Focal adhesion kinase controls cellular levels of p27/Kip1 and p21/Cip1 through Skp2-dependent and -independent mechanisms

Salidroside prevents gestational hypertension-induced impairment of offspring learning and memory via Wnt/Skp2 pathway

BACKGROUND

Salidroside (Sal) has been found to protect against multiple impairments caused by diabetes, and we designed this study to investigate the effect of Sal on gestational hypertension (GHP)-induced impairment of offspring learning and memory.

METHODS

We established a GHP rat model by intraperitoneal injection of NG-nitro-L-arginine methyl ester (L-NAME), and treated with Sal by daily gavage. We used Morris Water Maze test to evaluate the learning and memory ability of offspring rats. HE staining was used to measured the pathological changes in hippocampus of offspring. Immunohistochemistry, cellular immunofluorescence and western blot were used to detect the protein expression.

RESULTS

The learning and memory abilities of GHP offspring rats were significantly lower than those of normal rat offspring, while Sal treatment could significantly improve the learning and memory abilities of GHP offspring rats. HE staining did not reveal pathological differences in the hippocampus of normal rats, GHP rats and Sal-treated GHP offspring rats. However, Sal treatment can significantly increase the expression of Wnt1 and Skp2 protein, and decrease the expression of P27kiwf and P21waf1 protein in the hippocampus of GHP offspring rats. In vitro, Sal significantly promoted the proliferation and differentiation on neural stem cell, while Wnt1 knockdown could reverse these promotions by Sal. In the hippocampus of GHP offspring rats, Sal treatment significantly increased the expression of Tuj1, SOX2, Ki67 and DCX protein.

CONCLUSION

Salidroside significantly improves the learning and memory impairment of offspring caused by GHP, and its mechanism may be related to the fact that Salidroside promotes the proliferation and differentiation of neural stem cells by activating the Wnt1/Skp2 signaling pathway.

Molecular Regulation of Porcine Skeletal Muscle Development: Insights from Research on CDC23 Expression and Function

Cell division cycle 23 (CDC23) is a component of the tetratricopeptide repeat (TPR) subunit in the anaphase-promoting complex or cyclosome (APC/C) complex, which participates in the regulation of mitosis in eukaryotes. However, the regulatory model and mechanism by which the CDC23 gene regulates muscle production in pigs are largely unknown. In this study, we investigated the expression of CDC23 in pigs, and the results indicated that CDC23 is widely expressed in various tissues and organs. In vitro cell experiments have demonstrated that CDC23 promotes the proliferation of myoblasts, as well as significantly positively regulating the differentiation of skeletal muscle satellite cells. In addition, Gene Set Enrichment Analysis (GSEA) revealed a significant downregulation of the cell cycle pathway during the differentiation process of skeletal muscle satellite cells. The protein-protein interaction (PPI) network showed a high degree of interaction between genes related to the cell cycle pathway and CDC23. Subsequently, in differentiated myocytes induced after overexpression of CDC23, the level of CDC23 exhibited a significant negative correlation with the expression of key factors in the cell cycle pathway, suggesting that CDC23 may be involved in the inhibition of the cell cycle signaling pathway in order to promote the differentiation process. In summary, we preliminarily determined the function of CDC23 with the aim of providing new insights into molecular regulation during porcine skeletal muscle development.

SEMA6C: a novel adhesion-independent FAK and YAP activator, required for cancer cell viability and growth

Transmembrane semaphorins are signaling molecules, controlling axonal wiring and embryo development, which are increasingly implicated in human diseases. Semaphorin 6C (Sema6C) is a poorly understood family member and its functional role is still unclear. Upon targeting Sema6C expression in a range of cancer cells, we observed dramatic growth suppression, decreased ERK phosphorylation, upregulation of cell cycle inhibitor proteins p21, p27 and p53, and the onset of cell senescence, associated with activation of autophagy. These data are consistent with a fundamental requirement for Sema6C to support viability and growth in cancer cells. Mechanistically, we unveiled a novel signaling pathway elicited by Sema6C, and dependent on its intracellular domain, mediated by tyrosine kinases c-Abl and Focal Adhesion Kinase (FAK). Sema6C was found in complex with c-Abl, and induced its phosphorylation, which in turn led to FAK activation, independent of cell-matrix adhesion. Sema6C-induced FAK activity was furthermore responsible for increased nuclear localization of YAP transcriptional regulator. Moreover, Sema6C conferred YAP signaling-dependent long-term cancer cell survival upon nutrient deprivation. In conclusion, our findings demonstrate that Sema6C elicits a cancer promoting-signaling pathway sustaining cell viability and self-renewal, independent of growth factors and nutrients availability.

A review on regulation of cell cycle by extracellular matrix

The extracellular matrix (ECM) is a network of structural proteins, glycoproteins and proteoglycans that assists independent cells in aggregating and forming highly organized functional structures. ECM serves numerous purposes and is an essential component of tissue structure and functions. Initially, the role of ECM was considered to be confined to passive functions like providing mechanical strength and structural identity to tissues, serving as barriers and platforms for cells. The doors to understanding ECM's proper role in tissue functioning opened with the discovery of cellular receptors, integrins to which ECM components binds and influences cellular activities. Understanding and utilizing ECM's potential to control cellular function has become a topic of much interest in recent decades, providing different outlooks to study processes involved in developmental programs, wound healing and tumour progression. On another front, the regulatory mechanisms operating to prevent errors in the cell cycle have been topics of a titanic amount of studies. This is expected as many diseases, most infamously cancer, are associated with defects in their functioning. This review focuses on how ECM, through different methods, influences the progression of the somatic cell cycle and provides deeper insights into molecular mechanisms of functional communication between adhesion complex, signalling pathways and cell cycle machinery.

MicroRNA‑23a‑5p mediates the proliferation and differentiation of C2C12 myoblasts

Skeletal myogenesis is a highly ordered and complex biological process that is mediated by numerous regulatory factors. In previous studies, it has been demonstrated that microRNAs (miRs) and long non-coding RNAs (lncRNAs) serve key roles in skeletal myogenesis. The present study showed that the expression levels of miR-23a-5p showed a dynamic change from decrease to increase during C2C12 myoblast proliferation and differentiation. Functional analysis using 5-ethynyl-2′-deoxyuridine proliferation and Cell Counting Kit-8 detection assays indicated that overexpression of miR-23a-5p significantly promoted C2C12 myoblast proliferation compared with the negative control. In addition, in C2C12 myoblasts transfected with miR-23a-5p mimics, increased expression levels of regulators associated with cell proliferation (Cyclin E, CCND1 and Cyclin B) were observed compared with the negative control. By contrast, overexpression of miR-23a-5p decreased the expression levels of specific-myogenesis factors (MyoD, MyoG and Myf5) and decreased C2C12 myoblast differentiation. Luciferase activity assays indicated that miR-23a-5p suppressed the luciferase activity of lncDum. Further analysis demonstrated that miR-23a-5p not only showed an opposite expression level pattern compared with lncDum, which was first increased and then decreased, but also had an opposite effect on the proliferation and differentiation of C2C12 myoblasts compared with lncDum which inhibited cell proliferation and promoted cell differentiation. Taken together, these results indicated that miR-23a-5p may mediate the proliferation and differentiation of C2C12 myoblasts, which may be involved in lncDum regulation.

FAK Inhibition Induces Glioblastoma Cell Senescence-Like State through p62 and p27

Focal adhesion kinase (FAK) is a central component of focal adhesions that regulate cancer cell proliferation and migration. Here, we studied the effects of FAK inhibition in glioblastoma (GBM), a fast growing brain tumor that has a poor prognosis. Treating GBM cells with the FAK inhibitor PF-573228 induced a proliferative arrest and increased cell size. PF-573228 also reduced the growth of GBM neurospheres. These effects were associated with increased p27/CDKN1B levels and β-galactosidase activity, compatible with acquisition of senescence. Interestingly, FAK inhibition repressed the expression of the autophagy cargo receptor p62/SQSTM-1. Moreover, depleting p62 in GBM cells also induced a senescent-like phenotype through transcriptional upregulation of p27. Our results indicate that FAK inhibition arrests GBM cell proliferation, resulting in cell senescence, and pinpoint p62 as being key to this process. These findings highlight the possible therapeutic value of targeting FAK in GBM.

