Regulation of FAK Ser-722 phosphorylation and kinase activity by GSK3 and PP1 during cell spreading and migration

Engineered targeting OIP5 sensitizes bladder cancer to chemotherapy resistance via TRIP12-PPP1CB-YBX1 axis

Chemoresistance is an important cause of treatment failure in bladder cancer, and identifying genes that confer drug resistance is an important step toward developing new therapeutic strategies to improve treatment outcomes. In the present study, we show that gemcitabine plus cisplatin (GEM/DDP) therapy induces NF-κB signaling, which promotes p65-mediated transcriptional activation of OIP5. OIP5 recruits the E3 ubiquitin ligase TRIP12 to bind to and degrade the phosphatase PPP1CB, thereby enhancing the transcription factor activity of YBX1. This in turn upregulates drug-resistance-related genes under the transcriptional control of YBX1, leading to chemoresistance. Moreover, PPP1CB degradation can enhance the phosphorylation activity of IKKβ, triggering the NF-κB signaling cascade, which further stimulates OIP5 gene expression, thus forming a negative feedback regulatory loop. Consistently, elevated OIP5 expression was associated with chemoresistance and poor prognosis in patients with bladder cancer. Furthermore, we used a CRISPR/Cas9-based engineered gene circuit, which can monitor the progression of chemoresistance in real-time, to induce OIP5 knockout upon detection of increased NF-κB signaling. The gene circuit significantly inhibited tumor cell growth in vivo, underscoring the potential for synergy between gene therapy and chemotherapy in the treatment of cancer.

Helicobacter pylori and Epstein-Barr virus infection in cell polarity alterations

The asymmetrical distribution of the cellular organelles inside the cell is maintained by a group of cell polarity proteins. The maintenance of polarity is one of the vital host defense mechanisms against pathogens, and the loss of it contributes to infection facilitation and cancer progression. Studies have suggested that infection of viruses and bacteria alters cell polarity. Helicobacter pylori and Epstein-Barr virus are group I carcinogens involved in the progression of multiple clinical conditions besides gastric cancer (GC) and Burkitt's lymphoma, respectively. Moreover, the coinfection of both these pathogens contributes to a highly aggressive form of GC. H. pylori and EBV target the host cell polarity complexes for their pathogenesis. H. pylori-associated proteins like CagA, VacA OipA, and urease were shown to imbalance the cellular homeostasis by altering the cell polarity. Similarly, EBV-associated genes LMP1, LMP2A, LMP2B, EBNA3C, and EBNA1 also contribute to altered cell asymmetry. This review summarized all the possible mechanisms involved in cell polarity deformation in H. pylori and EBV-infected epithelial cells. We have also discussed deregulated molecular pathways like NF-κB, TGF-β/SMAD, and β-catenin in H. pylori, EBV, and their coinfection that further modulate PAR, SCRIB, or CRB polarity complexes in epithelial cells.

AKAP2-anchored protein phosphatase 1 controls prostatic neuroendocrine carcinoma cell migration and invasion

Prostate cancer (PC) is the second leading cause of cancer-related death in men. The growth of primary prostate cancer cells relies on circulating androgens and thus the standard therapy for the treatment of localized and advanced PC is the androgen deprivation therapy. Prostatic neuroendocrine carcinoma (PNEC) is an aggressive and highly metastatic subtype of prostate cancer, which displays poor prognosis and high lethality. Most of PNECs develop from prostate adenocarcinoma in response to androgen deprivation therapy, however the mechanisms involved in this transition and in the elevated biological aggressiveness of PNECs are poorly defined. Our current findings indicate that AKAP2 expression is dramatically upregulated in PNECs as compared to non-cancerous prostate tissues. Using a PNEC cell model, we could show that AKAP2 is localized both intracellularly and at the cell periphery where it colocalizes with F-actin. AKAP2 and F-actin interact directly through a newly identified actin-binding domain located on AKAP2. RNAi-mediated silencing of AKAP2 promotes the phosphorylation and deactivation of cofilin, a protein involved in actin turnover. This effect correlates with a significant reduction in cell migration and invasion. Co-immunoprecipitation experiments and proximity ligation assays revealed that AKAP2 forms a complex with the catalytic subunit of protein phosphatase 1 (PP1) in PNECs. Importantly, AKAP2-mediated anchoring of PP1 to the actin cytoskeleton regulates cofilin dephosphorylation and activation, which, in turn, enhances F-actin dynamics and favors migration and invasion. In conclusion, this study identified AKAP2 as an anchoring protein overexpressed in PNECs that controls cancer cell invasive properties by regulating cofilin phosphorylation.

GSK3 and lamellipodin balance lamellipodial protrusions and focal adhesion maturation in mouse neural crest migration

Neural crest cells are multipotent cells that delaminate from the neuroepithelium, migrating throughout the embryo. Aberrant migration causes developmental defects. Animal models are improving our understanding of neural crest anomalies, but in vivo migration behaviors are poorly understood. Here, we demonstrate that murine neural crest cells display actin-based lamellipodia and filopodia in vivo. Using neural crest-specific knockouts or inhibitors, we show that the serine-threonine kinase glycogen synthase kinase-3 (GSK3) and the cytoskeletal regulator lamellipodin (Lpd) are required for lamellipodia formation while preventing focal adhesion maturation. Lpd is a substrate of GSK3, and phosphorylation of Lpd favors interactions with the Scar/WAVE complex (lamellipodia formation) at the expense of VASP and Mena interactions (adhesion maturation and filopodia formation). This improved understanding of cytoskeletal regulation in mammalian neural crest migration has general implications for neural crest anomalies and cancer.

Canonical Wnt signaling induces focal adhesion and Integrin beta-1 endocytosis

During canonical Wnt signaling, the Wnt receptor complex is sequestered together with glycogen synthase kinase 3 (GSK3) and Axin inside late endosomes, known as multivesicular bodies (MVBs). Here, we present experiments showing that Wnt causes the endocytosis of focal adhesion (FA) proteins and depletion of Integrin β 1 (ITGβ1) from the cell surface. FAs and integrins link the cytoskeleton to the extracellular matrix. Wnt-induced endocytosis caused ITGβ1 depletion from the plasma membrane and was accompanied by striking changes in the actin cytoskeleton. In situ protease protection assays in cultured cells showed that ITGβ1 was sequestered within membrane-bounded organelles that corresponded to Wnt-induced MVBs containing GSK3 and FA-associated proteins. An in vivo model using Xenopus embryos dorsalized by Wnt8 mRNA showed that ITGβ1 depletion decreased Wnt signaling. The finding of a crosstalk between two major signaling pathways, canonical Wnt and focal adhesions, should be relevant to human cancer and cell biology.

GSK3 as a Regulator of Cytoskeleton Architecture: Consequences for Health and Disease

Glycogen synthase kinase 3 (GSK3) was initially isolated as a critical protein in energy metabolism. However, subsequent studies indicate that GSK-3 is a multi-tasking kinase that links numerous signaling pathways in a cell and plays a vital role in the regulation of many aspects of cellular physiology. As a regulator of actin and tubulin cytoskeleton, GSK3 influences processes of cell polarization, interaction with the extracellular matrix, and directional migration of cells and their organelles during the growth and development of an animal organism. In this review, the roles of GSK3–cytoskeleton interactions in brain development and pathology, migration of healthy and cancer cells, and in cellular trafficking of mitochondria will be discussed.

