T-cell antigen CD28 interacts with the lipid kinase phosphatidylinositol 3-kinase by a cytoplasmic Tyr(P)-Met-Xaa-Met motif.

Abstract

The T-cell antigen CD28 provides a costimulatory signal that is required for T-cefl proliferation. (residues 191-194). Mutation of the Y191 within the motif resulted in a complete loss ofbinding, while mutation ofM194 caused partial loss of binding. Bding analysis showed that the CD28 Y(P)-MXM motif bound to the p85 C-and N-terminal SH2 domans with an afnity comparable to that observed for PDGF-R and insulin receptor substrate 1. In terms of snaling, CD28 ligation induced a dramatic increase in the recruitment and association of PI 3-kinase with the receptor. CD28 is likely to use PI 3-klipase as the second signal leading to T-cell proliferation, an event with implications for anergy and peripheral T-cell tolerance.Activation of the resting T lymphocyte involves at least two steps: an antigen-specific signal generated by the T-cell receptor (TcR)2/CD3 and CD4/CD8-p56lck complexes, followed by a second signal delivered by an accessory cell (1). The CD28 antigen predominates in providing the costimulatory signals for T-cell stimulation (ref. 2; for reviews see refs. 1 and 3). It contains a single immunoglobulin-like domain and a 51-amino acid cytoplasmic tail (4). B7-1 and related B7-2/ B70 are also members of the immunoglobulin supergene family and serve as ligands for CD28 (5-7). Suboptimal proliferation induced by antigen, anti-CD3 or anti-CD2 antibody is augmented by CD28 ligation (for review see ref. 8). Likewise, CD28 ligation by B7 serves as an obligatory second step in T-cell activation (for review see ref.3). CD28-transgenic mice exhibit profound defects in mitogenic responses (9). CD28 signaling stabilizes mRNA for various lymphokines, in particular interleukin 2 (reviewed in refs. 1 and 8). T-cell nonresponsiveness or anergy can be reversed by CD28 engagement (1-3, 10), an event of potential importance in the generation of cytolytic responses against tumors (11,12).An important question concerns the mechanism by which CD28 regulates T-cell growth and the manner in which the CD28 signaling pathway relates to signals generated by the TcRC/CD3-CD4 complex. CD4 and CD8 associate with the protein-tyrosine kinase p56lck, while TcRC/CD3 is cou- By contrast, intracellular events generated by CD28 differ from those induced by TcRC/CD3 ligation. CD28 signaling appears to occur independent of conventional phosphatidylinositol hydrolysis and the Ca2 -dependent cyclophilincalcineurin pathway and is resistant to cyclosporin and FK506 (3,8). CD28 signaling, however, is sensitive to inhibitors of tyrosine kinases and to coligation with the protein-tyrosine phosphatase CD45 (3,8). CD28 ligation in the presence of phorbol ester induced the tyrosine phosphorylation of proteins at 75 and 100 kDa (3,8). This potentially unique pathway leads to DNA binding activity at an element located in the 5' interleukin 2 enhancer region (for review see refs. 1 and 3). PI 3-kinase is a heterodimer consisting of an adaptor subunit (p85) with two SH2 domains that is coupled to a p110 catalytic subunit and is important to signali...

T Cell Ig and Mucin Domain-1-Mediated T Cell Activation Requires Recruitment and Activation of Phosphoinositide 3-Kinase

“…Interestingly, interaction with p85 is a common feature shared by other T cell accessory molecules, such as CD28, ICOS, and CTLA-4. However, in contrast to these molecules, which preferentially bind the C-terminal SH2 domain of p85 (31)(32)(33)(34)(35), Tim-1 binds the amino-terminal SH2 domain, as revealed by the SH2 domain array. Another difference is that p85 binds to the CD28 family members via a consensus YXXM motif, whereas it binds to Tim-1 at a noncanonical sequence (YIVE).…”

“…Another difference is that p85 binds to the CD28 family members via a consensus YXXM motif, whereas it binds to Tim-1 at a noncanonical sequence (YIVE). Although the amino-terminal p85 SH2 domain has a 10-fold lower avidity for the YXXM motif than does the C-terminal SH2 domain (31), work from Songyang and colleagues (36) suggests that YMXM is the preferred target for both domains. We have attempted to coimmunoprecipitate an isolated N-terminal p85␣ SH2 domain construct with Tim-1, but have been unable to do so (unpublished data), possibly due to the low affinity of the interaction in the absence of other sequences.…”

Regulation of Sustained Actin Dynamics by the TCR and Costimulation as a Mechanism of Receptor Localization

“…It thus seems reasonable to assume that they exert the same function in the context of a T cell/APC interaction. Possible mediators of CD28 and LFA-1 signal transduction are phosphatidylinositol 3-kinase (44,45) and phospholipase C␥ (46).…”

Multiple Signals Required for Cyclic AMP-Responsive Element Binding Protein (CREB) Binding Protein Interaction Induced by CD3/CD28 Costimulation

“…2B). Because PI 3-kinase is known to be activated by CD28 (35)(36)(37), and PI 3-kinase activation promotes CREB phosphorylation (21), we also examined binding with another PI 3-kinase inhibitor, wortmannin, and did not detect any inhibitory effect on CREB-CBP binding (Not shown). Therefore, CD28 costimulation-induced CREB-CBP binding is mainly dependent on the ERK, CaMKIV, and p38 MAPK pathways.…”

“…Even though the essential role of CD28 is well recognized, the CD28-mediated costimulatory signals are not well understood. CD28-mediated signals are known to involve phosphatidylinositol 3-kinase (PI 3-kinase) (35)(36)(37), but PI 3-kinase alone cannot account for all CD28-mediated costimulatory events (38 -40). CD28 costimulation results in full activation of c-Jun Nterminal kinase (JNK) (41), yet signals other than JNK are required for the induction of IL-2 production (42).…”