IL-17A is a therapeutic target in many autoimmune diseases. Most nonhematopoietic cells express IL-17A receptors and respond to extracellular IL-17A by inducing proinflammatory cytokines. The IL-17A signal transduction triggers two broad, TRAF6- and TRAF5-dependent, intracellular signaling pathways to produce representative cytokines (IL-6) and chemokines (CXCL-1), respectively. Our limited understanding of the cross-talk between these two branches has generated a crucial gap of knowledge, leading to therapeutics indiscriminately blocking IL-17A and global inhibition of its target genes. In previous work, we discovered an elevated expression of 14-3-3 proteins in inflammatory aortic disease, a rare human autoimmune disorder with increased levels of IL-17A. Here we report that 14-3-3ζ is essential for IL-17 signaling by differentially regulating the signal-induced IL-6 and CXCL-1. Using genetically manipulated human and mouse cells, and ex vivo and in vivo rat models, we uncovered a function of 14-3-3ζ. As a part of the molecular mechanism, we show that 14-3-3ζ interacts with several TRAF proteins; in particular, its interaction with TRAF5 and TRAF6 is increased in the presence of IL-17A. In contrast to TRAF6, we found TRAF5 to be an endogenous suppressor of IL-17A–induced IL-6 production, an effect countered by 14-3-3ζ. Furthermore, we observed that 14-3-3ζ interaction with TRAF proteins is required for the IL-17A–induced IL-6 levels. Together, our results show that 14-3-3ζ is an essential component of IL-17A signaling and IL-6 production, an effect that is suppressed by TRAF5. To the best of our knowledge, this report of the 14-3-3ζ-TRAF5 axis, which differentially regulates IL-17A–induced IL-6 and CXCL-1 production, is unique.

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Interleukin (IL)-17A is an important cytokine associated with autoimmune diseases and host defense. The mechanism of its action depends upon its ability to induce pro-inflammatory cytokines, e.g., IL-6, IL-8 as well as anti-fungal genes, e.g., b-defensin, CCL-20, CXCL-1. Most non-hematopoietic cells express IL-17 receptors and respond to IL-17A. Several regulators of each of the two independent arms of IL-17A signaling- gene induction and mRNA stabilization of inflammatory genes, are known; however, there is limited knowledge of how two arms influence each other. We previously reported the increased presence of 14-3-3 proteins in the inflamed aortic tissue, an autoimmune disease with increased IL-17A levels. This study led us to investigate the role of 14-3-3zeta(z) in the IL-17A signaling. By genetic manipulations in human and mouse cells, we observed that 14-3-3z is required for the IL-17A-induced IL-6 production by fibroblast and epithelial cells. Contrary to IL-6, 14-3-3z suppressed the CXCL-1 production in response to IL-17A. In the absence of 14-3-3z, IL-17A induction of anti-fungal genes (b-defensin) was completely suppressed. The mechanism of 14-3-3z action depends upon its interaction with Traf/Act1/IL-17R signaling. Our results show that 14-3-3z is an essential component of IL-17A signaling and its interaction with receptor complex provides a new model of regulating the output in IL-17A effector cells. To the best of our knowledge, this is the first report of the 14-3-3z role in regulating IL-17A induced outputs.

Increased amount of autoantibodies in human sera are the hallmark of autoimmune diseases (Wang et al., 2015). In case of known antigen, detection of autoantibodies is done using laboratory based methods. However, in most autoimmune diseases, knowledge of self-antigen is still vague. We have developed an ELISA-based quantitative assay to detect the presence of autoantibodies as well as to measure the circulating autoantibodies in the sera of patients suffering from large vessel vasculitis (LVV), an autoimmune disease (Chakravarti et al., 2015). Using this assay, we detected the increase in anti-aortic antibodies in LVV patient's sera. We have further verified the results by independent biochemical techniques and found the specificity to be > 94% (Chakravarti et al., 2015). This method can be uniquely modified to suit any autoimmune, in particular organ specific, disease and thus has wider applications in the detection and quantification of autoantibodies.