Induction by activated macrophage-like THP-1 cells of apoptotic and necrotic cell death in intestinal epithelial Caco-2 monolayers via tumor necrosis factor-alpha

Intestinal epithelial cells interact with immune cells located in the intestinal epithelium via soluble factors. An in vitro model system using coculture was constructed to analyze the effect of macrophages on intestinal epithelial cells, and human intestinal epithelial-like Caco-2 monolayers and activated macrophage-like THP-1 cells were used in this study. Coculturing with THP-1 cells resulted in an increase of lactate dehydrogenase release from Caco-2 and a decrease in the transepithelial electrical resistance of the monolayers, showing that coculturing with THP-1 induced cell damage to Caco-2 cells. This disruption was significantly suppressed by adding anti-TNF-alpha antibody and etanercept, strongly suggesting that TNF-alpha secreted from THP-1 had caused cell damage to Caco-2 monolayers. The disrupted Caco-2 monolayers showed both apoptotic and necrotic characteristics by morphological and biochemical analyses. TNFRI and NF-kappaB seem to have been involved in this regulation. It is suggested that this phenomenon is similar in some respects to that observed with IBD and that this in vitro coculture system could be a good model for searching for the drugs or food substances that can be used to treat or prevent IBD.     

The changes in the neuronal PC12 and the intestinal epithelial Caco-2 cells during the coculture. The functional analysis using an in vitro coculture system

The interaction between intestinal epithelial cells andperipheral neuronal cells were examined using an invitro coculture system. Two cell lines, Caco-2 and PC12, were usedfor this experiment as an intestinal epithelial and entericneuronal cell model, respectively. By coculturing with fullydifferentiated Caco-2 cells, the neurite outgrowth was inducedin PC12 cells. This neurite outgrowth in PC12 was blocked byanti-nerve growth factor (NGF) polyclonal antibodies,suggesting that the neurite outgrowth in PC12 during thecoculture with Caco-2 cells was due to NGF secreted fromCaco-2 cells. On the other hand, coculturing with fullydifferentiated PC12 cells induced the decrease oftransepithelial electrical resistance in Caco-2 cellmonolayers. The permeability of lucifer yellow alsosignificantly increased, suggesting that the barrier functionand paracellular permeability of Caco-2 monolayers werealtered by coculturing with PC12 cells. The present studysuggests that this in vitro coculture system is a good modelfor the functional analysis of interaction among intestinalepithelial cells with different cell types.     

Glucagon-like peptide 2 improves intestinal wound healing through induction of epithelial cell migration in vitro-evidence for a TGF--beta-mediated effect

BACKGROUND/AIMS: In vitro studies suggest that glucagon-like peptide 2 (GLP-2), secreted from enteroendocrine cells in the gastrointestinal tract after food intake, is able to ameliorate mucosal injury in settings of human disease characterized by injury and dysfunction of the intestinal mucosal epithelium. We evaluated this potential of GLP-2 after epithelial trauma by using two in vitro models measuring intestinal epithelial cell proliferation and cell migration. MATERIALS AND METHODS: Injuries were induced in confluent monolayers of the small intestinal cells lines IEC-6 and IEC-18, as well as in the colonic cell lines Caco-2 and Colo 320. GLP-2 (50-500 nM) or other peptides were added to the media. Wound healing was investigated after 24 h by quantification of the number of cells migrating across the wound edge. Proliferation of cells was assessed by using photometric mitochondrial incorporation measurement of MTT (3-[4,5-Dimethylthiazol-2-yl]-2,5-diphenyl-tetrazolium bromide). Monoclonal TGF-beta antibodies were added to wounded monolayers to examine whether the GLP-2-induced wound healing was TGF-beta-mediated. RESULTS: Migration assessments revealed a significant stimulation of GLP-2-induced migration in IEC-6 and IEC-18 monolayers compared to the placebo group. No effect was observed in the colon cancer cell lines Caco-2 and Colo 320. Results of the proliferation assays show a significant inhibition of proliferation by GLP-2 in small intestinal cell lines whereas a dose-dependent stimulation of proliferation in colonic epithelial cells was observed. Addition of neutralizing TGF-beta1 antibodies to wounded IEC-6 and IEC-18 monolayers incubated with GLP-2 significantly reduced the number of migrating cells to the level of the placebo group. CONCLUSIONS: In our in vitro model, it was shown that the GLP-2-induced improvement of intestinal wound healing is TGF-beta-mediated. These effects were predominant in the epithelium of the small intestine compared to colonic epithelium. Our findings provide further insight into mechanisms leading to GLP-2-induced mucosal wound healing. These results suggest that GLP-2 or analogues of this peptide may potentially be useful for the treatment of intestinal disorders characterized by injury and ineffective repair of the intestinal mucosa.     

