Failure to process dentin matrix protein 1 (DMP1) into fragments leads to its loss of function in osteogenesis.
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Dentin matrix protein 1 (DMP1), an acidic protein important to the formation of bone and dentin, primarily exists as the processed NH(2)-terminal and COOH-terminal fragments in the extracellular matrix of the two tissues. Previous in vitro studies showed that the substitution of residue Asp(213) by Ala(213) (D213A) at a cleavage site blocked the processing of mouse DMP1 in cells. In this study, we generated transgenic mice expressing mutant D213A-DMP1 (WT/D213A-Tg mice) to test the hypothesis that the proteolytic processing of DMP1 is an activation step essential to osteogenesis. By crossbreeding WT/D213A-Tg mice with Dmp1 knock-out (Dmp1-KO) mice, we obtained mice expressing D213A-DMP1 in a Dmp1-KO background; these mice will be referred to as "Dmp1-KO/D213A-Tg" mice. Biochemical, radiological, and morphological approaches were used to characterize the skeletal phenotypes of Dmp1-KO/D213A-Tg mice compared with wild-type mice, Dmp1-KO mice, and Dmp1-KO mice expressing the normal Dmp1 transgene. Protein chemistry analyses showed that DMP1 was barely cleaved in the bone of the Dmp1-KO/D213A-Tg mice, indicating that D213A substitution effectively blocked the proteolytic processing of DMP1 in vivo. While the expression of the normal Dmp1 transgene completely rescued the phenotypic skeletal changes of the Dmp1-KO mice, the expression of the mutant D213A-Dmp1 transgene failed to do so. These results indicate that the full-length form of DMP1 is an inactive precursor and its proteolytic processing is an activation step essential to the biological functions of this protein in osteogenesis.
author list (cited authors)
Sun, Y., Prasad, M., Gao, T., Wang, X., Zhu, Q., D'Souza, R., Feng, J. Q., & Qin, C.
complete list of authors
Sun, Yao||Prasad, Monica||Gao, Tian||Wang, Xiaofang||Zhu, Qinglin||D'Souza, Rena||Feng, Jian Q||Qin, Chunlin