Inhibitory signaling blocks activating receptor clustering and induces cytoskeletal retraction in natural killer cells

Immunology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
The Journal of Cell Biology (Impact Factor: 9.83). 02/2011; 192(4):675-90. DOI: 10.1083/jcb.201009135
Source: PubMed


Natural killer (NK) lymphocytes use a variety of activating receptors to recognize and kill infected or tumorigenic cells during an innate immune response. To prevent targeting healthy tissue, NK cells also express numerous inhibitory receptors that signal through immunotyrosine-based inhibitory motifs (ITIMs). Precisely how signals from competing activating and inhibitory receptors are integrated and resolved is not understood. To investigate how ITIM receptor signaling impinges on activating pathways, we developed a photochemical approach for stimulating the inhibitory receptor KIR2DL2 during ongoing NK cell-activating responses in high-resolution imaging experiments. Photostimulation of KIR2DL2 induces the rapid formation of inhibitory receptor microclusters in the plasma membrane and the simultaneous suppression of microclusters containing activating receptors. This is followed by the collapse of the peripheral actin cytoskeleton and retraction of the NK cell from the source of inhibitory stimulation. These results suggest a cell biological basis for ITIM receptor signaling and establish an experimental framework for analyzing it.

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    • "60, 61, 62, 63, 64 Myosin IIA also is required for centripetal microcluster movement and this sustained retrograde flow of microclusters is required for sustained Ca2+ release and activation signaling.64, 65 Although the kinetics may be different in NK cells, microclusters of both activating and inhibitory receptors are present and appear to have similar dynamics compared with those in T cells.66, 67, 68, 69 Studies using NK target cell conjugates show that phosphorylated KIR2DL1-containing clusters originate in the periphery and coalesce in the center, thus reaffirming both the presence of microclusters and suggesting their utility in NK cells.67, "
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    • "Thus, NK cell populations, which variably express different activating and inhibitory receptors, may respond differentially upon encountering a potential target cell. However, the underlying principles that control NK cell activation remain the same: activating signals emanating from their corresponding receptors (mediated by tyrosine-kinase based signal transduction pathways), are integrated with repressive signals from inhibitory receptors (mediated by protein phosphatases), culminating in either target cell killing or in unresponsiveness (27, 60). "
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    • "Subsequently, it was shown that stimulation of NKG2A blocked the inside-out upregulation of integrin affinity in primary NK cells (10). Single cell imaging studies with NKL cells confirmed and extended these results by demonstrating that inhibitory signals antagonized IS formation, providing a reverse stop signal that encouraged migration rather than focused cytolysis (8, 9). Here, we demonstrate that engagement of ITIM-receptors disrupts IS formation in both resting and IL-2-cultured NK cells, which is largely consistent with these previous studies. "
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