The ER Ca²⁺ sensor STIM1 can activate osteoblast and odontoblast differentiation in mineralized tissues

Bone and dentin development requires temporal and spatial deposition of calcium phosphate mineral. A host of proteins works in concert to contribute to this tightly regulated process while malfunction in this scheme often leads to pathological defects. We have reported earlier that DMP1 stimulation of preosteoblasts leads to calcium release from internal Ca²⁺ stores and this store depletion is sensed by the ER Ca²⁺ sensor STIM1 (stromal interaction molecule 1). In this study, we first assessed the temporal and spatial localization of STIM1 protein during the development of bone and dentin by immunohistochemical methods. We further analyzed the function of STIM1 by establishing a stable MC3T3-E1 cell-line by overexpressing STIM1 (MC3T3-E1/STIM1 OE). Under mineralizing conditions, STIM1 overexpressing cells showed increased calcium deposits with higher expression of key osteogenic markers, such as Runx2 and type I collagen, BMP4 when compared with the control cells. Our results demonstrate that during mineralized matrix formation STIM1, the key ER sensor protein, can promote cellular differentiation in the presence of extracellular calcium.