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Biochemistry and Biophysics |
Department of Pediatrics, Division of Gastroenterology, Hepatology and Nutrition, Vanderbilt University School of Medicine, Nashville, Tennessee 37232
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ABSTRACT |
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 Top ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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B activation and one of its transcriptional targets, cIAP2 (c inhibitor of apoptosis protein 2) gene expression, and ERK/MAP kinase activation are all inhibited in TNF-treated kinase-inactive KSR-expressing young adult mouse colon cells. These antiapoptotic pathways are also inhibited by antisense-mediated down-regulation of KSR. However, TNF activation of p38 or stress-activated protein kinase/c-Jun NH2-terminal kinase is not inhibited by disruption of KSR signaling. Furthermore, inhibitors of both ERK and nuclear factor B activation synergistically enhance apoptosis of cells treated with TNF. These findings demonstrate that KSR plays a novel regulatory role in intestinal epithelial cells exposed to TNF by activating cell survival pathways. |
INTRODUCTION |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The balance between antiapoptotic and proapoptotic signals regulates the fate of cells exposed to various stimuli including TNF (13
, 14) . Antiapoptotic signals initiated by TNF, other cytokines, and growth factors include NFB (15, 16, 17, 18, 19)
, ERK1/ERK2/MAP kinase (20, 21, 22, 23)
, and phosphatidylinositol 3'-kinase/Akt (23
, 24)
, whereas other members of the MAP kinase family, including SAPK/JNK and p38, function as proapoptotic signals (25, 26, 27)
.
The ERK/MAP kinase pathway is necessary for TNFR1-mediated differentiating effects on intestinal cells (28)
. We recently reported that TNF activation of this pathway requires the kinase activity of KSR for threonine phosphorylation and activation of Raf-1 (29)
. In the present study, we demonstrate that KSR is an essential kinase in TNF signal transduction regulating intestinal epithelial cell fate. To determine the effect of inhibition of upstream activation of Raf-1/ERK/MAP kinase on TNF regulation of intestinal cell proliferation, we expressed KSR as a dominant-negative, kiKSR or asKSR to decrease endogenous KSR production in YAMC cells. We show that with inhibition of KSR, TNF induces apoptosis in intestinal cells. Furthermore, the consequences of kiKSR or asKSR expression include loss of activation of the antiapoptotic NFB and ERK/MAP kinase pathways. In contrast, there was no reduction in activation of potentially proapoptotic SAPK/JNK or p38 MAP kinases in TNF-treated colon cells expressing kiKSR or asKSR. These findings support our conclusion that KSR is a key regulatory kinase determining the fate of intestinal epithelial cells exposed to TNF.
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MATERIALS AND METHODS |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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-inducible promoter were grown on collagen-coated culture dishes as described previously (6
, 30)
. Briefly, cells were maintained in RPMI 1640 with 5% FBS under permissive conditions at 33°C in a humidified atmosphere with 5% CO2. Confluent cell monolayers were serum-starved (0.5% FBS) and IFN--deprived under nonpermissive conditions at 37°C for 24 h before all experiments. HeLa and A431 cells were grown in DMEM supplemented with 10% FBS at 37°C in a humidified atmosphere with 5% CO2.
Recombinant Plasmid Generation and Cellular Transfection.
asKSR-cDNA3.1(-)-expressing vector was constructed by subcloning wtKSR derived from pcDNA3-wtKSR construct (provided by Richard Kolesnick; Memorial Sloan-Kettering Cancer Center, New York, NY) by KpnI/NotI digestion into the pcDNA3.1(-) vector at NotI/KpnI sites. The pcDNA3.1(-) vector containing asKSR was confirmed by DNA sequencing using T7 promoter as 5' primer.
