* Departments of Microbiology and Molecular Genetics and
Food Science and Human Nutrition, and
Institute for Environmental Toxicology, Michigan State University, East Lansing, Michigan, 48824-1224; and
Department of Pediatrics, Hong Kong University, Hong Kong, China
Received January 13, 2003; accepted May 5, 2003
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ABSTRACT |
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Key Words: trichothecene; mycotoxin; mitogen-activated protein kinase; apoptosis; macrophage.
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INTRODUCTION |
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The molecular target of trichothecenes in leukocytes and other actively proliferating eukaryotic cells is the 60s ribosomal subunit (Middlebrook and Leatherman, 1989a,b
; Witt and Pestka, 1990
). Translational inhibitors that bind to ribosomes rapidly activate mitogen-activated protein kinases (MAPKs) and apoptosis in a process that has been termed the "ribotoxic stress response" (Iordanov et al., 1997
). MAPKs impact many physiological processes, including cell growth, differentiation, and apoptosis (Cobb, 1999
), and are important transducers of the immune response (Dong et al., 2002
). The primary MAPK subfamilies include: (1) p44 and p42 MAPKs, also known as extracellular signal-regulated protein kinase 1 and 2 (ERK1 and 2), (2) p54 and p46 c-Jun N-terminal kinase 1 and 2 (JNK1/2), also referred to as stress-activated protein kinases (SAPK 1/2); and (3) p38 MAPK. Both our laboratory and others have demonstrated that DON and other trichothecenes activate JNK, ERK, and p38 in vitro (Moon et al., 2002; Shifrin and Anderson, 1999
; Yang et al., 2000a
) and in vivo (Zhou et al., 2003
), suggesting that the ribotoxic stress response might be a critical transduction step during trichothecene toxicity. A major unresolved question regarding the ribotoxic stress response relates to the molecular linkage between ribosome interaction and MAPK activation (Laskin et al., 2002
).
Double-stranded RNA-(dsRNA)-activated protein kinase (PKR) is a widely-expressed serine/theonine protein kinase that can be activated by dsRNA, interferon, and other agents (Williams et al., 2001). The earliest described role of PKR was translational inhibition via phosphorylation of eukaryotic initiation factor 2
-subunit (eIF2
), which is an evolutionarily conserved antiviral response. Besides eIF2
phosphorylation and auto-phosphorylation activities, PKR appears to have a wide serine-theonine kinase substrate specificity. This kinase might also act through proteinprotein interactions, which do not require catalytic activity. PKR reportedly functions as a signal integrator for ligand-activated, stress-activated protein kinase pathways leading to stimulation of JNK and p38 (Goh et al., 2000
; Takizawa et al., 2002
; Williams, 2001
). The kinase is also believed to play a key role in mediating apoptosis induced by dsRNA, LPS, and TNF-
(Der et al., 1997
; Gil and Esteben, 2000; Yeung and Lau, 1998
; Yeung et al, 1996
). PKR potentially modulates induction of cytokines including TNF-
(Meusel et al., 2002
), IL-6, and IL-12 (Goh et al., 2000
). Our laboratory has previously observed that DON downregulates expression of P58Ipk, which is the 58-
Da cellular inhibitor of PKR (Yang et al., 2000b
). Thus, the potential exists for PKR to mediate early events leading to immunotoxicity associated with leukocyte exposure to DON and other trichothecenes and, additionally, to be an early step in the ribotoxic stress response.
The purpose of this study was to test the hypothesis that PKR is a critical upstream mediator of MAPK activation and apoptosis during the ribotoxic stress response. The results suggest that PKR can mediate activation of JNK, ERK, and p38 by DON and two other translational inhibitors, anisomycin and emetine. Furthermore, PKR contributes to the subsequent induction of apoptosis by these chemical agents.
