The activation of the phosphotyrosine phosphatase eta (r-PTP eta) is responsible for the somatostatin inhibition of PC Cl3 thyroid cell proliferation

The aim of this study was the characterization of the intracellular effectors of the antiproliferative activity of somatostatin in PC Cl3 thyroid cells. Somatostatin inhibited PC Cl3 cell proliferation through the activation of a membrane phosphotyrosine phosphatase. Conversely, PC Cl3 cells stably expressing the v-mos oncogene (PC mos) were completely insensitive to the somatostatin antiproliferative effects since somatostatin was unable to stimulate a phosphotyrosine phosphatase activity. In PC mos cells basal phosphotyrosine phosphatase activity was also reduced, suggesting that the expression of a specific phosphotyrosine phosphatase was impaired in these transformed cells. We suggested that this phosphotyrosine phosphatase could be r-PTP eta whose expression was abolished in the PC mos cells. To directly prove the involvement of r-PTP eta in somatostatin's effect, we stably transfected this phosphatase in PC mos cells. This new cell line (PC mos/PTP eta) recovered somatostatin's ability to inhibit cell proliferation, showing dose-dependence and time course similar to those observed in PC Cl3 cells. Conversely, the transfection of a catalytically inactive mutant of r-PTP eta did not restore the antiproliferative effects of somatostatin. PC mos/PTP eta cells showed a high basal phosphotyrosine phosphatase activity which, similarly to PC Cl3 cells, was further increased after somatostatin treatment. The specificity of the role of r-PTP eta in somatostatin receptor signal transduction was demonstrated by measuring its specific activity after somatostatin treatment in an immunocomplex assay. Somatostatin highly increased r-PTP eta activity in PCCl3 and PC mos/PTP eta (+300%, P < 0.01) but not in PCmos cells. Conversely, no differences in somatostatin-stimulated SHP-2 activity, (approximately +50%, P < 0.05), were observed among all the cell lines. The activation of r-PTP eta by somatostatin caused, acting downstream of MAPK kinase, an inhibition of insulin-induced ERK1/2 activation with the subsequent blockade of the phosphorylation, ubiquitination, and proteasome degradation of the cyclin-dependent kinase inhibitor p27(kip1). Ultimately, high levels of p27(kip1) lead to cell proliferation arrest. In conclusion, somatostatin inhibition of PC Cl3 cell proliferation requires the activation of r-PTP eta which, through the inhibition of MAPK activity, causes the stabilization of the cell cycle inhibitor p27(kip1).     

Somatostatin receptor 1 (SSTR1)-mediated inhibition of cell proliferation correlates with the activation of the MAP kinase cascade: role of the phosphotyrosine phosphatase SHP-2.

The mitogen activated protein (MAP) kinase cascade represents one of the major regulator of cell growth by hormones and growth factors. However, although the activation of this intracellular pathway has been often regarded as mediator of cell proliferation, in many cell types the increase in MAP kinase (also called extra-cellular signal regulated kinase: ERK) activity may result in cell growth arrest, depending on the length or the intensity of the stimulation. In this review we examine recent data concerning the effects of somatostatin on the MAP kinase cascade through one of its major receptor subtype, the somatostatin receptor 1 (SSTR1), stably expressed in CHO-K1 cells. Somatostatin inhibits the proliferative effects of basic FGF (bFGF) in CHO-SSTR1 cell line. However, in these cells, somatostatin robustly activates the MAP kinase and augments bFGF-induced stimulation of ERK. We show that the activation of ERK via SSTR1 is mediated by the betagamma subunit of a pertussis toxin-sensitive G-protein and requires both the small G protein Ras and the serine/threonine kinase Raf-1. Moreover the phosphatidyl inositol-3kinase and the cytosolic tyrosine kinase c-src participate in the signal transduction regulated by SSTRI to activate ERK, as well as it is involved the protein tyrosine phosphatase (PTP) SHP-2. Previous studies have suggested that somatostatin-stimulated PTP activity mediates the growth inhibitory actions of somatostatin, in CHO-SSTR1 cells. Thus, the activation of SHP-2 by SSTR1 may mediate the antiproliferative activity of somatostatin. SHP-2 may. in turn, regulate the activity of kinases upstream of ERK that require tyrosine dephosphorylation to be activated, such as c-src. Finally, the synergism between somatostatin and bFGF in the activation of ERK results in an increased expression of the cyclin-dependent kinase inhibitor p21cip/WAF1 as molecular effector of the antiproliferative activity of somatostatin.     

