title: The Galphai and Galphaq proteins mediate the effects of melatonin on steroid/thyroid hormone receptor transcriptional activity and breast cancer cell proliferation.
abstract: Melatonin, via its MT1 receptor, but not the MT2 receptor, can modulate the transcriptional activity of various nuclear receptors - estrogen receptor alpha (ERalpha) and retinoic acid receptor alpha (RARalpha), but not ERbeta- in MCF-7, T47D, and ZR-75-1 human breast cancer cell lines. The anti-proliferative and nuclear receptor modulatory actions of melatonin are mediated via the MT1 G protein-coupled receptor expressed in human breast cancer cells. However, the specific G proteins and associated pathways involved in the nuclear receptor transcriptional regulation by melatonin are not yet clear. Upon activation, the MT1 receptor specifically couples to the G(alphai2), G(alphai3), G(alphaq), and G(alphall) proteins, and via activation of G(alphai2) proteins, melatonin suppresses forskolin-induced 3',5'-cyclic adenosine monophosphate production, while melatonin activation of G(alphaq), is able to inhibit phospholipid hydrolysis and ATP's induction of inositol triphosphate production in MCF-7 breast cancer cells. Employing dominant-negative and dominant-positive) forms of these G proteins, we demonstrate that G(alphai2) proteins mediate the suppression of estrogen-induced ERalpha transcriptional activity by melatonin, while the G(q) protein mediates the enhancement of retinoid-induced RARalpha transcriptional activity by melatonin. However, the growth-inhibitory actions of melatonin are mediated via both G(alphai2) and G(alphaq) proteins.
authors.affiliation: Department of Structural and Cellular Biology, Tulane University School of Medicine, New Orleans, LA 70112, USA.
authors.forename: Ling
authors.initials: L
authors.lastname: Lai
authors.forename: Lin
authors.initials: L
authors.lastname: Yuan
authors.forename: Qi
authors.initials: Q
authors.lastname: Chen
authors.forename: Chunmin
authors.initials: C
authors.lastname: Dong
authors.forename: Lulu
authors.initials: L
authors.lastname: Mao
authors.forename: Brian
authors.initials: B
authors.lastname: Rowan
authors.forename: Tripp
authors.initials: T
authors.lastname: Frasch
authors.forename: Steven M
authors.initials: SM
authors.lastname: Hill
mesh_terms: D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000032:analysis; D006152:Cyclic GMP / Q000032:analysis; D004967:Estrogens / Q000502:physiology; D005260:Female; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000235:genetics / Q000502:physiology*; D005786:Gene Expression Regulation; D006801:Humans; D047468:Immunoprecipitation; D008156:Luciferases; D008550:Melatonin / Q000502:physiology*; D010761:Phosphorus Radioisotopes; D011863:Radioimmunoassay; D044122:Receptor, Melatonin, MT1 / Q000502:physiology*; D011960:Receptors, Estrogen / Q000235:genetics* / Q000378:metabolism; D018168:Receptors, Retinoic Acid / Q000235:genetics / Q000378:metabolism; D011988:Receptors, Thyroid Hormone / Q000235:genetics*; D000072482:Retinoic Acid Receptor alpha; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: D004967:Estrogens; D010761:Phosphorus Radioisotopes; C000607071:RARA protein, human; D044122:Receptor, Melatonin, MT1; D011960:Receptors, Estrogen; D018168:Receptors, Retinoic Acid; D011988:Receptors, Thyroid Hormone; D000072482:Retinoic Acid Receptor alpha; D005576:Colforsin; D000242:Cyclic AMP; D008156:Luciferases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D006152:Cyclic GMP; D008550:Melatonin