Dentin Matrix Protein 1 Regulates Dentin Sialophosphoprotein Gene Transcription during Early Odontoblast Differentiation

Abstract

Dentin mineralization requires transcriptional mechanisms to induce a cascade of gene expression for progressive development of the odontoblast phenotype. During cytodifferentiation of odontoblasts there is a constant change of actively transcribed genes. Thus, tissue-specific matrix genes that are silenced in early differentiation are expressed during the terminal differentiation process. Dentin sialophosphoprotein (DSPP) is an extracellular matrix, prototypical dentin, and a bone-specific gene, however, the molecular mechanisms by which it is temporally and spatially regulated are not clear. In this report, we demonstrate that dentin matrix protein 1 (DMP1), which is localized in the nucleus during early differentiation of odontoblasts, is able to bind specifically with the DSPP promoter and activate its transcription. We have identified the specific promoter sequence that binds specifically to the carboxyl end of DMP1. The DNA binding domain in DMP1 resides between amino acids 420 and 489. A chromatin immunoprecipitation assay confirmed the in vivo association of DMP1 with the DSPP promoter. Interactions between DMP1 and DSPP promoter thus provide the foundation to understand how DMP1 regulates the expression of the DSPP gene.Odontoblast differentiation is a well designed process that couples cell-cycle withdrawal with the synthesis of dentin matrix proteins. A number of macromolecules are involved in dentin mineralization. One such protein, dentin sialophosphoprotein (DSPP) 2 is produced by terminally differentiated odontoblasts and is known to modulate dentin mineralization. DSPP is a compound gene encoding for two proteins namely DSP (dentin sialoprotein) and PP (phosphophoryn) (1). Earlier reports have indicated DSPP as the sole odontoblast-specific gene (2); however, a recent report demonstrates low levels of expression in osteoblasts and calvarial tissue (3).Tissue-specific gene expression is complex and, among many events, requires the orderly binding of transcription factors to specific gene regulatory sequences, alteration of chromatin structure by acetyltransferases and demethylases, and recruitment of the RNA polymerase II complex (4). The temporal and spatial expression of DSPP is tightly regulated by the transcriptional elements in the promoter (5). In an attempt to identify the regulatory elements controlling the temporal and spatial expression of DSPP, a DSPP promoter of ϳ1.7 kb has been cloned and characterized to a certain extent (6). Deletion mapping experiments indicated the presence of various regulatory sequences (7). The activity of this promoter has been demonstrated by transgenic technology with a reporter construct expressing LacZ under the control of the DSPP promoter (5). It was reported that DSPP transcription is regulated by several positive and negative regulators of gene transcription in combination with the various signaling pathways/networks. Some of the negative factors known to down-regulate DSPP promoter activity have been reported earlier, including transforming growth f...

FAM20C Plays an Essential Role in the Formation of Murine Teeth

“…Previous studies have shown that DMP1, in addition to its direct role in matrix mineralization, also enters the nucleus in the unphosphorylated form and regulates the transcriptional expression of Dspp (21,28). The regulation of Dspp by DMP1 is further supported by our recent findings that the expression of the Dspp transgene driven by the 3.6-kb Col 1a1 promoter rescued the dentin defects in the Dmp1 knock-out mice.…”

Stress Chaperone GRP-78 Functions in Mineralized Matrix Formation

“…Recently, we have demonstrated that dentin matrix protein 1 (DMP1), an acidic phosphoprotein, initially identified from the extracellular dentin matrix and implicated in differentiation of mesenchymal cells and also in biomineralization (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23), binds to GRP-78 found on the plasma membrane of odontoblasts and is endocytosed via the caveolar pathway (24). In the present study we show that a similar physiological process occurs in pre-osteoblasts and osteoblasts.…”

Endoplasmic Reticulum Chaperone Protein GRP-78 Mediates Endocytosis of Dentin Matrix Protein 1

“…In the nucleus DMP1 played a regulatory role in the regulation of specific genes that control osteoblast and odontoblast differentiation (2,3). Specifically, we showed that DMP1 functions as a transcriptional regulator of the odontoblast specific gene dentin sialophosphoprotein (3).…”

“…Although initially isolated from the dentin matrix and thought to be unique to dentin and named accordingly, DMP1 has now been found to be present in all mineralized tissues of the vertebrate system (1)(2)(3).…”