Global chimeric exchanges within the intracellular face of the bradykinin B2 receptor with corresponding angiotensin II type Ia receptor regions: generation of fully functional hybrids showing characteristic signaling of the AT1a receptor.
The intracellular (IC) face of the G-protein coupled receptors (GPCR), bradykinin (BK) B2 and angiotensin (AT) 1a, is similar in sequence homology and in size. Both receptors are known to link to Galphai and Galphaq but differ markedly in a number of physiologic actions, particularly with respect to their hemodynamic action. We made single as well as multiple, global replacements within the IC of BKB2R with the corresponding regions of the AT1aR. When stably transfected into Rat-1 cells, these hybrid receptors all bound BK with high affinity. Single replacement of the intracellular loop 2 (IC2) or the distal 34 residues of the C-terminus (dCt) with the corresponding regions of AT1aR resulted in chimera, which turned over phosphotidylinositol (PI) and released arachidonic acid (ARA) as WT BKB2R. In contrast, incorporation of the AT1aR IC3 in a single replacement abolished signal transduction. However, the simultaneous exchange of IC2 and IC3 of BKB2R with AT1aR resulted in a receptor responding to BK with PI turnover and ARA release approximately 4-fold greater than WT BKB2R. Likewise, the simultaneous replacement of IC2 and dCt resulted in a 2.8- and 1.6-fold increase in PI turnover and ARA release, respectively. In contrast, the dual replacement of IC3 and dCt could not overcome the deleterious effects of the IC3 replacement, resulting in very low PI activation and ARA release. Replacement of all three IC domains (IC2, IC3, and dCt) resulted in PI closer to that of AT1aR than BKB2R. The uptake of the receptor chimeras was similar to that of WT BKB2R with the exception of the IC3/dCt dual mutant, which exhibited very poor internalization (18% at 60'). When transfected into Rat-1 cells, the AT1aR markedly increased the expression of connective tissue growth factor (CTGF) mRNA, while BK slightly decreased it. The dual IC2/dCt and triple IC2/IC3/dCt hybrids both upregulated CTGF mRNA in response to BK. These results show that the IC face of the BKB2R can be exchanged with that of AT1aR, producing hybrid receptors, which take on the functional characteristics of AT1aR. The characterization of the chimera with stepwise replacement of the IC domains should allow for assignment of specific roles to the individual loops and C-terminus in the signaling and internalization of the BKB2R and facilitate the generation of a receptor with BKB2R binding and AT1aR function.
Yu
Jun
J
Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Prado
Gregory N
GN
Taylor
Linda
L
Piserchio
Andrea
A
Gupta
Abhas
A
Mierke
Dale F
DF
Polgar
Peter
P
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D001920:Bradykinin / Q000494:pharmacology; D002460:Cell Line; D055513:Connective Tissue Growth Factor; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins; D015870:Gene Expression / Q000187:drug effects; D006133:Growth Substances / Q000235:genetics; D017874:Immediate-Early Proteins / Q000235:genetics; D036341:Intercellular Signaling Peptides and Proteins; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010940:Plant Proteins; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D044140:Receptor, Angiotensin, Type 1; D043782:Receptor, Bradykinin B2; D011945:Receptors, Angiotensin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D018002:Receptors, Bradykinin / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection
C526316:CCN2 protein, rat; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D006133:Growth Substances; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D010940:Plant Proteins; D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; D043782:Receptor, Bradykinin B2; D011945:Receptors, Angiotensin; D018002:Receptors, Bradykinin; D011993:Recombinant Fusion Proteins; C068831:drp90 protein, Glycine max; D055513:Connective Tissue Growth Factor; D001920:Bradykinin