Induction of glomerulopressin production by cyclic AMP

Isolated rat livers were perfused with gassed Krebs-Ringer-Bicarbonate and different doses of theophylline and dibutyryl cyclic AMP were added to the perfusing solution. The perfusates were ultrafiltrated through Diaflo UM-05 membranes. The glomerulopressin activity of the ultrafiltrates were assayed in the tonic tension contraction (TTC) of isolated stomach fundus from rats. As glomerulopressin is known to be a glucuronide, it was inactivated with beta-glucuronidase to confirm that the effect on the stomach fundus was due to the glomerulopressin and not to another substance. It was observed that doses of theophylline between 2 x 10(-3) M and 2 x 10(-5) M enhanced glomerulopressin production. However, there was no relationship between dose of theophylline and the response, and a dose of theophylline 2 x 10(-6) M has no activity. The perfusion with dibutyryl cyclic AMP at 5 x 10(-8) M increased the amount of glomerulopressin produced by the liver. This was a log-dose response of glomerulopressin production to dibutyryl cyclic AMP between 5 x 10(-8) M and 5 x 10(-4) M. Theophylline (2 x 10(-6) M) potentiated the activity of cyclic AMP (5 x 10(-8) M). These results support the view that cyclic AMP is intracellular mediator of the hepatic production of glomerulopressin.     

Induction of human defensins by intestinal Caco-2 cells after interactions with opportunistic Candida species

In this study we investigated the effects of Candida albicans, Candida krusei, Candida tropicalis and Candida parapsilosis on human beta-defensin 2 (HBD-2) production in Caco-2 intestinal cell line, and the production of alpha-defensins (human neutrophil peptides, HNP 1–3) in peripheral blood. Opportunistic pathogen yeasts can modulate the host immune function by inducing defensins, the natural antimicrobial peptides. Here we show that Candida spp. stimulated HBD-2 expression in and release from Caco-2 cells, with C. albicans inducing the highest levels of HBD-2. Similarly, HNP 1–3 secretion was significantly increased in whole blood after exposure to Candida yeast cells, with C. albicans producing the greatest effect. Our investigations underscore the important role of beta and alpha defensins produced by intestinal epithelial cells locally and neutrophils systemically in the antifungal defense against Candida.     

Dibutyryl cyclic AMP modulation of gap junctions in SW-13 human adrenal cortical tumor cells

Cultured human adrenal cortical adenocarcinoma cells (SW-13) form a confluent monolayer of epithelial-like cells when seeded into culture flasks. Following a 24-48 hr non-mitotic period, cells begin to divide and become confluent within a week after seeding at 5 X 10(4) cells/cm2. The SW-13 cells were exposed to dibutyryl cyclic AMP (DbcAMP), cyclic AMP (cAMP), sodium butyrate, and adrenocorticotropin (ACTH). The rate of SW-13 cell proliferation was measured with a DNA microfluorometric assay, as well as by procedures measuring the incorporation of 3H-thymidine. In addition, following administration of ACTH and DbcAMP, the fractional area of membrane covered by gap junctions was quantitated with freeze-fracture electron microscopic techniques. Dibutyryl cyclic AMP at a concentration of 1 X 10(-3) M decreased the growth rate of the cell population. There was a corresponding increase in the fractional area of gap junctions found on the cell membrane in 96-hr DbcAMP-treated cultures. ACTH (40 mU/ml) exposure failed to produce an increase in the fractional area of gap junctions or to alter the rate of cell proliferation. From these data it can be suggested that elevations in cAMP levels within the cell can be related to both the proliferation of gap junctions and the decrease in cell proliferation in the SW-13 tumor cell.     

Cyclic AMP and growth of Ehrlich ascites tumor cells. Lack of cyclic AMP elevation in nutritionally deprived cells and mechanism of retardation of growth by dibutryl cyclic AMP.

