Gαq/11 and Gβγ proteins and membrane signaling of calcitriol and estradiol

✍ Scribed by Véronique Le Mellay; Françoise Lasmoles; Michèle Lieberherr

• Book ID: 101260563
• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 187 KB
• Volume: 75
• Category: Article
• ISSN: 0730-2312
• DOI: 10.1002/(sici)1097-4644(19991001)75:1<138::aid-jcb14>3.0.co;2-i

✦ Synopsis

17␤-estradiol and 1,25-dihydroxyvitamin D 3 (calcitriol) rapidly increase (Ͻ 5 sec) the concentration of intracellular calcium by mobilizing Ca 2ϩ 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)-␤1 linked to a pertussis toxin (PTX)-insensitive G-protein, and estradiol via activation of PLC-␤2 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 (G␣ q/11 , G␣s, G␣i, G␤ and G␥) in female rat osteoblasts using Western immunoblotting. The action of calcitriol on InsP 3 formation and Ca 2ϩ mobilization in Fura-2-loaded confluent osteoblasts involved G␣ q/11 . The membrane effects of estradiol involved G␤␥; subunits, and principally G␤ subunits, but not ␣-subunits. These results may provide additional evidence for membrane receptors of steroid hormones. Since PLC-␤1 is the target effector of G␣ q/11 , whereas PLC-␤2 is only activated by ␤␥ subunits, this specificity may help to generate membrane receptor-specific responses in vivo. J.