Role of Focal Adhesion Kinase in Small-Cell Lung Cancer and Its Potential as a Therapeutic Target

Small-cell lung cancer (SCLC) represents 15% of all lung cancers and it is clinically the most aggressive type, being characterized by a tendency for early metastasis, with two-thirds of the patients diagnosed with an extensive stage (ES) disease and a five-year overall survival (OS) as low as 5%. There are still no effective targeted therapies in SCLC despite improved understanding of the molecular steps leading to SCLC development and progression these last years. After four decades, the only modest improvement in OS of patients suffering from ES-SCLC has recently been shown in a trial combining atezolizumab, an anti-PD-L1 immune checkpoint inhibitor, with carboplatin and etoposide, chemotherapy agents. This highlights the need to pursue research efforts in this field. Focal adhesion kinase (FAK) is a non-receptor protein tyrosine kinase that is overexpressed and activated in several cancers, including SCLC, and contributing to cancer progression and metastasis through its important role in cell proliferation, survival, adhesion, spreading, migration, and invasion. FAK also plays a role in tumor immune evasion, epithelial-mesenchymal transition, DNA damage repair, radioresistance, and regulation of cancer stem cells. FAK is of particular interest in SCLC, being known for its aggressiveness. The inhibition of FAK in SCLC cell lines demonstrated significative decrease in cell proliferation, invasion, and migration, and induced cell cycle arrest and apoptosis. In this review, we will focus on the role of FAK in cancer cells and their microenvironment, and its potential as a therapeutic target in SCLC.

Signalling involving MET and FAK supports cell division independent of the activity of the cell cycle-regulating CDK4/6 kinases

Deregulation of cyclin-dependent kinases 4 and 6 (CDK4/6) is highly prevalent in cancer; yet, inhibitors against these kinases are currently used only in restricted tumour contexts. The extent to which cancers depend on CDK4/6 and the mechanisms that may undermine such dependency are poorly understood. Here, we report that signalling engaging the MET proto-oncogene receptor tyrosine kinase/focal adhesion kinase (FAK) axis leads to CDK4/6-independent CDK2 activation, involving as critical mechanistic events loss of the CDKI p21CIP1 and gain of its regulator, the ubiquitin ligase subunit SKP2. Combined inhibition of MET/FAK and CDK4/6 eliminates the proliferation capacity of cancer cells in culture, and enhances tumour growth inhibition in vivo. Activation of the MET/FAK axis is known to arise through cancer extrinsic and intrinsic cues. Our work predicts that such cues support cell division independent of the activity of the cell cycle-regulating CDK4/6 kinases and identifies MET/FAK as a tractable route to broaden the utility of CDK4/6 inhibitor-based therapies in the clinic.

FBXW5 Promotes Tumorigenesis and Metastasis in Gastric Cancer via Activation of the FAK-Src Signaling Pathway

F-box/WD repeat-containing protein 5 (FBXW5) is a member of the FBXW subclass of F-box proteins. Despite its known function as a component of the Skp1-Cullin-F-box (SCF) ubiquitin ligase complex, the role of FBXW5 in gastric cancer tumorigenesis and metastasis has not been investigated. The present study investigates the role of FBXW5 in tumorigenesis and metastasis, as well as the regulation of key signaling pathways in gastric cancer; using in-vitro FBXW5 knockdown/overexpression cell line and in-vivo models. In-vitro knockdown of FBXW5 results in a decrease in cell proliferation and cell cycle progression, with a concomitant increase in cell apoptosis and caspase-3 activity. Furthermore, knockdown of FBXW5 also leads to a down regulation in cell migration and adhesion, characterized by a reduction in actin polymerization, focal adhesion turnover and traction forces. This study also delineates the mechanistic role of FBXW5 in oncogenic signaling as its inhibition down regulates RhoA-ROCK 1 (Rho-associated protein kinase 1) and focal adhesion kinase (FAK) signaling cascades. Overexpression of FBXW5 promotes in-vivo tumor growth, whereas its inhibition down regulates in-vivo tumor metastasis. When considered together, our study identifies the novel oncogenic role of FBXW5 in gastric cancer and draws further interest regarding its clinical utility as a potential therapeutic target.

Non-redundant functions of FAK and Pyk2 in intestinal epithelial repair

Adhesion signaling between epithelial cells and the extracellular matrix plays a critical role in maintaining tissue homeostasis and the response to tissue damage. Focal adhesion kinase (FAK) and its close relative Pyk2 are non-receptor tyrosine kinases that mediate adhesion signaling to promote cell proliferation, motility and survival. FAK has also been shown to act as a mechanosensor by modulating cell proliferation in response to changes in tissue compliance. We previously showed that mice lacking FAK in the intestinal epithelium are phenotypically normal under homeostatic conditions but hypersensitive to experimental colitis induced by dextran sulfate sodium (DSS). Here we report that Pyk2-deficient mice are also phenotypically normal under homeostatic conditions and are similarly hypersensitive to DSS-induced colitis. These data indicate that normal intestinal development and homeostatic maintenance can occur in the presence of either FAK or Pyk2, but that both kinases are necessary for epithelial repair following injury. In contrast, mice lacking both FAK and Pyk2 develop spontaneous colitis with 100% penetrance by 4 weeks of age. Normal colonic phenotype and function are restored upon treatment of the double knockout mice with antibiotics, implicating commensal bacteria or bacterial products in the etiology of the spontaneous colitis exhibited by these mice.

Effects of paclitaxel intervention on pulmonary vascular remodeling in rats with pulmonary hypertension

The aim of the present study was to investigate the effects of paclitaxel (PTX), at a non-cytotoxic concentration, on pulmonary vascular remodeling (PVR) in rats with pulmonary hypertension (PAH), and to explore the mechanisms underlying the PTX-mediated reversal of PVR in PAH. A total of 36 rats were divided into control group (n=12), model group (n=12) receiving a subcutaneous injection of monocrotaline (60 mg/kg) in the back on day 7 following left pneumonectomy and PTX group (n=12) with PTX (2 mg/kg) injection via the caudal vein 3 weeks following establishing the model. The degree of PVR among all groups, as well as the expression levels of Ki67, p27^Kip1 and cyclin B1, were compared. The mean pulmonary artery pressure, right ventricular hypertrophy index [right ventricle/(left ventricle + septum) ratio] and the thickness of the pulmonary arterial tunica media in the model group were 58.34±2.01 mmHg, 0.64±0.046 and 65.3±3.3%, respectively, which were significantly higher when compared with 23.30±1.14 mmHg, 0.32±0.028 and 16.2±1.3% in the control group, respectively (P<0.01). The mean pulmonary artery pressure, right ventricular hypertrophy index and thickness of the pulmonary arterial tunica media in the PTX group were 42.35±1.53 mmHg, 0.44±0.029 and 40.5±2.6%, respectively, which were significantly lower when compared with the model group (P<0.01). Compared with the control group, the expression levels of Ki67 and cyclin B1 in the model group were significantly increased (P<0.01), while p27^Kip1 expression was significantly reduced (P<0.01). Following PTX intervention, the expression levels of Ki67 and cyclin B1 were significantly reduced when compared with the model group (P<0.01), while p27^Kip1 expression was significantly increased (P<0.01). The results of the present study suggest that PTX, administered at a non-cytotoxic concentration, may reduce PAH in rats, and prevent the effects of PVR in PAH. These effects of PTX may be associated with increased expression of p27^Kip1 and decreased expression of cyclin B1.

