Beta Interferon Production Is Regulated by p38 Mitogen-Activated Protein Kinase in Macrophages via both MSK1/2- and Tristetraprolin-Dependent Pathways.

Autocrine or paracrine signaling by beta interferon (IFN-ß) is essential for many of the responses of macrophages to pathogen-associated molecular patterns. This feedback loop contributes to pathological responses to infectious agents and is therefore tightly regulated. We demonstrate here that macrophage expression of IFN-ß is negatively regulated by mitogen- and stress-activated kinases 1 and 2 (MSK1/2). Lipopolysaccharide (LPS)-induced expression of IFN-ß was elevated in both MSK1/2 knockout mice and macrophages. Although MSK1 and -2 promote the expression of the anti-inflammatory cytokine interleukin 10, it did not strongly contribute to the ability of MSKs to regulate IFN-ß expression. Instead, MSK1 and -2 inhibit IFN-ß expression via the induction of dual-specificity phosphatase 1 (DUSP1), which dephosphorylates and inactivates the mitogen-activated protein kinases p38 and Jun N-terminal protein kinase (JNK). Prolonged LPS-induced activation of p38 and JNK, phosphorylation of downstream transcription factors, and overexpression of IFN-ß mRNA and protein were similar in MSK1/2 and DUSP1 knockout macrophages. Two distinct mechanisms were implicated in the overexpression of IFN-ß: first, JNK-mediated activation of c-jun, which binds to the IFN-ß promoter, and second, p38-mediated inactivation of the mRNA-destabilizing factor tristetraprolin, which we show is able to target the IFN-ß mRNA.

Dimethyl fumarate blocks pro-inflammatory cytokine production via inhibition of TLR induced M1 and K63 ubiquitin chain formation.

Dimethyl fumarate (DMF) possesses anti-inflammatory properties and is approved for the treatment of psoriasis and multiple sclerosis. While clinically effective, its molecular target has remained elusive - although it is known to activate anti-oxidant pathways. We find that DMF inhibits pro-inflammatory cytokine production in response to TLR agonists independently of the Nrf2-Keap1 anti-oxidant pathway. Instead we show that DMF can inhibit the E2 conjugating enzymes involved in K63 and M1 polyubiquitin chain formation both in vitro and in cells. The formation of K63 and M1 chains is required to link TLR activation to downstream signaling, and consistent with the block in K63 and/or M1 chain formation, DMF inhibits NFκB and ERK1/2 activation, resulting in a loss of pro-inflammatory cytokine production. Together these results reveal a new molecular target for DMF and show that a clinically approved drug inhibits M1 and K63 chain formation in TLR induced signaling complexes. Selective targeting of E2s may therefore be a viable strategy for autoimmunity.