Galpha(q/11) and gbetagamma proteins and membrane signaling of calcitriol and estradiol.
17beta-estradiol and 1,25-dihydroxyvitamin D(3)()(calcitriol) rapidly increase (< 5 sec) the concentration of intracellular calcium by mobilizing Ca(2+) from the endoplasmic reticulum and forming inositol 1,4,5-trisphosphate (InsP(3)) and diacylglycerol. Calcitriol increases InsP(3) formation via activation of phospholipase C (PLC)-beta1 linked to a pertussis toxin (PTX)-insensitive G-protein, and estradiol via activation of PLC-beta2 linked to a PTX-sensitive G-protein. Since PLC are effectors of different subunits of various G-proteins, we looked for and identified several G-subunits (Galpha(q/11), Galphas, Galphai, Gbeta and Ggamma) in female rat osteoblasts using Western immunoblotting. The action of calcitriol on InsP(3) formation and Ca(2+) mobilization in Fura-2-loaded confluent osteoblasts involved Galpha(q/11). The membrane effects of estradiol involved Gbetagamma; subunits, and principally Gbeta subunits, but not alpha-subunits. These results may provide additional evidence for membrane receptors of steroid hormones. Since PLC-beta1 is the target effector of Galpha(q/11), whereas PLC-beta2 is only activated by betagamma subunits, this specificity may help to generate membrane receptor-specific responses in vivo.
Le Mellay
V
V
The Centre National de la Recherche Scientifique, 78350 Jouy-en-Josas, France.
Lasmoles
F
F
Lieberherr
M
M
D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002117:Calcitriol / Q000494:pharmacology*; D020013:Calcium Signaling / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D004958:Estradiol / Q000494:pharmacology*; D005260:Female; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D019204:GTP-Binding Proteins / Q000737:chemistry* / Q000276:immunology; D020962:Heterotrimeric GTP-Binding Proteins; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism; D010006:Osteoblasts / Q000187:drug effects; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D000906:Antibodies; C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D019269:Phosphatidylinositol 4,5-Diphosphate; D004958:Estradiol; D015544:Inositol 1,4,5-Trisphosphate; D019204:GTP-Binding Proteins; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins; D002117:Calcitriol