Role of Cbfa1 in ameloblastin gene transcription

Ameloblastin is a tooth-specific extracellular matrix protein that is thoug ht to play a role in enamel crystal formation in the developing dentition. The murine ameloblastin promoter functions in a cell type-specific manner a nd contains cas-acting elements that function both to enhance and to suppre ss transcription. The objective of this study was to determine whether the transcription factor Cbfa1, known to be essential for transcription of othe r mineralized tissue genes, is also required for ameloblastin transcription . Site-directed mutagenesis of the Cbfa1-binding site (-248 base pairs) ter med osteoblast-specific element 2 (OSE2) decreased ameloblastin promoter ac tivity by greater than 50% in ameloblast-like cells. No differences in prom oter activity were observed in two other oral tissue-derived cell lines tra nsfected with similar constructs. Nuclear factor binding to the ameloblasti n promoter was also shown to be cell type-specific and was altered by site- specific mutations in the OSE2 site. Cbfa1 was specifically shown to partic ipate in the DNA-protein complexes between nuclear factors and the amelobla stin OSE2 site by supershift electrophoretic mobility shift assays. The fin dings that Cbfa1 interacts with functionally important regions of the amelo blastin promoter while promoter activity is diminished in constructs contai ning site-directed mutations in the Cbfa1 site indicate that Cbfa1 possesse s an important function in transcription of the ameloblastin gene.