Phosphotyrosine Proteomic Study of Interferon Signaling Pathway Using a Combination of

Tyrosine phosphorylation is a type of post-translational modification that plays a crucial role in signal transduc-tion. Thus, the study of this modification at the proteomic level has great biological significance. However, because of the low abundance of tyrosine-phosphorylated proteins in total cell lysate, it is difficult to evaluate the dynamics of tyrosine phosphorylation at a global level. In this work, proteins carrying phosphotyrosine (pTyr) were first puri-fied from whole cell lysate by immunoprecipitation using anti-pTyr monoclonal antibodies. After tryptic digestion, phosphopeptides were further enriched by IMAC and an-alyzed by LC-MS. Quantitative changes of tyrosine phos-phorylation at the global level were evaluated using iso-topic labeling (introduced at the methyl esterification step prior to IMAC). Using this double enrichment approach, we characterized interferon (IFN)-induced pTyr pro-teomic changes in Jurkat cells. We observed induced phosphorylation on several well documented as well as novel tyrosine phosphorylation sites on proteins involved in IFN signal transduction, such as Tyk2, JAK1, and IF-NAR subunits. A specific site on -tubulin (Tyr-271) was observed to be phosphorylated upon treatment as well. Furthermore, our results suggest that LOC257106, a CDC42 GAP-like protein, is potentially involved in thi