Cell surface integrin α5ß1 clustering negatively regulates receptor tyrosine kinase signaling in colorectal cancer cells via glycogen synthase kinase 3

As a key process within the tissue microenvironment, integrin signaling can influence cell functional responses to growth factor stimuli. We show here that clustering of integrin α5ß1 at the plasma membrane of colorectal cancer-derived epithelial cells modulates their ability to respond to stimulation by receptor tyrosine kinase (RTK)-activating growth factors EGF, NRG and HGF, through GSK3-mediated suppression of Akt pathway. We observed that integrin α5ß1 is lost from the membrane of poorly organized human colorectal tumors and that treatment with the integrin-clustering antibody P4G11 is sufficient to induce polarity in a mouse tumor xenograft model. While adding RTK growth factors (EGF, NRG and HGF) to polarized colorectal cancer cells induced invasion and loss of monolayer formation in 2D and 3D, this pathological behavior could be blocked by P4G11. Phosphorylation of ErbB family members as well as MET following EGF, NRG and HGF treatment was diminished in cells pretreated with P4G11. Focusing on EGFR, we found that blockade of integrin α5ß1 increased EGFR phosphorylation. Since activity of multiple downstream kinase pathways were altered by these various treatments, we employed computational machine learning techniques to ascertain the most important effects. Partial least-squares discriminant analysis identified GSK3 as a major regulator of EGFR pathway activities influenced by integrin α5ß1. Moreover, we used partial correlation analysis to examine signaling pathway crosstalk downstream of EGF stimulation and found that integrin α5ß1 acts as a negative regulator of the AKT signaling cascade downstream of EGFR, with GSK3 acting as a key mediator. We experimentally validated these computational inferences by confirming that blockade of GSK3 activity is sufficient to induce loss of polarity and increase of oncogenic signaling in the colonic epithelial cells.

Glycogen synthase kinase 3β promotes osteosarcoma invasion and migration via regulating PTEN and phosphorylation of focal adhesion kinase

Aim: Typical features of human osteosarcoma are highly invasive and migratory capacities. Our study aimed to investigate the roles of glycogen synthase kinase 3β (GSK3β) in human osteosarcoma metastasis.

Methods: GSK3β expressions in clinical osteosarcoma tissues with or without metastasis were examined by immunohistochemical staining. The expressions of GSK3β, p-GSK3β^Ser9, and p-GSK3β^Tyr216 in human osteoblast cells (hFOB1.19) and human osteosarcoma cells (MG63, SaOS-2, and U2-OS) were detected by Western blotting. The GSK3β activity was measured by non-radio isotopic in vitro kinase assay. Migration and invasion abilities of MG-63 cells treated with small-molecular GSK3β inhibitors were respectively examined by monolayer-based wound-healing assay and transwell assay. The mRNA expressions of GSK3β, matrix metalloproteinase-2 (MMP-2), MMP-9, phosphatase with tensin homology (PTEN), and focal adhesion kinase (FAK) were detected after siRNA transfection for 72 h. Meanwhile, protein expressions of GSK3β, FAK, p-FAK^Y397, PTEN, MMP-2, and MMP-9 were measured by Western blotting.

Results: Clinical osteosarcoma tissues with metastasis showed higher GSK3β expressions. MG63 and U2-OS cells that were easy to occur metastasis showed significantly higher expressions and activities of GSK3β than SaOS-2 cells. Inhibition of GSK3β with small-molecular GSK3β inhibitors in MG63 cells significantly attenuated cell migration and invasion. These effects were associated with reduced expressions of MMP-2 and MMP-9. Moreover, increased PTEN and decreased p-FAK^Y397 expressions were observed following GSK3β knockdown by siRNA transfection. Conclusion: GSK3β might promote osteosarcoma invasion and migration via pathways associated with PTEN and phosphorylation of FAK.

Cdk5 and GSK3β inhibit fast endophilin-mediated endocytosis

Endocytosis mediates the cellular uptake of micronutrients and cell surface proteins. Fast Endophilin-mediated endocytosis, FEME, is not constitutively active but triggered upon receptor activation. High levels of growth factors induce spontaneous FEME, which can be suppressed upon serum starvation. This suggested a role for protein kinases in this growth factor receptor-mediated regulation. Using chemical and genetic inhibition, we find that Cdk5 and GSK3β are negative regulators of FEME. They antagonize the binding of Endophilin to Dynamin-1 and to CRMP4, a Plexin A1 adaptor. This control is required for proper axon elongation, branching and growth cone formation in hippocampal neurons. The kinases also block the recruitment of Dynein onto FEME carriers by Bin1. As GSK3β binds to Endophilin, it imposes a local regulation of FEME. Thus, Cdk5 and GSK3β are key regulators of FEME, licensing cells for rapid uptake by the pathway only when their activity is low.

Protein phosphatase 1 in tumorigenesis: is it worth a closer look?

Cancer cells take advantage of signaling cascades to meet their requirements for sustained growth and survival. Cell signaling is tightly controlled by reversible protein phosphorylation mechanisms, which require the counterbalanced action of protein kinases and protein phosphatases. Imbalances on this system are associated with cancer development and progression. Protein phosphatase 1 (PP1) is one of the most relevant protein phosphatases in eukaryotic cells. Despite the widely recognized involvement of PP1 in key biological processes, both in health and disease, its relevance in cancer has been largely neglected. Here, we provide compelling evidence that support major roles for PP1 in tumorigenesis.

Strictinin, a novel ROR1-inhibitor, represses triple negative breast cancer survival and migration via modulation of PI3K/AKT/GSK3ß activity

Triple Negative Breast Cancer (TNBC), the most aggressive subtype of breast cancer, is characterized by the absence of hormone receptors usually targeted by hormone therapies like Tamoxifen. Because therapy success and survival rates for TNBC lag far behind other breast cancer subtypes, there is significant interest in developing novel anti-TNBC agents that can target TNBC specifically, with minimal effects on non-malignant tissue. To this aim, our study describes the anti-TNBC effect of strictinin, an ellagitanin previously isolated from Myrothamnus flabellifolius. Using various in silico and molecular techniques, we characterized the mechanism of action of strictinin in TNBC. Our results suggest strictinin interacts strongly with Receptor Tyrosine Kinase Orphan like 1 (ROR1). ROR1 is an oncofetal receptor highly expressed during development but not in normal adult tissue. It is highly expressed in several human malignancies however, owing to its numerous pro-tumor functions. Via its interaction and inhibition of ROR1, strictinin reduced AKT phosphorylation on ser-473, inhibiting downstream phosphorylation and inhibition of GSK3β. The reduction in AKT phosphorylation also correlated with decreased cell survival and activation of the caspase-mediated intrinsic apoptotic cascade. Strictinin treatment also repressed cell migration and invasion in a beta-catenin independent manner, presumably via the reactivated GSK3ß’s repressing effect on microtubule polymerization and focal adhesion turnover. This could be of potential therapeutic interest considering heightened interest in ROR1 and other receptor tyrosine kinases as targets for development of anti-cancer agents. Further studies are needed to validate these findings in other ROR1-expressing malignancies but also in more systemic models of TNBC. Our findings do however underline the potential of strictinin and other ROR1-targeting agents as therapeutic tools to reduce TNBC proliferation, survival and motility.

Signalling of ERK1/2, P38MAPK and P90RSK in HIV-associated pre-eclampsia

Due to their significance in trophoblast differentiation and survival, we evaluated the expression of the cell signalling molecules; Extracellular signal-regulated kinase 1/2 (ERK1/2), Mitogen Activated Protein Kinase 38 (MAPK38) and p90 ribosomal protein S6 kinase (p90 RSK) in buffy coat samples. Eighty pregnant women attending a large hospital in Durban, South Africa were assigned into normotensive and pre-eclamptic groups and further stratified by their HIV status. The degree of phosphorylation of the analytes was determined using the Bio-Plex Pro^TM Cell Signalling Immunoassay. There was a significantly lower protein concentration of the analytes in the pre-eclamptic versus the normotensive patients, irrespective of HIV status (p < .0001). Also, there was no significant difference in expression of ERK1/2 (p = .4369), p38MAPK (p = .4720) and p90 RSK (p = .0188), according to HIV status. This study demonstrates a down-regulation of ERK1/2, p38MAPK and p90RSK prosurvival markers in pre-eclampsia. This implicates the involvement of the MAPK pathway in the pathogenesis of preeclampsia. Activation of these pathways may prove useful in increasing the body of evidence on prevention of placenta dysfunction and apoptosis. Impact statement What is already known on this subject? Preeclampsia occurring in co-morbidity with HIV is a public health problem among pregnant, black South-African women. There have been conflicting theories regarding the predisposition to the development of preeclampsia as a result of compromised immune response due to HIV infection. In normal pregnancies, the MAPK pathway plays a significant role in molecular processes involved in the cells including survival and differentiation of the placental trophoblast. ERK1/2, p38MAPK and p90RSK are members of the MAPK family, which are pro-apoptotic. Inhibition in the signalling of MAPKs has been found to result in oxidative stress, a process which contributes to the defective trophoblast invasion seen in preeclampsia. What do the results of this study add? The results from this study showed that there is no relationship between HIV infection and an increased predisposition to the development of preeclampsia. In addition, this study highlights a downregulation in the expression of ERK1/2, p38 MAPK and p90RSK in preeclampsia. What are the implications of these findings for clinical practice and/or further research? These findings demonstrate the potential of these analytes as biomarkers for the diagnosis of preeclampsia. Also, this may serve as a framework for further research in the prevention of preeclampsia by elucidating more on the pathway.

