This application describes a proposal that is based on the overall hypothesis that non-collagenous extracellular matrix proteins play vital roles in the formation of dentin by odontoblasts and in homeostatic mechanisms of formation and breakdown of bone by osteoblasts and osteoclasts. In particular, this proposal focuses upon members of a family of phosphorylated glycoproteins called sialic acid (SA)-rich proteins, also termed the SIBLING family. These proteins are single chains that contain a RGD sequence in a beta-turn-beta motif that is capable of interacting with cell surface integrins. They appear to act as initiators or controllers of apatite crystal formation as developing bone and dentin mineralize. Two members of this family, osteopontin (OPN) and bone sialoprotein (BSP) interact with avb3 integrins on osteoclasts and promote signaling and ultimately bone resorption. Recent data from our laboratory, as well as from other investigators, indicate that phosphoserines of OPN and BSP are necessary for their influences of SA-rich proteins on mineral formation and growth and on bone resorption. Dentin matrix protein 1 (DMP1) is a very acidic member of this SA-rich protein family that was discovered by gene cloning. To date, native DMP1 has not been isolated and characterized. Recently, we have identified DMP1 as a 150-200 kDa protein in dentin ECM. The large content of phosphoserine suggests that DMP1 may play an important role in mineral formation and growth and in bone resorption. In bone, DMP1 appears to be proteolytically processed to smaller fragments of Mr 57 kDa and 37 kDa. Another SA-rich protein, DSP, is coded on the same gene (dspp) as dentin phosphoprotein, DPP. The translation product of this gene, presumably a large precursor protein, DSPP, has not been demonstrated experimentally.
The Specific Aims for this application are: 1. To study the proteolytic processing of DSPP to DSP and DPP; 2. To isolate and characterize native DMP1, to test its potential biological functions and to study its biosynthesis and secretion in bone and dentin; 3. To characterize the 57 kDa and 37 kDa proteins from bone, to determine if they retain biological functions and to demonstrate the conversion of native DMP1 to 57 kDa and 37 kDa proteins in osteoblasts.
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