The control of cell motility and epithelial morphogenesis by Jun kinases

VRK2 anchors KSR1-MEK1 to endoplasmic reticulum forming a macromolecular complex that compartmentalizes MAPK signaling

The spatial and temporal regulation of intracellular signaling is determined by the spatial and temporal organization of complexes assembled on scaffold proteins, which can be modulated by their interactions with additional proteins as well as subcellular localization. The scaffold KSR1 protein interacts with MAPK forming a complex that conveys a differential signaling in response to growth factors. The aim of this work is to determine the unknown mechanism by which VRK2A downregulates MAPK signaling. We have characterized the multiprotein complex formed by KSR1 and the Ser-Thr kinase VRK2A. VRK2A is a protein bound to the endoplasmic reticulum (ER) and retains a fraction of KSR1 complexes on the surface of this organelle. Both proteins, VRK2A and KSR1, directly interact by their respective C-terminal regions. In addition, MEK1 is also incorporated in the basal complex. MEK1 independently interacts with the CA5 region of KSR1 and with the N-terminus of VRK2A. Thus, VRK2A can form a high molecular size (600-1,000 kDa) stable complex with both MEK1 and KSR1. Knockdown of VRK2A resulted in disassembly of these high molecular size complexes. Overexpression of VRK2A increased the amount of KSR1 in the particulate fraction and prevented the incorporation of ERK1/2 into the complex after stimulation with EGF. Neither VRK2A nor KSR1 interact with the VHR, MKP1, MKP2, or MKP3 phosphatases. The KSR1 complex assembled and retained by VRK2A in the ER can have a modulatory effect on the signal mediated by MAPK, thus locally affecting the magnitude of its responses, and can explain differential responses depending on cell type.

Lycopene inhibits angiogenesis both in vitro and in vivo by inhibiting MMP-2/uPA system through VEGFR2-mediated PI3K-Akt and ERK/p38 signaling pathways

SCOPE

Limited in vitro data show that lycopene may be anti-angiogenic but with unclear mechanisms. Here, we employed ex vivo and in vivo assays to substantiate the anti-angiogenic action of lycopene and determined its molecular mechanisms in human umbilical vein endothelial cells (HUVECs).

METHODS AND RESULTS

The anti-angiogenic activity of lycopene was confirmed by ex vivo rat aortic ring and in vivo chorioallantoic membrane assays. Furthermore, the in vivo matrigel plug assay in mice demonstrated that lycopene implanted s.c. at the highest dose used (400 μg/plug) completely inhibited the formation of vascular endothelial cells induced by vascular endothelial growth factor (VEGF). As expected, lycopene inhibited tube formation, invasion, and migration in HUVECs, and such actions were accompanied by reduced activities of matrix metalloproteinase-2, urokinase-type plasminogen activator, and protein expression of Rac1, and by enhancing protein expression of tissue inhibitors of metalloproteinase-2 and plasminogen activator inhibitor-1. Moreover, lycopene attenuated VEGF receptor-2 (VEGFR2)-mediated phosphorylation of extracellular signal-regulated kinase (ERK), p38, and Akt as well as protein expression of PI3K.

CONCLUSION

Our data demonstrate the anti-angiogenic effect of lycopene both in vitro and in vivo. The anti-angiogenic activity of lycopene may involve inhibition of MMP-2/uPA system through VEGFR2-mediated PI3K-Akt and ERK/p38 signaling pathways.

Transgenic expression of the Helicobacter pylori virulence factor CagA promotes apoptosis or tumorigenesis through JNK activation in Drosophila

Gastric cancer development is strongly correlated with infection by Helicobacter pylori possessing the effector protein CagA. Using a transgenic Drosophila melanogaster model, we show that CagA expression in the simple model epithelium of the larval wing imaginal disc causes dramatic tissue perturbations and apoptosis when CagA-expressing and non-expressing cells are juxtaposed. This cell death phenotype occurs through activation of JNK signaling and is enhanced by loss of the neoplastic tumor suppressors in CagA-expressing cells or loss of the TNF homolog Eiger in wild type neighboring cells. We further explored the effects of CagA-mediated JNK pathway activation on an epithelium in the context of oncogenic Ras activation, using a Drosophila model of metastasis. In this model, CagA expression in epithelial cells enhances the growth and invasion of tumors in a JNK-dependent manner. These data suggest a potential role for CagA-mediated JNK pathway activation in promoting gastric cancer progression.

The gastric pathogen Helicobacter pylori infects an estimated 50% of the world's population and is a major risk factor for the development of gastric cancer. Strains of H. pylori that can inject the CagA effector protein into host cells are known to be more virulent, but the potential contributions of host genetics to pathogenesis are not well-understood. Using transgenic Drosophila melanogaster, we show that the genetic context of both the host cells in which CagA is expressed and their neighboring cells changes CagA's effects on epithelial tissue. When CagA is expressed in a subset of cells within an epithelium, it disrupts tissue integrity and induces apoptosis through activation of JNK signaling, a pathway that functions to remove aberrant cells from an epithelium. CagA's proapoptotic effects are inhibited by neoplastic tumor suppressor genes in CagA-expressing cells, and by the tumor necrosis factor homolog Eiger in neighboring cells. In contrast, when CagA is coexpressed with oncogenic Ras in a Drosophila model of metastasis, it enhances the growth and invasion of tumors in a JNK-dependent manner. Our study demonstrates how changes in host genetics can cooperate with activation of JNK signaling by the bacterial virulence factor CagA to promote tumorigenesis.

c-Jun N-terminal kinase phosphorylation of MARCKSL1 determines actin stability and migration in neurons and in cancer cells

Cell migration is a fundamental biological function, critical during development and regeneration, whereas deregulated migration underlies neurological birth defects and cancer metastasis. MARCKS-like protein 1 (MARCKSL1) is widely expressed in nervous tissue, where, like Jun N-terminal protein kinase (JNK), it is required for neural tube formation, though the mechanism is unknown. Here we show that MARCKSL1 is directly phosphorylated by JNK on C-terminal residues (S120, T148, and T183). This phosphorylation enables MARCKSL1 to bundle and stabilize F-actin, increase filopodium numbers and dynamics, and retard migration in neurons. Conversely, when MARCKSL1 phosphorylation is inhibited, actin mobility increases and filopodium formation is compromised whereas lamellipodium formation is enhanced, as is cell migration. We find that MARCKSL1 mRNA is upregulated in a broad range of cancer types and that MARCKSL1 protein is strongly induced in primary prostate carcinomas. Gene knockdown in prostate cancer cells or in neurons reveals a critical role for MARCKSL1 in migration that is dependent on the phosphorylation state; phosphomimetic MARCKSL1 (MARCKSL1(S120D,T148D,T183D)) inhibits whereas dephospho-MARCKSL1(S120A,T148A,T183A) induces migration. In summary, these data show that JNK phosphorylation of MARCKSL1 regulates actin homeostasis, filopodium and lamellipodium formation, and neuronal migration under physiological conditions and that, when ectopically expressed in prostate cancer cells, MARCKSL1 again determines cell movement.

