Transcriptional regulation of dentin matrix protein 1 (DMP1) by AP-1 (c-fos/c-jun) factors

An amelogenin-based peptide hydrogel promoted the odontogenic differentiation of human dental pulp cells

Amelogenin can induce odontogenic differentiation of human dental pulp cells (HDPCs), which has great potential and advantages in dentine-pulp complex regeneration. However, the unstability of amelogenin limits its further application. This study constructed amelogenin self-assembling peptide hydrogels (L-gel or D-gel) by heating-cooling technique, investigated the effects of these hydrogels on the odontogenic differentiation of HDPCs and explored the underneath mechanism. The critical aggregation concentration, conformation, morphology, mechanical property and biological stability of the hydrogels were characterized, respectively. The effects of the hydrogels on the odontogenic differentiation of HDPCs were evaluated via alkaline phosphatase activity measurement, quantitative reverse transcription polymerase chain reaction, western blot, Alizarin red staining and scanning electron microscope. The mechanism was explored via signaling pathway experiments. Results showed that both the L-gel and D-gel stimulated the odontogenic differentiation of HDPCs on both Day 7 and Day 14, while the D-gel showed the highest enhancement effects. Meanwhile, the D-gel promoted calcium accumulation and mineralized matrix deposition on Day 21. The D-gel activated MAPK-ERK1/2 pathways in HDPCs and induced the odontogenic differentiation via ERK1/2 and transforming growth factor/smad pathways. Overall, our study demonstrated that the amelogenin peptide hydrogel stimulated the odontogenic differentiation and enhanced mineralization, which held big potential in the dentine-pulp complex regeneration.

Mineral Trioxide Aggregate (MTA) Upregulates the Expression of DMP1 in Direct Pulp Capping in the Rat Molar

Mineral trioxide aggregate (MTA) is an alternative endodontic material that predicts conductive or inductive calcified tissue formation from immature pulp mesenchymal stem cells (IPMSCs). The purpose of this study was to investigate whether MTA could promote reparative odontoblast differentiation via IPMSCs in the early phase of regeneration and compare with calcium hydroxide (CH). Direct pulp capping using calcium hydroxide (CH), MTA, and MTA with platelet-rich plasma (MTA + PRP) was performed on maxillary first molars of 8-week-old male Wistar rats (n = 36). After 3, 7, or 14 days, the teeth were analyzed for mineral density (MD) and volume of MD (VMD) via micro-focusing computed tomography (µCT), nestin, dentin matrix acidic phosphoprotein 1 (DMP1) immunohistochemistry, and real-time PCR for DMP1 mRNA expression. MTA stimulated the early phase differentiation of the IPMSCs into odontoblasts, with positive results for nestin and DMP1 compared with CH. Moreover, MTA + PRP stimulated calcified granule and dentin bridge formation through calcium mineral deposition, following the induction of DMP1 mRNA expression in IPMSCs. Our results suggested that the combination of MTA and PRP is an effective and clinically applicable method for activating endogenous dental pulp stem cells into odontoblasts in the early stages of pulp regeneration.

The Long Non-coding RNA lnc-DMP1 Regulates Dmp1 Expression Through H3K27Ac Modification

Several long non-coding RNAs (lncRNAs) have been reported regulate the expression of neighbor protein-coding genes at post-transcriptional, transcriptional and epigenetic levels. Dmp1 (Dentin matrix protein 1), encoding a non-collagenous extracellular matrix protein, plays an important role in dentin and bone mineralization. However, the transcriptional regulation of lncRNA on Dmp1 has not been reported. In this study, we identified a novel lncRNA named lnc-DMP1, which is near the Dmp1 gene region and undergoes remarkable changes during mandible development. lnc-DMP1 is co-localized and significantly expressed correlation with Dmp1 in embryonic and postnatal mouse mandibles. In MC3T3-E1 cells, lnc-DMP1 positively regulates DMP1 expression and skeletal mineralization. Furthermore, lnc-DMP1 induces the promoter activity of Dmp1 by modulating H3K27Ac enrichment in the Dmp1 promoter. In conclusion, our results indicate that lnc-DMP1 is a novel lncRNA near the Dmp1 gene region and regulates Dmp1 expression by modulating the H3K27 acetylation level of Dmp1 promoter.

