Absence of tRNA-guanine transglycosylase in a human colon adenocarcinoma cell line.

Queuosine (Q), found exclusively in the first position of the anticodons of tRNA(Asp), tRNA(Asn), tRNA(His) and tRNA(Tyr), is synthesized in eucaryotes by a base-for-base exchange of queuine, the base of Q, for guanine at tRNA position 34. This reaction is catalyzed by the enzyme tRNA-guanine transglycosylase (EC 2.4.2.29). We measured the specific release of queuine from Q-5'-phosphate (queuine salvage) and the extent of tRNA Q modification in 6 human tumors carried as xenografts in immune-deprived mice. Q-deficient tRNA was found in 3 of the tumors but it did not correlate with diminished queuine salvage. The low tRNA Q content of one tumor, the HxGC3 colon adenocarcinoma, prompted us to examine a HxGC3-derived cell line, GC3/M. GC3/M completely lacks Q in its tRNA and measurable tRNA-guanine transglycosylase activity; the first example of a higher eucaryotic cell which lacks this enzyme. Exposure of GC3/M cells to 5-azacytidine induces the transient appearance of Q-positive tRNA. This result suggests that at least one allele of the transglycosylase gene in GC3/M cells may have been inactivated by DNA methylation. In clinical samples, we found Q-deficient tRNA in 10 of 46 solid tumors, including 2 of 13 colonic carcinomas.     

Assembly of the tight junction: the role of diacylglycerol

Extracellular Ca2+ triggers assembly and sealing of tight junctions (TJs) in MDCK cells. These events are modulated by G-proteins, phospholipase C, protein kinase C (PKC), and calmodulin. In the present work we observed that 1,2-dioctanoylglycerol (diC8) promotes the assembly of TJ in low extracellular Ca2+, as evidenced by translocation of the TJ-associated protein ZO-1 to the plasma membrane, formation of junctional fibrils observed in freeze-fracture replicas, decreased permeability of the intercellular space to [3H]mannitol, and reorganization of actin filaments to the cell periphery, visualized by fluorescence microscopy using rhodamine-phalloidin. In contrast, diC8 in low Ca2+ did not induce redistribution of the Ca-dependent adhesion protein E-cadherin (uvomorulin). Extracellular antibodies to E-cadherin block junction formation normally induced by adding Ca2+. diC8 counteracted this inhibition, suggesting that PKC may be in the signaling pathway activated by E-cadherin-mediated cell-cell adhesion. In addition, we found a novel phosphoprotein of 130 kD which coimmunoprecipitated with the ZO-1/ZO-2 complex. Although the assembly and sealing of TJs may involve the activation of PKC, the level of phosphorylation of ZO-1, ZO-2, and the 130-kD protein did not change after adding Ca2+ or a PKC agonist. The complex of these three proteins was present even in low extracellular Ca2+, suggesting that the addition of Ca2+ or diC8 triggers the translocation and assembly of preformed TJ subcomplexes.     

Establishment and characterization of a new human colon adenocarcinoma cell line: BCS-TC2

A new cell line designated as BCS-TC2 was established in culture from a primary human colon adenocarcinoma. This cell line has been in continuous culture over a 36-month period. The cells grow as a monolayer sheet, displaying areas with a multilayered pattern as well as single cells and free-floating aggregates. The morphological, immunological, and ultrastructural features of these cells are in agreement with their epithelial origin. The characterization of this cell line indicated a 38 hr doubling time, and a colony forming efficiency of 2% in semisolid media and 22% in liquid culture, at low cell densities. These cells produce low amounts of carcinoembryonic antigen in culture (0.1 ng of CEA/10⁶ cells). Sub-cutaneous injection into athymic mice shows that these cells have a non-tumorigenic capacity. Chromosomal analysis showed a karyotype 46 XX,-15, +der (15), inv (16) (p13::q13). BCS-TC2 cell line, which maintains in culture several characteristics of the original tumor, represents a useful model system for cell biology studies of primary and non-metastatic tumors.     

