Effects of nonsteroidal anti-inflammatory drugs on proliferation and on induction of apoptosis in colon cancer cells by a prostaglandin-independent pathway

Nonsteroidal anti-inflammatory drugs (NSAIDs) decrease the incidence of and mortality from colon cancer. We observed that NSAIDs inhibit the proliferation rate, alter the cell cycle distribution, and induce apoptosis in colon cancer cell lines. We evaluated whether the inhibition by NSAIDs of prostaglandin (PG) synthesis is required for their effects on colon cancer cells by studying two human colon cancer cell lines: HCT-15 and HT-29. HCT-15, which lacks cyclooxygenase transcripts, does not produce PGs even when exogenously stimulated, whereas HT-29 produces PGE2, PGF2 alpha, and PGI2. HCT-15 and HT-29 cells, when treated for up to 72 hr with 200 microM sulindac sulfide (an active metabolite of sulindac) or 900 microM piroxicam, showed changes in proliferation, cell cycle phase distribution, and apoptosis. Treatment with PGE2, PGF2 alpha, and PGI2, following a variety of protocols, and at concentrations between 10(-6) and 10(-11) M, failed to reverse the effects of NSAIDs on these three parameters of cell growth. We concluded that NSAIDs inhibit the proliferation rate of the two colon cancer cell lines independent of their ability to inhibit PG synthesis. Thus, alternative mechanisms for their activity on tumor cell growth must be entertained. These observations may be relevant to the mechanism of colon tumor inhibition by NSAIDs.

Sulindac sulfide, an aspirin-like compound, inhibits proliferation, causes cell cycle quiescence, and induces apoptosis in HT-29 colon adenocarcinoma cells

Nonsteroidal antiinflammatory drugs (NSAIDs), have cancer preventive and tumor regressive effects in the human colon. They lower the incidence of and mortality from colorectal cancer and sulindac reduces the number and size of polyps in patients with familial adenomatous polyposis. We studied the effect of sulindac, and its metabolite sulindac sulfide, on the proliferation of HT-29 colon adenocarcinoma cells. Both compounds reduced the proliferation rate of these cells, changed their morphology, and caused them to accumulate in the G0/G1 phase of the cell cycle. These responses were time- and concentration-dependent and reversible. In addition, these compounds reduced the level and activity of several cyclin-dependent kinases (cdks), which regulate cell cycle progression. Sulindac and sulindac sulfide also induced apoptosis in these cells at concentrations that affected their proliferation, morphology, and cell cycle phase distribution. Sulindac sulfide was approximately sixfold more potent than sulindac in inducing these cellular responses. Our results indicate that inhibition of cell cycle progression and induction of apoptotic cell death contribute to the anti-proliferative effects of sulindac and sulindac sulfide in HT-29 cells. These findings may be relevant to the cancer preventive and tumor regressive effects of these compounds in humans.

Nonsteroidal antiinflammatory drugs inhibit the proliferation of colon adenocarcinoma cells: effects on cell cycle and apoptosis

Aspirin and other NSAIDs reduce the incidence of and mortality from colon cancer, but their mechanism of action remains unknown. We evaluated the effect of aspirin (ASA) and three other structurally unrelated NSAIDs (indomethacin, naproxen, and piroxicam) on cell proliferation, cell cycle phase distribution, and the development of apoptosis in HT-29 colon adenocarcinoma cells in vitro. All of the NSAIDs examined reduced the proliferation and altered the morphology of these cells in a time- and concentration-dependent manner. In addition, they altered the cell cycle phase distribution of these cells. They increased the proportion of cells in the G0/G1 phase and reduced the proportion in the S phase of the cell cycle. ASA and indomethacin also reduced the percentage of cells in the G2/M phase, whereas naproxen and piroxicam did not. Parallel to their effect on cell cycle, ASA and indomethacin also reduced the levels of p34cdc2 and p33cdk2, two cyclin-dependent kinases that are important for cell cycle progression. Finally, all the NSAIDs analyzed, except ASA, induced apoptosis in these cells. There as a rough correlation between the relative potency of these compounds in inducing apoptosis and their effectiveness in retarding cell proliferation. Our findings indicate that NSAIDs can reduce the proliferation of HT-29 colon cancer cells in vitro. In addition, they cause cell cycle quiescence and apoptosis, both of which could account for their anti-proliferative effect. These findings suggest possible mechanisms for the cancer preventive effects of these compounds in humans.

