Reversible Regulation of the Transformed Phenotype of Ornithine Decarboxylase- and Ras-Overexpressing Cells by Dominant-Negative Mutants of c-Jun

Silencing c-Jun inhibits autophagy and abrogates radioresistance in nasopharyngeal carcinoma by activating the PI3K/AKT/mTOR pathway

Background

Radioresistance plays an important role in the failure of radiotherapy (RT) for nasopharyngeal carcinoma (NPC), leading to poor prognosis. The purpose of this study was to explore the relationship between the expression of the c-Jun oncogene and the prognosis of NPC. In addition, we investigated the potential mechanisms of c-Jun in the regulation of tumor growth and radioresistance in NPC.

Methods

c-Jun expression in NPC tissues and nasopharyngeal mucosa tissues was evaluated using immunochemistry. c-Jun and its downstream targets were verified by dual-luciferase reporter assays. Inhibitors or activators were used to interfere with the PI3K/AKT/mTOR pathway. Protein expression was analyzed by western blotting. NPC nude mouse xenograft models were used to investigate the potential effects of c-Jun and ionizing radiation in vivo.

Results

The expression of c-Jun in NPC tissues was significantly higher than that in normal nasopharyngeal mucosa (NNM) tissues, and Cox regression analysis revealed that c-Jun overexpression was an independent risk factor for poor prognosis in NPC patients. Both in vitro and in vivo experiments verified that c-Jun targeted PI3K/AKT signaling. We also performed an in vivo study showing that c-Jun knockdown effectively suppressed NPC growth in a xenograft tumor model by autophagy inhibition, and these effects were accompanied by the upregulation of p-PI3K p-AKT, p-mTOR, and P62 and downregulation of LC3-II expression.

Conclusions

High expression of c-Jun was correlated with poor prognosis in NPC patients. c-Jun knockdown increased cell sensitivity to radiation by inhibiting autophagy activation via the PI3K/AKT/mTOR signaling pathway. The present study provides a theoretical basis for a promising treatment for radioresistant NPC by inhibiting c-Jun expression.

Prolyl 4-hydroxylase subunit alpha 1 (P4HA1) is a biomarker of poor prognosis in primary melanomas, and its depletion inhibits melanoma cell invasion and disrupts tumor blood vessel walls

Melanoma is an unpredictable, highly metastatic malignancy, and treatment of advanced melanoma remains challenging. Novel molecular markers based on the alterations in gene expression and the molecular pathways activated or deactivated during melanoma progression are needed for predicting the course of the disease already in primary tumors and for providing new targets for therapy. Here, we sought to identify genes whose expression in primary melanomas correlate with patient disease‐specific survival using global gene expression profiling. Many of the identified potential markers of poor prognosis were associated with the epithelial–mesenchymal transition, extracellular matrix formation, and angiogenesis. We studied further the significance of one of the genes, prolyl 4‐hydroxylase subunit alpha 1 (P4HA1), in melanoma progression. P4HA1 depletion in melanoma cells reduced cell adhesion, invasion, and viability in vitro. In melanoma xenograft assays, we found that P4HA1 knockdown reduced melanoma tumor invasion as well as the deposition of collagens, particularly type IV collagen, in the interstitial extracellular matrix and in the basement membranes of tumor blood vessels, leading to vessel wall rupture and hemorrhages. Further, P4HA1 knockdown reduced the secretion of collagen triple helix repeat containing 1 (CTHRC1), an important mediator of melanoma cell migration and invasion, in vitro and its deposition around tumor blood vessels in vivo. Taken together, P4HA1 is an interesting potential prognostic marker and therapeutic target in primary melanomas, influencing many aspects of melanoma tumor progression.

