Cytoskeleton reorganization induces the urokinase-type plasminogen activator gene via the Ras/extracellular signal-regulated kinase (ERK) signaling pathway

Moscatilin Inhibits Metastatic Behavior of Human Hepatocellular Carcinoma Cells: A Crucial Role of uPA Suppression via Akt/NF-κB-Dependent Pathway

Hepatocellular carcinoma (HCC) frequently shows early invasion into blood vessels as well as intrahepatic metastasis. Innovations of novel small-molecule agents to block HCC invasion and subsequent metastasis are urgently needed. Moscatilin is a bibenzyl derivative extracted from the stems of a traditional Chinese medicine, orchid Dendrobium loddigesii. Although moscatilin has been reported to suppress tumor angiogenesis and growth, the anti-metastatic property of moscatilin has not been elucidated. The present results revealed that moscatilin inhibited metastatic behavior of HCC cells without cytotoxic fashion in highly invasive human HCC cell lines. Furthermore, moscatilin significantly suppressed the activity of urokinase plasminogen activator (uPA), but not matrix metalloproteinase (MMP)-2 and MMP-9. Interestingly, moscatilin-suppressed uPA activity was through down-regulation the protein level of uPA, and did not impair the uPA receptor and uPA inhibitory molecule (PAI-1) expressions. Meanwhile, the mRNA expression of uPA was inhibited via moscatilin in a concentration-dependent manner. In addition, the expression of phosphorylated Akt, rather than ERK1/2, was inhibited by moscatilin treatment. The expression of phosphor-IκBα, and -p65, as well as κB-luciferase activity were also repressed after moscatilin treatment. Transfection of constitutively active Akt (Myr-Akt) obviously restored the moscatilin-inhibited the activation of NF-κB and uPA, and cancer invasion in HCC cells. Taken together, these results suggest that moscatilin impedes HCC invasion and uPA expression through the Akt/NF-κB signaling pathway. Moscatilin might serve as a potential anti-metastatic agent against the disease progression of human HCC.

Involvement of the C-terminal domain in cell surface localization and G-protein coupling of mGluR6

Metabotropic glutamate receptor 6, mGluR6, interacts with scaffold proteins and Gβγ subunits via its intracellular C-terminal domain (CTD). The mGluR6 pathway is critically involved in the retinal processing of visual signals. We herein investigated whether the CTD (residues 840-871) was necessary for mGluR6 cell surface localization and G-protein coupling using mGluR6-CTD mutants with immunocytochemistry, surface biotinylation assays, and electrophysiological approaches. We used 293T cells and primary hippocampal neurons as model systems. We examined C-terminally truncated mGluR6 and showed that the removal of up to residue 858 did not affect surface localization or glutamate-induced G-protein-mediated responses, whereas a 15-amino acid deletion (Δ857-871) impaired these functions. However, a 21-amino acid deletion (Δ851-871) restored surface localization and glutamate-dependent responses, which were again attenuated when the entire CTD was removed. The sequence alignment of group III mGluRs showed conserved amino acids resembling an ER retention motif in the CTD. These results suggest that the intracellular CTD is required for the cell surface transportation and receptor function of mGluR6, whereas it may contain regulatory elements for intracellular trafficking and signaling.

Enhanced wound healing of tissue-engineered human corneas through altered phosphorylation of the CREB and AKT signal transduction pathways

The cornea is a transparent organ, highly specialized and unique that is continually subjected to abrasive forces and occasional mechanical or chemical trauma because of its anatomical localization. Upon injury, the extracellular matrix (ECM) rapidly changes to promote wound healing through integrin-dependent activation of specific signal transduction mediators whose contribution is to favor faster closure of the wound by altering the adhesive and migratory properties of the cells surrounding the damaged area. In this study, we exploited the human tissue-engineered cornea (hTECs) as a model to study the signal transduction pathways that participate to corneal wound healing. By exploiting both gene profiling and activated kinases arrays, we could demonstrate the occurrence of important alterations in the level of expression and activation of a few mediators from the PI3K/Akt and CREB pathways in response to the ECM remodeling taking place during wound healing of damaged hTECs. Pharmacological inhibition of CREB with C646 considerably accelerated wound closure compared to controls. This process was considerably accelerated further when both C646 and SC79, an Akt agonist, were added together to wounded hTECs. Therefore, our study demonstrate that proper corneal wound healing requires the activation of Akt together with the inhibition of CREB and that wound healing in vitro can be altered by the use of pharmacological inhibitors (such as C646) or agonists (such as SC79) of these mediators.

STATEMENT OF SIGNIFICANCE

Corneal wounds account for a large proportion of all visual disabilities in North America. To our knowledge, this is the first time that a tissue-engineered human cornea (hTEC) entirely produced using normal untransformed human cells is used as a biomaterial to study the signal transduction pathways that are critical to corneal wound healing. Through the use of this biomaterial, we demonstrated that human corneal epithelial cells engaged in wound healing reduce phosphorylation of the signal transduction mediator CREB while, in the mean time, they increase that of AKT. By increasing the activation of AKT together with a decrease in CREB activation, we could considerably reduce wound closure time in our punch-damaged hTECs. Considering the increasing interest given to the reconstruction of different types of tissues, we believe these results will have a strong impact on the field of tissue-engineering and biomaterials. Altering the activation status of the Akt and CREB proteins might prove to be a therapeutically interesting avenue and may also find applications in wound healing of other tissues beside the cornea, such as the skin.

Identity, proliferation capacity, genomic stability and novel senescence markers of mesenchymal stem cells isolated from low volume of human bone marrow

Human bone marrow mesenchymal stem cells (hBM-MSCs) hold promise for treating incurable diseases and repairing of damaged tissues. However, hBM-MSCs face the disadvantages of painful invasive isolation and limited cell numbers. In this study we assessed characteristics of MSCs isolated from residual human bone marrow transplantation material and expanded to clinically relevant numbers at passages 3-4 and 6-7. Results indicated that early passage hBM-MSCs are genomically stable and retain identity and high proliferation capacity. Despite the chromosomal stability, the cells became senescent at late passages, paralleling the slower proliferation, altered morphology and immunophenotype. By qRT-PCR array profiling, we revealed 13 genes and 33 miRNAs significantly differentially expressed in late passage cells, among which 8 genes and 30 miRNAs emerged as potential novel biomarkers of hBM-MSC aging. Functional analysis of genes with altered expression showed strong association with biological processes causing cellular senescence. Altogether, this study revives hBM as convenient source for cellular therapy. Potential novel markers provide new details for better understanding the hBM-MSC senescence mechanisms, contributing to basic science, facilitating the development of cellular therapy quality control, and providing new clues for human disease processes since senescence phenotype of the hematological patient hBM-MSCs only very recently has been revealed.

Vasodilator-Stimulated Phosphoprotein (VASP) depletion from breast cancer MDA-MB-231 cells inhibits tumor spheroid invasion through downregulation of Migfilin, β-catenin and urokinase-plasminogen activator (uPA)

A hallmark of cancer cells is their ability to invade surrounding tissues and form metastases. Cell-extracellular matrix (ECM)-adhesion proteins are crucial in metastasis, connecting tumor ECM with actin cytoskeleton thus enabling cells to respond to mechanical cues. Vasodilator-stimulated phosphoprotein (VASP) is an actin-polymerization regulator which interacts with cell-ECM adhesion protein Migfilin, and regulates cell migration. We compared VASP expression in MCF-7 and MDA-MB-231 breast cancer (BC) cells and found that more invasive MDA-MB-231 cells overexpress VASP. We then utilized a 3-dimensional (3D) approach to study metastasis in MDA-MB-231 cells using a system that considers mechanical forces exerted by the ECM. We prepared 3D collagen I gels of increasing concentration, imaged them by atomic force microscopy, and used them to either embed cells or tumor spheroids, in the presence or absence of VASP. We show, for the first time, that VASP silencing downregulated Migfilin, β-catenin and urokinase plasminogen activator both in 2D and 3D, suggesting a matrix-independent mechanism. Tumor spheroids lacking VASP demonstrated impaired invasion, indicating VASP's involvement in metastasis, which was corroborated by Kaplan-Meier plotter showing high VASP expression to be associated with poor remission-free survival in lymph node-positive BC patients. Hence, VASP may be a novel BC metastasis biomarker.

