Background Rheumatoid arthritis (RA) is the most common inflammatory arthritis. B and T cells play a key role in the RA pathophysiology. RasGRP is a member of the CDC25 family of Ras guanyl nucleotide exchange factors. RasGRP1 is expressed in T and B cells whereas RasGRP3 is only expressed in B cells. In previous studies, we have shown that RasGRP3 gene expression level significantly decreased in peripheral blood mononuclear cells from RA patients responders to adalimumab and etanercept (anti-TNFa drugs), leading to the question of TNFα involvement in RasGRP1 and RasGRP3 pathways.
Objectives To study TNFα effects on RasGRP1 and RasGRP3 expression levels in vitro.
Materials and methods We measured, by qRT-PCR and western-blot, RasGRP1 and RasGRP3 expression levels in B and T cells isolated from buffy coat. In each condition, cells were cultured with or without TNFα for 24 or 48 h. Cell proliferation was evaluated by [3H] thymidine incorporation. To investigate the TNFα implication on signalling pathways, MAPK and apoptosis protein arrays were used.
Results In B cells, TNFα induced an increase of RasGRP1 and RasGRP3 gene expression levels without effect on B cells proliferation and BCR pathway phosphorylations, but apoptotic pathways were inhibited. In T cells, TNFα increased RasGRP1 gene expression level but RasGRP1 protein expression level decreased, inhibiting T cell proliferation and TCR pathway phosphorylations.
Conclusions This study suggests a link, never described previously, between RasGRP1 or RasGRP3 and the TNFa effects on T and B cells. While the response to anti-TNFα treatments in RA patients modulates RasGRP3 gene expression, TNFα inhibits RasGRP1 protein expression leading to TCR pathway inhibition, in vitro, in pathophysiological condition. The better understanding of TNFα effects on RasGRP proteins could permit a better understanding of the mechanisms of action of TNFα blocking agents on T and B cells.
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