Potentiation of trichothecene-induced leukocyte cytotoxicity and apoptosis by TNF-alpha and Fas activation

Dual Function of a Novel Bacterium, Slackia sp. D-G6: Detoxifying Deoxynivalenol and Producing the Natural Estrogen Analogue, Equol

Deoxynivalenol (DON) is a highly abundant mycotoxin that exerts many adverse effects on humans and animals. Much effort has been made to control DON in the past, and bio-transformation has emerged as the most promising method. However, useful and effective application of bacterial bio-transformation for the purpose of inhibiting DON remains urgently needed. The current study isolated a novel DON detoxifying bacterium, Slackia sp. D-G6 (D-G6), from chicken intestines. D-G6 is a Gram-positive, non-sporulating bacterium, which ranges in size from 0.2–0.4 μm × 0.6–1.0 μm. D-G6 de-epoxidizes DON into a non-toxic form called DOM-1. Optimum conditions required for degradation of DON are 37–47 °C and a pH of 6–10 in WCA medium containing 50% chicken intestinal extract. Besides DON detoxification, D-G6 also produces equol (EQL) from daidzein (DZN), which shows high estrogenic activity, and prevents estrogen-dependent and age-related diseases effectively. Furthermore, the genome of D-G6 was sequenced and characterized. Thirteen genes that show potential for DON de-epoxidation were identified via comparative genomics. In conclusion, a novel bacterium that exhibits the dual function of detoxifying DON and producing the beneficial natural estrogen analogue, EQL, was identified.

Trichothecenes: immunomodulatory effects, mechanisms, and anti-cancer potential

Paradoxically, trichothecenes have both immunosuppressive and immunostimulatory effects. The underlying mechanisms have not been fully explored. Early studies show that dose, exposure timing, and the time at which immune function is assessed influence whether trichothecenes act in an immunosuppressive or immunostimulatory fashion. Recent studies suggest that the immunomodulatory function of trichothecenes is also actively shaped by competing cell-survival and death-signaling pathways. Autophagy may also promote trichothecene immunosuppression, although the mechanism may be complicated. Moreover, trichothecenes may generate an "immune evasion" milieu that allows pathogens to escape host and vaccine immune defenses. Some trichothecenes, especially macrocyclic trichothecenes, also potently kill cancer cells. T-2 toxin conjugated with anti-cancer monoclonal antibodies significantly suppresses the growth of thymoma EL-4 cells and colon cancer cells. The type B trichothecene diacetoxyscirpenol specifically inhibits the tumor-promoting factor HIF-1 in cancer cells under hypoxic conditions. Trichothecin markedly inhibits the growth of multiple cancer cells with constitutively activated NF-κB. The type D macrocyclic toxin Verrucarin A is also a promising therapeutic candidate for leukemia, breast cancer, prostate cancer, and pancreatic cancer. The anti-cancer activities of trichothecenes have not been comprehensively summarized. Here, we first summarize the data on the immunomodulatory effects of trichothecenes and discuss recent studies that shed light on the underlying cellular and molecular mechanisms. These mechanisms include autophagy and major signaling pathways and their crosstalk. Second, the anti-cancer potential of trichothecenes and the underlying mechanisms will be discussed. We hope that this review will show how trichothecene bioactivities can be exploited to generate therapies against pathogens and cancer.

Protective effects of antioxidants on deoxynivalenol-induced damage in murine lymphoma cells

As contradictory results have been reported on the immunotoxic properties of deoxynivalenol (DON) in animal studies, we introduced a lymphoblast cell culture model in order to examine the effects of DON on lymphoblastic cell growth and metabolism as well as the preventive properties of free radical scavenger molecules against the DON-induced cell damage. Murine YAC-1 lymphoma cells were used because lymphoblasts have been shown to be sensitive to DON-induced immunotoxicity. Cells were quantified and their proliferative activity was measured by a proliferation test. Lipid peroxidation and protein oxidation were determined using assays quantifying thiobarbituric acid reactive substances (TBARS) and carbonylated proteins. Severely reduced cell counts were detected in DON-treated samples, confirmed by a 5-10 times lower proliferative activity. Significant increases in lipid peroxidation and protein oxidation were found in parallel incubated samples. The pre-incubation with free radical scavengers significantly reduced DON-induced changes to proteins and lipids as well as the tarnished cell viability and cell proliferation. These results suggest that YAC-1 lymphoma cells are a suitable model to investigate and elucidate the basic molecular and cellular mechanisms for possible immunotoxic effects of DON. With regard to the impact of free radical scavengers, the applied in-vitro model might enable the investigation of potential prophylactic and therapeutic effects before or even without harmful animal experiments and cost- and time-intensive expenses.