Transient transfection of pcDNA3.1(-)-asKSR vector was performed on cells with pcDNA3.1(-) vector used as control. For each well containing 3 x 105 cells, 10 µl of LipofectAMINE 2000 reagent (Life Technologies, Inc., Grand Island, NY) were diluted with 250 µl of OPTI-MEM I medium (Life Technologies, Inc.), incubated for 5 min at room temperature, and then combined with 2 µg of DNA in 250 µl of OPTI-MEM I medium. The DNA-LipofectAMINE 2000 reagent complex was incubated for 20 min at room temperature and then added to cells in 2.5 ml of OPTI-MEM I medium. After a 6-h incubation, YAMC and MSIE cells were changed to RPMI 1640 and incubated for 18 h. HeLa or A431 cells were changed to DMEM and incubated for 18 h. Then YAMC and MSIE cells were incubated in RPMI 1640 with 0.5% FBS at 37°C, and HeLa and A431 cells were incubated in DMEM with 0.5% FBS at 37°C for 6 h prior to all experiments. The level of KSR expression was detected using Western blot analysis with anti-KSR antibody (provided by Deborah Morrison; National Cancer Institute, Bethesda, MD).
Clonal cell lines stably expressing pFlag-cDNA3-wtKSR, pFlag-cDNA3-kiKSR, or pcDNA3 vector (KSR vectors were provided by Richard Kolesnick) were generated as described previously (29) . The kiKSR plasmid expresses a dominant-negative kiKSR as described previously (29 , 31) . Clonal cells were cultured in the presence of G418 (100 µg/ml) until 24 h prior to experiments. Expression was verified by Western blot analysis with anti-Flag M2 (Sigma Chemical Co., St. Louis, MO).
Preparation of Cellular Lysates.
Lysates were prepared from cells treated with murine TNF (100 ng/ml; Pepro Tech, Inc. Rocky Hill, NJ), for the indicated times. Cell monolayers were washed twice with ice-cold PBS and then scraped into cell lysis buffer [20 mM HEPES (pH 7.5), 1 mM orthovanadate, 50 mM ß-glycerolphosphate, 10 mM Na PPi, 10 µg/ml leupeptin, 10 µg/ml aprotinin, 18 µg/ml phenylmethylsulfonyl fluoride, and 1% Triton X-100]. The scraped suspensions were centrifuged (14,000 x g for 10 min) at 4°C, and protein content was determined using the DC protein assay (Bio-Rad Laboratories, Hercules, CA). Equal amounts of cellular lysate protein were mixed with Laemmli sample buffer (32)
and separated by SDS-PAGE for Western blot analysis with anti-Flag M2 (Sigma Chemical Co.), anti-phospho-IB
, anti-IB, anti-phospho-p38, anti-phospho-SAPK/JNK, anti-SAPK/JNK (Cell Signaling Technology, Beverly, MA), anti-cIAP2 (Santa Cruz Biotechnology, Santa Cruz, CA), anti-phospho-ERK1/ERK2 (Promega, Madison, WI), and anti-ERK1/ERK2 (Transduction Laboratory, San Diego, CA) antibodies.
Cell Proliferation Analysis.
Cells were prepared as described above, trypsinized, and counted; 400,000 cells/well were plated and permitted to attach for 24 h. Cells were then cultured under nonpermissive conditions for 24 h before treatment with TNF or EGF (10 ng/ml; a gift from Stanley Cohen; Vanderbilt University, Nashville, TN) for 48 h. At the conclusion, the cell number was determined by counting trypsinized cell suspensions as reported previously (6)
. The change in the number of untreated cells from the start of an experiment to the end of an experiment was standardized as 100% proliferation. The change in cell number in treated cell samples over the course of an experiment was then reported as a percentage relative to the untreated controls.
Immunofluorescence.
