Cementum protein 1 (CEMP1) induces a cementoblastic phenotype and reduces osteoblastic differentiation in periodontal ligament cells

Cementum is a calcified tissue covering the tooth root surface, which functions as rigid tooth-anchoring structure. Periodontal ligament is a unique non-mineralized connective tissue, and is a source of mineralized tissue forming cells such as cementoblasts and osteoblasts. The CEMP1 is a novel cementum component the presence of which appears to be limited to cementoblasts and their progenitors. In order to understand the function of CEMP1, we investigated CEMP1 expression during the differentiation of human periodontal ligament cells. Immunomagnetically enriched alkaline phosphatase (ALP)-positive periodontal ligament cells preferentially expressed CEMP1. CEMP1 expression was reduced when periodontal ligament cells differentiated to osteoblasts in vitro. Over-expression of CEMP1 in periodontal ligament cells enhanced cementoblast differentiation and attenuated periodontal and osteoblastic phenotypes. Our data demonstrate for the first time that the CEMP1 is not only a marker protein for cementoblast-related cells, but it also regulates cementoblast commitment in periodontal ligament cells.     

Promoter structure of mouse RANKL/TRANCE/OPGL/ODF gene

Receptor activator of NF-kappa B ligand (RANKL)/tumor necrosis factor-related activation induced cytokine (TRANCE)/osteoprotegerin ligand (OPGL)/osteoclast differentiation factor (ODF) is a membrane-bound signal transducer responsible for differentiation and maintenance of osteoclasts. To elucidate the mechanism regulating RANKL/TRANCE/OPGL/ODF gene expression, we cloned the 5'-flanking basic promoter region of the mouse RANKL/TRANCE/OPGL/ODF gene and characterized it by transient transfection studies and genomic Southern blot analysis. Inverted TATA- and CAAT-boxes and a putative Cbfa1/Osf2/AML3 binding domain constituted the basic promoter structure. The repeated half-sites for the vitamin D3 (VitD3) and glucocorticoid receptors were located at -935 and -640, respectively. Transient transfection studies revealed that short-term treatment with 1alpha,25(OH)2 VitD3 or dexamethasone increased luciferase activity up to 204% and 178%, respectively; on the other hand, treatment with dibutyryl cyclic AMP did not affect the promoter activity. Since the expression of Cbfa1/Osf2/AML3 is also regulated by VitD3, 1alpha,25(OH)2 VitD3 might affect RANKL/TRANCE/OPGL/ODF gene expression both directly and indirectly. CpG methylation was observed dominantly in mouse stromal cells, ST2, of a later passage which ceased to support in vitro osteoclastogenesis, suggesting that the methylation status of the CpG loci in the RANKL/TRANCE/OPGL/ODF gene promoter may be one of the influential cis-regulating factors.