Deoxynivalenol and its toxicity

Deoxynivalenol (DON) is one of several mycotoxins produced by certain Fusarium species that frequently infect corn, wheat, oats, barley, rice, and other grains in the field or during storage. The exposure risk to human is directly through foods of plant origin (cereal grains) or indirectly through foods of animal origin (kidney, liver, milk, eggs). It has been detected in buckwheat, popcorn, sorgum, triticale, and other food products including flour, bread, breakfast cereals, noodles, infant foods, pancakes, malt and beer. DON affects animal and human health causing acute temporary nausea, vomiting, diarrhea, abdominal pain, headache, dizziness, and fever. This review briefly summarizes toxicities of this mycotoxin as well as effects on reproduction and their antagonistic and synergic actions.

Baccharis megapotamica var. weirii poisoning in water buffalo (Bubalus bubalis)

An outbreak of an acute disease in buffalo ( Bubalus bubalis) caused by the ingestion of Baccharis megapotamica var. weirii occurred in the southern region of Brazil. Ten out of 50 buffalo died 24–48 hr after being introduced into a pasture containing abundant amounts of the plant. Factors influencing the ingestion of the plant and consequent toxicosis included hunger, stress caused by shipment, and unfamiliarity with the plant. Clinical signs included serous ocular discharge, incoordination, mild bloat, and muscle trembling. One buffalo was necropsied. Gross findings included dehydration, abundant liquid in the rumen, reddening of the mucosa of forestomachs, abomasum, and intestine, and edema of the wall of the rumen. The main histologic lesions were superficial to full thickness degeneration and necrosis of the stratified epithelium lining the forestomachs, necrosis of the intestinal mucosa, and widespread lymphoid necrosis. A calf ( Bos taurus) was fed a single dose of 5g/kg/body weight of B. megapotamica var. weirii harvested from the same site where the buffalo died. Twenty hours after the administration of the plant this calf died with clinical signs and lesions similar to those observed in the naturally poisoned buffalo.

Toxicological mechanisms and potential health effects of deoxynivalenol and nivalenol

Produced by the mould genus Fusarium, the type B trichothecenes include deoxynivalenol (DON), nivalenol (NIV) and their acetylated precursors. These mycotoxins often contaminate cereal staples, posing a potential threat to public health that is still incompletely understood. Understanding the mechanistic basis by which these toxins cause toxicity in experimental animal models will improve our ability to predict the specific thresholds for adverse human effects as well as the persistence and reversibility of these effects. Acute exposure to DON and NIV causes emesis in susceptible species such as pigs in a manner similar to that observed for certain bacterial enterotoxins. Chronic exposure to these mycotoxins at low doses causes growth retardation and immunotoxicity whereas much higher doses can interfere with reproduction and development. Pathophysiological events that precede these toxicities include altered neuroendocrine responses, upregulation of proinflammatory gene expression, interference with growth hormone signalling and disruption of gastrointestinal tract permeability. The underlying molecular mechanisms involve deregulation of protein synthesis, aberrant intracellular cell signalling, gene transactivation, mRNA stabilisation and programmed cell death. A fusion of basic and translational research is now needed to validate or refine existing risk assessments and regulatory standards for DON and NIV. From the perspective of human health translation, biomarkers have been identified that potentially make it possible to conduct epidemiological studies relating DON consumption to potential adverse human health effects. Of particular interest will be linkages to growth retardation, gastrointestinal illness and chronic autoimmune diseases. Ultimately, such knowledge can facilitate more precise science-based risk assessment and management strategies that protect consumers without reducing availability of critical food sources.