Development of a novel liquid crystal based cell traction force transducer system

Keratinocyte traction forces play a crucial role in wound healing. The aim of this study was to develop a novel cell traction force (CTF) transducer system based on cholesteryl ester liquid crystals (LC). Keratinocytes cultured on LC induced linear and isolated deformation lines in the LC surface. As suggested by the fluorescence staining, the deformation lines appeared to correlate with the forces generated by the contraction of circumferential actin filaments which were transmitted to the LC surface via the focal adhesions. Due to the linear viscoelastic behavior of the LC, Hooke's equation was used to quantify the CTFs by associating Young's modulus of LC to the cell induced stresses and biaxial strain in forming the LC deformation. Young's modulus of the LC was profiled by using spherical indentation and determined at approximately 87.1±17.2kPa. A new technique involving cytochalasin-B treatment was used to disrupt the intracellular force generating actin fibers, and consequently the biaxial strain in the LC induced by the cells was determined. Due to the improved sensitivity and spatial resolution (∼1μm) of the LC based CTF transducer, a wide range of CTFs was determined (10-120nN). These were found to be linearly proportional to the length of the deformations. The linear relationship of CTF-deformations was then applied in a bespoke CTF mapping software to estimate CTFs and to map CTF fields. The generated CTF map highlighted distinct distributions and different magnitude of CTFs were revealed for polarized and non-polarized keratinocytes.

Notch and Mef2 synergize to promote proliferation and metastasis through JNK signal activation in Drosophila

Genetic analyses in Drosophila revealed a synergy between Notch and the pleiotropic transcription factor Mef2 (myocyte enhancer factor 2), which profoundly influences proliferation and metastasis. We show that these hyperproliferative and invasive Drosophila phenotypes are attributed to upregulation of eiger, a member of the tumour necrosis factor superfamily of ligands, and the consequent activation of Jun N-terminal kinase signalling, which in turn triggers the expression of the invasive marker MMP1. Expression studies in human breast tumour samples demonstrate correlation between Notch and Mef2 paralogues and support the notion that Notch-MEF2 synergy may be significant for modulating human mammary oncogenesis.

Transcriptional activity of neural retina leucine zipper (Nrl) is regulated by c-Jun N-terminal kinase and Tip60 during retina development

Neural retina leucine zipper (Nrl), a key basic motif leucine zipper (bZIP) transcription factor, modulates rod photoreceptor differentiation by activating rod-specific target genes. In searching for factors that might couple with Nrl to modulate its transcriptional activity through posttranslational modification, we observed the novel interactions of Nrl with c-Jun N-terminal kinase 1 (JNK1) and HIV Tat-interacting protein 60 (Tip60). JNK1 directly interacted with and phosphorylated Nrl at serine 50, which enhanced Nrl transcriptional activity on the rhodopsin and Ppp2r5c promoters. Use of an inactive JNK1 mutant or treatment with a JNK inhibitor (SP600125) significantly reduced JNK1-mediated phosphorylation and transcriptional activity of Nrl in cultured retinal explants. We also found that Nrl activated rhodopsin and Ppp2r5c transcription by recruiting Tip60 to promote histone H3/H4 acetylation. The binding affinity of phospho-Nrl for Tip60 was significantly greater than that of the unphosphorylated Nrl. Thus, the histone acetyltransferase-containing Tip60 behaved as a coactivator in the Nrl-dependent transcriptional regulation of the rhodopsin and Ppp2r5c genes in the developing mouse retina. A transcriptional network of interactive proteins, including Nrl, JNK1, and Tip60, may be required to precisely control spatiotemporal photoreceptor-specific gene expression during retinal development.

Integrin-dependent activation of the JNK signaling pathway by mechanical stress

Mechanical force is known to modulate the activity of the Jun N-terminal kinase (JNK) signaling cascade. However, the effect of mechanical stresses on JNK signaling activation has previously only been analyzed by in vitro detection methods. It still remains unknown how living cells activate the JNK signaling cascade in response to mechanical stress and what its functions are in stretched cells.

We assessed in real-time the activity of the JNK pathway in Drosophila cells by Fluorescence Lifetime Imaging Microscopy (FLIM), using an intramolecular phosphorylation-dependent dJun-FRET (Fluorescence Resonance Energy Transfer) biosensor. We found that quantitative FRET-FLIM analysis and confocal microscopy revealed sustained dJun-FRET biosensor activation and stable morphology changes in response to mechanical stretch for Drosophila S2R+ cells. Further, these cells plated on different substrates showed distinct levels of JNK activity that associate with differences in cell morphology, integrin expression and focal adhesion organization.

These data imply that alterations in the cytoskeleton and matrix attachments may act as regulators of JNK signaling, and that JNK activity might feed back to modulate the cytoskeleton and cell adhesion. We found that this dynamic system is highly plastic; at rest, integrins at focal adhesions and talin are key factors suppressing JNK activity, while multidirectional static stretch leads to integrin-dependent, and probably talin-independent, Jun sensor activation. Further, our data suggest that JNK activity has to coordinate with other signaling elements for the regulation of the cytoskeleton and cell shape remodeling associated with stretch.

The biphasic nature of hypoxia-induced directional migration of activated human hepatic stellate cells

Liver fibrogenesis is sustained by pro-fibrogenic myofibroblast-like cells (MFs), mainly originating from activated hepatic stellate cells (HSC/MFs) or portal (myo)fibroblasts, and is favoured by hypoxia-dependent angiogenesis. Human HSC/MFs were reported to express vascular-endothelial growth factor (VEGF) and VEGF-receptor type 2 and to migrate under hypoxic conditions. This study was designed to investigate early and delayed signalling mechanisms involved in hypoxia-induced migration of human HSC/MFs. Signal transduction pathways and intracellular generation of reactive oxygen species (ROS) were evaluated by integrating morphological, cell, and molecular biology techniques. Non-oriented and oriented migration were evaluated by using wound healing assay and the modified Boyden's chamber assay, respectively. The data indicate that hypoxia-induced migration of HSC/MFs is a biphasic process characterized by the following sequence of events: (a) an early (15 min) and mitochondria-related increased generation of intracellular ROS which (b) was sufficient to switch on activation of ERK1/2 and JNK1/2 that were responsible for the early phase of oriented migration; (c) a delayed and HIF-1α-dependent increase in VEGF expression (facilitated by ROS) and its progressive, time-dependent release in the extracellular medium that (d) was mainly responsible for sustained migration of HSC/MFs. Finally, immunohistochemistry performed on HCV-related fibrotic/cirrhotic livers revealed HIF-2α and haem-oxygenase-1 positivity in hepatocytes and α-SMA-positive MFs, indicating that MFs were likely to be exposed in vivo to both hypoxia and oxidative stress. In conclusion, hypoxia-induced migration of HSC/MFs involves an early, mitochondrial-dependent ROS-mediated activation of ERK and JNK, followed by a delayed- and HIF-1α-dependent up-regulation and release of VEGF.

Role of JNK in mammary gland development and breast cancer

cJun NH(2)-terminal kinase (JNK) signaling has been implicated in the developmental morphogenesis of epithelial organs. In this study, we employed a compound deletion of the murine Jnk1 and Jnk2 genes in the mammary gland to evaluate the requirement for these ubiquitously expressed genes in breast development and tumorigenesis. JNK1/2 was not required for breast epithelial cell proliferation or motility. However, JNK1/2 deficiency caused increased branching morphogenesis and defects in the clearance of lumenal epithelial cells. In the setting of breast cancer development, JNK1/2 deficiency significantly increased tumor formation. Together, these findings established that JNK signaling is required for normal mammary gland development and that it has a suppressive role in mammary tumorigenesis.

Role of β-catenin in post-meiotic male germ cell differentiation

Though roles of β-catenin signaling during testis development have been well established, relatively little is known about its role in postnatal testicular physiology. Even less is known about its role in post-meiotic germ cell development and differentiation. Here, we report that β-catenin is highly expressed in post-meiotic germ cells and plays an important role during spermiogenesis in mice. Spermatid-specific deletion of β-catenin resulted in significantly reduced sperm count, increased germ cell apoptosis and impaired fertility. In addition, ultrastructural studies show that the loss of β-catenin in post-meiotic germ cells led to acrosomal defects, anomalous release of immature spermatids and disruption of adherens junctions between Sertoli cells and elongating spermatids (apical ectoplasmic specialization; ES). These defects are likely due to altered expression of several genes reportedly involved in Sertoli cell-germ cell adhesion and germ cell differentiation, as revealed by gene expression analysis. Taken together, our results suggest that β-catenin is an important molecular link that integrates Sertoli cell-germ cell adhesion with the signaling events essential for post-meiotic germ cell development and maturation. Since β-catenin is also highly expressed in the Sertoli cells, we propose that binding of germ cell β-catenin complex to β-catenin complex on Sertoli cell at the apical ES surface triggers a signaling cascade that regulates post-meiotic germ cell differentiation.