Effect of neuronal PC12 cells on the functional properties of intestinal epithelial Caco-2 cells

The effect of neuronal cells on the functional properties of intestinal epithelial cells was examined by using an in vitro coculture system. Two cell lines, Caco-2 and PC12, were respectively used as intestinal epithelial and enteric neuronal cell models. Coculture of differentiated Caco-2 cells with PC12 caused a significant decrease in the transepithelial electrical resistance (TER) value of the Caco-2 monolayer. The permeability to lucifer yellow (LY) was also significantly increased, suggesting that the tight junction (TJ) of the Caco-2 monolayers was modulated by coculturing with PC12. To identify the TJ-modulating factor presumably secreted from PC12, the effects of the major neurotransmitters on the TER value and LY transport were examined, but no influence was apparent. The TJ-modulating effect of PC12 was prevented by exposing PC12 to cycloheximide, suggesting that new protein synthesis in PC12 was necessary for this regulation.     

Attenuation by dietary taurine of dextran sulfate sodium-induced colitis in mice and of THP-1-induced damage to intestinal Caco-2 cell monolayers

The effects of dietary taurine on the experimental colitis induced by dextran sulfate sodium (DSS) in mice were evaluated. C57BL/6 female mice were given 3% DSS in drinking water for 5 d to induce acute colitis. Taurine at 2% was added to the drinking water 5 d before and during the DSS-treatment to investigate its preventive effect. Taurine supplementation significantly attenuated the weight decrease, diarrhea severity, colon shortening, and the increase in the colonic tissue myeloperoxidase activity induced by DSS. Taurine also significantly inhibited the increase in the expression of a pro-inflammatory chemokine, macrophage inflammatory protein 2 (MIP-2), but not of interleukin (IL)-1beta or tumor necrosis factor (TNF)-alpha mRNA. Furthermore, taurine significantly protected the intestinal Caco-2 cell monolayers from the damage by macrophage-like THP-1 cells in an in vitro coculture system. These results suggest that taurine prevented DSS-induced colitis partly in association with (1) its inhibitory effects on the secretion of MIP-2 from the intestinal epithelial cells and on the infiltration of such inflammatory cells as neutrophils and (2) its cytoprotective functions on the epithelial barrier from the direct toxicity of DSS and from the inflammatory cell-induced injury.     

Assessment system for dioxin absorption in the small intestine and prevention of its absorption by food factors

It has been reported that 90% of the amount of dioxin in the whole body is absorbed orally with food. However, a concise and simple system to assess dioxin absorption in the small intestine has not yet been established. The present study reports a new in vitro assessment system for this purpose. A stable dioxin-responsive cell line was established by introducing a plasmid that incorporates a xenobiotic-responsive element upstream of the luciferase gene into human hepatic HepG2 genomic DNA. Dioxin was added to the apical side of differentiated human intestinal epithelial Caco-2 cell monolayers that had been cultured on a semipermeable membrane, and the basal medium was recovered after an appropriate incubation time. To the recovered medium was added dioxin-responsive HepG2, and a luciferase assay was performed. The established stable cell line clearly showed dose-and time-dependent response to dioxin. When a food factor such as chlorophyll, which has been reported to increase dioxin excretion in in vivo studies, was added with dioxin, a significant decrease in dioxin permeability to the Caco-2 monolayer was observed. This assessment system would be useful to search for those food factors that could prevent dioxin absorption in the small intestine.     