Cyclic AMP levels in Ehrlich ascites tumor cells changed little after deprivation of cells of essential nutrients, serum, glucose and amino acids, deprival of each of which leads to marked inhibition of growth and protein synthesis. Cyclic AMP levels also changed little after the addition of these nutrients to deprived cells. Thus cyclic AMP is not likely to be the intracellular mediator for growth regulation by these three nutrients. Elevation of cyclic AMP levels for short periods by exposure of cells to choleratoxin or theophylline produced only slight changes in parameters of protein synthesis (polyribosome pattern and rate of [3H]leucine incorporation). An exposure for 1 day to dibutyryl cyclic AMP did not inhibit cell growth. However, prolonged exposure to dibutyryl cyclic AMP inhibited the multiplication of Ehrlich ascites cells both in suspension and in stationary cultures. No morphological effects were evident in the former; in the latter, cells attached firmly to the substratum and formed elongated cytoplasmic processes. Inhibition of cell multiplication by dibutyryl cyclic AMP was related to cell density and to serum concentration. Cells in dibutyryl cyclic AMP-containing media plated at low cell densities multiplied as rapidly as control cells. The final densities cells reached were determined by the serum concentration; in dibutyryl cyclic AMP-containing media these densities were about one-half those of respective control cells. Limitation of cell multiplication by dibutyryl cyclic AMP was reversed by the addition of serum, by resuspending cells at lower densities, or by resuspending cells in media without dibutyryl cyclic AMP. These findings suggested that dibutyryl cyclic AMP may affect the utilization of serum factors by cells. Dibutyryl cyclic AMP did not inactivate serum factors and did not change the rate at which cells depleted the growth medium of serum factors. Dibutyryl cyclic AMP may limit cell multiplication by increasing the cellular requirement for serum factors.     

Esterification of xanthophylls by human intestinal Caco-2 cells

We recently found that peridinin, which is uniquely present in dinoflagellates, reduced cell viability by inducing apoptosis in human colon cancer cells. Peridinin is also found in edible clams and oysters because the major food sources of those shellfish are phytoplanktons such as dinoflagellates. Little is known, however, about the fate of dietary peridinin and its biological activities in mammals. The aim of the present study was to investigate the enzymatic esterification of xanthophylls, especially peridinin which is uniquely present in dinoflagellates, using differentiated cultures of Caco-2 human intestinal cells. We found that peridinin is converted to peridininol and its fatty acid esters in differentiated Caco-2 cells treated with 5 μmol/L peridinin solubilized with mixed micelles. The cell homogenate was also able to deacetylate peridinin and to esterify peridininol. Other xanthophylls, such as fucoxanthin, astaxanthin and zeaxanthin, were also esterified, but at relatively lower rates than peridinin. In this study, we found the enzymatic esterification of xanthophylls in mammalian intestinal cells for the first time. Our results suggest that the esterification of xanthophylls in intestinal cells is dependent on their polarity.     

Induction of cyclic AMP phosphodiesterase in Blastocladiella emersonii and its relation to cyclic AMP metabolism.

Extracts of vegetative cells of Blastocladiella emersonii contain 5% or less of the cyclic AMP phosphodiesterase activity in zoospore extracts. This difference in activity could be accounted for entirely by an increase in the differential rate of phosphodiesterase synthesis during sporulation, beginning after a lag period of about 60 min and extending for at least an additional 90 min into the 4-h sporulation process. To examine the relation between enzyme synthesis and cyclic nucleotide metabolicm, we determined the substrate specificity of phosphodiesterase synthesized during sporulation and partially purified from zoospores. Zoospore extracts contain two components, separable by gel filtration chromatography, with cyclic AMP phosphodiesterase activity. The larger component accounts for 20% of the total activity and the smaller component for 80%. Both components show essentially an absolute substrate specificity for cyclic AMP among several cyclic purine and cyclic pyrimidine nucleotides tested. Nevertheless, we found no change in the total cyclic AMP content of sporulating cells before, during, or after enzyme activity increased. We speculate that some other component of cyclic AMP metabolism or function limits the rate of cyclic AMP hydrolysis in sporulating cells.     

Induction of serine dehydratase activity by cyclic AMP is restricted to S phase in synchronized CHO cells

Synchronized CHO cells were exposed to dibutyryl cyclic AMP plus testosterone. Cell cycle parameters (generation time, mitotic index and DNA synthesis) were relatively unperturbed by the hormone. Of the two enzymes observed, lactic dehydrogenase was unaffected by treatment with the hormone in log phase or synchronized populations. However, serine dehydratase was induced in log phase and synchronized populations to over 200% of controls. In synchronized cells, induction of enzyme activity was found to be primarily restricted to the latter part of S phase (9–11 hours into the cell cycle).     

Fibronectin blocks p38 and jnk activation by cyclic strain in Caco-2 cells

Diverse repetitive forces deform the intestinal epithelium and basement membrane. Such repetitive deformation induces intestinal epithelial proliferation, differentiation, and intracellular signaling. Although at least some deformation-induced signals probably involve integrins, the matrix-dependence of these signals is poorly understood. We compared rapid strain activation of p38 and jnk in human Caco-2 intestinal epithelial cells cultured on collagen I, collagen IV, laminin, and tissue fibronectin. These signals were inhibited in cells on a fibronectin substrate, but activated by strain on collagens and laminin. Furthermore, adding 300 microg/ml plasma fibronectin (approximately the concentration found in plasma) to the culture medium inhibited strain activation of p38 and jnk in cells cultured on collagen. Since tissue and plasma fibronectin levels vary in acute or chronic inflammatory or infectious conditions, these results suggest that tissue or plasma fibronectin may modulate the intestinal epithelial response to repetitive deformation.     