Loss of MAP3K1 enhances proliferation and apoptosis during retinal development

Precise coordination of progenitor cell proliferation and differentiation is essential for proper organ morphogenesis and function during mammalian development. The mitogen-activated protein kinase kinase kinase 1 (MAP3K1) has a well-established role in anterior eyelid development, as Map3k1-knockout mice have defective embryonic eyelid closure and an `eye-open at birth' (EOB) phenotype. Here, we show that MAP3K1 is highly expressed in the posterior of the developing eye and is required for retina development. The MAP3K1-deficient mice exhibit increased proliferation and apoptosis, and Müller glial cell overproduction in the developing retinas. Consequently, the retinas of these mice show localized rosette-like arrangements in the outer nuclear layer, and develop abnormal vascularization, broken down retinal pigment epithelium, photoreceptor loss and early onset of retinal degeneration. Although the retinal defect is associated with increased cyclin D1 and CDK4/6 expression, and RB phosphorylation and E2F-target gene upregulation, it is independent of the EOB phenotype and of JNK. The retinal developmental defect still occurs in knockout mice that have undergone tarsorrhaphy, but is absent in compound mutant Map3k1(+/ΔKD)Jnk1(-/-) and Map3k1(+/ΔKD)Jnk(+/-)Jnk2(+/-) mice that have EOB and reduced JNK signaling. Our results unveil a novel role for MAP3K1 in which it crosstalks with the cell cycle regulatory pathways in the prevention of retina malformation and degeneration.

c-Jun-N-Terminal Kinase Signaling Is Involved in Cyclosporine-Induced Epithelial Phenotypic Changes

Tubular epithelial cells play a central role in the pathogenesis of chronic nephropathies. Previous toxicogenomic studies have demonstrated that cyclosporine- (CsA-) induced epithelial phenotypic changes (EPCs) are reminiscent of an incomplete epithelial to mesenchymal transition (EMT) in a TGF-β-independent manner. Furthermore, we identified endoplasmic reticulum (ER) stress as a potential mechanism that may participate in the modulation of tubular cell plasticity during CsA exposure. Because c-jun-N-terminal kinase (JNK), which is activated during ER stress, is implicated in kidney fibrogenesis, we undertook the current study to identify the role of JNK signaling in EPCs induced by CsA. In primary cultures of human renal epithelial cells, CsA activates JNK signaling, and the treatment with a JNK inhibitor reduces the occurrence of cell shape changes, E-cadherin downregulation, cell migration, and Snail-1 expression. Our results suggest that CsA activates JNK signaling, which, in turn, may participate in the morphological alterations through the regulation of Snail-1 expression.

Mitogen-activated protein kinase kinase kinase 1 (MAP3K1) integrates developmental signals for eyelid closure

Developmental eyelid closure is an evolutionarily conserved morphogenetic event requiring proliferation, differentiation, cytoskeleton reorganization, and migration of epithelial cells at the tip of the developing eyelid. Many signaling events take place during eyelid closure, but how the signals converge to regulate the morphogenetic process remains an open and intriguing question. Here we show that mitogen-activated protein kinase kinase kinase 1 (MAP3K1) highly expressed in the developing eyelid epithelium, forms with c-Jun, a regulatory axis that orchestrates morphogenesis by integrating two different networks of eyelid closure signals. A TGF-α/EGFR-RhoA module initiates one of these networks by inducing c-Jun expression which, in a phosphorylation-independent manner, binds to the Map3k1 promoter and causes an increase in MAP3K1 expression. RhoA knockout in the ocular surface epithelium disturbs this network by decreasing MAP3K1 expression, and causes delayed eyelid closure in Map3k1 hemizygotes. The second network is initiated by the enzymatic activity of MAP3K1, which phosphorylates and activates a JNK-c-Jun module, leading to AP-1 transactivation and induction of its downstream genes, such as Pai-1. MAP3K1 inactivation reduces AP-1 activity and PAI-1 expression both in cells and developing eyelids. MAP3K1 is therefore the nexus of an intracrine regulatory loop connecting the TGF-α/EGFR/RhoA-c-Jun and JNK-c-Jun-AP-1 pathways in developmental eyelid closure.

Rhou maintains the epithelial architecture and facilitates differentiation of the foregut endoderm

Rhou encodes a Cdc42-related atypical Rho GTPase that influences actin organization in cultured cells. In mouse embryos at early-somite to early-organogenesis stages, Rhou is expressed in the columnar endoderm epithelium lining the lateral and ventral wall of the anterior intestinal portal. During foregut development, Rhou is downregulated in regions where the epithelium acquires a multilayered morphology heralding the budding of organ primordia. In embryos generated from Rhou knockdown embryonic stem (ES) cells, the embryonic foregut displays an abnormally flattened shape. The epithelial architecture of the endoderm is disrupted, the cells are depleted of microvilli and the phalloidin-stained F-actin content of their sub-apical cortical domain is reduced. Rhou-deficient cells in ES cell-derived embryos and embryoid bodies are less efficient in endoderm differentiation. Impaired endoderm differentiation of Rhou-deficient ES cells is accompanied by reduced expression of c-Jun/AP-1 target genes, consistent with a role for Rhou in regulating JNK activity. Downregulation of Rhou in individual endoderm cells results in a reduced ability of these cells to occupy the apical territory of the epithelium. Our findings highlight epithelial morphogenesis as a required intermediate step in the differentiation of endoderm progenitors. In vivo, Rhou activity maintains the epithelial architecture of the endoderm progenitors, and its downregulation accompanies the transition of the columnar epithelium in the embryonic foregut to a multilayered cell sheet during organ formation.

JNK2 promotes endothelial cell alignment under flow

Endothelial cells in straight, unbranched segments of arteries elongate and align in the direction of flow, a feature which is highly correlated with reduced atherosclerosis in these regions. The mitogen-activated protein kinase c-Jun N-terminal kinase (JNK) is activated by flow and is linked to inflammatory gene expression and apoptosis. We previously showed that JNK activation by flow is mediated by integrins and is observed in cells plated on fibronectin but not on collagen or basement membrane proteins. We now show thatJNK2 activation in response to laminar shear stress is biphasic, with an early peak and a later peak. Activated JNK localizes to focal adhesions at the ends of actin stress fibers, correlates with integrin activation and requires integrin binding to the extracellular matrix. Reducing JNK2 activation by siRNA inhibits alignment in response to shear stress. Cells on collagen, where JNK activity is low, align slowly. These data show that an inflammatory pathway facilitates adaptation to laminar flow, thereby revealing an unexpected connection between adaptation and inflammatory pathways.