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MATERIALS AND METHODS |
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U-937 human monocyte-like cells were stably transformed with plasmids containing a parental control expression vector pRC-CMV (Invitrogen, Carlsbad, CA) or a vector constructed with anti-sense PKR and designated as U9K-C2 and U9K-A1, respectively, as described previously (Der and Lau, 1995). Cells were maintained in RPMI 1640 medium supplemented with 5% (v/v) FBS, and 400 µg/ml Geneticin (Gibco, Rockville, MD) in 6% CO2 at 37°C.
Cells were treated with DON, anisomycin, or emetine (Sigma) over specified time intervals in the absence or presence of various pharmacological inhibitors, and then were analyzed for MAPK phosphorylation, PKR activation, DNA fragmentation, and/or caspase activity.
Detection of MAPK phosphorylation.
Cells were washed with ice-cold phosphate buffer, lysed in boiling lysis buffer (1% [w/v] sodium dodecylsulfate (SDS), 1.0 mM sodium ortho-vanadate, and 10 mM Tris pH 7.4), and sonicated for 5 s. Lysate was centrifuged at 12, 000 x g for 15 min at 4EC. Protein was measured in the resultant supernatant by a Bio-Rad DC protein assay kit (Bio-Rad Laboratories Inc, Melville, NY). Extracts (40 µg) were mixed with protein sample loading buffer (Amersham, Arlington Heights, IL), and boiled for 5 min before resolving on an 8% (w/v) acrylamide gel and transfer to a Hybond-P polyvinylidene difluoride (PVDF) membrane (Amersham). After blocking with TRIS buffered (pH 7.5, 0.01 M) saline containing 0.1% (v/v) Tween 20 and 3% (w/v) bovine serum albumin (TBST-BSA), the membrane was incubated for 1 h with MAPK antibodies (rabbit IgG, Cell Signaling, Beverly, MA) at 1:1500 dilution in TBST-BSA, and then were washed three times with TBST. These antibodies reacted with both mouse and human MAPKs. The membrane was then incubated with horseradish peroxidase (HRP)-conjugated donkey anti-rabbit IgG (Amersham Pharmacia Biotech, Piscataway, NJ) at 1:3000 dilution in TBST-BSA for MAPK detection. After washing three times with TBST, bound HRP-conjugated antibody was detected with an Enhanced Chemiluminescence (ECL) kit (Amersham) according to manufacturers instructions. Membranes were then stripped and reprobed with specific antibodies that recognize both phosphorylated and unphosphorylated forms of each MAPK as described above.
Detection of PKR activity.
For detection of the PKR phosphorylation and the phosphorylation of its substrate eIF2, extracts were subjected to electrophoresis and transferred to PVDF membranes as described above. Some cell cultures for eIF2
studies were preincubated for 1 h with Phosphatase Inhibitor Cocktail (1 µl/ml medium; Sigma) or with Complete Mini protease inhibitor (1 tablet/10 ml medium, Roche) prior to the addition of DON. These were incubated with phospho-PKR(thr451)-specific rabbit polyclonal antibodies (Calbiochem, Lajolla, CA) or phospho-eIF2
(Ser51)-specific rabbit polyclonal antibodies (Cell Signaling), followed by incubation with secondary antibodies and ECL detection as described above. The total protein levels of PKR or eIF2
loaded were assessed, after stripping and incubating with the antibodies, recognizing both phosphorylated and unphosphorylated forms of the proteins (Santa Cruz, Santa Cruz, CA).
Measurement of protein synthesis.