Phosphorylation of claudin-4 is required for tight junction formation in a human keratinocyte cell line

Extensive studies have identified a large number of the molecular components of cellular tight junctions (TJ), including the claudins, occludin and ZO-1/2, and also many of the physical interactions between these molecules. However, the regulatory mechanisms of TJ formation are as yet poorly understood. In HaCaT, a human epidermal keratinocyte cell line, TJ were newly formed when cells were cultured in the presence of SP600125, a JNK inhibitor. Moreover, claudin-4 was newly phosphorylated during this process. We found that claudin-4 contains a sequence which is phosphorylated by atypical PKC (aPKC). Kinase assay demonstrated that the 195th serine (serine195) of mouse claudin-4 was phosphorylated by aPKC in vitro. The 194th serine (serine194) of human claudin-4 corresponding to serine195 of mouse claudin-4 was phosphorylated in HaCaT cells when TJ were formed, and the phosphorylated claudin-4 co-localized with ZO-1 at TJ. aPKC activity was required for both the claudin-4 phosphorylation and TJ formation in HaCaT. Furthermore, overexpression of mutant claudin-4 protein S195A, which was not phosphorylated by aPKC, perturbed the TJ formation mediated by SP600125. These findings suggest that aPKC regulates TJ formation through the phosphorylation of claudin-4.     

Formation of tight junctions in epithelial cells. I. Induction by proteases in a human colon carcinoma cell line

The experimental modulation of tight junctions (TJ) was studied in the human adenocarcinoma cell line HT 29 by freeze-fracture electron microscopy. The cell line has virtually no TJ when grown in culture. TJ could be induced by mild treatment with a variety of endopeptidases (trypsin, chymotrypsin, collagenase, elastase, plasmin, thrombin, papain, and pronase). Pronase induced the formation of TJ at low (but not at high) concentrations. All exopeptidases studied were unable to induce the formation of TJ. At 0 degree C the trypsin-induced formation of TJ was greatly slowed down although not entirely inhibited. However, when cells were briefly treated with trypsin at 0 degree C and subsequently transferred to 37 degrees C in the presence of protease inhibitors, TJ were rapidly assembled. Thus an induction phase at low temperature and an assembly phase at high temperature could be experimentally separated. When cells were briefly trypsinized at 0 degrees and subsequently kept at 0 degree C without trypsin for several hours, TJ still formed abundantly upon incubation at 37 degrees C. It appears therefore that the effect produced by the protease is retained for long periods in the cold.     

Effect of tyrphostins on programmed cell death in colon adenocarcinoma cell line LS-180

Programmed cell death is an important process in the regulation of cellular proliferation, rest, differentiation and death. It is a genetically controlled process with characteristic biochemical and morphological features. Apoptosis directly regulates tumorigenesis and its induction could be a useful method of cancer therapy. Cancer cells could be influenced by some factors which induce apoptosis. We investigated the influence of tyrphostins, that specifically inhibits protein tyrosine kinases and stops the cell cycle in apoptosis of the colon adenocarcinoma cell line LS180. We used them at the concentration of 1-10 microM for 24 and 48 hours. We detected apoptosis using techniques that monitor either biochemical and morphological features of this process, such as staining with 7-amino-actinomycin D, staining with Grünwald-Giemsa, TUNEL reaction, in situ hybridization and with immunoperoxidase staining procedures. We examined the expression of genes and proteins connected with programmed cell death (p53, c-myc, p21, bcl-2). We estimated the results by cytophotometry and documented them by colour photography. We found that tyrphostin rapidly inhibits the cell cycle, particularly at the concentration of 5 microM. The expression of genes and proteins was strongly correlated with the increased apoptotic cell death conforming to the results of TUNEL and staining methods.     

