Annexin II is the membrane receptor that mediates the rapid actions of 1 alpha,25-dihydroxyvitamin D-3

1 alpha,25-Dihydroxyvitamin D-3 has been shown to exert its effects by both genomic (minutes to hours) and rapid (seconds to minutes) mechanisms. The genomic effects are mediated by interaction with the nuclear vitamin D rece ptor. We show that the vitamin D analog, [C-14]-1 alpha,25-dihydroxyvitamin D-3 bromoacetate, is specifically bound to a protein (molecular weight 36 kDa) in the plasma membrane of rat osteoblastlike cells (ROS 24/1). The pla sma membrane protein labeled with the bromoacetate analog was identified as annexin II by sequence determination and Western blot. Partially purified plasma membrane proteins (PI 6.9-7.4) and purified annexin II exhibited spe cific and saturable binding for [H-3]-1 alpha,25-dihydroxyvitamin D-3. Anti bodies to annexin II inhibited [C-14]-1 alpha,25-dihydroxyvitamin D-3 bromo acetate binding to ROS 24/1 plasma membranes, immunoprecipitated the ligand -protein complex, and inhibited 1 alpha,25-dihydroxyvitamin D-3-induced inc reases in intracellular calcium in ROS 24/1 cells. The results indicate tha t annexin II may serve as a receptor for rapid actions of 1 alpha,25-dihydr oxyvitamin D-3. (C) 2000 Wiley-Liss, Inc.