Inhibition of protein synthesis was measured by 3H leucine incorporation using a modification of the method of Yang et al. (2000a). Briefly, 2 x 105 in 50 µl of medium were added to each well of a 96-well tissue culture plate and cultured for 1 h. Various concentrations of DON anisomycin (AN) or emetine (EM) in 50 µl of medium along with 1 µCi of L-[3,4,53H(N)] leucine (NEN Life Science Products, Inc., Boston, MA; 5.6 Tbq/mmol) were then added. Cells were cultured for 3 h and supernatant transferred to a matching set of wells. Cells were suspended in 100 µl of 53 mM EDTA containing 0.5% (w/v) trypsin (GIBCO), then 25 µl of 50% (w/v) trichloroacetic acid (TCA) were added, absorbed to a glass filter paper using a Titertek cell harvester (Skatron Instruments, Inc., Sterling, VA), and filters were washed twice with cold 5% TCA and with 95% ethanol. The cell supernatant was also precipitated with TCA and harvested onto filters containing the corresponding precipitated cell protein. Thus, both total cellular and extracellular proteins containing radioactivity were measured. Radioactivity was measured in 5 ml of scintillation cocktail (Research Products International Col, Mount Prospect, IL) using a liquid scintillation counter (Packard Instrument Co., Downers Grove, IL).
DNA fragmentation assay.
DNA was extracted and electrophoresed as described by Sellins and Cohen (1987). Briefly, cells (1 x 107) in phosphate-buffered saline (pH 7.4) were centrifuged for 5 min (500 x g) at 4°C, and the pellet was suspended in 0.1 ml hypotonic lysing buffer (10 mM Tris, 10 mM EDTA, 0.5% [v/v] Triton X-100, pH 8.0). Cells were incubated at 4°C for 10 min. The resultant lysate was centrifuged for 30 min (20,000 x g) at 4°C. Supernatant containing fragmented DNA was digested for 1 h at 37°C with Rnase A (0.4 µg/µl) and then incubated for 1 h at 37°C with proteinase K (0.4 µg/µl). DNA was precipitated in 50% isopropanol and 0.5 M NaCl overnight at -20°C. The precipitate was centrifuged at 20,000 x g for 30 min at 4°C. The resultant pellet was air dried, resuspended in 10 mM Tris, 1 mM EDTA, pH 8.0, then electrophoresed at 75 V for 2 h in 2% agarose gel (5 x 106 cells equivalent per lane) in 90 mM Tris-borate buffer (pH 8.0) containing 2 mM EDTA. After electrophoresis, the gel was stained with ethidium bromide (0.5 µg/ml), and the nucleic acids were visualized with UV transilluminator. A 100-bp DNA ladder (GIBCO) was used as a molecular size marker.
Caspase-3 assay.
Cells were suspended in 200 µl of CHAPS buffer (100 mM HEPES [pH 7.5] containing 10% (w/v) sucrose, 0.5% (w/v) CHAPS, 1mM EDTA, 10 mM DTT, and 100 µl protease inhibitor cocktail (1:100) (Sigma), placed on ice for 30 min, sonicated briefly, and then centrifuged 10,000 x g for 10 min. Following protein determination, lysates (50 µg in 100 µl CHAPS buffer) were incubated with an equal volume (100 µl) of fluorogenic substrate consisting of 25 µM DEVD-AMC (Calbiochem, San Diego, CA) dissolved in CHAPS buffer at 37°C for 30 min. Substrate cleavage was detected by a CytoFluor II Microplate fluorescence reader (Biosearch, Bedford, MA) at excitation 360 nm and emission 460 nm.
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RESULTS |
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DISCUSSION |
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Recently, convincing evidence for at least one clear link between PKR and MAPK activation has been established (Takizawa et al., 2002). Specifically, a novel interaction was observed between PKR and apoptosis signal-regulating kinase (ASK1), a member of the MAPK kinase family. These conclusions were based on (1) colocalization and comimunoprecipitation of PKR and ASK1; (2) ASK1-mediated p38 phosphorylation in PKR deficient cells; and (3) reduced ASK-1 phosphorylation in PKR-deficient cells treated with poly (I)-poly (c), the classic activator of PKR. Further studies using these approaches could be used to better define the transduction mechanisms between PKR and MAPK during the ribotoxic stress response as well as the potential for cross-talk.