Cells were cultured on collagen-coated sterile glass cover slides and prepared as described above. In the indicated experiments, cells were preincubated for 30 min with NFB nuclear localization inhibitory peptide SN50 (100 µg/ml; BIOMOL Research Laboratories, Inc., Plymouth Meeting, PA), cell-permeable control peptide SN50M (100 µg/ml; Ref. 33
), or MEK1 inhibitor PD98059 (10 µM; Cell Signaling Technology); cells were treated with TNF, washed twice with ice-cold PBS, fixed in 1% paraformaldehyde in PBS for 10 min at 4°C, and then permeabilized with methanol for 5 min at -20°C. Once slides were air-dried and washed with PBS, the cells were incubated in 10% normal donkey serum in PBS (Zymed Laboratories Inc., San Francisco, CA) for 1 h. The slides were then incubated with rabbit anti-NFB p65 antibody (1:300; Santa Cruz Biotechnology) in PBS with 1% donkey serum overnight at 4°C. The slides were washed three times in PBS for 5 min and incubated with donkey antirabbit IgG-FITC (1:2000; Zymed Laboratories Inc.) in 10% donkey serum in PBS at room temperature. The slides were washed again and then dehydrated and mounted using Vectashield mounting medium (Vector Laboratories, Burlingame, CA). Immunofluorescence was observed by a LSM410 Confocal Laser Scanning Microscope from Carl Zeiss, Inc. (Oberkochen, Germany).
Apoptosis Assay.
Cells were cultured on collagen-coated chamber glass slides and prepared as described above. After TNF or cell-permeable C8-ceramide (BIOMOL Research Laboratories) treatment, apoptotic cells were labeled by ApopTag in Situ Apoptosis Detection Kits (Intergen Company, Purchase, NY) using terminal deoxynucleotidyl transferase for detection of positive cells, following the manufacturer’s guidelines. Apoptotic cells were labeled by anti-digoxigenin peroxidase conjugate and 3,3'-diaminobenzidine as substrate or FITC-conjugated anti-digoxigenin and dehydrated and mounted using Vectashield mounting medium. Slides were counterstained with DAPI by using 1 µg/ml DAPI in mounting medium. The cells were observed by DIC or fluorescence microscopy. Apoptotic TUNEL-positive cells were determined by counting at least 150 cells in randomly chosen fields and expressed as a percentage of the total number of cells counted.
IKK in Vitro Kinase Assays.
Cells were treated with TNF, and then lysates were prepared as described above, and IKK was recovered as detailed previously (34)
using polyclonal anti-IKK antibody (Santa Cruz Biotechnology). The immunoprecipitated IKK was recovered by centrifugation, washed with ice-cold cell lysis buffer plus 1 M NaCl, and then washed with kinase buffer [20 mM Tris-HCl (pH 7.4), 20 mM MgCl2, 20 mM ß-glycerolphosphate, 20 mM p-nitrophenolphosphate, 1 mM sodium orthovanadate, 1 mM EDTA, and 200 nM ATP with leupeptin (10 µg/ml), aprotinin (10 µg/ml), and phenylmethylsulfonyl fluoride (18 µg/ml)]. In some experiments, IKK was solubilized in Laemmli sample buffer for Western blot analysis with anti-IKK or anti-IKKß (Santa Cruz Biotechnology) antibodies. The in vitro kinase assays were performed by incubating immunoisolated IKK with GST-IB fusion protein (Santa Cruz Biotechnology) in 30 µl of kinase buffer at 37°C for 30 min as described previously (34)
. GST-IB fusion protein was then separated from immunoprecipitated IKK by centrifugation at 4°C. Recovered GST-IB in the supernatant was precipitated by incubation with glutathione-Sepharose 4B beads (Pharmacia Biotech, Piscataway, NJ) for 30 min at room temperature. GST-IB conjugated to beads was washed with PBS and prepared for SDS-PAGE and Western blot analysis with anti-phospho-IB or anti-IB.
Each individual experiment was repeated on at least three separate occasions with similar results. Proliferation and apoptosis data are presented as the means and SDs of triplicate samples. The statistical significance of the differences was determined using Student’s t test analysis. The level of statistical significance was set at P < 0.05.
