Kallikreins when activating bradykinin B2 receptor induce its redistribution on plasma membrane

The bradykinin (BK) B2 receptor (R) is directly activated by kallikreins and other serine proteases independent of BK release. Both the Galpha(i) and Galpha(q) proteins are involved, shown by the release of arachidonic acid and [Ca2+]i elevation. Site-directed mutagenesis of the receptor and the lack of heterogeneous desensitization of the human B2R by the BK and kallikrein emphasize among others the differences between activation by the proteases and the peptide. To characterize further the mechanism thereby kallikreins activate and desensitize the B2R we investigated the distribution of the human B2R tagged with the green fluorescent protein (B2-GFP(Ct)) on the plasma membrane of stably transfected Chinese hamster ovary (CHO) cells. We visualized the movement of B2-GFP(Ct) R with confocal fluorescence microscopy after activation by BK or a by serine protease. Continued exposure of the cells to BK led to B2R internalization within 15-20 min. Porcine pancreatic and human recombinant tissue kallikreins induced a rapid definite redistribution of receptors on the plasma membrane within 5 min, prior to internalization. These effects of kallikrein were blocked by the B2R antagonist HOE 140 and by the kallikrein inhibitor, aprotinin. The B2R was also activated by endoproteinases LysC and ArgC and trypsin, but these enzymes did not induce redistribution, only internalization. In control experiments, kallikrein had no effect on cells transfected to stably express the angiotensin-converting enzyme-green fluorescent protein (GFP). Thus, kallikreins when activating the BK B2R also trigger its redistribution on plasma membrane.