Characterization of the Src-regulated kinome identifies SGK1 as a key mediator of Src-induced transformation

Despite significant progress, our understanding of how specific oncogenes transform cells is still limited and likely underestimates the complexity of downstream signalling events. To address this gap, we use mass spectrometry-based chemical proteomics to characterize the global impact of an oncogene on the expressed kinome, and then functionally annotate the regulated kinases. As an example, we identify 63 protein kinases exhibiting altered expression and/or phosphorylation in Src-transformed mammary epithelial cells. An integrated siRNA screen identifies nine kinases, including SGK1, as being essential for Src-induced transformation. Accordingly, we find that Src positively regulates SGK1 expression in triple negative breast cancer cells, which exhibit a prominent signalling network governed by Src family kinases. Furthermore, combined inhibition of Src and SGK1 reduces colony formation and xenograft growth more effectively than either treatment alone. Therefore, this approach not only provides mechanistic insights into oncogenic transformation but also aids the design of improved therapeutic strategies.

The systemic understanding of oncogenic kinase signalling is still limited. Here, the authors combine chemical proteomics with functional screens to assess the impact of oncogenic Src on the expressed kinome and identify SGK1 as a critical mediator of Src-induced cell transformation.

O-GlcNAcylation regulates integrin-mediated cell adhesion and migration via formation of focal adhesion complexes

O-GlcNAcylation is a post-translational modification of a protein serine or threonine residue catalyzed by O-GlcNAc transferase (OGT) in the nucleus and cytoplasm. O-GlcNAcylation plays important roles in the cellular signaling that affect the different biological functions of cells, depending upon cell type. However, whether or not O-GlcNAcylation regulates cell adhesion and migration remains unclear. Here, we used the doxycycline-inducible short hairpin RNA (shRNA) system to establish an OGT knockdown (KD) HeLa cell line and found that O-GlcNAcylation is a key regulator for cell adhesion, migration, and focal adhesion (FA) complex formation. The expression levels of OGT and O-GlcNAcylation were remarkably suppressed 24 h after induction of doxycycline. Knockdown of OGT significantly promoted cell adhesion, but it suppressed the cell migration on fibronectin. The immunostaining with paxillin, a marker for FA plaque, clearly showed that the number of FAs was increased in the KD cells compared with that in the control cells. The O-GlcNAcylation levels of paxillin, talin, and focal adhesion kinase were down-regulated in KD cells. Interestingly, the complex formation between integrin β1, focal adhesion kinase, paxillin, and talin was greatly increased in KD cells. Consistently, levels of active integrin β1 were significantly enhanced in KD cells, whereas they were decreased in cells overexpressing OGT. The data suggest a novel regulatory mechanism for O-GlcNAcylation during FA complex formation, which thereby affects integrin activation and integrin-mediated functions such as cell adhesion and migration.

Targeting GSK3 signaling as a potential therapy of neurodegenerative diseases and aging

INTRODUCTION

Glycogen synthase kinase 3 (GSK3) is at the center of cellular signaling and controls various aspects of brain functions, including development of the nervous system, neuronal plasticity and onset of neurodegenerative disorders. Areas covered: In this review, recent efforts in elucidating the roles of GSK3 in neuronal plasticity and development of brain pathologies; Alzheimer's and Parkinson's disease, schizophrenia, and age-related neurodegeneration are described. The effect of microglia and astrocytes on development of the pathological states is also discussed. Expert opinion: GSK3β and its signaling pathway partners hold great promise as therapeutic target(s) for a multitude of neurological disorders. Activity of the kinase is often elevated in brain disorders. However, due to the wide range of GSK3 cellular targets, global inhibition of the kinase leads to severe side-effects and GSK3 inhibitors rarely reach Phase-2 clinical trials. Thus, a selective modulation of a specific cellular pool of GSK3 or specific down- or upstream partners of the kinase might provide more efficient anti-neurodegenerative therapies.

Glycogen synthase kinase 3 controls migration of the neural crest lineage in mouse and Xenopus

Neural crest migration is critical to its physiological function. Mechanisms controlling mammalian neural crest migration are comparatively unknown, due to difficulties accessing this cell population in vivo. Here we report requirements of glycogen synthase kinase 3 (GSK3) in regulating the neural crest in Xenopus and mouse models. We demonstrate that GSK3 is tyrosine phosphorylated (pY) in mouse neural crest cells and that loss of GSK3 leads to increased pFAK and misregulation of Rac1 and lamellipodin, key regulators of cell migration. Genetic reduction of GSK3 results in failure of migration. We find that pY-GSK3 phosphorylation depends on anaplastic lymphoma kinase (ALK), a protein associated with neuroblastoma. Consistent with this, neuroblastoma cells with increased ALK activity express high levels of pY-GSK3, and blockade of GSK3 or ALK can affect migration of these cells. Altogether, this work identifies a role for GSK3 in cell migration during neural crest development and cancer.

Defects in neural crest development cause neurocristopathies and cancer, but what regulates this is unclear. Here, the authors show that glycogen synthase kinase 3 (GSK3) regulates migration of neural crest cells, as shown on genetic deletion of GSK3 in the mouse, and that this acts via anaplastic lymphoma kinase.

Focal Adhesion Kinase (FAK) tyrosine 397E mutation restores the vascular leakage defect in endothelium-specific FAK-kinase dead mice

Focal adhesion kinase (FAK) inhibitors have been developed as potential anticancer agents and are undergoing clinical trials. In vitro activation of the FAK kinase domain triggers autophosphorylation of Y397, Src activation, and subsequent phosphorylation of other FAK tyrosine residues. However, how FAK Y397 mutations affect FAK kinase-dead (KD) phenotypes in tumour angiogenesis in vivo is unknown. We developed three Pdgfb-iCreert -driven endothelial cell (EC)-specific, tamoxifen-inducible homozygous mutant mouse lines: FAK wild-type (WT), FAK KD, and FAK double mutant (DM), i.e. KD with a putatively phosphomimetic Y397E mutation. These ECCre+;FAKWT/WT , ECCre+;FAKKD/KD and ECCre+;FAKDM/DM mice were injected subcutaneously with syngeneic B16F0 melanoma cells. Tumour growth and tumour blood vessel functions were unchanged between ECCre+;FAKWT/WT and ECCre-;FAKWT/WT control mice. In contrast, tumour growth and vessel density were decreased in ECCre+;FAKKD/KD and ECCre+;FAKDM/DM mice, as compared with Cre - littermates. Despite no change in the percentage of perfused vessels or pericyte coverage in either genotype, tumour hypoxia was elevated in ECCre+;FAKKD/KD and ECCre+;FAKDM/DM mice. Furthermore, although ECCre+;FAKKD/KD mice showed reduced blood vessel leakage, ECCre+;FAKDM/DM and ECCre-;FAKDM/DM mice showed no difference in leakage. Mechanistically, fibronectin-stimulated Y397 autophosphorylation was reduced in Cre+;FAKKD/KD ECs as compared with Cre+;FAKWT/WT cells, with no change in phosphorylation of the known Src targets FAK-Y577, FAK-Y861, FAK-Y925, paxillin-Y118, p130Cas-Y410. Cre+;FAKDM/DM ECs showed decreased Src target phosphorylation levels, suggesting that the Y397E substitution actually disrupted Src activation. Reduced VE-cadherin-pY658 levels in Cre+;FAKKD/KD ECs were rescued in Cre+FAKDM/DM ECs, corresponding with the rescue in vessel leakage in the ECCre+;FAKDM/DM mice. We show that EC-specific FAK kinase activity is required for tumour growth, angiogenesis, and vascular permeability. The ECCre+;FAKDM/DM mice restored the KD-dependent tumour vascular leakage observed in ECCre+;FAKKD/KD mice in vivo. This study opens new fields in in vivo FAK signalling. © 2017 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of Pathological Society of Great Britain and Ireland.