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RESULTS |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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. In contrast, neither wtKSR nor vector expression alters the antiproliferative effects of TNF. EGF stimulates proliferation in all four clonal cell lines. To determine the relationship between the level of dominant-negative KSR expression and cell loss, clonal cell lines expressing various levels of kiKSR were selected based on anti-Flag immunoblotting (Fig. 1C)
. Dominant-negative KSR expression induces cell loss in TNF-stimulated cells in a manner directly proportional to the level of kiKSR expression (Fig. 1B)
. TUNEL staining shows that TNF enhances apoptosis only in kiKSR-expressing cells (Fig. 2, A and B)
. Because we have shown cell-permeable ceramide to mimic the effect of TNF (100 ng/ml) on proliferation and signal transduction (35)
, we determined the effect of C8-ceramide on apoptosis. Similar to TNF, ceramide induces apoptosis only in kiKSR cells (Fig. 2A)
. Fig. 2C
shows that expression of an asKSR construct also induces apoptosis detected by TUNEL staining. The degree of apoptotic cell loss also correlates with the amount of dominant-negative KSR expression (data shown in Fig. 1, B and C
). Therefore, KSR appears to determine whether cells exposed to TNF undergo differentiation or apoptosis.
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B activation, an antiapoptotic signaling pathway in many cell lines (15, 16, 17, 18, 19)
. We studied nuclear translocation of the p65 subunit of NFB by immunostaining and confocal laser microscopy and verified function by determining cIAP2 expression. kiKSR expression, but not wtKSR or vector controls (Fig. 3A)
, inhibits translocation of the p65 subunit to the nucleus. cIAP2 has been identified as a target of NFB transcriptional activity, which protects against TNF-induced apoptosis (36
, 37)
. Therefore, we further studied the role of KSR on cIAP2 production. Lysates prepared from cells treated with TNF for Western blot analysis with anti-cIAP2 show that kiKSR expression inhibits TNF-stimulated cIAP2 production (Fig. 3B)
.
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and IKKß directly phosphorylate IB on serine sites (38)
, leading to IB degradation and NFB transcriptional activation (39
, 40)
. Expression of kiKSR inhibits TNF-stimulated IB phosphorylation and degradation in YAMC cells (Fig. 4A)
. In addition, TNF-stimulated IB phosphorylation and degradation are also inhibited by antisense-mediated down-regulation of endogenous KSR (Fig. 4B)
. Because we have shown that IKK is the predominant kinase responsible for IB phosphorylation in the mouse intestinal epithelial cell (34)
, we assessed IKK kinase activity toward IB. Immunoisolated IKK was prepared for in vitro kinase assays using GST-IB as substrate. TNF-stimulated IKK kinase activity toward IB is inhibited in cells expressing kiKSR (Fig. 5)
. Analysis of immunoisolated IKK shows no detectable recovery of IKKß, as reported previously (34)
.
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. In contrast, ERK1/ERK2 MAP kinase activation requires KSR, as we have reported previously (29)
. These data indicate that activation of SAPK/JNK and p38 MAP kinases appears to be independent of KSR kinase activity in TNF signal transduction pathways.
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B and ERK/MAP Kinase Activation Synergistically Prevents Apoptosis in YAMC Cells Exposed to TNF.B and ERK1/ERK2 in TNF antiapoptotic signal transduction, we used inhibitors of their activation. A chimeric peptide (SN50) containing the signal sequence of Kaposi’s fibroblast growth factor fused to the p50 nuclear localization sequence was shown to inhibit NFB nuclear translocation (33)
. Preincubation of YAMC cells with SN50 blocks both TNF-stimulated p65 NFB nuclear translocation (Fig. 7A)
and enhanced cIAP2 expression (Fig. 7B)
in YAMC cells. Neither the MEK1 inhibitor (PD98059) nor the inactive mutant peptide (SN50M) alters NFB activation or cIAP2 expression. As expected, PD98059 inhibits ERK1/ERK2 activation (Fig. 7B)
. Blocking ERK1/ERK2 activation induces no detectable increase of apoptosis in TNF-treated cells (Fig. 8)
, whereas blockade of NFB activation in cells treated with TNF increases apoptosis to 25%. However, inhibition of both ERK1/ERK2 and NFB synergistically increases apoptosis to >80% of cells treated with TNF. These results suggest that KSR regulates activation of two important signal transduction pathways determining whether or not cells exposed to TNF undergo apoptosis.