Underlying Mechanisms for Distant Metastasis - Molecular Biology

BACKGROUND

The formation of distant metastases constitutes a complex process with a variety of different genes and pathways involved. To improve patient survival, it is necessary to understand the underlying mechanisms of metastasis to allow for targeted intervention.

METHODS

This review provides an overview of the general concepts of metastasis, focusing on the most important genes and pathways involved and on interventional strategies.

RESULTS

Cancer cells undergo different steps to form metastasis: most prominently, local invasion, intravasation, survival in the circulation, arrest at a distant organ site and extravasation, micrometastasis formation, and metastatic colonization. In order to pass these steps, different molecular pathways are of major importance: EGF/RAS/RAF/MEK/ERK, PI3K/Akt/mTOR, HGF/Met, Wnt/β-catenin, and VEGF signaling. The HGF/Met regulator MACC1 and the Wnt signaling target S100A4 have been shown to play a major role in the metastatic process. Each gene and pathway provides an opportunity for therapeutic intervention.

CONCLUSION

Since metastasis represents a highly limiting factor in cancer therapy causing 90% of cancer deaths, it is imperative to reveal the underlying mechanisms. This is fundamental for uncovering prognostic markers and new targeted therapy options.

Transcriptional complexity and roles of Fra-1/AP-1 at the uPA/Plau locus in aggressive breast cancer

Plau codes for the urokinase-type plasminogen activator (uPA), critical in cancer metastasis. While the mechanisms driving its overexpression in tumorigenic processes are unknown, it is regulated by the AP-1 transcriptional complex in diverse situations. The AP-1 component Fra-1 being overexpressed in aggressive breast cancers, we have addressed its role in the overexpression of Plau in the highly metastatic breast cancer model cell line MDA-MB231 using ChIP, pharmacological and RNAi approaches. Plau transcription appears controlled by 2 AP-1 enhancers located -1.9 (ABR-1.9) and -4.1 kb (ABR-4.1) upstream of the transcription start site (TSS) of the uPA-coding mRNA, Plau-001, that bind Fra-1. Surprisingly, RNA Pol II is not recruited only at the Plau-001 TSS but also upstream in the ABR-1.9 and ABR-4.1 region. Most Pol II molecules transcribe short and unstable RNAs while tracking down toward the TSS, where there are converted into Plau-001 mRNA-productive species. Moreover, a minority of Pol II molecules transcribes a low abundance mRNA of unknown function called Plau-004 from the ABR-1.9 domain, whose expression is tempered by Fra-1. Thus, we unveil a heretofore-unsuspected transcriptional complexity at Plau in a reference metastatic breast cancer cell line with pleiotropic effects for Fra-1, providing novel information on AP-1 transcriptional action.

Microtubule stabilization attenuates vascular calcification through the inhibition of osteogenic signaling and matrix vesicle release

Vascular calcification is a strong predictor of cardiovascular morbidity and mortality, especially in individuals with chronic kidney disease or diabetes. The mechanism of vascular calcification has remained unclear, however, and no effective therapy is currently available. Our study was aimed at identifying the role of dynamic remodeling of microtubule cytoskeletons in hyperphosphatemia-induced vascular calcification. Exposure of primary cultures of mouse vascular smooth muscle cells (VSMCs) to inorganic phosphate (Pi) elicited ectopic calcification that was associated with changes in tubulin dynamics, induction of osteogenic signaling, and increased release of matrix vesicles. A microtubule depolymerizing agent enhanced Pi-dependent calcification, whereas microtubule stabilization by paclitaxel suppressed calcification both in VSMC cultures and in an ex vivo culture system for the mouse aorta. The inhibition of Pi-stimulated calcification by paclitaxel was associated with down-regulation of osteogenic signal and attenuation of matrix vesicle release. Our results indicate that microtubule plays a central role in vascular calcification, and that microtubule stabilization represents a potential new approach to the treatment of this condition.

The mechanism of neurogenic pulmonary edema in epilepsy

Neurogenic pulmonary edema (NPE) is found in many epilepsy patients at autopsy. It is a life-threatening complication, known for almost 100 years, but its etiopathogenesis is still not completely understood. In this study, we used the tremor rat (TRM: tm/tm) as an animal model of epilepsy to investigate the potential mechanisms of NPE under epileptic conditions. We performed reverse-phase high-pressure liquid chromatography assay, H&E and Masson staining, TUNEL assay, and Western blot experiments to determine the role of seizures in NPE. We found the level of catecholamine was higher in TRM rats. Also the occurrence of alveolar cell apoptosis was increased. Moreover, pulmonary vascular remodeling including the deposition of collagen and medial thickening was also found in TRM rats. Further study showed that cell apoptosis was mediated by increasing Bax, decreasing Bcl-2, and activating caspase-3. In addition, the protein level of phosphorylated ERK (p-ERK) was found to be decreased while phosphorylated JNK and phosphorylated p38 were upregulated in TRM rats. Thus, these findings suggest that pulmonary vascular remodeling and alveolar cell apoptosis might be involved in epilepsy-induced NPE and that the mitogen-activated protein kinase signal pathway was involved.

Dasatinib inhibits primary melanoma cell proliferation through morphology-dependent disruption of Src-ERK signaling

New strategies for the treatment of advanced melanoma are urgently required. The RAS/RAF/MAPK pathway and c-Src are deregulated in the majority of malignant melanomas, suggesting that they may interact functionally and are involved in the development and progression of the malignancy. Preclinical studies have demonstrated variable inhibition of melanoma cell growth by dasatinib in vitro. Src may act through different downstream signaling pathways. In the present study, we demonstrate that dasatinib induces changes in cell morphology, characterized by an arborized and contracted appearance, and accompanied by a reduction in cell proliferation in primary melanoma cells. This morphological change is demonstrated to be associated with the inhibition of nuclear translocation of activated ERK1/2. Together, these results indicate that Src may promote cell proliferation through the activation of the ERK signaling pathway in melanoma oncogenesis.

Fibrinolytic activation promoted by the cyclopentapeptide malformin: involvement of cytoskeletal reorganization

Malformin A₁, a cyclopentapeptide of fungal origin, enhances cellular fibrinolytic activity depending on the existence of a cofactor in blood plasma. However, the nature of this cofactor remains unknown. Here, we report that vitronectin acts as a plasma cofactor of malformin A₁. We purified the cofactor from bovine plasma by activity-based fractionation, and confirmed that vitronectin in conjunction with plasminogen supports the activity of malformin A₁ to promote the fibrinolytic activity of U937 cells. Malformin A₁ action was abolished by Arg-Gly-Asp peptide (a competitor of vitronectin-integrin binding), wortmannin (an inhibitor of signaling kinases), and cytochalasin B (an inhibitor of actin polymerization). Changes in actin organization and a decrease in filopodia were observed in cells treated with malformin A₁ and plasma. A focal localization of plasminogen on the cell surface was augmented by malformin A₁, whereas the amount of cell-surface-bound plasminogen was minimally altered by the treatment. Our results suggest the involvement of cytoskeletal reorganization via vitronectin signaling in the cellular fibrinolytic activity-enhancing action of malformin A₁.

