The human gonadotropin releasing hormone type I receptor is a functional intracellular GPCR expressed on the nuclear membrane.
The mammalian type I gonadotropin releasing hormone receptor (GnRH-R) is a structurally unique G protein-coupled receptor (GPCR) that lacks cytoplasmic tail sequences and displays inefficient plasma membrane expression (PME). Compared to its murine counterparts, the primate type I receptor is inefficiently folded and retained in the endoplasmic reticulum (ER) leading to a further reduction in PME. The decrease in PME and concomitant increase in intracellular localization of the mammalian GnRH-RI led us to characterize the spatial distribution of the human and mouse GnRH receptors in two human cell lines, HEK 293 and HTR-8/SVneo. In both human cell lines we found the receptors were expressed in the cytoplasm and were associated with the ER and nuclear membrane. A molecular analysis of the receptor protein sequence led us to identify a putative monopartite nuclear localization sequence (NLS) in the first intracellular loop of GnRH-RI. Surprisingly, however, neither the deletion of the NLS nor the addition of the Xenopus GnRH-R cytoplasmic tail sequences to the human receptor altered its spatial distribution. Finally, we demonstrate that GnRH treatment of nuclei isolated from HEK 293 cells expressing exogenous GnRH-RI triggers a significant increase in the acetylation and phosphorylation of histone H3, thereby revealing that the nuclear-localized receptor is functional. Based on our findings, we conclude that the mammalian GnRH-RI is an intracellular GPCR that is expressed on the nuclear membrane. This major and novel discovery causes us to reassess the signaling potential of this physiologically and clinically important receptor.
Re
Michelle
M
The Children's Health Research Institute, London, Canada.
Pampillo
Macarena
M
Savard
Martin
M
Dubuc
Céléna
C
McArdle
Craig A
CA
Millar
Robert P
RP
Conn
P Michael
PM
Gobeil
Fernand
F
Bhattacharya
Moshmi
M
Babwah
Andy V
AV
D015153:Blotting, Western; D002460:Cell Line; D004252:DNA Mutational Analysis; D005455:Fluorescent Antibody Technique; D006801:Humans; D007295:Inositol Phosphates / Q000378:metabolism; D009154:Mutation; D009685:Nuclear Envelope / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D011966:Receptors, LHRH / Q000235:genetics / Q000378:metabolism*
C484844:GNRHR protein, human; D007295:Inositol Phosphates; D043562:Receptors, G-Protein-Coupled; D011966:Receptors, LHRH