Transforming growth factor-beta1 is responsible for maturation-dependent spontaneous apoptosis of cultured gastric pit cells

Effect of TGF-beta1 on long-term synaptic plasticity and distribution of AMPA receptors in the CA1 field of the hippocampus

Using the methods of electrophysiology and immunohistochemistry, the effect of the transforming factor beta-1(TGF-β1), an anti-inflammatory cytokine, on the long-term post-tetanic potentiation (LTP) in CA1 field hippocampal slices and the distribution of the GluR1 subunit of the AMPA receptor has been studied. It was shown that TGF-β1 at a concentration of 10 ng/ml did not significantly affect the initial stage of LTP and substantially changed the distribution of synaptic AMPA receptors in response to tetanic stimulation. Twenty five minutes after the tetanization, the main pool of AMPA receptors (90%) was due to the postsynaptic density (PSD). By contrast, LTP in the presence of TGF-β1 was accompanied by less pronounced changes in the distribution of AMPA receptors. Their localization in both pre- and postsynaptic regions remained nearly the same as that in the control. It may be suggested that the normal distribution of AMPA receptors in spinous synapses promotes the stabilization of potentiated synapses, thereby retaining LTP for longer terms.

Transforming growth factor β1 increases p27 levels via synthesis and degradation mechanisms in the hyperproliferative gastric epithelium in rats

Throughout postnatal development, the gastric epithelium expresses Transforming Growth Factor beta1 (TGFβ1), but it is also exposed to luminal peptides that are part of milk. During suckling period, fasting promotes the withdrawal of milk-born molecules while it stimulates gastric epithelial cell proliferation. Such response can be reversed by exogenous TGFβ1, as it directly affects cell cycle through the regulation of p27 levels. We used fasting condition to induce the hyperproliferation of gastric epithelial cells in 14-day-old Wistar rats, and evaluated the effects of TGFβ1 gavage on p27 expression, phosphorylation at threonine 187 (phospho-p27^Thr187) and degradation. p27 protein level was reduced during fasting when compared to suckling counterparts, while phospho-p27^Thr187/p27 ratio was increased. TGFβ1 gavage reversed this response, which was confirmed through immunostaining. By using a neutralizing antibody against TGFβ1, we found that it restored the p27 and phosphorylation levels detected during fasting, indicating the specific role of the growth factor. We noted that neither fasting nor TGFβ1 changed p27 expression, but after cycloheximide administration, we observed that protein synthesis was influenced by TGFβ1. Next, we evaluated the capacity of the gastric mucosa to degrade p27 and we recorded a higher concentration of the remaining protein in pups treated with TGFβ1, suggesting augmented stability under this condition. Thus, we showed for the first time that luminal TGFβ1 increased p27 levels in the rat gastric mucosa by up- regulating translation and reducing protein degradation. We concluded that such mechanisms might be used by rapidly proliferating cells to respond to milk-born TGFβ1 and food restriction.

EVER2 protein binds TRADD to promote TNF-α-induced apoptosis

EVER1 and 2 confer resistance to cutaneous oncogenic human papillomavirus infections by downregulating the activating protein 1 (AP-1) signaling pathway. Defects in their expression are associated with susceptibility to epidermodysplasia verruciformis, which is characterized by persistent β-HPV infection, tumor necrosis factor alpha (TNF-α) overproduction in keratinocytes and the development of skin cancers. TNF-α-induced apoptosis is a key defense strategy, preventing the persistence of the virus within cells, but the role of EVER proteins in this cell death mechanism triggered by extrinsic stimuli is unknown. We show here that EVER2 induces TNF-α- and TRAIL-dependant apoptosis. It interacts with the N-terminal domain of TRADD, impairs the recruitment of TRAF2 and RIPK1 and promotes apoptosis. The skin cancer-associated EVER2 I306 allele results in an impaired TRADD-EVER2 interaction, with lower levels of cell death following treatment with TNF-α. These data highlight a new, critical function of EVER2 in controlling cell survival in response to death stimuli.

Capn8 promoter directs the expression of Cre recombinase in gastric pit cells of transgenic mice

Gastric pit cells are high-turnover epithelial cells of the gastric mucosa. They secrete mucus to protect the gastric epithelium from acid and pepsin. To investigate the genetic mechanisms underlying the physiological functions of gastric pit cells, we generated a transgenic mouse line, namely, Capn8-Cre, in which the expression of Cre recombinase was controlled by the promoter of the intracellular Ca(2+)-regulated cysteine protease calpain-8. To test the tissue distribution and excision activity of Cre recombinase, the Capn8-Cre transgenic mice were bred with the ROSA26 reporter strain and a mouse strain that carries Smad4 conditional alleles (Smad4(Co/Co)). Multiple-tissue PCR and LacZ staining demonstrated that Capn8-Cre transgenic mouse expressed Cre recombinase in the gastric pit cells. Cre recombinase activity was also detected in the liver and skin tissues. These data suggest that the Capn8-Cre mouse line described here could be used to dissect gene function in gastric pit cells.

