinct growth factors during epithelial mesenchymal transition of cancer progenitor cells and molecular targeting as novel cancer therapies

In this review, we describe the critical functions assumed by the interplay of epidermal growth factor, hedgehog, Wnt/beta-catenin, tumor growth factor-beta and integrin signaling cascades in tumorigenic and migrating cancer progenitor cells and activated stromal cells during carcinogenesis. These growth factors provide an important role for the sustained growth and survival of tumorigenic cancer progenitor cells and their progeny by up-regulating numerous mitotic and antiapoptotic signaling cascades. Furthermore, these potent morphogens may cooperate for inducing the molecular events associated with the epithelial-mesenchymal program in cancer cells including the alterations in epithelial cell shape and motility through the dissociation of intercellular adherens junctions. Of therapeutic interest, new strategies for the development of more effective clinical treatments against the locally aggressive and invasive cancers based on the molecular targeting of deregulated signaling elements in tumorigenic and migrating cancer cells and their local microenvironment are also described.

p120-catenin is required for the collective invasion of squamous cell carcinoma cells via a phosphorylation-independent mechanism

Loss of E-cadherin-mediated cell-cell junctions has been correlated with cancer cell invasion and poor patient survival. p120-catenin has emerged as a key player in promoting E-cadherin stability and adherens junction integrity and has been proposed as a potential invasion suppressor by preventing release of cells from the constraints imposed by cadherin-mediated cell-cell adhesion. However, it has been proposed that tyrosine phosphorylation of p120 may contribute to cadherin-dependent junction disassembly during invasion. Here, we use small interfering RNA (siRNA) in A431 cells to show that knockdown of p120 promotes two-dimensional migration of cells. In contrast, p120 knockdown impairs epidermal growth factor-induced A431 invasion into three-dimensional matrix gels or in organotypic culture, whereas re-expression of siRNA-resistant p120, or a p120 isoform that cannot be phosphorylated on tyrosine, restores the collective mode of invasion employed by A431 cells in vitro. Thus, p120 promotes A431 cell invasion in a phosphorylation-independent manner. We show that the collective invasion of A431 cells depends on the presence of cadherin-mediated (P- and E-cadherin) cell-cell contacts, which are lost in cells where p120 expression is knocked down. Furthermore, membranous p120 is maintained in invasive squamous cell carcinomas in tumours suggesting that p120 may be important for the collective invasion of tumours cells in vivo.

Involvement of p120 catenin in myopodial assembly and nerve-muscle synapse formation

At developing neuromuscular junctions (NMJs), muscles initially contact motor axons by microprocesses, or myopodia, which are induced by nerves and nerve-secreted agrin, but it is unclear how myopodia are assembled and how they influence synaptic differentiation at the NMJ. Here, we report that treatment of cultured muscle cells with agrin transiently depleted p120 catenin (p120ctn) from cadherin junctions in situ, and increased the tyrosine phosphorylation and decreased the cadherin-association of p120ctn in cell extracts. Whereas ectopic expression of wild-type p120ctn in muscle generated myopodia in the absence of agrin, expression of a specific dominant-negative mutant form of p120ctn, which blocks filopodial assembly in nonmuscle cells, suppressed nerve- and agrin-induction of myopodia. Significantly, approaching neurites triggered reduced acetylcholine receptor (AChR) clustering along the edges of muscle cells expressing mutant p120ctn than of control cells, although the ability of the mutant cells to cluster AChRs was itself normal. Our results indicate a novel role of p120ctn in agrin-induced myopodial assembly and suggest that myopodia increase muscle-nerve contacts and muscle's access to neural agrin to promote NMJ formation.

p120-ctn: A nexus for contextual signaling via Rho GTPases

p120 catenin (p120) is the prototypic member of a subfamily of armadillo repeat domain proteins involved in intercellular adhesion. Recent evidence indicates that p120 associates with classical cadherins and regulates their stability. Ectopic p120 expression results in a variety of morphological effects, and promotes cell migration. There is now strong evidence that p120 acts, at least in part, through regulation of Rho GTPases. The data suggest that p120 may act as a signaling nexus, conveying messages from the cellular micro- and macro-environment to the cell's interior. By regulating Rho GTPases in a context-dependent manner p120 can exert profound effects on cellular responses from synaptic plasticity to vesicle trafficking, as well as regulate the motile vs. sessile, and possibly the proliferative vs. quiescent phenotype of epithelial cells. Here, we review the new evidence on the relationship of p120 to Rho GTPases, and discuss potential roles for the p120-Rho connection in normal and malignant cells.

p120 catenin regulates dendritic spine and synapse development through Rho-family GTPases and cadherins

Both the cadherin-catenin complex and Rho-family GTPases have been shown to regulate dendrite development. We show here a role for p120 catenin (p120ctn) in regulating spine and synapse formation in the developing mouse brain. p120catenin gene deletion in hippocampal pyramidal neurons in vivo resulted in reduced spine and synapse densities along dendrites. In addition, p120 catenin loss resulted in reduced cadherin levels and misregulation of Rho-family GTPases, with decreased Rac1 and increased RhoA activity. Analyses in vitro indicate that the reduced spine density reflects aberrant Rho-family GTPase signaling, whereas the effects on spine maturation appear to result from reduced cadherin levels and possibly aberrant Rho-family GTPase signaling. Thus, p120ctn acts as a signal coordinator between cadherins and Rho-family GTPases to regulate cytoskeletal changes required during spine and synapse development.