L-Phenylalanine differentially activates G protein-coupled receptor signalling pathways

Abstract

The most abundant cell surface receptor in eukaryotes, G-protein coupled receptors (GPCRs) couple with heterotrimeric G proteins, utilizing active Gα and Gbg subunits, to initiate distinct intracellular signaling pathways implicated in cell functions and physiological responses. Several GPCRs are validated therapeutic drug targets, while the majority of GPCRs represent unexplored potential, with many studies aiming to define their signal transduction response, identify ligands, and determine their roles in diseases and disorders. Amino acids have become an interest of studies aiming to elucidate their role as ligands, with previous findings demonstrating that L-phenylalanine activates 12 Class A GPCRs. The aim of this study was to characterize the signal transduction response in multiple established signaling pathways for the L-phenylalanine - responsive GPCRs. This was investigated utilizing mammalian cells expressing a target GPCR and luciferase reporter for one of the Ga12/13, Gaq/11, Gbg, Gai/o, and Gas signaling pathways. Cells were treated with either L-phenylalanine or a control vehicle prior to luciferase assay examinations of their response. L-phenylalanine differentially activated GPCR signaling pathways, in a manner that was receptor-dependent, to preferentially increase or decrease cellular responses. Moreover, this response was not always limited to one preferential pathway, and not all receptors previously identified to be activated by L-phenylalanine were observed to significantly signal through the examined pathways. Elucidation of L-phenylalanine’s role in the regulation of cellular communication and function must be explored through independent receptor characterization due to its promiscuous receptor-dependent activation of GPCRs.