Really outside signaling

Reactive oxygen species (ROS) such as hydrogen peroxide (H₂O₂) pose a potential chemical threat in cells, so it was surprising enough when they turned up as essential signaling components downstream of receptor activation. Now Garrett DeYulia, Juan Cárcamo, David Golde (Memorial Sloan-Kettering Cancer Center, New York, NY) and colleagues have found that H₂O₂ can be generated outside cells, independent of any intracellular events, by ligand binding to cytokine receptors.

The group had earlier seen that extracellular catalase, which breaks down H₂O₂, inhibited signaling through the GM-CSF receptor. They now find that ligand binding to this receptor increases the amount of extracellular H₂O₂. This occurs even when the cells are fixed before ligand addition or with a version of the receptor...