New modes of ERK feedback regulation in T cell receptor signaling revealed by quantitative phosphoproteomic analysis (121.29)

Abstract Competing positive and negative signaling feedback pathways play a critical role in tuning the sensitivity of T cell receptor (TCR) activation by selectively enhancing responses to foreign ligands while suppressing signals from self-peptides. In response to TCR agonist engagement, ERK is activated to positively regulate TCR signaling through phosphorylation of Ser59 on Lck. To obtain a wide-scale view of the role of ERK in propagating TCR signaling, a quantitative phosphoproteomic analysis of 417 tyrosine phosphorylation sites by mass spectrometry was performed on Jurkat E6-1 cells in the presence of U0126, a MEK1/2 specific inhibitor of ERK activation. Relative to untreated cells, ERK-inhibited cells showed constitutive decreases in phosphorylation through a TCR stimulation time course on tyrosine residues found on upstream signaling proteins (CD3 chains, Lck, ZAP-70), as well as downstream signaling proteins (LAT, SLP-76, PLCγ1, Itk), consistent with ERK’s proposed role in TCR positive feedback signaling. Interestingly, ZAP-70 Tyr598 and CD3 ζ Tyr123 showed elevated phosphorylation in response to U0126 treatment, suggesting differential regulation of these sites via ERK feedback. Furthermore, elevated phosphorylation on the activation site of Fyn was observed in response to ERK inhibition. These findings shed light on novel signaling events that are regulated by this kinase which may fine tune TCR activation.