Complementary Phosphoproteomic Approaches Link IL-23R Downstream Signaling with Metabolic Adaptation in Lymphocytes

Interleukin (IL)-23 mediated signal transduction represents a major molecular mechanism underlying the pathology of inflammatory bowel disease (IBD), Crohn's disease (CD) and ulcerative colitis (UC). In addition, emerging evidence supports the role of IL-23-driven Th17 cells in inflammation. Components of the IL-23 signalling pathway, such as IL23R, JAK2 and STAT3, have been characterised, but elements unique to this network as compared to other interleukins have not been readily addressed. In this study, we have undertaken a multi-stage phosphoproteomics approach to better characterise downstream signalling events. To this end, we performed and compared phosphopeptide and phosphoprotein enrichment methodologies after activation of T lymphocytes by IL-23. We demonstrate the complementary nature of the two phosphor-enrichment approaches by maximising the capture of phosphorylation events. A total of 8069 unique phosphopeptides (containing 8344 unique sites), and 4317 unique phosphorylated proteins were identified, amongst which STAT3, PKM2, CDK6 and LASP-1 clearly showed induction of specific phosphorylation sites that were not readily observed after IL-2 stimulation. Interestingly, we observed subsequent translocation of STAT3 and PKM2 to the nucleus as well as increased phosphorylation especially of the nuclear portion at ~30 min after IL-23 stimulation, suggesting a wide range of cellular responses including proliferation and metabolic adaptation.