Actin cytoskeleton modulates ADMA-induced NF-kappaB nuclear translocation and ICAM-1 expression in endothelial cells

BACKGROUND

Asymmetric dimethylarginine (ADMA), an endogenous nitric oxide synthase (NOS) inhibitor, increases the activity of NF-κB (NF-κB) and then induces the expression of intercellular adhesion molecule-1 (ICAM-1). However, the mechanisms regulating ADMA-induced NF-κB activation are unknown. This study investigated the function of actin cytoskeleton for ADMA-induced NF-κB activation and ICAM-1 expression in endothelial cells.

MATERIAL/METHODS

Human umbilical vein endothelial cells (HUVEC) were cultured and left untreated or challenged for 24 h with 100 µM ADMA in the absence and presence of 5 µM cytochalasin D (Cyt D), or 1 µM Jasplakinolide (Jas). The form of actin cytoskeleton, the translocation of NF-κB, NF-κB DNA binding activity, and the expression of ICAM-1 were determined.

RESULTS

ADMA increased the formation of stress fiber in endothelial cells, and Cyt D clearly induced destabilization of the actin filaments. Either stabilizing or destabilizing the actin cytoskeleton prevented ADMA-induced NF-κB activation. It also showed that the inhibition of NF-κB activity was due to the impaired NF-κB nuclear translocation. Further, stabilizing or destabilizing the actin cytoskeleton inhibited the expression of the NF-κB target protein, ICAM-1.

CONCLUSIONS

Actin cytoskeleton may be engaged in modulated ADMA-induced NF-κB activation and thereby ICAM-1 expression in endothelial cells.

Linking cell structure to gene regulation: signaling events and expression controls on the model genes PAI-1 and CTGF

The microtubule and microfilament cytoskeletal systems as well as cell-to-cell contacts and cell-matrix interactions are critical regulators of cell structure and function. Alterations in cell shape profoundly influence signaling events and gene expression programs that impact a spectrum of biological responses including cell growth, migration and apoptosis. These same pathways also contribute to the progression of several important pathologic conditions (e.g., arteriosclerosis, vascular fibrosis, and endothelial dysfunction). Indeed, hemodynamic forces in the vascular compartment are established modifiers of endothelial and smooth muscle cell cytoarchitecture and orchestrate complex genetic and biological responses in concert with contributions from the extracellular matrix (ECM), growth factors (e.g., EGF, and TGF-beta) and cell adhesion receptors (e.g., integrins, and cadherins). The profibrotic matricellular proteins plasminogen activator inhibitor-1 (PAI-1) and connective tissue growth factor (CTGF) are prominent members of a subset of genes the expression of which is highly responsive to cell shape-altering stimuli (i.e., disruption of the actin-based and microtubule networks, shear strain and cyclic stretch). Since both PAI-1 and CTGF are major mediators of cardiovascular fibrotic disease, understanding cell structure-linked signaling cascades provides potential avenues for focused therapy. It is increasingly evident that growth factor receptors (EGFR) are activated by changes in cytoarchitecture and that the "repressive state" of certain signaling proteins (e.g., SMAD, and Rho-GEFs) is maintained by sequestration on cell structural networks. Functional repression can be relieved by cytoskeletal perturbations (e.g., in response to treatment with network-specific drugs) resulting in activation of signaling cascades (e.g., Rho, and MAPK) with associated changes in gene reprogramming. Recent studies document a complex network of both similar and unique signaling control elements leading to the induction of PAI-1 and CTGF in response to modifications in cell shape. The purpose of this review is to highlight our current understanding of "cell deformation"-responsive signaling cascades focusing on the potential value of targeting such pathways, and their model response genes (e.g., PAI-1, and CTGF), as a therapeutic option for the treatment of fibrotic diseases.

Differential requirement for MEK/ERK and SMAD signaling in PAI-1 and CTGF expression in response to microtubule disruption

Colchicine and nocodazole, both established microtubule disruptors, are useful tools to investigate cytoskeletal-dependent signaling cascades and the associated downstream transcriptional targets. Since cytoskeletal events impact pathophysiologic consequences in the vascular system, the signaling requirements underlying colchicine-stimulated expression of PAI-1 and CTGF, two prominent cell deformation-sensitive fibrosis-initiating proteins, were evaluated in vascular smooth muscle cells. Microtubule disruption rapidly induced EGFR transactivation (at the src kinase-sensitive EGFR(Y845) site) in a ROS-dependent manner. Genetic deficiency of EGFR, inhibition of EGFR signaling with AG1478 or introduction of a kinase-deficient EGFR construct effectively blocked colchicine-stimulated PAI-1 and CTGF expression. MEK/ERK involvement downstream of ROS generation was critical for PAI-1, but not CTGF, expression following cytoskeletal perturbation suggesting bifurcation of signaling pathways downstream of EGFR activation. Colchicine also stimulated SMAD2/3 phosphorylation by a Rho/ROCK-dependent mechanism independent of TGF-beta1 release or receptor activity. Rho/ROCK signaling initiated by tubulin network collapse was required for both CTGF and PAI-1 induction. Colchicine-initiated SMAD3 phosphorylation, however, was essential for PAI-1, but not CTGF, expression further highlighting divergence of signaling events downstream of Rho/ROCK that mediate microtubule deformation-associated changes in profibrotic gene transcription.

Transient dynamic actin cytoskeletal change stimulates the osteoblastic differentiation

Dynamic cytoskeletal changes appear to be one of intracellular signals that control cell differentiation. To test this hypothesis, we examined the effects of short-term actin cytoskeletal changes on osteoblastic differentiation. We found an actin polymerization interfering reagent, cytochalasin D, promoted osteoblastic differentiation in mouse preosteoblastic MC3T3-E1 cells. We also found that these effects were mediated by the protein kinase D (PKD) pathway. Short-term cytochalasin D treatment increased alkaline phosphatase (ALP) activity, osteocalcin (OCN) secretion, and mineralization of the extracellular matrix in MC3T3-E1 cells, with temporary changes in actin cytoskeleton. Furthermore, the disruption of actin cytoskeleton induced phosphorylation of 744/748 serine within the activation loop of PKD in a dose-dependent manner. The protein kinase C (PKC)/PKD inhibitor Go6976 suppressed cytochalasin D-induced acceleration of osteoblastic differentiation, whereas Go6983, a specific inhibitor of conventional PKCs, did not. Involvement of PKD signaling was confirmed by using small interfering RNA to knock down PKD. In addition, another actin polymerization interfering reagent, latrunculin B, also stimulated ALP activity and OCN secretion with PKD activation. On the other hand, the present data suggested that transient dynamic actin cytoskeletal reorganization could be a novel cellular signal that directly stimulated osteoblastic differentiation.

Actin-targeting natural compounds as tools to study the role of actin cytoskeleton in signal transduction

Actin cytoskeleton controls a vast range of cellular processes such as motility, cytokinesis, differentiation, vesicle transport, phagocytosis, muscle contraction. A growing literature clearly demonstrated that actin cytoskeleton can play a regulating role in several signalling pathways. Cells tightly regulate actin dynamics through numerous specific proteins in order to rapidly and locally respond to various stimuli. An obvious approach to determine the involvement of actin cytoskeleton in signalling pathways is the use of actin-targeting natural compounds. These drugs modulate actin dynamics, accelerating either polymerization or depolymerization, through various mechanisms. This review focus on the use of these actin-targeting drugs as tools to demonstrate the role of actin cytoskeleton in several signal transduction pathways such as those initiated from antigen receptor in T and B cells or those involving mitogen-activated protein kinases (MAPKs) or transcription factors NF-kappaB and SRF (serum response factor). In this last case (SRF), the use of various actin-targeting drugs participated in the elucidation of the molecular mechanism by which actin regulates SRF-mediated transcription.

