CD28 Individual Signaling Up-regulates Human IL-17A Expression by Promoting the Recruitment of RelA/NF-κB and STAT3 Transcription Factors on the Proximal Promoter.

Martina Kunkl,Loretta Tuosto,Silvana Caristi,Emanuele Monteleone,Nicla Porciello,Stefano Arcieri,Marta Mastrogiovanni

doi:10.3389/fimmu.2019.00864

Abstract

CD28 is an important co-stimulatory receptor for T lymphocytes that, in humans, delivers TCR-independent signal leading to the up-regulation of pro-inflammatory cytokines. We have recently reported that CD28 autonomous signaling induces the expression of IL-17A in peripheral CD4+ T lymphocytes from healthy donors, multiple sclerosis, and type 1 diabetes patients. Due to the relevance of IL-17A in the pathophysiology of several inflammatory and autoimmune diseases, we characterized the mechanisms and signaling mediators responsible for CD28-induced IL-17A expression. Here we show that CD28-mediated up-regulation of IL-17A gene expression depends on RelA/NF-κB and IL-6-associated STAT3 transcriptions factors. In particular, we found that CD28-activated RelA/NF-κB induces the expression of IL-6 that, in a positive feedback loop, mediates the activation and nuclear translocation of tyrosine phosphorylated STAT3 (pSTAT3). pSTAT3 in turn cooperates with RelA/NF-κB by binding specific sequences within the proximal promoter of human IL-17A gene, thus inducing its expression. Finally, by using specific inhibitory drugs, we also identified class 1A phosphatidylinositol 3-kinase (PI3K) as a critical upstream regulator of CD28-mediated RelA/NF-κB and STAT3 recruitments and trans-activation of IL-17A promoter. Our findings reveal a novel mechanism by which human CD28 may amplify IL-17A expression in human T lymphocytes and provide biological bases for immunotherapeutic approaches targeting CD28-associated class 1A PI3K to dampen IL-17A-mediated inflammatory response in autoimmune/inflammatory disorders.

Highlights

IL-17-producing cells constitute a pro-inflammatory Th17 cell subset that plays critical roles in adapting immune response against extracellular pathogens and, more importantly, in the pathophysiology of several inflammatory and autoimmune diseases [1,2,3]
In order to better characterize the molecular mechanisms of CD28-mediated IL-17A expression, we performed a detailed kinetic analysis of IL-17A gene expression and secretion by stimulating human CD4+ T cells from healthy blood (HD) with an agonistic anti-CD28 Ab (CD28.2) that has been described to bind the same epitope recognized by B7 molecules [48]
As we have previously observed for other pro-inflammatory cytokines [33], CD28-induced IL17A expression was not related to the preferential stimulation of effector/memory T cells, since no significant differences in IL-17A gene expression were observed upon stimulation of naïve (CD45RA, Figures S1A,S1C) or effector/memory (CD45RO, Figures S1B,S1C) CD4+ T cells with anti-CD28 Abs (Figure S1D)

Summary

Introduction

IL-17-producing cells constitute a pro-inflammatory Th17 cell subset that plays critical roles in adapting immune response against extracellular pathogens and, more importantly, in the pathophysiology of several inflammatory and autoimmune diseases [1,2,3]. The hallmark of Th17 cells is the production of the pro-inflammatory cytokines, IL-17A-F [4, 5]. The most reliable RORC [10], cytokines, such as IL-6, TGFβ, IL-21, IL-1β, IL-23, and associated signaling mediators have been described to promote IL-17 expression and Th17 cell differentiation in both human and mouse [11,12,13,14,15]. While the role of cytokines and associated signaling mediators regulating Th17 differentiation and IL-17 expression has been better defined in mouse [16,17,18,19,20], in humans is still controversial [14, 21, 22]. Key co-stimulatory molecules regulating IL-17 expression are continuingly to be identified and may be useful for the development of new antigen non-specific immunosuppressive therapies for immune based diseases

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Conclusion