Shiga toxin 1-induced cytokine production is mediated by MAP kinase pathways and translation initiation factor eIF4E in the macrophage-like THP-1 cell line

Abstract

Upon binding to the glycolipid receptor globotriaosylceramide, Shiga toxins (Stxs) undergo retrograde transport to reach ribosomes, cleave 28S rRNA, and inhibit protein synthesis. Stxs induce the ribotoxic stress response and cytokine and chemokine expression in some cell types. Signaling mechanisms necessary for cytokine expression in the face of toxin-mediated protein synthesis inhibition are not well characterized. Stxs may regulate cytokine expression via multiple mechanisms involving increased gene transcription, mRNA transcript stabilization, and/or increased translation initiation efficiency. We show that treatment of differentiated THP-1 cells with purified Stx1 resulted in prolonged activation of c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase (MAPK) cascades, and lipopolysaccharides (LPS) rapidly triggered transient activation of JNK and p38 and prolonged activation of extracellular signal-regulated kinase cascades. Simultaneous treatment with Stx1 + LPS mediated prolonged p38 MAPK activation. Stx1 increased eukaryotic translation initiation factor 4E (eIF4E) activation by 4.3-fold within 4-6 h, and LPS or Stx1 + LPS treatment increased eIF4E activation by 7.8- and 11-fold, respectively, within 1 h. eIF4E activation required Stx1 enzymatic activity and was mediated by anisomycin, another ribotoxic stress inducer. A combination of MAPK inhibitors or a MAPK-interacting kinase 1 (Mnk1)-specific inhibitor blocked eIF4E activation by all stimulants. Mnk1 inhibition blocked the transient increase in total protein synthesis detected in Stx1-treated cells but failed to block long-term protein synthesis inhibition. The MAPK inhibitors or Mnk1 inhibitor blocked soluble interleukin (IL)-1beta and IL-8 production or release by 73-96%. These data suggest that Stxs may regulate cytokine expression in part through activation of MAPK cascades, activation of Mnk1, and phosphorylation of eIF4E.

Shiga Toxins Activate the NLRP3 Inflammasome Pathway To Promote Both Production of the Proinflammatory Cytokine Interleukin-1β and Apoptotic Cell Death

“…One of the key challenges in understanding the pathogenesis of Stx-mediated disease is deciphering the mechanisms underlying the dysregulation of pro-and anti-inflammatory responses in toxin-resistant and toxin-sensitive host cells. Stxs regulate cytokine expression at the transcriptional stage through the transcription factors NF-B, AP-1, and Egr-1 (25,26,41), as well at the posttranscriptional stage through phosphorylation of eukaryotic translational initiation factors (56). Stxs trigger a ribotoxic stress response leading to the activation of three major MAPK signaling pathways (JNK, p38, and ERK), which in turn regulate cytokine and chemokine expression in macrophage-like THP-1 cells (42,56).…”

“…Stxs regulate cytokine expression at the transcriptional stage through the transcription factors NF-B, AP-1, and Egr-1 (25,26,41), as well at the posttranscriptional stage through phosphorylation of eukaryotic translational initiation factors (56). Stxs trigger a ribotoxic stress response leading to the activation of three major MAPK signaling pathways (JNK, p38, and ERK), which in turn regulate cytokine and chemokine expression in macrophage-like THP-1 cells (42,56). Furthermore, Stx1 alters the phosphorylation status of MAPKs, leading to differential MAPK activation and cytokine and chemokine expression by induction of the dual-specificity phosphatase DUSP1 in D-THP-1 cells (42).…”

p38 Mitogen-Activated Protein Kinase Mediates Lipopolysaccharide and Tumor Necrosis Factor Alpha Induction of Shiga Toxin 2 Sensitivity in Human Umbilical Vein Endothelial Cells

“…p38 MAPK is required for Stx2 sensitization. p38 MAPK has been shown to be involved in Stx-mediated cell death in other cell types (7,24,54). To determine which phase (i.e., induction or Stx2 challenge) of the experiment the p38 inhibitors targeted, cells were treated with inhibitor before and/or after treatment with the inducer (Fig.…”

Mnk kinases in cytokine signaling and regulation of cytokine responses

“…Mnk kinases are known to mediate the production of cytokines such as IL-6 [16], IL-8[19], IL-1β [19], MCP-1 [16] which are also induced by IL-17 signaling. Therefore, Mnk kinases may play a role in mediating the biological responses to IL-17 signaling.…”

“…Additionally the presence of the Mnk inhibitor also suppressed IL-1β-stimulated TNFα release [17]. Inhibition of Mnk kinases also negatively regulates post-transcriptional regulation of IFNγ and IL-4 in activated murine NK cells [18] and blocks Shiga toxin mediated release of IL-1β and IL-8 [19]. Thus Mnk kinases play important roles in the control of immune responses and elucidating the precise mechanisms of Mnk mediated post-transcriptional regulation of cytokine production will have important therapeutic implications.…”