VIP receptors and control of short circuit current in the human intestinal clonal cell line Cl.19A

The double stranded RNA analog poly-IC elicits both robust IFN-λ production and oncolytic activity in human gastrointestinal cancer cells

Purpose

Type III IFN (IFN-λ) is the dominant frontline response over type I IFN in human normal intestinal epithelial cells upon viral infection, this response being mimicked by the dsRNA analog poly-IC. Poly-IC also induces cell death in murine intestinal crypts ex vivo. Here we examined whether these innate defense functions of normal intestinal epithelial cells are recapitulated in gastrointestinal carcinoma cells so that they could be harnessed to exert both immunoadjuvant and oncolytic functions, an unknown issue yet.

Experimental design

Four human gastrointestinal carcinoma cell lines versus the Jurkat lymphoma cell line were used to assess the effects of intracellular poly-IC on i) IFN-λ secretion and cell proliferation and ii) role of NFκB signaling using the NFκB inhibitory peptide SN50 as a screening probe and a siRNA approach.

Results

Poly-IC induced in all cell lines except Jurkat both a robust IFN-λ secretion and a cytoreductive effect on adherent cells, restricted to proliferating cells and associated with cellular shedding and reduced clonogenicity of the shed cells. Collectively these findings demonstrate the oncolytic activity of poly-IC. Inhibiting NFκB in T84 cells using a siRNA approach decreased IFN-λ production without protecting the cells from the poly-IC oncolytic effects. In line with these findings IFN-λ, that upregulated the anti-viral protein MxA, was unable per se to alter T84 cell proliferation.

Conclusion

Our demonstration that poly-IC-induced concomitant recapitulation of two innate functions of normal intestine, i.e. IFN-λ production and cell death, by human gastrointestinal cancer cells opens new perspectives in gastrointestinal cancer treatment.

The Neuromodulation of the Intestinal Immune System and Its Relevance in Inflammatory Bowel Disease

One of the main tasks of the immune system is to discriminate and appropriately react to “danger” or “non-danger” signals. This is crucial in the gastrointestinal tract, where the immune system is confronted with a myriad of food antigens and symbiotic microflora that are in constant contact with the mucosa, in addition to any potential pathogens. This large number of antigens and commensal microflora, which are essential for providing vital nutrients, must be tolerated by the intestinal immune system to prevent aberrant inflammation. Hence, the balance between immune activation versus tolerance should be tightly regulated to maintain intestinal homeostasis and to prevent immune activation indiscriminately against all luminal antigens. Loss of this delicate equilibrium can lead to chronic activation of the intestinal immune response resulting in intestinal disorders, such as inflammatory bowel diseases (IBD). In order to maintain homeostasis, the immune system has evolved diverse regulatory strategies including additional non-immunological actors able to control the immune response. Accumulating evidence strongly indicates a bidirectional link between the two systems in which the brain modulates the immune response via the detection of circulating cytokines and via direct afferent input from sensory fibers and from enteric neurons. In the current review, we will highlight the most recent findings regarding the cross-talk between the nervous system and the mucosal immune system and will discuss the potential use of these neuronal circuits and neuromediators as novel therapeutic tools to reestablish immune tolerance and treat intestinal chronic inflammation.

Pathogenesis of human enterovirulent bacteria: lessons from cultured, fully differentiated human colon cancer cell lines

Hosts are protected from attack by potentially harmful enteric microorganisms, viruses, and parasites by the polarized fully differentiated epithelial cells that make up the epithelium, providing a physical and functional barrier. Enterovirulent bacteria interact with the epithelial polarized cells lining the intestinal barrier, and some invade the cells. A better understanding of the cross talk between enterovirulent bacteria and the polarized intestinal cells has resulted in the identification of essential enterovirulent bacterial structures and virulence gene products playing pivotal roles in pathogenesis. Cultured animal cell lines and cultured human nonintestinal, undifferentiated epithelial cells have been extensively used for understanding the mechanisms by which some human enterovirulent bacteria induce intestinal disorders. Human colon carcinoma cell lines which are able to express in culture the functional and structural characteristics of mature enterocytes and goblet cells have been established, mimicking structurally and functionally an intestinal epithelial barrier. Moreover, Caco-2-derived M-like cells have been established, mimicking the bacterial capture property of M cells of Peyer's patches. This review intends to analyze the cellular and molecular mechanisms of pathogenesis of human enterovirulent bacteria observed in infected cultured human colon carcinoma enterocyte-like HT-29 subpopulations, enterocyte-like Caco-2 and clone cells, the colonic T84 cell line, HT-29 mucus-secreting cell subpopulations, and Caco-2-derived M-like cells, including cell association, cell entry, intracellular lifestyle, structural lesions at the brush border, functional lesions in enterocytes and goblet cells, functional and structural lesions at the junctional domain, and host cellular defense responses.

