Regulation of the Cell Type-specific dentin sialophosphoprotein gene expression in mouse odontoblasts by a novel transcription repressor and an activator CCAAT-binding factor

Dentin sialophosphoprotein (DSPP) is an extracellular matrix protein that is cleaved into dentin sialoprotein (DSP) and dentin phosphoprotein (DPP) with a highly restricted expression pattern in tooth and bone. Mutations of the DSPP gene are associated with dentin genetic diseases. Regulation of tissue-specific DSPP expression has not been described. To define the molecular basis of this cell-specific expression, we characterized the promoter responsible for the cell-specific expression of the DSPP gene in odontoblasts. Within this region, DNase I footprinting and electrophoretic mobility shift assays delineated one element that contains an inverted CCAAT-binding factor site and a protein-DNA binding site using nuclear extracts from odontoblasts. A series of competitive electrophoretic mobility shift assay analyses showed that the protein-DNA binding core sequence, ACCCCCA, is a novel site sufficient for protein binding. These two protein-DNA binding sequences are conserved at the same proximal position in the mouse, rat, and human DSPP gene promoters and are ubiquitously present in the promoters of other tooth/bone genes. Mutations of the CCAAT-binding factor binding site resulted in a 5-fold decrease in promoter activity, whereas abolishment of the novel protein-DNA binding site increased promoter activity by about 4.6-fold. In contrast to DSPP, expression levels of the novel protein were significantly reduced during odontoblastic differentiation and dentin mineralization. The novel protein was shown to have a molecular mass of 72 kDa. This study shows that expression of the cell type-specific DSPP gene is mediated by the combination of inhibitory and activating mechanisms.     

Spatial and temporal regulation of a foreign gene by a prestalk-specific promoter in transformed Dictyostelium discoideum.

We analyzed a developmentally regulated prestalk-specific gene from Dictyostelium discoideum encoding a cathepsin-like protease. A hybrid gene was constructed by fusing 2.5 kilobases of 5' flanking sequences and part of the coding region of the gene in-frame to the Escherichia coli beta-glucuronidase gene and was transformed into D. discoideum cells. In cells transformed with this vector, the gene fusion showed the same temporal regulation as the endogenous gene during multicellular development and, like endogenous prestalk genes, was highly inducible by cyclic AMP in in vitro cell cultures. Moreover, immunofluorescence studies showed that the fusion protein had the same spatial distribution within the migrating pseudoplasmodium as the endogenous gene. The results indicate that the regions of the D. discoideum prestalk-specific cathepsin gene contain all the necessary information for proper temporal, spatial, and cyclic AMP regulation of a prestalk cell-type gene in D. discoideum transformants and leads the way for experiments to identify the cell-type-specific regulatory elements.     

人牙本质涎磷蛋白启动子驱动LacZ报告基因在人牙胚间充质细胞中表达

牙本质涎磷蛋白(DSPP)的表达是细胞向成牙本质细胞分化的标志。试图分析人DSPP启动子及构建人DSPP启动子驱动的Lac Z基因表达的报告体系,从而方便快捷检测细胞是否向成牙本质细胞分化。为了建立能表达DSPP的细胞体系,分离了人牙胚间充质细胞,并用地塞米松诱导培养液进行诱导,结果显示,该诱导培养液能有效地诱导人牙胚间充质细胞DSPP基因的表达。利用双荧光素酶报告系统对4段人DSPP基因5′上游区域(-4 000-+54、-2 500-+54、-1 447-+54和-1 027-+54)进行分析,结果显示-2 500-+54区域的启动子活性最高。5′上游区从?2 500 bp延长到?4 000 bp时,启动子活性下降;5′上游区从-2 500 bp缩短至-1 447 bp时,启动子活性下降;再次将-1 447 bp缩短至-1 027 bp时,启动子活性进一步下降。结果暗示在-4 000 bp至-2 500 bp区域存在转录抑制元件,-2 500 bp至-1 027 bp区域存在转录激活元件。用-2 500-+54启动子区域和Lac Z基因构建ph DSPP-Lac Z慢病毒报告载体,并分别在人牙胚间充质细胞和永生化人牙胚间充质细胞系ih EDMC4上检测ph DSPP-Lac Z报告载体的功能,通过X-Gal染色,结果显示在2种细胞牙向分化过程中均可检测到Lac Z基因的表达。研究构建的ph DSPP-Lac Z慢病毒报告载体可为诱导人源细胞牙向分化、牙齿发育、牙齿再生工程等研究中DSPP的表达检测提供一种更加便捷的手段。     