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B Degradation by TNF May Depend on Cell Type.B and ERK/MAP kinase is cell type dependent, MSIE, HeLa, and A431 cells were transfected with asKSR. Loss of endogenous KSR production inhibits TNF-stimulated ERK1/ERK2 phosphorylation and IB degradation in MSIE cells, similar to YAMC cells (Fig. 9)
. However, asKSR expression shows no effect on ERK/MAP kinase activation and IB degradation in either HeLa or A431 cells. These data suggest that KSR regulation of TNF-activated antiapoptotic signaling may be cell type specific.
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DISCUSSION |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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B, ERK1/ERK2 MAP kinases, or the serine/threonine protein kinase Akt. Furthermore, antisense-mediated down-regulation of KSR inhibits these antiapoptotic signals. Direct inhibition of NFB and ERK1/ERK2 activation synergistically recapitulates the apoptosis seen in kiKSR-expressing TNF-treated cells. In contrast, inhibiting KSR kinase activity does not alter TNF activation of the proapoptotic MAP kinases SAPK/JNK and p38. These findings place KSR kinase activity in a key regulatory role determining the fate of cells exposed to high levels of TNF.
The results of these studies suggest a role for KSR kinase activity in regulating critical physiological responses to TNF in cells. Zhang et al. (31)
have shown that TNF-regulated KSR kinase activity phosphorylates Raf-1 on threonine 268/269 in fibroblasts. A role for KSR in regulation of normal growth, development, and differentiation is implied by its isolation in genetic screening analysis as a loss of function mutation in the Ras signaling pathways of Drosophila and Caenorhabditis elegans (41, 42, 43)
. Whereas our previous work on TNF inhibition of intestinal cell proliferation predicts that a dominant-negative KSR should alter the differentiation response (28
, 29)
, the conversion to apoptosis was not anticipated. Furthermore, the regulation of NFB activation by kiKSR was an unexpected and novel finding.
NFB is held in an inactive state by IB binding in the cytoplasm. Following a variety of stimuli, the IKKs phosphorylate IB, leading to IB ubiquitination and degradation, thereby releasing NFB for nuclear translocation (recently reviewed in Refs. 44
and 45
). Our findings indicate that blockade of KSR kinase activity results in attenuation of IKK kinase activity isolated from TNF-treated cells (Fig. 5)
. Although the role of the KSR substrate Raf-1 (29
, 46)
in NFB activation is not fully understood, expression of a transforming Raf-1 induces NFB (47)
, and dominant-negative Raf-1 inhibits its activation (48)
. Experiments using mutant Raf-1 constructs recently demonstrated loss of ERK1/ERK2 MAP kinase activation, but not NFB activation or neuronal differentiation, indicating the divergence of multiple downstream pathways at Raf-1 (49)
. Although we have not proven in this report that Raf-1 is an intermediate in this pathway, dominant-negative KSR inhibits TNF activation of Raf-1 (29
, 31)
. Furthermore, KSR directly phosphorylates and activates Raf-1 in TNF-treated cells (29)
. Using an inhibitor of ERK1/ERK2 activation, we show that NFB activation is not downstream of MEK1 in the Raf-1 pathway (Fig. 7)
. Given the recently demonstrated bifurcation in Raf-1 signaling, we suggest that TNF regulation of NFB through KSR kinase activity in intestinal cells occurs via an alternative Raf-1 pathway. One consequence of this regulation is decreased expression of cIAP2 (Fig. 3B)
, which is reported to mediate NFB antiapoptotic effects (36
, 37
, 50)
. Importantly, the biological consequence of this alternative pathway appears to be the balance between proapoptotic and antiapoptotic signals. We have previously reported that either cell-permeable ceramide or sphingomyelinase can activate intestinal cell Raf-1/MEK/ERK and NFB pathways (29
, 35)
. Ceramide is generated by TNF via acid and neutral sphingomyelinase hydrolytic activities toward sphingomyelin (51)
and has been shown to activate KSR (31)
. Importantly, sphingomyelinase activation of ERK1/ERK2 in intestinal cells requires KSR kinase activity (29)
and has been shown to initiate IB degradation (52)
. Findings by other groups that ceramide induces apoptosis (53, 54, 55)
may partially be explained by cell context because our studies were performed in intestinal epithelial cells. The present study clearly shows (Figs. 4
and 9
) that KSR mediates ERK/MAP kinase activation and IB degradation by TNF in two intestinal cell lines; such effects were not observed in HeLa or A431 cells. Alternatively, the responses to ceramide may be differentially mediated based on the mechanism of generation. Knockout of the acid sphingomyelinase gene asmase-/- produced fibroblasts that were completely resistant to radiation-induced apoptosis but not TNF-induced apoptosis (56)
. Given that a number of TNF-stimulated effects in intestinal cells can be mimicked by ceramide, the induction of apoptosis by ceramide in KSR-inhibited mouse colon cells is not surprising.
