Pak2-mediated phosphorylation promotes RORγt ubiquitination and inhibits colonic inflammation

Abstract

Abstract Dysregulated Interleukin (IL)-17 expression and its downstream signaling is strongly linked to inflammatory bowel diseases (IBD). However, the molecular mechanisms by which the function of RORγt, the transcription factor of IL-17, is regulated remains elusive, which is absolutely necessary to develop advanced strategies to inhibit IL-17-mediated inflammation. By mass spectrometry-based approach, we have identified that Pak2, a Ser/Thr kinase, directly associates with RORγt. Pak2 recognizes a conserved KRLS motif within RORγt and phosphorylated the Serine (S) 316 within this motif. Genetic deletion of Pak2 in Th17 cells resulted in reduced RORγt phosphorylation, increased IL-17 expression and severe colitis upon adoptive transfer to Rag1 −/−mice. Similarly, reconstitution of RORγt-S316A mutant in Rorc −/−Th17 cells resulted in enhanced IL-17 expression and colitis severity. Mechanistically, we demonstrate that Pak2-mediated phosphorylation causes a conformational change resulting in exposure of the ubiquitin ligase Itch interacting PPLY motif and degradation of RORγt. Thus, we have uncovered a novel mechanism by which the activity of RORγt is regulated that can be exploited therapeutically. This work was supported by funds from the National Institutes of Health (R01-DK115668 and R01-AI155786) and Cancer Prevention Research Institute of Texas (RP160577 and RP190527), a translational pilot project grant from the Harold C. Simmons Comprehensive Cancer Center, UT Southwestern Medical Center (23001045) to K.V., and R01-DK117001 to K.V. and A.L.T.