Opposite effects of fasting on TGF-beta3 and TbetaRI distribution in the gastric mucosa of suckling and early weanling rats

OBJECTIVE

Our aim was to evaluate the effects of a dietary regimen (suckling or early weaning) and feeding status (fed or fasted) on the distribution of transforming growth factor-beta3 (TGF-beta3) and TGF receptor-I (TbetaRI) in the gastric epithelium of pups.

METHODS

Wistar rats were used. At 15 d, half of the pups were separated from dams and fed with hydrated powered chow. On day 17, suckling and early weanling rats were subjected to fasting (17h). Four different conditions were established: suckling fed and fasted and early weanling fed and fasted. At 18 d stomachs were collected under anesthesia and were fixed in 4% formaldehyde for immunohistochemistry. The number of immunostained epithelial cells per microscopic field was determined for TGF-beta3 and TbetaRI in longitudinal sections from the gastric mucosa.

RESULTS

We found that during suckling, fasting reduced the number of immunolabeled cells per field of both molecules when compared with the fed group (P<0.05), whereas in early weaning, food restriction increased TGF-beta3 and TbetaRI distributions (P<0.05). We also observed that TGF-beta3 and TbetaRI were more concentrated in parietal cells in the upper gland in suckling pups, whereas after early weaning these were displaced to parietal and chief cells at the bottom of the gland.

CONCLUSION

Suckling and early weaning directly influence TGF-beta3 and TbetaRI distributions in the gastric epithelium in response to fasting, such that early weaning anticipates the effects observed in adult rats. Furthermore, the differential concentrations of TGF-beta3 and TbetaRI indicate that they might be important for cell proliferation events in growth control.

NSAIDs suppress the expression of claudin-2 to promote invasion activity of cancer cells

Non-steroidal anti-inflammatory drugs (NSAIDs) show chemopreventive effects; however, the precise molecular mechanism of these effects is still unclear. On the other hand, the expression of proteins that form tight junctions (TJs) (such as claudins) in clinically isolated tumors is frequently altered relative to normal tissue. We previously reported that NSAIDs upregulate the expression of claudin-4 and that this upregulation contributes to NSAID-dependent inhibition of both migration activity and anchorage-independent growth of cancer cells. In the current study, we have systematically examined the effects of various NSAIDs on the expression of various TJ proteins and have found that NSAIDs specifically and drastically inhibit the expression of claudin-2. Overexpression or suppression of claudin-2 expression caused stimulation or inhibition, respectively, of the invasion and migration activity of cancer cells. Furthermore, NSAIDs inhibited the invasion and migration activity of cancer cells and this inhibition was suppressed by overexpression of claudin-2. In contrast, neither cell growth nor apoptosis induced by lack of anchorage of cancer cells was affected by overexpression or suppression of expression of claudin-2. These results suggest that inhibition of claudin-2 expression by NSAIDs contributes to NSAID-dependent inhibition of invasion of cancer cells in vitro and that it may be involved in the chemopreventive effects of NSAIDs by inhibiting metastasis in vivo.

In vivo effects of TGFbeta1 on the growth of gastric epithelium in suckling rats

As the content of Transforming Growth Factor-beta (TGFbeta) wanes in the milk of lactating rat, an increase in TGFbeta is observed in the gastric epithelia concomitant with differentiation of the glands upon weaning. Whereas TGFbeta has been shown to inhibit the proliferation of gastrointestinal cells in vitro, its functional significance and mechanisms of action have not been studied in vivo. Therefore, we administered TGFbeta1 (1 ng/g body wt.) to 14-day-old rats in which the gastric epithelium was induced to proliferate by fasting, and determined the involvement of signaling through Smads and the impact on epithelial cell proliferation and apoptosis. After the gavage, we observed the progressive increase of active TGFbeta1 while TbetaRII-receptor remained constant in the gastric mucosa. By immunohistochemistry, we showed Smad2/3 increase at 60 min (p<0.05) and Smad2 phosphorylation/activation and translocation to the nucleus most prominently between 0 and 30 min after treatment (p<0.05). Importantly, TGFbeta1 inhibited cell proliferation (p<0.05), which was estimated by BrDU pulse-labeling 12 h after gavage. Lower proliferation was reflected by increased p27(kip1) at 2 h (p<0.05). Also, TGFbeta1 increased apoptosis as measured by M30 labeling at 60 and 180 min (p<0.001), and by morphological features at 12 h (p<0.05). In addition, we observed higher levels of activated caspase 3 (17 kDa) from 0 to 30 min. Altogether, these data indicate a direct effect of TGFbeta1 signaling through Smads on both inhibiting proliferation, through alteration of cycle proteins, and inducing apoptosis of gastric epithelial cells in vivo. Further, the studies suggest a potential role for both milk and tissue-expressed TGFbeta1 in gastric growth during postnatal development.

