Activation of cyclic AMP-dependent protein kinases in human gut adenocarcinoma (HT 29) cells in culture

Transcriptomic profiling of intestinal epithelial cells in response to human, bovine and commercial bovine lactoferrins

Lactoferrin (Lf) is an iron-binding glycoprotein present in high concentration in human milk. It is a pleiotropic protein and involved in diverse bioactivities, such as stimulation of cell proliferation and immunomodulatory activities. Lf is partly resistant to proteolysis in the gastrointestinal tract. Thus, Lf may play important roles in intestinal development. Due to differences in amino acid sequences and isolation methods, Lfs from human and bovine milk as well as commercially available bovine Lf (CbLf) may differ functionally or exert their functions via various mechanisms. To provide a potential basis for further applications of CbLf, we compared effects of Lfs on intestinal transcriptomic profiling using an intestinal epithelial cell model, human intestinal epithelial crypt-like cells (HIEC). All Lfs significantly stimulated proliferation of HIEC and no significant differences were found among these three proteins. Microarray assays were used to investigate transcriptomic profiling of intestinal epithelial cells in response to Lfs. Selected genes were verified by RT-PCR with a high validation rate. Genes significantly regulated by hLf, bLf, and CbLf were 150, 395 and 453, respectively. Fifty-four genes were significantly regulated by both hLf and CbLf, whereas 129 genes were significantly modulated by bLf and CbLf. Although only a limited number of genes were regulated by all Lfs, the three Lfs positively influenced cellular development and immune functions based on pathway analysis using IPA (Ingenuity). Lfs stimulate cellular and intestinal development and immune functions via various signaling pathways, such as Wnt/β-catenin signaling, interferon signaling and IL-8 signaling.

Anti-proliferative action of endogenous dehydroepiandrosterone metabolites on human cancer cell lines

Dehydroepiandrosterone (DHEA) is a naturally occurring steroid synthesized in the adrenal cortex, gonads, brain, and gastrointestinal tract, and it is known to have chemopreventive and anti-proliferative actions on tumors. These effects are considered to be induced by the inhibition of glucose-6-phosphate dehydrogenase (G6PD) and/or HMG-CoA reductase (HMGR) activities. The present study was undertaken to investigate whether endogenous DHEA metabolites, i.e. DHEA-sulfate, 7-oxygenated DHEA derivatives, androsterone, epiandrosterone, and etiocholanolone, have anti-proliferative effects on cancer cells and to clarify which enzyme, G6PD or HMGR, is responsible for growth inhibition. Growth of Hep G2, Caco-2, and HT-29 cells, evaluated by 3-[4,5-dimethylthiazol]-2yl-2,5-diphenyl tetrazolium bromide (MTT) and bromodeoxyuridine incorporation assays, was time- and dose-dependently inhibited by addition of all DHEA-related steroids we tested. In particular, the growth inhibition due to etiocholanolone was considerably greater than that caused by DHEA in all cell lines. The suppression of growth of the incubated steroids was not correlated with the inhibition of G6PD (r=-0.031, n=9, NS) or HMGR (r=0.219, n=9, NS) activities. The addition of deoxyribonucleosides or mevalonolactone to the medium did not overcome the inhibition of growth induced by DHEA or etiocholanolone, while growth suppression by DHEA was partially prevented by the addition of ribonucleosides. These results demonstrate that endogenous DHEA metabolites also have an anti-proliferative action that is not induced by inhibiting G6PD or HMGR activity alone. These non-androgenic DHEA metabolites may serve as chemopreventive or anti-proliferative therapies.

