The thyrotropin-releasing hormone-receptor complex and G11alpha are both internalised into clathrin-coated vesicles.
It has been proposed that, after agonist binding, the thyrotropin-releasing hormone receptor (TRHR) becomes internalised associated with Gq, as part of a TRH-TRHR-Gq ternary complex [13]. We tested this hypothesis directly by examining the intracellular distribution of the TRHR and Gq/11 after agonist binding. The localisation of the TRH-TRHR complex and Gq/11alpha was studied by the biochemical isolation of clathrin-coated vesicles (CCVs). The internalised TRH-TRHR complex was localised in CCVs. The CCVs, which had internalised [3H]MeTRH, contained 4-fold higher levels of radiolabelled ligand than did CCVs from cells incubated with [3H]MeTRH at 4 degrees C. Like the receptor-ligand (RL) complex, G11alpha also translocated to these endocytic vesicles. For example, CCVs from cells with internalised TRH-TRHR complexes contained G11alpha, whereas CCVs from cells without internalised RL complexes lacked G11alpha. We conclude that, after agonist-induced TRHR-G11alpha coupling, both the TRH-TRHR complex and G11alpha are internalised in CCVs.
Petrou
C
C
Department of Molecular and Cellular Toxicology, Harvard School of Public Health, Boston, MA 02115, USA.
Tashjian
A H
AH
D000818:Animals; D001693:Biological Transport, Active; D002460:Cell Line; D002966:Clathrin / Q000378:metabolism*; D018699:Coated Vesicles / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D051381:Rats; D018025:Receptors, Thyrotropin-Releasing Hormone / Q000378:metabolism*; D015398:Signal Transduction; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*
D002966:Clathrin; D046911:Macromolecular Substances; D018025:Receptors, Thyrotropin-Releasing Hormone; D013973:Thyrotropin-Releasing Hormone; D019204:GTP-Binding Proteins