Rapid activation receptor- or IL-2-induced lytic granule convergence in human natural killer cells requires Src, but not downstream signaling.

Natural killer (NK) cells participate in host defense by surveying for and ultimately killing virally infected or malignant target cells. NK cell cytotoxicity is a tightly regulated process that proceeds stepwise from adhesion and activation to the secretion of preformed lytic granule contents onto a diseased or stressed cell. We previously characterized rapid dynein-dependent lytic granule convergence to the microtubule-organizing center (MTOC) as an early, prerequisite step in NK cell cytotoxicity. Although multiple activating receptors can trigger granule convergence, the specific signal or signals responsible remained unknown. Using live cell confocal microscopy, NK cell lytic granule movement after NK cell activation was captured and measured. Using inhibitors of common early signaling mediators, we show that Src kinases are required for lytic granule convergence, but downstream signals that promote actin rearrangement, MTOC polarization, and calcium mobilization are not. Exposure to interleukin 2 was also sufficient to induce lytic granule convergence, which required noncanonical Src-dependent signaling. Thus, NK cell lytic granule convergence, prompted by specific receptor-mediated and soluble cytokine signals, depends on a directly downstream early Src kinase-dependent signal and emphasizes the importance of this step in readying NK cells for cytotoxicity.

Cell biological steps and checkpoints in accessing NK cell cytotoxicity.

Natural killer (NK) cell-mediated cytotoxicity is governed by the formation of a lytic immune synapse in discrete regulated steps, which give rise to an extensive array of cellular checkpoints in accessing NK cell-mediated cytolytic defense. Appropriate progression through these cell biological steps is critical for the directed secretion of specialized secretory lysosomes and subsequent target cell death. Here we highlight recent discoveries in the formation of the NK cell cytolytic synapse as well as the molecular steps and cell biological checkpoints required for this essential host defense process.

YY1 and a unique DNA repeat element regulates the transcription of mouse CS1 (CD319, SLAMF7) gene.

CS1 (CD319, CRACC, SLAMF7, novel Ly9) activates NK cell-mediated cytotoxicity and proliferation of B lymphocytes during immune responses. The expression of CS1 is up regulated on B cells in multiple myeloma and systemic lupus erythematosus. In this study we describe the transcriptional regulation of mouse CS1 (mCS1) gene. We show that mCS1 gene transcription is regulated by YY1 (Ying Yang 1) and a unique (AG)n=36 DNA repeat element. YY1 is known to play a significant role in B cell development by regulating the pro B cell to pre B cell transition. The consensus DNA binding site for YY1 was detected using TRANSFAQ on the mCS1 promoter region. Mutations in the YY1 site led to a significant increase in mCS1 promoter activity indicating that YY1 represses mCS1 transcription. YY1 binds to the mCS1 promoter at the expected site in vivo and in vitro as tested by chromatin immunoprecipitation assays and super-shift EMSA assays respectively. Unique (CT)n=24 and (AG)n=36 DNA repeat elements are present on mCS1 promoter that are sensitive to S1 nuclease and engage in DNA triplex structure as confirmed by AFM (atomic force microscopy) imaging. Interestingly, the (AG)n=36 repeat element enhances mCS1 promoter activity.