The lens in focus: a comparison of lens development in Drosophila and vertebrates

The evolution of the eye has been a major subject of study dating back centuries. The advent of molecular genetics offered the surprising finding that morphologically distinct eyes rely on conserved regulatory gene networks for their formation. While many of these advances often stemmed from studies of the compound eye of the fruit fly, Drosophila melanogaster, and later translated to discoveries in vertebrate systems, studies on vertebrate lens development far outnumber those in Drosophila. This may be largely historical, since Spemann and Mangold's paradigm of tissue induction was discovered in the amphibian lens. Recent studies on lens development in Drosophila have begun to define molecular commonalities with the vertebrate lens. Here, we provide an overview of Drosophila lens development, discussing intrinsic and extrinsic factors controlling lens cell specification and differentiation. We then summarize key morphological and molecular events in vertebrate lens development, emphasizing regulatory factors and networks strongly associated with both systems. Finally, we provide a comparative analysis that highlights areas of research that would help further clarify the degree of conservation between the formation of dioptric systems in invertebrates and vertebrates.

EGF-induced ERK-activation downstream of FAK requires rac1-NADPH oxidase

Reactive oxygen species (ROS) function as signaling molecules mainly by reversible oxidation of redox-sensitive target proteins. ROS can be produced in response to integrin ligation and growth factor stimulation through Rac1 and its effector protein NADPH oxidase. One of the central roles of Rac1-NADPH oxidase is actin cytoskeletal rearrangement, which is essential for cell spreading and migration. Another important regulator of cell spread is focal adhesion kinase (FAK), a coordinator of integrin and growth factor signaling. Here, we propose a novel role for NADPH oxidase as a modulator of the FAK autophosphorylation site. We found that Rac1-NADPH oxidase enhanced the phosphorylation of FAK at Y397. This site regulates FAK's ability to act as a scaffold for EGF-mediated signaling, including activation of ERK. Accordingly, we found that EGF-induced activation of FAK at Y925, the following activation of ERK, and phosphorylation of FAK at the ERK-regulated S910-site depended upon NADPH oxidase. Furthermore, the inhibition of NADPH oxidase caused excessive focal adhesions, which is in accordance with ERK and FAK being modulators of focal adhesion dissociation. Our data suggest that Rac1 through NADPH oxidase is part of the signaling pathway constituted by FAK, Rac1, and ERK that regulates focal adhesion disassembly during cell spreading.

Dickkopf-1 is frequently overexpressed in ovarian serous carcinoma and involved in tumor invasion

Dickkopf-1 (DKK1) was known as a negative regulator of the Wnt signaling pathway, which played a crucial role in carcinogenesis. However, its function in human cancers remained elusive. In this study, we aimed to investigate the role of DKK1 in ovarian serous papillary adenocarcinoma (OSC) tumor progression and invasion. Quantitative real-time RT-PCR and Western blot analysis showed that the expression of DKK1 mRNA and protein in 32 OSC tissues were elevated as compared with those in 10 normal ovarian tissues (P = 0.005, P = 0.003, respectively). Immunohistochemical analysis in 178 clinical OSC samples showed that the expression of DKK1 was positively associated with FIGO stage (P = 0.016). Furthermore, the expression of DKK1 protein was positively associated with P-JNK1 protein expression in 178 OSC tissues. DKK1, P-JNK1 and the co-expression of DKK1 and P-JNK1 were all unfavorable prognosis factors for OSC patients (P < 0.0001). DKK1, alone or combined with P-JNK1, was an independent predictor for the 5 year survival (P = 0.015, P < 0.0001, respectively). DKK1 could promote OSC cells invasion and the growth of OSC nude mice xenograft. DKK1 in OSC cells could activate P-JNK1 expression and significantly promote formations of actin filaments and filopodia. Thus, DKK1, alone or combined with P-JNK1, was a novel prognostic predictor for OSC patients and contributed to the invasion of OSC.

Elimination of oncogenic neighbors by JNK-mediated engulfment in Drosophila

A newly emerged oncogenic cell in the epithelial population has to confront antitumor selective pressures in the host tissue. However, the mechanisms by which surrounding normal tissue exerts antitumor effects against oncogenically transformed cells are poorly understood. In Drosophila imaginal epithelia, clones of cells mutant for evolutionarily conserved tumor suppressor genes such as scrib or dlg lose their epithelial integrity and are eliminated from epithelia when surrounded by wild-type tissue. Here, we show that surrounding normal cells activate nonapoptotic JNK signaling in response to the emergence of oncogenic mutant cells. This JNK activation leads to upregulation of PVR, the Drosophila PDGF/VEGF receptor. Genetic and time-lapse imaging analyses reveal that PVR expression in surrounding cells activates the ELMO/Mbc-mediated phagocytic pathway, thereby eliminating oncogenic neighbors by engulfment. Our data indicate that JNK-mediated cell engulfment could be an evolutionarily conserved intrinsic tumor-suppression mechanism that eliminates premalignant cells from epithelia.

Intracellular reactive oxygen species are required for directional migration of resident and bone marrow-derived hepatic pro-fibrogenic cells

BACKGROUND & AIMS

Liver fibrogenesis is sustained by myofibroblast-like cells originating from hepatic stellate cells (HSC/MFs), portal fibroblasts or bone marrow-derived cells, including mesenchymal stem cells (MSCs). Herein, we investigated the mechanistic role of intracellular generation of reactive oxygen species (ROS) and redox-sensitive signal transduction pathways in mediating chemotaxis, a critical profibrogenic response for human HSC/MFs and for MSC potentially engrafting chronically injured liver.

METHODS

Intracellular generation of ROS and signal transduction pathways were evaluated by integrating morphological and molecular biology techniques. Chemokinesis and chemotaxis were evaluated by wound healing assay and modified Boyden's chamber assay, respectively. Additional in vivo evidence was obtained in human specimens from HCV-related cirrhosis.

RESULTS

Human MSCs and HSC/MFs migrate in response to a panel of polypeptide chemoattractants and extracellularly generated superoxide anion. All polypeptides induced a NADPH-oxidase-dependent intracellular rise in ROS, resulting in activation of ERK1/2 and JNK1/2. Moreover, menadione or 2,3-dimethoxy-1,4-naphthoquinone, which generate intracellular superoxide anion or hydrogen peroxide, respectively, induced ERK1/2 and JNK1/2 activation and migration. JNK1 activation was predominant for migration as shown by specific silencing. Finally, activation of ERK1/2 and JNK1/2 was found in extracts obtained from HSC/MFs during the course of an oxidative stress-mediated model of liver injury and phosphorylated JNK1/2 isoforms were detected in α-smooth muscle actin-positive myofibroblasts lining fibrotic septa in human cirrhotic livers.

CONCLUSIONS

Intracellular generation of ROS, through activation of specific signaling pathways, is a critical event for directional migration of HSC/MFs and MSCs.

Differentiation of neural stem cells influences their chemotactic responses to vascular endothelial growth factor

Although much effort has been devoted to the delineation of factors involved in the migration of neural stem/progenitor cells (NSCs), the relationship between the chemotactic response and the differentiation status of these cells remains elusive. In the present study, we found that NSCs in varying differentiation states possess different chemotactic responses to vascular endothelial growth factor (VEGF): first, the number of chemotaxing NSCs and the optimal concentrations of VEGF that induced the peak migration vary greatly; second, time-lapse video analysis shows that NSCs at certain differentiation states migrate more efficiently toward VEGF, although the migration speed remains unchanged irrespective of cell states; third, the phosphorylation status of Akt, ERK1/2, SAPK/JNK, and p38MAPK is closely related to the differentiation levels of NSCs subjected to VEGF; and, finally, although inhibition of ERK1/2 signaling significantly attenuates VEGF-stimulated transfilter migration of both undifferentiated and differentiating NSCs, NSCs show normal chemotactic response after treatment with inhibitors of SAPK/JNK or p38MAPK. Meanwhile, interference with PI3K/Akt signaling prevents only NSCs of 12 hr differentiation, but not NSCs of 1 day or 3 days differentiation, from migrating in response to VEGF. Moreover, blocking of PI3K/Akt or MAPK signaling impairs the migration efficiency and/or speed, the extent of which depends on the cell differentiation status. Collectively, these results demonstrate that differentiation of NSCs influences their chemotactic responses to VEGF: NSCs in varying differentiation states have different migratory capacities, thereby shedding light on optimization of the therapeutic potential of NSCs to be employed for neural regeneration after injury.

