Endogenously produced ganglioside GM3 endows etoposide and doxorubicin resistance by up-regulating Bcl-2 expression in 3LL Lewis lung carcinoma cells

The ganglioside patterns have been shown to dramatically change during cell proliferation and differentiation and in certain cell-cycle phases, brain development, and cancer malignancy. To investigate the significance of the ganglioside GM3 in cancer malignancy, we established GM3-reconstituted cells by transfecting the cDNA of GM3 synthase into a GM3-deficient subclone of the 3LL Lewis lung carcinoma cell line (Uemura, S. (2003) Glycobiology, 13, 207-216). The GM3-reconstituted cells were resistant to apoptosis induced by etoposide and doxorubicin. There were no changes in the expression levels of topoisomerase IIalpha or P-glycoprotein, or in the uptake of doxorubicin between the GM3-reconstituted cells and the mock-transfected cells. To understand the mechanism of the etoposide-resistant phenotype acquired in the GM3-reconstituted cells, we investigated their apoptotic signaling. Although no difference was observed in the phosphorylation of p53 at serine-15-residue site by etoposide between the GM3-reconstituted cells and mock-transfected cells, the activation of both caspase-3 and caspase-9 was specifically inhibited in the former. We found that the anti-apoptotic protein B-cell leukemia/lymphoma 2 (Bcl-2) was increased in the GM3-reconstituted cells. Moreover, wild-type 3LL Lewis lung carcinoma cells, which have an abundance of GM3, exhibited no DNA fragmentation following etoposide treatment and expressed higher levels of the Bcl-2 protein compared with the J5 subclone. Thus, these results support the conclusion that endogenously produced GM3 is involved in malignant phenotypes, including anticancer drug resistance through up-regulating the Bcl-2 protein in this lung cancer cell line.     

神经节苷脂GM_3对人白血病J6-2细胞PKC转位及DAG含量的影响

应用SDS PAGE及Western印迹技术检测神经节苷脂GM3 处理前后人白血病J6 2细胞不同类型PKC在细胞内的转位情况 ,同时利用高效薄板层析技术观察了细胞内DAG含量的变化 ,从而探讨GM3 抑制PKC活性的机制 .实验发现 ,GM3 处理后胞液PKCα明显增加 ,而颗粒结合PKCα则相对减少 ;GM3 对其它亚型PKC在细胞内分布无显著影响 .同时还发现 ,GM3 处理后细胞内DAG含量降低 (P <0 0 5 ) .结果表明 ,GM3 抑制PKCα由胞浆向质膜转位 ,对其它亚型PKC在细胞内转位无影响 .提示GM3 抑制的PKC亚型可能是PKCα .同时GM3 降低细胞内DAG含量 ,这可能与GM3抑制PKCα活性机制有关     

Stable transfection of DAOY cells with a GM3 synthase antisense construct and transient reduction in ganglioside content

Tumor cell gangliosides are bioactive molecules involved in tumor-host interactions. To investigate their role in tumor formation and angiogenesis, we sought to develop an inhibitory model targeting human GM3 synthase, an essential enzyme in the ganglioside synthesis pathway, by antisense transfection. We prepared a number of transfectants from DAOY human medulloblastoma cells and isolated clones that stably expressed a 560-bp fragment of human GM3 synthase cDNA, in either sense or antisense orientation, as well as clones transfected with an empty vector. Both sense and antisense clones permanently incorporated mammalian expression vectors into their genomes. The DAOY cell clones were screened for ganglioside content using total lipid extraction, ganglioside isolation, and HPTLC. One antisense-transfected clone, 7.2A, in which total ganglioside content was reduced by 70%, was selected for further study. All sense-and sham-transfectants had ganglioside levels not different from that of untransfected DAOY cells. After 10 passages however, while antisense mRNA expression was fully maintained, the ganglioside content of 7.2A cells had reverted to normal levels. Antisense RNA transfection can sometimes have a reversible effect on the expression of a target. Possible regulatory mechanisms of this previously unrecognized process of reversion to wild type phenotype are discussed.     