Curcumin, a natural plant phenolic food additive, inhibits cell proliferation and induces cell cycle changes in colon adenocarcinoma cell lines by a prostaglandin-independent pathway

Curcumin, the active ingredient of the rhizome of the plant turmeric (Curcuma longa Linn), a commonly used spice, prevents cancer in animal tumor models. Its mechanism of action is unknown; curcumin may act by inhibiting arachidonic acid metabolism. To explore the mechanism of curcumin's chemopreventive effect, we studied its role in proliferation and apoptosis in the HT-29 and HCT-15 human colon cancer cell lines. Curcumin dose-dependently reduced the proliferation rate of both cell lines, causing a 96% decrease by 48 hours. No apoptosis was detected. The antiproliferative effect was preceded by accumulation of the cells in the G2/M phase of cell cycle. The effect of curcumin was similar in both cell lines, which, however, differ in their ability to produce prostaglandins. We conclude that curcumin inhibits colon cancer cell proliferation in vitro mainly by accumulating cells in the G2/M phase and that this effect is independent of its ability to inhibit prostaglandin synthesis. The role of curcumin's antiproliferative effect in human colon cancer remains to be established.

Deoxycholic acid (DCA) causes ligand-independent activation of epidermal growth factor receptor (EGFR) and FAS receptor in primary hepatocytes: inhibition of EGFR/mitogen-activated protein kinase-signaling module enhances DCA-induced apoptosis

Previous studies have argued that enhanced activity of the epidermal growth factor receptor (EGFR) and the mitogen-activated protein kinase (MAPK) pathway can promote tumor cell survival in response to cytotoxic insults. In this study, we examined the impact of MAPK signaling on the survival of primary hepatocytes exposed to low concentrations of deoxycholic acid (DCA, 50 microM). Treatment of hepatocytes with DCA caused MAPK activation, which was dependent upon ligand independent activation of EGFR, and downstream signaling through Ras and PI(3) kinase. Neither inhibition of MAPK signaling alone by MEK1/2 inhibitors, nor exposure to DCA alone, enhanced basal hepatocyte apoptosis, whereas inhibition of DCA-induced MAPK activation caused approximately 25% apoptosis within 6 h. Similar data were also obtained when either dominant negative EGFR-CD533 or dominant negative Ras N17 were used to block MAPK activation. DCA-induced apoptosis correlated with sequential cleavage of procaspase 8, BID, procaspase 9, and procaspase 3. Inhibition of MAPK potentiated bile acid-induced apoptosis in hepatocytes with mutant FAS-ligand, but did not enhance in hepatocytes that were null for FAS receptor expression. These data argues that DCA is causing ligand independent activation of the FAS receptor to stimulate an apoptotic response, which is counteracted by enhanced ligand-independent EGFR/MAPK signaling. In agreement with FAS-mediated cell killing, inhibition of caspase function with the use of dominant negative Fas-associated protein with death domain, a caspase 8 inhibitor (Ile-Glu-Thr-Asp-p-nitroanilide [IETD]) or dominant negative procaspase 8 blocked the potentiation of bile acid-induced apoptosis. Inhibition of bile acid-induced MAPK signaling enhanced the cleavage of BID and release of cytochrome c from mitochondria, which were all blocked by IETD. Despite activation of caspase 8, expression of dominant negative procaspase 9 blocked procaspase 3 cleavage and the potentiation of DCA-induced apoptosis. Treatment of hepatocytes with DCA transiently increased expression of the caspase 8 inhibitor proteins c-FLIP-(S) and c-FLIP-(L) that were reduced by inhibition of MAPK or PI(3) kinase. Constitutive overexpression of c-FLIP-(s) abolished the potentiation of bile acid-induced apoptosis. Collectively, our data argue that loss of DCA-induced EGFR/Ras/MAPK pathway function potentiates DCA-stimulated FAS-induced hepatocyte cell death via a reduction in the expression of c-FLIP isoforms.

3-(Hydroxymethyl)-bearing phosphatidylinositol ether lipid analogues and carbonate surrogates block PI3-K, Akt, and cancer cell growth

Phosphatidylinositol 3-kinase (PI3-K) phosphorylates the 3-position of phosphatidylinositol to give rise to three signaling phospholipids. Binding of the pleckstrin homology (PH) domain of Akt to membrane PI(3)P's causes the translocation of Akt to the plasma membrane bringing it into contact with membrane-bound Akt kinase (PDK1 and 2), which phosphorylates and activates Akt. Akt inhibits apoptosis by phosphorylating Bad, thus promoting its binding to and blockade of the activity of the cell survival factor Bcl-x. Herein we present the synthesis and biological activity of several novel phosphatidylinositol analogues and demonstrate the ability of the carbonate group to function as a surrogate for the phosphate moiety. Due to a combination of their PI3-K and Akt inhibitory activities, the PI analogues 2, 3, and 5 proved to be good inhibitors of the growth of various cancer cell lines with IC(50) values in the 1-10 microM range. The enhanced Akt inhibitory activity of the axial hydroxymethyl-bearing analogue 5 compared to its equatorial counterpart 6 is rationalized based upon postulated differences in the H-bonding patterns of these compounds in complex with a homology modeling generated structure of the PH domain of Akt. This work represents the first attempt to examine the effects of 3-modified PI analogues on these two crucial cell signaling proteins, PI3-K and Akt, in an effort to better understand their cell growth inhibitory properties.