Dentin glycoprotein: the protein in the middle of the dentin sialophosphoprotein chimera

Dentin sialophosphoprotein (DSPP) is a major secretory product of odontoblasts and is critical for proper dentin formation. DSPP is believed to be processed into only two structural/functional domains: dentin sialoprotein (DSP) and dentin phosphoprotein (DPP). Here we report the isolation and characterization of a third domain of DSPP, designated dentin glycoprotein (DGP). DGP was isolated from a guanidine/EDTA extract of porcine tooth dentin by ion exchange, hydroxyapatite affinity, size exclusion, and RP-HPL chromatography. Endoproteinase lysine C digestion products of DGP were characterized by Edman sequencing and mass spectrometry. The porcine DGP backbone is the 81-amino acid segment of DSPP (Ser392 to Gly472) between the DSP and DPP domains. DGP has four phosphorylated serine residues (Ser453, Ser455, Ser457, and Ser462) and one glycosylated asparagine (Asn397). There are no other post-translational modifications. DGP is a stains-all positive protein with an apparent molecular mass on SDS-PAGE of 19 kDa, which is reduced by glycopeptidase A digestion to 16 kDa. A variety of glycans can be linked to Asn397. All are complex biantennary structures with a common N-linked pentasaccharide core (mannose3-N-acetylglucosamine2), most with a fucosyl residue on the innermost N-acetylglucosamine. The alpha1-3 and alpha1-6 arms are always galactose beta1-4 N-acetylglucosamine beta1-2 mannose, and either or both arms can be unsialidated or monosialidated. The calculated monoisotopic molecular masses of the different glycosylated forms of the DGP phosphoprotein are: unsialidated 10,523 and 10,670, monosialidated 10,815 and 10,961, and disialidated 11,106, and 11,252 Da, with the disialidated forms being the most abundant.     

Qualitative electron probe analysis of secretory ameloblasts and odontoblasts in the rat incisor

Summary Rapidly frozen growing rat incisors were freeze fractured and freeze dried in preparation for energy dispersive X-ray emission microanalysis in a scanning electron microscope. Ca levels were found to be elevated in the distal cell body of odontoblasts, whereas Ca was uniformly low over all parts of the cell body of secretory ameloblasts. The results suggest fundamental differences in the mechanisms by which these two cell types process Ca, and that Ca possibly diffuses through the secretory ameloblast layer on its way to the enamel.     

Spatial and temporal regulation of focal adhesion kinase activity in living cells

Focal adhesion kinase (FAK) is an essential kinase that regulates developmental processes and functions in the pathology of human disease. An intramolecular autoinhibitory interaction between the FERM and catalytic domains is a major mechanism of regulation. Based upon structural studies, a fluorescence resonance energy transfer (FRET)-based FAK biosensor that discriminates between autoinhibited and active conformations of the kinase was developed. This biosensor was used to probe FAK conformational change in live cells and the mechanism of regulation. The biosensor demonstrates directly that FAK undergoes conformational change in vivo in response to activating stimuli. A conserved FERM domain basic patch is required for this conformational change and for interaction with a novel ligand for FAK, acidic phospholipids. Binding to phosphatidylinositol 4,5-bisphosphate (PIP2)-containing phospholipid vesicles activated and induced conformational change in FAK in vitro, and alteration of PIP2 levels in vivo changed the level of activation of the conformational biosensor. These findings provide direct evidence of conformational regulation of FAK in living cells and novel insight into the mechanism regulating FAK conformation.     

Characterization of position-induced spatial and temporal regulation of transgene promoter activity in plants.

