Arthritis & Rheumatism, Volume 62,
November 2010 Abstract Supplement
Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Atlanta, Georgia November 6-11, 2010.
Toll-Like Receptor Signals Modify the ER Stress Response.
Goodall1, Jane C., McNeill2, Louise, Ellis2, Lou, Gaston2, J. Hill
During cellular stress, the decrease in protein translation caused by eIF2a phosphorylation reduces protein load in the endoplasmic reticulum (ER) which allows the cell a window of time to instigate a program of gene expression coined as the unfolded protein response (UPR). To allow the recovery of protein translation, GADD34 is activated in a negative feedback loop which dephosphorylates eIF2a and enables more efficient protein translation and recovery from cellular stress. We have previously shown that ER stress signals are induced following bacterial infection and that these signals synergise with Toll-like-receptor (TLR) signals to enhance the expression of cytokines such as IL-23.
The aim of this study was to determine if TLR signals have a reciprocal activity and modify the ER stress response and in particular the expression of GADD34, the molecule involved in translation recovery from ER stress. Monocyte derived dendritic cells (mDC) were subjected to ER stress using thapsigargin (TP) or tunicamycin (TM) in the presence or absence of different pattern recognition receptor (PRR) agonists. The expression of GADD34 mRNA and protein was induced by the ER stress stimuli, but was substantially enhanced by costimulation with LPS (TLR4), Curdlan (dectin 1) or peptidoglycan (TLR2 and NOD2) agonists.
MyD88 knockdown in the monocyte cell line THP-1, abrogated the ability of LPS to enhance GADD34 expression induced by ER stress stimuli, this effect was not seen in THP-1 cells expressing a control shRNA. This suggests that Myd88 dependent signals are required for LPS upregulation of GADD34 in the presence of ER stimulation. Using specific inhibitors for defined signalling pathways we identified that upregulation of GADD34 by LPS was dependent on the activity of p38Map kinase and ERK but not JNK and NF-kB. These inhibitors did not inhibit the upregulation of GADD34 by ER stress stimuli alone, suggesting that ER stress and LPS stimuli provide independent signals that synergise to enhance GADD34 expression.
ER stress and substantial upregulation of GADD34 expression was detected in mDC and THP-1 following infection with the intracellular bacterium, Chlamydia trachomatis (CT). To determine if the upregulation of GADD34 following intracellular bacterial infection was dependent on MyD88, THP-1 cells expressing MyD88 or a control shRNA were infected with CT and GADD34 expression was analysed. The upregulation of GADD34 was substantially reduced in THP-1 cells expressing MyD88 shRNA suggesting that MyD88 dependent TLR signals were required for this effect.
These data show that the regulation of protein translation has not only the potential to be modulated via ER stress but also via the stimulation of PRR pathways. This may have significant implications for the expression of pro-inflammatory or regulatory cytokines. We hypothesize that changes in GADD34 expression induced by TLRs will contribute significantly to the ability of myeloid cells to secrete pro-inflammatory cytokines in response to bacterial infection.
To cite this abstract, please use the following information:
Goodall, Jane C., McNeill, Louise, Ellis, Lou, Gaston, J. Hill; Toll-Like Receptor Signals Modify the ER Stress Response. [abstract]. Arthritis Rheum 2010;62 Suppl 10 :1424