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Quantitative analysis of resistance to NK attacks reveals stepwise killing kinetics

Choi, Paul (2014) Quantitative analysis of resistance to NK attacks reveals stepwise killing kinetics. Integrative biology, 6 (12). pp. 1153-1161. ISSN 1757-9708


Cellular agents of disease, such as microbial pathogens or cancerous cells, often survive
cytotoxic mechanisms from natural immunity and synthetic treatments. Survival can occur for
several reasons. Advantageous genetic mutations can directly counter cytotoxic mechanisms
(Gottesman). Isogenic cells can still exhibit different phenotypes such as varying sensitivities to
killing agents (Lewis, Spencer). Finally, even when all cells behave identically, the random
statistics of killing, which occur unpredictably on a cell-by-cell basis, mean that some cells will
survive longer than others purely due to chance.
In cancer, survival mechanisms are multi-faceted and complex (Whiteside). Tumors alter
immune responses at a systemic level via tissue interactions (Sica), while autonomous
mechanisms promote survival at the level of a single cancer cell (Deveraux). In the latter case,
individual cancer cells can evade detection by immune cells, and when detected, still resist the
ensuing attacks. While a number of molecular mechanisms for evasion and resistance have been
identified, understanding their physiological roles in tumors remains a challenging task.
A major pathway for immune-mediated killing of cancer cells involves granzyme B (GzmB), a
death-inducing protease that is delivered, usually by cytotoxic T lymphocytes (CTLs) or natural
killer (NK) cells, into the cytoplasm of cells targeted for removal (Chowdhury, Cullen). A
potential means for resisting GzmB activity is the human serpin PI-9, which strongly binds and
inhibits GzmB in biochemical assays (Sun). Cellular assays suggest that PI-9 may prevent
granzyme-mediated death (Bird, Medema, Cunningham, Jiang), although there are conflicting
reports (Godal). Thus, the finding that PI-9 is overexpressed in certain cancer tissues led to the
hypothesis that PI-9 may protect tumor cells from immune attacks (Medema, Bladergroen).
The physiological role of PI-9 based resistance remains unclear because many factors can
determine how a specific biochemical interaction regulates the overall immune-cancer
interaction. Even in cell culture models, analysis of PI-9 function has been mainly limited to
population measurements at single time points, which provides only a coarse description of
survival or death. Instead, we observe and track the fates of single cancer cells during NK attacks,
using fluorescent reporters to monitor the outcome of individual NK-cancer interactions. We find
that resistant tumor populations exhibit unusual death kinetics that are explained by multi-step
killing from sequential NK attacks. The combination of finite resistance and discrete cytotoxic
attacks results in distinct features in the regulation of death for at the level of both individual
cells and whole populations.

Item Type: Article
Date Deposited: 13 Oct 2016 00:45
Last Modified: 13 Oct 2016 00:45