Synthetic triterpenoids inhibit GSK3β activity and localization and affect focal adhesions and cell migration

Synthetic triterpenoids are a class of anti-cancer compounds that target many cellular functions, including apoptosis and cell growth in both cell culture and animal models. We have shown that triterpenoids inhibit cell migration in part by interfering with Arp2/3-dependent branched actin polymerization in lamellipodia (To et al., 2010). Our current studies reveal that Glycogen Synthase Kinase 3 beta (GSK3β), a kinase that regulates many cellular processes, including cell adhesion dynamics, is a triterpenoid-binding protein. Furthermore, triterpenoids were observed to inhibit GSK3β activity and increase cellular focal adhesion size. To further examine whether these effects on focal adhesions in triterpenoid-treated cells were GSK3β-dependent, GSK3β inhibitors (lithium chloride and SB216763) were used to examine cell adhesion and morphology as well as cell migration. Our results showed that GSK3β inhibitors also altered cell adhesion sizes. Moreover, these inhibitors blocked cell migration and displaced proteins at the leading edge of migrating cells, consistent with what was observed in triterpenoid-treated cells. Therefore, the triterpenoids may affect cell migration via a mechanism that targets and alters the activity and localization of GSK3β.

Feedback Activation of Basic Fibroblast Growth Factor Signaling via the Wnt/β-Catenin Pathway in Skin Fibroblasts

Skin wound healing is a complex process requiring the coordinated behavior of many cell types, especially in the proliferation and migration of fibroblasts. Basic fibroblast growth factor (bFGF) is a member of the FGF family that promotes fibroblast migration, but the underlying molecular mechanism remains elusive. The present RNA sequencing study showed that the expression levels of several canonical Wnt pathway genes, including Wnt2b, Wnt3, Wnt11, T-cell factor 7 (TCF7), and Frizzled 8 (FZD8) were modified by bFGF stimulation in fibroblasts. Enzyme-linked immunosorbent assay (ELISA) analysis also showed that Wnt pathway was activated under bFGF treatment. Furthermore, treatment of fibroblasts with lithium chloride or IWR-1, an inducer and inhibitor of the Wnt signaling pathway, respectively, promoted and inhibited cell migration. Also, levels of cytosolic glycogen synthase kinase 3 beta phosphorylated at serine⁹ (pGSK3β Ser⁹) and nuclear β-catenin were increased upon exposure to bFGF. Molecular and biochemical assays indicated that phosphoinositide 3-kinase (PI3K) signaling activated the GSK3β/β-catenin/Wnt signaling pathway via activation of c-Jun N-terminal kinase (JNK), suggesting that PI3K and JNK act at the upstream of β-catenin. In contrast, knock-down of β-catenin delayed fibroblast cell migration even under bFGF stimulation. RNA sequencing analysis of β-catenin knock-down fibroblasts demonstrated that β-catenin positively regulated the transcription of bFGF and FGF21. Moreover, FGF21 treatment activated AKT and JNK, and accelerated fibroblast migration to a similar extent as bFGF does. In addition, ELISA analysis demonstrated that both of bFGF and FGF21 were auto secretion factor and be regulated by Wnt pathway stimulators. Taken together, our analyses define a feedback regulatory loop between bFGF (FGF21) and Wnt signaling acting through β-catenin in skin fibroblasts.

The Interconnections between Autophagy and Integrin-Mediated Cell Adhesion

Autophagy is a cellular degradation process integral for promoting cellular adaptation during metabolic stress while also functioning as a cellular homeostatic mechanism. Mounting evidence also demonstrates that autophagy is induced upon loss of integrin-mediated cell attachments to the surrounding extracellular matrix (ECM). Analogous to its established cytoprotective role during nutrient starvation, autophagy protects cells from detachment-induced cell death, termed anoikis. Here, we review the significance of autophagy as an anoikis resistance pathway, focusing on the intracellular signals associated with integrins that modulate the autophagy response and dictate the balance between cell death and survival following loss of cell-matrix contact. In addition, we highlight recent studies demonstrating that autophagy functions in the upstream regulation of integrin-mediated cell adhesion via the control of focal adhesion remodeling, and discuss how these emerging interconnections between integrin-mediated adhesion pathways and autophagy influence cancer progression and metastasis.

Effects of mutations in Wnt/β-catenin, hedgehog, Notch and PI3K pathways on GSK-3 activity-Diverse effects on cell growth, metabolism and cancer

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase that participates in an array of critical cellular processes. GSK-3 was first characterized as an enzyme that phosphorylated and inactivated glycogen synthase. However, subsequent studies have revealed that this moon-lighting protein is involved in numerous signaling pathways that regulate not only metabolism but also have roles in: apoptosis, cell cycle progression, cell renewal, differentiation, embryogenesis, migration, regulation of gene transcription, stem cell biology and survival. In this review, we will discuss the roles that GSK-3 plays in various diseases as well as how this pivotal kinase interacts with multiple signaling pathways such as: PI3K/PTEN/Akt/mTOR, Ras/Raf/MEK/ERK, Wnt/beta-catenin, hedgehog, Notch and TP53. Mutations that occur in these and other pathways can alter the effects that natural GSK-3 activity has on regulating these signaling circuits that can lead to cancer as well as other diseases. The novel roles that microRNAs play in regulation of the effects of GSK-3 will also be evaluated. Targeting GSK-3 and these other pathways may improve therapy and overcome therapeutic resistance.

Tyrosine-protein phosphatase non-receptor type 12 expression is a good prognostic factor in resectable non-small cell lung cancer

Tyrosine-protein phosphatase non-receptor type 12 (PTPN12) has been considered to be a tumor suppressor in human cancer, but its clinical and prognostic significance in non-small cell lung cancer (NSCLC) has not been well elucidated.

A retrospective analysis of 215 patients with surgically resected NSCLCs from Sun Yat-Sen University Cancer Center between April 2002 and March 2005 was performed using immunohistochemistry and Western Blot to analyze PTPN12 expression. The association between PTPN12 expression and patient survival was investigated.

Western Blots showed that the expression level of PTPN12 were higher in normal paracancerous lung tissues than in NSCLC tissues. High PTPN12 expression was less common in the presence than in the absence of visceral pleural invasion (p=0.038). Patients with PTPN12-high tumors had a longer disease-free survival (DFS) (P<0.001) and overall survival (OS) (p<0.001), especially for those with non-squamous cell carcinoma (non-SCC) (DFS, p<0.001; OS, p<0.001). Multivariate analysis confirmed that PTPN12 positivity was associated with increased survival duration (DFS, p<0.001; OS, p<0.001), independent of prognostic indicator.

High PTPN12 expressive levels are associated with favorable survival duration in patients with NSCLC, especially those with non-SCC. Our study suggests that PTPN12 expression is a valuable prognostic biomarker for NSCLC patients.

