Differential expression and distribution of ezrin, radixin and moesin in human natural killer cells

CD16, the low-affinity FcIgG receptor (FccRIIIA), is predominantly expressed in human NK cells. Our recent findings indicate that CD16 expression on the outer membrane surface of NK cells is correlated with the membrane expression of phosphatidylcholinespecific phospholipase C (PC-PLC). In the present study we analyzed the trafficking of CD16 from the plasma membrane to cytoplasmic regions, after stimulation with specific mAb. The CD16 receptor is internalized, likely degraded and newly synthesized; its endocytosis is independent of ATP, but requires an integral and functional actin cytoskeleton. Antibody-mediated CD16 cross-linking results in an approximately twofold increase in PC-PLC enzymatic activity within 10 min. Analysis of PC-PLC and CD16 distribution in NK cell plasma membrane demonstrates that the proteins are physically associated and partially accumulated in lipid rafts. Pre-incubation of NK cells with a PC-PLC inhibitor, D609, causes a dramatic decrease both in CD16 receptor and PC-PLC enzyme expression on the plasma membrane. Interestingly, among phenotype PBL markers, only CD16 is strongly down-modulated by D609 treatment. CD16-mediated cytotoxicity is also reduced after D609 incubation. Taken together, these data suggest that the PC-PLC enzyme could play an important role in regulating CD16 membrane expression, the CD16-mediated cytolytic mechanism and CD16-triggered signal transduction.

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“…1G). Similar results were obtained when NK cells were incubated with Latrunculin A, which causes actin depolymerization [17] (data not shown).…”

Section: Resultssupporting

confidence: 84%

Functional role of phosphatidylcholine‐specific phospholipase C in regulating CD16 membrane expression in natural killer cells

et al. 2007

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“…This last finding was highly consistent with a recent study showing the importance in macrophages of the linkage between actin filaments and the membrane of the secondary phagosomes through the ERMs, and particularly through ezrin, for the occurrence of efficient phagocytosis (Defacque et al, 2000). Moreover, recent findings suggest that ezrin is involved in the intracellular traffic of NK granules (Ramoni et al, 2002), which together with melanosomes belong to a lysosomal-like vesicle family (Dell'Angelica et al, 2000). The ability of cytochalasin B to entirely abrogate the phagocytic activity of melanoma cells further suggests a key role of the actin cytoskeleton in this phenomenon.…”

Section: Discussionmentioning

confidence: 99%

Potent Phagocytic Activity Discriminates Metastatic and Primary Human Malignant Melanomas: A Key Role of Ezrin

Lugini

Lozupone

Matarrese

et al. 2003

Laboratory Investigation

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SUMMARY:Features of phagocytosis have been observed in human tumors, but the phagocytic apparatus of tumor cells and the mechanism(s) underlying this phenomenon have yet to be defined. To address the phenomenon of phagocytosis, its underlying mechanism(s), and its possible role in tumor biology, we used human melanoma cells as a prototypic model. Our results showed that a process of phagocytosis of apoptotic cells occurs in vivo in human melanoma. This finding was consistent with evidence that human melanoma cells in vitro express all of the known lysosomal and phagocytic markers on their cytoplasmic vesicles and that a process of phagocytosis occurs in these vesicles. However, exclusively human melanoma cells deriving from metastatic lesions possess an efficient phagocytic machinery responsible for a macrophage-like activity against latex beads, yeast, and apoptotic cells of different origins, which was comparable to that of human primary macrophages. Moreover, the actin-binding protein ezrin was expressed on phagocytic vacuoles of melanoma cells and of cells deriving from a human adenocarcinoma; both treatment with cytochalasin B and specific inhibition of ezrin synthesis strongly affected the phagocytic activity of melanoma cells. This suggests that the association with the actin cytoskeleton is a crucial requirement for the development of this phenomenon. Hence our data provide evidence for a potent phagocytic activity exerted by metastatic melanoma cells possibly involved in determining the level of aggressiveness of human melanoma. This suggests that the assessment of phagocytic activity may be exploited as a new tool to evaluate the malignancy of human melanoma. Moreover, our data suggest that gene therapy or drug treatments aimed at inhibiting actin assembly to the phagosomal membranes may be proposed as a new strategy for the control of tumor aggressiveness. (Lab Invest 2003, 83:1555-1567.

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“…Since previous studies demonstrated that exogenous expression of ezrin in NK-resistant cells induces uropod formation and sensitizes target cells to interleukin-2-activated killing [12] and ezrin is an important factor in the formation of immunological synapse between the NK cell and target tumor cells [13], we sought to test if repression of ezrin in A431 cells diminishes internaliza- To eliminate the potential off-target effect, we carried out another set of knockdown experiment using an siRNA targeting a different region of ezrin. Western blotting analyses indicate that the ezrin siRNA #2 caused a specific knockdown of ezrin protein level without affecting actin protein level (Supplementary information, Figure S3).…”

Section: Internalization Of Nk Cells Requires Ezrin In A431 Cellsmentioning

confidence: 99%

“…Importantly, suppression of ezrin results in severe defects in vesicular membrane trafficking and in plasma membrane-cytoskeletal remodeling of gastric parietal cells, confirming the role of ezrin in orchestrating membrane-cytoskeletal dynamics [11]. Interestingly, ezrin is polarized in uropods of NK-sensitive tumor cells and involved in NK target cell recognition [12,13].…”

Section: Introductionmentioning

confidence: 99%

Internalization of NK cells into tumor cells requires ezrin and leads to programmed cell-in-cell death

et al. 2009

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Differential expression and distribution of ezrin, radixin and moesin in human natural killer cells

Cited by 29 publications

References 27 publications

Functional role of phosphatidylcholine‐specific phospholipase C in regulating CD16 membrane expression in natural killer cells

Functional role of phosphatidylcholine‐specific phospholipase C in regulating CD16 membrane expression in natural killer cells

Potent Phagocytic Activity Discriminates Metastatic and Primary Human Malignant Melanomas: A Key Role of Ezrin

Internalization of NK cells into tumor cells requires ezrin and leads to programmed cell-in-cell death

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