Formation of neurons by non-neural adult stem cells: potential mechanism implicates an artifact of growth in culture

Trans-differentiation is a mechanism proposed to explain how tissue-specific stem cells could generate cells of other organs, thus supporting the emerging concept of enhanced adult stem cell plasticity. Although spontaneous cell fusion rather than trans-differentiation may explain some unexpected cell fate changes in vivo, such a mechanism does not explain potential trans-differentiation events in vitro, including the generation of neural cell types from cultured bone marrow-derived stem cells. Here we present evidence that shows that cultured bone marrow-derived stem cells express neural proteins and form structures resembling neurons under defined growth conditions. We demonstrate that these changes in cell structure and neural protein expression are not consistent with typical neural development. Furthermore, the ability of bone marrow-derived stem cells to adopt a neural phenotype in vitro may occur as a result of cellular stress in response to removing cells from their niche and their growth in alternative environmental conditions. These findings suggest a potential explanation for the growth behavior of cultured bone marrow-derived stem cells and highlight the need to carefully validate the plasticity of stem cell differentiation.

Nitrofen suppresses cell proliferation and promotes mitochondria-mediated apoptosis in type II pneumocytes

AIM

To characterize the molecular mechanisms of nitrofen-induced pulmonary hypoplasia.

METHODS

After administration of nitrofen to cultured type II A549 pneumocytes, cell proliferation and DNA synthesis were investigated by 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide colorimetry, colony formation assay, flow cytometry and [3H]-thymidine incorporation assay. Apoptosis was measured by terminal transferase-mediated dUTP nick-end-labeling, acridine orange-ethidium bromide staining and flow cytometry. Expression of proliferating cell nuclear antigen (PCNA) and apoptosis-related genes was assayed by immunofluorescence, RT-PCR and Western blot.

RESULTS

Nitrofen inhibited the cell proliferation of A549 cells in a dose- and time-dependent manner, accompanied by downregulation of PCNA. As a result, the DNA synthesis of nitrofentreated A549 cells decreased, while cell cycle was arrested at G0/G1 phase. Moreover, nitrofen induced apoptosis of A549 cells, which was not abolished by Z-Val-Ala- Asp(OCH3)- fluoromethylketone. In addition, nitrofen decreased the expression of Bcl-x( L), but not of Bcl-2, Bax, and Bak, resulting in a loss of mitochondrial membrane potential and the nuclear translocation of apoptosis-inducing factor (AIF). Meanwhile, nitrofen strongly activated the p38 mitogen-activated protein kinase (p38-MAPK). Pretreatment of cells with SB203580 (5 micromol/L) blocked nitrofen-induced phosphorylation of p38-MAPK and abolished nitrofen-induced AIF translocation and apoptosis in A549 cells.

CONCLUSION

Nitrofen suppresses the proliferation of cultured type II pneumocytes accompanied by the downregulation of PCNA, and induces mitochondria-mediated apoptosis involving the activation of p38-MAPK.

Induction of uPA gene expression by the blockage of E-cadherin via Src- and Shc-dependent Erk signaling

Loss of E-cadherin-mediated cell-cell adhesion and expression of proteolytic enzymes characterize the transition from benign lesions to invasive, metastatic tumor, a rate-limiting step in the progression from adenoma to carcinoma in vivo. A soluble E-cadherin fragment found recently in the serum and urine of cancer patients has been shown to disrupt cell-cell adhesion and to drive cell invasion in a dominant-interfering manner. Physical disruption of cell-cell adhesion can be mimicked by the function-blocking antibody Decma. We have shown previously in MCF7 and T47D cells that urokinase-type plasminogen activator (uPA) activity is up-regulated upon disruption of E-cadherin-dependent cell-cell adhesion. We explored the underlying molecular mechanisms and found that blockage of E-cadherin by Decma elicits a signaling pathway downstream of E-cadherin that leads to Src-dependent Shc and extracellular regulated kinase (Erk) activation and results in uPAgene activation. siRNA-mediated knockdown of endogenous Src-homology collagen protein (Shc) and subsequent expression of single Shc isoforms revealed that p46(Shc) and p52(Shc) but not p66(Shc) were able to mediate Erk activation. A parallel pathway involving PI3K contributed partially to Decma-induced Erk activation. This report describes that disruption of E-cadherin-dependent cell-cell adhesion induces intracellular signaling with the potential to enhance tumorigenesis and, thus, offers new insights into the pathophysiological mechanisms of tumor development.

Cellular mechanisms of neuronal damage from hyperthermia

Hyperthermia can cause brain damage and also exacerbate the brain damage produced by stroke and amphetamines. The developing brain is especially sensitive to hyperthermia. The severity of, and mechanisms underlying, hyperthermia-induced neuronal death depend on both temperature and duration of exposure. Severe hyperthermia can produce necrotic neuronal death. For a window of less severe heat stresses, cultured neurons exhibit a delayed death with apoptotic characteristics including cytochrome c release and caspase activation. Little is known about mechanisms of hyperthermia-induced damage upstream of these late apoptotic effects. This chapter considers several possible upstream mechanisms, drawing on both in vivo and in vitro studies of the nervous system and other tissues. Hyperthermia-induced damage in some non-neuronal cells includes endoplasmic reticular stress due to denaturing of nascent polypeptide chains, as well as nuclear and cytoskeletal damage. Evidence is presented that hyperthermia produces mitochondrial damage, including depolarization, in cultured mammalian neurons.

Synthesis, regulation and production of urokinase using mammalian cell culture: a comprehensive review

Urokinase, a serine protease, catalyzes the conversion of plasminogen to plasmin, which is responsible for dissolution of clots in blood vessels. It is an important drug for treatment of thromboembolic disease. Production of urokinase by mammalian cell culture has the following important steps: synthesis, regulation and secretion. Production and accumulation of this product in a bioreactor is a real challenge for biochemical engineers. Considerable information at molecular level needs to be understood for production of urokinase in order to correlate different parameters, which in turn can maximize the productivity. This information will be highlighted in this review. Moreover, urokinase production is a product-inhibited process. Therefore, in situ urokinase separation strategy is required to operate a bioreactor at its maximum urokinase formation rate. Integrated urokinase production and isolation processes developed recently will also be discussed briefly in this review.

PAI-1 expression is required for epithelial cell migration in two distinct phases of in vitro wound repair

Several proteases and their specific inhibitors modulate the interdependent processes of cell migration and matrix proteolysis as part of the global program of trauma repair. Expression of plasminogen activator inhibitor type-1 (PAI-1), a serine protease inhibitor (SERPIN) important in the control of barrier proteolysis and cell-to-matrix adhesion, for example, is spatially-temporally regulated following epithelial denudation injury in vitro as well as in vivo. PAI-1 mRNA/protein synthesis was induced early after epidermal monolayer scraping and restricted to keratinocytes comprising the motile cohort closely recapitulating, thereby, similar events during cutaneous healing. The time course of PAI-1 promoter-driven PAI-1-GFP fusion "reporter" expression in wound-juxtaposed cells approximated that of the endogenous PAI-1 gene confirming the location-specificity of gene regulation in this model. ERK activation was evident within 5 min after injury and particularly prominent in cells residing at the scrape-edge (suggesting a possible role in PAI-1 induction and/or the motile response) as was myosin light chain (MLC) phosphorylation. Indeed, MEK blockade with PD98059 or U0126 attenuated keratinocyte migration (by > or =60%), as did transient transfection of a dominant-negative ERK1 construct (40% decrease in monolayer repair), and completely inhibited PAI-1 transcript expression. Anti-sense down-regulation of PAI-1 synthesis (by 80-85%), or addition of PAI-1 neutralizing antibodies also inhibited injury site closure over a 24 h period establishing that PAI-1 was required for efficient long-term planar motility in this system. PAI-1 anti-sense transfection or actinomycin D transcriptional blockade, in contrast, did not affect the initial migratory response suggesting that residual PAI-1 protein levels (at least in transfectant cells and actinomycin D-treated cultures) may be sufficient to support early cell movement. Pharmacologic inhibition of keratinocyte MEK signaling effectively ablated scrape-induced PAI-1 mRNA expression but failed to attenuate wound-associated increases in cellular PAI-1 protein levels soon after monolayer injury. Collectively, these data suggest that basal PAI-1 transcripts may be mobilized for initial PAI-1 synthesis and, perhaps, the early motile response while maintenance of the normal rate of migration requires the prolonged PAI-1 expression that typically accompanies the repair response. To assess this possibility, scrape site closure studies were designed using keratinocytes isolated from PAI-1-/- mice. PAI-1-/- keratinocytes, in fact, had a significant wound healing defect evident even within the first 6 h following monolayer denudation injury. Addition of active PAI-1 protein to PAI-/- keratinocytes rescued the migratory phenotype that that approximating wild-type cells. These findings validate use of the present keratinocyte model to investigate injury-related controls on PAI-1 gene regulation and, collectively, implicate participation of PAI-1 in two distinct phases of epidermal wound repair.