Linear PADRE T helper epitope and carbohydrate B cell epitope conjugates induce specific high titer IgG antibody responses

Linear carbohydrate-peptide constructs based on the 13 amino acid nonnatural pan DR epitope (PADRE) and carbohydrate B cell epitopes are demonstrated to be potent immunogens. These data support our belief that PADRE should be considered as an alternative to more complex carriers for use in prophylaxis and therapeutic vaccines. Two model carbohydrate-PADRE glycoconjugates were used to demonstrate that PADRE could effectively provide T cell help for carbohydrate-specific Ab responses. Conjugates of PADRE covalently linked to the human milk oligosaccharide, lacto-N-fucopentose II or a dodecasaccharide derived from Salmonella typhimurium O-Ag induced high titer IgG Ab responses in mice, which were comparable to glycoconjugates employing human serum albumin (HSA) as the carrier protein. Different adjuvants, in combination with PADRE conjugates, allowed for the modulation of the isotype profile with alum supporting an IgG1 profile; QS-21 an IgG2a, 2b profile, while an alum/QS-21 mixture generated a balanced IgG1/IgG2b isotype profile. As defined by binding to synthetic glycoconjugates, dodecasaccharide-specific Abs exhibited fine specificity similar to protective polyclonal Ab responses previously reported for dodecasaccharide-protein conjugates. The same Abs bound to intact S. typhimurium cells, suggesting that biologically relevant specificities were produced. The affinity of the dodecasaccharide-specific Abs was further shown to be comparable to that of a well-characterized, high affinity monoclonal anti-carbohydrate Ab recognizing the same epitope.

Selected eicosanoids increase the proliferation rate of human colon carcinoma cell lines and mouse colonocytes in vivo

Eicosanoids have been implicated in colon carcinogenesis, but their role remains unclear. The levels of PGE2 are elevated in colon cancer tissues and in blood draining colon tumors. The effect of eicosanoids on the proliferation of colonic cells is unknown. We studied the effect of several prostaglandins (PGs) and leukotriene (LT)B4 on the proliferation rate of the human colon adenocarcinoma cell lines SW1116 and HT-29 and of 16,16-dimethyl PGE2 (dmPGE2) on the colon of BALB/c mice. PGs E2, F2 alpha, I2, the methyl ester of PGE2, dmPGE2, and LTB4 (10(-10), 10(-8), 10(-6) M), administered for up to 72 h, stimulated cell proliferation in SW1116 cells and all but PGF2 alpha and PGI2 stimulated proliferation in HT-29 cells. The proliferative effect was time- and concentration-dependent. However, in SW1116 cells the response to PGs was 'bell-shaped', being maximal at 10(-8) M, with the 10(-10) and 10(-6) M concentrations being less effective. In HT-29 cells, the addition of methyl groups to the PGE2 molecule increased the proliferative effect. None of these eicosanoids affected the distribution of these cells in the cell cycle or their rate of programmed cell death (apoptosis). dmPGE2 stimulated 3.6-fold the proliferation of colonocytes in normal BALB/c mice. This was determined by bivariate flow cytometric analysis of the expression of proliferating cell nuclear antigen (PCNA) in virtually pure populations of mouse colonocytes. dmPGE2 did not alter the cell cycle distribution of these cells. We conclude that several PGs as well as LTB4 stimulate the proliferation of human colon carcinoma cells in vitro, while dmPGE2 has a similar effect on mouse colonocytes in vivo. These findings raise the possibility that eicosanoids may contribute to colonic carcinogenesis by stimulating the proliferation rate of tumor cells in the colon.

Decreased Akt kinase activity and insulin resistance in C57BL/KsJ-Leprdb/db mice

Recent studies suggest that the serine/threonine kinase protein kinase B (PKB or Akt) is involved in the pathway for insulin-stimulated glucose transporter 4 (GLUT4) translocation and glucose uptake. In this study we examined the components of the Akt signaling pathway in skeletal muscle and adipose tissue in vivo from C57BL/KsJ-Lepr(db/db) mice (db/db), a model of obesity, insulin resistance, and type II diabetes. There were no changes in the protein levels of GLUT4, p85alpha, or Akt in tissues from db/db mice compared with non-diabetic littermate controls (+/+). In response to acute insulin administration, GLUT4 recruitment to the plasma membrane increased twofold in muscle and adipose tissue from +/+ mice, but was significantly reduced by 42-43% (P<0.05) in both tissues from db/db mice. Insulin increased Akt-Ser(473) phosphorylation by two- to fivefold in muscle and adipose tissue from all mice. However, in db/db mice, maximal Akt-Ser(473) phosphorylation was decreased by 32% (P<0.05) and 69% (P<0.05) in muscle and adipose tissue respectively. This decreased phosphorylation in db/db mice corresponded with a significant decrease in maximal Akt kinase activity using a glycogen synthase kinase-3 fusion protein as a substrate (P<0.05). The level of insulin-stimulated tyrosine phosphorylation of p85alpha from phosphatidylinositol 3 (PI 3)-kinase, which is upstream of Akt, was also reduced in muscle and adipose tissue from db/db mice (P<0.05); however, there was no change in extracellular signal-regulated kinase-1 or -2 phosphorylation. These data implicate decreased insulin-stimulated Akt kinase activity as an important component underlying impaired GLUT4 translocation and insulin resistance in tissues from db/db mice. However, impaired insulin signal transduction appears to be specific for the PI 3-kinase pathway of insulin signaling, while the MAP kinase pathway remained intact.

