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W T Butler

Publications and source records attributed to W T Butler.

At least 19 recordsLinked to original sources
PubMed2001

Identification and characterization of the carboxyl-terminal region of rat dentin sialoprotein.

Two acidic proteins, dentin sialoprotein (DSP) and dentin phosphoprotein (DPP), are present in the extracellular matrix of dentin but not in bone. These two proteins are expressed in odontoblasts and preameloblasts as a single cDNA transcript coding a large precursor protein termed dentin sialophosphoprotein (DSPP). DSPP is specifically cleaved into two unique proteins, DSP and DPP. However, the cleavage site(s) of DSPP and the mechanisms for regulating the cleavages are unknown. To identify the specific site(s) of DSPP that are cleaved when the initial translation product is converted to DSP and DPP, we performed a detailed analysis (Edman degradation and mass spectrometry) on selected tryptic peptides of a size originating from the COOH-terminal region of rat DSP. After cleavage with trypsin, the DSP fragments were separated by a two-dimensional method (size-exclusion chromatography followed by reversed phase high performance liquid chromatography). We characterized 13 peptides from various regions of DSP. The analyses showed that peptide Ile(409)-Tyr(421) was the major COOH-terminal fragment, ending at Tyr(421) only 9 residues from the NH(2) terminus of DPP. Peptide Gln(385)-His(406) represented a second, minor COOH-terminal peptide that terminated at His(406). Both of these residues are well beyond the COOH terminus predicted previously by two independent studies estimating that rat DSP contained 360-370 amino acids. Careful studies on two peptides showed that, among 9 potential casein kinase II phosphorylation sites, 2 serines were phosphorylated. We found that rat DSP was heterogeneous with respect to phosphorylation, because this same peptide sequence eluted in two discrete peaks, one with 2 phosphoserines and the other having 1. The finding that 3 lysines just preceding the COOH termini were modified by a 43-Da substituent (possibly a carbamoyl substituent) suggests that the lysines in this region were particularly susceptible to attachment of this substituent.

Amino Acid Sequence↗
PubMed2001

A comparative study of sialic acid-rich proteins in rat bone and dentin.

Four sialic acid-rich (SA-rich) proteins found in bone and dentin, osteopontin (OPN), bone sialoprotein (BSP), bone acidic glycoprotein-75 (BAG-75), and dentin matrix protein 1 (DMP1), share some common features. We used SDS-PAGE and Western immunoblots to analyze and compare SA-rich proteins in bone and dentin extracts from rats with a single chromatographic procedure. OPN was detected in dentin extracts, with a relative level less than one-seventieth of that in bone. Both bone and dentin BSP demonstrated an extremely broad distribution pattern, probably due to a high degree of heterogeneity in post-translational modifications. BAG-75 in both bone and dentin was detected as an 83 kDa band, dramatically distinct from that of DMPI. Using a polyclonal antibody raised against a purified bone 57 kDa protein (a portion of DMPI), we detected 150 kDa protein bands in bone fraction; the same bands were recognized by antirecombinant rat DMPI antibody. Bands from dentin migrating at about 150 kDa in earlier fractions and progressing to 200 kDa in later fractions showed a clear immunoreactivity to the anti-57 kDa antibody. We conclude that the majority of DMPI in rat bone is processed into fragments, whereas that in dentin remains intact.

Animals↗
PubMed2000

Regulation of no synthesis induced by inflammatory mediators in RAW264.7 cells: collagen prevents inhibition by osteopontin.

Osteopontin has been shown to inhibit the induction of inducible nitric oxide synthase (iNOS, or NOS2) by lipopolysaccharide and interferon-gamma in the RAW264.7 mouse monocyte/macrophage line and in primary mouse proximal tubule epithelial cells. However, the RAW264.7 cells become refractory to the action of OPN after several subcultures or under dilute culture conditions, possibly because of changes in the composition of the extracellular matrix. We make this suggestion because if the cells are plated on a collagen type I or collagen type IV substrate the inhibitory action of OPN is completely suppressed; this is not the case on substrates consisting of laminin, fibronectin, poly-D-lysine, or poly-(2-hydroxyethylmethylacrylate). These observations imply that macrophages are sensitive to regulation by OPN only in certain physiological contexts. Both hyaluronate, which binds CD44, and rat IgGs are also able to inhibit the induction of NO synthesis by the inflammatory mediators. The similar actions of HA and OPN are consistent with the possibility that CD44 may be a receptor for OPN.