Mitogen-activated protein kinases in apoptosis regulation

Cells are continuously exposed to a variety of environmental stresses and have to decide 'to be or not to be' depending on the types and strength of stress. Among the many signaling pathways that respond to stress, mitogen-activated protein kinase (MAPK) family members are crucial for the maintenance of cells. Three subfamilies of MAPKs have been identified: extracellular signal-regulated kinases (ERKs), c-Jun N-terminal kinases (JNKs), and p38-MAPKs. It has been originally shown that ERKs are important for cell survival, whereas JNKs and p38-MAPKs were deemed stress responsive and thus involved in apoptosis. However, the regulation of apoptosis by MAPKs is more complex than initially thought and often controversial. In this review, we discuss MAPKs in apoptosis regulation with attention to mouse genetic models and critically point out the multiple roles of MAPKs.

Hepatocyte growth factor inhibits the formation of the basement membrane of alveolar epithelial cells in vitro

Hepatocyte growth factor (HGF) is a pulmotrophic factor for the regeneration of injured pulmonary tissue. We investigated the role of HGF in basement membrane formation during wound healing by immortalized alveolar type II epithelial cells that could form a continuous basement membrane when they were cultured on collagen fibrils in the presence of entactin-contaminated laminin-1. Cells cultured with 5.0 ng/ml HGF neither formed a continuous basement membrane on collagen fibrils nor maintained a continuous basement membrane architecture on a basement membrane substratum. The cells showed increased secretion of matrix metalloproteinase-9 and urokinase-type plasminogen activator, and the HGF-induced inhibition of basement membrane formation was attenuated by addition of 200 ng/ml tissue inhibitor of matrix metalloproteinase-1. Cells sequentially exposed to HGF and 1.0 ng/ml transforming growth factor-β1 had enhanced basement membrane formation compared with those receiving these reagents in the reverse order or concurrently. HGF simultaneously stimulated proliferation and migration of the cells so that it advanced wound closure on the basement membrane substratum. The present results indicate that the role of HGF in wound healing is the stimulation of reepithelization, but this factor may also contribute to the degradation of the basement membrane.

Non-redundant Role of Shc in Erk Activation by Cytoskeletal Reorganization

We have shown previously that cytoskeletal reorganization (CSR) induced by pharmacological reagents such as colchicine or cytochalasins can up-regulate the urokinase-type plasminogen activator (uPA) gene via the Ras/Erk signaling pathway. In this present study using the small interfering RNA technique, we have found that ShcA adapter proteins play a rather active role in CSR-induced Erk activation, contrary to their mostly redundant role in other signaling pathways, e.g. growth factor-induced Erk activation, where Grb2 can bind directly to the receptor tyrosine kinase and activate Erk in the absence of ShcA. ShcA knockdown abolished CSR-induced activation of both Erk and the uPA promoter. Expression of small interfering RNA-escaping silent mutants of p52 or p46 but not p66 ShcA isoform efficiently rescued CSR-induced Erk activation. Moreover, we have shown that phosphorylation of either Tyr-239/Tyr-240 or Tyr-313 in p52(ShcA) can mediate CSR-induced Erk activation equally well. In a quest for molecules upstream of ShcA in this signaling, we found that CSR-induced ShcA tyrosine phosphorylation, its association with Grb2, Erk activation, and uPA gene expression were all dependent on Rho kinase, p38 mitogen-activated protein kinase, and Src. In summary, we have found a novel, non-redundant role for ShcA in contrast to its redundant role in many other signaling pathways.

Inhibition of angiogenesis and angiogenesis-dependent tumor growth by the cryptic kringle fragments of human apolipoprotein(a)

Apolipoprotein(a) (apo(a)) contains tandemly repeated kringle domains that are closely related to plasminogen kringle 4, followed by a single kringle 5-like domain and an inactive protease-like domain. Recently, the anti-angiogenic activities of apo(a) have been demonstrated both in vitro and in vivo. However, its effects on tumor angiogenesis and the underlying mechanisms involved have not been fully elucidated. To evaluate the anti-angiogenic and anti-tumor activities of the apo(a) kringle domains and to elucidate their mechanism of action, we expressed the last three kringle domains of apo(a), KIV-9, KIV-10, and KV, in Escherichia coli. The resultant recombinant protein, termed rhLK68, exhibited a dose-dependent inhibition of basic fibroblast growth factor-stimulated human umbilical vein endothelial cell proliferation and migration in vitro and inhibited the neovascularization in chick chorioallantoic membranes in vivo. The ability of rhLK68 to abrogate the activation of extracellular signal-regulated kinases appears to be responsible for rhLK68-mediated anti-angiogenesis. Furthermore, systemic administration of rhLK68 suppressed human lung (A549) and colon (HCT-15) tumor growth in nude mice. Immunohistochemical examination and in situ hybridization analysis of the tumors showed a significant decrease in the number of blood vessels and the reduced expression of vascular endothelial growth factor, basic fibroblast growth factor, and angiogenin, indicating that suppression of angiogenesis may have played a significant role in the inhibition of tumor growth. Collectively, these results suggest that a truncated apo(a), rhLK68, is a potent anti-angiogenic and anti-tumor molecule.

Pp60c-src mediates ERK activation/nuclear localization and PAI-1 gene expression in response to cellular deformation

Release of transcellular tension upon disruption of actin stress fibers with cytochalasin D (CD) and associated changes in cell morphology are reflected in the rapid transcription of "deformation-responsive" genes. For certain genes (e.g., urokinase plasminogen activator and its type-1 inhibitor PAI-1), de novo mRNA synthesis appears to require cell shape-dependent activation of the MAP kinases ERK1/2. ERK activation in response to microfilament disruption was inhibited completely by the broad-spectrum tyrosine kinase inhibitor genistein and the relatively src-kinase selective compound PP1. Such inhibitor sensitivity profiles suggested that src-family members, likely pp60(c-src), were important upstream elements in deformation-related ERK activation. pp60(c-src) kinase activity was elevated fourfold within 15 min after CD addition to quiescent R22 smooth muscle cells and declined quickly thereafter. CD-induced increases in the phosphorylation levels of both pp60(c-src) and IgG heavy chain (a substrate target in the coupled immunoprecipitation/in vitro pp60(c-src) kinase assay) were ablated completely by pretreatment with the src-type kinase inhibitor PP1. Prior PP1 exposure similarly repressed CD-stimulated PAI-1 transcript accumulation. Consistent with the pharmacologic findings, transfection of a dominant-negative pp60(c-src) expression construct (DN-Src) effectively suppressed (in a concentration-dependent manner) CD-induced PAI-1 synthesis in R22 cells. To more specifically address the potential involvement of src kinases in CD-initiated ERK mobilization, R22 cells were transiently co-transfected with DN-Src and Myc-tagged ERK2 expression constructs, serum-deprived then stimulated with CD. The effect of DN-Src expression on endogenous ERK1/2 activation and nuclear translocation was assessed in separate experiments. The phosphorylation levels of both exogenous (Myc-ERK2) and endogenous ERK1/2 targets was significantly reduced by DN-Src; nuclear accumulation of pERK1/2 was completely inhibited. These data indicate that pp60(c-src) is a critical upstream activator of the ERK cascade leading to PAI-1 transcription in response to cellular deformation stimuli.

