The iron-binding protein ferritin is expressed in cells of the osteoblastic lineage in vitro and in vivo

Ferritin, a metal-binding protein responsible for maintaining the bioavailability of iron, has been demonstrated in cells of the osteoblastic lineage. Messenger RNAs encoding the light and heavy chain subunits of ferritin were detected in ROS 17 2.8, ROS 25 1, and UMR106 rat osteosarcoma cell lines, in fetal rat calvaria, and in primary cultures of rat calvarial osteoblast-like cells. In vivo, the expression of ferritin light-chain mRNA was observed in both active osteoblasts and in osteocytes. A 450-kD iron-binding protein was immunoprecipitated from ROS 17 2.8 cells by an antiferritin antiserum. This protein comigrated with native ferritin, and could be dissociated into subunits comigrating with ferritin light and heavy chains. Addition of extracellular Fe⁵⁹-transferrin to cultures of ROS 17 2.8 cells resulted in the sequestration of the iron in intracellular ferritin. These observations demonstrate that cells of the osteoblastic lineage possess a functional ferritin-based iron uptake and storage system capable of regulating metal homeostasis in bone.