Deoxynivalenol: mechanisms of action, human exposure, and toxicological relevance

The trichothecene mycotoxin deoxynivalenol (DON) is produced in wheat, barley and corn following infestation by the fungus Fusarium in the field and during storage. Colloquially known as "vomitoxin" because of its emetic effects in pigs, DON has been associated with human gastroenteritis. Since DON is commonly detected in cereal foods, there are significant questions regarding the risks of acute poisoning and chronic effects posed to persons ingesting this trichothecene. A further challenge is how to best manage perceived risks without rendering critical food staples unavailable to an ever-expanding world population. In experimental animal models, acute DON poisoning causes emesis, whereas chronic low-dose exposure elicits anorexia, growth retardation, immunotoxicity as well as impaired reproduction and development resulting from maternal toxicity. Pathophysiologic effects associated with DON include altered neuroendocrine signaling, proinflammatory gene induction, disruption of the growth hormone axis, and altered gut integrity. At the cellular level, DON induces ribotoxic stress thereby disrupting macromolecule synthesis, cell signaling, differentiation, proliferation, and death. There is a need to better understand the mechanistic linkages between these early dose-dependent molecular effects and relevant pathological sequelae. Epidemiological studies are needed to determine if relationships exist between consumption of high DON levels and incidence of both gastroenteritis and potential chronic diseases. From the perspective of human health translation, a particularly exciting development is the availability of biomarkers of exposure (e.g. DON glucuronide) and effect (e.g. IGF1) now make it possible to study the relationship between DON consumption and growth retardation in susceptible human populations such as children and vegetarians. Ultimately, a fusion of basic and translational research is needed to validate or refine existing risk assessments and regulatory standards for this common mycotoxin.

Deoxynivalenol-induced proinflammatory gene expression: mechanisms and pathological sequelae

The trichothecene mycotoxin deoxynivalenol (DON) is commonly encountered in human cereal foods throughout the world as a result of infestation of grains in the field and in storage by the fungus Fusarium. Significant questions remain regarding the risks posed to humans from acute and chronic DON ingestion, and how to manage these risks without imperiling access to nutritionally important food commodities. Modulation of the innate immune system appears particularly critical to DON's toxic effects. Specifically, DON induces activation of mitogen-activated protein kinases (MAPKs) in macrophages and monocytes, which mediate robust induction of proinflammatory gene expression-effects that can be recapitulated in intact animals. The initiating mechanisms for DON-induced ribotoxic stress response appear to involve the (1) activation of constitutive protein kinases on the damaged ribosome and (2) autophagy of the chaperone GRP78 with consequent activation of the ER stress response. Pathological sequelae resulting from chronic low dose exposure include anorexia, impaired weight gain, growth hormone dysregulation and aberrant IgA production whereas acute high dose exposure evokes gastroenteritis, emesis and a shock-like syndrome. Taken together, the capacity of DON to evoke ribotoxic stress in mononuclear phagocytes contributes significantly to its acute and chronic toxic effects in vivo. It is anticipated that these investigations will enable the identification of robust biomarkers of effect that will be applicable to epidemiological studies of the human health effects of this common mycotoxin.

On the effects of the Fusarium toxin deoxynivalenol (DON) administered per os or intraperitoneal infusion to sows during days 63 to 70 of gestation

Six pregnant sows of 180.6 ± 5.6 kg were fed either a Fusarium-contaminated (4.42 mg DON and 48.3 µg ZON per kg, DON per os, n = 3) or a control diet (0.15 mg DON and 5 µg ZON/kg) in the period of days 63 and 70 of gestation. On day 63 of gestation, sows fed the control diet were implanted with an intraperitoneal osmotic minipump (delivery rate of 10 µL/h, for 7 days) containing 50 mg pure (98%) DON in 2 ml 50% DMSO (DON ip, n = 3). Frequent plasma samples were taken to estimate the kinetics after oral and ip DON exposure. The intended continuous delivery of DON by the intraperitoneal minipump could not be shown, as there was a plasma peak (Cmax) of 4.2-6.4 ng DON/mL either immediately (sow IP-2+3) or 2.5 h (sow IP-1) after implantation of the pump followed by a one-exponential decline with a mean half-time (t1/2) of 1.75-4.0 h and only negligible DON plasma concentrations after 12 h. Therefore, the DON ip exposure has to be regarded as one single dose 1 week before termination of experiment. The DON per os sows showed a mean basis level (after achieving a steady state) of DON plasma concentration of about 6-8 ng/mL, as also indicated by the plasma DON concentration at the termination of the experiment. On day 70, caesarean section was carried out, the fetuses were killed immediately after birth, and samples of plasma, urine, and bile were taken to analyze the concentration of DON and its metabolite de-epoxy-DON. At necropsy there were no macroscopic lesions observed in any organ of either sows or piglets. Histopathological evaluation of sows liver and spleen revealed no alterations. The proliferation rate of peripheral blood mononuclear cells (PBMC) with or without stimulation was not affected by the kind of DON treatment. The exposure of pregnant sows at mid-gestation (days 63-70, period of organogenesis) to a Fusarium toxin-contaminated diet (4.42 mg DON and 0.048 mg ZON per kg) or pure DON via intraperitoneal osmotic minipump did not cause adverse effects on health, fertility, maintenance of pregnancy, and performance of sows and their fetuses. However, DON was detected in fetus plasma, indicating that this toxin can pass the placental barrier and may cause changes in the proportion of white blood cells (lower monocyte and neutrophil and higher lymphocyte proportion in DON per os fetuses).