Binding and internalization of VIP in rat intestinal epithelial cells

We have prepared villous cells from the jejunum of the rat small intestine and studied the effects of divalent cations and bacitracin on the binding and internalization of VIP. Villous epithelial cells (4 x 10(6) cells/ml) were suspended in a Hepes-NaCl buffer with 1.0% BSA, (pH 7.4) and the cells were incubated for varying periods of time with 125I-VIP at 24 degrees C. Specific binding of radiolabeled VIP was maximal within 10 min (10%) and slowly declined to 9.0 percent after 30 min. In the presence of 1.0 mg/ml bacitracin, however, maximal specific binding of VIP was only 2.7 percent (P less than or equal to 0.001). The addition of CA2+ or Mg2+ to the buffer significantly decreased binding of VIP in a concentration dependent manner. At 8.0, 4.0, 2.0 and 1.0 mM Ca2+, binding of 125I-VIP decreased by 70, 60, 40 and 25 percent, whereas in the presence of the same concentrations of Mg2+ binding was decreased to 50, 38, 25 and 10 percent (P less than or equal to 0.01). To determine if epithelial cells internalize VIP, we bound 125I-VIP to villous cells and then differentiated surface-bound and internalized radioactivity by treating with trypsin (150 micrograms/ml). Surface bound radioligand was the same at both 24 and 4 degrees C (5.3%), while internalized 125I-VIP was 4.0% at 24 degrees C compared to only 1.0% at 4 degrees C (P less than or equal to 0.001). At 24 and 4 degrees C, both Ca2+ (4.0 mM) and Mg2+ (8.0 mM) decreased surface bound radioligand by 60 percent (P less than or equal to 0.01) and lowered internalized radioactivity. These data demonstrate that (1) bacitracin decreases the binding of VIP to small intestinal epithelial cells, (2) both Ca2+ and Mg2+ affect the binding of VIP to its surface receptor and (3) VIP is internalized into epithelial cells.

Effect of VIP on the glycogen metabolism of human colon adenocarcinoma cells studied by 13C nuclear magnetic resonance spectroscopy

Metabolic pathways of glucose utilization have been investigated in a human colon adenocarcinoma cell line (HT29) using carbon-13 Nuclear Magnetic Resonance spectroscopy. HT29 cells were adapted to grow on a polystyrene beaded microcarrier and were perfused when attached to the beads in a specially designed NMR cell. Abnormalities in carbohydrate metabolism already observed in several cancer cells were studied in HT29 cells fed with (1-13C)-enriched glucose. The cells were first perfused with a glucose-free medium for 2 h in order to deplete the intracellular store of glycogen, and they were subsequently perfused with a medium containing enriched glucose at an initial concentration of 5.5 mM. Sequential 13C-NMR spectra, recorded at 100.5 MHz (5 min accumulation), show that HT29 cells were able to utilize glucose through the glycolytic pathway while storing glucose as glycogen (glucose was utilized at a rate of 3.9 mumol/mg protein/hr). The glycolytic activity determined by the amount of lactic acid produced was 4.6 microns/mg protein/hr, corresponding to the formation of 1.2 lactic acid per glucose molecule. Glycogen accumulation corresponded to 16 micrograms/mg of protein. Treatment of HT29 with 10 nM vasoactive intestinal peptide (VIP) induced a transient decrease in the level of labelled glycogen to 50% of the initial value. Control level was recovered 12 min after VIP loading.

A human melanoma-derived cell line (IGR39) with a very high number of vasoactive-intestinal-peptide (VIP) receptors. 2. Effect of VIP on cAMP production and on cell-surface VIP-binding sites

Vasoactive intestinal peptide (VIP) stimulated in a dose-dependent manner the accumulation of cAMP in human melanoma-derived cell line IGR39. The maximal effect (about 100 times the basal level) was observed with 10 nM VIP. Half-maximum cAMP production was obtained at 0.78 nM VIP. VIP-related peptides were also potent in stimulating the cAMP production in IGR39 cells. The order of potency was VIP much greater than peptide histidine-methioninamide greater than human growth-hormone-releasing factor(1-44) greater than secretin greater than glucagon. Using the same conditions, IGR37 cells, a metastasic counterpart of IGR39 cells, displayed a weak stimulation of cAMP production. After exposure of IGR39 cells to 10 nM VIP, the cAMP response to a new stimulation by VIP was strongly reduced. This desensitization of IGR39 cells to VIP was rapid (t1/2 less than 2 min) and homologous. Preincubation of IGR39 cells in the presence of native VIP induced disappearance of the VIP-binding sites at the cell surface. This phenomenon was dependent on time and VIP concentration. Maximum effect (loss of 80% of binding capacity) was obtained after exposure of the cells at 37 degrees C with a VIP concentration of 1 microM. The t1/2 of maximum disappearance was less than 2 min and the concentration of VIP giving half-maximum decrease in binding of mono[125I]iodinated VIP (125I-VIP) was 8 nM. This phenomenon was also reversible since 85% of the VIP-binding capacity could be restored in less than 1 h by incubating IGR39 cells in a VIP-free medium. The IGR39 cell line should be a useful model for further study of the structure and function of the human VIP receptor.