Lovastatin alters cytoskeleton organization and inhibits experimental metastasis of mammary carcinoma cells

Lovastatin is a competitive inhibitor of 3-hydroxy 3-methylglutaryl coenzyme A reductase, the key regulatory enzyme of cholesterol biosynthesis. This enzyme catalyzes the formation of mevalonate, which is also the precursor of isoprenoid moieties, such as farnesol and geraniol, that are incorporated into several molecules essential for tumor cell signaling. Here, we describe that pretreatment with a non-cytotoxic concentration of lovastatin (10 microM) dramatically inhibited the metastatic ability of F311 mammary carcinoma cells in syngeneic BALB/c mice. Similarly, daily i.p. treatment of animals with a well-tolerated dose of lovastatin (10 mg/kg/day) significantly reduced the number of experimental lung metastases. In vitro, incubation of F3II monolayers in the presence of lovastatin caused a rounded-cell morphology. Immunofluorescence analysis revealed a lack of cortical actin organization, micrutubule disruption and inhibition of integrin-mediated focal contacts in lovastatin-treated cells. Exposure of F3II cells to lovastatin significantly inhibited tumor cell adhesion and migration, and coincubation with the cholesterol precursor mevalonate prevented these effects. Lovastatin reduced membrane localization of Rho protein, a signaling molecule involved in the regulation of actin-based cell motility that needs geranylation for membrane association and activation. In addition, lovastatin induced a dose-dependent inhibition in the secretion of urokinase, a key proteolytic enzyme during tumor invasion and metastasis, and a significant increase of tissue-type plasminogen activator, a marker of good prognosis in mammary cancer. These data suggest that antimetastatic properties of lovastatin are strongly associated with alterations in cytoskeleton organization and the consequent modulation of adhesion, motility and proteolysis.

Sustained activation of MEK1-ERK1/2 pathway in membrane skeleton occurs dependently on cell adhesion in megakaryocytic differentiation

A human megakaryoblastic cell line, CMK, was treated with 12-o-tetradecanoylphorbol-13-acetate (TPA) for differentiation-induction. We examined TPA-induced activation of the MEK1-ERK1/2 pathway in the 100,000g Triton X-insoluble fraction of CMK cells as the membrane skeleton and researched the relation of the MEK1-ERK1/2 activation with integrin expression. We found that this activation was divided into two phases: the first activation occurred transiently in the membrane skeleton fraction of the suspended cell status and diminished after 1h; and the second sustained activation was maintained by cell adhesion. TPA-treated CMK cells revealed increased expression of integrins alphaIIb and beta3 only when the cell adhesion persisted, regardless of the difference of culture substratum. Sustained activation of the MEK1-ERK1/2 pathway is generated in the membrane skeleton by continuous cell adhesion and seems to be essential to TPA-induced megakaryocytic differentiation of CMK cells.

Opposite changes in membrane fluidity mimic cold and heat stress activation of distinct plant MAP kinase pathways

Mitogen-activated protein kinases (MAPKs) appear to be ubiquitously involved in signal transduction during eukaryotic responses to extracellular stimuli. In plants, no heat shock-activated MAPK has so far been reported. Also, whereas cold activates specific plant MAPKs such as alfalfa SAMK, mechanisms of such activation are unknown. Here, we report a heat shock-activated MAPK (HAMK) immunologically related to ERK (Extracellular signal-Regulated Kinase) superfamily of protein kinases. Molecular mechanisms of heat-activation of HAMK and cold-activation of SAMK were investigated. We show that cold-activation of SAMK requires membrane rigidification, whereas heat-activation of HAMK occurs through membrane fluidization. The temperature stress- and membrane structure-dependent activation of both SAMK and HAMK is mimicked at 25 degrees C by destabilizers of microfilaments and microtubules, latrunculin B and oryzalin, respectively; but is blocked by jasplakinolide, a stabilizer of actin microfilaments. Activation of SAMK or HAMK by temperature, chemically modulated membrane fluidity, or by cytoskeleton destabilizers is inhibited by blocking the influx of extracellular calcium. Activation of SAMK or HAMK is also prevented by an antagonist of calcium-dependent protein kinases (CDPKs). In summary, our data indicate that cold and heat are sensed by structural changes in the plasma membrane that translates the signal via cytoskeleton, Ca2+ fluxes and CDPKs into the activation of distinct MAPK cascades.

MEK/ERK pathway mediates cell-shape-dependent plasminogen activator inhibitor type 1 gene expression upon drug-induced disruption of the microfilament and microtubule networks

Changes in cellular morphology induced as a consequence of direct perturbation of cytoskeletal structure with network-specific targeting agents(i.e. microfilament- or microtubule-disrupting drugs) results in the stimulated expression of a specific subset of genes. Transcription of c-fos, collagenase, transforming growth factor-β, actin,urokinase plasminogen activator and its type-1 inhibitor (PAI-1) appears to be particularly responsive to shape-activated signaling pathways. Cytochalasin D(CD) or colchicine treatment of contact-inhibited and serum-deprived vascular smooth muscle (R22) cells was used, therefore, as a model system to evaluate morphology-associated controls on PAI-1 gene regulation in the absence of added growth factors. PAI-1 transcript levels in quiescent R22 cells increased rapidly and in a CD-concentration-dependent fashion, with kinetics of expression paralleling the morphological changes. Colchicine concentrations that effectively disrupted microtubule structure and reduced the cellular`footprint' area (to approximately that of CD treatment) also stimulated PAI-1 synthesis. Shape-related increases in PAI-1 mRNA synthesis were ablated by prior exposure to actinomycin D. Unlike the mechanism of induction in growth-factor-stimulated cells, CD- and colchicine-induced PAI-1 expression required on-going protein synthesis (i.e. it was a secondary response). Although PAI-1 is a TGF-β-regulated gene and TGF-β expression is also shape dependent, an autocrine TGF-β loop was not a factor in CD-initiated PAI-1 transcription. Since CD exposure resulted in actin microfilament disruption and subsequent morphological changes, with uncertain effects on interactions between signaling intermediates or `scaffold'structures, a pharmacological approach was selected to probe the pathways involved. Signaling events leading to PAI-1 induction were compared with colchicine-treated cells. CD- as well as colchicine-stimulated PAI-1 expression was effectively and dose dependently attenuated by the MEK inhibitor PD98059 (in the 10 to 25 μM concentration range), consistent with the known MAP kinase dependency of PAI-1 synthesis in growth-factor-stimulated cells. Reduced PAI-1 mRNA levels upon exposure to genistein prior to CD addition correlated with inhibition of ERK1/2 activity, implicating a tyrosine kinase in shape-dependent MEK activation. Src-family kinases,moreover, appeared to be specific upstream elements in the CD- and colchicine-dependent pathways of PAI-1 transcription since both agents effectively activated pp60c-src kinase activity in quiescent R22 cells. The restrictive (src-family) kinase inhibitor PP1 completely inhibited induced, as well as basal, ERK activity in a coupled immunoprecipitation myelin-basic-protein-phosphorylation assay and ablated shape-initiated PAI-1 mRNA expression. These data suggest that PP1-sensitive tyrosine kinases are upstream intermediates in cell-shape-associated signaling pathways resulting in ERK1/2 activation and subsequent PAI-1 transcription. In contrast to the rapid and transient kinetics of ERK activity typical of serum-stimulated cells, the ERK1/2 response to CD and colchicine is both delayed and relatively sustained. Collectively, these data support a model in which MEK is a focal point for the convergence of shape-initiated signaling events leading to induced PAI-1 transcription.

