Inflammatory but not mitogenic contexts prime synovial fibroblasts for compensatory signaling responses to p38 inhibition

Abstract

Rheumatoid arthritis (RA) is a chronic inflammatory disorder that causes joint pain, swelling, and loss of function. Development of effective new drugs has proven challenging, in part because of the complexities and interconnected nature of intracellular signaling networks, which complicate the effects of pharmacological interventions. Here, we characterized the signaling pathways that are activated in RA and evaluated the multivariate effects of targeted inhibitors. Synovial fluids from RA patients activated the kinase signaling pathways JAK, JNK, p38, and MEK in synovial fibroblasts (SFs), a stromal cell type that promotes RA progression. Kinase inhibitors enhanced signaling of “off-target” pathways in a manner dependent on stimulatory context. For example, p38 inhibitors, which have been widely explored in clinical trials for RA, resulted in undesirable increases in nuclear factor κB (NFκB), JNK, and MEK signaling in SFs in inflammatory, but not mitogenic, contexts. CREB, a transcription factor that functions in part within a negative feedback loop in MAPK signaling, emerged as a key regulator of this context-dependence. CREB activation was induced predominately by p38 in response to inflammatory stimuli but by MEK in response to mitogenic stimuli; the effects of drugs targeting p38 or MEK were therefore markedly different in SFs cultured in mitogenic or inflammatory conditions. Together these findings illustrate how stimulatory context can alter pathway cross-talk even for a fixed network topology, suggest cross-talk by p38 in inflammatory contexts limited the benefit of p38 inhibitors in RA, and furthermore demonstrate the need for careful consideration of p38-targeted drugs in inflammation-related disorders.

Cell-to-Cell Heterogeneity in p38-Mediated Cross-Inhibition of JNK Causes Stochastic Cell Death

“…While most of these studies identified single, predominant mechanisms that were responsible for this crosstalk in specific cell types and under specific conditions, our quantitative measurements enabled us to quantitate the contribution of post-translational and transcriptional cross-inhibition in each response to various inflammatory and stress stimuli (Figure 2). Recently, Lauffenburger and his colleagues quantitatively demonstrated that p38 is a crucial factor for negative crosstalk to the JNK pathway under various conditions in synovial fibroblasts (Jones et al, 2018). The cross-inhibition by p38 generated cell-to-cell variability in JNK activity under all tested conditions, suggesting that this is a common mechanism underlying JNK and p38 signaling ( Figure 3C).…”

Critical role of IL‐1α in IL‐1β‐induced inflammatory responses: cooperation with NF‐κBp65 in transcriptional regulation

“…Although our results confirmed the mediatory role of the NF-kB pathway, we found that the inhibition of other MAPK pathways, specifically p38-MAPK, further enhanced IL-1a and IL-1b expression in RASFs. This is particularly of interest because a recent study by Jones et al (27) examined the potential reasons for the failure of p38 inhibitors in clinical trials for RA. The authors observed that the inhibition of p38 further activated "off-target" pathways, including NF-kB, JNK, and ERK, triggering a rapid induction of inflammation similar to that observed in cytokine-stimulated RASFs.…”

Substrate-based kinase activity inference identifies MK2 as driver of colitis

“…Because the p38 pathway plays an important role in inflammation, there was hope that inhibitors would show efficacy in the clinic. Nevertheless, systemic p38 inhibition in patients is associated with unacceptable side effects and tachyphylaxis [4,47], possibly due to feedback activation of NF-κB, JNK, and MEK signaling [48]. This limitation had led to the search for inhibitors that target other part of the p38 signaling pathway.…”