It has been reported that actin filaments associate with the Golgi network and contribute to the remodeling of this organelle during directed secretion 37. Furthermore, interfering with actin polymerization was shown to disrupt the Golgi and reduce directed secretion 38. We found that Golgin-97 codistributes with cytolytic granules in YTS cells (unpublished data). It will be

interesting to examine the effects of IQGAP1 deficiency on Golgi–actin interaction and establish whether the absence of perigranular actin in IQGAP1-deficient find more cells impacts on Golgi remodeling and functions. Such an effect could potentially contribute to the reduced cytolytic activity of IQGAP1-deficient NK cells. The functional roles of IQGAP1 in NK cells are unknown. However, the effects of IQGAP1 silencing on NK morphology and adhesion suggest that it may be important in limiting changes to cell shape and motility. Live cell analysis indicated that the silenced cells developed progressive extensions of micro projections that were normally short lived and smaller in wild-type cells. This appeared to be the basis for the resultant extended ABT-263 morphology of the silenced cells. The reduction of IQGAP1 also resulted in an increased

proportion of the cells forming conjugates with target cells. This could reflect an inability of these cells to release from non-productive interactions with the target cells. In each of these cases, the presence of IQGAP1 appeared Loperamide to correlate with the capacity to limit commitments to cytoskeletal changes associated with extension or adhesion. A recent study on murine NK cells suggested the formation of IQGAP1-mediated signalosomes upon NKG2D engagement, which facilitates Raf/MEK1/2/ERK1/2 signal transduction during cytokine and chemokine generation by these cells. The authors observe activation-dependent changes in the localization of IQGAP1 and in its colocalization with ERK1/2 24. Although we did not observe such redistribution

of IQGAP1 upon target cell engagement, the possibility of IQGAP1-mediating signal transduction possibly by associating with ERK1/2 in human NK cells is intriguing and warrants further study. The data presented here provide new information on the functional requirement for IQGAP1and on the distributional changes that occur during the formation and maturation of the NKIS. IQGAP1 is essential for MTOC mobilization and polarization. It also appears to play an important role in confining granule distribution in the cytosol of YTS cells, possibly through the organization of a filamentous actin network in the proximity of the granules. The similarities in the distribution patterns observed during synapse maturations suggest that IQGAP1 may play an analogous role in NK-like YTS cells, primary NK cells, and cytotoxic T cells. The human NK tumor cell-line YTS was maintained in RPMI 1640 (Gibco) supplemented with 15% fetal bovine serum (FBS).