The vasoactive intestinal peptide (VIP) receptor: recent data and hypothesis

Vasoactive intestinal peptide (VIP) is a neuropeptide with a broad range of biological activities in various tissues. After interaction with its membrane receptor, VIP generally induces a very large increase in the intracellular cyclic AMP level. Receptors for VIP have been described in numerous tissues and cell lines. The first results on VIP receptor structure have been obtained by covalent cross-linking using bifunctional reagents. The molecular mass of the different components characterized in this way differs greatly according to the species and the tissue used. This heterogeneity may reflect either a difference in the length of the cross-linked polypeptide backbone or differently glycosylated forms of the same polypeptide. The VIP binding site of intact human adenocarcinoma cells (HT29 cells) is an Mr 64,000 glycoprotein with 20kDa of N-linked oligosaccharide side chains containing sialic acid. The structure of the VIP binding site from HT29 cell is compared, first to the structure of the VIP receptor from other tissues, particularly that from rat liver, and second to the structure of the hepatic glucagon binding site. Recently, solubilization of the VIP receptor in an active form has provided a new way of studying this receptor. The HT29 cell line is an appropriate model to study the dynamics of the VIP receptor. After binding to its receptor, VIP is rapidly internalized, probably by receptor-mediated endocytosis. This internalization leads to a decrease in the cell surface receptor number and simultaneously to a homologous desensitization of adenylate cyclase. VIP is then degraded in the lysosomes, while most of the receptors are recycled back to the cell surface. The presence of an intracellular pool of unoccupied VIP receptors has been demonstrated after inactivation of the cell surface receptors by chymotrypsin. The kinetics of the receptor reappearance at the cell surface, after inactivation by chymotrypsin or after receptor-mediated endocytosis, indicate 2 possible intracellular pathways for occupied and unoccupied VIP receptors.

Photoaffinity labelling of the vasoactive-intestinal-peptide-binding site on intact human colonic adenocarcinoma cell line HT29-D4. Synthesis and use of photosensitive vasoactive-intestinal-peptide derivatives

N-Hydroxysuccinimidyl 4-azidobenzoate, a u.v.-sensitive heterobifunctional reagent, was used to synthesize photoreactive derivatives of the vasoactive intestinal peptide (VIP). Products of the reaction were purified by reverse-phase h.p.l.c. Three 4-azidobenzoyl-VIP (4-AB-VIP) derivatives were able to compete with monoiodinated 125I-VIP with an apparent KD of 2.5, 6.3 and 12.5 nM compared with 0.6 nM for native VIP. H.p.l.c.-purified mono[125I]iodinated VIP was used to synthesize 4-AB-125I-VIP derivatives. They were used to photoaffinity-label the VIP-binding site of HT29-D4 cells, a clone derived from the human colonic adenocarcinoma cell line HT29. Only one polypeptide, of Mr 70,000 +/- 5000 (mean +/- S.D.) was specifically labelled. The Mr of the component thus characterized was slightly higher than that of the major species (Mr 67,000) labelled after cross-linking experiments using 125I-VIP, conventional homobifunctional reagents and HT29 cells. Nevertheless, the specificity and extent of glycosylation of these two components were identical. These new photosensitive VIP derivatives should be useful tools with which to investigate further VIP-receptor structure and metabolism.

Hormonal control of fructose 2,6-bisphosphate concentration in the HT29 human colon adenocarcinoma cell line. Alpha 2-adrenergic agonists counteract effect of vasoactive intestinal peptide

Vasoactive intestinal peptide (VIP) was found to cause a dose-dependent decrease in fructose 2,6-bisphosphatase concomitant with an increase in cyclic AMP in cultured HT29 cancer cells from human colon. The maximum effect was a 41% decrease obtained with 10 nM-VIP, and half-maximum effect was obtained with 0.75 nM-VIP. The effect of 2.5 nM-VIP was almost totally counteracted (i.e. fructose 2,6-bisphosphate concentration was restored) by either adrenaline (1 microM) or the alpha 2-adrenergic agonist UK-14304 (1 microM); the alpha 2-agonist clonidine (1 microM) was less efficient, since the VIP effect was decreased by 72% only. The adrenaline effect was totally antagonized by 1 microM-yohimbine. It is concluded that, in the HT29 cancer cells, the fructose 2,6-bisphosphate-producing system is sensitive to variations of cyclic AMP concentration and is under the dual control of VIP and alpha 2-adrenergic receptors.