Phosphorylation of Serine 402 Regulates RacGAP Protein Activity of FilGAP Protein

FilGAP is a Rho GTPase-activating protein (GAP) that specifically regulates Rac. FilGAP is phosphorylated by ROCK, and this phosphorylation stimulates its RacGAP activity. However, it is unclear how phosphorylation regulates cellular functions and localization of FilGAP. We found that non-phosphorylatable FilGAP (ST/A) mutant is predominantly localized to the cytoskeleton along actin filaments and partially co-localized with vinculin around cell periphery, whereas phosphomimetic FilGAP (ST/D) mutant is diffusely cytoplasmic. Moreover, phosphorylated FilGAP detected by Phos-tag is also mainly localized in the cytoplasm. Of the six potential phosphorylation sites in FilGAP tested, only mutation of serine 402 to alanine (S402A) resulted in decreased cell spreading on fibronectin. FilGAP phosphorylated at Ser-402 is localized to the cytoplasm but not at the cytoskeleton. Although Ser-402 is highly phosphorylated in serum-starved quiescent cells, dephosphorylation of Ser-402 is accompanied with the cell spreading on fibronectin. Treatment of the cells expressing wild-type FilGAP with calyculin A, a Ser/Thr phosphatase inhibitor, suppressed cell spreading on fibronectin, whereas cells transfected with FilGAP S402A mutant were not affected by calyculin A. Expression of constitutively activate Arf6 Q67L mutant stimulated membrane blebbing activity of both non-phosphorylatable (ST/A) and phosphomimetic (ST/D) FilGAP mutants. Conversely, depletion of endogenous Arf6 suppressed membrane blebbing induced by FilGAP (ST/A) and (ST/D) mutants. Our study suggests that Arf6 and phosphorylation of FilGAP may regulate FilGAP, and phosphorylation of Ser-402 may play a role in the regulation of cell spreading on fibronectin.

GSK-3 as potential target for therapeutic intervention in cancer

The serine/threonine kinase glycogen synthase kinase-3 (GSK-3) was initially identified and studied in the regulation of glycogen synthesis. GSK-3 functions in a wide range of cellular processes. Aberrant activity of GSK-3 has been implicated in many human pathologies including: bipolar depression, Alzheimer's disease, Parkinson's disease, cancer, non-insulin-dependent diabetes mellitus (NIDDM) and others. In some cases, suppression of GSK-3 activity by phosphorylation by Akt and other kinases has been associated with cancer progression. In these cases, GSK-3 has tumor suppressor functions. In other cases, GSK-3 has been associated with tumor progression by stabilizing components of the beta-catenin complex. In these situations, GSK-3 has oncogenic properties. While many inhibitors to GSK-3 have been developed, their use remains controversial because of the ambiguous role of GSK-3 in cancer development. In this review, we will focus on the diverse roles that GSK-3 plays in various human cancers, in particular in solid tumors. Recently, GSK-3 has also been implicated in the generation of cancer stem cells in various cell types. We will also discuss how this pivotal kinase interacts with multiple signaling pathways such as: PI3K/PTEN/Akt/mTORC1, Ras/Raf/MEK/ERK, Wnt/beta-catenin, Hedgehog, Notch and others.

Focal adhesion kinase-mediated activation of glycogen synthase kinase 3β regulates IL-33 receptor internalization and IL-33 signaling

IL-33, a relatively new member of the IL-1 cytokine family, plays a crucial role in allergic inflammation and acute lung injury. Long form ST2 (ST2L), the receptor for IL-33, is expressed on immune effector cells and lung epithelia and plays a critical role in triggering inflammation. We have previously shown that ST2L stability is regulated by the ubiquitin-proteasome system; however, its upstream internalization has not been studied. In this study, we demonstrate that glycogen synthase kinase 3β (GSK3β) regulates ST2L internalization and IL-33 signaling. IL-33 treatment induced ST2L internalization, and an effect was attenuated by inhibition or downregulation of GSK3β. GSK3β was found to interact with ST2L on serine residue 446 in response to IL-33 treatment. GSK3β binding site mutant (ST2L(S446A)) and phosphorylation site mutant (ST2L(S442A)) are resistant to IL-33-induced ST2L internalization. We also found that IL-33 activated focal adhesion kinase (FAK). Inhibition of FAK impaired IL-33-induced GSK3β activation and ST2L internalization. Furthermore, inhibition of ST2L internalization enhanced IL-33-induced cytokine release in lung epithelial cells. These results suggest that modulation of the ST2L internalization by FAK/GSK3β might serve as a unique strategy to lessen pulmonary inflammation.

Platelet PI3Kβ and GSK3 regulate thrombus stability at a high shear rate

Class IA phosphoinositide 3-kinase β (PI3Kβ) is considered a potential drug target in arterial thrombosis, which is a major cause of death worldwide. Here we show that a striking phenotype of mice with selective p110β deletion in the megakaryocyte lineage is thrombus instability at a high shear rate, which is an effect that is not detected in the absence of p110α in platelets. The high shear rate-dependent thrombus instability in the absence of p110β is observed both ex vivo and in vivo with the formation of platelet emboli. Moreover, PI3Kβ is required for the recruitment of new platelets to a growing thrombus when a pathological high shear is applied. Treatment of human blood with AZD6482, a selective PI3Kβ inhibitor, phenocopies p110β deletion in mouse platelets, which highlights the role of the kinase activity of p110β. Within the growing platelet thrombus, p110β inactivation impairs the activating phosphorylations of Akt and the inhibitory phosphorylation of GSK3. In accord with these data, pharmacologic inhibition of GSK3 restores thrombus stability. Thus, platelet PI3Kβ is not essential for thrombus growth and stability at normal arterial shear but has a specific and critical role in maintaining the integrity of the formed thrombus on elevation of shear rate, suggesting a potential risk of embolization on treatment with PI3Kβ inhibitors.

GSK-3 signaling in developing cortical neurons is essential for radial migration and dendritic orientation

GSK-3 is an essential mediator of several signaling pathways that regulate cortical development. We therefore created conditional mouse mutants lacking both GSK-3α and GSK-3β in newly born cortical excitatory neurons. Gsk3-deleted neurons expressing upper layer markers exhibited striking migration failure in all areas of the cortex. Radial migration in hippocampus was similarly affected. In contrast, tangential migration was not grossly impaired after Gsk3 deletion in interneuron precursors. Gsk3-deleted neurons extended axons and developed dendritic arbors. However, the apical dendrite was frequently branched while basal dendrites exhibited abnormal orientation. GSK-3 regulation of migration in neurons was independent of Wnt/β-catenin signaling. Importantly, phosphorylation of the migration mediator, DCX, at ser327, and phosphorylation of the semaphorin signaling mediator, CRMP-2, at Thr514 were markedly decreased. Our data demonstrate that GSK-3 signaling is essential for radial migration and dendritic orientation and suggest that GSK-3 mediates these effects by phosphorylating key microtubule regulatory proteins.

DOI:http://dx.doi.org/10.7554/eLife.02663.001

In the brain, one of the most striking features of the cerebral cortex is that its neurons are organized into different layers that are specifically connected to one another and to other regions of the brain. How newly generated neurons find their appropriate layer during the development of the brain is an important question; and, in humans, when this process goes awry, it can often result in seizures and mental retardation.

An enzyme called GSK-3 regulates several major signaling pathways important to brain development. The GSK-3 enzyme switches other proteins on or off by adding phosphate groups to them.

Morgan-Smith et al. set out to better understand the role of GSK-3 in brain development by deleting the genes for this enzyme specifically in the cerebral cortex of mice. Mice have two genes that encode slightly different forms of the GSK-3 enzyme. Deleting both of these in different groups of neurons during brain development revealed that a major group of neurons need GSK-3 in order to migrate to the correct layer. Specifically, the movement of neurons from where they arise in the central region of the brain to the outermost layer (a process called radial migration) was disrupted when the GSK-3 genes were deleted.

Morgan-Smith et al. further found that cortical neurons without GSK-3 were unable to develop the shape needed to undertake radial migration because they failed to switch from having many branches to having just two main branches. Additional experiments revealed that these abnormalities did not depend on certain signaling pathways, such as the Wnt-signaling pathway or the PI3K signaling pathway that can control GSK-3 activity.

Instead, Morgan-Smith et al. found that two proteins that are normally targeted by the GSK-3 enzyme have fewer phosphate groups than normal in the cortical neurons that did not contain the enzyme: both of these proteins regulate the shape of neurons by interacting with the molecular ‘scaffolding’ within the cell. The GSK-3 enzyme was already known to modify the activities of many other proteins that affect the migration of cells. Thus, the findings of Morgan-Smith et al. suggest that this enzyme may coordinate many of the mechanisms thought to underlie this process during brain development.