Sustained activation of extracellular signal-regulated kinase by nerve growth factor regulates c-fos protein stabilization and transactivation in PC12 cells

The duration of intracellular signaling is thought to be a critical component in effecting specific biological responses. This paradigm is demonstrated by growth factor activation of the extracellular signal-regulated kinase (ERK) signaling cascade in the rat pheochromocytoma cell line (PC12 cells). In this model, sustained ERK activation induced by nerve growth factor (NGF) results in differentiation, whereas transient ERK activation induced by epidermal growth factor (EGF) results in proliferation in these cells. Recently, the immediate early gene product c-fos has been proposed to be a sensor for ERK signaling duration in fibroblasts. In this study, we ask whether this is true for NGF and EGF stimulation of PC12 cells. We show that NGF, but not EGF, can regulate both c-fos stability and activation in an ERK-dependent manner in PC12 cells. This is achieved through ERK-dependent phosphorylation of c-fos. Interestingly, distinct sites regulate enhanced stability and transactivation of c-fos. Phosphorylation of Thr325 and Thr331 are required for maximal NGF-dependent transactivation of c-fos. In addition, a consensus ERK binding site (DEF domain) is also required for c-fos transactivation. However, stability is controlled by ERK-dependent phosphorylation of Ser374, while phosphorylation of Ser362 can induce conformational changes in protein structure. We also provide evidence that sustained ERK activation is required for proper post-translational regulation of c-fos following NGF treatment of PC12 cells. Because these ERK-dependent phosphorylations are required for proper c-fos function, and occur sequentially, we propose that c-fos is a sensor for ERK signaling duration in the neuronal-like cell line PC12.     

Rapid internalization of exogenous ganglioside GM3 and its metabolism to ceramide in human myelogenous leukemia HL-60 cells compared with control ganglioside GM1

Incorporation and metabolism of exogenous GM3 in human myelogenous leukemia HL-60 cells were analyzed using ³H-labeled GM3 ([³H]GM3). [³H]GM3 was rapidly internalized into the cells (trypsin-resistant fraction) 8 times more than the control, ³H-labeled GM1 ([³H]GM1). In addition, not only incorporation but also metabolism of [³H]GM3 was more rapid than [³H]GM1 in HL-60 cells. Moreover, one of the metabolites was found to co-migrate with ceramide in thin-layer chromatography analysis and ceramide formation from exogenous GM3 is more rapid than that from exogenous GM1. These results suggested that there would be some preferential mechanism to produce ceramide from differentiation-inducible GM3 in HL-60 cells rather than from non-inducing GM1.     

CREB/Wnt10b mediates the effect of COX-2 on promoting BMP9-induced osteogenic differentiation via reducing adipogenic differentiation in mesenchymal stem cells

Bone morphogenetic protein 9 (BMP9) is one of the most potent osteogenic factors, which may be a potential candidate for bone tissue engineering. However, the osteogenic capacity of BMP9 still need to be further enhanced. In this study, we determined the effect of Wnt10b on BMP9-induced osteogenic differentiation in mesenchymal stem cell (MSCs) and the possible mechanism underlying this process. We introduced the polymerase chain reaction (PCR), Western blot analysis, histochemical stain, ectopic bone formation, and microcomputed tomography analysis to evaluate the effect of Wnt10b on BMP9-induced osteogenic differentiation. Meanwhile, PCR, Western blot analysis, chromatin immunoprecipitation, and immunoprecipitation were used to analyze the possible relationship between BMP9 and Wnt10b. We found that BMP9 upregulates Wnt10b in C3H10T1/2 cells. Wnt10b increases the osteogenic markers and bone formation induced by BMP9 in C3H10T1/2 cells, and silencing Wnt10b decreases these effects of BMP9. Meanwhile, Wnt10b enhances the level of phosphorylated Smad1/5/8 (p-Smad1/5/8) induced by BMP9, which can be reduced by silencing Wnt10b. On the contrary, Wnt10b inhibits adipogenic markers induced by BMP9, which can be decreased by silencing Wnt10b. Further analysis indicated that BMP9 upregulates cyclooxygenase-2 (COX-2) and phosphorylation of cAMP-responsive element binding (p-CREB) simultaneously. COX-2 potentiates the effect of BMP9 on increasing p-CREB and Wnt10b, while silencing COX-2 decreases these effects. p-CREB interacts with p-Smad1/5/8 to bind the promoter of Wnt10b in C3H10T1/2 cells. Our findings suggested that Wnt10b can promote BMP9-induced osteogenic differentiation in MSCs, which may be mediated through enhancing BMP/Smad signal and reducing adipogenic differentiation; BMP9 may upregulate Wnt10b via the COX-2/p-CREB-dependent manner.     

