Lack of a C-terminal tail in the mammalian gonadotropin-releasing hormone receptor confers resistance to agonist-dependent phosphorylation and rapid desensitization.
The mammalian gonadotropin-releasing hormone receptor (GnRH-R) is, at present, the only G-protein-coupled receptor that activates phospholipase C and lacks a C-terminal tail. We have previously demonstrated that this unique structural feature is associated with resistance to rapid desensitization of phosphoinositide signaling in COS-7 and HEK-293 cells (Heding, A., Vrecl, M., Bogerd, J., McGregor, A., Sellar, R., Taylor, P. L., and Eidne, K. A. (1998) J. Biol. Chem. 273, 11472-11477). Using receptors tagged with a nonapeptide of the influenza hemagglutinin protein to enable immunoprecipitation, we now demonstrate that the mammalian GnRH-R is not phosphorylated in an agonist-dependent manner. In contrast, the mammalian thyrotropin-releasing hormone receptor and the African catfish GnRH-R, both of which have a C-terminal tail, are phosphorylated in response to agonist challenge. Furthermore, chimeras of the mammalian GnRH-R with the C-terminal tail of either the mammalian thyrotropin-releasing hormone receptor or the catfish GnRH-R are also phosphorylated in an agonist-dependent manner. Only those receptors having C-terminal tails showed desensitization of phosphoinositide responses within 5-10 min of agonist challenge. We also show that the internalization of all these receptors when expressed transiently in COS-7 cells is similar. This dissociates receptor internalization from rapid desensitization and demonstrates that the lack of a C-terminal tail in the mammalian GnRH-R results in an inability of the receptor to undergo agonist-dependent phosphorylation and that this results directly in a resistance to rapid desensitization.
Willars
G B
GB
Department of Cell Physiology, University of Leicester, Maurice Shock Building, University Road, Leicester LE1 9HN, United Kingdom. gbw2@leicester.ac.uk
Heding
A
A
Vrecl
M
M
Sellar
R
R
Blomenröhr
M
M
Nahorski
S R
SR
Eidne
K A
KA
D000818:Animals; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D010716:Phosphatidylinositols / Q000378:metabolism; D010766:Phosphorylation; D011966:Receptors, LHRH / Q000819:agonists* / Q000737:chemistry / Q000378:metabolism
D010716:Phosphatidylinositols; D011966:Receptors, LHRH