Trichothecene-induced apoptosis has been previously suggested to involve activation of JNK 1/2 and p38 (Yang et al., 2000a). Notably, DON-dependent phosphorylation of JNK might almost entirely be mediated through PKR, whereas DON-dependent phosphorylation of ERK and p38 were only partially mediated through PKR. The data presented here suggest that PKR activation may be upstream of this process. PKR-mediated apoptosis is driven by a large number of stimuli including virus infection, dsRNA, LPS, TNF-
, serum depletion, and cytokine withdrawal (Gil and Esteban, 2000
). Furthermore, fibroblasts containing homozygous deletions in the PKR gene are resistant to apoptotic cell death in response to ds-RNA, TNF-
or LPS (Der et al., 1997
). Although, PKR upregulates several apoptosis-related genes including Fas, Bax, TNF-
, and p53, and is known to involve the FADD-caspase 8 pathway, the precise mechanisms are not yet fully understood (Balachandran et al., 2000
; Yeung et al., 1996
).
PKR-mediated activation of JNK, p38, and ERK may also contribute to DON-induced upregulation of cytokines, chemokines, and cyclooxygenase-2 that have been observed previously in RAW 264.7 and U-937 cells (Ji et al., 1998; Moon and Pestka, 2002
; Sugita-Konishi and Pestka, 2001
; Wong et al., 1998
; Zhou et al., 1997
). A major consequence of MAPK phosphorylation is the activation of transcription factors (Cobb, 1999
), which serve as immediate or downstream substrates of these kinases. For example, JNK 1/2 phosphorylates c-Jun, which is a component of AP-1 homodimer or heterodimer complexes (Dong et al., 2002
). Also, p38 (Bhat et al., 2002
) and ERK 1/2 (Hungness et al., 2002
) drive activation of C/EBP. Phosphorylation/activation of CREB/ATF members is mediated by JNK (Dong et al., 2002
), p38 (Bhat et al., 2002
), and ERK (Belmonte et al., 2001
). Finally, all three MAPK signaling pathways have been implicated in nuclear factor
B (NF-
B) activation through phosphorylation of its inhibitor I
B
(Alpert et al., 1999
; Lee et al., 1998
; Zhao and Lee, 1999
). PKR-driven MAPK activation and subsequent activation of the aforementioned transcription factors, as observed in vitro and in vivo following DON treatment (Wong, 2002; Zhou et al., 2003
), might likely play roles in these processes. Thus, it will be of interest to further define how PKR contributes to DON induction of proinflammatory genes.
Taken together, the data presented herein indicate that PKR is a transducer of the ribotoxic stress response that is initiated by trichothecenes and other translational inhibitors, and that evokes MAPK activation and culminates in apoptosis. Additional research is needed to discern the linkage between ribosomal binding by translational inhibitors and PKR activation as well as to understand how PKR mediates phosphorylation of the major MAPK families. In addition, there is need to examine whether these compounds can induce parallel signaling pathways that converge with PKR-directed pathways and, ultimately, generate diverse immunotoxic effects.
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ACKNOWLEDGMENTS |
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NOTES |
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REFERENCES |
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---|
Balachandran, S., Roberts, P. C., Kipperman, T., Bhalla, K. N., Compans, R. W., Archer, D. R., and Barber, G. N. (2000). /ß Interferons potentiate virus-induced apoptosis through activation of the FADD/caspase-8 death-signaling pathway. J. Virol. 74, 15131523.
Belmonte, N., Phillips, B. W., Massiera, F., Villageois, P., Wdziekonski, B., Saint-Marc, P., Nichols, J., Aubert, J., Saeki, K., Yuo, A., et al. (2001). Activation of extracellular signal-regulated kinases and CREB/ATF-1 mediate the expression of CCAAT/enhancer binding proteins ß and in preadipocytes. Mol. Endocrinol. 15, 20372049.
