Structure/function relationship of activating Ly-49D and inhibitory Ly-49G2 NK receptors

Murine NK cells express Ly-49 family receptors capable of either inhibiting or activating lytic function. The overlapping patterns of expression of th e various receptors have complicated their precise biochemical characteriza tion. Here we describe the use of the Jurkat T cell line as the model for t he study of Ly-49s. We demonstrate that Ly-49D is capable of delivering act ivation signals to Jurkat T cells even in the absence of the recently descr ibed Ly-49D-associated chain, DAP-12, Ly-49D signaling in Jurkat leads to t yrosine phosphorylation of TCR zeta and requires Syk/Zap70 family kinases a nd arginine 54 of Ly-49D, suggesting that Ly-49D signals via association wi th TCR zeta. Coexpression studies in 293-T cells confirmed the ability of L y-49D to associate with TCR zeta. In addition, we have used this model to s tudy the functional interactions between an inhibitory Ly-49 (Ly-49G2) and an activating Ly-49 (Ly-49D). Ly-49G2 blocks activation mediated by Ly-49D in an immunoreceptor tyrosine-based inhibitory motif (ITIM)-dependent manne r. In contrast, Ly-49G2 was incapable of inhibiting activation by the TCR e ven though human killer cell inhibitory receptor (KIR) (KIR3DL2(GL183)) eff ectively inhibits TCR, Both the ability of Ly-49G2 to block Ly-49D activati on and the failure of Ly-49G2 to inhibit TCR signaling were confirmed in pr imary murine NK cells and NK/T cells, respectively. These data demonstrate the dominant effects of the inhibitory receptors over those that activate a nd suggest an inability of the Ly-49 type II inhibitory receptors to effici ently inhibit type I transmembrane receptor signaling in T cells and NK cel ls.