Exogenous nitric oxide stimulates the odontogenic differentiation of rat dental pulp stem cells

Nitric oxide (NO) is thought to play a pivotal regulatory role in dental pulp tissues under both physiological and pathological conditions. However, little is known about the NO functions in dental pulp stem cells (DPSCs). We examined the direct actions of a spontaneous NO gas-releasing donor, NOC-18, on the odontogenic capacity of rat DPSCs (rDPSCs). In the presence of NOC-18, rDPSCs were transformed into odontoblast-like cells with long cytoplasmic processes and a polarized nucleus. NOC-18 treatment increased alkaline phosphatase activity and enhanced dentin-like mineralized tissue formation and the expression levels of several odontoblast-specific genes, such as runt related factor 2, dentin matrix protein 1 and dentin sialophosphoprotein, in rDPSCs. In contrast, carboxy-PTIO, a NO scavenger, completely suppressed the odontogenic capacity of rDPSCs. This NO-promoted odontogenic differentiation was activated by tumor necrosis factor-NF-κB axis in rDPSCs. Further in vivo study demonstrated that NOC-18-application in a tooth cavity accelerated tertiary dentin formation, which was associated with early nitrotyrosine expression in the dental pulp tissues beneath the cavity. Taken together, the present findings indicate that exogenous NO directly induces the odontogenic capacity of rDPSCs, suggesting that NO donors might offer a novel host DPSC-targeting alternative to current pulp capping agents in endodontics.

Dentin Matrix Protein 1 (DMP1): New and Important Roles for Biomineralization and Phosphate Homeostasis

Previously, non-collagenous matrix proteins, such as DMP1, were viewed with little biological interest. The last decade of research has increased our understanding of DMP1, as it is now widely recognized that this protein is expressed in non-mineralized tissues, as well as in cancerous lesions. Protein chemistry studies have shown that the full length of DMP1, as a precursor, is cleaved into two distinct forms: the C-terminal and N-terminal fragments. Functional studies have demonstrated that DMP1 is essential in the maturation of odontoblasts and osteoblasts, as well as in mineralization via local and systemic mechanisms. The identification of DMP1 mutations in humans has led to the discovery of a novel disease: autosomal-recessive hypophosphatemic rickets. Furthermore, the regulation of phosphate homeostasis by DMP1 through FGF23, a newly identified hormone that is released from bone and targeted in the kidneys, sets a new direction for research that associates biomineralization with phosphate regulation.

Root and Eruption Defects in c-Fos Mice Are Driven by Loss of Osteoclasts

c-Fos homozygous mice lack osteoclasts with a failure of the teeth to erupt and with an arrest of root development. Here, we characterize the defects associated with the failure in root development and the loss of the tooth-bone interface, and we investigate the underlying causes. We show that, while homozygous c-Fos mice have no multinucleated osteoclasts, heterozygous mice have a reduction in the number of osteoclasts with a reduction in the tooth-bone interface during development and subtle skeletal defects postnatally. In the homozygous mutants bone is found to penetrate the tooth, particularly at the apical end, physically disrupting the root forming HERS (Hertwig's epithelial root sheath) cells. The cells of the HERS continue to proliferate but cannot extend downward due to the presence of bone, leading to a loss of root formation. Tooth germ culture showed that the developing tooth invaded the static bone in mutant tissue, rather than the bone encroaching on the tooth. Although c-Fos has been shown to be expressed in developing teeth, the defect in maintenance of the tooth-bone interface appears to be driven solely by the lack of osteoclasts, as this defect can be rescued in the presence of donor osteoclasts. The rescue suggests that signals from the tooth recruit osteoclasts to clear the bone from around the tooth, allowing the tooth to grow, form roots, and later erupt.