Bhat, R. V., Beedu, S. R., Ramakrishna, Y., and Munshi, K. L. (1989). Outbreak of trichothecene mycotoxicosis associated with consumption of mould-damaged wheat production in Kashmir Valley, India. Lancet 1, 3537.[CrossRef][ISI][Medline]
Bhat, N. R., Feinstein, D. L., Shen, Q., and Bhat, A. N. (2002). p38 MAPK-mediated transcriptional activation of inducible nitric oxide synthase in glial cells: Roles of nuclear factors, NF-B, CREB, C/EBP, and ATF2. J. Biol. Chem. 277, 2958429592.
Bondy, G. S., and Pestka, J. J. (2000). Immunomodulation by fungal toxins. J. Toxicol. Environ. Health B Crit. Rev. 3, 109143.[CrossRef][ISI][Medline]
Chu, W. M., Ballard, R., Carpick, B. W., Williams, B. R., and Schmid, C. W. (1998). Potential Alu function: Regulation of the activity of double-stranded RNA-activated kinase PKR. Mol. Cell Biol. 18, 5868.
Cobb, M. H. (1999). MAP kinase pathways. Prog. Biophys. Mol. Biol. 71, 479500.[CrossRef][ISI][Medline]
Cooley, J. D., Wong, W. C., Jumper, C. A., and Straus, D. C. (1998). Correlation between the prevalence of certain fungi and sick-building syndrome. Occup. Environ. Med. 55, 579584.[Abstract]
Der, S. D., and Lau, A. S. (1995). Involvement of the double-stranded, RNA-dependent kinase PKR in interferon expression and interferon-mediated antiviral activity 1. Proc. Natl. Acad. Sci. U.S.A. 92, 88418845.[Abstract]
Der, S. D., Yang, Y. L., Weissmann, C., and Williams, B. R. (1997). A double-stranded RNA-activated protein kinase-dependent pathway mediating stress-induced apoptosis. Proc. Natl. Acad. Sci. U.S.A 94, 32793283.
Dong, C., Davis, R. J., and Flavell, R. A. (2002). MAP kinases in the immune response. Annu. Rev. Immunol. 20, 5572.[CrossRef][ISI][Medline]
Etzel, R. A., Montana, E., Sorenson, W. G., Kullman, G. J., Allan, T. M., Dearborn, D. G., Olson, D. R., Jarvis, B. B., and Miller, J. D. (1998). Acute pulmonary hemorrhage in infants associated with exposure to Stachybotrys atra and other fungi. Arch. Pediatr. Adolesc. Med. 152, 757762.
Gil, J., and Esteban, M. (2000). Induction of apoptosis by the dsRNA-dependent protein kinase (PKR): mechanism of action. Apoptosis 5, 107114.[CrossRef][ISI][Medline]
Goh, K. C., deVeer, M. J., and Williams, B. R. G. (2000). The protein kinase PKR is required for p38 MAPK activation and the innate immune response to bacterial endotoxin. EMBO J. 19, 42924297.
Hungness, E. S., Luo, G. J., Pritts, T. A., Sun, X., Robb, B. W., Hershko, D., and Hasselgren, P. O. (2002). Transcription factors C/EBP-ß and - regulate IL-6 production in IL-1ß-stimulated human enterocytes. J. Cell Physiol. 192, 6470.[CrossRef][ISI][Medline]
Iordanov, M. S., Pribnow, D., Magun, J. L., Dinh, T. H., Pearson, J. A., Chen, S. L., and Magun, B. E. (1997). Ribotoxic stress response: Activation of the stress-activated protein kinase JNK1 by inhibitors of the peptidyl transferase reaction and by sequence-specific RNA damage to the -sarcin/ricin loop in the 28S rRNA. Mol. Cell Biol. 17, 33733381.[Abstract]
Ji, G. E., Park, S. Y., Wong, S. S., and Pestka, J. J. (1998). Modulation of nitric oxide, hydrogen peroxide, and cytokine production in a clonal macrophage model by the trichothecene vomitoxin (deoxynivalenol). Toxicology 125, 203214.[CrossRef][ISI][Medline]
Laskin, J. D., Heck, D. E., and Laskin, D. L. (2002). The ribotoxic stress response as a potential mechanism for MAP kinase activation in xenobiotic toxicity. Toxicol. Sci. 69, 289291.