Divergent roles of lysyl oxidase family members in ornithine decarboxylase- and RAS-transformed mouse fibroblasts and human melanoma cells

We have previously shown that proto-oncoprotein c-Jun is activated in ornithine decarboxylase (ODC)- and RAS-transformed mouse fibroblasts, and that the transformed morphology of these cells can be reversed by expressing the transactivation domain deletion mutant of c-Jun (TAM67). Here, we found that lysyl oxidase (Lox), encoding an extracellular matrix-modifying enzyme, is downregulated in a c-Jun-dependent manner in ODC-transformed fibroblasts (Odc cells). In addition to Lox, the Lox family members Lox-like 1 and 3 (Loxl1 and Loxl3) were found to be downregulated in Odc as well as in RAS-transformed fibroblasts (E4), whereas Lox-like 4 (Loxl4) was upregulated in Odc and downregulated in E4 cells compared to normal N1 fibroblasts. Tetracycline-regulatable LOX re-expression in Odc cells led to inhibition of cell growth and invasion in three-dimensional Matrigel in an activity-independent manner. On the contrary, LOX and especially LOXL2, LOXL3, and LOXL4 were found to be upregulated in several human melanoma cell lines, and LOX inhibitor B-aminopropionitrile inhibited the invasive growth of these cells particularly when co-cultured with fibroblasts in Matrigel. Knocking down the expression of LOX and especially LOXL2 in melanoma cells almost completely abrogated the invasive growth capability. Further, LOXL2 was significantly upregulated in clinical human primary melanomas compared to benign nevi, and high expression of LOXL2 in primary melanomas was associated with formation of metastases and shorter survival of patients. Thus, our studies reveal that inactive pro-LOX (together with Lox propeptide) functions as a tumor suppressor in ODC- and RAS-transformed murine fibroblasts by inhibiting cell growth and invasion, and active LOX and LOXL2 as tumor promoters in human melanoma cells by promoting their invasive growth.

Gene expression analyses of primary melanomas reveal CTHRC1 as an important player in melanoma progression

Melanoma is notorious for its high tendency to metastasize and its refractoriness to conventional treatments after metastasis, and the responses to most targeted therapies are short-lived. A better understanding of the molecular mechanisms behind melanoma development and progression is needed to develop more effective therapies and to identify new markers to predict disease behavior. Here, we compared the gene expression profiles of benign nevi, and non-metastatic and metastatic primary melanomas to identify any common changes in disease progression. We identified several genes associated with inflammation, angiogenesis, and extracellular matrix modification to be upregulated in metastatic melanomas. We selected one of these genes, collagen triple helix repeat containing 1 (CTHRC1), for detailed analysis, and found that CTHRC1 was expressed in both melanoma cells and the associated fibroblasts, as well as in the endothelium of tumor blood vessels. Knockdown of CTHRC1 expression by shRNAs in melanoma cells inhibited their migration in Transwell assays and their invasion in three-dimensional collagen and Matrigel matrices. We also elucidated the possible down-stream effectors of CTHRC1 by gene expression profiling of the CTHRC1-knockdown cells. Our analyses showed that CTHRC1 is regulated coordinately with fibronectin and integrin β3 by the pro-invasive and -angiogenic transcription factor NFATC2. We also found CTHRC1 to be a target of TFGβ and BRAF. These data highlight the importance of tumor stroma in melanoma progression. Furthermore, CTHRC1 was recognized as an important mediator of melanoma cell migration and invasion, providing together with its regulators-NFATC2, TGFβ, and BRAF-attractive therapeutic targets against metastatic melanomas.

Osteopontin promotes the invasive growth of melanoma cells by activating integrin αvβ3 and down-regulating tetraspanin CD9