Effect of aspirin on induction of apoptosis in HT-29 human colon adenocarcinoma cells

Aspirin (ASA) and other nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit colorectal tumorigenesis. Apoptosis is a critical determinant of tissue mass homeostasis and may play a role in carcinogenesis. We studied the effect of ASA on the survival of a human colon cancer cell line using more sensitive methods than we had applied previously. ASA induced apoptosis in HT-29 colon adenocarcinoma cells at concentrations > or =1 mM as established by: (a) morphological changes consistent with apoptosis in cells examined by fluorescence microscopy and semi-thin cell sections, and (b) DNA strand breaks: 45% of the cells were TdT-mediated dUTP nick end labeling (TUNEL) positive at 3 mM at 72 hr, and 70% were positive by the comet assay. Electron microscopy also confirmed the induction of apoptosis by ASA. ASA-induced apoptosis was not associated with: (a) a ladder pattern on genomic DNA electrophoresis, or (b) a subdiploid peak on flow cytometry. Apoptotic bodies were virtually absent on standard morphological assessments and only a few were detected on semi-thin sections. For the above reasons, this apoptosis induced by ASA is "atypical," and the unusual features of ASA-induced apoptosis, besides their taxonomic value, may offer clues to the mechanisms that control the process of apoptosis or perhaps the cancer chemopreventive properties of this compound. These findings demonstrate that ASA induces apoptosis in human colon cancer cells, bolstering the hypothesis that apoptosis may be a mechanism by which NSAIDs inhibit colon carcinogenesis. These findings should be examined in animal and/or clinical research studies in vivo.

Ionizing radiation modulates vascular endothelial growth factor (VEGF) expression through multiple mitogen activated protein kinase dependent pathways

We investigated the role of radiation-induced mitogen activated protein kinase (MAPK) pathway activity in the regulation of proliferation, cell survival and vascular endothelial growth factor (VEGF) production in primary astrocytes and in T9 and RT2 glioblastoma cells derived from Fisher 344 rats. In these cells, ionizing radiation (2 Gy) caused activation of the MAPK pathway which was blocked by specific inhibitor drugs. Blunting of radiation-induced MAPK activity weakly enhanced radiation-induced apoptosis 24 h after exposure in RT2 cells. Furthermore, blunting of MAPK activation weakly enhanced the ability of radiation to reduce RT2 cell growth in clonogenic growth assays. These findings argue that inhibition of MAPK signaling reduces proliferation and enhances cell killing by ionizing radiation in transformed astrocytes. Proliferation and survival of cancer cells has been linked in vivo to enhanced expression of angiogenic growth factors. Recently we demonstrated that the gene product of a novel rodent radiation-responsive gene, progression elevated gene 3 (PEG-3), could enhance vascular endothelial growth factor (VEGF) promoter activity in rodent fibroblasts, leading to increased VEGF protein levels and tumorigenic behavior in vivo. Thus PEG-3 and VEGF expression could be expected to directly correlate with the oncogenic potential of transformed cells. RT2 cells expressed more PEG-3 and VEGF protein than T9 cells, and were more tumorigenic in vivo than T9 cells. Radiation activated the PEG-3 promoter via MAPK signaling and ectopic over-expression of PEG-3 enhanced both basal MAPK activity and basal VEGF promoter activity. Basal MAPK activity partially correlated with basal VEGF promoter activity and VEGF protein levels in primary astrocytes, T9 and RT2 cells. Radiation increased the activity of the VEGF promoter and VEGF protein levels in primary astrocytes, T9 and RT2 cells which were dependent upon MAPK function. Furthermore, inhibition of AP-1 transcription factor signaling by dominant negative c-Jun (TAM67) also significantly reduced basal, and to a lesser extent radiation-induced, VEGF promoter function in RT2 cells. Collectively, our data demonstrate that radiation-induced MAPK signaling can both protect cells from radiation-induced cell death as well as enhance protein levels of pro-angiogenic factors such as VEGF. Enhanced VEGF expression in RT2 cells may be mediated via MAPK and JNK pathway signaling which converges upon the AP-1 transcription factor complex.

