Internalization of NK cells into tumor cells requires ezrin and leads to programmed cell-in-cell death.
Cytotoxic lymphocytes are key players in the orchestration of immune response and elimination of defective cells. We have previously reported that natural killer (NK) cells enter target tumor cells, leading to either target cell death or self-destruction within tumor cells. However, it has remained elusive as to the fate of NK cells after internalization and whether the heterotypic cell-in-cell process is different from that of the homotypic cell-in-cell event recently named entosis. Here, we show that NK cells undergo a cell-in-cell process with the ultimate fate of apoptosis within tumor cells and reveal that the internalization process requires the actin cytoskeletal regulator, ezrin. To visualize how NK cells enter into tumor cells, we carried out real-time dual color imaging analyses of NK cell internalization into tumor cells. Surprisingly, most NK cells commit to programmed cell death after their entry into tumor cells, which is distinctively different from entosis observed in the homotypic cell-in-cell process. The apoptotic cell death of the internalized NK cells was evident by activation of caspase 3 and DNA fragmentation. Furthermore, NK cell death after internalization is attenuated by the caspase inhibitor, Z-VAD-FMK, confirming apoptosis as the mode of NK cell death within tumor cells. To determine protein factors essential for the entry of NK cells into tumor cells, we carried out siRNA-based knockdown analysis and discovered a critical role of ezrin in NK cell internalization. Importantly, PKA-mediated phosphorylation of ezrin promotes the NK cell internalization process. Our findings suggest a novel regulatory mechanism by which ezrin governs NK cell internalization into tumor cells.
School of Bioscience and Bioengineering, South China University of Technology, Guangzhou 510641, China.
Shan
S
Wang
Zhen
Z
Guo
Peng
P
Xia
Tingting
T
Liu
Jufang
J
Wang
Shan
S
Li
Lihua
L
Sun
Jianxin
J
Lu
Qian
Q
Wen
Mingqian
M
Zhou
Li
L
Ma
Xia
X
Ding
Xiaoning
X
Wang
Xuebiao
X
Yao
D000199:Actins / Q000378:metabolism; D000590:Amino Acid Chloromethyl Ketones / Q000494:pharmacology; D017209:Apoptosis / Q000502:physiology*; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D053938:DNA Fragmentation; D015536:Down-Regulation / Q000235:genetics; D004705:Endocytosis / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000235:genetics; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007694:Killer Cells, Natural / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D009369:Neoplasms / Q000276:immunology* / Q000378:metabolism; D010587:Phagocytosis / Q000502:physiology*; D010766:Phosphorylation; D034741:RNA, Small Interfering / Q000235:genetics; D000099149:Ezrin
D000199:Actins; D000590:Amino Acid Chloromethyl Ketones; D053148:Caspase 3; D017868:Cyclic AMP-Dependent Protein Kinases; D003598:Cytoskeletal Proteins; D004791:Enzyme Inhibitors; D034741:RNA, Small Interfering; D000099149:Ezrin; C096713:benzyloxycarbonylvalyl-alanyl-aspartyl fluoromethyl ketone