Distinct efficacies for two endogenous ligands on a single cognate gonadoliberin receptor.
A cDNA encoding a putative gonadoliberin receptor was cloned from the pituitary of the African catfish. Conceptual translation predicts a protein of 379 amino acids which shows typical characteristics of GTP-binding-protein-coupled receptors. The isolated cDNA was stable expressed in human embryonic kidney (HEK) 293 cells which were used for studies on gonadoliberin-activated second messenger systems (inositol phosphate production; increase in cAMP and/or intracellular Ca2+). The isolated cDNA encoded a functional receptor, designated catfish gonadoliberin receptor (cfGnRH-R), which had an amino acid sequence similarity of 38% with mammalian gonadoliberin receptors. In contrast to its mammalian counterparts which lack an intracellular carboxy-terminal domain, the cfGnRH-R contains an additional 49 amino acid residues. From the two endogenous gonadoliberins in African catfish, chicken gonadoliberin-II had a several hundredfold higher potency than catfish gonadoliberin to activate cfGnRH-R-associated second messenger systems in transfected HEK 293 cells. This is in line with the previously determined higher gonadotropin-release capacity of chicken gonadoliberin-II in catfish. Stimulation of second messenger systems with chicken gonadoliberin-II, but not with catfish gonadoliberin, resulted in a biphasic effect and chicken gonadoliberin-II led to a higher maximum stimulation than catfish gonadoliberin. Challenging cfGnRH-R simultaneously with chicken gonadoliberin-II and catfish gonadoliberin did not lead to additive effects. In contrast, two types of mutual inhibitory effects were recorded. These data indicate that a single cognate cfGnRH-R couples with distinct efficacies to signal transduction systems upon stimulation by the two endogenous gonadoliberins which, in addition, may interact negatively.
Tensen
C
C
Department of Experimental Zoology, University of Utrecht, The Netherlands.
Okuzawa
K
K
Blomenröhr
M
M
Rebers
F
F
Leurs
R
R
Bogerd
J
J
Schulz
R
R
Goos
H
H
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002645:Chickens; D005399:Fishes / Q000502:physiology*; D018507:Gene Expression Regulation, Developmental; D007987:Gonadotropin-Releasing Hormone / Q000737:chemistry / Q000502:physiology*; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D008024:Ligands; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011966:Receptors, LHRH / Q000502:physiology*; D011994:Recombinant Proteins
D007295:Inositol Phosphates; D008024:Ligands; D011966:Receptors, LHRH; D011994:Recombinant Proteins; D007987:Gonadotropin-Releasing Hormone