Effects of alpha-difluoromethylornithine-induced polyamine depletion on the radiosensitivity of a human colon carcinoma cell line

The effect of the polyamine biosynthesis inhibitor alpha-difluoromethylornithine (DFMO) on the in vitro radiation response of Clone A human colon adenocarcinoma cells was investigated. Analysis of intracellular polyamine levels showed that exposure of Clone A cells to 1 mM DFMO for 96 h reduced putrescine and spermidine to nondetectable levels, while spermine was decreased by approximately 50%. This DFMO treatment protocol enhanced the radiosensitivity of Clone A cells, which was reflected by a decrease in both the Do and Dq. The addition of putrescine (1 mM) for the final 48 h of DFMO exposure restored polyamine levels and returned clone A radiosensitivity to that of control cells. These results indicate that polyamine depletion by DFMO sensitizes Clone A tumor cells to ionizing radiation.     

Iron depletion decreases proliferation and induces apoptosis in a human colonic adenocarcinoma cell line, Caco2

Iron is essential for maintaining cellular metabolism of most organisms. Iron chelators such as desferrioxamine have been used clinically in the treatment of iron overload diseases. In the present study, we used human colon adenocarcinoma cells as a proliferating cell model to validate that desferrioxamine inhibits cell proliferation and induces apoptosis. Proteomic analysis revealed that proteins involved in cell proliferation, signal transduction, metabolism and protein synthesis were significantly regulated by the availability of iron, rendering a close correlation between cell apoptosis and the disturbance of mitochondrial, signaling and metabolic pathways. These results provide new insights into the mechanisms of cell proliferation inhibition attributed to iron depletion.     

The effect of chitosan and other polycations on tight junction permeability in the human intestinal Caco-2 cell line(1)

Chitosan is a polycationic compound widely employed as dietary supplement and also present in pharmaceutical preparations. Although it has been approved for human consumption, its possible side effects have not been widely investigated and the available data in the literature are still controversial. Several polycationic substances have been shown to affect tight junction permeability in epithelial cell models in vitro. In this study we have compared the effects of chitosan and other polycations (polyethylenimine, poly-L-lysines of different molecular weights) on the integrity of tight junctions and of the actin cytoskeleton in the human intestinal Caco-2 cell line. We have measured trans-epithelial electrical resistance and paracellular passage of the extracellular marker inulin, and we have localized F-actin and tight junctional proteins (ZO1 and occludin) in cell monolayers treated with various concentrations of each polycation. Fluorescent poly-L-lysines were also employed to determine their association with the cell monolayer. Our results indicate that all polycations investigated are able to induce a reversible increase in tight junction permeability. This effect is concentration and energy dependent, affected by the extracellular concentration of divalent cations (calcium, magnesium and manganese) and it is associated with morphological changes in the F-actin cytoskeleton, as well as in the localization of tight junctional proteins. Chitosan, in particular, was the only cationic polymer that displayed an irreversible effect on tight junctions at the highest concentration tested (0.01%). These results indicate that oral ingestion of chitosan may have more widespread health effects by altering intestinal barrier function, thus allowing the entrance into the circulation of potentially toxic and/or allergenic substances.     

Characteristics of seven clones of the WiDr human colon adenocarcinoma cell line

Summary Seven clonal populations were derived from the WiDr human colon adenocarcinoma cell line and were characterized with respect to chromosome number, DNA content, and tumorigenicity in nude mide. There was no correlation between tumor volume and either DNA content or chromosome number; but there were wide differences among the clones regarding the size of tumors they were able to produce in nude mice.     

Establishment and characterization of a cell line derived from human colon adenocarcinoma (HuCCL-14)

A continuous human colon carcinoma cell line (HuCCL-14) was established whose cells possess an epithelial-like morphology and are capable of growing in soft agar and on monolayers of normal cells. HuCCL-14 cells yielded high levels of carcinoembryonic antigen, and the analysis of their chromosomal constitution revealed a mode of 70 chromosomes per cell. HuCCL-14 cells produce malignant tumors when injected into nude mice. Preliminary virologic studies indicate the release of RNA particles having a density of 1.15--1.19 g/ml.     