MicroRNAs determine human intestinal epithelial cell fate

MicroRNAs (miRNAs) are small, non-coding RNA molecules that post-transcriptionally regulate gene expression. Evidence has shown that miRNAs play important roles in various cellular processes, including proliferation, differentiation and survival. The intestinal epithelium is regenerated throughout life, and enterocytes undergo differentiation during migration along the crypt/villus axis. Our study aimed at establishing the expression profiles of miRNAs during intestinal epithelial cell (IEC) differentiation and determining a miRNA "signature" that distinguishes between small and large IECs. MiRNA arrays were employed to profile miRNA expression in two IEC models: the enterocyte-like Caco2-BBE and the colonocyte-like HT29-Cl.19A cell lines. Microarray data showed that in both cell lineages, the differentiated stage exhibited a different miRNA expression profile from undifferentiated stage. Interestingly, Caco2-BBE cells were distinguished from HT29-Cl.19A cells by their unique miRNA expression profile. Notably, HT29-Cl.19A cells exhibited down-regulation of miR-1269 and up-regulation of miR-99b and miR-125a-5p compared with Caco2-BBE cells. Most importantly, transfection of Caco2-BBE cells with mature miR-99b, mature miR-125a-5p and antisense of mature miR-1269 decreased growth rate and trans-epithelial resistance of the cells, indicating their shift toward HT29-Cl.19A cell phenotype. In conclusion, our study shows that miRNAs might play a role in determining the unique physiological characteristics of IECs.

Gastrointestinal dysfunction in mice with a targeted mutation in the gene encoding vasoactive intestinal polypeptide: a model for the study of intestinal ileus and Hirschsprung's disease

In 1970, Drs. Said and Mutt isolated a novel peptide from porcine intestinal extracts with powerful vasoactive properties, and named it vasoactive intestinal peptide (VIP). Since then, the biological actions of VIP in the gut as well as its signal transduction pathways have been extensively studied. A variety of in vitro and in vivo studies have indicated that VIP, expressed in intrinsic non-adrenergic non-cholinergic (NANC) neurons, is a potent regulator of gastrointestinal (GI) motility, water absorption and ion flux, mucus secretion and immune homeostasis. These VIP actions are believed to be mediated mainly by interactions with highly expressed VPAC(1) receptors and the production of nitric oxide (NO). Furthermore, VIP has been implicated in numerous physiopathological conditions affecting the human gut, including pancreatic endocrine tumors secreting VIP (VIPomas), insulin-dependent diabetes, Hirschsprung's disease, and inflammatory bowel syndromes such as Crohn's disease and ulcerative colitis. To further understand the physiological roles of VIP on the GI tract, we have begun to analyze the anatomical and physiological phenotype of C57BL/6 mice lacking the VIP gene. Herein, we demonstrate that the overall intestinal morphology and light microscopic structure is significantly altered in VIP(-/-) mice. Macroscopically there is an overall increase in weight, and decrease in length of the bowel compared to wild type (WT) controls. Microscopically, the phenotype was characterized by thickening of smooth muscle layers, increased villi length, and higher abundance of goblet cells. Alcian blue staining indicated that the latter cells were deficient in mucus secretion in VIP(-/-) mice. The differences became more pronounced from the duodenum to the distal jejunum or ileum of the small bowel but, became much less apparent or absent in the colon with the exception of mucus secretion defects. Further examination of the small intestine revealed larger axonal trunks and unusual unstained patches in myenteric plexus. Physiologically, the VIP(-/-) mice showed an impairment in intestinal transit. Moreover, unlike WT C57BL/6 mice, a significant percentage of VIP(-/-) mice died in the first postnatal year with overt stenosis of the gut.