Animals↗
PubMed2000

Dentin sialoprotein (DSP) has limited effects on in vitro apatite formation and growth.

Sialoproteins such as bone sialoprotein (BSP) and dentin sialoprotein (DSP) accumulate at the mineralization fronts in bone and dentin, respectively, suggesting they have some function in the mineralization process. BSP, a highly phosphorylated protein rich in polyglutamate repeats, is an effective nucleator of hydroxyapatite (HA) formation in vitro. The present study examines the effect of DSP, a low phosphorylated but related sialoprotein, on the formation and growth of HA. In vitro, in a gelatin gel diffusion system, DSP at low concentrations (<25 microg/ml) slightly increased the yield of HA formed at 3.5 and 5 days, while at higher concentrations (50-100 microg/ml) it slightly inhibited accumulation. Fewer mineral crystals were formed in the presence of high concentrations of DSP but they tended to aggregate (making them appear larger by electron microscopic analysis) than those formed in DSP-free gels. X-ray diffraction line broadening analysis failed to show significant changes in c-axis crystal dimensions with increasing DSP concentration. When HA-seed crystals were coated with DSP before inclusion in the gelatin gel there was a reduction in mineral accumulation relative to HA-seeds which had not been coated with DSP, but the extent of inhibition was significantly less than that seen in this system with other mineralized tissue matrix sialoproteins, such as osteopontin or BSP. The low affinity of DSP for well-characterized seed crystals and the limited effect of this protein on HA formation and growth suggest that the role of DSP in dentin is not primarily that of a mineralization regulator.

Animals↗
PubMed2000

Enhanced expression of osteopontin by high glucose. Involvement of osteopontin in diabetic macroangiopathy.

Atherosclerotic vascular disease is a major complication of diabetic patients. Osteopontin has recently been implicated in the development of atherosclerosis. In the present study, we have investigated the effects of high glucose on expression of osteopontin in cultured rat aortic smooth muscle cells. High concentrations of glucose increased osteopontin secretion from the cells, and the increased secretion was completely inhibited by an inhibitor of protein kinase C, GF109203X. Northern blot analysis confirmed the enhanced effect of glucose on expression of osteopontin mRNA. Promoter activity of osteopontin, measured using the osteopontin promoter/luciferase expression vector system, was increased by high glucose, and the enhanced effect was completely inhibited by GF109203X. Glucosamine also increased the promoter activity of osteopontin. Azaserine, an inhibitor of glutamine:fructose-6-phosphate amidotransferase, the key enzyme of the hexosamine pathway, profoundly inhibited high glucose-mediated increase in the promoter activity. Taken together, these data indicate that high glucose enhances the expression of osteopontin at the transcriptional level possibly through the activation of protein kinase C as well as the hexosamine pathway. Our results suggest that osteopontin could play a role in the development of diabetic vascular complications.

Animals↗
PubMed1999

Enhanced expression of osteopontin by high glucose in cultured rat aortic smooth muscle cells.

Atherosclerotic vascular disease is a major complication of diabetic patients, and osteopontin has recently been implicated in the development of atherosclerosis. In the present study, we have investigated the effects of high glucose on expression of osteopontin in cultured rat aortic smooth muscle cells. High concentrations of glucose increased osteopontin secretion from the cells, and the increased secretion was completely inhibited by an inhibitor of protein kinase C, GF109203X. Northern blot analysis confirmed the enhanced effect of glucose on expression of osteopontin mRNA. Promoter activity of osteopontin, measured using the osteopontin promoter/luciferase expression vector system, was increased by high glucose, and the enhanced effect was completely inhibited by GF109203X. Glucosamine also increased the promoter activity of osteopontin, and azaserine, an inhibitor of glutamine:fructose-6-phosphate amidotransferase (the key enzyme of the hexosamine pathway), profoundly inhibited high glucose-mediated increase in the promoter activity. Taken together, these data indicate that high glucose enhances the expression of osteopontin at the transcriptional level possibly through the activation of protein kinase C as well as the hexosamine pathway. Our results suggest that osteopontin could play a role in the development of diabetic vascular complications.

Animals↗
PubMed1999

Osteopontin (OPN) distribution in premalignant and malignant lesions of oral epithelium and expression in cell lines derived from squamous cell carcinoma of the oral cavity.