TNF was originally isolated based on its biological function of tumor regression following bacterial infection (6)
. However, in many cells, TNF fails to induce apoptosis by initiating antiapoptotic signal transduction pathways (15, 16, 17, 18, 19)
. Our findings indicate that KSR kinase activity is an antiapoptotic effector of TNF signal transduction via regulation of both the Raf-1/MEK1/ERK signaling cassette and NFB. The antiapoptotic effects of these two pathways appear to be functionally redundant, in that inhibition of either pathway alone is insufficient to fully recapitulate the effect of inhibiting both pathways (Fig. 8)
, whereas inhibition of both NFB and ERK1/ERK2 MAP kinase synergistically recapitulates the effects of KSR signal blockade in TNF-treated cells. Whereas the mechanisms determining KSR kinase activity are not known, it is presumed that a number of the identified serine and threonine phosphorylation sites regulate both protein-protein interactions and kinase activity (57, 58, 59)
. Regulation of KSR kinase activity is therefore a potential therapeutic target in inflammatory conditions where reducing the apoptotic effects of high-level TNF appears to be involved in the pathogenesis of disease (60, 61, 62, 63)
. Alternatively, in tumor cells resistant to TNF-induced apoptosis, inhibition of KSR activity could shift the response to apoptosis (15
, 27
, 64
, 65)
. Our results show that KSR kinase activity is necessary to maintain the balance between proapoptotic and antiapoptotic signals in TNF- or ceramide-treated intestinal epithelial cells. From these studies, we conclude that KSR serves a regulatory role in determining the fate of intestinal epithelial cells exposed to TNF and may therefore prove a novel therapeutic target for modulating inflammatory or tumoricidal activities.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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1 Supported by NIH Grants T32 DK07673, DK56008, and F32 DK10105 and by a Research Fellowship Award from the Crohn’s and Colitis Foundation of America and a Turner Scholar Award. 
2 To whom requests for reprints should be addressed, at Department of Pediatrics, Division of Gastroenterology, Hepatology and Nutrition, S4322 MCN, 21st and Garland Avenue, Nashville, TN 37232-2576. Phone: (615) 322-7449; Fax: (615) 343-8915; E-mail: d-brent.polk{at}mcmail.vanderbilt.edu
3 The abbreviations used are: TNF, tumor necrosis factor; cIAP, c inhibitor of apoptosis protein; DAPI, 4',6-diamidino-2-phenylindole; DIC, differential interference contrast; EGF, epidermal growth factor; ERK, extracellular signal-regulated kinase; FBS, fetal bovine serum; IBD, inflammatory bowel disease; IKK, IB kinase; KSR, kinase suppressor of Ras; MAP, mitogen-activated protein; MEK, MAP kinase/ERK kinase; MSIE, mouse small intestinal epithelial; NFB, nuclear factor B; SAPK/JNK, stress-activated protein kinase/c-Jun NH2-terminal kinase; TNFR, TNF receptor; YAMC, young adult mouse colon; asKSR, antisense KSR; kiKSR, kinase-inactive KSR; wtKSR, wild-type KSR; TUNEL, terminal deoxynucleotidyl transferase-mediated nick end labeling; GST, glutathione S-transferase; MEK, MAP/ERK kinase.