An intracellular multi-effector complex mediates somatostatin receptor 1 activation of phospho-tyrosine phosphatase eta

The receptor-like phosphotyrosine phosphatase eta (PTPeta) is an important intracellular effector of the cytostatic action of SST. Here we characterize, in Chinese hamster ovary-k1 cells, the intracellular pathway that from somatostatin receptor 1 (SSTR1), leads to the activation of PTPeta and that involves, in a multimeric complex and sequential activation, the tyrosine kinases Janus kinase (JAK) 2 and Src, and the cytosolic phosphotyrosine phosphatase SHP-2. We show that inhibitors of JAK2 and Src and dominant-negative mutants of SHP-2 and Src abolished the SSTR1-mediated PTPeta activation, suggesting that all these effectors participate in the activation of PTPeta. In basal conditions, JAK2 forms a multimeric complex with SHP-2, Src and PTPeta. In response to SST, JAK2 is activated in a G protein-dependent manner, dissociates from and phosphorylates SHP-2, increasing its activity. Subsequently, SHP-2 dissociates from Src, dephosphorylates the Src inhibitory tyrosine-529, and causes an autocatalytical increase of the phosphorylation of Src tyrosine 418, located inside its kinase activation loop. Active Src, in turn, controls the activity of PTPeta, via a direct interaction and phosphorylation of the phosphatase. These data for the first time depict an intracellular pathway involving a precise sequence of interactions and cross-activation among tyrosine phosphatases and kinases acting upstream of PTPeta. In particular the sequential activation of JAK2, SHP-2, and Src conveys the molecular signaling from SSTR1 to the activation of this phosphatase that is responsible for the final biological effects of SST.     

Inhibition of matrix metalloproteinase-9 gene expression by an isoflavone metabolite, irisolidone in U87MG human astroglioma cells

Matrix metalloproteinase-9 (MMP-9) plays an important role in mediating the invasion and angiogenic process of malignant gliomas. This study was undertaken to determine if an isoflavone metabolite, irisolidone, inhibits MMP-9 expression in human astroglioma cells. Irisolidone was found to inhibit the secretion and protein expression of MMP-9 induced by PMA in U87 MG glioma cells, accompanied by the inhibition of MMP-9 mRNA expression and promoter activity. Further mechanistic studies revealed that irisolidone inhibits the binding of NF-κB and AP-1 to the MMP-9 promoter and suppresses the PMA-induced phosphorylation of ERK and JNK, which are upstream signaling molecules in MMP-9 expression. The Matrigel-invasion assay showed that irisolidone suppresses the in vitro invasiveness of glioma cells. Therefore, the strong inhibition of MMP-9 expression by irisolidone might be a potential therapeutic modality for controlling the growth and invasiveness of gliomas.     

LRRC4 inhibits the proliferation of human glioma cells by modulating the expression of STMN1 and microtubule polymerization

LRRC4 is a tumor suppressor of glioma, and it is epigenetically inactivated commonly in glioma. Our previous study has shown that induction of LRRC4 expression inhibits the proliferation of glioma cells. However, little is known about the mechanisms underlying the action of LRRC4 in glioma cells. We employed two-dimensional fluorescence differential gel electrophoresis (2-D DIGE) and MALDI -TOF/TOF-MS/MS to identify 11 differentially expressed proteins, including the significantly down-regulated STMN1 expression in the LRRC4-expressing U251 glioma cells. The levels of STMN1 expression appeared to be positively associated with the pathogenic degrees of human glioma. Furthermore, induction of LRRC4 over-expression inhibited the STMN1 expression and U251 cell proliferation in vitro, and the glioma growth in vivo. In addition, induction of LRRC4 or knockdown of STMN1 expression induced cell cycle arrest in U251 cells, which was associated with modulating the p21, cyclin D1, and cyclin B expression, and the ERK phosphorylation, and inhibiting the CDK5 and cdc2 kinase activities, but increasing the microtubulin polymerization in U251 cells. LRRC4, at least partially by down-regulating the STMN1expression, acts as a major glioma suppressor, induces cell cycle arrest and modulates the dynamic process of microtubulin, leading to the inhibition of glioma cell proliferation and growth. Potentially, modulation of LRRC4 or STMN1 expression may be useful for design of new therapies for the intervention of glioma.     