Activation and signaling status of human lamina propria T lymphocytes

In this study, proliferative responses of human lamina propria T lymphocytes were examined in vitro. The response of lamina propria T lymphocytes to Sepharose-bound anti-CD3 antibody plus interleukin 2 was significantly lower than the response of autologous peripheral blood T lymphocytes, whereas the responses of lamina propria T lymphocytes to anti-T11(2/3) antibodies plus sheep erythrocytes or anti-CD28 antibody plus interleukin 2 were largely preserved. After coculture with mucosa supernatant, peripheral blood T lymphocytes showed a similar pattern of reactivity as lamina propria T lymphocytes. This reduced reactivity to T-cell antigen receptor stimulation appears to exist at the level of signal transduction, because triggering of CD3 induces low amounts of intracellular inositol 1,4,5-triphosphate and no free calcium increase in lamina propria T lymphocytes when compared with peripheral blood T lymphocytes. This study indicates that the antigen receptor-dependent activation pathway of lamina propria T lymphocytes for proliferation is down-regulated by intestinal mucosa derived factor(s) and that the alternative pathways mediated by CD2 or CD28 are largely preserved. Based on previous data that lamina propria T lymphocytes can provide help to B cells, it is possible that these alternative activation pathways play an important role in T-B cell interaction in the gut.

Proliferative and cytolytic potentials of purified human tumor-infiltrating T lymphocytes. Impaired response to mitogen-driven stimulation despite T-cell receptor expression

Using limiting dilution analysis (LDA) we have previously shown that in most instances, the frequency (F) of proliferative T lymphocyte precursors (PTL-P) was strikingly reduced in tumor-infiltrating lymphocytes (TIL). In this study involving 19 cases, we show that the impaired clonogenic potential of CD2+ TILs is primarily caused by an intrinsic defect rather than to suppressor T cells or to a direct effect of the tumor cells usually present in the culture system. This was demonstrated by experiments in which the F of PTL-Ps was quantitated both in highly purified CD2+ TILs (using a cell-sorter) and in non-purified TIL suspensions (still containing tumor cells), which originated from the same biopsy specimen. The F of PTL-Ps was virtually identical in either sorted or nonsorted suspensions and the data from LDA were always consistent with the single-hit Poisson model, indicating that no suppressor cells interfered with growth of CD2+ TIL. Stimulation of sorted CD2+ TIL in low-density cultures by either phytohemagglutinin or anti-CD3-monoclonal antibody (MAb) indicated that the antigen-dependent activation pathway was impaired, although structurally intact T-cell receptor (TCR) complexes were apparently expressed, as assessed by immunofluorescence. The depressed proliferative response of CD2+ TIL could not be reversed in vitro when phorbol-esters were used in combination with ionomycin, which bypass the TCR. Nevertheless, 180 clones obtained from 8 cases were analyzed for their cytolytic activity. The majority mediated specific lytic activity (against unknown antigens), as assessed by lectin-dependent cell cytotoxicity, whereas only 6% of them manifested lymphokine-activated killing on appropriate targets.

T cells of the human intestinal lamina propria are high producers of interleukin-10

BACKGROUND AND AIM

Some of the recently observed functional features characteristic of immunocompetent cells residing in the human intestinal lamina propria could be mediated by interleukin-10 (IL-10). To investigate the role of IL-10 in the human intestinal mucosa, the regulation of IL-10 production by lamina propria T lymphocytes (LPL-T) was determined and compared with that of peripheral blood T lymphocytes (PBL-T).

METHODS

Following activation by using different stimuli, IL-10 release by LPL-T and PBL-T into the supernatant was measured by enzyme linked immunosorbent assay (ELISA). In parallel, cell growth was determined by [3H]-thymidine incorporation.

RESULTS

Neither LPL-T nor PBL-T release IL-10 constitutively. Triggering through CD2 or the T cell receptor (TCR)/CD3 complex in the presence of autologous monocytes induces significantly greater IL-10 secretion by LPL-T than by PBL-T. Engagement of the CD45 receptor enhances IL-10 release and proliferation of CD2 triggered CD45RO+ PBL-T. In contrast, it reduces CD2 induced IL-10 production by LPL-T without altering cell growth significantly.

CONCLUSIONS

Activated LPL-T release relatively high amounts of IL-10. Enhanced IL-10 production by activated LPL-T, in comparison with activated PBL-T, is not only related to the presence of a higher proportion of CD45RO+ T cells in the intestinal lamina propria, but is also caused by increased sensitivity of LPL-T to CD2 co-stimulation. The differential responsiveness of LPL-T, compared with PBL-T, to CD45 engagement demonstrates that CD45 could be involved in the altered CD2 reactivity of LPL-T.

