Antibody and B7/BB1-mediated ligation of the CD28 receptor induces tyrosine phosphorylation in human T cells.

Abstract

StlmmaryCD28 is an adhesion receptor expressed as a 44-kD dimer on the surface of a major subset of human T cells. The CD28 receptor regulates the production of multiple lymphokines, including interleukin 2 (Ib2), by activation of a signal transduction pathway that is poorly understood. Here we show that ligation of CD28 by a monoclonal antibody (mAb) or by a natural ligand, B7/BB1, induces protein tyrosine phosphorylation that is distinct from T cell receptor (TCR)-induced tyrosine phosphorylation. CD28-induced protein tyrosine phosphorylation was greatly enhanced in cells that had been preactivated by ligation of the TCR, or by pretreatment with phorbol esters. Rapid and prolonged tyrosine phosphorylation of a single substrate, ppl00, was induced in T cells after interaction with B7/BB1 presented on transfected Chinese hamster ovary (CHO) cells. Anti-B7 mAb inhibited B7/BB1 receptor-induced tyrosine phosphorylation, indicating that B7-CD28 interaction was required. CD28-induced tyrosine phosphorylation was independent of the TCR because it occurred in a variant of the Jurkat T cell line that does not express the TCR. Herbimycin A, a protein tyrosine kinase inhibitor, could prevent CD28-induced tyrosine phosphorylation and CD28-induced I1.-2 production in normal T cells. The simultaneous crosslinking of CD28 and CD45, a tyrosine phosphatase, could prevent tyrosine phosphorylation of ppl00. These results suggest that specific tyrosine phosphorylation, particularly of ppl00, occurs directly as a result ofCD28 ligand binding and is involved in transducing the signal delivered through CD28 by accessory cells that express the B7/BB1 receptor. Thus, this particular form of signal transduction may be relevant to lymphokine production and, potentially may provide a means to study the induction of self-tolerance, given the putative role of the costimulatory signal in the induction of T cell activation or anergy.

CD28 Ligation Induces Tyrosine Phosphorylation of Pyk2 but Not Fak in Jurkat T Cells

“…3A). These results are similar to those previously reported (11)(12)(13)24). No enhanced tyrosine phosphorylation could be detected in WCL as a result of concurrently ligating CD28 and TCR (Fig.…”

“…PTKs have been shown to be critical for CD28-mediated T cell activation (12,23). Here we identify the PTK Pyk2 as a potential player in CD28 signaling, as this kinase became tyrosine-phosphorylated after CD28 ligation.…”

“…Phosphorylated immunoreceptor tyrosine-based activation motifs interact with the Src homology (SH) 2 domains of the Syk/Zap family PTKs, leading to the activation of these PTKs and in turn to the phosphorylation of an array of cellular proteins (16, 18 -21). Similarly, CD28 signaling pathways involve the phosphorylation of several proteins on tyrosine residues (11)(12)(13)(22)(23)(24)(25)(26)(27)(28). Indeed, such phosphorylations are critical for CD28 function (12,23).…”

“…Similarly, CD28 signaling pathways involve the phosphorylation of several proteins on tyrosine residues (11)(12)(13)(22)(23)(24)(25)(26)(27)(28). Indeed, such phosphorylations are critical for CD28 function (12,23). The cytoplasmic region of CD28 becomes rapidly tyrosine-phosphorylated after CD28 ligation, presumably by Fyn and Lck (24,29).…”

Increased cytolytic T lymphocyte activity and decreased B7 responsiveness are associated with CD28 down-regulation on CD8+ T cells from HIV-infected subjects

“…This combined stimulation results in production of multiple cytokines and, in CD8' T cells, induces cytolytic activity [8][9][10][11][12][13][14]. Wilhin the normal peripheral CD8^ T cell population, the subset expressing CD28 was first reported to contain the CTL, whereas CD28"CD8^ T cells showed a suppressor activity [15,16].…”