Cannabinoids induce glioma stem-like cell differentiation and inhibit gliomagenesis

Glioma stem-like cells constitute one of the potential origins of gliomas, and therefore, their elimination is an essential factor for the development of efficient therapeutic strategies. Cannabinoids are known to exert an antitumoral action on gliomas that relies on at least two mechanisms: induction of apoptosis of transformed cells and inhibition of tumor angiogenesis. However, whether cannabinoids target human glioma stem cells and their potential impact in gliomagenesis are unknown. Here, we show that glioma stem-like cells derived from glioblastoma multiforme biopsies and the glioma cell lines U87MG and U373MG express cannabinoid type 1 (CB(1)) and type 2 (CB(2)) receptors and other elements of the endocannabinoid system. In gene array experiments, CB receptor activation altered the expression of genes involved in the regulation of stem cell proliferation and differentiation. The cannabinoid agonists HU-210 and JWH-133 promoted glial differentiation in a CB receptor-dependent manner as shown by the increased number of S-100beta- and glial fibrillary acidic protein-expressing cells. In parallel, cannabinoids decreased the cell population expressing the neuroepithelial progenitor marker nestin. Moreover, cannabinoid challenge decreased the efficiency of glioma stem-like cells to initiate glioma formation in vivo, a finding that correlated with decreased neurosphere formation and cell proliferation in secondary xenografts. Gliomas derived from cannabinoid-treated cancer stem-like cells were characterized with a panel of neural markers and evidenced a more differentiated phenotype and a concomitant decrease in nestin expression. Overall, our results demonstrate that cannabinoids target glioma stem-like cells, promote their differentiation, and inhibit gliomagenesis, thus giving further support to their potential use in the management of malignant gliomas.     

Inhibition of sphingosine kinase 1 suppresses proliferation of glioma cells under hypoxia by attenuating activity of extracellular signal-regulated kinase

Objectives: Sphingosine kinase (SphK), which is regulated by hypoxia, catalyses phosphorylation of sphingosine to produce sphingosine‐1‐phosphate, which stimulates invasiveness of gliomas. However, whether SphK is involved in proliferation of glioma cells under hypoxic conditions is not clearly understood. In this study, we have investigated the role of SphK in of proliferation glioma cells under hypoxia. Materials and methods: Effects of small interfering RNA (siRNA) on SphKs, SKI (inhibitor of SphK) and U0126 (inhibitor of ERK) on proliferation of glioma cells under hypoxia were studied using CCK‐8 assay and flow cytometry. Protein expression profiles were evaluated by Western blot analysis. Results:  SKI suppressed proliferation of glioma cells under hypoxia. Similarly, downregulation of SphKs by siRNA inhibited glioma cell proliferation, and the cell cycle was arrested in G₂/M phase when SphK1 was inhibited. In addition, inhibition of SphK1 attenuated phosphorylation of ERK in hypoxic conditions. Furthermore, U0126 markedly inhibited cell population growth and arrested cells in G₂/M as effectively as SKI. However, silencing SphK2 induced cell cycle arrest in the S phase and it showed little effect on hypoxia‐induced activation of ERK. Conclusions: SphK1 and SphK2 are involved in proliferation of glioma cells in hypoxic conditions through distinct signalling pathways. SphK1, but not SphK2, promotes cell population expansion in hypoxic conditions by activating ERK.     

Antitumor activity of methyl gallate by inhibition of focal adhesion formation and Akt phosphorylation in glioma cells

Background

Methyl gallate (MG) possesses a wide range of biological properties that include anti-oxidant, anti-inflammatory, and anti-microbial activities. However, its anti-tumor activity has not been extensively examined in cancer cells. Thus, we examined the effect of MG in both glutamate-induced rat C6 and human U373 glioma cell proliferation and migration.

Methods

MG was isolated from the stem bark of Acer barbinerve. Cell viability and migration were analyzed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and scratch wound-healing assay, respectively. Focal adhesion formation was detected with immunofluorescence.

