Inhibition of interleukin-1-stimulated NF-kappaB RelA/p65 phosphorylation by mesalamine is accompanied by decreased transcriptional activity.
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Nuclear factor kappaB (NF-kappaB) is an inducible transcription factor that regulates genes important in immunity and inflammation. The activity of NF-kappaB is highly regulated: transcriptionally active NF-kappaB proteins are sequestered in the cytoplasm by inhibitory proteins, IkappaB. A variety of extracellular signals, including interleukin-1 (IL-1), activate NF-kappaB by inducing phosphorylation and degradation of IkappaB, allowing nuclear translocation and DNA binding of NF-kappaB. Many of the stimuli that activate NF-kappaB by inducing IkappaB degradation also cause phosphorylation of the NF-kappaB RelA (p65) polypeptide. The transactivating capacity of RelA is positively regulated by phosphorylation, suggesting that in addition to cytosolic sequestration by IkappaB, phosphorylation represents another mechanism for control of NF-kappaB activity. In this report, we demonstrate that mesalamine, an anti-inflammatory aminosalicylate, dose-dependently inhibits IL-1-stimulated NF-kappaB-dependent transcription without preventing IkappaB degradation or nuclear translocation and DNA binding of the transcriptionally active NF-kappaB proteins, RelA, c-Rel, or RelB. Mesalamine was found to inhibit IL-1-stimulated RelA phosphorylation. These data suggest that pharmacologic modulation of the phosphorylation status of RelA regulates the transcriptional activity of NF-kappaB, independent of nuclear translocation and DNA binding. These findings highlight the importance of inducible phosphorylation of RelA in the control of NF-kappaB activity. (+info)
Discordant expression of tissue factor and its activity in polarized epithelial cells. Asymmetry in anionic phospholipid availability as a possible explanation.
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Recent studies have shown a discrepancy between the level of tissue factor (TF) expression and the level of TF procoagulant activity on the apical and basolateral surface domains of polarized epithelial cells. The present investigation was performed to elucidate possible reasons for the discordant expression of TF and its activity on the surface of polarized epithelial cells using a human intestinal epithelial cell line, Caco-2 and Madin-Darby canine kidney epithelial cells, type II (MDCK-II). Functional activity of coagulation factor VIIa (VIIa) in complex with TF was 6- to 7-fold higher on the apical than the basolateral surface in polarized Caco-2 cells. In contrast, no significant difference was found in the formation of TF/VIIa complexes between the apical and basolateral surface. Confocal microscopy of Caco-2 cells showed TF expression on both the apical and the basolateral surface domains. Studies with MDCK-II cells showed that the specific functional activity of TF expressed on the apical cell surface was 5-fold higher than on the basolateral surface. To test whether differential expression of TF pathway inhibitor (TFPI) on the apical and basolateral surface could account for differences in TF/VIIa functional activity, we measured cell-surface-bound TFPI activity in Caco-2 cells. Small but similar amounts of TFPI were found on both surfaces. Further, addition of inhibitory anti-TFPI antibodies induced a similar enhancement of TF/VIIa activity on both surface domains. Because the availability of anionic phospholipids on the outer leaflet of the cell membrane could regulate TF/VIIa functional activity, we measured the distribution of anionic phospholipids on the apical and basolateral surface by annexin V binding and thrombin generation. The results showed that the anionic phospholipid content on the basolateral surface, compared with the apical surface, was 3- to 4-fold lower. Mild acid treatment of polarized Caco-2 cells, which markedly increased the anionic phospholipid content on the basolateral surface membrane, increased the TF/VIIa activity on the basolateral surface without affecting the number of TF/VIIa complexes formed on the surface. Overall, our data suggest that an uneven expression of TF/VIIa activity between the apical and basolateral surface of polarized epithelial cells is caused by differences in anionic phospholipid content between the two surface domains and not from a polar distribution of TFPI. (+info)
Modulation of intracellular growth of Listeria monocytogenes in human enterocyte Caco-2 cells by interferon-gamma and interleukin-6: role of nitric oxide and cooperation with antibiotics.