Apigenin and LY294002 prolong EGF-stimulated ERK1/2 activation in PC12 cells but are unable to induce full differentiation

In rat pheochromocytoma cell line (PC12) cells, initial epidermal growth factor (EGF)-stimulated extracellular signal-regulated protein kinases 1/2 (ERK1/2) phosphorylation was similar to that promoted by nerve growth factor (NGF), but declined rapidly. Pre-treatment with apigenin or LY294002 sustained EGF-stimulated ERK1/2 phosphorylation whereas wortmannin partially blocked initial ERK1/2 phosphorylation. Changes in ERK1/2 phosphorylation correlated with alterations in p90 ribosomal S6 kinase activity. Wortmannin, LY294002 and apigenin totally blocked growth factor-induced protein kinase B phosphorylation. However, none of them potentiated Raf activation, which was in fact decreased by LY290042 and wortmannin. The sustained EGF-induced ERK1/2 activation promoted by apigenin was not sufficient to commit PC12 cells to differentiate, which was achieved by stimulation with NGF, either alone or in the presence of apigenin.     

Impact of cholesterol depletion on shape changes, actin reorganization, and signal transduction in neutrophil-like HL-60 cells

Stimulation of neutrophils with chemotactic peptide induces actin reorganization, formation of actin-rich protrusions, and development of polarity. Shape changes and actin polymerization can also be induced by phorbol ester-mediated direct activation of protein kinase C (PKC). We have investigated the role of cholesterol in stimulus-dependent motile events and in activation of signaling pathways in neutrophil-like differentiated HL-60 cells. Depletion of plasma membrane cholesterol using methyl-beta-cyclodextrin (MbetaCD) prevented chemotactic peptide and phorbol ester-induced shape changes and increases in cytoskeletal actin. Cholesterol depletion almost completely suppressed chemotactic peptide-mediated activation of p42/44 mitogen-activated protein kinase (MAPK). Phosphorylation of protein kinase B on Thr-308, which is indicative of activation of phosphatidylinositol 3-kinase, was in contrast only partially inhibited. Stimulus-mediated membrane recruitment of different PKC isoforms was differentially affected by treatment of cells with MbetaCD. Membrane recruitment of PKCalpha induced by chemotactic peptide or phorbol ester was suppressed, whereas that of PKCbetaII was only partially affected. Membrane association of PKCdelta was almost insensitive to cholesterol depletion. In summary, our results implicate an important role of cholesterol-containing lipid microdomains (rafts) especially in chemotactic peptide-induced activation of MAPK pathways and in chemotactic peptide- and phorbol ester-mediated activation of PKCalpha.     

Magnesium restriction induces granulocytic differentiation and expression of P27Kip1 in human leukemic HL-60 cells

When cultured in Mg restricted medium, human leukemic HL-60 cells develop morphological and functional granulocytic differentiation. In 0.03 mM Mg, cells display the distinctive features of differentiation, without appreciable inhibition of proliferation. In 0.01 mM Mg, cells show terminal differentiation, accompanied by clear inhibition of proliferation. Such cells accumulate in the G0/G1 phase and subsequently die via apoptosis, similar to HL-60 cells that have been induced to differentiate by DMSO. These phenotypic changes are associated with a marked increase in the expression level of the cyclin dependent kinase inhibitor p27^Kip1. Cyclin E expression is also slightly increased in Mg restricted cells, whereas no changes are observed in the expression level of cyclin D1. We also show that during differentiation cell total Mg decreases, whereas [Mg²⁺]_i increases in both Mg-depleted and DMSO-treated cells. These data suggest that the maturation process is paralleled by a redistribution of intracellular Mg, leading to a shift from the bound to the free form. These changes could modulate the kinetics of Mg-dependent enzyme(s) that are involved in the control of the differentiation pathway. We propose that this model may represent an useful tool for the study of the mechanisms of cell differentiation and related events, such as aging and death. J. Cell. Biochem. 70:313–322, 1998. © 1998 Wiley-Liss, Inc.     

Regulation of glycogen synthase kinase-3beta by products of lipid peroxidation in human neuroblastoma cells

