Identification and characterization of a novel protein, periostin, with restricted expression to periosteum and periodontal ligament and increased expression by transforming growth factor beta

We had previously identified the cDNA for a novel protein called osteoblast -specific factor 2 (OSF-2) from an MC3T3-E1 cDNA library using subtraction hybridization and differential screening techniques. Here we describe the l ocalization, regulation, and potential function of this protein. Immunohist ochemistry using specific antiserum revealed that in adult mice, the protei n is preferentially expressed in periosteum and periodontal ligament, indic ating its tissue specificity and a potential role in bone and tooth formati on and maintenance of structure, Based on this observation and the fact tha t other proteins have been called OSF-2, the protein was renamed "periostin ," Western blot analysis showed that periostin is a disulfide linked 90 kDa protein secreted by osteoblasts and osteoblast-like cell lines. Nucleotide sequence revealed four periostin transcripts that differ in the length of the C-terminal domain, possibly caused by alternative splicing events. Reve rse transcription- polymerase chain reaction analysis revealed that these i soforms are not expressed uniformly but are differentially expressed in var ious cell lines. Both purified periostin protein and the periostin-Fc recom binant protein supported attachment and spreading of MC3T3-E1 cells, and th is effect was impaired by antiperiostin antiserum, suggesting that periosti n is involved in tell adhesion. The protein is highly homologous to beta ig -h3, a molecule induced by transforming growth factor beta (TGF-beta) that promotes the adhesion and spreading of fibroblasts, Because TGF-beta has dr amatic effects on periosteal expansion and the recruitment of osteoblast pr ecursors, this factor was tested for its effects on periostin expression, B y Western blot analysis, TGF-beta increased periostin expression in primary osteoblast cells. Together, these data suggest that periostin may play a r ole in the recruitment and attachment of osteoblast precursors in the perio steum.