Preliminary evaluation of OR51E2 receptor stimulation of cAMP levels in HANA3A cells

Olfactory receptor 51E2 (OR51E2) is a G protein-coupled receptor traditionally associated with the olfactory epithelium, yet increasingly recognized for its physiological significance in non-olfactory tissues, including cancer tissues. Despite its classification as a propionate-sensitive receptor, the full pharmacological profile of its ligand-binding pocket remains a subject of investigation. Understanding how various organic ligands interact with this receptor not only clarifies the mechanisms of human olfaction but also provides a foundation for treating olfactory dysfunctions through the precise pharmacological modulation of receptor activity. This study aimed to characterize the signaling response of OR51E2 to a diverse panel of organic ligands using a heterologous expression system. HANA3A cells, a specialized HEK293-derived lineage, were transfected with the human OR51E2 gene, the chaperone protein RTP1S to ensure proper membrane trafficking, and the GloSensor plasmid for real-time monitoring of intracellular cyclic AMP (cAMP). A panel of six compounds - propionic acid, 19-hydroxyandrostenedione (19-OH AD), glycine, urea, palmitic acid, and the receptor-independent control forskolin - was evaluated. Functional assays, i.e., the stimulation of cAMP levels measured by the bioluminescent assay Glo Sensor, demonstrated that propionic acid elicited a specific, mild cAMP response in OR51E2-expressing cells, while 19-OH AD, glycine, urea, and palmitic acid failed to trigger significant activation. Forskolin was utilized as a robust positive control, confirming cellular viability and the integrity of the receptor-independent cAMP signaling pathway. The findings validate the efficacy of the GloSensor platform in HANA3A cells for olfactory receptor screening and contribute to the growing body of literature regarding the selective activation of ectopic ORs, which may serve as potential therapeutic targets in metabolic and oncogenic pathways.