Baccharis Pteronioides Toxicity in Livestock and Hamsters

Baccharis pteronioides DC has been intermittently associated with livestock poisoning in the southwestern United States. In 2004, nearly 100 cows were reported poisoned by B. pteronioides in southern New Mexico. Initial field studies and postmortem examinations found drought conditions, evidence of B. pteronioides consumption, and a reported mortality of nearly 40%. Because postmortem materials were unsuitable for further examination, plant samples were collected for feeding trials and chemical evaluation. Forty-eight Syrian hamsters (8 weeks old) were randomly divided into 4 groups and dosed with 0, 50, 100, and 200 mg of B. pteronioides for 10 days. After dosing, the hamsters were necropsied; sera were analyzed biochemically; and tissues were collected and evaluated histologically. The hamsters treated with 200 mg and several of the 100-mg animals developed anorexia and diarrhea. These animals developed multiple hemorrhagic infarcts in the liver and kidney, with severe hemorrhagic enteritis. Histologically, the higher-dosed animals had severe necrotizing vasculitis with vascular thrombosis of hepatic and renal vessels. Many glomerular capillaries contained fibrin thrombi. The superficial intestinal and colonic mucosa was necrotic, with extensive hemorrhage and proliferation of luminal bacteria. Lower-dosed animals had mild hepatocellular swelling, with proliferation of intestinal and gastric bacteria and yeast. The findings indicate that at high doses, B. pteronioides is toxic to hamsters and produces lesions that are very similar to bacterial endotoxin–produced vasculitis and infarction. Research to purify and identify the toxin, the toxic dose, and mechanism of toxicity are ongoing.

Docosahexaenoic acid consumption inhibits deoxynivalenol-induced CREB/ATF1 activation and IL-6 gene transcription in mouse macrophages

The mycotoxin deoxynivalenol (DON) induces IgA nephropathy in mice by upregulating IL-6 expression, which is suppressed by (n-3) PUFA consumption. The purpose of this study was to test the hypothesis that consumption of the (n-3) PUFA docosahexaenoic acid (DHA) interferes with DON-induced transcriptional and post-transcriptional upregulation of IL-6 mRNA in murine macrophages. DON evoked expression of IL-6 mRNA and IL-6 heterogenous nuclear RNA (hnRNA), an indicator of ongoing IL-6 transcription, in macrophages elicited from mice fed control AIN-93G diet for 4 wk, whereas expression of both RNA species was suppressed in macrophages from mice fed AIN-93G modified to contain 30 g DHA/kg diet for the same time period. DON enhanced IL-6 mRNA stability similarly in macrophages from control and DHA-fed mice suggesting that (n-3) PUFA effects were not post-transcriptional. DON upregulated binding activity of cAMP response element binding protein (CREB) and activator protein (AP-1) to their respective consensus sequences in nuclear extracts from control-fed mice, whereas both activities were suppressed in nuclear extracts from DHA-fed mice. DON induced phosphorylation of CREB at Ser-133 and ATF1 at Ser-63 as well as intranuclear binding of phospho-CREB/ATF1 to the cis element of the IL-6 promoter in control macrophages, whereas both activities were inhibited in macrophages from DHA-fed mice. DHA consumption blocked DON-induced phosphorylation of the CREB kinase AKT. Inhibition of AKT suppressed both CREB/ATF1 phosphorylation and IL-6 transcription. These data suggest that DHA consumption suppresses DON-induced IL-6 transcription in macrophages in part by interfering with AKT-dependent phosphorylation and subsequent binding of CREB/ATF1 to the IL-6 promoter.

