Physical Interaction of Jab1 with Human Serotonin 6 G-protein-coupled Receptor and Their Possible Roles in Cell Survival

The 5-HT₆ receptor (5-HT₆R) is one of the most recently cloned serotonin receptors, and it plays important roles in Alzheimer disease, depression, and learning and memory disorders. However, unlike the other serotonin receptors, the cellular mechanisms of 5-HT₆R are poorly elucidated relative to its significance in human brain diseases. Here, using a yeast two-hybrid assay, we found that the human 5-HT₆R interacts with Jun activation domain-binding protein-1 (Jab1). We also confirmed a physical interaction between 5-HT₆R and Jab1 using glutathione S-transferase pulldown, fluorescence resonance energy transfer, co-immunoprecipitation, and immunocyto(histo)chemistry assays. The manipulation of Jab1 expression using Jab1 small interference RNA decreased 5-HT₆R-mediated activity and cell membrane expression of 5-HT₆R, whereas overexpression of Jab1 produced no significant effect. In addition, we demonstrated that the activation of 5-HT₆R induced the translocation of Jab1 into the nucleus and increased c-Jun phosphorylation and the interaction between Jab1 and c-Jun. Furthermore, we found that 5-HT₆R and Jab1 were up-regulated in middle cerebral artery occlusion-induced focal cerebral ischemic rats and in cultured cells exposed to hypoxic insults, suggesting possible protective roles for 5-HT₆R and Jab1. These findings suggest that Jab1 provides a novel signal transduction pathway for 5-HT₆R and may play an important role in 5-HT₆R-mediated behavior changes in the brain.