Shiga toxins activate translational regulation pathways in intestinal epithelial cells.
Shiga toxins (Stxs) cause irreversible damage to eukaryotic ribosomes, yet cellular intoxication of intestinal epithelial cells (IECs) results in increased synthesis of selected proteins, notably cytokines. How mRNA translation is maintained in this circumstance is unclear. This study was designed to assess whether Stx-induced alterations in host signal transduction machinery permit translation despite protein synthesis inhibition. A key step of translation is recruitment of initiation machinery to the 5' mRNA cap. This event occurs in part via interaction of the 5' cap with the cap binding protein, eIF4E, whose activity is positively regulated by phosphorylation and negatively regulated by binding to the translational repressor 4E-BP1. Following Stx treatment of IECs, eIF4E phosphorylation was detected by Western blotting using phospho-specific antibodies. Treatment with the p38 inhibitor, SB202190, or either of the ERK1/2 inhibitors, PD98059 and U0126, partially blocked Stx1-induced eIF4E phosphorylation. The Mnk1 inhibitor, CGP57380, blocked both basal and Stx-induced eIF4E phosphorylation. Interestingly, pretreatment with CGP57380 did not alter basal protein synthesis, but diminished the ability of cells to maintain translation following Stx1 challenge. Stx1 also induced hyperphosphorylation of 4E-BP1 and phosphorylation of S6Kinase; both effects were blocked by rapamycin. These data are novel observations showing that Stxs regulate multiple signal transduction pathways controlling translation in host cells, and support a role for eIF4E phosphorylation in maintaining host cell translation despite ribosomal intoxication.
Colpoys
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Division of Geographic Medicine and Infectious Diseases, 750 Washington Street Box 041, Boston, MA 02111, USA.
Cochran
B H
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Carducci
Tessa M
TM
Thorpe
C M
CM
D048868:Adaptor Proteins, Signal Transducing; D000814:Aniline Compounds / Q000494:pharmacology; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D039561:Eukaryotic Initiation Factor-4E / Q000235:genetics / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D014176:Protein Biosynthesis; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors; D011687:Purines / Q000494:pharmacology; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000235:genetics / Q000378:metabolism; D022603:Shiga Toxins / Q000378:metabolism* / Q000494:pharmacology; D020123:Sirolimus / Q000494:pharmacology; D048051:p38 Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors
D048868:Adaptor Proteins, Signal Transducing; D000814:Aniline Compounds; C466997:CGP 57380; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D039561:Eukaryotic Initiation Factor-4E; D047908:Intracellular Signaling Peptides and Proteins; D010750:Phosphoproteins; D011687:Purines; D012333:RNA, Messenger; D022603:Shiga Toxins; C491395:MKNK1 protein, human; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D048052:Mitogen-Activated Protein Kinase 3; D048051:p38 Mitogen-Activated Protein Kinases; D020123:Sirolimus