Characterization of an electrogenic sodium/glucose cotransporter in a human colon epithelial cell line

In this study, we have characterized the Na/glucose transporter in polarized monolayers formed by the clonal human colon carcinoma cell line HT-29-D4. Isotopic tracer flux measurements show that differentiated HT-29-D4 cells possess a sodium-dependent α-methyl-D-glucopyranoside (AMG) uptake that is competed for by increasing concentrations of D-glucose, D-galactose, and phlorizin. This transport is exclusively localized on the apical side of the epithelium. Kinetic data demonstrate the existence of a single Michaelian sodium-dependent AMG transporter with a Km of 1.2 ± 0.12 mM and a Vmax of 3.24 ± 0.25 nmol/mg of protein per min. Hill analysis reveals a coefficient of 1.9 ± 0.03, consistent with at least two sodium ions involved in AMG transport. Interestingly, the cotransporter function is not modulated by glucose in the culture medium. Transepithelial electrical parameter measurements show that the transepithelial potential difference (Vt) is glucose dependent and phlorizin sensitive. Antibodies directed against a peptide of the rabbit intestinal glucose cotransporter (Ser402-Lys420) recognize, in western blot experiments, the characteristic bands of the cotransporter on a crude membrane preparation of differentiated HT-29-D4 cells and react strongly with the apical domain of the monolayer in immunofluorescence experiments. We conclude that HT-29-D4 cells express the sodium/glucose cotransporter SGLT1 at their apical membrane and that this transporter generates the basal transepithelial potential difference. © 1995 Wiley-Liss, Inc.     

Characterization of the WIDR: a human colon carcinoma cell line.

We describe the establishment and characterization of WiDr, a cell line derived from a human colon carcinoma. It produces carcinoembryonic antigen in culture, and has a doubling time of 15 hr with plating efficiency of 51%. The HLA antigenic profile and the allozyme genetic signature (composed of eight gene-enzyme systems) of WiDr cells are different from those of HeLa cells. Furthermore, WiDr cells possess three marker chromosomes, again distinct from the HeLa marker chromosomes. Finally, it is highly tumorigenic in four different xenogeneic animal models. Based on these studies, WiDr represents a useful model cell line for tumor cell biology investigations.     

MicroRNA expression profile of colon cancer stem-like cells in HT29 adenocarcinoma cell line

Increasing evidence has suggested cancer stem cells (CSCs) are considered to be responsible for cancer formation, recurrence, and metastasis. Recently, many studies have also revealed that microRNAs (miRNAs) strongly implicate in regulating self renewal and tumorigenicity of CSCs in human cancers. However, with respect to colon cancer, the role of miRNAs in stemness maintenance and tumorigenicity of CSCs still remains to be unknown. In the present study, we isolated a population of colon CSCs expressing a CD133 surface phenotype from human HT29 colonic adenocarcinoma cell line by Flow Cytometry Cell Sorting. The CD133⁺ cells possess a greater tumor sphere-forming efficiency in vitro and higher tumorigenic potential in vivo. Furthermore, the CD133⁺ cells are endowed with stem/progenitor cells-like property including expression of “stemness” genes involved in Wnt2, BMI1, Oct3/4, Notch1, C-myc and other genes as well as self-renewal and differentiation capacity. Moreover, we investigated the miRNA expression profile of colon CSCs using miRNA array. Consequently, we identified a colon CSCs miRNA signature comprising 11 overexpressed and 8 underexpressed miRNAs, such as miR-429, miR-155, and miR-320d, some of which may be involved in regulation of stem cell differentiation. Our results suggest that miRNAs might play important roles in stemness maintenance of colon CSCs, and analysis of specific miRNA expression signatures may contribute to potential cancer therapy.     