Enhanced Dentinogenesis of Pulp Progenitors by Early Exposure to FGF2

Members of the fibroblast growth factor (FGF) family play essential and important roles in primary and reparative dentinogenesis. Although there appears to be a general agreement on the effects of FGF signaling on the proliferation of pulp cells, there are conflicting results regarding its effects on odontoblast differentiation. We recently examined the effects of continuous exposure of dental pulp cells to FGF2 and showed that the effects of FGF2 on differentiation of progenitor cells into odontoblasts were stage specific and dependent on the stage of cell maturity. The purpose of this study was to gain further insight into cellular and molecular mechanisms regulating the stimulatory effects of FGF2 on odontoblast differentiation. To do so, we examined the effects of early and limited exposure of pulp cells from a series of green fluorescent protein (GFP) reporter transgenic mice that display stage-specific activation of transgenes during odontoblast differentiation to FGF2. Our results showed that early and limited exposure of pulp cells to FGF2 did not have significant effects on the extent of mineralization but induced significant increases in the expression of Dmp1 and Dspp and the number of DMP1-GFP(+) and DSPP-Cerulean(+) odontoblasts. Our results also showed that the stimulatory effects of FGF2 on odontoblast differentiation were mediated through FGFR/MEK/Erk1/2 signaling, increases in Bmp2, and activation of the BMP/BMPR signaling pathway. These observations show that early and limited exposure of pulp cells to FGF2 alone promotes odontoblast differentiation and provides critical insight for applications of FGF2 in dentin regeneration.

Role of dentin matrix protein 1 in cartilage redifferentiation and osteoarthritis

OBJECTIVE

The aim of this study was to test the possible involvement, relevance and significance of dentin matrix protein 1 (DMP1) in chondrocyte redifferentiation and OA.

METHODS

To examine the function of DMP1 in vitro, bone marrow stromal cells (BMSCs) and articular chondrocytes (ACs) were isolated and differentiated in micromasses in the presence or absence of DMP1 small interfering RNA and analysed for chondrogenic phenotype. The association of DMP1 expression with OA progression was analysed time dependently in the OA menisectomy rat model and in grade-specific OA human samples.

RESULTS

It was found that DMP1 was strongly related to chondrogenesis, which was evidenced by the strong expression of DMP1 in the 14.5-day mouse embryonic cartilage development stage and in femoral heads of post-natal days 0 and 4. In vitro chondrogenesis in BMSCs and ACs was accompanied by a gradual increase in DMP1 expression at both the gene and protein levels. In addition, knockdown of DMP1 expression led to decreased chondrocyte marker genes, such as COL2A1, ACAN and SOX9, and an increase in the expression of COL10A and MMP13 in ACs. Moreover, treatment with IL-1β, a well-known catabolic culprit of proteoglycan matrix loss, significantly reduced the expression of DMP1. Furthermore, we also observed the suppression of DMP1 protein in a grade-specific manner in knee joint samples from patients with OA. In the menisectomy-induced OA model, an increase in the Mankin score was accompanied by the gradual loss of DMP1 expression.

CONCLUSION

Observations from this study suggest that DMP1 may play an important role in maintaining the chondrogenic phenotype and its possible involvement in altered cartilage matrix remodelling and degradation in disease conditions like OA.

Integrating multiple resources to identify specific transcriptional cooperativity with a Bayesian approach

MOTIVATION

Limited cohort of transcription factors is capable to structure various gene-expression patterns. Transcriptional cooperativity (TC) is deemed to be the main mechanism of complexity and precision in regulatory programs. Although many data types generated from numerous experimental technologies are utilized in an attempt to understand combinational transcriptional regulation, complementary computational approach that can integrate diverse data resources and assimilate them into biological model is still under development.

RESULTS

We developed a novel Bayesian approach for integrative analysis of proteomic, transcriptomic and genomic data to identify specific TC. The model evaluation demonstrated distinguishable power of features derived from distinct data sources and their essentiality to model performance. Our model outperformed other classifiers and alternative methods. The application that contextualized TC within hepatocarcinogenesis revealed carcinoma associated alterations. Derived TC networks were highly significant in capturing validated cooperativity as well as revealing novel ones. Our methodology is the first multiple data integration approach to predict dynamic nature of TC. It is promising in identifying tissue- or disease-specific TC and can further facilitate the interpretation of underlying mechanisms for various physiological conditions.

CONTACT

tieliushi01@gmail.com

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Short-term effect of low-intensity pulsed ultrasound on an ex-vivo 3-d tooth culture

We investigated the short-term effect of LIPUS on human dentin-pulp complex in vitro. We collected sixty-three premolars from patients who needed the extraction. The premolars were sectioned transversely into 600-μm-thick slices, and then divided into five groups according to LIPUS application time (control, 5, 10, 15 and 20 min). LIPUS transducer produced an incident intensity of 30 mW/cm(2). After 24 h, tissue was harvested for histomorphometrical analysis and RT-PCR (Genes of interest: Collagen I, DMP1, DSPP, TGF β1, RANKL and OPG). Histomorphometric analysis showed no significant difference among the five groups in the odontoblast count and predentin thickness. RT-PCR demonstrated no expression of TGF β1, low amounts of DSPP, a twofold increase in collagen I expression in the 5- and 10-minute LIPUS groups and a threefold increase in DMP1 expression in the 10-minute LIPUS group. LIPUS application was stimulatory to the dentin-pulp complex in vitro and increased the expression of collagen I and DMP1.