α-Amylase expressed in human small intestinal epithelial cells is essential for cell proliferation and differentiation

α-Amylase, which plays an essential role in starch degradation, is expressed mainly in the pancreas and salivary glands. Human α-amylase is also detected in other tissues, but it is unclear whether the α-amylase is endogenously expressed in each tissue or mixed exogenously with one expressed by the pancreas or salivary glands. Furthermore, the biological significance of these α-amylases detected in tissues other than the pancreas and salivary glands has not been elucidated. We discovered that human α-amylase is expressed in intestinal epithelial cells and analyzed the effects of suppressing α-amylase expression. α-Amylase was found to be expressed at the second-highest messenger RNA level in the duodenum in human normal tissues after the pancreas. α-Amylase was detected in the cell extract of Caco-2 intestinal epithelial cells but not secreted into the culture medium. The amount of α-amylase expressed increased depending on the length of the culture of Caco-2 cells, suggesting that α-amylase is expressed in small intestine epithelial cells rather than the colon because the cells differentiate spontaneously upon reaching confluence in culture to exhibit the characteristics of small intestinal epithelial cells rather than colon cells. The α-amylase expressed in Caco-2 cells had enzymatic activity and was identified as AMY2B, one of the two isoforms of pancreatic α-amylase. The suppression of α-amylase expression by small interfering RNA inhibited cell differentiation and proliferation. These results demonstrate for the first time that α-amylase is expressed in human intestinal epithelial cells and affects cell proliferation and differentiation. This α-amylase may induce the proliferation and differentiation of small intestine epithelial cells, supporting a rapid turnover of cells to maintain a healthy intestinal lumen.     

Regulation of the human taurine transporter by TNF-alpha and an anti-inflammatory function of taurine in human intestinal Caco-2 cells

We investigated whether or not the inflammatory cytokines affect the activity of taurine transporter (TAUT) in human intestinal Caco-2 cells. Among the cytokines, tumor necrosis factor alpha(TNF-alpha) markedly augmented the TAUT activity. A kinetic analysis of the TAUT activity in TNF-alpha-treated Caco-2 cells suggests that this up-regulation was associated with both an increase in the amount of TAUT and an increase in its affinity. Considering these results, it seems that intracellular taurine plays a role in the intestinal epithelial cells under such an inflammatory condition as that caused by an excessive amount of TNF-alpha secreted by macrophages. To verify this hypothesis, we examined the effect of taurine on inflamed intestinal cells by using a co-culture system of Caco-2 cells with human macrophage-like THP-1 cells. The result shows that taurine significantly repressed the damage to Caco-2 cells caused by TNF-alpha secreted by THP-1 cells. Thus, taurine may be a useful substance against intestinal inflammation.     

Nitric oxide attenuates hydrogen peroxide-induced barrier disruption and protein tyrosine phosphorylation in monolayers of intestinal epithelial cell

The intestinal epithelium provides a barrier to the transport of harmful luminal molecules into the systemic circulation. A dysfunctional epithelial barrier is closely associated with the pathogenesis of a variety of intestinal and systemic disorders. We investigated here the effects of nitric oxide (NO) and hydrogen peroxide (H(2)O(2)) on the barrier function of a human intestinal epithelial cell line, Caco-2. When treated with H(2)O(2), Caco-2 cell monolayers grown on permeable supports exhibited several remarkable features of barrier dysfunction as follows: a decrease in transepithelial electrical resistance, an increase in paracellular permeability to dextran, and a disruption of the intercellular junctional localization of the scaffolding protein ZO-1. In addition, an induction of tyrosine phosphorylation of numerous cellular proteins including ZO-1, E-cadherin, and beta-catenin, components of tight and adherens junctions, was observed. On the other hand, combined treatment of Caco-2 monolayers with H(2)O(2) and an NO donor (NOC5 or NOC12) relieved the damage to the barrier function and suppressed the protein tyrosine phosphorylation induced by H(2)O(2) alone. These results suggest that NO protects the barrier function of intestinal epithelia from oxidative stress by modulating some intracellular signaling pathways of protein tyrosine phosphorylation in epithelial cells.     