Results

Treatment of C6 and U373 glioma cells with MG significantly reduced cell viability, migration, and Akt phosphorylation level. Glutamate stimulation markedly increased the level of ERK1/2 phosphorylation. However, cells treated with MG displayed decreased ERK1/2 phosphorylation. Inhibition of ERK1/2 by MG or MEK1/2 inhibitor significantly inhibited paxillin phosphorylation at Ser⁸³ and focal adhesion turn-over produced inefficient glioma cell migration. In addition, activation of Akt and ERK1/2 upon glutamate stimulation was independently regulated by Ca^2 + and protein kinase C activity, respectively, via the α-amino-3-hydroxy-5-methy-4-isoxazolepropionate acid glutamate receptor and metabotropic glutamate receptor.

General significance

Our results clearly indicate that MG has a strong anti-tumor effect through the down-regulation of the Akt and ERK1/2 signaling pathways. Thus, methyl gallate is a potent anti-tumor and novel therapeutic agent for glioma.     

Arsenic trioxide induces different gene expression profiles of genes related to growth and apoptosis in glioma cells dependent on the p53 status

We have previously reported that As(2)O(3) affected cell cycle progression and cyclins D1 and B1 expression in two glioma cell lines differing in p53 status (U87MG-wt; T98G-mutated). In the present study, we further demonstrated that As(2)O(3) affected proliferation, viability and apoptosis of the two cell lines in a dose- and time-dependent manner, and T98G cells were more sensitive than U87MG cells to As(2)O(3) -induced apoptosis and inhibition of proliferation and viability. We further investigated the expression profiles of genes related with apoptosis and cell cycle in the two cell lines with a human cDNA-microarray (SuperArray) spotted with 267 genes of apoptosis and cell cycle. Thirty five genes were upregulated and 15 genes downregulated at least 2-fold by As(2)O(3) in U87-MG cells; whereas, 38 genes were upregulated and 21 genes downregulated at least 2-fold in T98G cells by As(2)O(3). After As(2)O(3) treatment, p53 expression was upregulated 56.5-fold in T98G cells, but only 6.0-fold in U87MG cells. The results indicate that As(2)O(3) suppresses the growth of U87MG cells mainly by regulating expression of genes of cell cycle arrest, stress and toxicity; whereas As(2)O(3) affects T98G cells mainly by regulating expression of genes belonging to Bcl-2, tumor necrotic factor receptor and ligand families. The data may be helpful for optimizing As(2)O(3) as an anti-cancer drug in the treatment of gliomas.     

Glioma Cell Proliferation Controlled by ERK Activity-Dependent Surface Expression of PDGFRA

Increased PDGFRA signaling is an essential pathogenic factor in many subtypes of gliomas. In this context the cell surface expression of PDGFRA is an important determinant of ligand sensing in the glioma microenvironment. However, the regulation of spatial distribution of PDGFRA in glioma cells remains poorly characterized. Here, we report that cell surface PDGFRA expression in gliomas is negatively regulated by an ERK-dependent mechanism, resulting in reduced proliferation of glioma cells. Glioma tumor tissues and their corresponding cell lines were isolated from 14 patients and analyzed by single-cell imaging and flow cytometry. In both cell lines and their corresponding tumor samples, glioma cell proliferation correlated with the extent of surface expression of PDGFRA. High levels of surface PDGFRA also correlated to high tubulin expression in glioma tumor tissue in vivo. In glioma cell lines, surface PDGFRA declined following treatment with inhibitors of tubulin, actin and dynamin. Screening of a panel of small molecule compounds identified the MEK inhibitor U0126 as a potent inhibitor of surface PDGFRA expression. Importantly, U0126 inhibited surface expression in a reversible, dose- and time-dependent manner, without affecting general PDGFRA expression. Treatment with U0126 resulted in reduced co-localization between PDGFRA and intracellular trafficking molecules e.g. clathrin, RAB11 and early endosomal antigen-1, in parallel with enhanced co-localization between PDGFRA and the Golgi cisternae maker, Giantin, suggesting a deviation of PDGFRA from the endosomal trafficking and recycling compartment, to the Golgi network. Furthermore, U0126 treatment in glioma cells induced an initial inhibition of ERK1/2 phosphorylation, followed by up-regulated ERK1/2 phosphorylation concomitant with diminished surface expression of PDGFRA. Finally, down-regulation of surface PDGFRA expression by U0126 is concordant with reduced glioma cell proliferation. These findings suggest that manipulation of spatial expression of PDGFRA can potentially be used to combat gliomas.     

