Differential regulation of gonadotropin-releasing hormone secretion and gene expression by androgen: membrane versus nuclear receptor activation.
Steroid hormones induce rapid membrane receptor-mediated effects that appear to be separate from long-term genomic events. The membrane receptor-mediated effects of androgens on GT1-7 GnRH-secreting neurons were examined. We observed androgen binding activity with a cell-impermeable BSA-conjugated testosterone [testosterone 3-(O-carboxymethyl)oxime (T-3-BSA)] and were able to detect a 110-kDa protein recognized by the androgen receptor (AR) monoclonal MA1-150 antibody in the plasma membrane fraction of the GT1-7 cells by Western analysis. Further, a transfected green fluorescent protein-tagged AR translocates and colocalizes to the plasma membrane of the GT1-7 neuron. Treatment with 10 nM 5alpha-dihydrotestosterone (DHT) inhibits forskolin-stimulated accumulation of cAMP, through a pertussis toxin-sensitive G protein, but has no effect on basal cAMP levels. The inhibition of forskolin-stimulated cAMP accumulation by DHT was blocked by hydroxyflutamide, a specific inhibitor of the nuclear AR. DHT, testosterone (T), and T-3-BSA, all caused significant elevations in intracellular calcium concentrations ([Ca(2+)](i)). T-3-BSA stimulates GnRH secretion 2-fold in the GT1-7 neuron, as did DHT or T. Interestingly GnRH mRNA levels were down-regulated by DHT and T as has been reported, but not by treatment with T-3-BSA or testosterone 17beta-hemisuccinate BSA. These studies indicate that androgen can differentially regulate GnRH secretion and gene expression through specific membrane-mediated or nuclear mechanisms.
Shakil
Tarranum
T
Department of Physiology, University of Toronto, Toronto General Hospital Research Institute, University Health Network, Toronto, Ontario, Canada M5S 1A8.
Hoque
A N Ehsanul
AN
Husain
Mansoor
M
Belsham
Denise D
DD
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D013196:Dihydrotestosterone / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D007987:Gonadotropin-Releasing Hormone / Q000378:metabolism*; D007700:Kinetics; D009474:Neurons / Q000502:physiology*; D037342:Pertussis Toxin / Q000494:pharmacology; D011944:Receptors, Androgen / Q000235:genetics / Q000502:physiology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D011944:Receptors, Androgen; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; D013196:Dihydrotestosterone; D005576:Colforsin; D007987:Gonadotropin-Releasing Hormone; D000242:Cyclic AMP; D037342:Pertussis Toxin; D015056:1-Methyl-3-isobutylxanthine