Therapeutic Potential of Focal Adhesion Kinase Inhibition in Small Cell Lung Cancer

Small cell lung cancer (SCLC) has a poor prognosis. Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase regulating cell proliferation, survival, migration, and invasion, which is overexpressed and/or activated in several cancers, including SCLC. We wanted to determine whether FAK contributes to SCLC aggressive behavior. We first evaluated the effect of FAK small-molecule inhibitor PF-573,228 in NCI-H82, NCI-H146, NCI-H196, and NCI-H446 SCLC cell lines. PF-573,228 (0.1-5 μmol/L) inhibited FAK activity by decreasing phospho-FAK (Tyr397), without modifying total FAK expression. PF-573,228 decreased proliferation, decreased DNA synthesis, induced cell-cycle arrest in G₂-M phases, and increased apoptosis in all cell lines. PF-573,228 also decreased motility in adherent cell lines. To make sure that these effects were not off-target, we then used a genetic method to inhibit FAK in NCI-H82 and NCI-H446, namely stable transduction with FAK shRNA and/or FAK-related nonkinase (FRNK), a splice variant lacking the N-terminal and kinase domains. Although FAK shRNA transduction decreased total and phospho-FAK (Tyr397) expression, it did not affect proliferation, DNA synthesis, or progression through cell cycle. However, restoration of FAK-targeting (FAT) domain (attached to focal adhesion complex where it inhibits pro-proliferative proteins such as Rac-1) by FRNK transduction inhibited proliferation, DNA synthesis, and induced apoptosis. Moreover, although FAK shRNA transduction increased active Rac1 level, FRNK reexpression in cells previously transduced with FAK shRNA decreased it. Therefore, FAK appears important in SCLC biology and targeting its kinase domain may have a therapeutic potential, while targeting its FAT domain should be avoided to prevent Rac1-mediated protumoral activity.

miR4673 improves fitness profile of neoplastic cells by induction of autophagy

Therapeutic resistance of neoplasms is mainly attributed to gradual evolution of mutational profile1. Here, we demonstrate a microRNA-mediated mechanism that effectively improves fitness of SKBR3 mammary carcinoma cells by cytoplasmic reprogramming. The reprogramming is triggered by endogenous miR4673 transcribed from notch-1 locus. The miRNA downregulates cdk-18, a cyclin-dependent kinase that regulates M-G1 transition in cycling cells2,3. Suppression of cdk-18 triggers mitophagy and autophagy. Due to high autophagic flux, oestrogen receptor-1+/progesterone receptor+/p53+ (Esr1+/Pr+/p53+) SKBR3 cells are coerced into an Esr1-/Prlow/p53-profile. Increased mitophagy in combination with proteasomal degradation of p53 transiently arrests the cycling cells at G0 and enhances radio-resistance of the SKBR3 population. These findings highlight the impact on cancer therapy of non-encoded neoplastic resistance, arising as a consequence of miRNA-mediated autophagic reprogramming that uncouples phenotype and genotype.

An In Vitro Model of Cellular Quiescence in Primary Human Dermal Fibroblasts

Cellular quiescence is a reversible mode of cell cycle exit that allows cells and organisms to withstand unfavorable stress conditions. The factors that underlie the entry, exit, and maintenance of the quiescent state are crucial for understanding normal tissue development and function as well as pathological conditions such as chronic wound healing and cancer. In vitro models of quiescence have been used to understand the factors that contribute to quiescence under well-controlled experimental conditions. Here, we describe an in vitro model of quiescence that is based on neonatal human dermal fibroblasts. The fibroblasts are induced into quiescence by antiproliferative signals, contact inhibition, and serum-starvation (mitogen withdrawal). We describe the isolation of fibroblasts from skin, methods for inducing quiescence in isolated fibroblasts, and approaches to manipulate the fibroblasts in proliferating and quiescent states to determine critical regulators of quiescence.

Atorvastatin prevents endothelial dysfunction in high glucose condition through Skp2-mediated degradation of FOXO1 and ICAM-1

OBJECTIVE

The 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor atorvastatin has been reported to exert vasculo-protective action in diabetes. We investigated the vasculo-protective mechanism of atorvastatin by evaluating its effect on two major pathogenic molecules, FOXO1 and ICAM1, mediated by S-phase kinase-associated protein 2 (Skp2) in diabetic endothelial dysfunction. APPROACH AND RESULTS: [1] FOXO1: Hyperglycemic condition increased FOXO1 protein level in endothelial cells, which was reversed by atorvastatin. This atorvastatin effect was obliterated by treatment of protease inhibitor, suggesting that atorvastatin induces degradation of FOXO1. Immunoprecipitation showed that atorvastatin facilitated the binding of Skp2 to FOXO1, leading to ubiquitination and degradation of FOXO1. [2] ICAM-1: Increased ICAM1 in high glucose condition was reduced by atorvastatin. But this effect of atorvastatin was obliterated when Skp2 was inhibited, suggesting that atorvastatin enhances binding of Skp2 to ICAM1 leading to degradation. Actually, ubiquitination and degradation of ICAM-1 were reduced when Skp2 was inhibited. In vitro monocyte adhesion assay revealed that atorvastatin reduced monocyte adhesion on endothelial cells in high glucose condition, which was reversed by Skp2 knock-down.

CONCLUSION

Atorvastatin strengthens Skp2 binding to FOXO1 or ICAM1, leading to ubiquitination and degradation. Skp2-dependent ubiquitination of major pathogenic molecules is the key mechanism for statin's protective effect on endothelial function in diabetes.

Suppression of integrin α3β1 by α9β1 in the epidermis controls the paracrine resolution of wound angiogenesis

The development of novel therapies to promote wound healing is hindered by our poor understanding of how different integrins function together in the epidermis. Longmate et al. show that cross-suppression by integrins within the epidermis controls paracrine signals that regulate wound angiogenesis. Integrin α9β1 suppresses the proangiogenic functions of α3β1 during late-stage wound healing, leading to the normalization of blood vessel density in the wound bed.

Development of wound therapies is hindered by poor understanding of combinatorial integrin function in the epidermis. In this study, we generated mice with epidermis-specific deletion of α3β1, α9β1, or both integrins as well as keratinocyte lines expressing these integrin combinations. Consistent with proangiogenic roles for α3β1, α3-null keratinocytes showed reduced paracrine stimulation of endothelial cell migration and survival, and wounds of epidermis-specific α3 knockout mice displayed impaired angiogenesis. Interestingly, α9β1 in keratinocytes suppressed α3β1-mediated stimulation of endothelial cells, and wounds of epidermis-specific α9 knockout mice displayed delayed vascular normalization and reduced endothelial apoptosis, indicating that α9β1 cross-suppresses α3β1 proangiogenic functions. Moreover, α9β1 inhibited α3β1 signaling downstream of focal adhesion kinase (FAK) autoactivation at the point of Src-mediated phosphorylation of FAK Y861/Y925. Finally, α9β1 cross-suppressed many α3β1-dependent genes, including the gene that encodes MMP-9, which we implicated as a regulator of integrin-dependent cross talk to endothelial cells. Our findings identify a novel physiological context for combinatorial integrin signaling, laying the foundation for therapeutic strategies that manipulate α9β1 and/or α3β1 during wound healing.

Suppression of B-Raf(V600E) cancers by MAPK hyper-activation

B-Raf(V600E) activates MEK/MAPK signalling and acts as oncogenic driver of a variety of cancers, including melanoma, colorectal and papillary thyroid carcinoma. Specific B-Raf(V600E) kinase inhibitors (e.g., Vemurafenib) prove initial efficacy in melanoma followed shortly by acquired resistance, while failing in most other B-Raf(V600E) cancers due to primary resistance. Resistance is due to acquired mutations in the Ras/Raf/MEK/MAPK pathway and/or other oncogenic drivers that bypass B-Raf(V600E). Surprisingly, hyper-activation of MAPK by inhibiting its protein phosphatase 2A by a synthetic long-chain fatty acid analogue (MEDICA), results in oncogene-induced growth arrest and apoptosis of B-Raf(V600E) cancer cells. Growth arrest is accompanied by MAPK-mediated serine/threonine phosphorylation and suppression of a variety of oncogenic drivers that resist treatment by B-Raf(V600E) kinase inhibitors, including ErbB members, c-Met, IGFR, IRS, STAT3 and Akt. The combined activities of mutated B-Raf and MEDICA are required for generating hyper-activated MAPK, growth arrest and apoptosis, implying strict specificity for mutated B-Raf cancer cells.

