Dentin sialophosphoprotein-derived proteins in the dental pulp

Porcine dentin sialophosphoprotein (dspp),the most abundant noncollagenous protein in dentin,is critical for proper mineralization of tooth dentin. dspp is processed by proteases into 3 major domains: dentin sialoprotein (dsp),dentin glycoprotein (dgp),and dentin phosphoprotein (dpp). there are at least 2 mrna variants expressed from the dspp gene: one encodes the full-length dspp protein (dsp+dgp+dpp); the other encodes only dsp. the shorter transcript is generated through the use of a polyadenylation signal within intron 4,immediately following the dsp coding region (dgp and dpp are encoded by exon 5). we fractionated dspp-derived proteins from the dental pulp of developing porcine incisors using heparin chromatography. dsp was identified,but little dpp could be detected in any fractions. bmp-1 digestion of dspp-derived proteins extracted from dental pulp did not generate new dpp bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (indicating an absence of intact dspp),although the results suggested another bmp-1 cleavage site within dsp. we further purified dspp-derived protein by reversed-phase high-performance liquid chromatography. its amino acid composition was similar to dsp. expression of the full-length dspp mrna by quantitative real-time polymerase chain reaction analysis was significantly higher in odontoblasts than in pulp,while expression of the dsp-only mrna was almost equal in odontoblasts and in the body of the pulp. expression of the full-length dspp mrna was also significantly higher than the expression of dsp-only mrna in odontoblasts. both the full-length and the dsp-only dspp mrna showed only trace expression in the pulp tip. we conclude that use of the 3′ polyadenylation signal in exon 5 predominates in fully differentiated odontoblasts,while both polyadenylation signals are used throughout odontoblast differentiation. © international & american associations for dental research.