Identification and characterization of the novel Col10a1 regulatory mechanism during chondrocyte hypertrophic differentiation

The majority of human skeleton develops through the endochondral pathway, in which cartilage-forming chondrocytes proliferate and enlarge into hypertrophic chondrocytes that eventually undergo apoptosis and are replaced by bone. Although at a terminal differentiation stage, hypertrophic chondrocytes have been implicated as the principal engine of bone growth. Abnormal chondrocyte hypertrophy has been seen in many skeletal dysplasia and osteoarthritis. Meanwhile, as a specific marker of hypertrophic chondrocytes, the type X collagen gene (COL10A1) is also critical for endochondral bone formation, as mutation and altered COL10A1 expression are often accompanied by abnormal chondrocyte hypertrophy in many skeletal diseases. However, how the type X collagen gene is regulated during chondrocyte hypertrophy has not been fully elucidated. We have recently demonstrated that Runx2 interaction with a 150-bp mouse Col10a1 cis-enhancer is required but not sufficient for its hypertrophic chondrocyte-specific reporter expression in transgenic mice, suggesting requirement of additional Col10a1 regulators. In this study, we report in silico sequence analysis of this 150-bp enhancer and identification of its multiple binding factors, including AP1, MEF2, NFAT, Runx1 and TBX5. Using this enhancer as bait, we performed yeast one-hybrid assay and identified multiple candidate Col10a1-interacting genes, including cyclooxygenase 1 (Cox-1) and Cox-2. We have also performed mass spectrometry analysis and detected EF1-alpha, Fus, GdF7 and Runx3 as components of the specific complex formed by the cis-enhancer and nuclear extracts from hypertrophic MCT (mouse chondrocytes immortalized with large T antigen) cells that express Col10a1 abundantly. Notably, some of the candidate genes are differentially expressed in hypertrophic MCT cells and have been associated with chondrocyte hypertrophy and Runx2, an indispensible Col10a1 regulator. Intriguingly, we detected high-level Cox-2 expression in hypertrophic MCT cells. Electrophoretic mobility shift assay and chromatin immunoprecipitation assays confirmed the interaction between Cox-2 and Col10a1 cis-enhancer, supporting its role as a candidate Col10a1 regulator. Together, our data support a Cox-2-containing, Runx2-centered Col10a1 regulatory mechanism, during chondrocyte hypertrophic differentiation.

Leptin administration prevents spontaneous gestational diabetes in heterozygous Lepr(db/+) mice: effects on placental leptin and fetal growth

Gestational diabetes mellitus (GDM) results from an interaction between susceptibility genes and the diabetogenic effects of pregnancy. During pregnancy, mice heterozygous for the lepin receptor (db/+) gain more weight, are glucose intolerant, and produce macrosomic fetuses compared with wild-type (+/+) mothers, suggesting that an alteration in leptin action may play a role in GDM and fetal overgrowth. To investigate whether leptin administration or pair-feeding can reduce adiposity and thereby prevent GDM and neonatal overgrowth, we examined energy balance, glucose and insulin tolerance, and fetal growth in pregnant db/+ and +/+ mice treated with recombinant human leptin-IgG during late pregnancy. Leptin reduced food intake and adiposity in pregnant db/+ mice to levels similar to pregnant +/+ mice and significantly reduced maternal weight gain. Maternal glucose levels were markedly lower during glucose and insulin challenge tests in leptin-treated db/+ mice relative to db/+ and pair-fed controls. Despite reduced energy intake and improved glucose tolerance, leptin administration did not reduce fetal overgrowth in offspring from db/+ mothers. Fetal and placental leptin levels were 1.3- to 1.5-fold higher in offspring from db/+ mothers and remained unchanged with leptin administration, whereas leptin treatment in +/+ mothers or pair-feeding decreased placental leptin concentration and reduced fetal birth weight. Our results provide evidence that leptin administration during late gestation can reduce adiposity and improve glucose tolerance in the db/+ mouse model of spontaneous GDM. However, fetal and placenta leptin levels are higher in db/+ mothers and are subject to reduced negative feedback in response to leptin treatment. These data suggest that alterations in placenta leptin may contribute to the regulation of fetal growth independently of maternal glucose levels.

Field emission properties of N-doped capped single-walled carbon nanotubes: A first-principles density-functional study

The geometrical structures and field emission properties of pristine and N-doped capped (5,5) single-walled carbon nanotubes have been investigated using first-principles density-functional theory. The structures of N-doped carbon nanotubes are stable under field emission conditions. The calculated work function of N-doped carbon nanotube decreases drastically when compared with pristine carbon nanotube, which means the enhancement of field emission properties. The ionization potentials of N-doped carbon nanotubes are also reduced significantly. The authors analyze the field emission mechanism in terms of energy gap between the lowest unoccupied molecular orbital and the highest occupied molecular orbital, Mulliken charge population, and local density of states. Due to the doping of nitrogen atom, the local density of states at the Fermi level increases dramatically and donor states can be observed above the Fermi level. The authors' results suggest that the field emission properties of carbon nanotubes can be enhanced by the doping of nitrogen atom, which are consistent with the experimental results.