A paradigm shift: Cancer therapy with peptide-based B-cell epitopes and peptide immunotherapeutics targeting multiple solid tumor types: Emerging concepts and validation of combination immunotherapy

There is a recognizable and urgent need to speed the development and application of novel, more efficacious anti-cancer vaccine therapies that inhibit tumor progression and prevent acquisition of tumor resistance. We have created and established a portfolio of validated peptide epitopes against multiple receptor tyrosine kinases and we have identified the most biologically effective combinations of EGFR (HER-1), HER-2, HER-3, VEGF and IGF-1R peptide vaccines/mimics to selectively inhibit multiple receptors and signaling pathways. The strategy is based on the use of chimeric conformational B-cell epitope peptides incorporating "promiscuous" T-cell epitopes that afford the possibility of generating an enduring immune response, eliciting protein-reactive high-affinity anti-peptide antibodies as potential vaccines and peptide mimics that act as antagonists to receptor signaling that drive cancer metastasis. In this review we will summarize our ongoing studies based on the development of combinatorial immunotherapeutic strategies that act synergistically to enhance immune-mediated tumor killing aimed at addressing mechanisms of tumor resistance for several tumor types.

FAK is required for Schwann cell spreading on immature basal lamina to coordinate the radial sorting of peripheral axons with myelination

Without Focal Adhesion Kinase (FAK), developing murine Schwann cells (SCs) proliferate poorly, sort axons inefficiently, and cannot myelinate peripheral nerves. Here we show that FAK is required for the development of SCs when their basal lamina (BL) is fragmentary, but not when it is mature in vivo. Mutant SCs fail to spread on fragmentary BL during development in vivo, and this is phenocopied by SCs lacking functional FAK on low laminin (LN) in vitro. Furthermore, SCs without functional FAK initiate differentiation prematurely, both in vivo and in vitro. In contrast to their behavior on high levels of LN, SCs lacking functional FAK grown on low LN display reduced spreading, proliferation, and indicators of contractility (i.e., stress fibers, arcs, and focal adhesions) and are primed to differentiate. Growth of SCs lacking functional FAK on increasing LN concentrations in vitro revealed that differentiation is not regulated by G1 arrest but rather by cell spreading and the level of contractile actomyosin. The importance of FAK as a critical regulator of the specific response of developing SCs to fragmentary BL was supported by the ability of adult FAK mutant SCs to remyelinate demyelinated adult nerves on mature BL in vivo. We conclude that FAK promotes the spreading and actomyosin contractility of immature SCs on fragmentary BL, thus maintaining their proliferation, and preventing differentiation until they reach high density, thereby promoting radial sorting. Hence, FAK has a critical role in the response of SCs to limiting BL by promoting proliferation and preventing premature SC differentiation.

The differential susceptibilities of MCF-7 and MDA-MB-231 cells to the cytotoxic effects of curcumin are associated with the PI3K/Akt-SKP2-Cip/Kips pathway

Background

The mechanism underlying the differential cytotoxicity of curcumin in various cancer types, however, remains largely unclear. The aims of this study is to examine the concentration- and time-related effects of curcumin on two different breast cancer cells, MCF-7 and MDA-MB-231, and investigated the functional changes induced by curcumin treatment, as well as their relationship to the PI3K/Akt-SKP2-Cip/Kips pathway.

Methods

First, WST-1 and clonogenic assay were performed to determine the cytotoxicity of curcumin in MCF-7 and MDA-MB-231 cells. Then, the expression of CDK interacting protein/Kinase inhibitory protein (Cip/Kips) members (p27, p21 and p57) and S-phase kinase-associated protein-2 (SKP2) was investigated by QRT PCR and Western Blotting. Curcumin’s effect on PI3K (phosphatidylinositol 3-kinase) /Akt and its substrates Foxo1 and Foxo3a were then studied by Western Blotting. Small interfering RNAs (siRNAs) targeting SKP2 was used to explore the relationship between SKP2 and Cip/Kips members. Finally, WST-1 assay was tested to explore the concomitant treatment with curcumin and the inhibition of PKB or SKP2 signaling on curcumin sensitivity in MCF-7 and MDA-MB-231 cells.

Results

We demonstrated MCF-7 and MDA-MB-231 cells exhibited differential responses to curcumin by WST-1 and clonogenic assay (MDA-MB-231 cells was sensitive, and MCF-7 cells was resistant), which were found to be related to the differential curcumin-mediated regulation of SKP2-Cip/Kips (p21 and p27 but not p57) signaling. The differential cellular responses were further linked to the converse effects of curcumin on PI3K/Akt and its substrates Foxo1 and Foxo3a. Importantly, PI3K inhibitor wortmannin could counteract both curcumin-induced phosphorylation of Akt and up-regulation of SKP2 in MCF-7 cells. Subsequent WST-1 assay demonstrated concomitant treatment with curcumin and wortmannin or SKP2 siRNA not only further augmented curcumin sensitivity in MDA-MB-231 cells but also overcame curcumin resistance in MCF-7 cells.

Conclusions

Our study established PI3K/Akt-SKP2-Cip/Kips signaling pathway is involved in the mechanism of action of curcumin and revealed that the discrepant modulation of this pathway by curcumin is responsible for the differential susceptibilities of these two cell types to curcumin.

The balance between cell cycle arrest and cell proliferation: control by the extracellular matrix and by contact inhibition

To understand the dynamics of the cell cycle, we need to characterize the balance between cell cycle arrest and cell proliferation, which is often deregulated in cancers. We address this issue by means of a detailed computational model for the network of cyclin-dependent kinases (Cdks) driving the mammalian cell cycle. Previous analysis of the model focused on how this balance is controlled by growth factors (GFs) or the levels of activators (oncogenes) and inhibitors (tumour suppressors) of cell cycle progression. Supra-threshold changes in the level of any of these factors can trigger a switch in the dynamical behaviour of the Cdk network corresponding to a bifurcation between a stable steady state, associated with cell cycle arrest, and sustained oscillations of the various cyclin/Cdk complexes, corresponding to cell proliferation. Here, we focus on the regulation of cell proliferation by cellular environmental factors external to the Cdk network, such as the extracellular matrix (ECM), and contact inhibition, which increases with cell density. We extend the model for the Cdk network by including the phenomenological effect of both the ECM, which controls the activation of the focal adhesion kinase (FAK) that promotes cell cycle progression, and cell density, which inhibits cell proliferation via the Hippo/YAP pathway. The model shows that GFs and FAK activation are capable of triggering in a similar dynamical manner the transition to cell proliferation, while the Hippo/YAP pathway can arrest proliferation once cell density passes a critical threshold. The results account for the dependence or independence of cell proliferation on serum and/or cell anchorage to ECM. Whether the balance in the Cdk network is tilted towards cell cycle arrest or proliferation depends on the direction in which the threshold associated with the bifurcation is passed once the cell integrates the multiple, internal or external signals that promote or impede progression in the cell cycle.

