Identification of functional bradykinin B2 receptors endogenously expressed in HEK293 cells

The human embryonic kidney (HEK) 293 cell line is widely used in cell biology research. Although HEK293 cells have been meticulously studied, our knowledge about endogenous G protein-coupled receptors (GPCR) in these cells is incomplete. While studying the effects of bradykinin (BK), a potent growth factor for renal cells, we unexpectedly discovered that BK activates extracellular signal-regulated protein kinase 1 and 2 (ERK) in HEK293 cells. Thus, we hypothesized that HEK293 cells possess endogenous BK receptors. RT-PCR demonstrated the presence of mRNAs for BK B1 and BK B2 receptors in HEK293 cells. Western blotting with BK B1 and BK B2 receptor antibodies confirmed this result at the protein level. To establish that BK receptors are functional, we employed fluorescent measurements of intracellular Ca2+, measured changes in extracellular acidification rate (ECAR) as a reflection of the Na+/H+ exchange (NHE) with a Cytosensor™ microphysiometer, and assessed ERK activation by Western blotting with a phospho-specific ERK antibody. Exposure of HEK293 cells to BK produced a concentration-dependent rise in intracellular Ca2+ (EC50 = 36.5 ± 8.0 × 10−9 M), a rapid increase in tyrosine phosphorylation of ERK (EC50 = 9.8 ± 0.4 × 10−9 M), and elevation in ECAR by ∼20%. All of these signals were blocked by HOE-140 (B2 receptor antagonist) but not by des-Arg10-HOE-140 (B1 receptor antagonist). We conclude that HEK293 cells express endogenous functional BK B2 receptors, which couple to the mobilization of intracellular Ca2+, increases in ECAR and increases in ERK phosphorylation.