Vasoactive intestinal peptide and forskolin regulate proliferation of the HT29 human colon adenocarcinoma cell line.

Although several lines of evidence implicate cAMP in the regulation of intestinal cell proliferation, the precise role of this second messenger in the control of the human colon cancer cell cycle is still unclear. In order to investigate the role of cAMP in HT29 cell proliferation, we have tested the effect of vasoactive intestinal peptide (VIP) and forskolin on DNA synthesis and cell number, focusing on the time-dependent efficacy of the treatment. The cells were arrested in G0/G1 phase by incubation for 24 h in serum-free medium and proliferation was re-initiated by addition of either 85 nM insulin or 0.5% fetal calf serum. In the presence of fetal calf serum, G1/S transition was found to occur earlier than with insulin. Exposure of the HT29 cells to 10(-5) M forskolin in the early stages of growth induction (within 12 h from FCS addition or within 14 h from insulin treatment) resulted in a significant inhibition of DNA synthesis and a delayed entry in the S phase. By contrast, VIP (10(-7) M) was inhibitory only when added within a narrow window (10 to 12 h or 12 to 14 h following FCS or insulin addition, respectively). The difference in efficiency of forskolin and VIP to inhibit cell proliferation may be correlated with their own potency to promote long-lasting cAMP accumulation. The combination of VIP plus forskolin had synergistic effects on both cAMP accumulation and cell-growth inhibition. Taken together, our data indicate that cAMP may act at a step in the late G1 or G1/S transition.     

Phosphofructokinase 2 and glycolysis in HT29 human colon adenocarcinoma cell line. Regulation by insulin and phorbol esters.

Kinetic properties of phosphofructokinase 2 (PFK2) and regulation of glycolysis by phorbol 12-myristate 13-acetate (PMA) and insulin were investigated in highly glycolytic HT29 colon cancer cells. PFK2 was found to be inhibited by citrate and, to a lesser extent, by phosphoenolpyruvate and ADP, but to be insensitive to inhibition by sn-glycerol phosphate. From these kinetic data, PFK2 from HT29 cells appears different from the liver form, but resembles somewhat the heart isoenzyme. Fructose 2,6-bisphosphate (Fru-2,6-P2) levels, glucose consumption and lactate production are increased in a dose-dependent manner in HT29 cells treated with PMA or insulin. The increase in Fru-2,6-P2 can be related to an increase in the Vmax. of PFK2, persisting after the enzyme has been precipitated with poly(ethylene glycol), without change in the Km for fructose 6-phosphate. The most striking effects of PMA and insulin on Fru-2,6-P2 production are observed after long-term treatment (24 h) and are abolished by actinomycin, cycloheximide and puromycin, suggesting that protein synthesis is involved. Furthermore, the effects of insulin and PMA on glucose consumption, lactate production, Fru-2,6-P2 levels and PFK2 activity are additive, and the effect of insulin on Fru-2,6-P2 production is not altered by pre-treatment of the cells with the phorbol ester. This suggests that these effects are exerted by separate mechanisms.     

The glucose transporter GLUT1 and the tight junction protein occludin in nasal olfactory mucosa.

The nervous cells in the brain and the peripheral nerves are isolated from the external environment by the blood-brain, blood-cerebrospinal fluid and blood-nerve barriers. The glucose transporter GLUT1 mediates the specific transfer of glucose across these barriers. The olfactory system is unique in that its sensory cells, olfactory receptor neurons, are embedded in the nasal olfactory epithelium and send their axons directly to the olfactory bulb of the brain. Only the apical parts of the olfactory receptor neurons are exposed to the lumen, and these serve as sensors for smell. Immunohistochemical examination showed that the tight junction protein occludin was present in the junctions of the olfactory epithelium. Endothelial cells in the blood vessels in the lamina propria of the olfactory mucosa were also positive for occludin. These observations suggest that the olfactory system is guarded from both the external environment and the blood. GLUT1 was abundant in these occludin-positive endothelial cells, suggesting that GLUT1 may serve in nourishing the cells of the olfactory system. Taken together, GLUT1 and occludin may serve as part of the machinery for the specific transfer of glucose in the olfactory system while preventing the non-specific entry of substances.     