Stimulation of periodontal ligament stem cells by dentin matrix protein 1 activates mitogen-activated protein kinase and osteoblast differentiation

BACKGROUND

Periodontitis can ultimately result in tooth loss. Many natural and synthetic materials have been tried to achieve periodontal regeneration, but the results remain variable and unpredictable. We hypothesized that exogenous treatment with dentin matrix protein 1 (DMP1) activates specific genes and results in phenotypic and functional changes in human periodontal ligament stem cells (hPDLSCs).

METHODS

hPDLSCs were isolated from extracted teeth and cultured in the presence or absence of DMP1. Quantitative polymerase chain reactions were performed to analyze the expression of several genes involved in periodontal regeneration. hPDLSCs were also processed for immunocytochemical and Western blot analysis using phosphorylated extracellular signal-regulated kinase (pERK) and ERK antibodies. Alkaline phosphatase and von Kossa staining were performed to characterize the differentiation of hPDLSCs into osteoblasts. Field emission scanning electron microscopic analysis of the treated and control cell cultures were also performed.

RESULTS

Treatment with DMP1 resulted in the upregulation of genes, such as matrix metalloproteinase-2, alkaline phosphatase, and transforming growth factor β1. Activation of ERK mitogen-activated protein kinase signaling pathway and translocation of pERK from the cytoplasm to the nucleus was observed. Overall, DMP1-treated cells showed increased expression of alkaline phosphatase, increased matrix, and mineralized nodule formation when compared with untreated controls.

CONCLUSION

DMP1 can orchestrate a coordinated expression of genes and phenotypic changes in hPDLSCs by activation of the ERK signaling pathway, which may provide a valuable strategy for tissue engineering approaches in periodontal regeneration.

Identification of secretory odontoblasts using DMP1-GFP transgenic mice

Terminal differentiation of odontoblasts from dental papilla is a long process involving several intermediate steps and changes in the transcriptional profile and expression of proteins secreted by cells in the odontoblast lineage. Transgenic mouse lines in which GFP expression is under the control of tissue- and stage specific promoters have provided powerful experimental tools for identification and isolation of cells at specific stages of differentiation along a lineage. Our previous studies showed utilization of pOBCol3.6GFP and pOBCol2.3GFP animals for identification of odontoblasts at early and late stages of polarization respectively. In the present study we used the DMP1-GFP transgenic animal as an experimental model to examine its expression during the differentiation of odontoblasts from progenitor cells in vivo and in vitro. Our observations showed that DMP1-GFP transgene is first activated in secretory/functional odontoblasts engaged in secretion of predentin and then transiently expressed at high levels in newly differentiated odontoblasts. Expression of DMP1-GFP was down-regulated in highly differentiated odontoblasts. The temporal and spatial pattern of expression of DMP1-GFP transgene closely mimics the expression of endogenous DMP1. This transgenic animal will facilitate studies of gene expression and biological functions in secretory/functional odontoblasts.

Calcium-mediated stress kinase activation by DMP1 promotes osteoblast differentiation

Calcium signaling and calcium transport play a key role during osteoblast differentiation and bone formation. Here, we demonstrate that DMP1 mediated calcium signaling, and its downstream effectors play an essential role in the differentiation of preosteoblasts to fully functional osteoblasts. DMP1, a key regulatory bone matrix protein, can be endocytosed by preosteoblasts, triggering a rise in cytosolic levels of calcium that initiates a series of downstream events leading to cellular stress. These events include release of store-operated calcium that facilitates the activation of stress-induced p38 MAPK leading to osteoblast differentiation. However, chelation of intracellular calcium and inhibition of the p38 signaling pathway by specific pharmacological inhibitors and dominant negative plasmid suppressed this activation. Interestingly, activated p38 MAPK can translocate to the nucleus to phosphorylate transcription factors that coordinate the expression of downstream target genes such as Runx 2, a key modulator of osteoblast differentiation. These studies suggest a novel paradigm by which DMP1-mediated release of intracellular calcium activates p38 MAPK signaling cascade to regulate gene expression and osteoblast differentiation.