The potential role of 4-hydroxynonenal (HNE), a major product of membrane lipid peroxidation, in regulating glycogen synthase kinase-3beta (GSK3beta) activity was examined in human neuroblastoma IMR-32 cells. The inhibition of GSK3beta activity by HNE was observed by in vitro kinase assays with two substrates, the synthetic glycogen synthase peptide-2 and the human recombinant tau. GSK3beta activity is regulated by Ser9 (inhibitory) and Tyr216 (stimulatory) phosphorylation. By using specific activity-dependent phospho-antibodies, immunoblot analysis revealed that HNE induces an increase in phosphorylation of GSK3beta in Ser9, enhancing basal phosphatidylinositol 3-kinase (PI3K)/AKT and extracellular signal-regulated kinase 2 (ERK2) signalling pathways. Ser9-GSK3beta phosphorylation induced by HNE was abolished by treatment with LY294002 or U0126, two inhibitors of PI3K/AKT and ERK pathways, respectively. These experiments provide evidence for a crucial role of the PI3K/AKT and ERK2 pathways as intracellular targets of HNE that mediate the inhibition of GSK3beta activity in regulating cellular response to HNE in viable cells under conditions in which membrane lipid peroxidation occurs. These data support a key role for GSK3beta as a mediator of the signalling pathways activated by oxidative stress, and therefore it may be included among the redox-sensitive enzymes.     

Triptolide, a diterpenoid triepoxide, induces antitumor proliferation via activation of c-Jun NH2-terminal kinase 1 by decreasing phosphatidylinositol 3-kinase activity in human tumor cells

Triptolide, a diterpenoid triepoxide extracted from the Chinese herb Tripterygium wilfordii Hook f., exerts antitumorigenic actions against several tumor cells, but the intracellular target signal molecule(s) for this antitumorigenesis activity of triptolide remains to be identified. In the present study, we demonstrated that triptolide, in a dose-dependent manner, inhibited the proliferation of human fibrosarcoma HT-1080, human squamous carcinoma SAS, and human uterine cervical carcinoma SKG-II cells. In addition, triptolide was found to decrease phosphatidylinositol 3-kinase (PI3K) activity. A PI3K inhibitor, LY-294002, mimicked the triptolide-induced antiproliferative activity in HT-1080, SAS, and SKG-II cells. There was no change in the activity of Akt or protein kinase C (PKC), both of which are downstream effectors in the PI3K pathway. Furthermore, the phosphorylation of Ras, Raf, and mitogen-activated protein/extracellular signal-regulated kinase 1/2 was not modified in HT-1080 cells treated with triptolide. However, the phosphorylation of c-Jun NH(2)-terminal kinase 1 (JNK1) was found to increase in both triptolide- and LY-294002-treated cells. Furthermore, the triptolide-induced inhibition of HT-1080 cell proliferation was not observed by JNK1 siRNA-treatment. These results provide novel evidence that PI3K is a crucial target molecule in the antitumorigenic action of triptolide. They further suggest a possible triptolide-induced inhibitory signal for tumor cell proliferation that is initiated by the decrease in PI3K activity, which in turn leads to the augmentation of JNK1 phosphorylation via the Akt and/or PKC-independent pathway(s). Moreover, it is likely that the activation of JNK1 is required for the triptolide-induced inhibition of tumor proliferation.     

Mechanisms of hepatocyte growth factor-mediated signaling in differentiation of pancreatic ductal epithelial cells into insulin-producing cells

Pancreatic ductal epithelial cells (PDECs) were induced to differentiate into insulin-producing cells by hepatocyte growth factor (HGF) in our previous study, but the mechanism through which this induction occurs is still unknown. HGF is a ligand that activates a tyrosine kinase encoded by the c-Met proto-oncogene. This activation is followed by indirect activation of multiple downstream signal transduction pathways (including MAPKs and the PI3K/AKT signaling pathways) that initiate various biological effects. Therefore, we speculated that the differentiation of PDECs is through either the MAPK signaling pathway or the PI3K/AKT signaling pathway. To test this hypothesis, isolated PDECs from adult rats were stimulated by adding HGF to their medium for 28 days. Then, the expression levels of several protein kinases, including MAPKs (ERK1/2, p38, and JNK) and AKT, were determined by Western blotting to determine if specific protein kinases are activated in these pathways. Subsequently, re-isolated from adult rats and cultured PDECs were pre-treated with specific inhibitors of proteins shown to be activated in these signaling pathways; these cells were then induced to differentiate by the addition of HGF. The expression levels of protein kinases were determined by Western blotting, and the differentiation rate of insulin-positive cells was determined by flow cytometry. The change of PDEC differentiation rates were compared between the groups in which cells with or without inhibitors pretreatment to determine the specific signaling pathway(s) that may be involved in HGF-induced differentiation of PDECs. After isolating PDECs and stimulating them with HGF for 28 days, the expression levels of phosphorylated ERK1/2 as well as total and phosphorylated AKT of cultured cells were significantly increased compared to the normal control group (p < 0.05), suggesting that the signaling pathways involving ERK1/2 and Akt (MEK-ERK and PI3K-AKT) are activated during HGF-induced PDEC differentiation. MEK1/2 or PI3K inhibitors were separately added to the culture medium of PDECs pre-treated with HGF. These results show that compared to the HGF-treated group, the differentiation rate of insulin-positive cells was significantly decreased in the HGF/LY294002 (PI3K inhibitor) group (13.47 ± 1.57% vs. 33.47 ± 1.34%, p < 0.05); however, the differentiation rate of insulin-positive cells was not significantly different in the HGF/PD98059 (MEK1/2 inhibitor) group. These data suggest that HGF induces PDECs to differentiate into insulin-producing cells through the PI3K/AKT signaling pathway.     