Proteasome modulating agents induce rAAV2-mediated transgene expression in human intestinal epithelial cells

Intestinal gene transfer offers promise as a therapeutic option for treatment of both intestinal and non-intestinal diseases. Recombinant adeno-associated virus serotype 2, rAAV2, based vectors have been utilized to transduce lung epithelial cells in culture and in human subjects. rAAV2 transduction of intestinal epithelial cells, however, is limited both in culture and in vivo. Proteasome-inhibiting agents have recently been shown to enhance rAAV2-mediated transgene expression in airway epithelial cells. We hypothesized that similar inhibition of proteasome-related cellular processes can function to induce rAAV2 transduction of intestinal epithelial cells. Our results demonstrate that combined treatment with proteasome-modulating agents MG101 (N-acetyl-L-leucyl-L-leucyl-L-norleucine) and Doxorubicin synergistically induces rAAV2-mediated luciferase transgene expression by >400-fold in undifferentiated Caco-2 cells. In differentiated Caco-2 monolayers, treatment with MG101 and Doxorubicin induces transduction preferentially from the basolateral cell surface. In addition to Caco-2 cells, treatment with MG101 and Doxorubicin also results in enhanced rAAV2 transduction of HT-29, T84, and HCT-116 human intestinal epithelial cell lines. We conclude that MG101 and Doxorubicin mediate generic effects on intestinal epithelial cells that result in enhanced rAAV2 transduction. Use of proteasome-modulating agents to enhance viral transduction may facilitate the development of more efficient intestinal gene transfer protocols.     

Cellular internalization of lactoferrin in intestinal epithelial cells

We studied the cellular internalization of lactoferrin (Lf) in an intestinal epithelial cell line, Caco-2, to investigate the mechanism of biological actions of ingested Lf. RT-PCR and Western blotting analyses revealed that differentiated Caco-2 cells express LfR mRNA and its protein with a 34 kD molecular weight under reducing conditions. Biotin-labeled Lf showed specific binding to the cellular membrane of differentiated Caco-2 cells with a dissociation constant (Kd) of 0.16 microM. The cellular internalization of Lf was studied in differentiated Caco-2 cells grown as monolayers on Transwell inserts, and compared to that of human transferrin (Tf). After labeling with fluorescent dye, either Lf or Tf was added to Caco-2 cells from the apical side or the basolateral one. Laser scanning confocal microscopy showed that labeled Lf was internalized only from the apical side and localized to the nuclei. On the other hand, labeled Tf was internalized from the basolateral side, not from the apical side, and localized in the cytoplasm. The internalization of labeled Lf was inhibited by excess of unlabeled Lf, but not of Tf. The internalization of labeled Lf, but not of labeled Tf, was also suppressed by heparin. This indicates that a heparin-binding site in the N-terminal region of Lf could be important for the internalization of Lf. These findings suggest that ingested Lf might be internalized by the intestinal epithelium in a manner different from Tf and might function in the nucleus.     

Luminal-applied flagellin is internalized by polarized intestinal epithelial cells and elicits immune responses via the TLR5 dependent mechanism

Bacteria release flagellin that elicits innate responses via Toll-like receptor 5 (TLR5). Here, we investigated the fate of apically administrated full length flagellin from virulent and avirulent bacteria, along with truncated recombinant flagellin proteins in intestinal epithelial cells and cellular responses. Flagellin was internalized by intestinal epithelial cell (IEC) monolayers of IEC-18. Additionally, apically applied flagellin was internalized by polarized human Caco-2BBe and T-84 cells in a TLR5 dependent mechanism. More, flagellin exposure did not affect the integrity of intestinal monolayers. With immunofluorescent staining, internalized flagellin was detected in both early endosomes as well as lysosomes. We found that apical exposure of polarized Caco-2BBe and T-84 to flagellin from purified Salmonella, Escherichia coli O83:H1 (isolate from Crohn's lesion) or avirulent E. coli K12 induced comparable levels of basolateral IL-8 secretion. A recombinant protein representing the conserved amino (N) and carboxyl (C) domains (D) of the flagellin protein (ND1/2ECHCD2/1) induced IL-8 secretion from IEC similar to levels elicited by full-length flagellins. However, a recombinant flagellin protein containing only the D3 hypervariable region elicited no IL-8 secretion in both cell lines compared to un-stimulated controls. Silencing or blocking TLR5 in Caco-2BBe cells resulted in a lack of flagellin internalization and decreased IL-8 secretion. Furthermore, apical exposure to flagellin stimulated transepithelial migration of neutrophils and dendritic cells. The novel findings in this study show that luminal-applied flagellin is internalized by normal IEC via TLR5 and co-localizes to endosomal and lysosomal compartments where it is likely degraded as flagellin was not detected on the basolateral side of IEC cultures.     