The influence of high glucose on the Cip/Kip family expression profiles in HRECs

Neovascularization is the main characteristic of the proliferative stage of diabetic retinopathy. It has been proven that cell cycle regulation is involved in angiogenesis. The cell cycle regulators, Cip/Kip protein family, belong to the cyclin-dependent kinase inhibitors, are versatile proteins, and except for their function in cell cycle regulation, they also participate in transcription, apoptosis and migration. The expression profiles of the Cip/Kip family in human retina microvascular endothelial cells (HRECs) under normal or high glucose conditions has not been described before. This study was undertaken to determine the expression profiles of the Cip/Kip family proteins, e.g., proteins which are influenced by high glucose and in what manner. Western blot and immunofluorescence analyses were used to investigate the protein expression profiles. Only p21(cip1) and p27(kip1) were detected in HRECs, and they were located in the nucleus. P21(cip1) protein abundance was higher than p27(kip1) in HRECs. Incubation of HRECs in medium containing 30 mM D-glucose for 48 h resulted in downregulation of p21(cip1) protein expression, but had no influence on p27(kip1) protein levels or p21(cip1) mRNA abundance. These results were accompanied by cell cycle G1 phase exit and a lower cell survival rate. Our data show for the first time that high glucose changes the Cip/Kip family expression profiles in HRECs, which may be the foundation for the investigation of the role of the Cip/Kip family in the pathogenesis of diabetic retinopathy.

RHOA-FAK is a required signaling axis for the maintenance of KRAS-driven lung adenocarcinomas

Non-small cell lung cancer (NSCLC) often expresses mutant KRAS together with tumor-associated mutations of the CDKN2A locus, which are associated with aggressive, therapy-resistant tumors. Here, we unravel specific requirements for the maintenance of NSCLC that carries this genotype. We establish that the extracellular signal-regulated kinase (ERK)/RHOA/focal adhesion kinase (FAK) network is deregulated in high-grade lung tumors. Suppression of RHOA or FAK induces cell death selectively in mutant KRAS;INK4A/ARF-deficient lung cancer cells. Furthermore, pharmacologic inhibition of FAK caused tumor regression specifically in the high-grade lung cancer that developed in mutant Kras;Cdkn2a-null mice. These findings provide a rationale for the rapid implementation of genotype-specific targeted therapies using FAK inhibitors in patients with cancer.

SIGNIFICANCE

Targeted therapies are effective for only a small fraction of patients with cancer. We report that FAK inhibitors exert potent antitumor effects in NSCLCs that express mutant KRAS in association with INK4A/ARF deficiency. These results reveal a novel genotype-specific vulnerability of cancer cells that can be exploited for therapeutic purposes.

Neurofibromatosis type 2 protein, NF2: an uncoventional cell cycle regulator

Neurofibromatosis type 2 protein (NF2) is an underappreciated tumor suppressor involved in a broad range of nervous system tumors. Inactivation of the NF2 gene leads to neurofibromatosis type-2, which is characterized by multiple benign nervous system tumors and mutations in the gene have been demonstrated in many other tumor types as well. All tumors, regardless of location or grade, lack a fundamental control over cell cycle progression. Historically, NF2 is an unconventional tumor suppressor protein in that it does not directly influence the cell cycle. NF2 links receptors at the plasma membrane to their cytoplasmic kinases to facilitate contact inhibition. However, NF2 can also interact with an array of cytoplasmic and nuclear proteins that affect cell cycle progression. Furthermore, through some of these pathways, NF2 may reverse the functional inhibition of conventional tumor suppressor pathways. Here we review mechanisms utilized by NF2 to regain control of the cell cycle.

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.

Loss of NF1 expression in human endothelial cells promotes autonomous proliferation and altered vascular morphogenesis

Neurofibromatosis is a well known familial tumor syndrome, however these patients also suffer from a number of vascular anomalies. The loss of NFl from the endothelium is embryonically lethal in mouse developmental models, however little is known regarding the molecular regulation by NF1 in endothelium. We investigated the consequences of losing NF1 expression on the function of endothelial cells using shRNA. The loss of NF1 was sufficient to elevate levels of active Ras under non-stimulated conditions. These elevations in Ras activity were associated with activation of downstream signaling including activation of ERK, AKT and mTOR. Cells knocked down in NF1 expression exhibited no cellular senescence. Rather, they demonstrated augmented proliferation and autonomous entry into the cell cycle. These proliferative changes were accompanied by enhanced expression of cyclin D, phosphorylation of p27^KIP, and decreases in total p27^KIP levels, even under growth factor free conditions. In addition, NF1-deficient cells failed to undergo normal branching morphogenesis in a co-culture assay, instead forming planar islands with few tubules and branches. We find the changes induced by the loss of NF1 could be mitigated by co-expression of the GAP-related domain of NF1 implicating Ras regulation in these effects. Using doxycycline-inducible shRNA, targeting NF1, we find that the morphogenic changes are reversible. Similarly, in fully differentiated and stable vascular-like structures, the silencing of NF1 results in the appearance of abnormal vascular structures. Finally, the proliferative changes and the abnormal vascular morphogenesis are normalized by low-dose rapamycin treatment. These data provide a detailed analysis of the molecular and functional consequences of NF1 loss in human endothelial cells. These insights may provide new approaches to therapeutically addressing vascular abnormalities in these patients while underscoring a critical role for normal Ras regulation in maintaining the health and function of the vasculature.

Cytotoxic effects of gold nanoparticles: a multiparametric study

The in vitro labeling of therapeutic cells with nanoparticles (NPs) is becoming more and more common, but concerns about the possible effects of the NPs on the cultured cells are also increasing. In the present work, we evaluate the effects of poly(methacrylic acid)-coated 4 nm diameter Au NPs on a variety of sensitive and therapeutically interesting cell types (C17.2 neural progenitor cells, human umbilical vein endothelial cells, and PC12 rat pheochromocytoma cells) using a multiparametric approach. Using various NP concentrations and incubation times, we performed a stepwise analysis of the NP effects on cell viability, reactive oxygen species, cell morphology, cytoskeleton architecture, and cell functionality. The data show that higher NP concentrations (200 nM) reduce cell viability mostly through induction of reactive oxygen species, which was significantly induced at concentrations of 50 nM Au NPs or higher. At these concentrations, both actin and tubulin cytoskeleton were deformed and resulted in reduced cell proliferation and cellular differentiation. In terms of cell functionality, the NPs significantly impeded neurite outgrowth of PC12 cells up to 20 nM concentrations. At 10 nM, no significant effects on any cellular parameter could be observed. These data highlight the importance of using multiple assays to cover the broad spectrum of cell-NP interactions and to determine safe NP concentrations and put forward the described protocol as a possible template for future cell-NP interaction studies under comparable and standardized conditions.

Focal adhesion kinase is a phospho-regulated repressor of Rac and proliferation in human endothelial cells

Focal adhesion kinase (FAK) is critically positioned to integrate signals from the extracellular matrix and cellular adhesion. It is essential for normal vascular development and has been implicated in a wide range of cellular functions including the regulation of cell proliferation, migration, differentiation, and survival. It is currently being actively targeted therapeutically using different approaches. We have used human endothelial cells as a model system to compare the effects of inhibiting FAK through several different approaches including dominant negatives, kinase inhibitors and shRNA. We find that manipulations of FAK signaling that result in inhibition of FAK 397 phosphorylation inhibit proliferation and migration. However, abolition of FAK expression using stable (shRNA) or transient (siRNA) approaches does not interfere with these cellular functions. The ability to regulate cell proliferation by FAK manipulation is correlated with the activation status of Rac, an essential signal for the regulation of cyclin-dependent kinase inhibitors. The knockdown of FAK, while not affecting cellular proliferation or migration, dramatically interferes with vascular morphogenesis and survival, mirroring in vivo findings. We propose a novel model of FAK signaling whereby one of the multifunctional roles of FAK as a signaling protein includes FAK as a phospho-regulated repressor of Rac activation, with important implications on interpretation of research experiments and therapeutic development.

The C terminus of talin links integrins to cell cycle progression

Talin recruits and activates focal adhesion proteins required for cell cycle progression.

