title: Apelin receptor homodimer-oligomers revealed by single-molecule imaging and novel G protein-dependent signaling.
abstract: The apelin receptor (APJ) belongs to family A of the G protein-coupled receptors (GPCRs) and is a potential pharmacotherapeutic target for heart failure, hypertension, and other cardiovascular diseases. There is evidence APJ heterodimerizes with other GPCRs; however, the existence of APJ homodimers and oligomers remains to be investigated. Here, we measured APJ monomer-homodimer-oligomer interconversion by monitoring APJ dynamically on cells and compared their proportions, spatial arrangement, and mobility using total internal reflection fluorescence microscopy, resonance energy transfer, and proximity biotinylation. In cells with <0.3 receptor particles/μm2, approximately 60% of APJ molecules were present as dimers or oligomers. APJ dimers were present on the cell surface in a dynamic equilibrium with constant formation and dissociation of receptor complexes. Furthermore, we applied interference peptides and MALDI-TOF mass spectrometry to confirm APJ homo-dimer and explore the dimer-interfaces. Peptides corresponding to transmembrane domain (TMD)1, 2, 3, and 4, but not TMD5, 6, and 7, disrupted APJ dimerization. APJ mutants in TMD1 and TMD2 also decreased bioluminescence resonance energy transfer of APJ dimer. APJ dimerization resulted in novel functional characteristics, such as a distinct G-protein binding profile and cell responses after agonist stimulation. Thus, dimerization may serve as a unique mechanism for fine-tuning APJ-mediated functions.
authors.affiliation: Department of Physiology, School of Medicine, Shandong University, Jinan, Shandong, 250012 P.R. China.|Neurobiology Institute, Jining Medical University, Jining, Shandong, 272067 P.R. China.
authors.forename: Xin
authors.initials: X
authors.lastname: Cai
authors.affiliation: Neurobiology Institute, Jining Medical University, Jining, Shandong, 272067 P.R. China.
authors.forename: Bo
authors.initials: B
authors.lastname: Bai
authors.affiliation: Neurobiology Institute, Jining Medical University, Jining, Shandong, 272067 P.R. China.
authors.forename: Rumin
authors.initials: R
authors.lastname: Zhang
authors.affiliation: Neurobiology Institute, Jining Medical University, Jining, Shandong, 272067 P.R. China.
authors.forename: Chunmei
authors.initials: C
authors.lastname: Wang
authors.affiliation: Neurobiology Institute, Jining Medical University, Jining, Shandong, 272067 P.R. China.|Division of Biomedical Sciences, Warwick Medical School, University of Warwick, Coventry, CV4 7AL, UK.
authors.forename: Jing
authors.initials: J
authors.lastname: Chen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000073861:Apelin / Q000737:chemistry / Q000378:metabolism; D000075244:Apelin Receptors / Q000819:agonists / Q000737:chemistry / Q000378:metabolism*; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism; D002470:Cell Survival; D006224:Cricetinae; D003412:Cricetulus; D031541:Fluorescence Resonance Energy Transfer; D019204:GTP-Binding Proteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000378:metabolism; D061307:Human Umbilical Vein Endothelial Cells / Q000378:metabolism; D006801:Humans; D017354:Point Mutation / Q000235:genetics; D000072417:Protein Domains; D055503:Protein Multimerization; D015398:Signal Transduction; D000072760:Single Molecule Imaging / Q000379:methods*
chemical_list: D000073861:Apelin; D000075244:Apelin Receptors; D049452:Green Fluorescent Proteins; D019204:GTP-Binding Proteins