Glioma-specific cation conductance regulates migration and cell cycle progression

In this study, we have investigated the role of a glioma-specific cation channel assembled from subunits of the Deg/epithelial sodium channel (ENaC) superfamily, in the regulation of migration and cell cycle progression in glioma cells. Channel inhibition by psalmotoxin-1 (PcTX-1) significantly inhibited migration and proliferation of D54-MG glioma cells. Both PcTX-1 and benzamil, an amiloride analog, caused cell cycle arrest of D54-MG cells in G(0)/G(1) phases (by 30 and 40%, respectively) and reduced cell accumulation in S and G(2)/M phases after 24 h of incubation. Both PcTX-1 and benzamil up-regulated expression of cyclin-dependent kinase inhibitor proteins p21(Cip1) and p27(Kip1). Similar results were obtained in U87MG and primary glioblastoma multiforme cells maintained in primary culture and following knockdown of one of the component subunits, ASIC1. In contrast, knocking down δENaC, which is not a component of the glioma cation channel complex, had no effect on cyclin-dependent kinase inhibitor expression. Phosphorylation of ERK1/2 was also inhibited by PcTX-1, benzamil, and knockdown of ASIC1 but not δENaC in D54MG cells. Our data suggest that a specific cation conductance composed of acid-sensing ion channels and ENaC subunits regulates migration and cell cycle progression in gliomas.     

MiR-483-5p suppresses the proliferation of glioma cells via directly targeting ERK1

MicroRNAs (miRNAs) exhibit tumor-specific expression signatures and play crucial roles in tumorigenesis by targeting oncogenes. Here, through analyzing the miRNA-array profiles of human glioblastoma tissues and the adjacent normal brain tissues, we found miR-483-5p was significantly down-regulated in gliomas, which was confirmed in both human glioma specimens and cell lines. The overexpression of miR-483-5p suppressed glioma cell proliferation and induced a G0/G1 arrest. In contrast, miR-483-5p inhibition promoted cell proliferation. Furthermore, by a dual-luciferase reporter assay and expression analysis, we identified extracellular signal-regulated kinase 1 (ERK1) as a direct target of miR-483-5p. ERK1 knockdown can block cell proliferation induced by miR-483-5p inhibition. Thus, our findings provide the first evidence that miR-483-5p can serve as a tumor suppressor in gliomas.     

Role of gonadotropin-releasing hormone (GnRH) in ovarian cancer

The expression of GnRH (GnRH-I, LHRH) and its receptor as a part of an autocrine regulatory system of cell proliferation has been demonstrated in a number of human malignant tumors, including cancers of the ovary. The proliferation of human ovarian cancer cell lines is time- and dose-dependently reduced by GnRH and its superagonistic analogs. The classical GnRH receptor signal-transduction mechanisms, known to operate in the pituitary, are not involved in the mediation of antiproliferative effects of GnRH analogs in these cancer cells. The GnRH receptor rather interacts with the mitogenic signal transduction of growth-factor receptors and related oncogene products associated with tyrosine kinase activity via activation of a phosphotyrosine phosphatase resulting in downregulation of cancer cell proliferation. In addition GnRH activates nucleus factor κB (NFκB) and protects the cancer cells from apoptosis. Furthermore GnRH induces activation of the c-Jun N-terminal kinase/activator protein-1 (JNK/AP-1) pathway independent of the known AP-1 activators, protein kinase (PKC) or mitogen activated protein kinase (MAPK/ERK).     