Effects of diets with cereal grains contaminated by graded levels of two Fusarium toxins on selected immunological and histological measurements in the spleen of gilts1,2

Feeding experiments with diets containing Fusarium toxin-contaminated wheat were conducted to clarify the pathogenesis of immunological effects of Fusarium toxins to porcine spleen cells. Contaminated diets were fed to 36 Landrace prepubertal gilts for 35 d. Concentrations (as-fed basis) of the indicator toxins deoxynivalenol (DON) and zearalenone (ZON), respectively, were 210 and 4 (control--group I), 3,070 and 88 (group II), 6,100 and 235 (group III), and 9,570 and 358 microg/kg (group IV). No signs of hyperestrogenism or uterotrophic effects were observed because of dietary treatments. The feeding of mycotoxin-contaminated diets did not cause gross pathological findings in the spleens of animals. In vivo, no inhibitory effects were detected on concanavalin A-stimulation of blood lymphocytes; however, the proliferation rate of splenocytes was inhibited (P < 0.05) in pigs fed the diet with the highest DON/ZON concentration. With in vitro studies, lower proliferation rates of blood lymphocytes and splenocytes preexposed to DON were detected. Serum IgA concentrations of pigs in group II were increased (P < 0.05) compared with the baseline value before feeding the DON/ZON diet. The histopathological data indicated elevated (P < 0.05) iron staining in the red pulp of spleens in gilts from groups I to IV after 35 d of feeding. The presence of hemosiderin particles in the spleen sections was confirmed by transmission electron microscopic investigation. Together, the results provide evidence of spleen dysfunction (hemosiderosis) in the absence of clinical signs, especially in pigs fed higher concentrations (groups III and IV) of Fusarium toxin-contaminated wheat.

Beneficial pleiotropic actions of melatonin in an experimental model of septic shock in mice: regulation of pro-/anti-inflammatory cytokine network, protection against oxidative damage and anti-apoptotic effects

Septic shock, the most severe problem of sepsis, is a lethal condition caused by the interaction of a pathogen-induced long chain of sequential intracellular events in immune cells, epithelium, endothelium, and the neuroendocrine system. The lethal effects of septic shock are associated with the production and release of numerous pro-inflammatory biochemical mediators including cytokines, nitric oxide and toxic oxygen and nitrogen radicals, together with development of massive apoptosis. As melatonin has remarkable properties as a cytokine modulator, antioxidant and anti-apoptotic agent, the present study was designed to evaluate the possible protective effect of melatonin against LPS-induced septic shock in Swiss mice. We observed that intraperitoneally (i.p.) administered-melatonin (10 mg/kg) 30 min prior, and 1 hr after i.p. LPS injection (0.75 mg/animal) markedly protected mice from the LPS lethal effects with 90% survival rates for melatonin and 20% for LPS-injected mice after 72 hr. The melatonin effect was mediated by modulating the release of pro-/anti-inflammatory cytokine levels, protection from oxidative damage and counteracting apoptotic cell death. Melatonin was able to partially counteract the increase in LPS-induced pro-inflammatory cytokine levels such as tumor necrosis factor-alpha, IL-12 and interferon-gamma at the local site of injection, while it increased the production of the anti-inflammatory cytokine IL-10 both locally and systemically. Furthermore, melatonin inhibited the LPS-induced nitrite/nitrate and lipid peroxidation levels in brain and liver and counteracted the sepsis-associated apoptotic process in spleen. In conclusion, we have demonstrated that melatonin improves the survival of mice with septic shock via its pleiotropic functions as an immunomodulator, antioxidant and anti-apoptotic mediator.

The proportions of Streptomyces californicus and Stachybotrys chartarum in simultaneous exposure affect inflammatory responses in mouse RAW264.7 macrophages

Adverse health outcomes associated with moisture-damaged buildings originate from an exposure consisting of complex interactions between various microbial species and other indoor pollutants. The concentrations and proportions of microbial components in such environments can vary greatly with the growth conditions. In this study, we aimed to evaluate the effects of simultaneous exposure with modified proportions of actinobacteria Streptomyces californicus and fungi Stachybotrys chartarum on inflammatory responses (cytokines macrophage inflammatory protein 2 [MIP2], interleukin 6 [IL-6] and tumor necrosis factor a [TNFa]; nitric oxide) and cytotoxicity (MTT-test and DNA content analysis) in mouse RAW264.7 macrophage cell line. Five different proportions of microbial spores were studied (Str. californicus: S. chartarum 10:1; 5:1; 1:1; 1:5; 1:10). RAW264.7 cells were coexposed to the total dose of 3x10(5) spores/ml for 24 h and also both of these microbial spores on their own at the respective doses. At least the 1.5-fold synergistic increase in cytokine production of RAW264.7 macrophages was detected when coexposure contained an equal amount or more fungal spores (S. chartarum) than bacterial spores (Str. californicus) compared to the sum response caused by these microbial spores separately. On the contrary, NO production after coexposure was nearly 40% less than the sum response induced by the microbial spores separately, when coexposure contains 5 times more bacterial than fungal spores. In addition, coexposure slightly changed the cytotoxic potency of the spores. The present results revealed that mutual proportions of fungal and bacterial spores in simultaneous exposure affect the nature of their interactions leading to increased or suppressed production of inflammatory mediators in RAW264.7 macrophages.