Induction of apoptosis in Caco-2 and HT-29 human intestinal epithelial cells by enterohemolysin produced by classic enteropathogenic Escherichia coli

AIMS: Detect the cytotoxic effects of the Enterohemolysin from enteropathogenic Escherichia coli C3888 (O 26: H-) on Caco 2 and HT-29-human epithelial intestinal cells. METHODS AND RESULTS: The Caco 2 and HT-29 cells, which were treated with Enterohemolysin (EHly) within 10-15 min, became round, lost attachment to substrate, showed extensive surface blebbing, nucleus shrank, and the chromatin became more compact. After 10 min of exposure to the EHly, the cells showed lactate dehydrogenase (LDH) leakage and reduction of mitochondrial activity. The cells showed disorganization of the actin fibers at 15 min. The death of these human epithelial intestinal cells by apoptosis was confirmed by annexin V. CONCLUSIONS: Enterohemolysin induced apoptosis on human epithelial intestinal cells. SIGNIFICANCE AND IMPACT OF THE STUDY: The finding of EHly cytotoxic activity suggests the involvement of this hemolysin in the (Enteropathogenic Escherichia coli) EPEC infection mechanism and may facilitate the understanding of the diarrhea caused by EPEC.     

The elicitation of phytoalexins by Ca2+ and cyclic AMP in carrot cells

Addition of calcium ionophore A23187 or dibutyryl cyclic AMP (dBcAMP) to carrot (Daucus carota L.) cell culture induced the production of 6-methoxymellein, a phytoalexin of carrot, in a dose-dependent manner. Several reagents known to suppress the cytoplasmic calcium concentration appreciably inhibited elicitor-promoted phytoalexin production in carrot cells. The addition of elicitor to the carrot culture caused a rapid increase in the intracellular level of cyclic AMP. Treatments of the cells with theophylline or cholera toxin stimulated the biosynthesis of 6-methoxymellein even in the absence of elicitor. These observations suggested that Ca²⁺ and cyclic AMP participate as second messengers in the regulation of 6-methoxymellein production in cultured carrot cells. Addition of verapamil to carrot cell culture markedly inhibited 6-methoxymellein production when it was added within 30 min after elicitor-treatment of the cells, but no inhibitory effect was observed after 60 min. The results suggest that these messengers function in an early stage of the elicitation process. Carrot cells which were previously treated with verapamil accumulated only small amounts of 6-methoxymellein following the addition of dBcAMP. In contrast, cells incubated initially with dBcAMP accumulated the phytoalexin at levels comparable to the control when verapamil was added to the culture.     

Exogenous steroids alter steroidogenesis in cultured Y-1 adrenal tumor cells by actions preceding cyclic AMP

Using cultured Y-1 mouse adrenal tumor cells which produce 20 alpha-hydroxy-4-pregnen-3-one (20-DHP), it was found that 0.01 mM corticosterone and deoxycorticosterone increased basal and inhibited ACTH-induced 20-DHP production during consecutive 30 and 120 min incubations. Steroid effects were concentration-dependent and reversible. Six other steroids tested did not stimulate 20-DHP production and varied in ability to inhibit ACTH-stimulated steroidogenesis. Experiments demonstrated that 20-DHP production following treatment with cholera toxin, N,0'-dibutyryl cyclic AMP (dbcAMP), or pregnenolone was not inhibited by exogenous steroids. Corticosterone (0.01 mM) increased basal and inhibited ACTH-induced intracellular cyclic AMP (cAMP) production. Cytochalasin D, a microfilament perturbing agent, inhibited steroid-stimulated 20-DHP production, suggesting that ACTH and steroid stimulation mechanisms were similar. These findings taken together suggest that exogenous steroids can alter steroidogenesis by modifying plasma membrane adenylate cyclase activity.     

Bacterial adenylate cyclase increases cyclic AMP and hormone release in pituitary tumor cells

Calmodulin-activated, adenylate cyclase toxin, a virulence factor produced by the human respiratory pathogen Bordetella pertussis, elicits marked accumulation of cyclic AMP in cell lines from rat pituitary tumors. This effect is associated with and apparently responsible for an enhanced release of prolactin and/or growth hormone from GH3, GH4C1 and 235-1 cells. The utility of this novel toxin in probing cyclic AMP-mediated responses is supported by these observations and studies with pertussis and cholera toxins.