Physiological significance of thromboxane A(2) receptor dimerization.
The thromboxane A(2) receptor (TP), one of the G protein-coupled receptors (GPCRs), consists of two splicing variants, TPalpha and TPbeta, which differ in their C-terminal regions. In the present study, we investigated whether TPalpha and TPbeta formed homo- or hetero-dimers and whether the dimerization changed the function of TP. The immunofluorescent analysis using human embryonic kidney (HEK) 293 cells expressing either FLAG-tagged TPalpha or TPbeta showed that TPalpha is mainly distributed on plasma membranes and TPbeta existed on plasma membranes and within the cells. Co-immunoprecipitation analysis using HEK293 cells expressing both TPalpha and TPbeta showed that TPalpha and TPbeta formed homo- and hetero-dimers. U46619, a TP agonist, caused phosphoinositide hydrolysis and elevation of [Ca(2+)](i) in a concentration-dependent manner in Chinese hamster ovary (CHO) cells expressing TPalpha or TPbeta. The responses were observed to a greater extent in the cells expressing TPalpha than TPbeta. In the cells expressing both TPalpha and TPbeta, U46619-induced responses were observed to a lesser extent than in the cells expressing TPalpha alone. Furthermore, [(3)H]SQ29548 binding showed that the level of the cell surface expression of TP was the following order: the cells expressing TPalpha > TPalpha and TPbeta > TPbeta. These results indicate that TPalpha and TPbeta formed homo- and hetero-dimers, and TP-mediated signaling may be regulated by the hetero-dimer.
Department of Cellular Signaling, Graduate School of Pharmaceutical Sciences, Tohoku University, Japan.
Masako
M
Sasaki
Katsutoshi
K
Miyosawa
Satoko
S
Ohkubo
Norimichi
N
Nakahata
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D017398:Alternative Splicing; D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic; D016466:CHO Cells; D002462:Cell Membrane / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D005231:Fatty Acids, Unsaturated; D049452:Green Fluorescent Proteins; D006801:Humans; D006834:Hydrazines / Q000378:metabolism; D018613:Microscopy, Confocal; D009842:Oligopeptides; D010455:Peptides; D020033:Protein Isoforms / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D044244:Receptors, Thromboxane A2, Prostaglandin H2 / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins; D015398:Signal Transduction; D014162:Transfection
D019086:Bridged Bicyclo Compounds, Heterocyclic; D005231:Fatty Acids, Unsaturated; D006834:Hydrazines; D009842:Oligopeptides; D010455:Peptides; D020033:Protein Isoforms; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; C045749:SQ 29548; C085706:FLAG peptide