The objectives of this study were to assess the immunolocalization of human osteopontin (OPN) in oral lesions and to identify human cell lines of oral squamous cell carcinoma (OSCC) origin that express OPN mRNA. OPN was localized using immunohistochemistry in the following oral specimens: normal epithelium (n=6), epithelial hyperplasia (n=4), epithelial dysplasia (n=28), carcinoma in situ (n=11) and squamous cell carcinoma (n=43). Cell lines UMSCC-1, MDA TU 138, MDA 686LN, SCC4, SCC9, SCC25, CAL 27 and MDA 1483 were characterized for OPN mRNA expression using Northern blotting. OPN was not detected in normal oral epithelium. Intracellular and intercellular immunoreactivity was seen in 75% of hyperplasias, 57% of dysplasias, 54% of carcinoma in situ and 67% of squamous cell carcinomas. UMSCC-1 expressed high levels of OPN mRNA. We conclude that OPN protein is detectable in premalignant and malignant lesions arising from oral epithelium. UMSCC-1 may be a useful cell line in which to conduct in vitro studies designed to clarify the role of OPN in OSCC.

Adolescent↗
PubMed1998

Modulation of osteopontin post-translational state by 1, 25-(OH)2-vitamin D3. Dependence on Ca2+ influx.

In osteoblastic ROS 17/2.8 cells, 1,25-(OH)2-vitamin D3 stimulates transcription of the extracellular matrix phosphoprotein osteopontin (OPN). We now show post-translational regulation of OPN production by 1,25-(OH)2D3. Prior to transcriptional up-regulation of OPN, 1, 25-(OH)2D3 induces a shift in OPN isoelectric point (pI) from 4.6 to 5.1. Loading equal amounts of OPN recovered from ROS 17/2.8 cells exposed to 1,25-(OH)2D3 or carrier for 3 h reveals that the pI shift represents reduced phosphorylation. Trypsin cleavage patterns of OPN produced after 1,25-(OH)2D3 treatment indicates phosphorylation changes in the resulting peptides. Using structural analogs to 1, 25-(OH)2D3, we found that analog AT (25-(OH)-16-ene-23-yne-D3), which triggers Ca2+ influx but does not bind to the vitamin D receptor, mimicked the OPN pI shift, whereas analog BT (1, 25-(OH)2-22-ene-24-cyclopropyl-D3), which binds to the vitamin D receptor without triggering Ca2+ influx, did not. Likewise, inclusion of the Ca2+ channel blocker nifedipine blocks the charge conversion of OPN. Isolation of OPN from rat femurs and tibiae demonstrates the existence of two OPN charge forms in vivo. We conclude that 1,25-(OH)2D3 regulates OPN not only at the transcriptional level, but also modulates OPN phosphorylation state. The latter involves a short term (<3 h) treatment and is associated with membrane-initiated Ca2+ influx.

Animals↗
PubMed1998

Dentin sialoprotein, dentin phosphoprotein, enamelysin and ameloblastin: tooth-specific molecules that are distinctively expressed during murine dental differentiation.

Dentin sialophosphoprotein [designated DSPP and cleaved into dentin sialoprotein (DSP) and dentin phosphoprotein (DPP)], enamelysin and ameloblastin are each expressed in unique fashions during tooth development. It is possible that these components participate in cell differentiation and the conversion of unmineralized matrix into mineralized structures. In order to delineate the timing and the positioning of these three molecules in a physiological context, we compared their expression profiles by performing in situ hybridization experiments on consecutive sections in developing mouse tissues. Hybridization signals were uniquely detected for DSPP mRNA in odontoblasts and preameloblasts, for enamelysin mRNA in odontoblasts and in the facing ameloblast layer, and for ameloblastin mRNA in preodontoblasts, polarizing odontoblasts and ameloblasts. Immunohistochemistry showed that DSP and ameloblastin transcripts were translated into proteins that were deposited at the apical pole of the differentiated cells (odontoblasts and ameloblasts, respectively). The interrelated expression profiles found for these tooth-specific molecules illustrate the importance of a specific molecular network to initiate highly regulated processes such as cytodifferentiation and the subsequent mineralization.

Ameloblasts↗
PubMed1998

Dentin matrix proteins.