Lee, F. S., Peters, R. T., Dang, L. C., and Maniatis, T. (1998). MEKK1 activates both IB kinase
and I
B kinase ß. Proc. Natl. Acad. Sci. U.S.A. 95, 93199324.
Li, F. Q., Li, Y. W., Luo, X. Y., and Yoshizawa, T. (2002). Fusarium toxins in wheat from an area in Henan Province, PR, China, with a previous human red mould intoxication episode. Food Addit. Contam. 19, 163167.
Li, F. Q., Luo, X. Y., and Yoshizawa, T. (1999). Mycotoxins (trichothecenes, zearalenone, and fumonisins) in cereals associated with human red-mold intoxications stored since 1989 and 1991 in China. Nat. Toxins 7, 9397.[CrossRef][ISI][Medline]
Liu, W. M., Chu, W. M., Choudary, P. V., and Schmid, C. W. (1995). Cell stress and translational inhibitors transiently increase the abundance of mammalian SINE transcripts. Nucleic Acids Res. 23, 17581765.[Abstract]
Meusel, T. R., Kehoe, K. E., and Imani, F. (2002). Protein kinase R regulates double-stranded RNA induction of TNF- but not IL-1ß mRNA in human epithelial cells. J. Immunol. 168, 64296435.
Middlebrook, J. L., and Leatherman, D. L. (1989a). Binding of T-2 toxin to eukaryotic cell ribosomes. Biochem. Pharmacol. 38, 31033110.[CrossRef][ISI][Medline]
Middlebrook, J. L., and Leatherman, D. L. (1989b). Differential association of T-2 and T-2 tetraol with mammalian cells. J. Pharmacol. Exp. Ther. 250, 860866.[Abstract]
Moon, Y., and Pestka, J. J. (2002). Vomitoxin-induced cyclooxygenase-2 gene expression in macrophages mediated by activation of ERK and p38 but not JNK mitogen-activated protein kinases. Toxicol. Sci.69, 373382.
Rotter, B. A., Prelusky, D. B., and Pestka, J. J. (1996). Toxicology of deoxynivalenol (vomitoxin). J. Toxicol. Environ. Health 48, 134.[ISI][Medline]
Scott, P. M. (1990). Trichothecenes in grains. CFW Review 35, 661666.
Sellins, K.S., and Cohen, J.J. (1987). Gene induction by gamma-irradiation leads to DNA fragmentation in lymphocytes. J. Immunol. 139, 31993206.
Shifrin, V. I., and Anderson, P. (1999). Trichothecene mycotoxins trigger a ribotoxic stress response that activates c-Jun N-terminal kinase and p38 mitogen-activated protein kinase and induces apoptosis. J. Biol. Chem. 274, 1398513992.
Sugita-Konishi, Y., and Pestka, J. J. (2001). Differential upregulation of TNF-, IL-6, and IL-8 production by deoxynivalenol (vomitoxin) and other 8-ketotrichothecenes in a human macrophage model. J. Toxicol. Environ. Health A. 64, 619636.[CrossRef][ISI][Medline]
Takizawa, T., Tatematsu, C., and Nakanishi, Y. (2002). Double-stranded RNA-activated protein kinase interacts with apoptosis signal-regulating kinase 1: Implications for apoptosis signaling pathways. Eur. J. Biochem. 269, 61266132.
Williams, B. R. (1999). PKR; A sentinel kinase for cellular stress. Oncogene 18, 61126120.[CrossRef][ISI][Medline]
Williams, B. R. (2001). Signal integration via PKR. Sci. STKE. 2001, RE2.
