Lack of Evidence for AT1R/B2R Heterodimerization in COS-7, HEK293, and NIH3T3 Cells HOW COMMON IS THE AT1R/B2R HETERODIMER?

It has been suggested previously (AbdAlla, S., Lother, H., and Quitterer, U. (2000) Nature 407, 94-98) that the angiotensin II type 1 receptor (AT(1)R) and the bradykinin B2 receptor (B2R)form constitutive heterodimers. Furthermore they demonstrate that AT(1)R signaling significantly increases in the presence of the B2R. These findings suggest that heterodimerization and potentiation of AT(1)R signaling is a universal phenomenon that occurs as a natural consequence of simultaneous expression of the two receptors. Hence this potential interaction is of great pharmacological and biological interest that adds an additional layer of complexity to the understanding of the cross-talk between the renin-angiotensin and kallikrein-kinin systems. Given the remarkable significance of this finding, scientists from four independent research groups have set out to reproduce and further examine the potential AT(1)R/B2R interaction. We have investigated functional potentiation by the B2R of AT(1)R signaling in three different cell lines using multiple assays including phosphoinositide hydrolysis, ERK activation, beta-arrestin recruitment, and receptor selection and amplification technology, and we have examined dimerization using bioluminescence resonance energy transfer and regulated secretion/aggregation technology. However, although both the AT(1)Rs and B2Rs were functional in our systems and the systems were fine tuned to detect small changes in receptor function, we failed to detect any functional modulation by or physical interaction between the two receptor proteins. In contrast to the previous observations, our data collectively suggest that AT(1)R/B2R heterodimerization does not occur as a natural consequence of their simultaneous expression in the same cell nor does the B2R influence the AT(1)R signaling.