1alpha,25(OH)2-vitamin D3 membrane-initiated calcium signaling modulates exocytosis and cell survival.
1alpha,25(OH)(2)-vitamin D(3) (1,25D) is considered a bone anabolic hormone. 1,25D actions leading to bone formation involve gene transactivation, on one hand, and modulation of cytoplasmic signaling, on the other. In both cases, a functional vitamin D receptor (VDR) appears to be required. Here we study 1,25D-stimulated calcium signaling that initiates at the cell membrane and leads to exocytosis of bone materials and increased osteoblast survival. We found that rapid 1,25D-induction of exocytosis couples to cytoplasmic calcium increase in osteoblastic ROS 17/2.8 cells. In addition, we found that elevation of cytoplasmic calcium concentration is involved in 1,25D anti-apoptotic effects via Akt activation in ROS 17/2.8 cells and non-osteoblastic CV-1 cells. In both cases, 1,25D-stimulated elevation of intracellular calcium is due in part to activation of L-type Ca(2+) channels. We conclude that 1,25D bone anabolic effects that involve increased intracellular Ca(2+) concentration in osteoblasts can be explained at two levels. At the single-cell level, 1,25D promotes Ca(2+)-dependent exocytotic activities. At the tissue level, 1,25D protects osteoblasts from apoptosis via a Ca(2+)-dependent Akt pathway. Our studies contribute to the understanding of the molecular basis of bone diseases characterized by decreased bone formation and mineralization.
Xiaoyu
Zhang
Z
Department of Biochemistry, University of California-Riverside, Riverside, CA 92521, USA.
Payal
Biswas
B
Melissa
Owraghi
O
Zanello
Laura P
LP
D000818:Animals; D002117:Calcitriol / Q000378:metabolism*; D020013:Calcium Signaling; D045744:Cell Line, Tumor; D002470:Cell Survival; D005089:Exocytosis; D051381:Rats
D002117:Calcitriol