Proteolytic processing of dentin sialophosphoprotein (DSPP) is essential to dentinogenesis.
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DSPP, which plays a crucial role in dentin formation, is processed into the NH(2)-terminal and COOH-terminal fragments. We believe that the proteolytic processing of DSPP is an essential activation step for its biological function in biomineralization. We tested this hypothesis by analyzing transgenic mice expressing the mutant D452A-DSPP in the Dspp-knock-out (Dspp-KO) background (referred to as "Dspp-KO/D452A-Tg" mice). We employed multipronged approaches to characterize the dentin of the Dspp-KO/D452A-Tg mice, in comparison with Dspp-KO mice and mice expressing the normal DSPP transgene in the Dspp-KO background (named Dspp-KO/normal-Tg mice). Our analyses showed that 90% of the D452A-DSPP in the dentin of Dspp-KO/D452A-Tg mice was not cleaved, indicating that D452A substitution effectively blocked the proteolytic processing of DSPP in vivo. While the expression of the normal DSPP fully rescued the dentin defects of the Dspp-KO mice, expressing the D452A-DSPP failed to do so. These results indicate that the proteolytic processing of DSPP is an activation step essential to its biological function in dentinogenesis.