Necroptosis of Lung Epithelial Cells Triggered by Ricin Toxin and Bystander Inflammation

Abstract

Background/Aims: The ribosome-inactivating proteins include the biothreat agent, ricin toxin (RT). When inhaled, RT causes near complete destruction of the lung epithelium coincident with a proinflammatory response that includes TNF family cytokines, which are death- inducing ligands. We previously demonstrated that the combination of RT and TNF-related apoptosis inducing ligand (TRAIL) induces caspase-dependent apoptosis, while RT and TNF-α or RT and Fas ligand (FasL) induces cathepsin-dependent cell death in lung epithelial cells. We hypothesize that airway macrophages constitute a major source of cytokines that drive lung epithelial cell death. Methods: Here, we show that RT-induced apoptosis of the monocytic cell line, U937, leads to the bystander killing of the lung epithelial cell line, A549. U937 cells were treated with ricin. Following this, A549 cells were treated with supernatants from U937 cells and death was measured by WST-1 viability assay Results: Upon RT-induced U937 cell death, released RT and FasL contributed to A549 cell death. U937 cells also released nuclear protein HMGB1. The release of RT, FasL, and HMGB1 triggered A549 cell necroptosis, rather than cathepsin-dependent killing observed previously with RT and FasL. Reactive oxygen species (ROS) were produced in A549 cells due to HMGB1 ligation of the receptor for advanced glycation end products (RAGE). Conclusion: These findings demonstrate the potential for bystander necroptosis of lung epithelial cells during RT toxicosis which may perpetuate or increase the proinflammatory response.

Heterophyllin: A New Adenia Toxic Lectin with Peculiar Biological Properties

“…Increasing experimental evidence is demonstrating that RIPs can induce cell death through different mechanisms in addition to apoptosis. In particular, necroptosis [ 15 , 43 , 44 ] and mechanisms involving oxidative stress [ 15 , 45 , 46 ] have been recently described. To investigate the involvement of various cell death mechanisms, experiments were performed by pre-treating cells with scavengers of oxidative stress and with inhibitors of apoptosis and necroptosis.…”