c-Jun is required for TGF-β-mediated cellular migration via nuclear Ca²⁺ signaling

Tumor progression involves the acquisition of invasiveness through a basement membrane. The c-jun proto-oncogene is overexpressed in human tumors and has been identified at the leading edge of human breast tumors. TGF-β plays a bifunctional role in tumorigenesis and cellular migration. Although c-Jun and the activator protein 1 (AP-1) complex have been implicated in human cancer, the molecular mechanisms governing cellular migration via c-Jun and the role of c-Jun in TGF-β signaling remains poorly understood. Here, we analyze TGF-β mediated cellular migration in mouse embryo fibroblasts using floxed c-jun transgenic mice. We compared the c-jun wild type with the c-jun knockout cells through the use of Cre recombinase. Herein, TGF-β stimulated cellular migration and intracellular calcium release requiring endogenous c-Jun. TGF-β mediated Ca(2+) release was independent of extracellular calcium and was suppressed by both U73122 and neomycin, pharmacological inhibitors of the breakdown of PIP(2) into IP(3). Unlike TGF-β-mediated Ca(2+) release, which was c-Jun dependent, ATP mediated Ca(2+) release was c-Jun independent. These studies identify a novel pathway by which TGF-β regulates cellular migration and Ca(2+) release via endogenous c-Jun.

MAGI-3 competes with NHERF-2 to negatively regulate LPA2 receptor signaling in colon cancer cells

BACKGROUND & AIMS

Lysophosphatidic acid (LPA) is a potent inducer of colon cancer and LPA receptor type 2 (LPA(2)) is overexpressed in colon tumors. LPA(2) interacts with membrane-associated guanylate kinase with inverted orientation-3 (MAGI-3) and the Na+/H+ exchanger regulatory factor 2 (NHERF-2), but the biological effects of these interactions are unknown. We investigated the roles of MAGI-3 and NHERF-2 in LPA(2)-mediated signaling in human colon cancer cells.

METHODS

We overexpressed or knocked down MAGI-3 in HCT116 and SW480 cells. The effects of MAGI-3 and NHERF-2 in LPA-induced cell migration, invasion, inositol phosphate generation, and nuclear factor-κB activation were determined. Expression of MAGI-3 and NHERF-2 in human colon tumor tissues was analyzed using tissue microarray analysis.

RESULTS

NHERF-2 promoted migration and invasion of colon cancer cells, whereas MAGI-3 inhibited these processes. MAGI-3 competed with NHERF-2 for binding to LPA(2) and phospholipase C-β3. However, NHERF-2 and MAGI-3 reciprocally regulated LPA(2)-induced phospholipase C activity. MAGI-3 increased the interaction of LPA(2) with Gα(12), whereas NHERF-2 preferentially promoted interaction between LPA(2) and Gα(q). MAGI-3 decreased the tumorigenic capacity of LPA(2) by attenuating the activities of nuclear factor-κB and c-Jun N-terminal kinase. MAGI-3 and NHERF-2 were expressed differentially in colon adenocarcinomas, consistent with their opposing effects.

CONCLUSIONS

LPA(2) is dynamically regulated by 2 distinct PDZ proteins via modulation of G-protein coupling and receptor signaling. MAGI-3 is a negative regulator of LPA(2) signaling.

c-Jun N-terminal kinase 2 (JNK2) enhances cell migration through epidermal growth factor substrate 8 (EPS8)

Membrane-bound receptors induce biochemical signals to remodel the actin cytoskeleton and mediate cell motility. In association with receptor tyrosine kinases, several downstream mitogen-induced kinases facilitate cell migration. Here, we show a role for c-Jun N-terminal kinase 2 (JNK2) in promoting mammary cancer cell migration through inhibition of epidermal growth factor substrate 8 (EPS8) expression, a key regulator of EGF receptor (R) signaling and trafficking. Using jnk2(-/-) mice, we found that EPS8 expression is higher in polyoma middle T antigen (PyVMT)jnk2(-/-) mammary tumors and jnk2(-/-) mammary glands compared with the respective jnk2(+/+) controls. The inverse relationship between the jnk2 and eps8 expression was also associated with cancer progression in that patients with basal-type breast tumors expressing high jnk2 and low eps8 experienced poor disease-free survival. In mammary tumor cell lines, the absence of jnk2 greatly reduces cell migration that is rescued by EPS8 knockdown. Subsequent studies show that JNK2 enhances formation of the EPS8-Abi-1-Sos-1 complex to augment EGFR activation of Akt and ERK, whereas the absence of JNK2 promotes ESP8/RN-Tre association to inhibit endocytotic trafficking of the EGFR. Together, these studies unveil a critical role for JNK2 and EPS8 in receptor tyrosine kinase signaling and trafficking to convey distinctly different effects on cell migration.

Rab11 regulates JNK and Raf/MAPK-ERK signalling pathways during Drosophila wing development

Developmental signalling pathways are regulated by intracellular vesicle trafficking in multicellular organisms. In our earlier communication, we have shown that mutation in Rab11 (a subfamily of the Ypt/Rab gene family) results in the activation of JNK signalling pathways in Drosophila eye. Here, we report that Rab11 regulates JNK and Raf/MAPK-ERK signalling pathways during Drosophila wing development. Using immunofluorescence and immunohistochemical analyses, we show that overexpression of Rab11 in mutant wing imaginal disc cells triggers the induction of apoptosis and activation of JNK and ERK. Further, using a genetic approach it has been shown that Rab11 interacts with the components of these pathways during Drosophila wing development. In addition to this, in Rab11 mutant wing imaginal discs JNK activity was monitored using puc(E)⁶⁹, a P-lacZ enhancer-trap line inserted in puckered (puc). A strong induction of puc in Rab11 mutant wing imaginal disc cells provided a strong support that Rab11 regulates the JNK signalling pathway during Drosophila wing development.

C-jun inhibits mammary apoptosis in vivo

c-jun, which is overexpressed in a number of human cancers encodes a critical component of the AP-1 complex. c-jun has been shown to either induce or inhibit cellular apoptosis. Germ line deletion of both c-jun alleles is embryonically lethal. To determine the role of the endogenous c-jun gene in apoptosis, we performed mammary epithelial cell-targeted somatic deletion using floxed c-jun (c-jun(f/f)) conditional knockout mice. Laser capture microdissection demonstrated endogenous c-jun inhibits expression of apoptosis inducing genes and reactive oxygen species (ROS)-reducing genes (MnSOD, catalase). ROS have been implicated in apoptosis and undergo enzymatic elimination via MnSOD and CuZnSOD with further detoxification via catalase. c-jun-mediated survival was in part dependent on ROS production. c-jun-mediated repression of MnSOD and catalase occurred via mitochondrial complex I and NOX I. Collectively, these studies define a pivotal role of endogenous c-jun in promoting cell survival via maintaining mitochondrial integrity and expression of the key regulators of ROS production.

