Blocking the janus-activated kinase pathway reduces tumor necrosis factor alpha-induced interleukin-18 bioactivity by caspase-1 inhibition.
BACKGROUND
Our objective was to examine the role of the janus-activated kinase (JAK) pathway in the modulation of tumor necrosis factor-α (TNF)-induced-IL-18 bioactivity by reduction of caspase-1 function.


METHODS
Caspase-1 expression in rheumatoid arthritis (RA) synovial fibroblasts treated with TNF was assessed by qRT-PCR and Western blot. Interleukin (IL)-18 was assessed by enzyme-linked immunosorbent assay (ELISA) in cell lysates and conditioned media and detected by immunofluorescence (IF) staining in RA synovial fibroblasts. The critical pathways for TNF-induced caspase-1 expression were determined by using chemical inhibitors of signaling followed by TNF stimulation. IL-18 bioactivity was assessed using human myelomonocytic KG-1 cells.


RESULTS
TNF induced RA synovial fibroblast caspase-1 expression at the protein level in a time-dependant manner (P < 0.05). Blocking the JAK pathway reduced TNF-induced-caspase-1 expression at the transcriptional and protein levels by approximately 60% and 40%, respectively (P < 0.05). Blocking the JAK pathway reduced TNF-induced-caspase-1 expression at the transcriptional, protein, and activity levels by approximately 60%, 40%, and 53%, respectively (P < 0.05). We then confirmed by IF that TNF-induced IL-18 and investigated roles of the ERK1/2 and JAK pathways. Blocking the JAK pathway, TNF induced intracytoplasmic granular IL-18 expression suggesting a defect of caspase-1. Finally, blocking the JAK pathway, we observed a reduction of IL-18 bioactivity by 52% in RA synovial fibroblasts (P < 0.05).


CONCLUSIONS
These results provide a new way to regulate TNF-induced-IL-18 bioactivity by blocking capase-1. These data present a novel role for JAK inhibition in RA patients and emphasize JAK inhibition use as a new therapeutic option in RA management.
Hubert
H
Marotte
Pei-Suen
PS
Tsou
Tatiana
T
Fedorova
Adam J
AJ
Pinney
Benjamin
B
Lewis
Alisa E
AE
Koch
D001172:Arthritis, Rheumatoid / Q000276:immunology* / Q000378:metabolism; D015153:Blotting, Western; D020170:Caspase 1 / Q000276:immunology*; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D005347:Fibroblasts / Q000276:immunology / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D006801:Humans; D020382:Interleukin-18 / Q000276:immunology* / Q000378:metabolism; D053612:Janus Kinases / Q000276:immunology* / Q000378:metabolism; D060888:Real-Time Polymerase Chain Reaction; D015398:Signal Transduction / Q000276:immunology; D013583:Synovial Membrane / Q000276:immunology / Q000378:metabolism; D014409:Tumor Necrosis Factor-alpha / Q000276:immunology* / Q000378:metabolism
D020382:Interleukin-18; D014409:Tumor Necrosis Factor-alpha; D053612:Janus Kinases; D020170:Caspase 1