Received 5/25/01. Accepted 10/17/01.
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REFERENCES |
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TopABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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for Crohn’s disease. N. Engl. J. Med., 337: 1029-1035, 1997. regulates proliferation in a mouse intestinal cell line. Gastroenterology, 112: 1231-1240, 1997.[Medline]
B in preventing TNF--induced cell death. Science (Wash. DC), 274: 782-784, 1996.B to the rescue: RELs, apoptosis and cellular transformation. Trends Genet., 15: 229-235, 1999.[Medline]
-induced apoptosis by NF-B. Science (Wash. DC), 274: 787-789, 1996.B. Trends Cell Biol., 8: 107-111, 1998.[Medline]
B activation is required for human endothelial survival during exposure to tumor necrosis factor- but not interleukin-1ß or lipopolysaccharide. J. Biol. Chem., 274: 28808-28815, 1999.B pathways in survival and activation of osteoclasts. J. Cell Biol., 148: 333-342, 2000. from antiproliferative to proliferative ligand in mouse intestinal epithelial cells by regulating mitogen-activated protein kinase. Exp. Cell Res., 249: 349-358, 1999.[Medline]
activation of extracellular signal-regulated kinase/mitogen-activated protein kinase in intestinal epithelial cells. Cancer Res., 61: 963-969, 2001.B by a synthetic peptide containing a cell membrane-permeable motif and nuclear localization sequence. J. Biol. Chem., 270: 14255-14258, 1995.B kinase phosphorylation of IB in mouse intestinal epithelial cells. J. Biol. Chem., 274: 36631-36636, 1999.B activation in mouse colonocytes. Gastroenterology, 116: 602-609, 1999.[Medline]
B control. Proc. Natl. Acad. Sci. USA, 94: 10057-10062, 1997.B antiapoptosis: induction of TRAF1 and TRAF2 and c-IAP1 and c-IAP2 to suppress caspase-8 activation. Science (Wash. DC), 281: 1680-1683, 1998.B kinase that activates the transcription factor NF-B. Nature (Lond.), 388: 548-554, 1997.[Medline]
B to the ubiquitin-proteasome pathway. Genes Dev., 9: 1586-1597, 1995.B: a lesson in family values. Cell, 80: 529-532, 1995.[Medline]
B kinase (IKK) and NF-B activation. J. Biol. Chem., 274: 27339-27342, 1999.B. Curr. Opin. Cell Biol., 11: 226-232, 1999.[Medline]
B by oncogenic Raf in HEK 293 cells occurs through autocrine recruitment of the stress kinase cascade. Oncogene, 17: 685-690, 1998.[Medline]
B in mammalian cells through a Raf-1-mediated pathway. J. Biol. Chem., 270: 24435-24441, 1995. degradation in a cell-free system. J. Biol. Chem., 269: 13760-13765, 1994. therapy in rheumatoid arthritis. J. Immunol., 163: 1521-1528, 1999., TNF) in the induction of epithelial cell death and renewal. Eur. J. Immunol., 28: 730-744, 1998.[Medline]
and not by the FasL-Fas interaction: effect of pentoxifylline on the development of mucosal atrophy. Gut, 45: 229-235, 1999.B. Science (Wash. DC), 274: 784-787, 1996.This article has been cited by other articles:
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|
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|
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|
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|
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|
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F. Yan and D. B. Polk Probiotic Bacterium Prevents Cytokine-induced Apoptosis in Intestinal Epithelial Cells J. Biol. Chem., December 20, 2002; 277(52): 50959 - 50965. [Abstract] [Full Text] [PDF]
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