Quantitative Phosphoproteomic Analysis Reveals a Role for Serine and Threonine Kinases in the Cytoskeletal Reorganization in Early T Cell Receptor Activation in Human Primary T Cells

Abstract

Protein phosphorylation-dephosphorylation events play a primary role in regulation of almost all aspects of cell function including signal transduction, cell cycle, or apoptosis. Thus far, T cell phosphoproteomics have focused on analysis of phosphotyrosine residues, and little is known about the role of serine/threonine phosphorylation in early activation of the T cell receptor (TCR). Therefore, we performed a quantitative mass spectrometry-based analysis of the global phosphoproteome of human primary T cells in response to 5 min of TCR activation with anti-CD3 antibody. Combining immunoprecipitation with an antiphosphotyrosine antibody, titanium dioxide phosphopeptide enrichment, isobaric tag for the relative and absolute quantitation methodology, and strong cation exchange separation, we were able to identify 2814 phosphopeptides. These unique sites were employed to investigate the site-specific phosphorylation dynamics. Five hundred and seventeen phosphorylation sites showed TCR-responsive changes. We found that upon 5 min of stimulation of the TCR, specific serine and threonine kinase motifs are overrepresented in the set of responsive phosphorylation sites. These phosphorylation events targeted proteins with many different activities and are present in different subcellular locations. T lymphocytes are able to recognize specific antigenic peptides presented by molecules of the major histocompatibility complex on the surface of other cell types. This interaction is mediated by a dimeric specialized molecule called T cell receptor (TCR), 1 which is part of a larger membrane complex in association with CD3 ␥, ␦, , and chains. The binding between TCR and the major histocompatibility complex-antigen is of relatively low affinity, and it is stabilized by the association with co-receptors (CD4 or CD8). All of these molecules in turn recruit, via their intracellular domains, different polypeptides to carry out signal transduction. In addition to antigen recognition, coactivation by CD28 is required to trigger full activation of the T cell, which expresses then different cell surface molecules and releases soluble mediators (cytokines) that promote changes in the activity of different target cell types (1).During the TCR-major histocompatibility complex-antigen recognition, T cells undergo considerable membrane and cytoskeletal rearrangements that lead to the formation of the immunological synapse (IS). During this maturation, precise molecular reorganizations occur at the interface between T cells and an antigen presenting cell. Cell motility, polarization, and receptor relocalization events are dependent on the lymphocyte cytoskeleton and are necessary for the maturation of the IS. TCR, co-receptors, intracellular signaling molecules, and adhesion receptors polarize to the IS and form small aggregates known as microclusters (2, 3), processes all dependent on functional microtubule and actin cytoskeleton. This results in the stabilization and functional maturation of the signaling complexes.Protein phosphorylation...

Site-specific Phosphorylation of Kindlin-3 Protein Regulates Its Capacity to Control Cellular Responses Mediated by Integrin αIIbβ3

“…These data indicate the importance of Thr 482 and Ser 484 also in ␤ 1 integrin activation, suggesting a general mechanism for phosphorylation of kindlin-3-induced integrin activation. Supporting this conclusion, recent phosphoproteomic analyses identified Thr 482 phosphorylation in T cells upon T cell receptor stimulation with anti-CD3 antibody (64) and Ser 484 as a target of phosphorylation upon platelet activation by thrombin (65). In rat kindlin-3, Thr but not an Ser is present, whereas in mouse kindlin-3, Ser but not Thr is present.…”

Quantitative Phosphoproteomics Reveals Extensive Cellular Reprogramming during HIV-1 Entry

“…Strengthening the association with T cell activation, upregulated T cell receptor (TCR)-responsive phosphorylation sites from both Jurkat (Mayya et al, 2009) (OR: 19.2, p = 0.039) and primary CD4 + T cells (Ruperez et al, 2012) (OR: 4.3, p = 8.7 × 10 -5 ) were overrepresented among HIV-responsive phosphorylation sites (Table S4). We also generated an interaction network using the STRING database (Figure 3A) and found a striking segregation between cytoplasmic and nuclear localized genes and discreet functional modules of genes that regulate microtubules, actin and T cell activation – all processes that have been clearly linked to HIV-1 biology (Figure 3A) (Liu et al, 2009; Stevenson et al, 1990).…”

A Combined Omics Approach to Generate the Surface Atlas of Human Naive CD4+ T Cells during Early T-Cell Receptor Activation

“…Most of the already existing studies regarding T-cell biology are often conducted in Jurkat T-cell lines instead of primary T cells, focusing on proteomic events during activation close to the TCR, located in lipid rafts (12)(13)(14). Other studies focused on T-cell subproteomes within the early stages of T-cell differentiation and investigated proteomic changes in the nucleus of activated human cord blood CD4 ϩ T cells after interleukin-4 stimulation (15) or focused on changes of the global phosphoproteome of human primary T cells in response to 5 min of TCR activation with ␣CD3 (16). In vitro manipulated T cells were previously analyzed such as 7-day cultures of in vitro differentiated T helper 1 and T helper 2 cells (17), however, the surface proteome of human naive CD4 ϩ T cells and how these proteins change during the early time window of ␣CD3/␣CD28 activation has not been investigated so far.…”