Identification of Avian Sarcoplasmic Reticulum Ca2+-ATPase (SERCA3) as a Novel 1,25(OH)2D3 Target Gene in the Monocytic Lineage

Osteoclasts are postmitotic, multinucleated giant cells generated by the fusion of hematopoietic mononuclear precursors from the monocyte–macrophage lineage. In culture, adherent macrophages from blood-derived monocytes grow, gather, and fuse together to form multinucleated osteoclast-like cells. These events are controlled by 1,25(OH)2D3. To sort out new 1,25(OH)2D3 target genes involved in osteoclast differentiation, we have performed an RT-PCR differential display using mRNA from macrophages induced for 10 h by 1,25(OH)2D3 compared to nontreated cells. We have identified a new target gene, a chick ATP-dependent Ca2+ pump, ChkSERCA3. Although the level of the corresponding transcript increases during the differentiation process from macrophages to osteoclast-like cells, its steady-state level is downregulated by hormone treatment. The action of 1,25(OH)2D3 on the Ca2+-ATPase gene expression is independent of de novo protein synthesis and is hormone dose dependent. This expression in adult chick was restricted to the hematopoietic cell lineage, spleen, lung, intestine, and brain, whereas no expression was detected in embryos. The function of the protein can be predicted from its high homology with the other members of the SR ATP-dependent Ca2+ pump family, i.e., storage and control of cytosolic Ca2+ directly regulated by 1,25(OH)2D3, further supporting the critical role for intracellular calcium in highly specialized cells such as osteoclasts.