The effect of modifying the culture medium on cell polarity in a human colon carcinoma cell line

The human colonic cancer cell line HT29, when grown in DMEM, forms a morphologically unpolarized cell culture in which the cells are covered with irregular microvilli and devoid of belt zonula occludens type tight junctions. However, by modifying the culture medium and growing the cells in RPMI, a different morphology was obtained. A large number of intracellular luminae appeared and at late confluency 90–95% of cells exhibited an epical brush border after four subsequent passages. Junctional complexes and a well developed zonula occludens were revealed under the apical brush border. Immuno-electron microscopical localization of specific markers, sucrase isomaltase (SI), secretory components (SC) and β2 microglobulin (β2M) showed that SI was limited to the apical surface, whereas 2M and SC were located at the basolateral surfaces. These results indicate that modification of culture conditions affects the ability of HT29 cells to express epithelial cell polarity.     

Detection and characterization of the Ah receptor for 2,3,7,8-tetrachlorodibenzo-p-dioxin in the human colon adenocarcinoma cell line LS180.

The Ah (aromatic hydrocarbon) receptor mediates induction of aryl hydrocarbon hydroxylase (AHH; an enzyme activity associated with cytochrome P450IA1) by polycyclic aromatic hydrocarbon carcinogens such as 3-methylcholanthrene (MC) and benzo[a]pyrene (BP) and the halogenated toxin 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Until recently the AhR seemed to be present only at very low levels in human cells and tissue. With a modified assay (the presence of sodium molybdate and a reduction in the amount of charcoal used to adsorb "excess" ligand) we found that cytosol from LS180 cells contains a high concentration of AhR (400-500 fmol/mg cytosolic protein) when detected by [3H]TCDD or [3H]MC. Cytosolic receptor also was detected with [3H]BP but at a level that was 35% of that detected with [3H]TCDD or [3H]MC. These levels are similar to those found in mouse Hepa-1 hepatoma cells in which AhR has been extensively characterized. The apparent binding affinity (Kd) of the cytosolic receptor for [3H]TCDD and for [3H]MC was about 5 nM. As with Hepa-1, the human LS180 cytosolic AhR sedimented at about 9 S on sucrose gradients when detected with [3H]TCDD, [3H]BP or [3H]MC. The nuclear-associated ligand.receptor complex recovered from cells incubated in culture with [3H]TCDD sedimented at about 6.2 S. The 9.8 S cytosolic form corresponds to a multimeric protein of a relative molecular mass (Mr) of about 285,000 whereas the 6.2 S nuclear receptor corresponds to a multimeric protein of Mr 175,000. The smallest specific ligand-binding subunit (detected by sodium dodecyl sulfate-polyacrylamide electrophoresis under denaturing conditions of receptor photoaffinity labeled with [3H]TCDD) was about Mr 110,000. AHH activity was induced in cells exposed in culture to TCDD or benz[a]anthracene (BA). The EC50 was 4 x 10(-10) M for TCDD and 1.5 x 10(-5) M for BA. For both inducers the EC50 in LS180 cells was shifted about one log unit to the right as compared to the EC50 for AHH induction in mouse Hepa-1 cells. The lower sensitivity of the LS180 cells to induction of AHH activity by TCDD or BA is consistent with the lower affinity of TCDD and MC for binding to human AhR. The ligand-binding properties, physicochemical properties, and mode of action of the AhR in this human cell line are therefore very similar to those of the extensively characterized AhR in rodent cells and tissues.