Human homologs of the putative G protein-coupled membrane progestin receptors (mPRalpha, beta, and gamma) localize to the endoplasmic reticulum and are not activated by progesterone.
The steroid hormone progesterone exerts pleiotrophic functions in many cell types. Although progesterone controls transcriptional activation through binding to its nuclear receptors, it also initiates rapid nongenomic signaling events. Recently, three putative membrane progestin receptors (mPRalpha, beta, and gamma) with structural similarity to G protein-coupled receptors have been identified. These mPR isoforms are expressed in a tissue-specific manner and belong to the larger, highly conserved family of progestin and adiponectin receptors found in plants, eubacteria, and eukaryotes. The fish mPRalpha has been reported to mediate progesterone-dependent MAPK activation and inhibition of cAMP production through coupling to an inhibitory G protein. To functionally characterize the human homologs, we established human embryonic kidney 293 and MDA-MB-231 cell lines that stably express human mPRalpha, beta, or gamma. For comparison, we also established cell lines expressing the mPRalpha cloned from the spotted seatrout (Cynoscion nebulosus) and Japanese pufferfish (Takifugu rubripes). Surprisingly, we found no evidence that human or fish mPRs regulate cAMP production or MAPK (ERK1/2 or p38) activation upon progesterone stimulation. Furthermore, the mPRs did not couple to a highly promiscuous G protein subunit, Galpha(q5i), in transfection studies or provoke Ca(2+) mobilization in response to progesterone. Finally, we demonstrate that transfected mPRs, as well as endogenous human mPRalpha, localize to the endoplasmic reticulum, and that their expression does not lead to increased progestin binding either in membrane preparations or in intact cells. Our results therefore do not support the concept that mPRs are plasma membrane receptors involved in transducing nongenomic progesterone actions.
Krietsch
Tom
T
Endokrinologikum Hamburg, Falkenried 88, 20251 Hamburg, Germany.
Fernandes
Maria Sofia
MS
Kero
Jukka
J
Lösel
Ralf
R
Heyens
Maria
M
Lam
Eric W-F
EW
Huhtaniemi
Ilpo
I
Brosens
Jan J
JJ
Gellersen
Birgit
B
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D008969:Molecular Sequence Data; D010473:Perciformes / Q000378:metabolism; D010802:Phylogeny; D011374:Progesterone / Q000494:pharmacology; D043562:Receptors, G-Protein-Coupled / Q000819:agonists / Q000032:analysis / Q000037:antagonists & inhibitors* / Q000378:metabolism; D011980:Receptors, Progesterone / Q000819:agonists / Q000032:analysis* / Q000378:metabolism; D023741:Takifugu / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
D002118:Calcium; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D011374:Progesterone; D043562:Receptors, G-Protein-Coupled; D011980:Receptors, Progesterone; D048051:p38 Mitogen-Activated Protein Kinases; C513556:PAQR7 protein, human; C513557:PAQR8 protein, human; C516723:PAQR5 protein, human