Quantitative differences in transgene expression between independent transformants are generally ascribed to different integration sites of the transgene (position effect). The contribution of spatial and temporal changes in transgene promoter activity to these position-induced differences in transgene expression in planta are characterized, using the firefly luciferase (luc) reporter system. The activity of three different promoters (Cauliflower Mosaic Virus (CaMV) 35S, modified CaMV 35S and the promoter of an Arabidopsis thaliana Lipid Transfer Protein gene) was shown to vary not only among independent transformants, but also between leaves on the same plant and within a leaf. The differences in local LUC activity between leaves and within a leaf correlated with differences in local luc mRNA steady-state levels. Imaging of LUC activity in the same leaves over a 50 d period, shows that individual transformants can show different types of temporal regulation. Both the spatial and the temporal type of luc transgene expression pattern are inherited by the next generation. It is concluded that previously reported position-induced quantitative differences in transgene expression are probably an accumulated effect of differences in spatial and temporal regulation of transgene promoter activity.     

Characterization of the human interleukin-2 receptor beta-chain gene promoter: regulation of promoter activity by ets gene products.

The interleukin-2 receptor (IL-2R) beta chain (IL-2R beta) is an essential signaling component of high- and intermediate-affinity IL-2Rs. Our laboratory previously reported that a DNA fragment containing 857 bp of 5'-flanking sequence of the human IL-2R beta gene exhibited promoter activity. We have now further characterized the promoter and delineated cis-acting regulatory regions. The region downstream of -363 is critical for basal and phorbol myristate acetate-inducible IL-2R beta promoter activity and contains at least three enhancer-like regions. Among them, the -56 to -34 enhancer was the most potent and had high-level activity in two T-cell lines but not in nonlymphoid HeLaS3 and MG63 cells. This enhancer contains a GGAA Ets binding site which bound two Ets family proteins, Ets-1 and GA-binding protein in vitro. Mutation of the Ets motif strongly diminished both promoter and enhancer activities. We conclude that this Ets binding site plays a key role in regulating basal and phorbol myristate acetate-inducible IL-2R beta promoter activity and may also contribute to tissue-specific expression of the IL-2R beta gene.     

In vivo activity of the hepatitis B virus core promoter: tissue specificity and temporal regulation.

The contribution of the hepatitis B virus enhancers I and II in the regulation of the activity of the core and the X promoters was assessed in transgenic mice. Surprisingly, despite the presence of heterologous promoters linked 5' of the X gene, the transgene expression is mostly due to core promoter (Cp) activity present in the X coding sequence. Moreover, the restriction of Cp activity to hepatic tissue required the combined action of both enhancers I and II, whereas the proximity of these two enhancers was insufficient to confer tissue specificity on Xp activity. Furthermore, the liver-specific activity of the Cp was developmentally regulated in an enhancer I-independent manner.     

Co-distribution of annexin VI and actin in secretory ameloblasts and odontoblasts of rat incisor

Summary Annexin VI and actin were detected by immunoblot analysis in the enamel- and dentin-related portions of dental tissues. Annexin VI was found mainly in the particulate fraction whereas actin was detected in both the soluble and particulate fractions. By immunoelectron microscopy, annexin VI antibodies conjugated with colloidal gold were seen to label the mitochondria, the cytosol and the nucleus of secretory ameloblasts and odontoblasts of rat incisor. In the processes of these cell, the plasmalemmal undercoat was labeled. Antiactin antibodies labeled the desmosome-like junctions, the cytosol, and the mitochondria of the cell bodies. Extensive labeling was seen at the periphery of the Tomes' processes and odontoblast processes. These results suggest that annexin VI may play a role in Ca²⁺-regulation in the cell bodies, especially as a calcium receptor protein in the mitochondria. Moreover, annexin VI and actin seem to be co-distributed in secretory processes. Thus, these proteins might be both involved in exocytotic and endocytotic events.     

Macrophage inflammatory protein-3alpha and beta-defensin-2 stimulate dentin sialophosphoprotein gene expression in human pulp cells

