Reactive oxygen species (ROS) serve as mediators of signal transduction. However, mechanisms of how ROS influence the target molecules to elicit signaling event have not been defined. Our laboratory recently accumulated evidence for the role of protein carbonylation in the mechanism of ROS signaling. This concept originated from experiments in which pulmonary artery smooth muscle cells were treated with endothelin-1 to understand the mechanism of cell growth. Endothelin-1 was found to promote protein carbonylation in an endothelin receptor- and Fenton reaction-dependent manner. Mass spectrometry identified proteins that are carbonylated in response to endothelin-1, including annexin A1. Our experiments generated a hypothesis that endothelin-1-mediated carbonylation and subsequent degradation of annexin A1 promote cell growth. This mechanism was found also to occur in response to other signaling activators such as serotonin and platelet-derived growth factor in smooth muscle cells of pulmonary circulation, systemic circulation, and the airway, as well as in cardiac muscle cells, suggesting the universal role of this pathway. We also discovered a process of decarbonylation that defines transient kinetics of carbonylation signals in certain conditions. We propose that protein carbonylation and decarbonylation serve as a mechanism of signal transduction.