Comparative study on sodium transport and Na+,K+-ATPase activity in Caco-2 and rat jejunal epithelial cells: effects of dopamine

The present study reports on the effects of dopamine on sodium transepithelial transport and Na+,K+-ATPase activity in Caco-2 cells, a human epithelial intestinal cell line which undergoes enterocyte differentiation in culture, and jejunal epithelial cells from 20 day old Wistar rats. Addition of amphotericin B to the mucosal side stimulated Isc in a concentration dependent manner (Caco-2 cells, EC50=0.9 [0.5, 1.7] microM; rat jejunum, EC50=7.4 [0.8; 70.1] microM). The presence of 1 microM dopamine did not change the effect of amphotericin B in Caco-2 cells, but produced a significant (P<0.05) decrease in the maximal effect of amphotericin B in the rat jejunum. Dopamine (1 microM), added to the serosal side, did not change the Isc profile in Caco-2 cells, but produced a significant increase in the rat jejunum. This effect was antagonized by SKF 83566 (1 microM), but not S-sulpiride (1 microM), and was mimicked by SKF 38393 (10 nM), but not by quinerolane (10 nM). Basal Na+,K+-ATPase activity (in nmol Pi mg protein(-1) min(-1)) in Caco-2 cells (49.5+/-0.2) was similar to that observed in isolated rat jejunal epithelial cells (52.3+/-3.4). Dopamine (1 microM) significantly (P<0.05) decreased Na+,K+-ATPase activity in rat jejunal epithelial cells, but failed to inhibit Na+,K+-ATPase in Caco-2 cells. This effect of dopamine was antagonized by SKF 83566 (1 microM), but not S-sulpiride (1 microM), and was mimicked by SKF 38393 (10 nM), but not by quinerolane (10 nM). The specific binding of [3H]-Sch 23390 to the rat intestinal mucosa was saturable with an apparent dissociation constant (KD) of 2.4 (0.4; 4.5) nM and maximum receptor density of 259.8+/-32.6 fmol/mg protein. No significant specific binding of [3H]-Sch 23390 was observed in membranes from Caco-2 cells. In conclusion, the results obtained show that D1-like receptor mediated effects of dopamine in the rat jejunum on sodium absorption are absent in Caco-2 cells, most probably because this cell line does not express D1-like dopamine receptors, which ultimately are responsible for the inhibitory effect of the amine upon intestinal Na+,K+-ATPase.     

Enteric glia inhibit intestinal epithelial cell proliferation partly through a TGF-beta1-dependent pathway

Although recent studies have shown that enteric neurons control intestinal barrier function, the role of enteric glial cells (EGCs) in this control remains unknown. Therefore, our goal was to characterize the role of EGCs in the control of intestinal epithelial cell proliferation using an in vivo transgenic and an in vitro coculture model. Assessment of intestinal epithelial cell proliferation after ablation of EGCs in transgenic mice demonstrated a significant increase in crypt cell hyperplasia. Furthermore, mucosal glial network (assessed by immunohistochemical detection of S-100beta) is altered in colon adenocarcinoma compared with control tissue. In an in vitro coculture model of subconfluent Caco-2 cells seeded onto Transwell filters with EGCs, Caco-2 cell density and [3H]thymidine incorporation were significantly lower than in control (Caco-2 cultured alone). Flow cytometry analysis showed that EGCs had no effect on Caco-2 cell viability. EGCs induced a significant increase in Caco-2 cell surface area without any sign of cellular hypertrophy. These effects by EGCs were also seen in various transformed or nontransformed intestinal epithelial cell lines. Furthermore, TGF-beta1 mRNA was expressed, and TGF-beta1 was secreted by EGCs. Exogenously added TGF-beta1 reproduced partly the EGC-mediated effects on cell density and surface area. In addition, EGC effects on Caco-2 cell density were significantly reduced by a neutralizing TGF-beta antibody. In conclusion, EGCs have profound antiproliferative effects on intestinal epithelial cells. Functional alterations in EGCs may therefore modify intestinal barrier functions and be involved in pathologies such as cancer or inflammatory bowel diseases.     