Overexpression of osteopontin (OPN) is strongly associated with the invasiveness/metastasis of many cancers, including melanomas. However, the molecular mechanisms of OPN in these processes remain poorly understood. We found that forced expression of OPN in early vertical-growth-phase melanoma cells dramatically increased their migration/invasion and growth/survival in a three-dimensional collagen I gel. Neutralizing antibodies to OPN, integrin β1, and integrin αvβ3, but not to CD44, negated the effects of OPN. Conversely, knocking down OPN in metastatic melanoma cells abrogated the invasive growth. OPN overexpression activated and OPN knockdown inactivated αvβ3 and αvβ5 integrins, negligibly affecting their expression. We further found OPN expression to inversely correlate with tetraspanin CD9 expression. Early-stage melanoma cells displayed low OPN and high CD9 expression, and conversely, metastatic cells displayed high OPN and low CD9 expression. Overexpression of OPN in vertical-growth-phase melanoma cells induced down-regulation of CD9, and knockdown of OPN in metastatic melanoma cells up-regulated CD9. Reversion of these CD9 changes abolished the effects of OPN. Furthermore, knockdown of CD9 in early-stage melanoma cells stimulated their invasive capacity in three-dimensional collagen. Similarly, microarray analyses of benign nevi and primary melanomas from different stages revealed an inverse correlation between OPN and CD9. These data suggest that OPN promotes melanoma cell invasion by activating integrin αvβ3 and down-regulating CD9, a putative metastasis suppressor.

TGF-β signaling, activated stromal fibroblasts, and cysteine cathepsins B and L drive the invasive growth of human melanoma cells

Accumulating evidence indicates that interactions between cancer cells and stromal cells are important for the development/progression of many cancers. Herein, we found that the invasive growth of melanoma cells in three-dimensional-Matrigel/collagen-I matrices is dramatically increased on their co-culture with embryonic or adult skin fibroblasts. Studies with fluorescent-labeled cells revealed that the melanoma cells first activate the fibroblasts, which then take the lead in invasion. To identify the physiologically relevant invasion-related proteases involved, we performed genome-wide microarray analyses of invasive human melanomas and benign nevi; we found up-regulation of cysteine cathepsins B and L, matrix metalloproteinase (MMP)-1 and -9, and urokinase- and tissue-type plasminogen activators. The mRNA levels of cathepsins B/L and plasminogen activators, but not MMPs, correlated with metastasis. The invasiveness/growth of the melanoma cells with fibroblasts was inhibited by cell membrane-permeable inhibitors of cathepsins B/L, but not by wide-spectrum inhibitors of MMPs. The IHC analysis of primary melanomas and benign nevi revealed cathepsin B to be predominantly expressed by melanoma cells and cathepsin L to be predominantly expressed by the tumor-associated fibroblasts surrounding the invading melanoma cells. Finally, cathepsin B regulated TGF-β production/signaling, which was required for the activation of fibroblasts and their promotion of the invasive growth of melanoma cells. These data provide a basis for testing inhibitors of TGF-β signaling and cathepsins B/L in the therapy of invasive/metastatic melanomas.

Transforming growth factor beta-induced (TGFBI) is an anti-adhesive protein regulating the invasive growth of melanoma cells

Melanoma is a malignancy characterized by high invasive/metastatic potential, with no efficient therapy after metastasis. Understanding the molecular mechanisms underlying the invasive/metastatic tendency is therefore important. Our genome-wide gene expression analyses revealed that human melanoma cell lines WM793 and especially WM239 (vertical growth phase and metastatic cells, respectively) overexpress the extracellular matrix (ECM) protein transforming growth factor β induced (TGFBI). In adhesion assays, recombinant TGFBI was strongly anti-adhesive for both melanoma cells and skin fibroblasts. TGFBI further impaired the adhesion of melanoma cells to the adhesive ECM proteins fibronectin, collagen-I, and laminin, known to interact with it. Unexpectedly, WM239 cells migrated/invaded more effectively in three-dimensional collagen-I and Matrigel cultures after knockdown of TGFBI by shRNA expression. However, in the physiological subcutaneous microenvironment in nude mice, after TGFBI knockdown, these cells showed markedly impaired tumor growth and invasive capability; the initially formed small tumors later underwent myxoid degeneration and completely regressed. By contrast, the expanding control tumors showed intense TGFBI staining at the tumor edges, co-localizing with the fibrillar fibronectin/tenascin-C/periostin structures that characteristically surround melanoma cells at invasion fronts. Furthermore, TGFBI was found in similar fibrillar structures in clinical human melanoma metastases as well, co-localizing with fibronectin. These data imply an important role for TGFBI in the ECM deposition and invasive growth of melanoma cells, rendering TGFBI a potential target for therapeutic interventions.