The unique and cooperative roles of the Grainy head-like transcription factors in epidermal development reflect unexpected target gene specificity

The Grainy head-like 3 (Grhl3) gene encodes a transcription factor that plays essential roles in epidermal morphogenesis during embryonic development, with deficient mice exhibiting failed skin barrier formation, defective wound repair, and loss of eyelid fusion. Despite sharing significant sequence homology, overlapping expression patterns, and an identical core consensus DNA binding site, the other members of the Grhl family (Grhl1 and -2) fail to compensate for the loss of Grhl3 in these processes. Here, we have employed diverse genetic models, coupled with biochemical studies, to define the inter-relationships of the Grhl factors in epidermal development. We show that Grhl1 and Grhl3 have evolved complete functional independence, as evidenced by a lack of genetic interactions in embryos carrying combinations of targeted alleles of these genes. In contrast, compound heterozygous Grhl2/Grhl3 embryos displayed failed wound repair, and loss of a single Grhl2 allele in Grhl3-null embryos results in fully penetrant eyes open at birth. Expression of Grhl2 from the Grhl3 locus in homozygous knock-in mice corrects the wound repair defect, but these embryos still display a complete failure of skin barrier formation. This functional dissociation is due to unexpected differences in target gene specificity, as both GRHL2 and GRHL3 bind to and regulate expression of the wound repair gene Rho GEF 19, but regulation of the barrier forming gene, Transglutaminase 1 (TGase1), is unique to GRHL3. Our findings define the mechanisms underpinning the unique and cooperative roles of the Grhl genes in epidermal development.

Effects of transfection of ICAP-1α and its mutants on adhesion and migration of 2H-11 cells

This study examined the effect of integrin cytoplasmic domain-associated protein 1α (ICAP-1α) and its mutatants T38A and I138A on the adhesion, migration and tube formation of 2H-11 cells. rAAV-ICAP-1α, rAAV-T38A and rAAV-I138A were constructed. After infection, the expression of ICAP-1α and p-ERK1/2, p-c-Jun protein was measured by Western blotting. Adhesion ability was evaluated by using MTT. Cell migration was determined by using Boyden chamber method. Tube formation test was conducted on Matrigel. The results showed that in ICAP-1α, T38A and I138A groups, ICAP-1α protein expression was increased. In T38A and I138A groups, phospho-ERK1/2, phospho-c-Jun protein expressions were significantly increased as compared with the control group and the GFP group. ICAP-1α group protein expression was obviously decreased when compared with the control group and the GFP group. Cell adhesion ratio was 0.1429±0.0080 in control group, 0.1434±0.0077 in GFP group and the ratio in T38A and I138A groups increased to 0.3210±0.0082 and 0.3250±0.0079, respectively. In ICAP-1α group, the ratio was decreased to 0.1005±0.0073. In T38A and I138A groups, the number of migrating 2H-11 cells was increased to 31.45±3.20 and 33.10±5.40 against 18.51±2.80 in control group and 20.47±3.12 in GFP group. In ICAP-1α group, the number was decreased to 12.06±1.72. The number of tube-like structures was increased to 20.41±2.54 in T38A and to 22.26±3.07 in I138A groups as compared to those of control group 12.45±1.84 and GFP group 13.63±2.71. In ICAP-1α group, the number of tube-like structures was decreased to 8.32±1.24. It was suggested that rAAV-T38A and rAAV-I138A transfection can substantially increase 2H-11 cell adhesion, migration and angiogenisis, while rAAV-ICAP-1α can greatly inhibit the effect. These effects might be correlated with ERK1/2 and c-Jun protein phosphorylation.

A targeted UAS-RNAi screen in Drosophila larvae identifies wound closure genes regulating distinct cellular processes

Robust mechanisms for tissue repair are critical for survival of multicellular organisms. Efficient cutaneous wound repair requires the migration of cells at the wound edge and farther back within the epidermal sheet, but the genes that control and coordinate these migrations remain obscure. This is in part because a systematic screening approach for in vivo identification and classification of postembryonic wound closure genes has yet to be developed. Here, we performed a proof-of-principle reporter-based in vivo RNAi screen in the Drosophila melanogaster larval epidermis to identify genes required for normal wound closure. Among the candidate genes tested were kinases and transcriptional mediators of the Jun N-terminal kinase (JNK) signaling pathway shown to be required for epithelial sheet migration during development. Also targeted were genes involved in actin cytoskeletal remodeling. Importantly, RNAi knockdown of both canonical and noncanonical members of the JNK pathway caused open wounds, as did several genes involved in actin cytoskeletal remodeling. Our analysis of JNK pathway components reveals redundancy among the upstream activating kinases and distinct roles for the downstream transcription factors DJun and DFos. Quantitative and qualitative morphological classification of the open wound phenotypes and evaluation of JNK activation suggest that multiple cellular processes are required in the migrating epidermal cells, including functions specific to cells at the wound edge and others specific to cells farther back within the epidermal sheet. Together, our results identify a new set of conserved wound closure genes, determine putative functional roles for these genes within the migrating epidermal sheet, and provide a template for a broader in vivo RNAi screen to discover the full complement of genes required for wound closure during larval epidermal wound healing.

Regulation of mixed-lineage kinase activation in JNK-dependent morphogenesis

Normal cells respond appropriately to various signals, while sustaining proper developmental programs and tissue homeostasis. Inappropriate signal reception, response or attenuation, can upset the normal balance of signaling within cells, leading to dysfunction or tissue malformation. To understand the molecular mechanisms that regulate protein-kinase-based signaling in the context of tissue morphogenesis, we analyzed the domain requirements of Drosophila Slpr, a mixed-lineage kinase (MLK), for Jun N-terminal kinase (JNK) signaling. The N-terminal half of Slpr is involved in regulated signaling whereas the C-terminal half promotes cortical protein localization. The SH3 domain negatively regulates Slpr activity consistent with autoinhibition via a conserved proline motif. Also, like many kinases, conserved residues in the activation segment of the catalytic domain regulate Slpr. Threonine 295, in particular, is essential for function. Slpr activation requires dual input from the MAP4K Misshapen (Msn), through its C-terminal regulatory domain, and the GTPase Rac, which both bind to the LZ-CRIB region of Slpr in vitro. Although Rac is sufficient to activate JNK signaling, our results indicate that there are Slpr-independent functions for Rac in dorsal closure. Finally, expression of various Slpr constructs alone or with upstream activators reveals a wide-ranging response at the cell and tissue level.

ALDH1L1 inhibits cell motility via dephosphorylation of cofilin by PP1 and PP2A

Here we report that ALDH1L1 (FDH, a folate enzyme with tumor suppressor-like properties) inhibits cell motility. The underlying mechanism involves F-actin stabilization, re-distribution of cytoplasmic actin towards strong preponderance of filamentous actin, and formation of actin stress fibers. A549 cells expressing FDH demonstrated a much slower recovery of GFP-actin fluorescence in a FRAP assay, as well as an increase in G-actin polymerization and a decrease in F-actin depolymerization rates in pyren-actin fluorescence assays indicating the inhibition of actin dynamics. These effects were associated with robust dephosphorylation of the actin depolymerizing factor cofilin by PP1 and PP2A serine/threonine protein phosphatases but not the cofilin-specific phosphatases slingshot and chronophin. In fact, the PP1/PP2A inhibitor calyculin prevented cofilin dephosphorylation and restored motility. Inhibition of FDH-induced apoptosis by the JNK inhibitor SP600125 or the pan-caspase inhibitor zVAD-fmk did not restore motility or levels of phospho-cofilin, indicating that the observed effects are independent from FDH function in apoptosis. Interestingly, cofilin siRNA or expression of phosphorylation-deficient S3A cofilin mutant resulted in a decrease of G-actin and the actin stress fiber formation, the effects seen upon FDH expression. In contrast, the expression of S3D mutant, mimicking constitutive phosphorylation, prevented these effects further supporting the cofilin-dependent mechanism. Dephosphorylation of cofilin and inhibition of motility in response to FDH can be also prevented by the increased folate in media. Furthermore, folate depletion itself, in the absence of FDH, resulted in cofilin dephosphorylation and inhibition of motility in several cell lines. Our experiments showed that these effects were folate-specific and not a general response to nutrient starvation. Overall, this study demonstrates the presence of distinct intracellular signaling pathways regulating motility in response to folate status and points toward mechanisms involving folates in promoting a malignant phenotype.

