Stressor-Actuated\nProximity Labeling for Reporting\nCellular Interaction

Cell-cell interactions determine the activation state\nand function\nof cells. When host cells are exposed to stressors such as microorganisms,\nimmune defense machinery is activated to release H<sub>2</sub>O<sub>2</sub>, providing direct evidence of the relevant cellular physiological\nprocesses. Inspired by the fact that peroxidase can catalyze proximity\nlabeling in the presence of exogenous H<sub>2</sub>O<sub>2</sub>,\na stressor-actuated proximity labeling (SAPL) strategy is developed\nto report the process information on cell–cell interactions\nby recording stress levels. The stressors are covalently modified\nwith horseradish peroxidase (HRP) and the H<sub>2</sub>O<sub>2</sub> released by the host cells in response to the stressors triggers\nHRP-based proximity labeling. Using a fungal mimic or live fungi as\nstressors, the stress levels of different host cells are compared\nby in situ imaging of the labeling signals. The ability to accumulate\nstress signals allows SAPL to more sensitively differentiate between\ninteractions involving different macrophage phenotypes. SAPL is also\na powerful tool for real-time, in situ monitoring of the effects of\nsurface modifications on cellular interactions. Thus, the SAPL strategy\nrepresents a new perspective in the monitoring of cell–cell\ninteractions using endogenous effector molecules.