Witt, M. F., and Pestka, J. J. (1990). Uptake of the naturally occurring 3--hydroxy isomer of T-2 toxin by a murine B-cell hybridoma. Food Chem. Toxicol. 28, 2128.[CrossRef][ISI][Medline]
Wong, M. L., and Yen, Y. R. (1998). Protein synthesis in pseudorabies virus-infected cells: Decreased expression of protein kinase PKR, and effects of 2-aminopurine and adenine. Virus Res. 56, 199206.[CrossRef][ISI][Medline]
Wong, S. S., Zhou, H. R., Marin-Martinez, M. L., Brooks, K., and Pestka, J. J. (1998). Modulation of IL-1 ß, IL-6, and TNF- secretion and mRNA expression by the trichothecene vomitoxin in the RAW 264.7 murine macrophage cell line. Food Chem. Toxicol. 36, 409419.[CrossRef][ISI][Medline]
Wong, S. S., Zhou, H. R., and Pestka, J. J. (2002). Effects of vomitoxin (deoxynivalenol) on the binding of transcription factors AP-1, NF-B, and NF-IL6 in RAW 264.7 macrophage cells. J. Toxicol. Environ. Health A. 65, 11611180.[CrossRef][ISI][Medline]
Wu, S. Y., Kumar, K. U., and Kaufman, R. J. (1998). Identification and requirement of three ribosome-binding domains in dsRNA-dependent protein kinase (PKR). Biochemistry 37, 1381613826.[CrossRef][ISI][Medline]
Yang, G. H., Jarvis, B. B., Chung, Y. J., and Pestka, J. J. (2000a). Apoptosis induction by the satratoxins and other trichothecene mycotoxins: Relationship to ERK, p38 MAPK, and SAPK/JNK activation. Toxicol. Appl. Pharmacol. 164, 149160.[CrossRef][ISI][Medline]
Yang, G. H., Li, S., and Pestka, J. J. (2000b). Downregulation of the endoplasmic reticulum chaperone GRP78/BiP by vomitoxin (deoxynivalenol). Toxicol. Appl. Pharmacol. 162, 207217.[CrossRef][ISI][Medline]
Yeung, M. C., Chang, D. L., Camantigue, R. E., and Lau, A. S. (1999). Inhibitory role of the host apoptogenic gene PKR in the establishment of persistent infection by encephalomyocarditis virus in U937 cells. Proc. Natl. Acad. Sci. U.S.A 96, 1186011865.
Yeung, M. C., and Lau, A. S. (1998). Tumor suppressor p53 as a component of the tumor necrosis factor-induced, protein kinase PKR-mediated apoptotic pathway in human promonocytic U937 cells. J. Biol. Chem.273, 2519825202.
Yeung, M. C., Liu, J., and Lau, A. S. (1996). An essential role for the interferon-inducible, double-stranded RNA-activated protein kinase PKR in the tumor necrosis factor-induced apoptosis in U937 cells. Proc. Natl. Acad. Sci. U.S.A 93, 1245112455.
Zhao, Q., and Lee, F. S. (1999). Mitogen-activated protein kinase/ERK kinase kinases 2 and 3 activate nuclear factor-kappaB through IB kinase-
and I
B kinase-ß. J. Biol. Chem. 274, 83558358.
Zhou, H. R., Islam, Z., and Pestka, J. J. (2003). Rapid, sequential activation of mitogen-activated protein kinases and transcription factors precedes proinflammatory cytokine mRNA expression in spleens of mice exposed to the trichothecene vomitoxin (deoxynivalenol). Toxicol. Sci. 72, 13042.
Zhou, H. R., Yan, D., and Pestka, J. J. (1997). Differential cytokine mRNA expression in mice after oral exposure to the trichothecene vomitoxin (deoxynivalenol): Dose response and time course. Toxicol. Appl. Pharmacol. 144, 294305.[CrossRef][ISI][Medline]