Molecular identification and structural requirement of vasoactive intestinal peptide (VIP) receptors in the human colon adenocarcinoma cell line, HT-29

The human colon adenocarcinoma cell line HT-29 in culture exhibits a cyclic AMP production system highly sensitive to vasoactive intestinal peptide (VIP), making HT-29 cells a unique cultured cell system for studying the mechanism of VIP action [Laburthe, Rousset, Boissard, Chevalier, Zweibaum & Rosselin (1978) Proc. Natl. Acad. Sci. U.S.A. 75, 2772-2775]. The quantitative characteristics of VIP receptors in HT-29 cells and their structural requirement and molecular size were studied. 125I-labeled VIP bound in a time-dependent manner to HT-29 cell homogenates. At equilibrium (60 min incubation at 30 degrees C), unlabelled VIP in the 0.01-10 nM concentration range competed with 125I-VIP for binding to cell homogenates. Scatchard analysis of binding data gave a straight line, indicating that VIP bound to a single population of sites with a KD of 0.12 +/- 0.02 nM and a capacity of 120 +/- 9 fmol/mg of protein. The structural requirement of these receptors was studied with peptides structurally related to VIP, either natural or synthetic. Several peptides inhibited 125I-VIP binding to HT-29 cell homogenates with the following order of potency, which is typical of the human VIP receptor: VIP (IC50 = 0.1 nM) greater than VIP-(2-28)-peptide (IC50 = 13 nM) greater than human growth hormone releasing factor (IC50 = 56 nM) greater than peptide histidine isoleucine amide (IC50 = 80 nM) greater than secretin (IC50 greater than 10 000 nM). To characterize the molecular component(s) of the VIP receptor in HT-29 cells, 125I-VIP was covalently bound to cell homogenates by using the cross-linker dithiobis(succinimidyl propionate). Sodium dodecyl sulphate/polyacrylamide-gel autoradiographic studies of affinity-labelled cell homogenates revealed two major bands, corresponding to 125I-VIP-protein complexes of Mr 66 000 and 16 000. The labelling of the Mr-66 000 component was specific, since it was abolished by native VIP, whereas that of the Mr-16 000 component was not. Densitometric scanning of autoradiographs indicated that the labelling of the Mr-66 000 complex was inhibited by low VIP concentrations in the 0.1-10 nM range (IC50 = 0.6 nM), but was unaffected by 1 microM-glucagon or octapeptide of cholecystokinin. It was also decreased by VIP-(2-28)-peptide with a potency 1% that of VIP. Assuming that one molecule of 125I-VIP bound per molecule of protein, one protein of Mr 63 000 was identified as a component of the VIP receptor in HT-29 cells.

Activation of cyclic AMP-dependent protein kinase by VIP in blood mononuclear cells

Vasoactive intestinal peptide stimulated cyclic AMP-dependent protein kinase activity in human blood mononuclear cells. The simultaneous presence of a phosphodiesterase inhibitor was required to elicit maximal activation. The apparent Ka value of half the maximal stimulation was about 60 pmol. Secretin exhibited a 170-times lower potency. Other peptides such as glucagon or insulin had no effect even at 1 microM.

Activity of glycogen metabolizing enzymes in glucose deprived HT 29 adenocarcinoma cell-line

When deprived of glucose, the cultured HT 29 adenocarcinoma cells are able to mobilize their glycogen within 4 hours. Glycogen phosphorylase is strongly activated during the first hour of glucose starvation. Then, while the a/a + b ratio for phosphorylase is declining, glycogen synthase is partially converted into the a form; this conversion does occur although glycogen phosphorylase is far from being totally inactivated. After 4 hours, activity of both a and total forms of glycogen synthase decrease. Cell UDP-glucose and glucose-6-P levels are declining during the 24 hours period of glucose starvation. Cell ATP content decreases by only 50 percent over the same period of time.