Enhancers of glp-1, a gene required for cell-signaling in Caenorhabditis elegans, define a set of genes required for germline development

The distal tip cell (DTC) regulates the proliferation or differentiation choice in the Caenorhabditis elegans germline by an inductive mechanism. Cell signaling requires a putative receptor in the germline, encoded b y the glp-1 gene, and a putative signal from the DTC, encoded by the lag-2 gene. Both glp-1 and lag-2 belong to multigene gene families whose members are essential for cell signaling during development of various tissues in insects and vertebrates as well as C. elegans. Relatively little is known about how these pathways regulate cell fate choice. To identify additional genes involved in the glp-1 signaling pathway, we carried out screens for genetic enhancers of glp-1. We recovered mutations in five new genes, named ego (enhancer of glp-1), and two previously identified genes, lag-1 and glp-4, that strongly enhance a weak glp-1 loss-of-function phenotype in the germline. Ego mutations cause multiple phenotypes consistent with the idea that gene activity is required for more than one aspect of germline and, in some cases, somatic development. Based on genetic experiments, glp-1 appears to act upstream of ego-1 and ego-3. We discuss the possible functional relationships among these genes in light of their phenotypes and interactions with glp-1.

Silencing of Jagged1 inhibits cell growth and invasion in colorectal cancer

Dysregulated Notch signaling has a critical role in the tumorigenesis. Jagged1, a Notch ligand, is overexpressed in various human cancers. Recent studies revealed the involvement of Jagged1 in colorectal cancer (CRC) development. These basic studies provide a promising potential for inhibition of the Notch pathway for the treatment of CRC. Herein, we aimed to investigate the consequences of targeting Jagged1 using shRNA on CRC both in vitro and in vivo to test their potential to inhibit this key element for CRC treatment. We found that downregulation of Jagged1 with lentiviral Jagged1-shRNA resulted in decreased colon cancer cell viability in vitro, most likely mediated through reduced cell proliferation. Importantly, Jagged1 knockdown induced G₀/G₁ phase cell cycle arrest, with reduced Cyclin D1, Cyclin E and c-Myc expression. Silencing of Jagged1 reduced the migration and invasive capacity of the colon cancer cells in vitro. Furthermore, colon cancer cells with knockdown of Jagged1 had much slower growth rate than control cells in a xenograft mouse model in vivo, with a marked downregulation of cell proliferation markers (PCNA, Ki-67, and c-Myc) and metastasis markers (MMP-2 and MMP-9). These findings rationalize a mechanistic approach to CRC treatment based on Jagged1-targeted therapeutic development.

MAPK dependence of DNA damage repair: ionizing radiation and the induction of expression of the DNA repair genes XRCC1 and ERCC1 in DU145 human prostate carcinoma cells in a MEK1/2 dependent fashion

PURPOSE

To examine the role of mitogen-activated protein kinase (MAPK) signalling on the induction by ionizing radiation of the nucleotide excision repair gene (ERCC1), the X-ray cross-complementing group 1 protein (XRCC1) and the repair of radiation-induced DNA damage.

MATERIALS AND METHODS

The expression of ERCC1 and XRCC1 was examined in DU145 human prostate cancer cells following exposure to ionizing radiation. We characterized the MAPK dependence of this expression through RT-PCR analysis, Western analysis, transcription inhibition and measurement of the activation of each promoter. Pre-exposure with the specific MEK1/2 inhibitor PD980059 (10 microM) was used to blunt radiation induction of MAPK without suppressing basal levels of MAPK activity. In addition, we examined the MAPK dependence of DNA damage repair by measuring radiation-induced micronucleus formation and the removal of and nicking activity associated with AP sites.

RESULTS

Irradiation caused a time-dependent, MAPK-dependent increase in the protein levels of both ERCC1 and XRCC1. For each gene product, the protein level increase followed an increase in mRNA, which also was MAPK-dependent. Radiation also enhanced the activities of the ERCC1 and XRCC1 promoters in an MAPK-dependent fashion. Inhibition of transcription by DRB abolished the radiation-induced increase of ERCC1 and XRCC1 proteins. Inhibition of radiation-induced MAPK also diminished the ability of DU145 cells to remove AP sites and increased the number of cells displaying micronuclei following radiation exposure.

CONCLUSIONS

These findings demonstrate a role for radiation-induced MAPK signalling in the regulation of DNA repair enzyme levels and DNA repair. Radiation-induced protein expression of ERCC1 and XRCC1 appears to require de novo transcription. These data suggest a significant role for MAPK signalling in the early response to DNA damage caused by ionizing radiation.