Comparison of in vitro cytotoxicity of Fusarium mycotoxins,deoxynivalenol, T-2 toxin and zearalenone on selected human epithelial cell lines

Three human epithelial cell lines (CaCo-2, HEp-2 and HeLa) implicated as potential targets for three Fusarium toxins were tested for the extent of survival on exposure to increasing toxin concentration and incubation periods. Cytotoxicity assay using 3(4,5-dimethylthiazol-2-yl)2,5-diphenyltetrazolium bromide (MTT) was carried out with deoxynivalenol (DON), T-2 toxins and zearalenone (ZON) on CaCo-2, HEp-2 and HeLa cell lines. Of the three cell lines used, HeLa was the most sensitive, eliciting cell death after 2 days exposure at 100 ng ml(-1)with T-2 toxin. HeLa was the only cell line to exhibit cytotoxicity towards ZON showing cell death at 1000 ng ml(-1)after 2 days which increased to 4 days, showing substantial cell death at 200 ng ml(-1). HEp-2 was sensitive to DON showing cell death after 2 days (100 ng ml(-1)) with complete cell death occurring at 200 ng ml(-1) after 4 days of exposure. Substantial cytoxicity of T-2 towards HEp-2 occurred after 2 days at 1000 ng ml(-1) and complete cell death occurred with 100 ng ml(-1) at day 4. The CaCo-2 cell line was generally resistant to the mycotoxins tested between 100 and 1000 ng ml(-1). This study shows that cytotoxicity of Fusarium toxins to epithelium cell lines is concentration- and time- dependant and results from ZON-HeLa interaction indicate possible cell type-mycotoxin specificity.

Ribotoxic Stress Response to the Trichothecene Deoxynivalenol in the Macrophage Involves the Src Family Kinase Hck

Trichothecene mycotoxins and other translational inhibitors activate mitogen-activated protein kinase (MAPKs) by a mechanism called the "ribotoxic stress response," which drives both cytokine gene expression and apoptosis in macrophages. The purpose of this study was to identify upstream kinases involved in the ribotoxic stress response using the trichothecene deoxynivalenol (DON) and the RAW 264.7 macrophage as models. DON (100 to 1000 ng/ml) dose-dependently induced phosphorylation of c-Jun N-terminal protein kinase (JNK), extracellular signal-regulated kinase (ERK), and p38 MAPKs. MAPK phosphorylation in response to DON exposure occurred as early as 5 min, was maximal from 15 to 30 min, and lasted up to 8 h. Preincubation with inhibitors of protein kinase C, protein kinase A, or phospholipase C had no effect on DON-induced MAPK phosphorylation. In contrast, the Src family tyrosine kinase inhibitors, PP1 (4-amino-5-[4-methylphenyl)]-7-[t-butyl]pyrazolo[3,4-d]-pyrimidine) and, PP2 (4-amino-5-[4-chlorophenyl]-7-[t-butyl]pyrazolo[3,4-d]-pyrimidine) concentration-dependently impaired phosphorylation of all three MAPK families. PP1 suppressed DON-induced phosphorylation of the MAPK substrates c-jun, ATF-2, and p90(Rsk). MAPK phosphorylation by two other translational inhibitors, anisomycin and emetine, were similarly Src-dependent. PP1 reduced DON-induced increases in nuclear levels and binding activities of several transcription factors (NF-kappaB, AP-1, and C/EBP), which corresponded to decreases in TNF-alpha production, caspase-3 activation, and apoptosis. Tyrosine phosphorylation of hematopoeitic cell kinase (Hck), a Src found in macrophages, was detectable within 1 to 5 min after DON addition, and this was suppressed by PP1. Knockdown of Hck expression with siRNAs confirmed involvement of this Src in DON-induced TNF-alpha production and caspase activation. Taken together, activation of Hck and possibly other Src family tyrosine kinases are likely to be critical signals that precede both MAPK activation and induction of resultant downstream sequelae by DON and other ribotoxic stressors.