UC Davis

Our immune system responds to extracellular cues to protect our health by coordinatingnecessary cell functions from cell motility to apoptosis. Engineering signaling pathways controlling these processes is rapidly becoming a powerful approach for developing new biomedical technology, with cancer immunotherapies serving as a prominent example. However, most current strategies rely on modifying or repurposing endogenous human signaling cascades. This can result in unintended crosstalk between the synthetic signaling pathways and the complex native signaling of human cells. Two-component systems (TCS) could address this challenge and establish a scientific foundation for systematically improving and adding to the natural abilities of cells to sense and respond to their environment in a robust yet flexible manner. With a newly paved avenue for engineering cell communication, researchers could develop strategic signaling cascades in any human cell for their specific research interests. Importantly, TCS are absent in human cells, but present in all three domains of life, and offer diverse yet simple and linear signaling pathways. In TCS, ligand binding modulates a histidine kinase (HK) sensor, a protein characteristically containing separate ligand binding and HK domains. When activated, the HK transfers a phosphoryl group to the response regulator (RR), and the phosphorylated RR activates a specific downstream response through mechanisms ranging from protein-to-protein interactions to transcription. In its inactive state, the HK acts as a phosphatase. These studies focus on a light-sensitive LOV TCS and a nitric oxide-sensitive Hno TCS as candidate model pathways for modifying mammalian cells. We demonstrated constitutive activity with the LOV pathway and tested several modifications to achieve light sensitivity. While some modifications affected pathway output, all tested pathways appeared to have light-independent constitutive activity.