The ubiquitin ligase MuRF1 protects against cardiac ischemia/reperfusion injury by its proteasome-dependent degradation of phospho-c-Jun

Despite improvements in interventions of acute coronary syndromes, primary reperfusion therapies restoring blood flow to ischemic myocardium leads to the activation of signaling cascades that induce cardiomyocyte cell death. These signaling cascades, including the mitogen-activated protein kinase signaling pathways, activate cardiomyocyte death in response to both ischemia and reperfusion. We have previously identified muscle ring finger-1 (MuRF1) as a cardiac-specific protein that regulates cardiomyocyte mass through its ubiquitin ligase activity, acting to degrade sarcomeric proteins and inhibit transcription factors involved in cardiac hypertrophy signaling. To determine MuRF1's role in cardiac ischemia/reperfusion (I/R) injury, cardiomyocytes in culture and intact hearts were challenged with I/R injury in the presence and absence of MuRF1. We found that MuRF1 is cardioprotective, in part, by its ability to prevent cell death by inhibiting Jun N-terminal kinase (JNK) signaling. MuRF1 specifically targets JNK's proximal downstream target, activated phospho-c-Jun, for degradation by the proteasome, effectively inhibiting downstream signaling and the induction of cell death. MuRF1's inhibitory affects on JNK signaling through its ubiquitin proteasome-dependent degradation of activated c-Jun is the first description of a cardiac ubiquitin ligase inhibiting mitogen-activated protein kinase signaling. MuRF1's cardioprotection in I/R injury is attenuated in the presence of pharmacologic JNK inhibition in vivo, suggesting a prominent role of MuRF1's regulation of c-Jun in the intact heart.

Inhibition of AP-1 suppresses cervical cancer cell proliferation and is associated with p21 expression

AP-1, a transcription factor comprised primarily of Jun and Fos family proteins, regulates genes involved in proliferation, differentiation and oncogenesis. Previous studies demonstrated that elevated expression of Jun and Fos family member proteins is associated with numerous human cancers and in cancer-relevant biological processes. In this study we used a dominant-negative mutant of c-Jun, Tam67, which interferes with the functional activity of all AP-1 complexes, to investigate the requirement of AP-1 in the proliferation and cell cycle progression of cervical cancer cells. Transient and stable expression of Tam67 in CaSki cervical cancer cells resulted in decreased AP-1 activity that correlated with a significant inhibition of cell proliferation and anchorage-independent colony formation. Inhibiting AP-1 activity resulted in a two-fold increase in cells located in the G2/M phase of the cell cycle and an accompanying increase in the expression of the cell cycle regulatory protein, p21. The increase in p21 was associated with a decrease in HPV E6 expression and an increase in p53. Importantly, blocking the induction of p21 in CaSki-Tam67-expressing cells accelerated their proliferation rate to that of CaSki, implicating p21 as a key player in the growth arrest induced by Tam67. Our results suggest a role for AP-1 in the proliferation, G2/M progression and inhibition of p21 expression in cervical cancer.

Identification of integrins alpha6 and beta7 as c-Jun- and transformation-relevant genes in highly invasive fibrosarcoma cells