HMGB1 is secreted by immunostimulated enterocytes and contributes to cytomix-induced hyperpermeability of Caco-2 monolayers

High-mobility group box 1 (HMGB1), a cytokine-like proinflammatory protein, is secreted by activated macrophages and released by necrotic cells. We hypothesized that immunostimulated enterocytes might be another source for this mediator. Accordingly, Caco-2 cells or primary mouse intestinal epithelial cells (IECs) were incubated with "cytomix" (a mixture of TNF, IL-1, and IFN-) for various periods. HMGB1 in cell culture supernatants was detected by Western blot analysis and visualized in Caco-2 cells with the use of fluorescence confocal and immunotransmission electron microscopy. Caco-2 cells growing on filters in diffusion chambers were stimulated with cytomix for 48 h in the absence or presence of anti-HMGB1 antibody, and permeability to fluorescein isothiocyanate-dextran (average molecular mass, 4 kDa; FD4) was assessed. Cytomix-stimulated Caco-2 cells secreted HMGB1 into the apical but not the basolateral compartments of diffusion chambers. Although undetectable at 6 and 12 h after the start of incubation with cytomix, HMGB1 was present in supernatants after 24 h of incubation. HMGB1 secretion by Caco-2 monolayers also was induced when the cells were exposed to FSL-1, a Toll-like receptor (Tlr)-2 agonist, or flagellin, a Tlr5 agonist, but not lipopolysaccharide, a Tlr4 agonist. Cytomix also induced HMGB1 secretion by primary IECs. Cytoplasmic HMGB1 is localized within vesicles in Caco-2 cells and is secreted, at least in part, associated with exosomes. Incubating Caco-2 cells with cytomix increased FD4 permeation, but this effect was significantly decreased in the presence of anti-HMGB1 antibody. Collectively, these data support the view that HMGB1 is secreted by immunostimulated enterocytes. This process may exacerbate inflammation-induced epithelial hyperpermeability via an autocrine feedback loop. exosome; toll-like receptor; flagellin     

Chickpea protein hydrolysate as a substitute for serum in cell culture

The growth of mammalian cells in vitro requires the use of rich culture media that are prepared by combining serum with specific nutrient formulations. Serum, the most expensive component of culture media, provides a complex mixture of growth factors and nutrients. Protein hydrolysates that can support in vitro cell growth and eliminate or reduce the need to use serum have been obtained from different sources. Here we describe the use of two food grade proteases to produce a chickpea protein hydrolysate that has been added to cell culture medium in order to determine whether it can be used as a substitute for serum. Medium containing the hydrolysate has been tested using two human cells lines: the monocytic THP-1 cell line which grows in suspension, and the epithelial Caco-2 cell line which grows as a monolayer. The chickpea protein hydrolysate was a good substitute for serum in the first case, but did not allow growth of Caco-2 cells. Supplementation of culture media with this inexpensive and safe hydrolysate would greatly reduce the cost of cell culture.     

Recognition of intestinal epithelial HIF-1alpha activation by Pseudomonas aeruginosa