Involvement of PKC-iota in glioma proliferation

Abstract.   Atypical protein kinase C-iota (PKC-ι) protects cells against apoptosis and may play a role in cell proliferation. However, in vivo , the status and function of PKC-ι in human normal brain tissue, gliomas, benign and malignant meningiomas as well as its in vitro status in proliferating and confluent glioma cells, remains unknown. Objectives : The objectives of our research were to determine whether expression of PKC-ι is altered either in gliomas or in benign and malignant meningiomas, compared to normal brain. In addition, we wished to establish the expression of PKC-ι in proliferating plus in cell cycle-arrested glioma cell lines, as well as the relationship between PKC-ι siRNA on PKC-ι protein content and cell proliferation. Materials and Methods : Western blot analyses for PKC-ι were performed on 12 normal brain biopsies, 15 benign meningiomas, three malignant meningiomas and three gliomas. Results : Results demonstrated no ( n  = 9) or very weak ( n  = 3) detection of PKC-ι in normal brain tissue. In comparison, PKC-ι was robustly present in the majority of the benign meningiomas. Similarly, PKC-ι was abundant in all malignant meningiomas and gliomas. Western blotting for PKC-ι in confluent or proliferating glioma cell lines depicted substantial quantities of PKC-ι in proliferating T98G and U-138MG glioma cells. In contrast, confluent cells had either 71% (T98G) or 21% (U-138MG) less PKC-ι than proliferating cells. T98 and U-138 MG glioma cells treated with 100 n m PKC-ι siRNA had lower levels of cell proliferation compared to control siRNA-A and complete down-regulation of PKC-ι protein content. Conclusion : These results support the concept that presence of PKC-ι may be required for cell proliferation to take place.     

Variation of T-type calcium channel protein expression affects cell division of cultured tumor cells

In this study we investigated the T-type calcium channel and its involvement in the cell division of U87MG cultured glioma cells and N1E-115 neuroblastoma cells. Using Western blot analysis, we found that expression of both alpha1G and alpha1H subunits of the T-type calcium channel decreased during conditions associated with a decrease in proliferation as evidenced by increased expression of cyclin D1, a marker for non-proliferating cells. Both serum starvation and application of mibefradil, a selective T-type calcium channel antagonist, resulted in a 50% decrease in the expression of alpha1G and alpha1H and a 700-900% increase in levels of cyclin D1 in U87MG and N1E-115 cells, respectively. Furthermore, overexpression of the alpha1H subunit resulted in a two-fold increase in cell proliferation compared to control cultures or cultures receiving an empty vector. In contrast, blocking expression of the alpha1G subunit using antisense oligonucleotides lead to a 70% decrease in proliferation of U87MG and N1E-115 cells compared to control cultures or cultures receiving a scrambled oligonucleotide. Our findings suggest that proliferation of U87MG glioma cells and N1E-115 is regulated by T-type calcium channel expression.     

A mutant receptor tyrosine phosphatase,CD148, causes defects in vascular development

Vascularization defects in genetic recombinant mice have defined critical roles for a number of specific receptor tyrosine kinases. Here we evaluated whether an endothelium-expressed receptor tyrosine phosphatase, CD148 (DEP-1/PTPeta), participates in developmental vascularization. A mutant allele, CD148(DeltaCyGFP), was constructed to eliminate CD148 phosphatase activity by in-frame replacement of cytoplasmic sequences with enhanced green fluorescent protein sequences. Homozygous mutant mice died at midgestation, before embryonic day 11.5 (E11.5), with vascularization failure marked by growth retardation and disorganized vascular structures. Structural abnormalities were observed as early as E8.25 in the yolk sac, prior to the appearance of intraembryonic defects. Homozygous mutant mice displayed enlarged vessels comprised of endothelial cells expressing markers of early differentiation, including VEGFR2 (Flk1), Tal1/SCL, CD31, ephrin-B2, and Tie2, with notable lack of endoglin expression. Increased endothelial cell numbers and mitotic activity indices were demonstrated. At E9.5, homozygous mutant embryos showed homogeneously enlarged primitive vessels defective in vascular remodeling and branching, with impaired pericyte investment adjacent to endothelial structures, in similarity to endoglin-deficient embryos. Developing cardiac tissues showed expanded endocardial projections accompanied by defective endocardial cushion formation. These findings implicate a member of the receptor tyrosine phosphatase family, CD148, in developmental vascular organization and provide evidence that it regulates endothelial proliferation and endothelium-pericyte interactions.     