Relation between chloride secretion and intracellular cyclic adenosine monophosphate in a cloned human intestinal cell line HT-29 cl 19A

The relation between the intracellular cyclic adenosine monophosphate (cAMP) content and the electrogenic chloride secretion induced by cholera toxin was studied in secretory HT-29 cl 19A cell monolayers. Cells were treated by the mucosal addition of cholera toxin (5 micrograms/ml) for 10, 45, or 90 minutes in Ussing chambers. After 10 minutes, the mean (SEM) intracellular cAMP content (3.2 (0.2) pmol/mg protein) and short circuit current (Isc) (1.9 (0.3) microA.cm-2) did not differ significantly from the corresponding basal values. At 45 minutes, a significant increase in the Isc (22.2 (5.7) microA.cm-2) was accompanied by a significant elevation in cAMP (10(1.7) pmol/mgh protein). At 90 minutes, when the stimulated Isc plateaued (35.2 (5.2) microA.cm-2), the cAMP value (99.2 (23.8) pmol/mg protein) increased further. The protein kinase C (PKC) activity of the cells was not affected by cholera toxin. Treatment of cell monolayers by different concentrations of DbcAMP (10(5), 5 x 10(-5), 10(-3) M) showed that the minimal concentration of DbcAMP (serosal) which significantly increased the Isc (delta 4.5 microA.cm-2) was 10(-4) M, and that this was accompanied by an increase in cAMP of delta 6.7 pmol/mg protein: Compared with DbcAMP, cholera toxin stimulated the Isc (at 45 minutes) to a much higher degree with a comparable elevation of cAMP. It is concluded that in cl 19A cells there is a threshold value of increase in intracellular cAMP that induces chloride secretion. Cholera toxin stimulated chloride secretion can be explained predominantly by an increase in intracellular cAMP that is unrelated to PKC activity.

ATP-stimulated electrolyte and mucin secretion in the human intestinal goblet cell line HT29-Cl.16E

The response of confluent monolayers of HT29-Cl.16E cells to stimulation by extracellular ATP and ATP analogues was investigated in terms of mucin and electrolyte secretion. Mucin secretion was measured as release of glucosamine-labeled macromolecules trapped at the stacking/running gel interface of polyacrylamide gels and electrolyte secretion as short-circuit current (Isc). Luminal ATP stimulated a transient increase in the release of mucins and of Isc corresponding to a secretory Cl- current. Both secretions peaked at 3 to 5 min after addition of ATP. Maximal ATP-stimulated mucin secretion over 15 min was up to 18-fold above control with an apparent ED50 of approximately 40 microM. Maximal peak Isc after stimulation with ATP was approximately 35 microA/cm2 with an apparent ED50 of about 0.4 mM. ATP-dependent Isc was at least in part due to Cl- secretion since removal of Cl- from the medium reduced the peak Isc by 40% and the Isc integrated over 40 min by 80%. The secretory responses were not associated with cell damage as assessed by failure of ethidium bromide to enter into the cells, absence of release of lactate dehydrogenase, maintenance of monolayer conductance, viability, and responses to repeated applications of ATP. The order of efficacy of nucleotide agonists was similar for both processes with ATP > ADP > AMP > or = adenosine. Luminal ATP was much more effective than basolateral addition of this compound. These results suggest involvement of a luminal P2-type receptor which can initiate signaling pathways for granule fusion and mucin release as well as for activation of Cl- channels. P2-receptor-stimulated mucin and Isc release was strongly inhibited by a 30 min preincubation with the classical K+ channel blockers quinine (1 mM), quinidine (1 mM), and Ba2+ (3 mM). Experiments with amphotericin B to measure separately the conductance changes of either luminal or basolateral plasma membrane revealed that quinidine did not directly block the ATP-induced basolateral K+ or the luminal anion channels. The quinidine inhibition after preincubation is therefore most easily explained by interference with granule fusion and location of anion channels in granule membranes. Luminal P2 receptors may play a role in intestinal defense mechanisms with both fluid and mucin secretion aiding in the removal of noxious agents from the mucosal surface.