Integrins are cell adhesion receptors that sense the extracellular matrix (ECM) environment. One of their functions is to regulate cell fate decisions, although the question of how integrins initiate intracellular signaling is not fully resolved. In this paper, we examine the role of talin, an adapter protein at cell–matrix attachment sites, in outside-in signaling. We used lentiviral small hairpin ribonucleic acid to deplete talin in mammary epithelial cells. These cells still attached to the ECM in an integrin-dependent manner and spread. They had a normal actin cytoskeleton, but vinculin, paxillin, focal adhesion kinase (FAK), and integrin-linked kinase were not recruited to adhesion sites. Talin-deficient cells showed proliferation defects, and reexpressing a tail portion of the talin rod, but not its head domain, restored integrin-mediated FAK phosphorylation, suppressed p21 expression, and rescued cell cycle. Thus, talin recruits and activates focal adhesion proteins required for proliferation via the C terminus of its rod domain. Our study reveals a new function for talin, which is to link integrin adhesions with cell cycle progression.

TRB3 mediates homocysteine-induced inhibition of endothelial cell proliferation

Hyperhomocysteinemia (HHcy) has been shown to induce endothelial dysfunction, an early event in the progression of atherosclerosis. However, the underlying mechanism of endothelial cell injury in HHcy has not been clearly elucidated. In this study, we examined the effect of homocysteine on tribbles-related protein 3 (TRB3)-mediated cell-cycle arrest in human umbilical vein endothelial cells (HUVECs). Treatment of HUVECs with homocysteine (0-250 µmol/L) resulted in inhibition of cell proliferation assessed by [(3)H]-thymidine incorporation into DNA. Homocysteine induced cell-cycle arrest in the G1 phase by up-regulating the protein levels of p27(kip1). Under these conditions, homocysteine did not induce endoplasmic reticulum stress. However, homocysteine up-regulated the expression of TRB3, thus leading to the dephosphorylation of Akt (Thr308). Knock-down of endogenous TRB3 using siRNA significantly suppressed the inhibitory effect of homocysteine on the proliferation of HUVECs. Homocysteine-induced TRB3 expression was mediated by the cAMP/cAMP response element-binding protein (CREB) pathway. These results demonstrate that TRB3 is a critical molecule in the homocysteine-mediated cell-cycle arrest in endothelial cells.

Mitogenic Signaling by the gep Oncogene Involves the Upregulation of S-Phase Kinase-Associated Protein 2

The gep oncogene, defined by the activated mutant of the α-subunit of the G protein G(12) (Gα(12)Q229L or Gα(12)QL), potently stimulates the proliferation of many different cell types in addition to inducing neoplastic transformation of several fibroblast cell lines. While it has been demonstrated that Gα(12)QL accelerates G1- to S-phase cell cycle progression, the precise mechanism through which Gα(12) communicates to cell cycle machinery is largely unknown. In the present study, we report that the activated-mutational as well as receptor-mediated-Gα(12) transmits its proliferative signals to cell cycle machinery by modulating the levels of the S-phase kinase-associated protein 2 (Skp2), an E3 ubiquitin ligase, involved in the regulation of the cyclin-dependent kinase inhibitor (CKI), p27(Kip1). Our results show that the expression of Gα(12)QL leads to an increase in the levels of Skp2 with a correlatable decrease in p27(Kip1) levels and subsequent increase in the activities of specific CDKs. By demonstrating that the transient expression of Gα(12)QL induces an increase in Skp2 levels with resultant downregulation of p27(Kip1) in both NIH3T3 and human astrocytoma 1321N1 cells, we establish here that the effect of Gα(12) on Skp2/p27(Kip1) is cell type independent. In addition, we demonstrate that LPA-stimulated proliferation and changes in Skp2 and p27(Kip1) levels in 1321N1 cells could be inhibited by the expression of a dominant-negative mutant of Gα(12), thereby pointing to the critical role of Gα(12) in LPA-mediated mitogenic signaling. Our findings also indicate that LPA as well as Gα(12)-mediated upregulation of Skp2 requires a yet to be characterized mechanism involving JNK. Since Skp2 has been identified as an oncogene, and it is overexpressed in many cancers, our results presented here describe for the first time that Skp2 is a novel target in the cell cycle machinery through which Gα(12) and its cognate receptors transmit their oncogenic signals.

AMPKα2 deletion exacerbates neointima formation by upregulating Skp2 in vascular smooth muscle cells

RATIONALE

Adenosine monophosphate-activated protein kinase (AMPK), a metabolic and redox sensor, is reported to suppress cell proliferation of nonmalignant and tumor cells. Whether AMPKα alters vascular neointima formation induced by vascular injury is unknown.

OBJECTIVE

The aim of this study was to determine the roles of AMPKα in the development of vascular neointima hyperplasia and to elucidate the underlying mechanisms.

METHODS AND RESULTS

Vascular smooth muscle cell (VSMC) proliferation and neointimal hyperplasia were evaluated in cultured VSMCs and wire-injured mouse carotid arteries from wild-type (WT, C57BL/6J), AMPKα2(-/-), and AMPKα1(-/-) mice. Mouse VSMCs derived from aortas of AMPKα2(-/-) mice exhibited increased proliferation compared with either WT or AMPKα1(-/-) VSMCs. Further, deletion of AMPKα2 but not AMPKα1 reduced the level of p27(Kip1), a cyclin-dependent kinase inhibitor, and increased the level of S-phase kinase-associated protein 2 (Skp2), a known E3 ubiquitin ligase for p27(Kip1), through activation of p52 nuclear factor kappa B (NF-κB)-2. Moreover, either pharmacological (ie, through compound C) or genetical (ie, through AMPKα2-specific siRNA) inhibition of AMPK decreased p27(Kip1) levels but increased the abundance of Skp2 in human VSMCs. Furthermore, gene silencing of Skp2 reversed the levels of p27(Kip1) and VSMCs proliferation. Finally, neointima formation after mechanical arterial injury was increased in AMPKα2(-/-) but not AMPKα1(-/-) mice.

CONCLUSIONS

These findings indicate that deletion of AMPKα2 through p52-Skp2-mediated ubiquitination and degradation of p27(Kip1) accentuates neointimal hyperplasia in response to wire injury.

Inhibitors of Src and focal adhesion kinase promote endocrine specification: impact on the derivation of β-cells from human pluripotent stem cells

Stepwise approaches for the derivation of β-cells from human embryonic stem cells have been described. However, low levels of endocrine specification limit the final yield of insulin-producing β-cells. In this study, we show that the pyrrolo-pyrimidine Src family kinase (SFK) inhibitor PP2 effectively promotes the endocrine specification of human embryonic stem cell derivatives based on its capacity to induce the expression of proendocrine transcription factors (NGN3, NEUROD1, NKX2.2, and PAX4) and to significantly increase the final yield of insulin-positive cells. We further demonstrate that PP2 inhibits the activation of focal adhesion kinase (FAK), and selective inhibition of this kinase is also sufficient to induce early endocrine commitment based on increased expression of NGN3, NEUROD1, and NKX2.2. Additional studies using dominant negative constructs and isolated human fetal pancreata suggest that c-Src is at least partially responsible for inhibiting early endocrine specification. Mechanistically, we propose that inhibition of SFK/FAK signaling can promote endocrine specification by limiting activation of the TGFβR/Smad2/3 pathway. Moreover, we show that inhibition of SFK/FAK signaling suppresses cell growth, increases the expression of the β-cell-associated cyclin-dependent kinase inhibitor p57kip2, and simultaneously suppresses the expression of Id1 and Id2. This study has important implications for the derivation of β-cells for the cell-based therapy of diabetes and sheds new light on the signaling events that regulate early endocrine specification.

MicroRNA-24 regulates vascularity after myocardial infarction

BACKGROUND

Myocardial infarction leads to cardiac remodeling and development of heart failure. Insufficient myocardial capillary density after myocardial infarction has been identified as a critical event in this process, although the underlying mechanisms of cardiac angiogenesis are mechanistically not well understood.