U0126, a mitogen-activated protein kinase kinase inhibitor, inhibits the invasion of human A375 melanoma cells

The anti-invasive ability of the mitogen-activated protein kinase (MAPK) kinase inhibitor, U0126, was examined in human A375 melanoma cells in vitro. The effect was compared to that of PD98059, another commonly used MEK (MAPK kinase) inhibitor. U0126 or PD98059 showed a dose-dependent inhibition of A375 cell invasion through growth factor-reduced Matrigel. U0126 was more potent than PD98059 in suppressing tumor cell invasion. Both compounds significantly decreased urokinase plasminogen activator (uPA) and matrix metalloproteinases-9 (MMP-9) concentrations in conditioned media. At 5 microM, U0126 inhibited phosphorylation of the MEK 1/2 to a non-detectable level within 24 h. The phosphorylation of extracellular signal-related kinase 1/2 was also dramatically suppressed by the treatment with 10 microM U0126 or 40 microM PD98059. Both compounds suppressed the protein expression of c-Jun, but not c-Fos. The expression of uPA and MMP-9 was also inhibited. Our data suggest that U0126 is an effective agent in inhibiting human A375 melanoma cell invasion and that the effect is partially due to the decreased production of uPA and MMP-9.

TGF-β1-induced PAI-1 gene expression requires MEK activity and cell-to-substrate adhesion

The type-1 inhibitor of plasminogen activator (PAI-1) is an important physiological regulator of extracellular matrix (ECM) homeostasis and cell motility. Various growth factors mediate temporal changes in the expression and/or focalization of PAI-1 and its protease target PAs, thereby influencing cell migration by barrier proteolysis and/or ECM adhesion modulation. TGF-β1, in particular, is an effective inducer of matrix deposition/turnover, cell locomotion and PAI-1 expression. Therefore, the relationship between motility and PAI-1 induction was assessed in TGF-β1-sensitive T2 renal epithelial cells. PAI-1 synthesis and its matrix deposition in response to TGF-β1 correlated with a significant increase in cell motility. PAI-1 expression was an important aspect in cellular movement as PAI-1-deficient cells had significantly impaired basal locomotion and were unresponsive to TGF-β1. However, the induced migratory response to this growth factor was complex. TGF-β1 concentrations of 1-2 ng/ml were significantly promigratory, whereas lower levels (0.2-0.6 ng/ml) were ineffective and final concentrations ≥5 ng/ml inhibited T2 cell motility. This same growth factor range progressively increased PAI-1 transcript levels in T2 cells consistent with a bifunctional role for PAI-1 in cell migration. TGF-β1 induced PAI-1 mRNA transcripts in quiescent T2 cells via an immediate-early response mechanism. Full TGF-β1-stimulated expression required tyrosine kinase activity and involved MAPK/ERK kinase (MEK). MEK appeared to be a major mediator of TGF-β1-dependent PAI-1 expression and T2 cell motility since PD98059 effectively attenuated both TGF-β1-induced ERK1/2 activation and PAI-1 transcription as well as basal and growth factor-stimulated planar migration. Since MEK activation in response to growth factors is adhesion-dependent, it was important to determine whether cellular adhesive state influenced TGF-β1-mediated PAI-1 expression in the T2 cell system. Cells maintained in suspension culture (i.e., over agarose underlays) in growth factor-free medium or treated with TGF-β1 in suspension expressed relatively low levels of PAI-1 transcripts compared with the significant induction of PAI-1 mRNA evident in T2 cells upon stimulation with TGF-β1 during adhesion to a fibronectin-coated substrate. Attachment to fibronectin alone (i.e., in the absence of added growth factor) was sufficient to initiate PAI-1 transcription, albeit at levels considerably lower than that induced by the combination of cell adhesion in the presence of TGF-β1. T2 cells allowed to attach to vitronectin-coated surfaces also expressed PAI-1 transcripts but to a significantly reduced extent relative to cells adherent to fibronectin. Moreover, newly vitronectin-attached cells did not exhibit a PAI-1 inductive response to TGF-β1, at least during the short 2 hour period of combined treatment. PAI-1 mRNA synthesis in response to substrate attachment, like TGF-β1-mediated induction in adherent cultures, also required MEK activity as fibronectin-stimulated PAI-1 expression was effectively attenuated by the MEK inhibitor PD98059. These data indicate that cellular adhesive state modulates TGF-β1 signaling to particular target genes (i.e., PAI-1) and that MEK is a critical mediator of the PAI-1+/promigratory phenotype switch induced by TGF-β1 in T2 cells.

Mechanical strains induced by tubular flow affect the phenotype of proximal tubular cells

The effects of flow-induced mechanical strains on the phenotype of proximal tubular cells were addressed in vivo and in vitro by subjecting LLC-PK(1) and mouse proximal tubular cells to different levels of flow. Laminar flow (1 ml/min) induced a reorganization of the actin cytoskeleton and significantly inhibited the expression of plasminogen activators [tissue-type (tPA) activity: 25% of control cells; tPA mRNA: 70% of control cells; urokinase (uPA) mRNA: 56% of control LLC-PK(1) cells]. In vivo, subtotal nephrectomy (Nx) decreased renal fibrinolytic activity and uPA mRNA content detectable in proximal tubules. Nx also induced a reinforcement of the apical domain of the actin cytoskeleton analyzed by immunofluorescence. These effects of flow on tPA and uPA mRNA were prevented in vitro when reorganization of the actin cytoskeleton was blocked by cytochalasin D and were associated, in vitro and in vivo, with an increase in shear stress-responsive element binding activity detected by an electrophoretic mobility shift assay in proximal cell nuclear extracts. These results demonstrate that tubular flow affects the phenotype of renal epithelial cells and suggest that flow-induced mechanical strains could be one determinant of tubulointerstitial lesions during the progression of renal diseases.

The ras signaling pathway in mammary tumorigenesis and metastasis

The Ras superfamily of GTPases act as important regulatory switches to co-ordinate extracellular stimuli with activation of intracellular signaling pathways and appropriate biological responses. The Ras branch of this superfamily includes H-, K- and N-Ras, which are commonly mutated in particular human cancers, but notably not in those of the breast. Instead, in breast cancer the signaling pathways involving these GTPases may be upregulated due to increased coupling to growth factor receptors or other tyrosine kinases commonly overexpressed in this disease, or increased expression of regulators, the Ras protein itself, or downstream effectors. Functional studies utilizing both in vitro and in vivo models demonstrate that Ras signaling can regulate a variety of endpoints relevant to breast cancer progression, including anchorage dependent and independent growth, tumorigenesis, steroid sensitivity and invasion. Finally, analysis of the processing and signaling mechanisms of the Ras superfamily has identified potential targets for therapeutic intervention.

ERK signalling in metastatic human MDA-MB-231 breast carcinoma cells is adapted to obtain high urokinase expression and rapid cell proliferation

Increased urokinase plasminogen activator (u-PA) production is associated with tumor invasion and metastasis in several malignancies, including breast cancer. The mechanisms underlying constitutive u-PA expression are not well understood. We examined the relationship between the signal strength of the ERK pathway and the level of u-PA expression in the metastatic human breast cancer cell line MDA-MB-231. Treatment with the MEK1 inhibitor PD98059 resulted in decreased ERK1/2 phosphorylation and decreased u-PA mRNA and protein expression. Inhibition of ERK1/2 activity also led to decreased cell proliferation and to decreased cyclin D1 expression. Less than 5% of total ERK1/2 was phosphorylated in exponentially growing MDA-MB-231 cells, and ERK1/2 activity could be stimulated by okadaic acid. Okadaic acid did not stimulate u-PA expression, but induced strong expression of the cdk-inhibitor p21Cip1. These findings suggest that ERK1/2 signaling is tuned to a level which results in high u-PA expression and rapid cell proliferation.