DOI:http://dx.doi.org/10.7554/eLife.02663.002

Focal adhesion kinase is a regulator of F-actin dynamics: New insights from studies in the testis

During spermatogenesis, spermatogonia (2n, diploid) undergo a series of mitotic divisions as well as differentiation to become spermatocytes, which enter meiosis I to be followed by meiosis II to form round spermatids (1n, haploid), and then differentiate into spermatozoa (1n, haploid) via spermiogenesis. These events take place in the epithelium of the seminiferous tubule, involving extensive junction restructuring at the Sertoli-Sertoli and Sertoli-germ cell interface to allow the transport of developing germ cells across the epithelium. Although structural aspects of these cell-cell junctions have been studied, the underlying mechanism(s) that governs these events has yet to be explored. Earlier studies have shown that a non-receptor protein tyrosine kinase known as focal adhesion kinase (FAK) is a likely regulator of these events due to the stage-specific and spatiotemporal expression of its various phosphorylated/activated forms at the testis-specific anchoring junctions in the testis, as well as its association with actin regulatory proteins. Recent studies have shown that FAK, in particular its two activated phosphorylated forms p-FAK-Tyr⁴⁰⁷ and p-FAK-Tyr³⁹⁷, are crucial regulators in modulating junction restructuring at the Sertoli cell-cell interface at the blood-testis barrier (BTB) known as the basal ectoplasmic specialization (basal ES), as well as at the Sertoli-spermatid interface called apical ES during spermiogenesis via its effects on the filamentous (F)-actin organization at the ES. We herein summarize and critically evaluate the current knowledge regarding the physiological significance of FAK in regulating BTB and apical ES dynamics by governing the conversion of actin filaments at the ES from a “bundled” to a “de-bundled/branched” configuration and vice versa. We also provide a molecular model on the role of FAK in regulating these events based on the latest findings in the field.

Multifaceted roles of GSK-3 and Wnt/β-catenin in hematopoiesis and leukemogenesis: opportunities for therapeutic intervention

Glycogen synthase kinase-3 (GSK-3) is well documented to participate in a complex array of critical cellular processes. It was initially identified in rat skeletal muscle as a serine/threonine kinase that phosphorylated and inactivated glycogen synthase. This versatile protein is involved in numerous signaling pathways that influence metabolism, embryogenesis, differentiation, migration, cell cycle progression and survival. Recently, GSK-3 has been implicated in leukemia stem cell pathophysiology and may be an appropriate target for its eradication. In this review, we will discuss the roles that GSK-3 plays in hematopoiesis and leukemogenesis as how this pivotal kinase can interact with multiple signaling pathways such as: Wnt/β-catenin, phosphoinositide 3-kinase (PI3K)/phosphatase and tensin homolog (PTEN)/Akt/mammalian target of rapamycin (mTOR), Ras/Raf/MEK/extracellular signal-regulated kinase (ERK), Notch and others. Moreover, we will discuss how targeting GSK-3 and these other pathways can improve leukemia therapy and may overcome therapeutic resistance. In summary, GSK-3 is a crucial regulatory kinase interacting with multiple pathways to control various physiological processes, as well as leukemia stem cells, leukemia progression and therapeutic resistance. GSK-3 and Wnt are clearly intriguing therapeutic targets.

PDK1 regulates platelet activation and arterial thrombosis

The effects of phosphoinositide-dependent protein kinase 1 (PDK1), a master kinase in the phosphoinositide 3-kinase/Akt pathway, on platelet activation are unknown. Accordingly, platelet-specific PDK1-deficient mice were characterized to elucidate the platelet-related function(s) of PDK1. We found that PDK1 deficiency caused mild thrombocytopenia. The aggregation of PDK1(-/-) platelets was diminished in response to low levels of thrombin, U46619, and adenosine 5'-diphosphate. Further results demonstrated that PDK1 regulates thrombin-induced platelet activation by affecting αIIbβ3-mediated outside-in signaling. This result provided an explanation for the diminished spreading of PDK1(-/-) platelets on immobilized fibrinogen (Fg) and the decreased rate of clot retraction in platelet-rich plasma (PRP) containing PDK1(-/-) platelets. PDK1 deficiency diminished agonist-induced Akt Ser473 phosphorylation and thoroughly abolished Akt Thr308 and Gsk3β Ser9 phosphorylation in response to agonist treatment and platelet spreading, respectively. A Gsk3β inhibitor fully restored the aggregation of PDK1(-/-) platelets in response to low levels of thrombin, normal spreading of PDK1(-/-) platelets on Fg, and normal clot retraction in PRP containing PDK1(-/-) platelets. Those results indicated that Gsk3β is one of the major downstream effectors of PDK1 in thrombin-induced platelet activation and αIIbβ3-mediated outside-in signaling. In addition, in vivo data demonstrated that PDK1 is an important regulator in arterial thrombosis formation.

Lithium chloride inhibits vascular smooth muscle cell proliferation and migration and alleviates injury-induced neointimal hyperplasia via induction of PGC-1α

The proliferation and migration of vascular smooth muscle cells (VSMCs) contributes importantly to the development of in-stent restenosis. Lithium has recently been shown to have beneficial effects on the cardiovascular system, but its actions in VSMCs and the direct molecular target responsible for its action remains unknown. On the other hand, PGC-1α is a transcriptional coactivator which negatively regulates the pathological activation of VSMCs. Therefore, the purpose of the present study is to determine if lithium chloride (LiCl) retards VSMC proliferation and migration and if PGC-1α mediates the effects of lithium on VSMCs. We found that pretreatment of LiCl increased PGC-1α protein expression and nuclear translocation in a dose-dependent manner. MTT and EdU incorporation assays indicated that LiCl inhibited serum-induced VSMC proliferation. Similarly, deceleration of VSMC migration was confirmed by wound healing and transwell assays. LiCl also suppressed ROS generation and cell cycle progression. At the molecular level, LiCl reduced the protein expression levels or phosphorylation of key regulators involved in the cell cycle re-entry, adhesion, inflammation and motility. In addition, in vivo administration of LiCl alleviated the pathophysiological changes in balloon injury-induced neointima hyperplasia. More importantly, knockdown of PGC-1α by siRNA significantly attenuated the beneficial effects of LiCl on VSMCs both in vitro and in vivo. Taken together, our results suggest that LiCl has great potentials in the prevention and treatment of cardiovascular diseases related to VSMC abnormal proliferation and migration. In addition, PGC-1α may serve as a promising drug target to regulate cardiovascular physiological homeostasis.

Tools for protein posttranslational modifications analysis: FAK, a case study

Recent advances in mass spectrometry have resulted in an exponential increase in annotation of posttranslational modifications (PTMs). Just in the Swiss-Prot Knowledgebase, there are 89,931 of a total of 27 characterized PTM types reported experimentally. A single protein can be dynamically modified during its lifetime for regulation of its function. Considering a PTM can occur at different levels and the number of different PTMs described, the number of possibilities for a single protein is unthinkable. Narrowing the study to a single PTM can be rather unmerited considering that most proteins are heavily modified. Currently crosstalk between PTMs is plentifully reported in the literature. The example of amino acids serine and threonine on one hand and lysine on the other hand, as targets of different modifications, demand a more global analysis approach of a protein. Besides the direct competition for the same amino acid, a PTM can directly or indirectly influence other PTMs in the same protein molecule by for example steric hindrance due to close proximity between the modifications or creation of a binding site such as an SH2 binding domain for protein recruitment and further modifications. Given the complexity of PTMs a number of tools have been developed to archive, analyze, and visualize modifications. VISUALPROT is presented here to demonstrate the usefulness of visualizing all annotated protein features such as amino acid content, domains, amino acid modification sites and single amino acid polymorphisms in a single image. VISUALPROT application is demonstrated for the protein focal adhesion kinase (FAK) as an example. FAK is a highly phosphorylated cytoplasmatic tyrosine kinase comprising different domains and regions. FAK is crucial for integrating signals from integrins and receptor tyrosine kinases in processes such as cell survival, proliferation, and motility.

