EXPLORATION OF DOPAMINE AND SEROTONIN RECEPTOR HETEROMERIZATION AND ITS CONSEQUENTIAL ALTERATIONS USING GPCR-BASED FLUORESCENT SENSORS

G protein-coupled receptors (GPCRs) have priorly been recognized to be functional in a monomeric form; however, a growing body of scientific evidence stands to the point that several classes GPCRs are architecturally structured in a homomeric, heteromeric, and oligomeric complexes, arising to the functional diversity of GPCRs. Monoaminergic GPCRs such as dopamine and serotonin receptors are witnessed to establish heteromer and impacted to G protein-dependent signaling alterations. Herein, we made use of the genetically encoded GPCR-based fluorescent sensor to study the pharmacological activity and the possible heteromerization between dopamine D2 and serotonin 2C (5HT_2C) receptors. To that aim, we employed the human D2 and 5HT_2C receptor-based sensor, GRAB_DA1h and GRAB_5HT1.0, respectively. Our investigation was conducted in HEK293T cell and characterized drug responses toward the classic full agonists using plate-reader assays. Besides, we also used fluorescence microscopy to dissect the real-time calcium responses generated upon agonist and antagonist application. We found that coexpression of GRAB_DA1h and 5HT_2C did not portray a significant difference in DA binding, corresponded to the reverse experiment of GRAB_5HT1.0 and D2 in 5HT binding. Nevertheless, calcium responses showed possible transactivation D2 receptor agonist that might be influential to G_q/11-dependent signaling of 5HT_2C receptor. This work demonstrates the GPCR fluorescent sensor can be used as a tool to elucidate and characterize using various agonists and coexpression of different receptor subtypes may have triggered the crosstalk between two protomers. However, the downstream signaling cascades of G_q/11 and G_i/o that may have been affected upon coexpression deserves further investigation.