Differential effects of histamine, vasoactive intestinal polypeptide, prostaglandin E2 and somatostatin on cyclic AMP-dependent protein kinase activation in gastric glands isolated from the guinea pig fundus and antrum

Histamine, vasoactive intestinal polypeptide (VIP), secretin and prostaglandin E2 (PGE2) stimulate cyclic AMP-dependent protein kinase activity in gastric glands isolated from the guinea pig fundus and antrum. The effects are observed in the absence of any cyclic AMP phosphodiesterase inhibitor and maximal stimulation of the protein kinases occurs within 0.5 min of incubation at 20 degrees C. As shown by dose-response studies, VIP is equally potent in the antrum as in the fundus (identical values of the activation constant are found in both types of gland, Ka = 2.5 . 10(-9) M); a similar situation occurs for PGE2 action (but with Ka = 2.0 . 10(-8) M), whereas the potency of histamine is higher in the fundus (ka = 8.0 . 10(-6)M) than in the antrum (Ka = 5.0 . 10(-5) M). Secretin also increases the protein kinase activity ratio but with a 1000 times lower potency than VIP. In fundic glands, histamine (10(-3) M) is the activator of by far the greatest efficacy (increasing protein kinase activity at 4 times of the basal value) as compared with the effect obtained with 10(-6) M PGE2 (2.7 times) and 10(-7) M VIP (1.4 times). In contrast, VIP has greater efficacy (2.3 times) than histamine (2.1 times) in antral glands, whereas PGE2 is equally active in the two parts of the gastric mucosa. In addition, somatostatin (10(-6) M) inhibits partially (30%) and specifically the protein kinase activation stimulated by histamine, whereas it has no effect on VIP- and PGE2-induced activation. The results are consistent with increased cyclic AMP levels in response to these effectors in this system. A physiological role of histamine on acid-secreting parietal cells, of VIP on nonparietal cells and of PGE2 on both cell types, mediated by the cyclic AMP/protein kinase system is proposed.

Parallel activation of cyclic AMP phosphodiesterase and cyclic AMP-dependent protein kinase in two human gut adenocarcinoma cells (HT 29 and HRT 18) in culture, by vasoactive intestinal peptide (VIP) and other effectors activating the cyclic AMP system

Vasoactive intestinal peptide (VIP), secretin, catecholamines and prostaglandin E1 (PGE1) in the presence of a cyclic nucleotide phosphodiesterase inhibitor stimulate the accumulation of cyclic AMP in two colorectal carcinoma cell lines (HT 29 and HRT 18) with subsequent activation of the cyclic AMP-dependent protein kinases. In HT 29 cells incubated without phosphodiesterase inhibitor, 10(-9) M VIP promotes a rapid and specific activation of the lower Km cyclic AMP phosphodiesterase (1.7-fold); at 25 degrees C the effect is maintained for more than 15 min, while at 37 degrees C the activity returns to basal value within 15 min. As shown by dose-response studies, VIP is by far the most effective inducer (Ka equals 4 x 10(-10) M) of the cyclic AMP phosphodiesterase activity; partial activation of the enzyme is obtained by 3 x 10(-7) M secretin, 10(-5) M isoproterenol and 10(-5) M PGE1; PGE2 and epinephrine are without effect. In HRT 18 cells VIP is less active (Ka equals 2 x 10(-9) M) whereas 10(-6) M PGE1, 10(-6) M PGE2 and 10(-5) M epinephrine are potent inducers of th phosphodiesterase activity. The positive cell response to dibutyryl-cyclic AMP further indicates that cyclic AMP is a mediator in the phosphodiesterase activation process. The incubation kinetics and dose response effects of the various agonists on the cyclic AMP-dependent protein kinase activity determined for both cell types in the same conditions show a striking similarity to those of phosphodiesterase. Thus coordinate regulation of both enzymes by cyclic AMP was observed in all incubation conditions.

Specific activation of cyclic AMP-dependent protein kinase(s) by H2-histamine agonists in isolated gastric mucosal cells from guinea-pig

Histamine stimulated cyclic AMP-dependent protein kinase activity in dispersed mucosal cells from guinea-pig gastric fundus (Ka = 5 microM). The H2-agonists dimaprit and impromidine produced similar effects, while the H1-agonist 2-(2-pyridyl) ethylamine had only a weak one. The H2-antagonist cimetidine competitively inhibited 0.1 mM histamine stimulation (Ki = 2 microM). In contrast, the H1-antagonist diphenhydramine had no effect up to 1 mM.