Determining role of 14-3-3zeta in IL-17A signaling

Summary Interleukin-17 (IL-17), a pro-inflammatory cytokine, is pathogenic in autoimmune diseases such as Inflammatory Arthritis (IA). IA affects more than 1% of the worldwide population and remains incurable to date1. Ectopic IL17A expression in mice induces IA phenotype and provides a model to study mechanisms2. Activation of IL-17A receptor (IL-17R) recruits a signaling complex consisting of Act1 and TRAFs (Tumor Necrosis Factor Receptor Associated Factors). Activation of TRAF6 or TRAF2/5 results in transcriptional (IL6) and post- transcriptional (CXCL1) outcomes of IL-17A cytokine. TRAFs often interact with each other and influence signaling outcomes. The crosstalk between the TRAF6 and TRAF2/5 branches in IL-17A signaling remains unknown. Our recent PNAS publications showed that 14-3-3z is a novel component of IL-17R signaling and suppresses IA. In IL-17A signaling, 14-3-3z connects the two TRAF branches, inhibits TRAF5 but promotes TRAF6. There are two motifs on 14-3-3z that interact and show specificity to TRAF5 and TRAF6 binding. We also showed that TRAF5 inhibits TRAF6-dependent IL-17A signaling. Our new preliminary data show that 14- 3-3z modifies TRAFs and their interactions with other cellular proteins, thus providing clues to its mechanism. Our long-term goal is to understand how 14-3-3z bridges TRAFs in IL-17R signaling and diseases. We hypothesize that “14-3-3z has a dual role in IL-17 signaling by executing the opposing functions of TRAFs, leading to the prevention of IA.” We propose to investigate the molecular mechanisms and physiological relevance of the 14-3-3z-TRAF axis in regulating IL-17R signaling and inflammatory arthritis with three specific aims. The first two aims will examine how 14-3-3z regulates TRAF5 and TRAF6 activity, connects two branches, and gain an in-depth understanding of 14-3-3z’s function in IL-17R signaling. In the third aim, we will examine the physiological relevance of the 14-3-3z-TRAF axis using an innovative IL-17A gene transfer model to study 14-3-3z role in chronic IL-17A and IA pathogenesis using 14-3-3z knockout animals. Successful completion of this proposal will provide mechanistic insight into how 14-3-3z modifies TRAF proteins and their activity, regulates IL-17R signaling, and suppresses IA. This study is innovative because by studying 14-3-3z’s role in TRAF biology, we examine the molecular basis of a novel fundamental immune regulatory axis in IL-17R signaling and IA. Our study is significant because understanding 14-3-3z action on TRAFs advances our fundamental knowledge of protein biochemistry, immunology, IL-17R signaling, IA pathogenesis, and other autoimmune diseases. IA is a challenging disease with limited therapeutic options; therefore, a deeper understanding of IA pathogenesis is desired. And, as TRAFs play a critical role in many receptor signaling, the implications of 14-3-3z functions go beyond IL-17R signaling to many other autoimmune and infectious diseases.