Understanding the mechanisms of tumor cell invasion is essential for our attempts to prevent cancer deaths. We screened by DNAmicroarrays the c-Jun- and transformation-related gene expression changes in S-adenosylmethionine decarboxylase (AdoMetDC)-overexpressing mouse fibroblasts that are highly invasive in vivo, and their derivatives expressing a tetracycline-inducible dominant-negative mutant of c-Jun (TAM67) or c-Jun shRNA. Among the small set of target genes detected were integrins alpha6 and beta7, cathepsin L and thymosin beta4, all upregulated in the AdoMetDC-transformed cells and downregulated upon reversal of transformation by TAM67 or c-Jun shRNA. The upregulation of integrin alpha6 subunit, pairing with integrin beta1, endowed the transformed cells with the capability to attach to basement membrane laminin and to spread. Further, inhibition of integrin alpha6 or beta1 function with neutralizing antibodies blocked the invasiveness of AdoMetDC-transformants and human HT-1080 fibrosarcoma cells in three-dimensional Matrigel. Moreover, immunohistochemical analyses showed strong integrin alpha6 staining in high-grade human fibrosarcomas. Our data show that c-Jun can regulate all three key steps of invasion: cell adhesion (integrin alpha6), basement membrane/extracellular matrix degradation (cathepsin L) and cell migration (thymosin beta4). In addition, this is the first study to associate integrin beta7, known as a leukocyte-specific integrin binding to endothelial/epithelial cell adhesion molecules, with the transformed phenotype in cells of nonleukocyte origin. As tumor cell invasion is a prerequisite for metastasis, the observed critical role of integrin alpha6beta1 in fibrosarcoma cell invasion/spreading allures testing antagonists to integrin alpha6beta1, alone or combined with inhibitors of cathepsin L and thymosin beta4, as chemotherapeutic agents.

Blockade of AP-1 activity by dominant-negative TAM67 can abrogate the oncogenic phenotype in latent membrane protein 1-positive human nasopharyngeal carcinoma

Although activating protein-1 (AP-1) transcription factors play an important role in mediating metastasis for nasopharyngeal carcinoma (NPC), the biological and physiological functions of AP-1, in relation to the oncogenic phenotype of NPC, are not fully understood. Our previous study showed that the latent membrane protein 1 (LMP1) mediated a primary dimer form of c-jun and jun B. In this study, we used a NPC cell line that express a specific inhibitor of AP-1, a dominant-negative c-jun mutant (TAM67), to investigate the role of AP-1 in regulating the NPC oncogenic phenotype. First, we observed that TAM67 inhibited cell growth in vitro and in vivo. Next, with Western blotting, we discovered that TAM67 impaired the cyclin D1/cdk4 complex but had little effect on the cyclin E/cdk2 complex, concomitantly with inhibiting Rb phosphorylation. RT-PCR and luciferase assay results demonstrated that the levels of cyclin D1 mRNA and the promoter activity in TAM67 transfectants were reduced as compared with control cells. Thereby, we show that blockade of AP-1 transcriptional activity has a negative impact on cyclin D1 transcription. We obtained the first evidence that TAM67 prevented NPC growth both in vitro and in vivo. AP-1 appears to be a novel target for treating or preventing LMP1-positive NPC effectively.

Suppression of FHL2 expression induces cell differentiation and inhibits gastric and colon carcinogenesis

BACKGROUND AND AIMS

FHL2 (4-1/2 LIM protein 2) is an adapter and modifier in protein interactions that is expressed mainly in the heart and ovary. It functions in a cell type- or promoter-specific manner. The aims of this study were to examine its expression in gastrointestinal cancers and to determine its role in cell differentiation and tumorigenesis.

METHODS

FHL2 expression in cancerous and normal gastrointestinal cells was detected by reverse-transcription polymerase chain reaction, immunoblotting, and immunohistochemistry. The effect of FHL2 suppression by both antisense and siRNA methods on cell differentiation and growth were evaluated in vitro and in vivo.

RESULTS

FHL2 expression was up-regulated in gastrointestinal cancer, compared with matched normal tissues. Stable transfection of gastric cancer cell line, AGS, and colon cancer cell line, Lovo, with antisense FHL2 induced lengthened or shuttle-shape morphologic changes with long or dendritic-like cytoplasmic processes and decreased the nuclear:cytoplasmic ratio. FHL2 antisense induced expressions of carcinoembryonic antigen and E-cadherin and the maturation of F-actin. Furthermore, FHL2 antisense inhibited the transcriptions of some oncogenes including cox-2, survivin, c-jun, and hTERT, and suppressed the promoter activity of activator protein-1 and hTERT. Suppression of FHL2 inhibited serum-dependent, anchorage-dependent and -independent cell growth, and suppressed de novo tumor formation in nude mice xenograft.