Human intestinal epithelial cell monolayers (Caco-2) subjected to hypoxia and reoxygenation release soluble factors into the apical medium that activate the virulence of the opportunistic pathogen Pseudomonas aeruginosa to express the potent barrier-dysregulating protein PA-I lectin/adhesin. In this study, we defined the role of hypoxia-inducible factor (HIF)-1alpha in this response. We tested the ability of medium from Caco-2 cells with forced expression of HIF-1alpha to increase PA-I expression in P. aeruginosa and found that medium from Caco-2 cells overexpressing HIF-1alpha increased PA-I expression compared with medium from control cells (P < 0.001, ANOVA). To identify the components responsible for this response, medium was fractionated by molecular weight and subjected to mass spectroscopy, which identified adenosine as the possible mediator. Both adenosine and its immediate downstream metabolite inosine induced PA-I expression in P. aeruginosa in a dose-dependent fashion. Because inosine was not detectable in the medium of Caco-2 cells exposed to hypoxia or overexpressing HIF-1alpha, we hypothesized that P. aeruginosa itself might metabolize adenosine to inosine. Using mutant and parental strains of P. aeruginosa, we demonstrated that P. aeruginosa metabolized adenosine to inosine via adenosine deaminase and that the conditioned medium enhanced the extracellular accumulation of inosine. Together, these results provide evidence that P. aeruginosa can recognize and respond to extracellular end products of intestinal hypoxia that are released after activation of HIF-1alpha. The ability of P. aeruginosa to metabolize adenosine to inosine may represent a subversive microbial virulence strategy that deprives the epithelium of the cytoprotective actions of adenosine.     

IEX-1 suppresses apoptotic damage in human intestinal epithelial Caco-2 cells induced by co-culturing with macrophage-like THP-1 cells

We have reported previously that apoptosis of intestinal epithelial Caco-2 cells is induced by co-culturing with human macrophage-like THP-1 cells, mainly via the action of TNFα (tumour necrosis factor α) secreted from THP-1 cells [Satsu, Ishimoto, Nakano, Mochizuki, Iwanaga and Shimizu (2006) Exp. Cell Res. 312, 3909-3919]. Our recent DNA microarray analysis of co-cultured Caco-2 cells showed that IEX-1 (immediate early-response gene X-1) is the most significantly increased gene during co-culture [Ishimoto, Nakai, Satsu, Totsuka and Shimizu (2010) Biosci. Biotechnol. Biochem. 74, 437-439]. Hence, we investigated the role of IEX-1 in the co-culture-induced damage of Caco-2 cells. We showed that IEX-1 expression induced in Caco-2 cells was suppressed by anti-TNFα antibody treatment. Experiments using IEX-1-overexpressing and -knockdown Caco-2 cells suggested that IEX-1 was involved in the suppression of Caco-2 cell damage. Increases in caspase 3 activity and TNFR1 (TNF receptor 1) mRNA expression were shown in IEX-1-knockdown Caco-2 cells, suggesting that IEX-1 plays a role in the suppression of apoptosis and protects cells by controlling sensitivity to TNFα under both normal and inflammatory conditions.     

Invasion of human epithelial cells by Campylobacter upsaliensis

Few data exist on the interaction of Campylobacter upsaliensis with host cells, and the potential for this emerging enteropathogen to invade epithelial cells has not been explored. We have characterized the ability of C. upsaliensis to invade both cultured epithelial cell lines and primary human small intestinal cells. Epithelial cell lines of intestinal origin appeared to be more susceptible to invasion than non-intestinal-derived cells. Of three bacterial isolates studied, a human clinical isolate, CU1887, entered cells most efficiently. Although there was a trend towards more efficient invasion of Caco-2 cells by C. upsaliensis CU1887 at lower initial inocula, actual numbers of intracellular organisms increased with increasing multiplicity of infection and with prolonged incubation period. Confocal microscopy revealed C. upsaliensis within primary human small intestinal cells. Both Caco-2 and primary cells in non-confluent areas of the infected monolayers were substantially more susceptible to infection than confluent cells. The specific cytoskeletal inhibitors cytochalasin B, cytochalasin D and vinblastine attenuated invasion of Caco-2 cells in a concentration-dependent manner, providing evidence for both microtubule- and microfilament-dependent uptake of C. upsaliensis. Electron microscopy revealed the presence of organisms within Caco-2 cell cytoplasmic vacuoles. C. upsaliensis is capable of invading epithelial cells and appears to interact with host cell cytoskeletal structures in order to gain entry to the intracellular environment. Entry into cultured primary intestinal cells ex vivo provides strong support for the role of host cell invasion during human enteric C. upsaliensis infection.