Angiotensin II (AngII) and bradykinin are hormones that generally exert opposing actions on the cardiovascular system. AngII, via the AT1 receptor causes vasoconstriction and hypertension, while bradykinin, via the B2 receptor causes vasodilation and hypotension. Although the two receptors can act independently of one another, several years ago it was reported that they are able to form a heteromeric complex that has unique pharmacological properties. In two high profile papers, AbdAlla et al (1, 2) described the constitutive formation of an AT1-B2 receptor heteromer, which resulted in increased AngII-mediated signalling and was involved in the AngII hypersensitivity associated with pre-eclampsia. However, the validity of these studies was questioned by a collaboration of several groups who were unable to find any evidence for a physical or a function interaction between the two receptors (3). As a consequence of these conflicting studies, the existence of the AT1-B2 receptor heteromer has remained controversial.
We have investigated the existence of the AT1-B2 receptor heteromer using the G protein-coupled receptor (GPCR) heteromer identification technology (GPCR-HIT) (4). This assay enables the identification of receptor heteromers through their proximity with interacting proteins. Using this assay, we have found evidence in support of the existence of the AT1-B2 receptor heteromer. We found that the heteromer was able to recruit the GPCR regulatory protein arrestin in a bradykinin-dependent manner. Additionally, the heteromer also internalised and trafficked through the cell upon treatment with bradykinin. The close proximity of the two receptors was confirmed using a variation of the GPCR-HIT assay, which monitors receptor-ligand binding rather than protein-protein interactions.