The Role of TTP Phosphorylation in the Regulation of Inflammatory Cytokine Production by MK2/3

Abstract

Tristetraprolin (TTP) is an RNA-binding protein and an essential factor of posttranscriptional repression of cytokine biosynthesis in macrophages. Its activity is temporally inhibited by LPS-induced p38 MAPK /MAPKAPK2/3-mediated phosphorylation, leading to a rapid increase in cytokine expression. We compared TTP expression and cytokine production in mouse bone marrow-derived macrophages of different genotypes: wild type, MAPKAP kinase 2 (MK2) deletion (MK2 knockout [KO]), MK2/3 double deletion (MK2/3 double KO [DKO]), TTP-S52A-S178A (TTPaa) knock-in, as well as combined MK2 KO/TTPaa and MK2/3 DKO/TTPaa. The comparisons reveal that MK2/3 are the only LPS-induced kinases for S52 and S178 of TTP and the role of MK2 and MK3 in the regulation of TNF biosynthesis is not restricted to phosphorylation of TTP at S52/S178 but includes independent processes, which could involve other TTP phosphorylations (such as S316) or other substrates of MK2/3 or p38 MAPK. Furthermore, we found differences in the dependence of various cytokines on the cooperation between MK2/3 deletion and TTP mutation ex vivo. In the cecal ligation and puncture model of systemic inflammation, a dramatic decrease of cytokine production in MK2/3 DKO, TTPaa, and DKO/TTPaa mice compared with wild-type animals is observed, thus confirming the role of the MK2/3/TTP signaling axis in cytokine production also in vivo. These findings improve our understanding of this signaling axis and could be of future relevance in the treatment of inflammation.

Context-Dependent IL-1 mRNA-Destabilization by TTP Prevents Dysregulation of Immune Homeostasis Under Steady State Conditions

“…We then asked whether the differences in TTP expression are accompanied by changes in phosphorylated (i.e., activated) MAPKAPK2 (MK2), a kinase known as important regulator of TTP expression. MK2 phosphorylates TTP at least on two residues (S52 and T178 in the mouse TTP) causing its stabilization and thereby increased expression ( 38 , 39 ). In agreement, MK2 was phosphorylated in BMDCs but not in BMDMs prior to LPS treatment ( Supplemental Figure 1D ).…”

“…Cell type-specific post-translational modification of TTP may also contribute to the context-dependent function of TTP. Recent studies revealed that TTP contains a large number of phosphorylation sites with so far unexplained biological functions ( 39 , 49 ).…”

The δ-Opioid Receptor Differentially Regulates MAPKs and Anti-inflammatory Cytokines in Rat Kidney Epithelial Cells Under Hypoxia

“…A large number of experimental data have confirmed that MAPK signal pathways are closely related to the regulation of anti-inflammatory cytokines, such as Bcl-6, TTP, and IL-10 (Pantoja-Escobar et al, 2019;Ronkina et al, 2019;Zhang et al, 2019) although there are still controversies with some showing an inhibitory effect of MAPKs on certain anti-inflammatory cytokines in BV2 cell line (Lee et al, 2015) and others having different opinions in bone marrow cells and microglial cells (Chi et al, 2006;Correa et al, 2010). In the kidney or renal cells, however, there is a lack of information on the relationship between MAPKs and anti-inflammatory cytokines in hypoxic condition.…”

Tristetraprolin Overexpression in Non-hematopoietic Cells Protects Against Acute Lung Injury in Mice

“…A number of studies have shown that TTP is phosphorylated at multiple sites by p38-regulated kinase MAPK-activated protein kinase 2 (MAPKAPK2) and that TTP activity is significantly affected by its phosphorylation status ( 32 – 34 ). TTP phosphorylation has been shown to result in reduced TTP activity/reduced binding of TTP to AREs, thus resulting in stabilization of its target mRNAs ( 35 ).…”