Phosphorylation of mitochondrial phospholipid scramblase 3 by protein kinase C-delta induces its activation and facilitates mitochondrial targeting of tBid

Phospholipid scramblase 3 (PLS3) is a member of the phospholipid scramblase family present in mitochondria. PLS3 plays an important role in regulation of mitochondrial morphology, respiratory function, and apoptotic responses. PLS3 is phosphorylated by PKC-delta at Thr21 and is the mitochondrial target of PKC-delta-induced apoptosis. Cells with overexpression of PLS3, but not the phosphoinhibitory mutant PLS3(T21A), are more susceptible to apoptosis induced by AD198, an extranuclear targeted anthracycline that activates PKC-delta. Here we report that the phosphomimetic mutant of PLS3(T21D) by itself can induce apoptosis in HeLa cells. Using proteoliposomes with addition of pyrene-labeled phosphatidylcholine (PC) at the outer leaflet, we measured the lipid flip-flop activity of PLS3 and its phosphorylation mutant. PLS3(T21D) is more potent than wild-type PLS3 or PLS3(T21A) to transfer pyrene-PC from the outer leaflet to the inner leaflet of liposomes. Based on our previous finding that PLS3 enhances tBid-induced mitochondrial damages, we tested the hypothesis that PLS3 enhances cardiolipin translocation to mitochondrial surface and facilitates tBid targeting. Fluorescein-labeled tBid(G94E) was used as a probe to quantify cardiolipin on the surface of mitochondria. Mitochondria from cells treated with AD198 or cells expressing PLS3(T21D) had a higher level of tBid-binding capacity than control cells or cells expressing wild-type PLS3. These findings indicate that phosphorylation of PLS3 by PKC-delta induces PLS3 activation to facilitate mitochondrial targeting of tBid and apoptosis.     

Coexpression of oncostatin M and its receptors and evidence for STAT3 activation in human ovarian carcinomas

The expression of oncostatin M and leukemia inhibitory factor (LIF), JAK-STAT activators and members of the interleukin-6 family of cytokines, were examined in a series of primary ovarian carcinomas using immunohistochemistry. The malignant epithelial cells of all 29 ovarian carcinomas examined expressed oncostatin M; none expressed LIF. Oncostatin M can activate two related receptors, one consisting of a low-affinity LIF receptor subunit, LIFR beta, which forms a heterocomplex with the gp130 signal transducing protein and can recognize both oncostatin M and LIF, and a second heterocomplex consisting of a subunit that specifically recognizes oncostatin M, OSMR beta, and the gp130 protein. By immunohistochemistry, 25 of 25 ovarian carcinomas examined expressed the LIFR beta subunit in the malignant epithelial cells (all samples express gp130), and two-thirds the ovarian carcinomas studied expressed OSMR beta mRNA as determined by RT-PCR. Thus oncostatin M and its receptors are commonly coexpressed in malignant ovarian epithelial cells, and represent a potential autocrine loop in this tumor type. STAT3, of one the signaling proteins downstream of the oncostatin M/LIF receptors, was found in its phosphorylated, activated form (phosphotyrosine 705 STAT3) in the malignant epithelial cells of 17 of 23 ovarian carcinomas examined (74%) as determined by immunohistochemistry; this suggests that this protein is constitutively activated in most ovarian carcinomas, as it is in many other human malignancies. Recombinant human Oncostatin M (rhOSM) can induce the transient tyrosine 705 phosphorylation of STAT3 in serum-starved LIFR beta/OSMR beta expressing ovarian carcinoma cell lines, but does not alter cell growth and effects only a modest increase in the apoptotic rate in these cultured cells. Oncostatin M and its receptors may be part of a network of cytokine systems within ovarian carcinomas that may act to maintain STAT3 in its activated form, a phenomenon associated with the malignant phenotype.