KIR2DL4 Differentially Signals Downstream Functions in Human NK Cells through Distinct Structural Modules

Abstract

KIR2DL4 (2DL4) is a member of the killer cell Ig-like receptor (KIR) family in human NK cells. It can stimulate potent cytokine production and weak cytolytic activity in resting NK cells, but the mechanism for 2DL4-mediated signaling remains unclear. In this study we characterized the signaling pathways stimulated by 2DL4 engagement. In a human NK-like cell line, KHYG-1, cross-linking of 2DL4 activated MAPKs including JNK, ERK, and p38. Furthermore, 2DL4 cross-linking resulted in phosphorylation of IκB kinase β (IKKβ) and the phosphorylation and degradation of IκBα, which indicate activation of the classical NF-κB pathway. Engagement of 2DL4 was also shown to activate the transcription and translation of a variety of cytokine genes, including TNF-α, IFN-γ, MIP1α, MIP1β, and IL-8. Pharmacological inhibitors of JNK, MEK1/2 and p38, blocked IFN-γ, IL-8, and MIP1α production, suggesting that MAPKs are regulating 2DL4-mediated cytokine production in a nonredundant manner. Activation of both p38 and ERK appear to be upstream of the stimulation of NF-κB. Mutation of a transmembrane arginine in 2DL4 to glycine (R/G mutant) abrogated FcεRI-γ association, as well as receptor-mediated cytolytic activity and calcium responses. Surprisingly, the R/G mutant still activated MAPKs and the NF-κB pathway and selectively stimulated the production of MIP1α, but not that of IFN-γ or IL-8. In conclusion, we provide evidence that the activating functions of 2DL4 can be compartmentalized into two distinct structural modules: 1) through transmembrane association with FcεRI-γ; and 2) through another receptor domain independent of the transmembrane arginine.