Phosphate: known and potential roles during development and regeneration of teeth and supporting structures

Inorganic phosphate (P(i)) is abundant in cells and tissues as an important component of nucleic acids and phospholipids, a source of high-energy bonds in nucleoside triphosphates, a substrate for kinases and phosphatases, and a regulator of intracellular signaling. The majority of the body's P(i) exists in the mineralized matrix of bones and teeth. Systemic P(i) metabolism is regulated by a cast of hormones, phosphatonins, and other factors via the bone-kidney-intestine axis. Mineralization in bones and teeth is in turn affected by homeostasis of P(i) and inorganic pyrophosphate (PPi), with further regulation of the P(i)/PP(i) ratio by cellular enzymes and transporters. Much has been learned by analyzing the molecular basis for changes in mineralized tissue development in mutant and knock-out mice with altered P(i) metabolism. This review focuses on factors regulating systemic and local P(i) homeostasis and their known and putative effects on the hard tissues of the oral cavity. By understanding the role of P(i) metabolism in the development and maintenance of the oral mineralized tissues, it will be possible to develop improved regenerative approaches.

Small integrin-binding ligand N-linked glycoproteins (SIBLINGs): multifunctional proteins in cancer

Numerous components and pathways are involved in the complex interplay between cancer cells and their environment. The family of glycophosphoproteins comprising osteopontin, bone sialoprotein, dentin matrix protein 1, dentin sialophosphoprotein and matrix extracellular phosphoglycoprotein - small integrin-binding ligand N-linked glycoproteins (SIBLINGs) - are emerging as important players in many stages of cancer progression. From their detection in various human cancers to the demonstration of their key functional roles during malignant transformation, invasion and metastasis, the SIBLINGs are proteins with potential as diagnostic and prognostic tools, as well as new therapeutic targets.

Differential transcriptional expression profiles of juvenile and adult calvarial bone

BACKGROUND

It has widely been observed that young children are capable of reossifying large calvarial defects, while adults lack this endogenous tissue-engineering capacity. The ability of juvenile animals to regenerate calvarial defects has been investigated in multiple animal models, including mice. In this study, the authors used cDNA microarrays to investigate the expression of osteogenesis-associated genes upstream and downstream of Runx2 in juvenile and adult mouse calvaria.

METHODS

Nonsuture-associated parietal bone discs were harvested from 6-day-old (n = 50) and 60-day-old (n = 35) male CD-1 mice. After separation of the underlying dura mater and overlying pericranium, the calvarial discs were snap-frozen and RNA was extracted from pooled samples of calvaria for microarray analysis. Genes analyzed included cytokines, receptors, and cell-surface and matrix proteins both upstream and downstream of Runx2.

RESULTS

Genes associated with the Runx2 pathway had notably higher levels in the juvenile versus adult calvaria. All genes except for osteocalcin were expressed at least twofold higher in the juvenile calvaria. This pattern was validated with quantitative real-time polymerase chain reaction. In addition, mRNA for potent osteoinductive growth factors was present at higher levels in the juvenile compared with the adult calvaria.

CONCLUSIONS

These findings reflect a genomic environment of active osteoblast differentiation and ossification in the juvenile calvaria compared with the adult "quiescent" calvarial tissue. These data suggest that a decreased osteogenic potential of adult calvarial osteoblasts may, in part, explain the inability of adult animals to heal calvarial defects.

Histochemical evidence of the initial chondrogenesis and osteogenesis in the periosteum of a rib fractured model: implications of osteocyte involvement in periosteal chondrogenesis

We have examined cellular events at the early stages of periosteal chondrogenesis and osteogenesis induced by bone fracture, using a well-standardized rib fracture model of the mouse. The initial cellular event was recognized as considerable proliferation in the deeper layer referred to as the "cambium layer" of the periosteum, as evidenced by numerous proliferating cell nuclear antigen-positive cells. The periosteal cartilage and bone were then regenerated directly from the region of the most-differentiated cell, i.e., mature osteoblasts of the cambium layer both close to and distant from the fracture site. Therefore, periosteal osteoblasts appeared to have the potential to differentiate into chondrogenic and osteoblastic lineages. CD31-positive blood vessels were uniformly localized along the periosteum that was regenerating cartilage and bone, being therefore indicative of less influence on the initiation of osteochondrogenesis. In contrast, however, the regenerated periosteal cartilage or bone extended from the cortical bones included dead or living osteocytes, respectively. Empty lacunae and lacunae embedded with amorphous materials were found close to the regenerated cartilage, while intact osteocytes persisted adjacent to the regenerated bone. The embedded lacunae with amorphous materials would render the tissue fluid, nutrients, oxygen, and several secretory factors such as dentin matrix protein-1 impossible to be delivered to the periosteal osteoblasts that interconnect osteocytes via gap junctions. Our study thus provides two major clues on initial cellular events in response to bone fracture: the potentiality of periosteal osteoblastic differentiation into a chondrogenic lineage, and a putative involvement of osteocytes in periosteal cartilage and bone regeneration.