Dentinogenesis consists of highly controlled events occurring a short distance from the periphery of odontoblasts: it involves formation of extracellular collagen fibrils that act as an undergirding for deposition of plate-like carbonate apatite crystals. Odontoblasts also form a set of matrix proteins that are probably secreted at the mineralization front. Although most of these proteins are similar to those of bone, and differ from soft tissue proteins, dentin contains two unique proteins. Dentin phosphoprotein (DPP) is rich in aspartic acid (D) and phosphoserine (S*) and binds large amounts of calcium. DPP contains repeating sequences of DS*S* and S*D in discrete areas of the protein. DS*S* repeats form ridges of phosphates and carboxyllates while the S*D sequences give rise to ridges with phosphates and carboxyllates on opposing sides of the peptide chain. These structures undoubtedly have functional significance since DPP is involved in promotion of mineral initiation and in control of mineral size and shape. Dentin sialoprotein (DSP), found only in dentin, is a 53 kDa glycoprotein rich in aspartic acid, serine, glutamic acid and glycine. DSP is made by odontoblasts and also by pre-ameloblasts, but not by osteoblasts or other cell types. The gene for DSP is now known to be continuous with that of DPP. Thus, DSP and DPP must be secreted as a single protein which is then proteolytically processed to form the individual components found in the dentin matrix. Significantly, the DSP/DPP gene has been localized to human chromosome 4q21 at a site implicated in dentinogenesis imperfecta type II.

Amino Acid Sequence↗
PubMed1998

Comparative analysis of mouse DSP and DPP expression in odontoblasts, preameloblasts, and experimentally induced odontoblast-like cells.

Dentin sialoprotein (DSP) and dentin phosphoproteins (DPP) are uniquely expressed by differentiating and fully differentiated mature odontoblasts. It is likely that DSP and DPP actively participate in the conversion of predentin to dentin. To compare the expression patterns of DPP and DSP, we constructed mouse cDNA probes. Northern analyses confirmed their specific expressions in tooth germ-derived RNA and showed that the probes reacted with similar or identical multiple transcripts. In situ hybridization indicated that DSP and DPP transcripts were uniquely detected and codistributed in developing mouse odontoblasts and preameloblasts. These data, as well as the adjacent positioning of the DSP and DPP coding sequences, suggest that common regulatory mechanisms control DSP and DPP expressions. Dental papillae cultures, in which odontoblast differentiation was experimentally induced with TGFbeta1 combined with heparin, were used to show that the two molecules are also coexpressed under in vitro conditions.

Ameloblasts↗
PubMed1998

Dentin-specific proteins in MDPC-23 cell line.

Only four established odontoblast-like cell lines have been reported in the literature (1-6). Of the four, only two synthesize dentin-specific proteins. These studies report that the cell line MO6-G3 synthesizes phosphophoryn (DPP), dentin sialoprotein (DSP) and dentin matrix protein-1 (DMP-1) while MDPC-23 synthesizes DSP, but not DMP-1. The objective of the present study was to determine whether polyclonal antibodies to rat DSP and DPP would label odontoblasts on microscopic sections of day-19 fetal mouse incisor odontoblasts as well as cultured cells of the MDPC-23 cell line. The spontaneously immortalized MDPC-23 cell line was derived from fetal mouse molar papillae, made continuous by the 3T6 method and cloned by dilution. These cultures have been passaged 77 times after cloning, form multilayered nodules, and have high alkaline phosphatase activity. The data show positive reactivity in odontoblasts in 19-d mouse fetal incisors as well as in cultures of MDPC-23 cells by fluorescence and confocal microscopy. In addition, these cultures were characterized by phase microscopy and scanning and transmission electron microscopy. These findings suggest that MDPC-23 cells are of the odontoblast lineage.

Animals↗
PubMed1998

Cloned 3T6 cell line from CD-1 mouse fetal molar dental papillae.

Only primary pulpal cell cultures and one virally transformed mouse cell culture have been formally reported in the literature to synthesize proteins such as phosphophoryn which are unique to dentin matrix. In the present study, a mixed culture was derived from dental papilla cells of 18-19 fetal day CD-1 mouse mandibular first molars, maintained on a 3T6 plating regimen, and subsequently cloned after 28 passages. This cloned cell line (MDPC-23) exhibited several unique features, some of which were characteristic of odontoblasts in vivo. The features of this cell line included (1) epithelioid morphology of all cells with multiple cell membrane processes, (2) high alkaline phosphatase activity in all cells, (3) formation of multilayered nodules and multilayered cultures when maintained in ascorbic acid and beta-glycerophosphate, and (4) expression of two markers for odontoblast differentiation, i.e. dentin phosphoprotein and dentin sialoprotein.

Animals↗
PubMed1998

Expression of dentin sialoprotein (DSP) and other molecular determinants by a new cell line from dental papillae, MDPC-23.

