PD-1 immunoreceptor inhibits B cell receptor-mediated signaling by recruiting src homology 2-domain-containing tyrosine phosphatase 2 to phosphotyrosine

PD-1 is an immunoreceptor that belongs to the immunoglobulin (Ig) superfami ly and contains two tyrosine residues in the cytoplasmic region. Studies on PD-1-deficient mice have shown that PD-1 plays critical roles in establish ment and/or maintenance of peripheral tolerance, but the mode of action is totally unknown. To study the molecular mechanism for negative regulation o f lymphocytes through the PD-1 receptor, we generated chimeric molecules co mposed of the IgG Fc receptor type IIB (Fc gamma RIIB) extracellular region and the PD-1 cytoplasmic region and expressed them in a B lymphoma cell li ne, IIA1.6. Coligation of the cytoplasmic region of PD-1 with the B cell re ceptor(BCR) in IIA1.6 transformants inhibited BCR-mediated growth retardati on, Ca2+ mobilization, and tyrosine phosphorylation of effector molecules, including Ig beta, Syk, phospholipase C-gamma2 (PLC gamma2), and ERK1/2, wh ereas phosphorylation of Lyn and Dok was not affected. Mutagenesis studies indicated that these inhibitory effects do not require the N-terminal tyros ine in the immunoreceptor tyrosine-based inhibitory motif-like sequence, bu t do require the other tyrosine residue in the C-terminal tail. This tyrosi ne was phosphorylated and recruited src homology 2-domain-containing tyrosi ne phosphatase 2 (SHP-2) on coligation of PD-1 with BCR. These results show that PD-1 can inhibit BCR signaling by recruiting SHP-2 to its phosphotyro sine and dephosphorylating key signal transducers of BCR signaling.