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Distinct Ca2+ response patterns in human natural killer cells during induction of necrosis or apoptosis of target
1Department of Physiology, Tokyo Women's Medical College, Japan.
Abstract:
Human CD3-, CD16+ natural killer cells (NKs) induced necrosis in the cell line K562 and the minor population of MOLT-4, while induced apoptosis in the majority of MOLT-4, in one-to-one cell interaction. Simultaneous Ca2+ imaging of NK and target cells revealed remarkable differences in changes of cytosolic Ca2+ concentration ([Ca2+]i) during the process of distinct target cell killing. A rapid [Ca2+]i rise in NK was generated within 2 min after contact with any target. For induction of necrosis, the [Ca2+]i rise in NK reached a peak of 580 +/- 195 nM (mean +/- SD, n = 41) and was followed by an abrupt large [Ca2+]i rise in target cells probably due to Ca2+ entry through pores formed by perforin which was released from NK. The interval between onsets of NK and target Ca2+ responses (Tnk-t) was shorter than 3 min in most cases. Target cells were soon permeabilized, and NK Ca2+ responses ceased in 14 +/- 7 min. For induction of apoptosis, NK Ca2+ responses were relatively smaller (405 +/- 125 nM, n = 16), and Tnk-t was widely scattered up to 30 min. NK Ca2+ responses lasted much longer in a form of Ca2+ oscillations (total duration, 66 +/- 33 min) in parallel with target Ca2+ responses, and ceased as apoptotic changes such as cellular and nuclear fragmentation advanced. The difference in Tnk-t suggests that rapid synchronous release of perforin tends to cause necrosis rather than apoptosis. The duration of NK Ca2+ responses suggests that some 'off signals' may be transmitted to NK following recognition of target cell damage.
Insights
Human natural killer (NK) cells induce necrosis or apoptosis in target cells, differing in calcium signaling dynamics. Rapid NK calcium rises and short NK-target intervals favor necrosis, while prolonged oscillations suggest apoptosis signaling.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Natural killer (NK) cells are crucial for innate immunity, eliminating target cells through programmed cell death.
- NK cell cytotoxicity can manifest as either necrosis or apoptosis, depending on various factors.
- Cytosolic calcium concentration ([Ca2+]i) plays a pivotal role in cellular signaling, including immune cell activation and target cell lysis.
Purpose of the Study:
- To investigate the distinct calcium signaling patterns in human NK cells and target cells during necrosis versus apoptosis induction.
- To elucidate the relationship between NK cell calcium responses, perforin release, and the mode of target cell death.
Main Methods:
- Utilized a co-culture system of human CD3-, CD16+ NK cells and K562/MOLT-4 target cells.
- Performed simultaneous calcium imaging of both NK and target cells during cell-to-cell interactions.
- Analyzed cytosolic Ca2+ concentration ([Ca2+]i) changes, NK-target calcium response intervals (Tnk-t), and NK cell response durations.
Main Results:
- NK cells exhibited rapid [Ca2+]i rises within 2 minutes of target cell contact, regardless of the death pathway.
- Necrosis induction was associated with a higher peak [Ca2+]i in NK cells, a rapid subsequent rise in target cells, and a short Tnk-t (<3 min).
- Apoptosis induction involved smaller NK [Ca2+]i responses, widely scattered Tnk-t (up to 30 min), and prolonged Ca2+ oscillations in NK cells (66 ± 33 min).
Conclusions:
- The kinetics of NK cell calcium signaling and perforin release differentially regulate target cell necrosis and apoptosis.
- A rapid and synchronous perforin release likely promotes necrosis, indicated by a short Tnk-t.
- Prolonged NK cell calcium responses suggest the involvement of 'off signals' that modulate cytotoxicity during apoptosis induction.