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The influence of interferon (IFN)-gamma and interleukin (IL)-6 on the intracellular growth of Listeria monocytogenes phagocytosed from the apical pole was examined in polarized Caco-2 cells. IFN-gamma (from the apical pole) and IL-6 (from the basolateral pole) considerably reduced the bacterial intracellular growth, an effect largely abolished by l-monomethyl arginine. Both cytokines caused overexpression of inducible nitric oxide synthase. IL-6, but not IFN-gamma, caused a partial restriction of L. monocytogenes in phagosomes and largely prevented the cytosolic forms from being surrounded by actin. Ampicillin was bacteriostatic in unstimulated cells but modestly bactericidal in cells treated with IFN-gamma and IL-6. Azithromycin (a macrolide) was fairly bactericidal and sparfloxacin (a fluoroquinolone) highly bactericidal in all situations. IFN-gamma and IL-6 may therefore be important determinants in the protection of epithelial cells from intracellular multiplication of L. monocytogenes. Ampicillin may fail in their absence, requiring the use of other antibiotics such as the fluoroquinolones. (+info)
PKC-dependent regulation of transepithelial resistance: roles of MLC and MLC kinase.
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The mechanisms by which protein kinase C (PKC) activation results in increased transepithelial resistance (TER) are unknown [G. Hecht, B. Robinson, and A. Koutsouris. Am. J. Physiol. 266 (Gastrointest. Liver Physiol. 29): G214-G221, 1994]. We have previously shown that phosphorylation of the regulatory light chain of myosin II (MLC) is associated with decreases in TER and have suggested that contraction of the perijunctional actomyosin ring (PAMR) increases tight junction (TJ) permeability [J. R. Turner, B. K. Rill, S. L. Carlson, D. Carnes, R. Kerner, R. J. Mrsny, and J. L. Madara. Am. J. Physiol. 273 (Cell Physiol. 42): C1378-C1385, 1997]. We therefore hypothesized that PKC activation alters TER via relaxation of the PAMR. Activation of PKC by the phorbol ester phorbol 12-myristate 13-acetate (PMA) resulted in a progressive dose-dependent increase in TER that was apparent within 15 min (111% of controls) and maximal within 2 h (142% of controls). Similar increases were induced by a diacylglycerol analog, and the effects of both PMA and the diacylglycerol analog were prevented by the PKC inhibitor bisindolylmaleimide I. PMA treatment caused progressive decreases in MLC phosphorylation, by 12% at 15 min and 41% at 2 h. Phosphorylation of MLC kinase (MLCK) increased by 64% within 15 min of PMA treatment and was stable over 2 h (51% greater than that of controls). Thus increases in MLCK phosphorylation preceded decreases in MLC phosphorylation. These data suggest that PKC regulates TER via decreased phosphorylation of MLC, possibly due to inhibitory phosphorylation of MLCK. The decreased phosphorylation of MLC likely reduces PAMR tension, leading to decreased TJ permeability. (+info)
Biosynthesis and secretion of the mannose 6-phosphate receptor and its ligands in polarized Caco-2 cells.
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We have analyzed the transport of newly synthesized mannose 6-phosphate (Man-6-P)-bearing proteins (i.e., lysosomal enzymes) in the polarized human colon adenocarcinoma cell line, Caco-2, by subjecting filter-grown cells to a pulse-chase labeling protocol using [(35)S]methionine, and the resulting cell lysate, apical medium, and basolateral medium were immunoprecipitated with insulin-like growth factor II/Man-6-P receptor (IGF-II/MPR)-specific antisera. The results showed that the majority of secreted lysosomal enzymes accumulated in the apical medium at >2 h of chase and that this polarized distribution was facilitated by the IGF-II/MPR selectively endocytosing lysosomal enzymes from the basolateral surface. Treatment with various agents known to affect vesicular transport events demonstrated that incubations at 16 degrees C or incubations with brefeldin A inhibited the secretion of lysosomal enzymes from both the apical and basolateral surface, whereas treatment with nocodazole selectively blocked apical secretion. In contrast, incubation with NH4Cl or nocodazole had a stimulatory effect on basolateral secretion. Taken together, these results demonstrate that the sorting of Man-6-P-containing proteins into the apical and basolateral secretory pathways is regulated by distinct components of the intracellular trafficking machinery. (+info)
Requirement of the MAP kinase cascade for cell cycle progression and differentiation of human intestinal cells.
