Arsenic trioxide (AT) is a novel human neutrophil pro‐apoptotic agent: effects of catalase on AT‐induced apoptosis, degradation of cytoskeletal proteins and de novo protein synthesis

Abstract

Summary The anti‐cancer drug arsenic trioxide (AT) induces apoptosis in a variety of transformed or proliferating cells. However, little is known regarding its ability to induce apoptosis in terminally differentiated cells, such as neutrophils. Because neutropenia has been reported in some cancer patients after AT treatment, we hypothesised that AT could induce neutrophil apoptosis, an issue that has never been investigated. Herein, we found that AT‐induced neutrophil apoptosis and gelsolin degradation via caspases. AT did not increase neutrophil superoxide production and did not induce mitochondrial generation of reactive oxygen species. AT‐induced apoptosis in PLB‐985 and X‐linked chronic granulomatous disease (CGD) cells (PLB‐985 cells deficient in gp91phox mimicking CGD) at the same potency. Addition of catalase, an inhibitor of H2O2, reversed AT‐induced apoptosis and degradation of the cytoskeletal proteins gelsolin, α‐tubulin and lamin B1. Unexpectedly, AT‐induced de novo protein synthesis, which was reversed by catalase. Cycloheximide partially reversed AT‐induced apoptosis. We conclude that AT induces neutrophil apoptosis by a caspase‐dependent mechanism and via de novo protein synthesis. H2O2 is of major importance in AT‐induced neutrophil apoptosis but its production does not originate from nicotinamide adenine dinucleotide phosphate dehydrogenase activation and mitochondria. Cytoskeletal structures other than microtubules can now be considered as novel targets of AT.

The intriguing normal acute inflammatory response in mice lacking vimentin

“…This was expected not only because of the importance of vimentin in the cell architecture and a variety of cell functions and responses, but also because we have demonstrated recently that vimentin is an important target cleaved by caspases in spontaneous or agent-induced neutrophil apoptosis [12,[14][15][16][17][18]. In addition, some vimentin-cleaved fragments have been found to be pro-apoptotic themselves [29].…”

“…Mitochondrial ROS production was assessed using dihydrorhodamine 123 (DHR123), as described previously [14,27]. Briefly, neutrophils were incubated at a final concentration of 1 ¥ 10 6 cells/ml in HBSS-0·3% BSA containing 1 mM DHR123 for 5 min at 37°C before adding stimuli.…”

“…Mitochondrial ROS production was assessed by flow cytometry using DHR123 [14,27]. PMA was used as a positive control [14,27].…”

“…Using the murine air pouch model, we have also demonstrated that vimentin was cleaved when neutrophils harvested from lipopolysaccharide (LPS)-induced air pouches were incubated in vitro with the potent pro-apoptotic plant lectin Viscum album agglutinin-I [18]. Given the importance of vimentin in general immunology [9,[19][20][21][22][23], inflammation and biology of neutrophils [10][11][12][13][14]17], and the fact that a generation of mice totally devoid of vimentin could develop and reproduce normally [3], we decided to investigate the role of vimentin during an inflammatory response in vivo and on neutrophil cell functions in vitro, two situations which have been curiously not or poorly investigated.…”

“…We have documented recently that several cytoskeletal proteins, including the two IF proteins vimentin and lamin B1, are cleaved via caspase activation in human apoptotic neutrophils [10][11][12][13][14], as well as in promyelocytes and eosinophils [15,16]. More recently, we demonstrated that among the different cytoskeletal proteins we have tested, paxillin, gelsolin, vinculin, a-and b-tubulin, only the IF protein vimentin and lamin B1 were expressed on the cell surface of apoptotic neutrophils, suggesting that neutrophils may be a source of autoantigens for the development of autoantibodies directed against vimentin and lamin B1 associated with various rheumatic diseases [17].…”