PTPN12 controls PTEN and the AKT signalling to FAK and HER2 in migrating ovarian cancer cells

Several tyrosine phosphatases control cell motility; understanding their signaling helps to decipher cancer mechanisms. Previously, we found that the negative regulation of migration exerted by PTPN12 in ovarian cancer SKOV-3 cells involves direct FAK Y397 targeting, in HER2-dependent way. In this study, we describe that PTPN12 silencing depresses also PTEN RNA and protein. This, in turn, contributes to regulate FAK, through the activation of the PI3K/AKT pathway, resulting in GSK3 inactivation and decreased FAK phosphorylation at the inhibitory and GSK3 target S722. Altogether, in SKOV-3 cells, both PTPN12 and PTEN signaling merge on FAK which is negatively regulated through Y397 dephosphorylation (directly by PTPN12) and S722 phosphorylation (through PTEN/AKT/GSK3). Although HER2 activity sustains SKOV-3 cell motility, the HER2 inhibitor Ag825 impairs migration only in PTPN12 silenced cells, suggesting the ability of PTPN12 to affect HER2. This hypothesis is supported by the finding that, in migrating cells, Ag825 decreases HER2 phosphorylation at Y1248, Y1221/2, and Y877 (i.e., inactivates HER2) only after PTPN12 silencing. Conversely, cell exposure to the PI3K inhibitor LY294002 increases HER2 phosphorylation, suggesting the involvement of PI3K/AKT in HER2 regulation. Altogether, the results reveal a new PTEN mechanism in the control cell migration and suggest a complex cross-talk between PTPN12 and HER2.

Epstein-Barr virus latent membrane protein-2A induces ITAM/Syk- and Akt-dependent epithelial migration through αv-integrin membrane translocation

Epstein-Barr virus (EBV) is a highly prevalent herpesvirus associated with epithelial cancers, including nasopharyngeal carcinoma (NPC). The EBV protein latent membrane protein 2 (LMP2) is expressed in NPC tumor tissue and has been shown to induce transformation, inhibit differentiation, and promote migration of epithelial cells. In this study, the effect of LMP2A on migration of human epithelial cells was further analyzed. LMP2A expression induced migration in human foreskin keratinocytes (HFK) and HaCaT keratinocytes measured by wound healing scratch assay and chemoattractant-induced Transwell migration assay. The induction of migration by LMP2A required the ITAM signaling domain of LMP2A and activation of the Syk tyrosine kinase. LMP2A-induced Transwell migration required the Akt signaling pathway, and activation of Akt by LMP2A required the ITAM signaling domain of LMP2A. LMP2A also induced phosphorylation of the Akt target GSK3β, a Wnt signaling mediator that has been shown to regulate the activity of focal adhesion kinase (FAK), a tyrosine kinase activated by clustering and ligand interaction of integrins. Inhibition of either FAK or its signaling mediator Src kinase inhibited LMP2A-induced migration. Interestingly, αV-integrin was greatly increased in membrane-enriched fractions by LMP2A, and a neutralizing antibody to αV-integrin blocked migration, suggesting that the effects of LMP2A on membrane-localized αV-integrin promoted migration. The results of this study indicate that LMP2A expression in human epithelial cells induces αV-integrin-dependent migration through a mechanism requiring ITAM-mediated Syk and Akt activation and inducing membrane translocation or stabilization of αV-integrin and FAK activation. The specific effects of LMP2A on an integrin with a diverse repertoire of ligand specificities could promote migration of different cell types and be initiated by multiple chemoattractants.

3,3'Diindolylmethane suppresses vascular smooth muscle cell phenotypic modulation and inhibits neointima formation after carotid injury

BACKGROUND

3,3'Diindolylmethane (DIM), a natural phytochemical, has shown inhibitory effects on the growth and migration of a variety of cancer cells; however, whether DIM has similar effects on vascular smooth muscle cells (VSMCs) remains unknown. The purpose of this study was to assess the effects of DIM on the proliferation and migration of cultured VSMCs and neointima formation in a carotid injury model, as well as the related cell signaling mechanisms.

METHODOLOGY/PRINCIPAL FINDINGS

DIM dose-dependently inhibited the platelet-derived growth factor (PDGF)-BB-induced proliferation of VSMCs without cell cytotoxicity. This inhibition was caused by a G0/G1 phase cell cycle arrest demonstrated by fluorescence-activated cell-sorting analysis. We also showed that DIM-induced growth inhibition was associated with the inhibition of the expression of cyclin D1 and cyclin-dependent kinase (CDK) 4/6 as well as an increase in p27(Kip1) levels in PDGF-stimulated VSMCs. Moreover, DIM was also found to modulate migration of VSMCs and smooth muscle-specific contractile marker expression. Mechanistically, DIM negatively modulated PDGF-BB-induced phosphorylation of PDGF-recptorβ (PDGF-Rβ) and the activities of downstream signaling molecules including Akt/glycogen synthase kinase(GSK)3β, extracellular signal-regulated kinase1/2 (ERK1/2), and signal transducers and activators of transcription 3 (STAT3). Our in vivo studies using a mouse carotid arterial injury model revealed that treatment with 150 mg/kg DIM resulted in significant reduction of the neointima/media ratio and proliferating cell nuclear antigen (PCNA)-positive cells, without affecting apoptosis of vascular cells and reendothelialization. Infiltration of inflammatory cells was also inhibited by DIM administration.

CONCLUSION

These results demonstrate that DIM can suppress the phenotypic modulation of VSMCs and neointima hyperplasia after vascular injury. These beneficial effects on VSMCs were at least partly mediated by the inhibition of PDGF-Rβ and the activities of downstream signaling pathways. The results suggest that DIM has the potential to be a candidate for the prevention of restenosis.

Results of the 2nd scientific workshop of the ECCO (III): basic mechanisms of intestinal healing

The second scientific workshop of the European Crohn's and Colitis Organization (ECCO) focused on the relevance of intestinal healing for the disease course of inflammatory bowel disease (IBD). The objective was to better understand basic mechanisms, markers for disease prediction, detection and monitoring of intestinal healing, impact of intestinal healing on the disease course of IBD as well as therapeutic strategies. The results of this workshop are presented in four separate manuscripts. This section describes basic mechanisms of intestinal healing, identifies open questions in the field and provides a framework for future studies.

The role of GSK3beta in the development of the central nervous system

Glycogen synthase kinase 3β (GSK3β) is a multifunctional serine/threonine kinase. It is particularly abundant in the developing central nervous system (CNS). Since GSK3β has diverse substrates ranging from metabolic/signaling proteins and structural proteins to transcription factors, it is involved in many developmental events in the immature brain, such as neurogenesis, neuronal migration, differentiation and survival. The activity of GSK3β is developmentally regulated and is affected by various environmental/cellular insults, such as deprivation of nutrients/trophic factors, oxidative stress and endoplasmic reticulum stress. Abnormalities in GSK3β activity may disrupt CNS development. Therefore, GSK3β is a critical signaling protein that regulates brain development. It may also determine neuronal susceptibility to damages caused by various environmental insults.

Kisspeptin-10 inhibits cell migration in vitro via a receptor-GSK3 beta-FAK feedback loop in HTR8SVneo cells

Kisspeptin inhibits cancer cell metastasis and placental trophoblast cell migration. Kisspeptin gene expression in the placenta and circulating kisspeptin levels change during normal pregnancy and they are altered in preeclampsia. We therefore assessed the effect of kisspeptin-10 on the in vitro migration of a human placental cell line derived from first trimester extravillious trophoblasts (HTR8SVneo). HTR8SVneo cells specifically bound 125I-Kisspeptin-10 but kisspeptin-10 did not induce inositol phosphate production. Cell migration was inhibited by kisspeptin-10 with a maximal inhibition at 100nM. The signaling pathways involved in inhibition of cell migration were examined. Treatment with kisspeptin-10 elicited phosphorylation of GSK3 beta at Ser9 (which inhibits activity), with a 3-fold increase at 5 min. Transient phosphorylation of ERK1/2 and p38MAPK peaked at 10min. Phosphorylation of focal adhesion kinase (FAK) at Tyr925 increased 3-fold at 10 min. Inhibition of GSK3 beta correlated with release of beta-catenin into the cytoplasm. These signaling events were differentially blocked by inhibitors of G(q/11), Src, EGFR, PI(3)K, PKC and MEK. The data suggest that kisspeptin/GPR54 EGF-receptor transactivation leads to phosphorylation of ERK1/2, causing activation of p90rsk which in turn inhibits GSK3 beta via Ser9 phosphorylation. Inactivation of GSK3 beta results in release of beta-catenin into the cytoplasm, affecting cell-cell adhesion and Tyr925 phosphorylation of FAK, which increases phosphorylation of ERK1/2 via RAS/Raf-1 creating a feedback loop to enhance the effects on migration. These findings indicate that kisspeptin-10 inhibits the migration of human placental trophoblast-derived HTR8SVneo cells by stimulating complex ERK1/2-p90rsk-GSK3 beta-FAK feedback interactions.