JNK inhibition arrests cotranslational degradation

Adhesion to fibronectin stimulates protein synthesis (translation) of fibroblasts. Protein synthesis stimulation is dependent from the activation of beta(1)-integrin. beta(1)-Integrin elicits a PI3K cascade that modulates eIF4F (eukaryotic initiation factor 4F) complex formation. In the attempt to further dissect elements of the PI3K cascade that might be responsible for fibronectin-stimulated translation, we used pharmacological inhibitors of known kinases. We found that JNK inhibition, by SP600125 treatment, increased (35)S-methionine incorporation. Paradoxically, the increase in methionine incorporation was associated to a reduction of initiation of translation. These data imply that, during the adhesion of fibroblasts to fibronectin, conspicuous protein degradation occurs. Indeed, we found that inhibition of the proteasome by MG132 also increased methionine incorporation. Cotranslational degradation depended on PI3K activation. In spite of this, serum promoted translation, but not cotranslational degradation. The crosstalk between translation and degradation was further analyzed by studying the phosphorylation of initiation factors. Briefly, inhibition of JNK leads to eIF2alpha phosphorylation, which may account for the decrease in initiation of translation. In conclusion, beta(1)-integrin-activated translation causes the synthesis of short-lived proteins, whose degradation is controlled by the JNK pathway. We hypothesize that JNK is a general regulator of cotranslational degradation.

Inhibition of JNK1 expression decreases migration and invasion of mouse hepatocellular carcinoma cell line in vitro

c-Jun N-terminal kinase (JNK) is located in focal adhesion plaque (FAP). JNK is necessary to growth, morphogenesis, and differentiation of cells; especially JNK1 has a close relation with tumors. In this study, we silenced JNK1 by using short hairpin RNA (shRNA) and examined the effect on migration and invasion of mouse hepatocellular carcinoma (HCC) cell line Hca-F in vitro. Three shRNA expression vectors (JNK1shRNA-1, JNK1shRNA-2, and JNK1shRNA-3) were constructed and transfected to Hca-F cells stably. The most effective shRNA was selected by detecting the expression levels of mRNA and protein. Transwell assay was performed to detect the ability of migration and invasion of cells. A negative control sequence (JNK1shRNA control) and non-transfected normal Hca-F cells were treated as control groups. The "Results" showed that the expression vectors of pSilencer-JNK1shRNA were constructed and transfected to Hca-F cells successfully. The most effective shRNA was JNK1shRNA-2. The expressions of mRNA and protein of JNK1 in Hca-F cells after transfection of JNK1shRNA-2 were decreased significantly compared with the other groups (all, P<0.01; all, P<0.05). The ability of migration and invasion was decreased after down-regulation of JNK1 expression (all, P<0.05). These results suggest that the inhibition of JNK1 expression can decrease ability of migration and invasion of mouse hepatocellular carcinoma cell line in vitro. JNK1 plays an important role in lymphatic metastasis of HCC. It may be a new target for gene therapy of lymphatic metastasis of HCC.

Imaginal discs: Renaissance of a model for regenerative biology

Many animals display a capacity to regenerate tissues or even a complete body. One of the main goals of regenerative biology is to identify the genes and genetic networks necessary for this process. Drosophila offers an ideal model system for such studies. The wide range of genetic and genomic approaches available for use in flies has helped in initiating the deciphering of the mechanisms underlying regeneration, and the results may be applicable to other organisms, including mammals. Moreover, most models of regeneration require experimental manipulation, whereas in Drosophila discrete domains can be ablated by genetically induced methods. Here, we present a summary of current research into imaginal disc regeneration and discuss the power of this tissue as a tool for understanding the genetics of regeneration.

Structure-based design of a photocontrolled DNA binding protein

Photocontrolled transcription factors could be powerful tools for probing the role of transcriptional processes in settings that are spatially or temporally complex. We report the structure-based design of a photocontrolled bZIP-type DNA binding protein that is a hybrid of the prototypical homodimeric bZIP protein GCN4 and photoactive yellow protein (PYP), a blue-light-sensitive protein from Halorhodospira halophila. A fusion of the C-terminal zipper region of GCN4-bZIP with the N-terminal cap of PYP was designed based on examination of available crystal structure data, analysis of amino acid preference rules for leucine zippers, and mutational and amino acid conservation data for PYP, together with Rosetta-guided structural modeling. The designed fusion protein GCN4Delta25PYP-v2 is monomeric in the dark; fluorescence, circular dichroism, NMR, and analytical ultracentrifugation data indicate that the zipper domain is hidden. DNA binding in the dark causes substantial structural reorganization of GCN4Delta25PYP-v2 with concomitant slowing of the photocycle, consistent with conformational coupling of the DNA binding domain and the light-sensitive domain of the protein. Consistent with this finding, blue-light irradiation causes a 2-fold increase in specific DNA binding affinity that reverses in the dark. The structure-based approach suggests strategies for enhancing this activity and for producing a family of related photocontrolled proteins for manipulating bZIP activity.

Key signalling nodes in mammary gland development and cancer. Mitogen-activated protein kinase signalling in experimental models of breast cancer progression and in mammary gland development

Seven classes of mitogen-activated protein kinase (MAPK) intracellular signalling cascades exist, four of which are implicated in breast disease and function in mammary epithelial cells. These are the extracellular regulated kinase (ERK)1/2 pathway, the ERK5 pathway, the p38 pathway and the c-Jun N-terminal kinase (JNK) pathway. In some forms of human breast cancer and in many experimental models of breast cancer progression, signalling through the ERK1/2 pathway, in particular, has been implicated as being important. We review the influence of ERK1/2 activity on the organised three-dimensional association of mammary epithelial cells, and in models of breast cancer cell invasion. We assess the importance of epidermal growth factor receptor family signalling through ERK1/2 in models of breast cancer progression and the influence of ERK1/2 on its substrate, the oestrogen receptor, in this context. In parallel, we consider the importance of these MAPK-centred signalling cascades during the cycle of mammary gland development. Although less extensively studied, we highlight the instances of signalling through the p38, JNK and ERK5 pathways involved in breast cancer progression and mammary gland development.

The waved with open eyelids (woe) locus is a hypomorphic mouse mutation in Adam17

The waved with open eyes (woe) locus is a spontaneous recessive mouse mutation that exhibits wavy fur, eyelids open at birth, and enlarged heart and esophagus. In this study, we confirmed the previously identified woe phenotypes and additionally identified anterior eye segment defects, absence of the meibomian glands, and defects in the semilunar cardiac valves. Positional cloning identified a C794T substitution in the Adam17 gene that ablates a putative exonic splicing enhancer (ESE) sequence in exon 7 resulting in aberrant Adam17 splicing. The predominant woe transcript, Adam17(Delta)(exon7), lacks exon 7 resulting in an in-frame deletion of 90 bp and a putative Adam17(Delta252-281) protein lacking residues 252-281 from the metalloprotease domain. Western blot analysis in woe identified only the precursor form of Adam17(Delta252-281) protein. Absence of cleavage of the prodomain renders Adam17(Delta252-281) functionally inactive; however, constitutive and stimulated shedding of Adam17 substrates was detected in woe at significantly reduced levels. This residual Adam17 shedding activity in woe most likely originates from full-length Adam17(T265M) encoded by the Adam17(C794T) transcript identified expressed at severely reduced levels. These results show that even small amounts of functional Adam17 allow woe mice to survive into adulthood. In contrast to Adam17(-/-) mice that die at birth, the viability of woe mice provides an excellent opportunity for studying the role of Adam17 throughout postnatal development and homeostasis.