CONCLUSIONS

Suppression of FHL2 induces cell differentiation and inhibits tumorigenesis. Antisense or siRNA methods targeting FHL2 is a promising strategy for treatment of gastrointestinal cancers.

Human papillomavirus E7 repression in cervical carcinoma cells initiates a transcriptional cascade driven by the retinoblastoma family, resulting in senescence

This work demonstrates a central role for the retinoblastoma (Rb) family in driving the transcriptional program of induced and replicative senescence. HeLa cervical carcinoma cells rapidly undergo senescence when the human papillomavirus (HPV) type 18 E7 gene in these cells is repressed by the bovine papillomavirus (BPV) E2 protein. This senescence response requires the endogenous Rb pathway but not the p53 pathway. Microarray analysis 6 days after BPV E2 introduction into HeLa cells identified 224 cellular genes induced by E7 repression and 354 repressed genes. Many repressed genes were involved in cell cycle progression, and numerous induced genes encoded lysosomal proteins. These gene expression changes were blocked by constitutive expression of the wild-type HPV16 E7 or adenovirus E1A gene, but not by E7 or E1A mutants defective for Rb binding. Short hairpin RNAs targeting the Rb family also inhibited these gene expression changes and blocked senescence. Therefore, surprisingly, the transcriptional response to BPV E2 expression was entirely dependent on E7 repression and activation of the Rb family, and the BPV E2 protein did not directly affect the expression of cellular genes. Activation of the Rb family repressed E2F-responsive genes and stimulated transcriptional activators, thereby mobilizing multiple signals, such as repression of B-MYB and DEK, that were independently sufficient to induce senescence. There was extensive overlap between the transcriptional profiles of senescent, late-passage primary human fibroblasts and senescent cervical carcinoma cells, suggesting that this Rb family-mediated transcriptional cascade also plays a central role in replicative senescence.

A new inducible RNAi xenograft model for assessing the staged tumor response to mTOR silencing

Human xenograft tumor models are widely used for efficacy evaluation of potential cancer targets. siRNA is usually stably introduced into tumor cells prior to transplantation. However, silencing of the cancer therapeutic target usually results in reduced cell growth/survival in vitro and/or failure to establish tumors in vivo, thus hindering tumor response-based efficacy evaluation. The present study explored a new tumor response model based on regulated RNAi, which is more relevant from a clinical standpoint. As a proof of principle, an inducible lentiviral RNAi vector was used to silence the known cancer therapeutic target mTOR upon induction with Doxycycline (DOX). The responses to DOX-induced mTOR silencing were tested both in vitro and in vivo for prostate cancer PC3 models. Significant reduction in cancer cell survival was observed due to cell cycle arrest and apoptosis when mTOR silencing was induced in vitro. mTOR silencing also caused tumor regression for the early-staged PC3 tumors (100% tumor regressed and 45% became tumor-free). The advanced-staged tumors also demonstrated significant responses (100% regressed). Therefore, our results demonstrate the powerful utility of this new inducible xenograft tumor model for efficacy evaluation of cancer targets, and it provides a direct in vivo efficacy validation of mTOR as a cancer therapeutic target.

