Toll-Like Receptor 2-Tpl2-Dependent ERK Signaling Drives Inverse Interleukin 12 Regulation in Dendritic Cells and Macrophages

Abstract

This study investigated responses to Toll-like receptor 2 (TLR2)-driven extracellular signal-related kinase (ERK) signaling in dendritic cells (DCs) versus macrophages. TLR2 signaling was induced with Pam3Cys-Ser-Lys4, and the role of ERK signaling was interrogated pharmacologically with MEK1/2 inhibitor U0126 or genetically with bone-marrow-derived macrophages or DCs from Tpl2-/- mice. We assessed cytokine production via ELISA or V-PLEX, and mRNA levels were assessed via qRT-PCR. In macrophages, blockade of ERK signaling by pharmacologic or genetic approaches inhibited IL-10 expression and increased expression of the p40 subunit shared by IL-12 and IL-23 (IL-12/23p40). In DCs, blockade of ERK signaling similarly inhibited IL-10 expression but decreased IL-12/23p40 expression, opposite to the effect of ERK signaling blockade on IL-12/23p40 in macrophages. This difference in IL-12/23p40 regulation correlated with differential expression of transcription factors cFos and IRF1, which are known to regulate IL-12 family members, including IL-12 and IL-23. Thus, the impact of ERK signaling in response to TLR2 stimulation differs between macrophages and DCs, potentially regulating their distinctive functions in the immune system. ERK-mediated suppression of IL-12/23p40 in macrophages may prevent excessive inflammation and associated tissue damage following TLR2-stimuation, while ERK-mediated induction of IL-12/23p40 in DCs may promote priming of Th1 responses. Greater understanding of the role that ERK signaling plays in different immune cell types may inform the development of host-directed therapy and optimal adjuvanticity for a number of infectious pathogens.

The S1 spike protein of SARS-CoV-2 upregulates the ERK/MAPK signaling pathway in DC-SIGN-expressing THP-1 cells

“… 25 ERK signaling is also involved in the production of tumor necrosis factor α and interleukin-10 in myeloid dendritic cells. 18 In addition, Groft and co-workers 26 reported that the toll-like receptor 2 transduces ERK signaling and mediates the induction of interleukin-12, which may promote the priming of Th1 responses in dendritic cells. Knowledge of DC-SIGN-mediated ERK signaling is currently accumulating, 27 although these reports suggest that ERK signaling has an essential role in the immune responses of dendritic cells.…”

MEK1/2 inhibition decreases pro-inflammatory responses in macrophages from people with cystic fibrosis and mitigates severity of illness in experimental murine methicillin-resistant Staphylococcus aureus infection

“…While reduction of pro-inflammatory mediators may limit inflammation associated tissue damage, there was also a moderate reduction in IL-10, which has anti-inflammatory effects. It was previously demonstrated that murine macrophages treated with the MEK1/2 inhibitor U0126 resulted in a decrease in Il10 expression following Pam3CSK4 stimulation with a corresponding increase in Il12p40 (Il12b) expression ( Groft et al., 2020 ). We did not observe significant reduction of Il12a or Il12b expression in macrophages treated with MEK1/2 inhibitors following either LPS, Pam3CSK4, or FSL1 stimuli, with modest trends towards increased expression.…”

IFITM3 regulates virus-induced inflammatory cytokine production by titrating Nogo-B orchestration of TLR responses

“…These differences may reflect the different cell types studies. Indeed, signalling pathways downstream of TLR2 have previously been observed to be divergent in DCs in macrophages (Groft et al, 2020), implying differential regulation of TLR-induced cytokine responses in different myeloid cells. In support of this hypothesis, Ifitm3 has no impact on MCMV-induced cytokine responses by murine macrophages (Stacey et al, 2017).…”