Involvement of MEKK1/ERK/P21Waf1/Cip1 signal transduction pathway in inhibition of IGF-I-mediated cell growth response by methylglyoxal

The abnormal accumulation of methylglyoxal (MG), a physiological glucose metabolite, is strongly related to the development of diabetic complications by affecting the metabolism and functions of organs and tissues. These disturbances could modify the cell response to hormones and growth factors, including insulin-like growth factor-1 (IGF-I). In this study, we investigated the effect of MG on IGF-I-induced cell proliferation and the mechanism of the effect in two cell lines, a human embryonic kidney cell line (HEK293), and a mouse fibroblast cell line (NIH3T3). MG rendered these cells resistant to the mitogenic action of IGF-I, and this was associated with stronger and prolonged activation of ERK and over-expression of P21(Waf1/Cip1). The synergistic effect of MG with IGF-I in activation of ERK was completely abolished by PD98059 but not by a specific PI3K inhibitor, LY294002, or a specific PKC inhibitor, bisindolylmaleimide. Blocking of Raf-1 activity by expression of a dominant negative form of Raf-1 did not reduce the enhancing effect of MG on IGF-I-induced activation of ERK. However, transfection of a catalytically inactive form of MEKK1 resulted in inactivation of the MG-induced activation of ERK and partial inhibition of the enhanced activation of ERK and over-expression of p21(Waf1/Cip1) induced by co-stimulation of MG and IGF-I. These results suggested that the alteration of intracellular milieu induced by MG through a MEKK1-mediated and PI3K/PKC/Raf-1-independent pathway resulted in the modification of cell response to IGF-I for p21(Waf1/Cip1)-mediated growth arrest, which may be one of the crucial mechanisms for MG to promote the development of chronic clinical complications in diabetes.     

GBP3 promotes glioma cell proliferation via SQSTM1/p62-ERK1/2 axis

Guanylate binding proteins (GBPs) are interferon-inducible large GTPases and play a crucial role in cell-autonomous immunity. However, the biology function of GBPs in cancer remains elusive. GBP3 is specifically expressed in adult brain. Here we show that GBP3 is highly elevated in human glioma tumors and glioma cell lines. Overexpression of GBP3 dramatically increased glioma cell proliferation whereas silencing GBP3 by RNA interference produced opposite effects. We further showed that GBP3 expression was able to induce sequestosome-1(SQSTM1, also named p62) expression and activate extracellular signal-regulated kinase (ERK1/2). The SQSTM1-ERK1/2 signaling cascade was essential for GBP3-promoted cell growth because depletion of SQSTM1 markedly reduced the phosphorylated ERK1/2 levels and GBP3-mediated cell growth, and inhibition of mitogen-activated protein kinase/ERK kinase abolished GBP3-induced glioma cell proliferation. Consistently, GBP3 overexpression significantly promoted glioma tumor growth in vivo and its expression was inversely correlated with the survival rate of glioma patients. Taken together, these results for the first time suggest that GBP3 contributes to the proliferation of glioma cells via regulating SQSTM1-ERK1/2 pathway, and GBP3 might represent as a new potential therapeutic target against glioma.     

The effect of laparoscopic surgery in stage II and III right-sided colon cancer: a retrospective study

Background

We examined the association of tumor-derived hepatocyte growth factor (HGF) with the clinicopathological features of gliomas and investigated the effect of HGF inhibition on the biological behavior of tumor cells in vitro in order to determine whether HGF is a valuable prognostic predictor for glioma patients.

Methods

Seventy-six cases of glioma were collected. The tumor-derived HGF expression, cell proliferation index (PI) and intratumoral microvessels were evaluated by immunohistochemistry. Correlation between immunostaining and clinicopathological parameters, as well as the follow-up data of patients, was analyzed statistically. U87MG glioma cells were transfected with short interference (si)-RNA for HGF, and the cell viability, migratory ability and chemosensitivity to cisplatin were evaluated in vitro.

Results

Both high HGF expression in tumor cells (59.2%, 45/76) and high PI were significantly associated with high-grade glioma and increased microvessels in tumors (P?<?0.05). However, only histological grading (P?=?0.004) and high-expression of HGF (P?=?0.008) emerged as independent prognostic factors for the overall survival of glioma patients. The tumor-derived HGF mRNA and protein expressions were significantly decreased in vitro after transfection of HGF siRNA. HGF siRNA inhibited the cell growth and reduced cell migratory ability. Moreover, HGF siRNA transfection enhanced the chemosensitivity of U87MG glioma cells to cisplatin.

Conclusion

This study indicated that there was significant correlation among tumor cell-derived HGF, cell proliferation and microvessel proliferation in gliomas. HGF might influence tumor progression by modulating the cell growth, migration and chemoresistance to drugs. Increased expression of HGF may be a valuable predictor for prognostic evaluation of glioma patients.