Runx2 is involved in regulating amelotin promoter activity and gene expression in ameloblasts

Amelotin (Amtn) is an enamel matrix protein that plays an essential role in enamel biomineralization. The Runt-related transcription factor 2 (Runx2) is critical for tooth and bone development. Here we studied the role of Runx2 in the regulation of Amtn gene expression in ameloblasts. Immunohistochemistry data showed that Runx2 protein was strongly expressed in the nuclei of ameloblasts during the transition to maturation stages of mouse incisor development. Reverse transcription-polymerase chain reaction (RT-PCR) showed that Runx2 and Amtn were co-expressed in ameloblast-lineage cell (ALC) culture. Runx2 knockdown led to a decrease in Amtn expression. Over-expression of Runx2 resulted in an increase in Amtn expression as well as an enhanced Amtn promoter activity. Site-directed mutagenesis of the putative Runx2 binding site (-1342/-1336) in the Amtn promoter caused a decrease in the basal promoter activity, and showed no response to Runx2 overexpression. Overall, these results suggested that Runx2 played an essential role in regulating Amtn gene expression by specifically binding to the Amtn promoter during amelogenesis.