METHODS AND RESULTS

Here, we show that the small noncoding RNA microRNA-24 (miR-24) is enriched in cardiac endothelial cells and considerably upregulated after cardiac ischemia. MiR-24 induces endothelial cell apoptosis, abolishes endothelial capillary network formation on Matrigel, and inhibits cell sprouting from endothelial spheroids. These effects are mediated through targeting of the endothelium-enriched transcription factor GATA2 and the p21-activated kinase PAK4, which were identified by bioinformatic predictions and validated by luciferase gene reporter assays. Respective downstream signaling cascades involving phosphorylated BAD (Bcl-XL/Bcl-2-associated death promoter) and Sirtuin1 were identified by transcriptome, protein arrays, and chromatin immunoprecipitation analyses. Overexpression of miR-24 or silencing of its targets significantly impaired angiogenesis in zebrafish embryos. Blocking of endothelial miR-24 limited myocardial infarct size of mice via prevention of endothelial apoptosis and enhancement of vascularity, which led to preserved cardiac function and survival.

CONCLUSIONS

Our findings indicate that miR-24 acts as a critical regulator of endothelial cell apoptosis and angiogenesis and is suitable for therapeutic intervention in the setting of ischemic heart disease.

High intracellular iron oxide nanoparticle concentrations affect cellular cytoskeleton and focal adhesion kinase-mediated signaling

Iron oxide nanoparticle internalization exerts detrimental effects on cell physiology for a variety of particles, but little is known about the mechanism involved. The effects of high intracellular levels of four types of iron oxide particles (Resovist, Endorem, very small organic particles, and magnetoliposomes (MLs)) on the viability and physiology of murine C17.2 neural progenitor cells and human blood outgrowth endothelial cells are reported. The particles diminish cellular proliferation and affect the actin cytoskeleton and microtubule network architectures as well as focal adhesion formation and maturation. The extent of the effects correlates with the intracellular concentration (= iron mass) of the particles, with the biggest effects for Resovist and MLs at the highest concentration (1000 microg Fe mL(-1)). Similarly, the expression of focal adhesion kinase (FAK) and the amount of activated kinase (pY397-FAK) are affected. The data suggest that high levels of perinuclear localized iron oxide nanoparticles diminish the efficiency of protein expression and sterically hinder the mature actin fibers, and could have detrimental effects on cell migration and differentiation.

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.

FAK mediates the activation of cardiac fibroblasts induced by mechanical stress through regulation of the mTOR complex

AIMS

Cardiac fibroblasts are activated by mechanical stress, but the underlying mechanisms involved remain poorly understood. In this study, we investigated whether focal adhesion kinase (FAK) plays a role in the activation of cardiac fibroblasts in response to cyclic stretch.

METHODS AND RESULTS

Neonatal (NF-P3/80--third passage, 80% confluence) and adult (AF-P1/80--first passage, 80% confluence) rat cardiac fibroblasts were exposed to cyclic stretch (biaxial, 1 Hz), which enhanced FAK phosphorylation at Tyr397. Proliferation (anti-5-bromo-2'-deoxyuridine and anti-Ki67 nuclear labelling), differentiation into myofibroblasts (expression of alpha-smooth muscle actin--alpha-SMA), and the activity of matrix metalloproteinase-2 were equally enhanced in stretched NF-P3/80 and AF-P1/80. Treatment with the integrin inhibitor RGD peptide impaired FAK phosphorylation and increased apoptosis (TUNEL) in non-stretched and stretched NF-P3/80, whereas FAK silencing induced by small interfering RNA modestly enhanced apoptosis only in stretched cells. RGD peptide or FAK silencing suppressed the activation of NF-P3/80 invoked by cyclic stretch. In addition, NF-P3/80 depleted of FAK were defective in AKT Ser473, TSC-2 Thr1462, and S6 kinase Thr389 phosphorylation induced by cyclic stretch. The activation of NF-P3/80 invoked by cyclic stretch was prevented by pre-treatment with the mammalian target of rapamycin (mTOR) inhibitor rapamycin, whereas supplementation with the amino acid, leucine, activated S6K and rescued the stretch-induced activation of NF-P3/80 depleted of FAK.

CONCLUSIONS

These findings demonstrate a critical role for the mTOR complex, downstream from FAK, in mediating the activation of cardiac fibroblasts in response to mechanical stress.

Targeting fibroblast activation protein inhibits tumor stromagenesis and growth in mice

Membrane-bound proteases have recently emerged as critical mediators of tumorigenesis, angiogenesis, and metastasis. However, the mechanisms by which they regulate these processes remain unknown. As the cell surface serine protease fibroblast activation protein (FAP) is selectively expressed on tumor-associated fibroblasts and pericytes in epithelial tumors, we set out to investigate the role of FAP in mouse models of epithelial-derived solid tumors. In this study, we demonstrate that genetic deletion and pharmacologic inhibition of FAP inhibited tumor growth in both an endogenous mouse model of lung cancer driven by the K-rasG12D mutant and a mouse model of colon cancer, in which CT26 mouse colon cancer cells were transplanted into immune competent syngeneic mice. Interestingly, growth of only the K-rasG12D-driven lung tumors was also attenuated by inhibition of the closely related protease dipeptidyl peptidase IV (DPPIV). Our results indicate that FAP depletion inhibits tumor cell proliferation indirectly, increases accumulation of collagen, decreases myofibroblast content, and decreases blood vessel density in tumors. These data provide proof of principle that targeting stromal cell-mediated modifications of the tumor microenvironment may be an effective approach to treating epithelial-derived solid tumors.

Loss of anchorage in checkpoint-deficient cells increases genomic instability and promotes oncogenic transformation

Mammalian cells generally require both mitogens and anchorage signals in order to proliferate. An important characteristic of many tumour cells is that they have lost this anchorage-dependent cell-cycle checkpoint, allowing them to proliferate without signals provided by their normal microenvironment. In the absence of anchorage signals from the extracellular matrix, many cell types arrest cell-cycle progression in G1 phase as a result of Rb-dependent checkpoints. However, despite inactivation of p53 and Rb proteins, SV40LT-expressing cells retain anchorage dependency, suggesting the presence of an uncharacterised cell-cycle checkpoint, which can be overridden by coexpression of oncogenic Ras. We report here that, although cyclin-CDK complexes persisted in suspension, proliferation was inhibited in LT-expressing cells by the CDK inhibitor p27(Kip1) (p27). Interestingly, this did not induce a stable arrest, but aberrant cell-cycle progression associated with stalled DNA replication, rereplication and chromosomal instability, which was sufficient to increase the frequency of oncogenic transformation. These results firstly indicate loss of anchorage in Rb- and p53-deficient cells as a novel mechanism for promotion of genomic instability; secondly suggest that anchorage checkpoints that protect normal cells from inappropriate proliferation act deleteriously in Rb- and p53-deficient cells to promote tumourigenesis; and thirdly indicate caution in the use of CDK inhibitors for cancer treatment.

Signal transduction by focal adhesion kinase in cancer

Cellular interactions with extracellular matrix play essential roles in tumor initiation, progression and metastasis. Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase identified as a key mediator of signaling by integrins, a major family of cell surface receptors for extracellular matrix, as well as other receptors in both normal and cancer cells. FAK is activated by integrins through disruption of an auto-inhibitory intra-molecular interaction between its kinase domain and the amino terminal FERM domain. The activated FAK forms a binary complex with Src family kinases which can phosphorylate other substrates and trigger multiple intracellular signaling pathways to regulate various cellular functions. Subcellular localization of FAK in focal adhesions is essential for FAK signaling, which is another distinguishing feature of the kinase. Integrin-FAK signaling has been shown to activate a number of signaling pathways through phosphorylation and protein-protein interactions to promote tumorigenesis. FAK also plays a prominent role in tumor progression and metastasis through its regulation of both cancer cells and their microenvironments including cancer cell migration, invasion, epithelial to mesenchymal transition, and angiogenesis. More recently, a role for FAK in tumor initiation and progression has been demonstrated directly using xenograft as well as conditional knockout mouse models. In agreement with these experimental data, overexpression and activation of FAK have been found in a variety of human cancers. A number of small molecule inhibitors for FAK have been developed and in various phases of testing for cancer treatments. Overall, the intensive research on FAK signaling in cancer have yielded a wealth of information on this pivotal kinase and these and future studies are leading to potentially novel therapies for cancer.

