Desensitization as A3 adenosine receptor regulation: physiopathological implications

A3 adenosine receptors are subjected to fast desensitisation, internalisation and down regulation after agonist exposure. As almost all G-protein coupled receptors, these regulatory mechanisms are mediated by receptor phosphorylation in a process that results in the recruitment of arrestins. Receptor phosphorylation is a flexible and dynamic process in which the receptors are regulated in a unique manner depending on the cell type in which the receptors are expressed. This rapid regulatory mechanism has an important pathophysiological role: in fact the impairment of receptor responses obtained following agonist exposure may be therapeutically equivalent to antagonist occupancy and suggest the use of agonists in different pathological conditions in which the activity of A3 receptors should be regulated, such as neurodegenerative and cancer diseases. In this scenario, phosphorylation offers a mechanism of regulating the signalling outcome of G-protein coupled receptors that can be tailored to meet specific physiological role.