Cross-regulation of cytokine signalling: pro-inflammatory cytokines restrict IL-6 signalling through receptor internalisation and degradation

Abstract

The inflammatory response involves a complex interplay of different cytokines which act in an auto- or paracrine manner to induce the so-called acute phase response. Cytokines are known to crosstalk on multiple levels, for instance by regulating the mRNA stability of targeted cytokines through activation of the p38-MAPK pathway. In our study we discovered a new mechanism that answers the long-standing question how pro-inflammatory cytokines and environmental stress restrict immediate signalling of interleukin (IL)-6-type cytokines. We show that p38, activated by IL-1β, TNFα or environmental stress, impairs IL-6-induced JAK/STAT signalling through phosphorylation of the common cytokine receptor subunit gp130 and its subsequent internalisation and degradation. We identify MK2 as the kinase that phosphorylates serine 782 in the cytoplasmic part of gp130. Consequently, inhibition of p38 or MK2, deletion of MK2 or mutation of crucial amino acids within the MK2 target site or the di-leucine internalisation motif blocks receptor depletion and restores IL-6-dependent STAT activation as well as gene induction. Hence, a novel negative crosstalk mechanism for cytokine signalling is described, where cytokine receptor turnover is regulated in trans by pro-inflammatory cytokines and stress stimuli to coordinate the inflammatory response.

Discovery of a Novel Orally Active Small-Molecule gp130 Inhibitor for the Treatment of Ovarian Cancer

“…The role of phospho-S782 in gp130 was first documented in 2000 to downregulate gp130 cell surface expression (5). Recently, it has been reported that phospho-S782-associated downregulation of gp130 cell surface expression is mediated by immediate internalization (46). Indeed, phosphorylation of many transmembrane receptors at Ser/Thr residues is commonly associated with the negative modulation of receptor activity (47).…”

“…8). SC144 binding induces conformational changes and activity loss in the cell surface-bound gp130 receptor, exposing the Ser782 residue to protein kinases such as CaMKII, CaMKIV, and MK2 (6,46). The decrease in gp130 activity leads to the inactivation of downstream signaling pathways involving Stat3 and Akt.…”

The p38‐Mediated Rapid Down‐Regulation of Cell Surface gp130 Expression Impairs Interleukin‐6 Signaling in the Synovial Fluid of Juvenile Idiopathic Arthritis Patients

“…Stress-induced p38 MAPK has been highlighted as a key player in previous studies investigating the cross-talk regulation of IL-6 signaling (8,10,18,37). Furthermore, p38 plays a crucial role in the induction and maintenance of chronic inflammation and is strongly activated in inflammatory arthritis (38).…”

“…In hepatocytes, the internalization of gp130 in response to p38-inducing stimuli was found to require phosphorylation of serine residue 782 in the cytoplasmic tail, which is proximal to the di-leucine internalization motif (10). In primary monocytes, stimulation with IL-1␤ promoted the phosphorylation of gp130 serine 782 ( Figure 6A), indicating that this residue may act as a stress sensor not only in hepatocytes, but also in monocytes.…”

“…More recently, it has been shown that proinflammatory cytokines, such as IL-1␤, TNF␣, and lipopolysaccharide (LPS), rapidly inhibit IL-6 signaling through a SOCS-3-independent mechanism that instead involves p38 MAPK (8,9). In hepatocytes, p38-dependent activation of the downstream MAPK leads to the phosphorylation of gp130 on serine residue 782, which is located close to the dileucine internalization motif, promoting the internalization and degradation of the receptor (10). In inflamed joints, where many different cytokines act together and the biologic outcome depends critically on the ability of a specific cell type to integrate the diverse signals, cytokine cross-talk can be particularly important.…”