Receptors for gut regulatory peptides

Receptors for regulatory peptides (hormones or neurotransmitters) play a pivotal role in the ability of cells to taste the rich neuroendocrine environment of the gut. Recognition of low concentration of peptides with a high specificity and translation of the peptide-receptor interaction into a biological response through different signalling pathways (adenylyl cyclase-cAMP or phospholipase C-phosphatidylinositol) are crucial properties of receptors. While many new receptors have been identified and thereafter characterized functionally during the 1980s, molecular biology now emerges as the privileged way for the structural characterization and discovery of receptors. Different strategies of receptor cloning have been developed which may or may not require prior receptor purification. Among cloning strategies that do not require receptor purification, homology screening of cDNA libraries, expression of receptor cDNA or mRNA in Xenopus laevis oocytes or in COS cells, and the polymerase chain reaction method achieved great success, e.g. cloning of receptors for cholecystokinin, gastrin, glucagon-like peptide 1, gastrin-releasing peptide/bombesin, neuromedin K, neuropeptide Y, neurotensin, opioids, secretin, somatostatin, substance K, substance P and vasoactive intestinal peptide. All these receptors belong to the superfamily of G-protein-coupled receptors which consist of a single polypeptide chain (350-450 amino acids) with seven transmembrane segments, an N-terminal extracellular domain and a C-terminal cytoplasmic domain. In this chapter, we have detailed the properties of three receptors which play an important role in digestive tract physiology and illustrate various signal transduction pathways: pancreatic beta-cell galanin receptors which mediate inhibition of insulin release and intestinal epithelial receptors for vasoactive intestinal peptide and peptide YY, which mediate the stimulation and inhibition of water and electrolyte secretion, respectively.

Increased growth adaptability to 5-fluorouracil and methotrexate of HT-29 sub-populations selected for their commitment to differentiation

Adaptation of the heterogeneous human colon carcinoma cell line HT-29 to lethal concentrations of methotrexate (MTX) and 5-fluorouracil (FUra) was shown to result in the emergence of sub-populations of cells all stably committed to differentiation. It was postulated that these populations result from selection of a few cells present in the parental line which possess, associated with their ability to differentiate, particular advantages allowing them to adapt to adverse conditions such as MTX or FUra. The purpose of the present study was to further verify this hypothesis by investigating whether HT-29 sub-populations selected for the commitment of all cells to differentiation would spontaneously be more resistant and adaptable than the parental cells to MTX and FUra. This study included a mucus-secreting clone (HT29-16E), a transporting clone (HT29-19A), and an enterocytic population selected by glucose deprivation (HT29-Glc-/+). Although all 3 populations show only a slight increase in their spontaneous resistance to both drugs, as substantiated by the values of IC50 which are only less than 2-fold higher than in parental cells, they are more adaptable as judged by growth curves, over a 50-day culture period, under exposure to 1 microM FUra and 0.1 microM MTX. In sharp contrast to parental cells, which, at these concentrations, show a high rate of mortality, all 3 populations, although growing slowly, reach densities more or less close, depending on the drug and population concerned, to that of control untreated cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of functional receptors for vasoactive intestinal peptide (VIP) in rat peritoneal macrophages

Functional vasoactive intestinal peptide (VIP) receptors have been characterized in rat peritoneal macrophages. The binding depended on time, temperature and pH, and was reversible, saturable and specific. Scatchard analysis of binding data suggested the presence of two classes of binding sites: a class with high affinity (kd = 1.1 +/- 0.1 nM) and low capacity (11.1 +/- 1.5 fmol/10(6) cells), and a class with low affinity (kd = 71.6 +/- 10.2 nM) and high capacity (419.0 +/- 80.0 fmol/10(6) cells). Structural requirements of these receptors were studied with peptides structurally or not structurally related to VIP. Several peptides inhibited 125I-VIP binding to rat peritoneal macrophages with the following order of potency: VIP greater than rGRF greater than hGRF greater than PHI greater than secretin. Glucagon, insulin, somatostatin, pancreastatin and octapeptide of cholecystokinin (CCK 26-33) were ineffective. VIP induced an increase of cyclic AMP production. Half-maximal stimulation (ED50) was observed at 1.2 +/- 0.5 nM VIP, and maximal stimulation (3-fold above basal levels) was obtained between 0.1-1 microM. Properties of these binding sites strongly support the concept that VIP could behave as regulatory peptide on the macrophage function.