Transient increase in anti-p-ATF2 immunoreactivity in the late secretion ameloblasts apical to the transition zone of rat incisors

Activating transcription factor 2 (ATF2) was localized in the ameloblasts of rat incisors by immunohistochemistry. A specific antibody against phosphorylated ATF2 (p-ATF2), which is an activated form of ATF2, was detected from the proliferation zone to maturation ameloblasts just after the transition. In the secretion zone, a transient increase in p-ATF2 was observed in the late secretion ameloblast nuclei, where a stronger reactivity of p-ATF2 extended from 1 mm apical to the transition to the transition zone, whereas ameloblast nuclei in most of the maturation zone exhibited either weak or no reactivity. A similar pattern was also observed in the case of c-Jun immunohistochemistry, except for in most of the maturation zone, where strong c-Jun reactivity was detected. Thus, ATF-2 and c-Jun are deeply involved in amelogenesis and, in particular, ATF2 is related to the proliferation, differentiation, secretion and transition zones.

Transcriptional Regulation of Dentin Matrix Protein 1 by JunB and p300 during Osteoblast Differentiation

Dentin matrix protein 1 (DMP1) is an acidic noncollagenous protein localized specifically in the mineralized matrix of bone and dentin. Expression analyses demonstrate that DMP1 is differentially regulated in osteoblasts and odontoblasts. Earlier we have reported on the transcriptional regulation of DMP1 by c-Fos and c-Jun (AP-1) transcription factors. Results from earlier study indicate that c-Fos and c-Jun play an important role in early osteoblast differentiation, whereas they do not have a significant effect on the terminally differentiated osteoblasts. In this paper, we demonstrate a regulatory mechanism by which JunB transcriptionally controls the expression of DMP1 during osteoblast differentiation. The cooperative interaction of JunB with p300 has been shown to dramatically modulate the DMP1 promoter activity during mineralization. Immunoprecipitation and chromatin immunoprecipitation analysis demonstrate the interaction of JunB and p300 in vivo. Further, phosphorylation of JunB at Ser-79 was found to be essential for its interaction with p300. Intrinsic histone acetyltransferase activity of p300 also plays a critical role in regulating DMP1 gene expression.

The CCAAT enhancer-binding protein (C/EBP)beta and Nrf1 interact to regulate dentin sialophosphoprotein (DSPP) gene expression during odontoblast differentiation

Terminal differentiation of odontoblasts, the principal cells in dentin formation, proceeds by synthesis of type I collagen and noncollagenous proteins. DSP and DPP are specific markers for terminally differentiated odontoblasts and are encoded by a single gene DSPP (dentin sialophosphoprotein). In an attempt to understand the molecular mechanisms required for tissue-specific expression of the DSPP gene, we have identified a novel interaction between two bZIP transcription factors, Nrf1 and the CCAAT enhancer-binding protein (C/EBP)beta. This interaction was confirmed by both immunoprecipitation and chromatin immunoprecipitation assays. In undifferentiated odontoblasts, Nrf1 and C/EBPbeta repress DSPP promoter activity individually and synergistically by cooperatively interacting with each other. This mutual interaction is facilitated by the bZIP domains in both the proteins. The repression domain in both Nrf1 and C/EBPbeta was determined, and deletion of this domain abolished transcriptional repression. In fully differentiated odontoblasts, the loss of interaction between Nrf1 and C/EBPbeta results in an increased DSPP transcription. Further, this interaction was found to be dependent on phosphorylation at Ser(599) of Nrf1. Thus, the physical interaction between Nrf1 and C/EBPbeta provide a novel mechanism for the transcriptional regulation of DSPP in odontoblasts.