Regulation of cell proliferation by the antizyme inhibitor: evidence for an antizyme-independent mechanism

The antizyme inhibitor was discovered as a protein that binds to the regulatory protein antizyme and inhibits the ability of antizyme to interact with the enzyme ornithine decarboxylase (ODC). Blocking antizyme activity subsequently leads to increased intracellular levels of ODC and increased ODC enzymatic activity. We now report that antizyme inhibitor is a positive modulator of cell growth. Overexpression of antizyme inhibitor in NIH-3T3 mouse fibroblasts or in AT2.1 Dunning rat prostate carcinoma cells resulted in an increased rate of cell proliferation and an increase in saturation density of the cultured cells. This was accompanied by an increase in intracellular levels of the polyamine putrescine. In AT2.1 cells, antizyme inhibitor overexpression also increased the ability of the cells to form foci when grown under anchorage-independent conditions. In order to determine the role of antizyme on antizyme inhibitor activity we created an antizyme inhibitor mutant, AZI(Delta117-140), which lacks the putative antizyme-binding domain. We show that this mutant fails to bind to antizyme, but remains capable of inducing increased rates of cell proliferation, suggesting that antizyme inhibitor has antizyme-independent functions. Silencing antizyme inhibitor expression leads to diminished levels of cyclin D1 and to reduced cell proliferation. Antizyme inhibitor is capable of preventing cyclin D1 degradation, and this effect is at least partially independent of antizyme. We show that wild-type antizyme inhibitor and the AZI(DeltaY) mutant are capable of direct interaction with cyclin D1 suggesting a potential mechanism for the antizyme-independent effects. Together, our data suggest a novel function for antizyme inhibitor in cellular growth control.

Thymosin beta4 is a determinant of the transformed phenotype and invasiveness of S-adenosylmethionine decarboxylase-transfected fibroblasts

S-adenosylmethionine decarboxylase (AdoMetDC) is a key enzyme in the synthesis of polyamines essential for cell growth and proliferation. Its overexpression induces the transformation of murine fibroblasts in both sense and antisense orientations, yielding highly invasive tumors in nude mice. These cell lines hence provide a good model to study cell invasion. Here, the gene expression profiles of these cells were compared with their normal counterpart by microarray analyses (Incyte Genomics, Palo Alto, CA, and Affymetrix, Santa Clara, CA). Up-regulation of the actin sequestering molecule thymosin beta4 was the most prominent change in both cell lines. Tetracycline-inducible expression of thymosin beta4 antisense RNA caused a partial reversal of the transformed phenotype. Further, reversal of transformation by dominant-negative mutant of c-Jun (TAM67) caused reduction in thymosin beta4 mRNA. Interestingly, a sponge toxin, latrunculin A, which inhibits the binding of thymosin beta4 to actin, was found to profoundly affect the morphology and proliferation of the AdoMetDC transformants and to block their invasion in three-dimensional Matrigel. Thus, thymosin beta4 is a determinant of AdoMetDC-induced transformed phenotype and invasiveness. Up-regulation of thymosin beta4 was also found in ras-transformed fibroblasts and metastatic human melanoma cells. These data encourage testing latrunculin A-like and other agents interfering with thymosin beta4 for treatment of thymosin beta4-overexpressing tumors with high invasive and metastatic potential.

Urokinase plasminogen activator receptor is upregulated by Helicobacter pylori in human gastric cancer AGS cells via ERK, JNK, and AP-1

The gastric pathogen Helicobacter pylori (H. pylori) is suggested to be associated with gastric cancer progression. In this study, we investigated the effect of H. pylori on urokinase plasminogen activator receptor (uPAR) expression which has been known to correlate closely with gastric cancer invasion. H. pylori induced the uPAR expression in a time- and concentration-dependent manner. Specific inhibitors and inactive mutants of MEK-1 and JNK were found to suppress the H. pylori-induced uPAR expression and the uPAR promoter activity. Electrophoretic mobility shift assay and transient transfection study using an AP-1 decoy oligonucleotide confirmed that the activation of AP-1 is involved in the H. pylori-induced uPAR upregulation. The AGS cells treated with H. pylori showed a remarkably enhanced invasiveness, and this effect was partially abrogated by uPAR-neutralizing antibodies. These results suggest that H. pylori induces uPAR expression via Erk-1/2, JNK, and AP-1 signaling pathways and, in turn, stimulates the cell invasiveness in human gastric cancer AGS cells.