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Small Heterodimer Partner (SHP) interacts with diverse transcription factors such as Runx2 and regulates many cellular events including differentiation, proliferation, and energy metabolism. SHP is reported to be a positive regulator of BMP2-induced bone formation. This study aimed to clarify the role of SHP in odontoblast differentiation and matrix mineralization. Rat tooth germs were isolated, and gene expression was determined by RT-PCR and real-time PCR. Localization of SHP protein expression was identified by immunofluorescent analysis. Primary human dental pulp cells (HDPCs) were cultured with BMP2 and/or Ad-siSHP. Matrix mineralization was evaluated by Alizarin red staining. Transient transfection experiment was performed with the SHP or Dlx5 expressional plasmids and the DSPP gene. In tooth germs from post-natal days 3 to 9, BMP-2 and SHP expression increased with DSPP and DMP1 mRNA expression. In an immunostaining study, SHP was expressed in odontoblasts and surrounding osteoblasts. When HDPCs were cultured with BMP2 in mineralization-inducing medium, SHP expression also increased with an increase in DSPP expression. Down-regulation of SHP by Ad-siSHP inhibited matrix mineralization. In transient transfection experiments, overexpression of SHP was shown to enhance DSPP promoter activity through interactions between SHP and Dlx5. These results suggest that SHP may mediate BMP2 signaling to promote mineralization of the dentin matrix. [ABSTRACT FROM PUBLISHER]