Mixed lineage kinase-3/JNK1 axis promotes migration of human gastric cancer cells following gastrin stimulation

Gastrin is a gastrointestinal peptide hormone, secreted by the gastric G cells and can exist as a fully processed amidated form (G17) or as unprocessed forms. All forms of gastrin possess trophic properties towards the gastrointestinal mucosa. An understanding of the signaling pathways involved is important to design therapeutic approaches to target gastrin-mediated cellular events. The studies described here were designed to identify the signaling pathways by which amidated gastrin (G17) mediates cancer cell migration. These studies indicated a time- and dose-dependent increase in gastric cancer cell migration after G17 stimulation, involving cholecystokinin 2 receptor. G17-induced migration was preceded by activation of MAPK pathways and was antagonized after pretreatment with SP600125, a pharmacological inhibitor of c-Jun-NH(2)-terminal kinase (JNK) pathway. Knockdown of endogenous JNK1 expression via small interference RNA (JNK1-siRNA) inhibited G17-induced phosphorylation of c-Jun and migration, and overexpression of wild-type JNK1 or constitutive active JNK1 promoted G17-induced migration. Studies designed to identify the MAPK kinase kinase member mediating JNK activation indicated the involvement of mixed lineage kinase-3 (MLK3), which was transiently activated upon G17 treatment. Inhibition of MLK3 pathway via a pan-MLK inhibitor or knockdown of MLK3 expression by MLK3-siRNA antagonized G17-induced migration. Incubation with G17 also resulted in an induction of matrix metalloproteinase 7 promoter activity, which is known to mediate migration and invasion pathways in cancer cells. Modulation of MLK3, JNK1, and c-Jun pathways modulated G17-induced matrix metalloproteinase 7 promoter activation. These studies indicate that the MLK3/JNK1 axis mediates G17-induced gastric cancer cell migration, which can be targeted for designing novel therapeutic strategies for treating gastric malignancies.

Cyclic mechanical stretch decreases cell migration by inhibiting phosphatidylinositol 3-kinase- and focal adhesion kinase-mediated JNK1 activation

Epithelial cell migration during wound healing requires coordinated signaling pathways that direct polarization of the leading and trailing ends of the cells, cytoskeletal organization, and remodeling of focal adhesions. These inherently mechanical processes are disrupted by cyclic stretch (CS), but the specific signaling molecules involved in this disruption are not well understood. In this study, we demonstrate that inhibition of phosphatidylinositol 3-kinase (PI3K) or expression of a dominant-negative form of PI3K caused inhibition of airway epithelial cell wound closure. CS caused a sustained decrease in activation of PI3K and inhibited wound healing. Expression of constitutively active PI3K stimulated translocation of Tiam1 to the membrane, increased Rac1 activity, and increased wound healing of airway epithelial cells. Increased Rac1 activity resulted in increased phosphorylation of JNK1. PI3K activation was not regulated by association with focal adhesion kinase. Restoration of efficient cell migration during CS required coexpression of constitutively active PI3K, focal adhesion kinase, and JIP3.

Interaction between Drosophila bZIP proteins Atf3 and Jun prevents replacement of epithelial cells during metamorphosis

Epithelial sheet spreading and fusion underlie important developmental processes. Well-characterized examples of such epithelial morphogenetic events have been provided by studies in Drosophila, and include embryonic dorsal closure, formation of the adult thorax and wound healing. All of these processes require the basic region-leucine zipper (bZIP) transcription factors Jun and Fos. Much less is known about morphogenesis of the fly abdomen, which involves replacement of larval epidermal cells (LECs) with adult histoblasts that divide, migrate and finally fuse to form the adult epidermis during metamorphosis. Here, we implicate Drosophila Activating transcription factor 3 (Atf3), the single ortholog of human ATF3 and JDP2 bZIP proteins, in abdominal morphogenesis. During the process of the epithelial cell replacement, transcription of the atf3 gene declines. When this downregulation is experimentally prevented, the affected LECs accumulate cell-adhesion proteins and their extrusion and replacement with histoblasts are blocked. The abnormally adhering LECs consequently obstruct the closure of the adult abdominal epithelium. This closure defect can be either mimicked and further enhanced by knockdown of the small GTPase Rho1 or, conversely, alleviated by stimulating ecdysone steroid hormone signaling. Both Rho and ecdysone pathways have been previously identified as effectors of the LEC replacement. To elicit the gain-of-function effect, Atf3 specifically requires its binding partner Jun. Our data thus identify Atf3 as a new functional partner of Drosophila Jun during development.

c-Jun induces mammary epithelial cellular invasion and breast cancer stem cell expansion

The molecular mechanisms governing breast tumor cellular self-renewal contribute to breast cancer progression and therapeutic resistance. The ErbB2 oncogene is overexpressed in approximately 30% of human breast cancers. c-Jun, the first cellular proto-oncogene, is overexpressed in human breast cancer. However, the role of endogenous c-Jun in mammary tumor progression is unknown. Herein, transgenic mice expressing the mammary gland-targeted ErbB2 oncogene were crossed with c-jun(f/f) transgenic mice to determine the role of endogenous c-Jun in mammary tumor invasion and stem cell function. The excision of c-jun by Cre recombinase reduced cellular migration, invasion, and mammosphere formation of ErbB2-induced mammary tumors. Proteomic analysis identified a subset of secreted proteins (stem cell factor (SCF) and CCL5) induced by ErbB2 expression that were dependent upon endogenous c-Jun expression. SCF and CCL5 were identified as transcriptionally induced by c-Jun. CCL5 rescued the c-Jun-deficient breast tumor cellular invasion phenotype. SCF rescued the c-Jun-deficient mammosphere production. Endogenous c-Jun thus contributes to ErbB2-induced mammary tumor cell invasion and self-renewal.

Drosophila morphogenesis: tissue force laws and the modeling of dorsal closure

Dorsal closure, a stage of Drosophila development, is a model system for cell sheet morphogenesis and wound healing. During closure, two flanks of epidermal tissue progressively advance to reduce the area of the eye-shaped opening in the dorsal surface, which contains amnioserosa tissue. To simulate the time evolution of the overall shape of the dorsal opening, we developed a mathematical model, in which contractility and elasticity are manifest in model force-producing elements that satisfy force-velocity relationships similar to muscle. The action of the elements is consistent with the force-producing behavior of actin and myosin in cells. The parameters that characterize the simulated embryos were optimized by reference to experimental observations on wild-type embryos and, to a lesser extent, on embryos whose amnioserosa was removed by laser surgery and on myospheroid mutant embryos. Simulations failed to reproduce the amnioserosa-removal protocol in either the elastic or the contractile limit, indicating that both elastic and contractile dynamics are essential components of the biological force-producing elements. We found it was necessary to actively upregulate forces to recapitulate both the double and single-canthus nick protocols, which did not participate in the optimization of parameters, suggesting the existence of additional key feedback mechanisms.

Signaling "cross-talk" is integrated by transcription factors in the development of the anterior segment in the eye

Extracellular signaling "cross-talk" between tissues is an important requirement for development of many organs yet the underlying mechanisms generally remain poorly understood. The anterior segment of the eye, which is constructed from four embryonic lineages, provides a unique opportunity to genetically dissect developmental processes such as signaling "cross-talk" without fear of inducing lethality. In the current review, we summarize recent data showing that PITX2, a homeodomain transcription factor, integrates retinoic acid and canonical Wnt/beta-catenin signaling during anterior segment development. Because the requirements for retinoic acid signaling, canonical Wnt/beta-catenin signaling, and PITX2 are not unique to the eye, this newly identified pathway may have relevance elsewhere during development and in tissue homeostasis.