The cJun N-terminal kinase (JNK) signaling pathway mediates induction of urokinase-type plasminogen activator (uPA) by the alkylating agent MNNG

The monofunctional alkylating agent N-methyl-N-nitro-N-nitrosoguanidine (MNNG) is a widespread environmental carcinogen that causes DNA lesions, leading to cell death. However, MNNG can also trigger a cell-protective response by inducing the expression of DNA repair/transcription-related genes. We demonstrate that the urokinase-type plasminogen activator (uPA) gene product, a broad spectrum extracellular protease to which no DNA repair function has been assigned, is transcriptionally induced by MNNG in C2C12 and NIH3T3 cells. This induction required an AP1-enhancer element located at −2.4 kilobase (kb), because it was abrogated by deletion of this site. MNNG was found to induce the activation of JNK/SAPK and p38 mitogen-activated protein kinases (MAPKs). Accordingly, we attempted to assess the contribution of each of these MNNG-inducible MAPKs to uPA gene induction by this alkylating agent. Coexpression of dominant negative versions of kinases of the JNK pathway, such as catalytically inactive forms of MEKK1, MKK7, and JNKK, and of cytoplasmic JNK-inhibitor JIP-1, as well as treatment of cells with curcumin (which blocks JNK activation by MNNG), inhibited MNNG-induced uPA transcriptional activity. In contrast, neither dominant negative MKK6 nor SB203580, which specifically inhibit p38 MAP kinase activation, abrogated the MNNG-induced effect. Taken together, our results show that the JNK signaling pathway links external MNNG stimulation and AP1-dependent uPA gene expression, providing the first functional dissection of a transcription-coupled signal transduction pathway for MNNG.

The cJun N-terminal kinase (JNK) signaling pathway mediates induction of urokinase-type plasminogen activator (uPA) by the alkylating agent MNNG

The monofunctional alkylating agent N-methyl-N-nitro-N-nitrosoguanidine (MNNG) is a widespread environmental carcinogen that causes DNA lesions, leading to cell death. However, MNNG can also trigger a cell-protective response by inducing the expression of DNA repair/transcription-related genes. We demonstrate that the urokinase-type plasminogen activator (uPA) gene product, a broad spectrum extracellular protease to which no DNA repair function has been assigned, is transcriptionally induced by MNNG in C2C12 and NIH3T3 cells. This induction required an AP1-enhancer element located at −2.4 kilobase (kb), because it was abrogated by deletion of this site. MNNG was found to induce the activation of JNK/SAPK and p38 mitogen-activated protein kinases (MAPKs). Accordingly, we attempted to assess the contribution of each of these MNNG-inducible MAPKs to uPA gene induction by this alkylating agent. Coexpression of dominant negative versions of kinases of the JNK pathway, such as catalytically inactive forms of MEKK1, MKK7, and JNKK, and of cytoplasmic JNK-inhibitor JIP-1, as well as treatment of cells with curcumin (which blocks JNK activation by MNNG), inhibited MNNG-induced uPA transcriptional activity. In contrast, neither dominant negative MKK6 nor SB203580, which specifically inhibit p38 MAP kinase activation, abrogated the MNNG-induced effect. Taken together, our results show that the JNK signaling pathway links external MNNG stimulation and AP1-dependent uPA gene expression, providing the first functional dissection of a transcription-coupled signal transduction pathway for MNNG.

Urinary-type plasminogen activator (uPA) expression and uPA receptor localization are regulated by alpha 3beta 1 integrin in oral keratinocytes

Expression of urinary-type plasminogen activator (uPA) and its receptor (uPAR) is correlated with matrix proteolysis, cell adhesion, motility, and invasion. To evaluate the functional link between adhesion and proteolysis in gingival keratinocytes (pp126), cells were treated with immobilized integrin antibodies to induce integrin clustering. Clustering of alpha(3) and beta(1) integrin subunits, but not alpha(2), alpha(5), alpha(6), or beta(4), enhanced uPA secretion. Bead-immobilized laminin-5 and collagen I, two major alpha(3)beta(1) ligands, also induced uPA expression. Coordinate regulation of the serpin plasminogen activator inhibitor 1 was also apparent; however, a net increase in uPA activity was predominant. alpha(3)beta(1) integrin clustering induced extracellular signal-regulated kinase 1/2 phosphorylation, and both uPA induction and extracellular signal-regulated kinase activation were blocked by the mitogen-activated protein kinase/extracellular signal-regulated kinase kinase inhibitor PD98059. Integrin aggregation also promoted a dramatic redistribution of uPAR on the cell surface to sites of clustered alpha(3)beta(1) integrins. Co-immunoprecipitation of beta(1) integrin with uPAR provided further evidence that protein-protein interactions between uPAR and beta(1) integrin control uPAR distribution. As a functional consequence of uPA up-regulation and uPA-mediated plasminogen activation, the globular domain of the laminin-5 alpha(3) subunit, a major pp126 matrix protein, was proteolytically processed from a 190-kDa form to a 160-kDa species. Laminin-5 containing the 160-kDa alpha(3) subunit efficiently nucleates hemidesmosome formation and reduces cell motility. Together, these data suggest that multivalent aggregation of the alpha(3)beta(1) integrin regulates proteinase expression, matrix proteolysis, and subsequent cellular behavior.

Disruption of actin cytoskeleton induces chondrogenesis of mesenchymal cells by activating protein kinase C-alpha signaling

Disruption of actin cytoskeleton with cytochalasin D has been known to induce chondrogenic differentiation of chick embryo limb bud mesenchymal cells. However, the mechanism(s) for the induction of chondrogenesis by cytochalasin D is not yet clearly known. In the present study, we examined possible involvement of protein kinase C (PKC) and extracellular signal-regulated protein kinase (Erk-1) in chondrogenesis of mesenchymal cells induced by disruption of actin cytoskeleton. Disruption of actin cytoskeleton with cytochalasin D or latrunculin B induced chondrogenesis of mesenchymal cells cultured at subconfluent cell density, as determined by type II collagen expression. Among the expressed PKC isoforms, cytochalasin D dramatically increased expression and activation of PKCalpha in a dose-dependent manner, and inhibition or downregulation of PKCalpha blocked cytochalasin D-induced chondrogenesis. Cytochalasin D also downregulated Erk-1 phosphorylation that is associated with chondrogenesis. Our results, therefore, suggest that disruption of actin cytoskeleton induces chondrogenesis of mesenchymal cells by activating PKCalpha and by inhibiting Erk-1 signaling.

Phosphorylation of paxillin via the ERK mitogen-activated protein kinase cascade in EL4 thymoma cells

Intracellular signals can regulate cell adhesion via several mechanisms in a process referred to as "inside-out" signaling. In phorbol ester-sensitive EL4 thymoma cells, phorbol-12-myristate 13-acetate (PMA) induces activation of extracellular signal-regulated kinase (ERK) mitogen-activated protein kinases and promotes cell adhesion. In this study, clonal EL4 cell lines with varying abilities to activate ERKs in response to PMA were used to examine signaling events occurring downstream of ERK activation. Paxillin, a multifunctional docking protein involved in cell adhesion, was phosphorylated on serine/threonine residues in response to PMA treatment. This response was correlated with the extent and time course of ERK activation. PMA-induced phosphorylation of paxillin was inhibited by compounds that block the ERK activation pathway in EL4 cells, primary murine thymocytes, and primary murine splenocytes. Paxillin was phosphorylated in vitro by purified active ERK2. Two-dimensional electrophoresis revealed that PMA treatment generated a complex pattern of phosphorylated paxillin species in intact cells, some of which were generated by ERK-mediated phosphorylation in vitro. An ERK pathway inhibitor interfered with PMA-induced adhesion of sensitive EL4 cells to substrate. These findings describe a novel inside-out signaling pathway by which the ERK cascade may regulate events involved in adhesion.