| P2Y receptors are a family of seven transmembrane spanning G protein-coupled receptors that are activated by nucleotides and nucleotide-sugars. The P2Y14-R is activated by nucleotide sugars, although little is known about the physiological role(s) of this receptor. With a view toward generating pharmacological reagents for studies of P2Y14-R, one goal of this dissertation was to apply a rational structure-activity relationship approach to develop novel ligands for the P2Y14-R. Guided by molecular modeling studies of the P2Y14-R, iterative design of synthetic ligands produced a multitude of compounds which were assessed for agonist activity at the P2Y14-R. From these studies, several novel agonists were identified for the P2Y14-R, including 2-thio-UDP-Glc, which exhibited greater than six-fold higher potency than UDP-Glc. Other novel agonists identified included several UDP-sugars. Using a COS-7 cell system in which recombinant P2Y14-R were co-expressed with the chimeric G protein, Galphaq/i, UDP was identified as a competitive antagonist at the P2Y 14-R. In contrast, in studies comparing the pharmacological selectivity of the rat P2Y14-R to that of the human P2Y14-R in the same cell system, UDP was found to be an agonist at the rat P2Y14-R. Another goal of this work was to examine the signal transduction pathways downstream of P2Y14-R activation, and for these studies, stable cell lines expressing P2Y14-R in HEK293 and in C6 glioma cells were developed. This approach allowed study of P2Y14-R coupled to native G proteins, and P2Y14-R-dependent inhibition of adenylyl cyclase was observed. P2Y14-R activation also promoted pertussis toxin-sensitive phosphorylation of ERK1/2. Moreover, native P2Y14-R were detected in differentiated HL-60 cells by RT-PCR, and in these cells, UDP-Glc promoted pertussis toxin-sensitive activation of ERK1/2. The work presented here provides a foundation for future development of pharmacological agents for the P2Y14 receptor. Furthermore, this work establishes that the P2Y14-R couples to Gi and the MAP kinase signaling pathway, and provides robust cell model systems for future studies of P2Y14-R function. |