The purpose of this study was to characterize the molecular expression of a spontaneously immortalized and cloned cell line (MDPC-23) derived from 18-19 day CD-I fetal mouse molar dental papillae to determine if these cells were odontoblast-like. Western blots showed that a protein band, at approximately 105 kDa, reacting positively with anti-DSP antibodies and co-migrating with mouse DSP, was present in lysates of cells from passages 7, 37 and 77, in serum-free conditioned medium from passage 37 cells, and in mouse dentin extract. A minor band at 55 kDa was also apparent in cell lysates. Using a cDNA probe for a 486bp mouse DSP coding sequence, DSP or DSP-PP mRNA expression was detected by Northern analysis as well as Southern analysis after RT-PCR in all three passages. It was also shown that in these cells 1,25 (OH)2 vitamin D3 upregulated both osteopontin and osteocalcin mRNA, and dexamethasone downregulated alkaline phosphatase and alpha2(I) collagen mRNA. Thus, MDPC-23 cells express proteins which are common to mineralizing tissue. The expression of DSP and DSP-PP strongly suggests that this cell line is from the odontoblast lineage.

Animals↗
PubMed1997

Extracellular matrix proteins of dentine.

Bone and dentine extracellular matrix proteins are similar, consisting primarily of type I collagen, acidic proteins and proteoglycans. Although collagen forms the lattice for deposition of calcium and phosphate for formation of carbonate apatite, the non-collagenous proteins are believed to control initiation and growth of the crystals. Despite this similarity, dentine contains three unique proteins apparently absent from bone and other tissue: dentine phosphophoryn (DPP), dentine matrix protein 1 (DMP1) and dentine sialoprotein (DSP). DPP and DMP1 are acidic phosphoproteins probably involved in the control of mineralization processes. DPP may localize in gap regions of collagen and initiate apatite crystal formation by binding large quantities of calcium in a conformation that promotes this process. Extensive studies have been conducted in our laboratory on the nature, biosynthesis, localization and gene structure of DSP. Immunolocalization studies showed that rat DSP, a 53 kDa sialic acid-rich glycoprotein, was synthesized by young and mature odontoblasts, and by dental pulp cells and pre-ameloblasts, but not by ameloblasts, osteoblasts, chondrocytes or other cell types. The cDNA sequence indicated that DSP was a 366-residue protein with several potential N-glycosylation sites, as well as phosphorylation sites, but that the amino acid sequence was dissimilar to that of other known proteins. Northern blot analysis detected several mRNA species near 4.6 and 1.5 kb, indicative of alternative splicing events. Evidence for two DSP genes was obtained, further complicating this picture. Recent in situ hybridization studies utilizing rat and mouse molars and incisors indicated that DSP mRNA was expressed by young odontoblasts and odontoblasts in animals of all ages. Transcripts were also observed in pre-ameloblasts. The expression of DSP mRNA ceased when these cells matured to become secretory ameloblasts. DSP transcripts were not detected in osteoblasts or other cell types. The transient expression in pre-ameloblasts suggests a role of epithelial-mesenchymal interactions in the formation of the tooth.

Amino Acid Sequence↗
PubMed1997

Improved immunohistochemical staining of osteopontin (OPN) in paraffin-embedded archival bone specimens following antigen retrieval: anti-human OPN antibody recognizes multiple molecular forms.

Studies to assess osteopontin (OPN) localization in adult human bone using immunochemical techniques produce conflicting results due to variations in tissue processing or antibody immunoreactivity. The present study was designed to resolve these discrepancies using well-characterized antibodies and improved antigen detection. An anti-osteopontin (alpha-OPN) antiserum was developed that recognizes various soluble molecular weight forms of human OPN, including monomeric, cleaved, and dimerized products. An affinity column of full length recombinant human OPN (rOPN) coupled to support was used to purify alpha-OPN antibodies. Western analysis showed that the affinity-purified antibodies recognized numerous molecular weight forms of OPN. These antibodies were used to study the distribution of OPN in adult human bone using immunohistochemical techniques combined with an antigen retrieval protocol utilizing a newly developed antigen retrieval solution, Retriev-Alltrade mark (Bronco Technologies Inc, Pasadena, TX). Immunolocalization of OPN in archival bone specimens prior to antigen retrieval produced no demonstrable immunostaining even at high concentrations of alpha-OPN. Use of the antigen retrieval protocol restored OPN immunoreactivity, with strong staining apparent in cement lines, osteoblasts, osteocytes, canaliculi, osteoid, and bone matrix. We conclude that antigen retrieval restores immunochemical recognition of OPN in archival specimens containing bone without increasing nonspecific binding.

Adult↗