Failure to process dentin matrix protein 1 (DMP1) into fragments leads to its loss of function in osteogenesis.
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.
Sun
Yao
Y
Department of Biomedical Sciences, Baylor College of Dentistry, Texas A&M University System Health Science Center, Dallas, Texas 75246, USA.
Prasad
Monica
M
Gao
Tian
T
Wang
Xiaofang
X
Zhu
Qinglin
Q
D'Souza
Rena
R
Feng
Jian Q
JQ
Qin
Chunlin
C
D019943:Amino Acid Substitution; D000818:Animals; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D020125:Mutation, Missense; D010012:Osteogenesis / Q000502:physiology*; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*
C513308:Dmp1 protein, mouse; D016326:Extracellular Matrix Proteins; D011498:Protein Precursors