title: Shiga toxin 1-induced proinflammatory cytokine production is regulated by the phosphatidylinositol 3-kinase/Akt/mammalian target of rapamycin signaling pathway.
abstract: Shiga toxin 1 (Stx1) transiently increases the expression of proinflammatory cytokines by macrophage-like THP-1 cells in vitro. Increased cytokine production is partly due to activation of the translation initiation factor eIF4E through a mitogen-activated protein kinase (MAPK)- and Mnk1-dependent pathway. eIF4E availability for translation initiation is regulated by association with eIF4E binding proteins (4E-BP). In this study, we showed that Stx1 transiently induced 4E-BP hyperphosphorylation, which may release eIF4E for translation initiation. Phosphorylation of 4E-BP at priming sites T37 and T46 was not altered by Stx1 but was transiently increased at S65, concomitant with increased cytokine expression. Using kinase inhibitors, we showed that 4E-BP phosphorylation was dependent on phosphatidylinositol 3-kinase (PI3K), Akt, and mammalian target of rapamycin (mTOR) activation but did not require MAPKs. Stx1 treatment resulted in increased levels of cytosolic Ca(2+). PI3K and Akt activation led to the phosphorylation and inactivation of the positive cytokine regulator glycogen synthase kinase 3alpha/beta (GSK-3alpha/beta). PI3K, Akt, and mTOR inhibitors and small interfering RNA knockdown of Akt expression all increased, whereas a GSK-3alpha/beta inhibitor decreased, Stx1-induced soluble tumor necrosis factor alpha and interleukin-1beta production. Overall, these findings suggest that despite transient activation of 4E-BP, the PI3K/Akt/mTOR pathway negatively influences cytokine induction by inactivating the positive regulator GSK-3alpha/beta.
authors: Department of Microbial and Molecular Pathogenesis, College of Medicine, Texas A&M University System Health Science Center, College Station, Texas 77843-1114, USA.
authors: Rama P
authors: RP
authors: Cherla
authors: Sang-Yun
authors: SY
authors: Lee
authors: Renée A
authors: RA
authors: Mulder
authors: Moo-Seung
authors: MS
authors: Lee
authors: Vernon L
authors: VL
authors: Tesh
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism; D018797:Cell Cycle Proteins; D045744:Cell Line, Tumor; D016207:Cytokines / Q000096:biosynthesis*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D020935:MAP Kinase Signaling System; D051379:Mice; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011494:Protein Kinases / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D022622:Shiga Toxin 1 / Q000633:toxicity*; D015398:Signal Transduction / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002118:Calcium; D018797:Cell Cycle Proteins; D016207:Cytokines; D038362:Glycogen Synthase Kinase 3; D000071679:Glycogen Synthase Kinase 3 beta; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D011494:Protein Kinases; D051057:Proto-Oncogene Proteins c-akt; D022622:Shiga Toxin 1; D058570:TOR Serine-Threonine Kinases; C087000:EIF4EBP1 protein, human; C546842:MTOR protein, human; C546843:mTOR protein, mouse; C448021:glycogen synthase kinase 3 alpha