title: The A3 adenosine receptor: an enigmatic player in cell biology.
abstract: Adenosine is a primordial signaling molecule present in every cell of the human body that mediates its physiological functions by interacting with 4 subtypes of G-protein-coupled receptors, termed A1, A2A, A2B and A3. The A3 subtype is perhaps the most enigmatic among adenosine receptors since, although several studies have been performed in the years to elucidate its physiological function, it still presents in several cases a double nature in different pathophysiological conditions. The 2 personalities of A3 often come into direct conflict, e.g., in ischemia, inflammation and cancer, rendering this receptor as a single entity behaving in 2 different ways. This review focuses on the most relevant aspects of A3 adenosine subtype activation and summarizes the pharmacological evidence as the basis of the dichotomy of this receptor in different therapeutic fields. Although much is still to be learned about the function of the A3 receptor and in spite of its duality, at the present time it can be speculated that A3 receptor selective ligands might show utility in the treatment of ischemic conditions, glaucoma, asthma, arthritis, cancer and other disorders in which inflammation is a feature. The biggest and most intriguing challenge for the future is therefore to understand whether and where selective A3 agonists or antagonists are the best choice.
authors.affiliation: Department of Clinical and Experimental Medicine, Pharmacology Unit and Interdisciplinary Center for the Study of Inflammation, Ferrara, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Gessi
authors.forename: Stefania
authors.initials: S
authors.lastname: Merighi
authors.forename: Katia
authors.initials: K
authors.lastname: Varani
authors.forename: Edward
authors.initials: E
authors.lastname: Leung
authors.forename: Stephen
authors.initials: S
authors.lastname: Mac Lennan
authors.forename: Pier Andrea
authors.initials: PA
authors.lastname: Borea
mesh_terms: D058909:Adenosine A3 Receptor Agonists; D058918:Adenosine A3 Receptor Antagonists; D000818:Animals; D002490:Central Nervous System / Q000378:metabolism; D016503:Drug Delivery Systems; D006801:Humans; D007107:Immune System / Q000378:metabolism; D007249:Inflammation / Q000503:physiopathology*; D008024:Ligands; D015428:Myocardial Reperfusion Injury / Q000378:metabolism; D009369:Neoplasms / Q000378:metabolism; D043684:Receptor, Adenosine A3 / Q000378:metabolism*; D015398:Signal Transduction
chemical_list: D058909:Adenosine A3 Receptor Agonists; D058918:Adenosine A3 Receptor Antagonists; D008024:Ligands; D043684:Receptor, Adenosine A3