1-ALPHA,25-DIHYDROXYVITAMIN D-3 STIMULATION OF OSTEOPONTIN EXPRESSIONIN RAT CLONAL DENTAL-PULP CELLS

Osteopontin (OPN) is a major phosphorylated non-collagenous protein is olated from bone. Rat clonal dental-pulp cell lines RPC-C2A and RDP4-1 produce and secrete OPN as a principal phosphoprotein. 1 alpha,25-dih ydroxyvitamin D-3 [1,25(OH)(2)D-3] is a potent calcitropic hormone whi ch regulates calcified tissue metabolism including the synthesis of ex tracellular matrix proteins. The effects of 1,25(OH)(2)D-3 on the expr ession of OPN mRNA and the synthesis of OPN protein by pulp cells in v itro were investigated. In RPC-C2A cells, 1,25(OH)(2)D-3 markedly stim ulated synthesis of both [(PO4)-P-32]- and [S-35]-methionine-labelled OPN. Phosphorylated OPN synthesis increased dose-dependently and showe d a maximum level at 48 h after addition of 10(-11)-10(-7) M 1,25(OH)( 2)D-3. Similar stimulation was also observed in RDP4-1 cells. Northern hybridization analysis revealed that 1,25(OH)(2)D-3 greatly increased the level of OPN mRNA in both pulp cell lines. Examination of the tim e course of the effects of 1,25(OH)(2)D-3 on the level of OPN mRNA in RPC-C2A cells by dot-blot analysis showed that stimulation was detecta ble at 24 h and reached a maximum at 48 h after exposure to 10(-7) M 1 ,25(OH)(2)D-3. These findings indicate that 1,25(OH)(2)D-3 stimulates the production of dental-pulp OPN by a mechanism that involves de novo synthesis and transcriptional control.