Mechanical stretch decreases FAK phosphorylation and reduces cell migration through loss of JIP3-induced JNK phosphorylation in airway epithelial cells

JNK is a nonreceptor kinase involved in the early events that signal cell migration after injury. However, the linkage to early signals required to initiate the migration response to JNK has not been defined in airway epithelial cells, which exist in an environment subjected to cyclic mechanical strain (MS). The present studies demonstrate that the JNK/stress-activated protein kinase-associated protein 1 (JSAP1; also termed JNK-interacting protein 3, JIP3), a scaffold factor for MAPK cascades that links JNK activation to focal adhesion kinase (FAK), are both associated and activated following mechanical injury in 16HBE14o- human airway epithelial cells and that both FAK and JIP3 phosphorylation seen after injury are decreased in cells subjected to cyclic MS. Overexpression of either wild-type (WT)-FAK or WT-JIP3 enhanced phosphorylation and kinase activation of JNK and reduced the inhibitory effect of cyclic MS. These results suggest that cyclic MS impairs signaling of cell migration after injury via a pathway that involves FAK-JIP3-JNK.

Overexpression of catalase delays G0/G1- to S-phase transition during cell cycle progression in mouse aortic endothelial cells

Although it is understood that hydrogen peroxide (H(2)O(2)) promotes cellular proliferation, little is known about its role in endothelial cell cycle progression. To assess the regulatory role of endogenously produced H(2)O(2) in cell cycle progression, we studied the cell cycle progression in mouse aortic endothelial cells (MAECs) obtained from mice overexpressing a human catalase transgene (hCatTg), which destroys H(2)O(2). The hCatTg MAECs displayed a prolonged doubling time compared to wild-type controls (44.0 +/- 4.7 h versus 28.6 +/- 0.8 h, p<0.05), consistent with a diminished growth rate and H(2)O(2) release. Incubation with aminotriazole, a catalase inhibitor, prevented the observed diminished growth rate in hCatTg MAECs. Inhibition of catalase activity with aminotriazole abrogated catalase overexpression-induced antiproliferative action. Flow cytometry analysis indicated that the prolonged doubling time was principally due to an extended G(0)/G(1) phase in hCatTg MAECs compared to the wild-type cells (25.0 +/- 0.9 h versus 15.9 +/- 1.4 h, p< 0.05). The hCatTg MAECs also exhibited decreased activities of the cyclin-dependent kinase (Cdk) complexes responsible for G(0)/G(1)- to S-phase transition in the cell cycle, including the cyclin D-Cdk4 and cyclin E-Cdk2 complexes. Moreover, the reduction in cyclin-Cdk activities in hCatTg MAECs was accompanied by increased protein levels of two Cdk inhibitors, p21 and p27, which inhibit the Cdk activity required for the G(0)/G(1)- to S-phase transition. Knockdown of p21 and/or p27 attenuated the antiproliferative effect of catalase overexpression in MAECs. These results, together with the fact that catalase is an H(2)O(2) scavenger, suggest that endogenously produced H(2)O(2) mediates MAEC proliferation by fostering the transition from G(0)/G(1) to S phase.

Adenovirus-mediated delivery of p27(KIP1) to prevent wound healing after experimental glaucoma filtration surgery

AIM

The aim of the study was to evaluate the outcome of adenovirus-mediated p27(KIP1) (Ad-p27) expression on wound healing after filtration surgery and to investigate the inhibition of cell proliferation induced by Ad-p27.

METHODS

We constructed the adenovirus recombinant vector Ad-p27 and administered it to a rabbit model of glaucoma filtration surgery by subconjunctival injection; phosphate-buffered saline (PBS) and mitomycin C (MMC) were used as controls. Intraocular pressure (IOP), bleb scores, and anterior chamber depths were observed during a 28-d period. Histological examinations, fluorescence observations and Western blot analyses were evaluated.

RESULTS

Ad-p27 enhanced the surgical outcome and inhibited cell proliferation when compared with PBS. Bleb scores in the Ad-p27-treated eyes were higher than those in the PBS-treated eyes on d 7 (P<0.01), 14 (P<0.01) and 21 (P<0.05). On d 28, IOP remained significantly decreased in the Ad-p27 group compared with the PBS group (P<0.05). However, no differences in bleb scores or IOPs were observed between the Ad-p27 and MMC groups. Histological analysis showed that total cell numbers were markedly reduced, and less scar tissue was observed at the surgical site in eyes treated with Ad-p27. The number of fibroblasts was decreased in Tenon's capsule in Ad-p27-treated eyes; however, a marked and diffuse signal from the green fluorescent protein (GFP) was observed in fibroblasts. Western blot analysis revealed a high level of p27(KIP1) expression in conjunctival epithelium (P<0.01), relatively high expression in superficial scleral stroma (P<0.01), and low expression in corneal epithelium in the Ad-p27 group.

CONCLUSIONS

Ad-p27 administration significantly improves the outcome of filtration surgery and inhibits postoperative proliferation in rabbit eyes. These findings suggest that p27(KIP1) is a potential adjunctive agent for inhibition of wound healing after filtration surgery.

The neurofibromatosis 2 protein, merlin, regulates glial cell growth in an ErbB2- and Src-dependent manner

Individuals with the inherited cancer predisposition syndrome neurofibromatosis 2 (NF2) develop several central nervous system (CNS) malignancies, including glial cell neoplasms (ependymomas). Recent studies have suggested that the NF2 protein, merlin (or schwannomin), may regulate receptor tyrosine kinase signaling, intracellular mitogenic growth control pathways, or adherens junction organization in non-nervous-system cell types. For this report, we used glial fibrillary acidic protein conditional knockout mice and derivative glia to determine how merlin regulates CNS glial cell proliferation. We show that the loss of merlin in glial cells results in increased proliferation in vitro and in vivo. Merlin regulation of glial cell growth reflects deregulated Src activity, such that pharmacologic or genetic inhibition of Src activation reduces Nf2(-/-) glial cell growth to wild-type levels. We further show that Src regulates Nf2(-/-) glial cell growth by sequentially regulating FAK and paxillin phosphorylation/activity. Next, we demonstrate that Src activation results from merlin regulation of ErbB2 activation and that genetic or pharmacologic ErbB2 inhibition reduces Nf2(-/-) glial cell Src/Src effector activation and proliferation to wild-type levels. Lastly, we show that merlin competes with Src for direct binding to ErbB2 and present a novel molecular mechanism for merlin regulation of ErbB2-dependent Src signaling and growth control.

Nidus vespae protein inhibiting proliferation of HepG2 hepatoma cells through extracellular signal-regulated kinase signaling pathways and inducing G1 cell cycle arrest

A protein named NVP(1) was isolated from Nidus vespae. The aim of the present study was to elucidate whether and how NVP(1) modulates the proliferation of HepG2 cells. NVP(1) at a concentration of 6.6 microg/ml could arrest the cell cycle at stage G1 and inhibit the mRNA expression of cyclinB, cyclinD1 and cyclinE. NVP(1) suppressed cdk2 protein expression, but increased p27 and p21 protein expression. However, NVP(1) did not alter p16 protein expression levels. NVP(1) promoted apoptosis in HepG2 cells as indicated by nuclear chromatin condensation, and in addition, the extracellular signal-regulated kinase (ERK) signaling pathway was activated. Moreover, the p-ERK protein expression level was attenuated when the HepG2 cells were pretreated with ERK inhibitor PD98059. These results demonstrate that NVP(1) inhibits proliferation of HepG2 through ERK signaling pathway. NVP(1) could be a potential drug for liver cancer.