An extracellular matrix protein of dentine, enamel, and bone shares common antigenic determinants with keratins.

EDTA-soluble proteins extracted from rabbit dentine were injected into mice and antibodies were prepared by the hybridoma technique. A monoclonal antibody, MC9B5, was found to react with a 68 kd protein, a major component of the EDTA-soluble proteins present in rabbit and rat dentine. Weston immunoblotting demonstrated that the antigen was also present in rat enamel and bone. By indirect immunofluorescence, MC9B5 was found to specifically stain epithelial filamentous cytoskeletal structures. Double staining experiments using MC9B5 and antikeratin antibodies showed extensive co-localization on the epithelial cell cytoskeleton. Furthermore, the 68 kd extracellular matrix protein was recognized in dentine, enamel, and bone extracts by antikeratin antibodies as shown by immunoblotting. These data support a structural relationship between a mineralized tissue extracellular protein and keratins.