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The intracellular signaling pathways responsible for cell cycle arrest and establishment of differentiated cells along the gut axis remain largely unknown. In the present study, we analyzed the regulation of p42/p44 mitogen-activated protein kinase (MAPK) in the process of proliferation and differentiation of human intestinal cells. In vitro studies were done in Caco-2/15 cells, a human colon cancer cell line that spontaneously differentiates into an enterocyte phenotype. In vivo studies were performed on cryostat sections of human fetal intestinal epithelium by indirect immunofluorescence. We found that inhibition of the p42/p44 MAPK signaling by the PD-98059 compound or by ectopic expression of the MAPK phosphatase-1 strongly attenuated E2F-dependent transcriptional activity in Caco-2/15 cells. p42/p44 MAPK activities dramatically decreased as soon as Caco-2/15 cells reached confluence. However, significant levels of activated p42 MAPK were detected in differentiated Caco-2/15 cells. Addition of PD-98059 during differentiation interfered with sustained activation of p42 MAPK and sucrase-isomaltase expression. Although p42/p44 MAPKs were expressed in both the villus tip and crypt cells, their phosphorylated and active forms were detected in the undifferentiated crypt cells. Our results indicate that elevated p42/p44 MAPK activities stimulate cell proliferation of intestinal cells, whereas low sustained levels of MAPK activities correlated with G1 arrest and increased expression of sucrase-isomaltase. (+info)
Cryptosporidium parvum apical complex glycoprotein CSL contains a sporozoite ligand for intestinal epithelial cells.
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Cryptosporidiosis, caused by the apicomplexan parasite Cryptosporidium parvum, has become a well-recognized diarrheal disease of humans and other mammals throughout the world. No approved parasite-specific drugs, vaccines, or immunotherapies for control of the disease are currently available, although passive immunization with C. parvum-specific antibodies has some efficacy in immunocompromised and neonatal hosts. We previously reported that CSL, an approximately 1,300-kDa conserved apical glycoprotein of C. parvum sporozoites and merozoites, is the antigenic species mechanistically bound by neutralizing monoclonal antibody 3E2 which elicits the circumsporozoite precipitate (CSP)-like reaction and passively protects against C. parvum infection in vivo. These findings indicated that CSL has a functional role in sporozoite infectivity. Here we report that CSL has properties consistent with being a sporozoite ligand for intestinal epithelial cells. For these studies, native CSL was isolated from whole sporozoites by isoelectric focusing (IEF) following observations that the approximately 1,300-kDa region containing CSL as seen by sodium dodecyl sulfate-polyacrylamide gel electrophoresis was comprised of approximately 15 molecular species (pI 3 to 10) when examined by two-dimensional (2-D) electrophoresis and silver staining. A subset of six approximately 1,300-kDa species (pI 4.0 to 6.5) was specifically recognized by 3E2 in 2-D Western immunoblots of IEF-isolated CSL. Isolated native CSL bound specifically and with high affinity to permissive human intestinal epithelial Caco-2 cells in a dose-dependent, saturable, and self-displaceable manner. Further, CSL specifically bound to the surface of live Caco-2 cells inhibited sporozoite attachment and invasion. In addition, sporozoites having released CSL after incubation with 3E2 and occurrence of the CSP-like reaction did not attach to and invade Caco-2 cells. These findings indicate that CSL contains a sporozoite ligand which facilitates attachment to and invasion of Caco-2 cells and, further, that ligand function may be disrupted by CSL-reactive monoclonal antibody. We conclude that CSL is a rational target for passive or active immunization against cryptosporidiosis. (+info)
Transport of thiamine in human intestine: mechanism and regulation in intestinal epithelial cell model Caco-2.
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The present study examined the intestinal uptake of thiamine (vitamin B(1)) using the human-derived intestinal epithelial cells Caco-2 as an in vitro model system. Thiamine uptake was found to be 1) temperature and energy dependent and occurred with minimal metabolic alteration; 2) pH sensitive; 3) Na(+) independent; 4) saturable as a function of concentration with an apparent Michaelis-Menten constant of 3.18 +/- 0.56 microM and maximal velocity of 13.37 +/- 0.94 pmol. mg protein(-1). 3 min(-1); 5) inhibited by the thiamine structural analogs amprolium and oxythiamine, but not by unrelated organic cations tetraethylammonium, N-methylnicotinamide, and choline; and 6) inhibited in a competitive manner by amiloride with an inhibition constant of 0.2 mM. The role of specific protein kinase-mediated pathways in the regulation of thiamine uptake by Caco-2 cells was also examined using specific modulators of these pathways. The results showed possible involvement of a Ca(2+)/calmodulin (CaM)-mediated pathway in the regulation of thiamine uptake. No role for protein kinase C- and protein tyrosine kinase-mediated pathways in the regulation of thiamine uptake was evident. These results demonstrate the involvement of a carrier-mediated system for thiamine uptake by Caco-2 intestinal epithelial cells. This system is Na(+) independent and is different from the transport systems of organic cations. Furthermore, a CaM-mediated pathway appears to play a role in regulating thiamine uptake in these cells. (+info)