A role for both Ets and C/EBP transcription factors and mRNA stabilization in the MAPK-dependent increase in p21 (Cip-1/WAF1/mda6) protein levels in primary hepatocytes

In primary hepatocytes and HepG2 hepatoma cells, prolonged activation of the p42/44 mitogen-activated protein kinase (MAPK) pathway is associated with a reduction in DNA synthesis, mediated by increased expression of the cyclin-dependent kinase inhibitor protein p21 (Cip-1/WAF1/mda6) (p21). This study was performed to evaluate the contribution of transcriptional and post-transcriptional regulation in this response. Prolonged activation of the MAPK pathway in wild-type or p21 null hepatocytes caused a large decrease and increase, respectively, in DNA synthesis. Prolonged activation of the MAPK pathway in either wild-type or p21 antisense HepG2 cells also caused large decreases and increases, respectively, in DNA synthesis. MAPK signaling increased the phosphorylation of the transcription factors Ets2, C/EBPalpha, and C/EBPbeta, and rapidly increased transcription from the p21 promoter via multiple Ets- and C/EBP-elements within the enhancer region. Eight hours after MAPK activation, loss of C/EBPbeta or Ets2 function significantly reduced MAPK-stimulated transcription from the p21 promoter and abolished increased p21 protein expression. At this time, MAPK signaling increased both p21 mRNA and p21 protein stabilities that were also demonstrated to be essential for a profound increase in p21 protein levels. Thirty-six hours after MAPK activation, transcription from the p21 promoter was still significantly reduced in cells without either C/EBPbeta or Ets2 function; however, these cells were now capable of exhibiting a partial increase in p21 protein expression. In contrast, loss of C/EBPalpha function modestly reduced MAPK-stimulated transcription from the p21 promoter but strongly inhibited the ability of prolonged MAPK activation to increase protein levels of p21. This data suggested that prolonged enhancement of p21 protein levels may be under posttranscriptional control. In agreement with this hypothesis, prolonged MAPK signaling further increased p21 mRNA stability at 36 h, compared with the 8-h time point. Our data argue that MAPK signaling increased p21 promoter activity via multiple transcription factors, which alone were insufficient for a robust prolonged increase in p21 protein levels in primary hepatocytes, and that to increase p21 protein levels also required enhanced stabilization of p21 mRNA and p21 protein. Collectively, these data suggest that loss of transcription factor and mRNA/protein stabilization functions correlates with an inability of MAPK signaling to cause growth arrest versus proliferation in primary hepatocytes.

Apoptosis: one of the mechanisms that maintains unresponsiveness of the intestinal mucosal immune system

Intestinal mucosa is constantly exposed to environmental AGS: Activation of lamina propria (LP) T cells by luminal Ags may lead to the production of inflammatory cytokines and subsequent mucosal inflammation and tissue damage. However, in normal circumstances, LP T cells do not respond to antigenic stimulation. The mechanisms of this unresponsiveness in healthy subjects are not fully understood. In this study, we found by in vivo analysis that, except for T cells in lymph nodules of the mucosa, 15% of LP T cells underwent apoptosis in normal individuals. In contrast, there was a marked reduction in apoptosis of LP T cells in patients with inflammatory bowel disease (Crohn's disease and ulcerative colitis) and those with specific colitis. Our findings suggest that apoptosis might be a mechanism that turns off mucosal T cell responses to environmental Ags in healthy subjects, and resistance to apoptosis could be an important cause of mucosal immune dysregulation and tissue inflammation in colitis.

Hepatitis C virus genotype-3a core protein enhances sterol regulatory element-binding protein-1 activity through the phosphoinositide 3-kinase-Akt-2 pathway

Hepatitis C virus genotype-3a (HCV-3a) is directly linked to the development of steatosis. We previously showed that, through sterol regulatory element binding protein-1 (SREBP-1), HCV-3a core protein upregulates the promoter activity of fatty acid synthase, a major enzyme involved in de novo lipid synthesis. In this study, we investigated whether HCV-3a core can activate SREBP-1 and studied the role of phosphoinositide 3-kinase (PI3K)-Akt-2 pathway in modulating SREBP-1 activity by HCV-3a core. To determine whether HCV-3a core could activate SREBP-1, the level of mature SREBP-1 was analysed by Western blotting. Our results showed that the level of mature SREBP-1 was enhanced by HCV-3a core protein after transient expression and in the chimeric HCV-3a core/1b replicon cells in comparison to controls. To investigate the role of the PI3K-Akt-2 pathway in SREBP-1 activation by HCV-3a core, PI3K and Akt-2 activity was inhibited by using the chemical inhibitor LY294002, a dominant-negative Akt-2 plasmid, or knockdown of Akt-2 by small hairpin RNA. Our results showed that inhibition of PI3K and Akt-2 was associated with reduced SREBP-1 activation by HCV-3a core. These results indicate a role for PI3K and Akt-2 in increasing SREBP-1 activity by HCV-3a core protein and provide a mechanism of steatosis caused by HCV.