Assessing cumulative health risks from exposure to environmental mixtures - three fundamental questions

Differential exposure to mixtures of environmental agents, including biological, chemical, physical, and psychosocial stressors, can contribute to increased vulnerability of human populations and ecologic systems. Cumulative risk assessment is a tool for organizing and analyzing information to evaluate the probability and seriousness of harmful effects caused by either simultaneous and/or sequential exposure to multiple environmental stressors. In this article we focus on elucidating key challenges that must be addressed to determine whether and to what degree differential exposure to environmental mixtures contributes to increased vulnerability of exposed populations. In particular, the emphasis is on examining three fundamental and interrelated questions that must be addressed as part of the process to assess cumulative risk: a) Which mixtures are most important from a public health perspective? and b) What is the nature (i.e., duration, frequency, timing) and magnitude (i.e., exposure concentration and dose) of relevant cumulative exposures for the population of interest? c) What is the mechanism (e.g., toxicokinetic or toxicodynamic) and consequence (e.g., additive, less than additive, more than additive) of the mixture's interactive effects on exposed populations? The focus is primarily on human health effects from chemical mixtures, and the goal is to reinforce the need for improved assessment of cumulative exposure and better understanding of the biological mechanisms that determine toxicologic interactions among mixture constituents.

Induction of claudin-4 by nonsteroidal anti-inflammatory drugs and its contribution to their chemopreventive effect

Nonsteroidal anti-inflammatory drugs (NSAID) have shown chemopreventive effects in both preclinical and clinical studies; however, the precise molecular mechanism governing this response remains unclear. We used DNA microarray techniques to search for genes whose expression is induced by the NSAID indomethacin in human gastric carcinoma (AGS) cells. Among identified genes, we focused on those related to tight junction function (claudin-4, claudin-1, and occludin), particularly claudin-4. Induction of claudin-4 by indomethacin was confirmed at both mRNA and protein levels. NSAIDs, other than indomethacin (diclofenac and celecoxib), also induced claudin-4. All of the tested NSAIDs increased the intracellular Ca2+ concentration. Other drugs that increased the intracellular Ca2+ concentration (thapsigargin and ionomycin) also induced claudin-4. Furthermore, an intracellular Ca2+ chelator [1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid] inhibited the indomethacin-dependent induction of claudin-4. These results strongly suggest that induction of claudin-4 by indomethacin is mediated through an increase in the intracellular Ca2+ concentration. Overexpression of claudin-4 in AGS cells did not affect cell growth or the induction of apoptosis by indomethacin. On the other hand, addition of indomethacin or overexpression of claudin-4 inhibited cell migration. Colony formation in soft agar was also inhibited. Suppression of claudin-4 expression by small interfering RNA restored the migration activity of AGS cells in the presence of indomethacin. Based on these results, we consider that the induction of claudin-4 and other tight junction-related genes by NSAIDs may be involved in the chemopreventive effect of NSAIDs through the suppression of anchorage-independent growth and cell migration.

Retinoic acid stimulates the dynamics of mouse gastric epithelial progenitors

The gastric epithelial progenitors proliferate and undergo bipolar migration associated with their differentiation into pit, parietal, and zymogenic cell lineages. Retinoids have long been known to modulate proliferation and differentiation of various renewing epithelia, and the expression of their receptors has been demonstrated in the gastric mucosa. The aim of this study was to examine the effects of retinoic acid on progenitor cell proliferation and cell lineage formation in the mouse stomach. By using subcutaneously inserted osmotic pumps, mice were continuously infused with all-trans retinoic acid (5 mg/kg per day) for 3 days. To label S-phase cells and their progeny, bromodeoxyuridine was administered for different time intervals. Analysis of gastric mucosal tissues of retinoic acid-treated mice revealed a significant increase in the number of S-phase progenitor cells and an enhancement in the production of their progeny. The life span of pit cells was reduced, and their apoptosis became apparent at the luminal surface. Immunofluoresence probing of pit, parietal and enteroendocrine cell lineages in control and retinoic acid-treated mice showed no significant change in their labeling pattern. However, there was an increase in the labeled gland area of zymogenic cells. In conclusion, 3-day treatment of retinoic acid enhances the proliferation of gastric epithelial progenitors and the dynamics of their progeny.

Molecular mechanism of adaptive cytoprotection induced by ethanol in human gastric cells

Adaptive cytoprotection is the process by which the pretreatment of cells with low concentrations of a noxious agent prevents the damage caused by a subsequent exposure of those cells to higher concentrations of that same agent. In this study, a human gastric carcinoma cell line was used to examine the molecular mechanism of adaptive cytoprotection induced by ethanol. Pretreatment of cells with 1%-4% ethanol made cells resistant to a subsequent exposure to 8% ethanol. This adaptive cytoprotection was accompanied by an increase in prostaglandin E2 synthesis and was partially inhibited by inhibitors of cyclooxygenase-2, but not by an inhibitor of cyclooxygenase-1. Furthermore, the adaptive cytoprotection was not dependent on newly synthesized proteins and was inhibited by a protein tyrosine kinase inhibitor. Based on these results, it is proposed that the stimulation of cyclooxygenase-2-dependent prostaglandin E2 synthesis, which is regulated post-translationally by protein tyrosine phosphorylation, plays an important role in adaptive cytoprotection induced by ethanol in gastric cells.