Macrophage inflammatory protein (MIP)-3alpha and beta-defensin (BD)-2 have antimicrobial activity and chemotactic activity for immature dendritic cells, natural killer cells, and memory T cells. However, it remains unknown if the widespread effects of these peptides also include an influence on the differentiation of mesenchymal cells. Pulp cells have the capacity to differentiate into odontoblasts and to form dentin. The aim of this study was to determine if inflammatory leukocyte products influence the capacity of pulp cells to differentiate. Dentin sialophosphoprotein (DSPP) is a tooth-specific protein being expressed mostly by odontoblast cells. In the present study, we investigated effects of MIP-3alpha and BD-2 on the DSPP and osteopontin (OPN) gene expression in cultures of human pulp-derived fibroblastic cells (HP cells). HP cells expressed mRNA for the CC chemokine receptor (CCR) 6 to which both MIP-3alpha and BD-2 can bind. Real-time PCR showed that MIP-3alpha and BD-2 significantly increased DSPP mRNA levels, although BD-2 increased DSPP mRNA levels less than MIP-3alpha. MIP-3alpha and BD-2 increased OPN mRNA levels very slightly. MIP-3alpha and BD-2 possessed antibacterial activity against Streptococcus mutans and Lactobacillus casei, which are involved in caries, although the antibacterial activity of MIP-3alpha was lower than that of BD-2. These findings suggest the MIP-3alpha and BD-2 have the ability to stimulate odontoblast differentiation in addition to their more traditional role in inflammation and have potential in the removal of bacteria in infected soft dentin and pulp tissues.     

Spatial and temporal regulation of tenascin-R glycosylation in the cerebellum

The cellular adhesion molecule tenascin-R is a multifunctional extracellular matrix component expressed exclusively in the central nervous system. The expression of tenascin-R by oligodendrocytes and small interneurons in the hippocampus and cerebellum is highly regulated during development of these regions. This complex glycoprotein displays both adhesive and anti-adhesive properties that contribute to the formation and maintenance of synapses. We have determined that tenascin-R associated with Purkinje cell bodies and their dendrites in the molecular layer of the cerebellum bears N-linked oligosaccharides terminating with beta1,4-linked GalNAc-4-SO(4), whereas tenascin-R in other regions of the cerebellum does not bear this modification. Expression of this unique sulfated carbohydrate structure is also temporally regulated, increasing throughout cerebellar development. The most dramatic increase in GalNAc-4-SO(4) occurs between postnatal days 14 and 21, corresponding to a period of Purkinje cell dendrite extension and synaptogenesis. The spatially and temporally regulated addition of this unique sulfated carbohydrate to tenascin-R may serve to modulate its adhesive/anti-adhesive or other biological properties in vivo.     

Porcine dentin sialophosphoprotein: length polymorphisms, glycosylation, phosphorylation, and stability

Dentin sialophosphoprotein (DSPP) is critical for proper mineralization of tooth dentin, and mutations in DSPP cause inherited dentin defects. Dentin phosphoprotein (DPP) is the C-terminal cleavage product of DSPP that binds collagen and induces intrafibrillar mineralization. We isolated DPP from individual pigs and determined that its N-terminal and C-terminal domains are glycosylated and that DPP averages 155 phosphates per molecule. Porcine DPP is unstable at low pH and high temperatures, and complexing with collagen improves its stability. Surprisingly, we observed DPP size variations on SDS-PAGE for DPP isolated from individual pigs. These variations are not caused by differences in proteolytic processing or degrees of phosphorylation or glycosylation, but rather to allelic variations in Dspp. Characterization of the DPP coding region identified 4 allelic variants. Among the 4 alleles, 27 sequence variations were identified, including 16 length polymorphisms ranging from 3 to 63 nucleotides. None of the length variations shifted the reading frame, and all localized to the highly redundant region of the DPP code. The 4 alleles encode DPP domains having 551, 575, 589, or 594 amino acids and completely explain the DPP size variations. DPP length variations are polymorphic and are not associated with dentin defects.     

Isolation of the Chinese rose sHSP gene promoter and its differential regulation analysis in transgenic Arabidopsis plants

In our previous study, we identified a Rosa chinensis heat shock protein (HSP) gene, RcHSP17.8, which was induced by abiotic stresses, such as high temperature and osmotic stress. To analyze the expression of RcHSP17.8 and the function of cis-acting elements in the promoter region, a 1,910 bp fragment of the upstream sequence of the RcHSP17.8 translation initiation codon and five promoter deletion fragments were fused to a β-glucuronidase (GUS) report gene. These plasmids were transferred to Arabidopsis thaliana via Agrobacterium. GUS staining was seen in all the organs, especially in the vascular tissues after heat treatment. In transgenic Arabidopsis, GUS expression driven by the full length promoter was significantly higher under heat shock, but no GUS activity was detected under other abiotic stresses. Deletion analysis indicated that the region from −178 to −771 was essential for the promoter’s response to high temperature.