GSK3 as a Sensor Determining Cell Fate in the Brain

Glycogen synthase kinase 3 (GSK3) is an unusual serine/threonine kinase that controls many neuronal functions, including neurite outgrowth, synapse formation, neurotransmission, and neurogenesis. It mediates these functions by phosphorylating a wide range of substrates involved in gene transcription, metabolism, apoptosis, cytoskeletal dynamics, signal transduction, lipid membrane dynamics, and trafficking, amongst others. This complicated list of diverse substrates generally follow a more simple pattern: substrates negatively regulated by GSK3-mediated phosphorylation favor a proliferative/survival state, while substrates positively regulated by GSK3 favor a more differentiated/functional state. Accordingly, GSK3 activity is higher in differentiated cells than undifferentiated cells and physiological (Wnt, growth factors) and pharmacological inhibitors of GSK3 promote the proliferative capacity of embryonic stem cells. In the brain, the level of GSK3 activity influences neural progenitor cell proliferation/differentiation in neuroplasticity and repair, as well as efficient neurotransmission in differentiated adult neurons. While defects in GSK3 activity are unlikely to be the primary cause of neurodegenerative diseases, therapeutic regulation of its activity to promote a proliferative/survival versus differentiated/mature functional environment in the brain could be a powerful strategy for treatment of neurodegenerative and other mental disorders.

GSK-3: Functional Insights from Cell Biology and Animal Models

Glycogen synthase kinase-3 (GSK-3) is a widely expressed and highly conserved serine/threonine protein kinase encoded in mammals by two genes that generate two related proteins: GSK-3α and GSK-3β. GSK-3 is active in cells under resting conditions and is primarily regulated through inhibition or diversion of its activity. While GSK-3 is one of the few protein kinases that can be inactivated by phosphorylation, the mechanisms of GSK-3 regulation are more varied and not fully understood. Precise control appears to be achieved by a combination of phosphorylation, localization, and sequestration by a number of GSK-3-binding proteins. GSK-3 lies downstream of several major signaling pathways including the phosphatidylinositol 3′ kinase pathway, the Wnt pathway, Hedgehog signaling and Notch. Specific pools of GSK-3, which differ in intracellular localization, binding partner affinity, and relative amount are differentially sensitized to several distinct signaling pathways and these sequestration mechanisms contribute to pathway insulation and signal specificity. Dysregulation of signaling pathways involving GSK-3 is associated with the pathogenesis of numerous neurological and psychiatric disorders and there are data suggesting GSK-3 isoform-selective roles in several of these. Here, we review the current knowledge of GSK-3 regulation and targets and discuss the various animal models that have been employed to dissect the functions of GSK-3 in brain development and function through the use of conventional or conditional knockout mice as well as transgenic mice. These studies have revealed fundamental roles for these protein kinases in memory, behavior, and neuronal fate determination and provide insights into possible therapeutic interventions.

How focal adhesion kinase achieves regulation by linking ligand binding, localization and action

Focal adhesion kinase (FAK) has an astonishing number of ligands and functions, which enable it to contribute to embryonic development and human health. FAK can promote different effects in similar cellular environments or similar effects in different cellular environments. Recent advances in structural and cellular analysis of FAK are starting to reveal the interrelationships between the conformations, localizations, interactions, and functions of FAK. This review focuses on our emerging understanding of how the structural framework of FAK mechanistically allows it to integrate manifold stimuli into environment-specific functions.

PI3K-dependent GSK3ß(Ser9)-phosphorylation is implicated in the intestinal epithelial cell wound-healing response

Introduction

The ability of the intestinal epithelial barrier to respond to various injurious insults is an essential component of intestinal homeostasis. However, the molecular mechanisms responsible for wound-healing and repair in the intestine are poorly understood. The glycogen synthase kinase 3ß (GSK3ß) has been implicated in various biological processes such as cellular motility, cell spreading and recently inflammation.

Aim

To investigate the role of GSK3ß in intestinal epithelial cell restitution.

Methods

Rat intestinal epithelial IEC18 cells were serum-starved for 16 to 24h and wounded by multiple scraping. Akt(Ser473)-, GSK3ß(Ser9)- and RelA(Ser536)-phosphorylation were determined by Western blot using specific phospho-antibodies. The inhibitors AG1478 (1 µM) and Ly294002 (25 µM) were used to block EGF-R autophosphorylation and PI3K-activation, respectively. ß-catenin/LEF/TCF dependent transcription was determined by reporter gene assay (TOP/FOP system). C-myc gene expression was evaluated by real-time RT-PCR. GSK3ß^−/− mouse embryonic fibroblasts were used to characterize the role of GSK3ß in wounding-induced cell migration.

Results

Wounding induced GSK3ß(Ser9) phosphorylation in IEC-18 cells, which led to ß-catenin accumulation as well as nuclear translocation of ß-catenin. ß-catenin stabilization/nuclear translocation led to enhanced LEF-TCF transcriptional activity and subsequent c-myc mRNA accumulation in wounded cell monolayers. Blocking PI3K/Akt signaling with Ly294002 prevented wound-induced GSK3ß(Ser9) phosphorylation as well as ß-catenin nuclear translocation and significantly attenuated restitution. Additionally, wounding induced rapid NF-kB(Ser536) phosphorylation, which was inhibited by AG1478, but not by Ly294002. GSK3ß^−/− cells demonstrated significantly attenuated wound-induced restitution compared to wild-type cells.

Conclusion

We conclude that PI3K-mediated GSK3ß phosphorylation is involved in the intestinal epithelial wound-healing response. Phosphorylation of GSK3ß may be important for intestinal restitution by promoting cell motility in response to wounding.

Calcineurin-NFAT signaling critically regulates early lineage specification in mouse embryonic stem cells and embryos

Self-renewal and pluripotency are hallmarks of embryonic stem cells (ESCs). However, the signaling pathways that trigger their transition from self-renewal to differentiation remain elusive. Here, we report that calcineurin-NFAT signaling is both necessary and sufficient to switch ESCs from an undifferentiated state to lineage-specific cells and that the inhibition of this pathway can maintain long-term ESC self-renewal independent of leukemia inhibitory factor. Mechanistically, this pathway converges with the Erk1/2 pathway to regulate Src expression and promote the epithelial-mesenchymal transition (EMT), a process required for lineage specification in response to differentiation stimuli. Furthermore, calcineurin-NFAT signaling is activated when the earliest differentiation event occurs in mouse embryos, and its inhibition disrupts extraembryonic lineage development. Collectively, our results demonstrate that the NFAT and Erk1/2 cascades form a signaling switch for early lineage segregation in mouse ESCs and provide significant insights into the regulation of the balance between ESC self-renewal and early lineage specification.

What Are the bona fide GSK3 Substrates?

Nearly 100 proteins are proposed to be substrates for GSK3, suggesting that this enzyme is a fundamental regulator of almost every process in the cell, in every tissue in the body. However, it is not certain how many of these proposed substrates are regulated by GSK3 in vivo. Clearly, the identification of the physiological functions of GSK3 will be greatly aided by the identification of its bona fide substrates, and the development of GSK3 as a therapeutic target will be highly influenced by this range of actions, hence the need to accurately establish true GSK3 substrates in cells. In this paper the evidence that proposed GSK3 substrates are likely to be physiological targets is assessed, highlighting the key cellular processes that could be modulated by GSK3 activity and inhibition.