bluuebunny/crossref_metadata_2025_split huggingface dataset:
Mechanisms of glucocorticoid action in bone cells
Authors: Delany Anne M. , Dong Yu , Canalis Ernesto 
Published: May 2005

AbstractGlucocorticoids play an important role in the normal regulation of bore remodeling; however continued exposure of bone to glucocorticoid excess results in osteoporosis. In vivo, glucocorticoids stimulate bone resorption and decreasae bone formation, and in vitro studies have shown that while glucocorticoids stimulateosteoblastic differentiation, they have important inhibitory actions on bone formation. Glucocorticoids have manyeffects on osteoblast gene expression, including down‐regulation of type 1 collagen and osteocalcin, and up‐regulation of interstitial collagenase. The synthesis and activity of osteoblast growth factors can be modulated by glucocorticoids as well. For example, insulin‐like growth factor 1 (IGF‐1) is an important stimulator of osteoblast function, and expression of IGF‐1 is decreased by glucocorticoids. The activity of IGF 1 can be modified by IGF binding proteins (IGFBPs), and theirsynthesis is also regulated by glucocorticoids. Thus, glucocorticoid action on osteoblasts can be direct, by activating or repressing osteoblast gene expression, or indirect by altering the expression or activity of osteoblast growth factors. Further investigation of the mechanisms by which glucocorticoids mnodulate gene expression in bore cells will contribute to our understanding or steroid hormone biology and will provide a basis for the design of effective treatments for glucocorticoid‐induced osteoporosis.
Blockade of osteoclast‐mediated bone resorption through occupancy of the integrin receptor: A potential approach to the therapy of osteoporosis
Authors: Dresner‐Pollak Rivka , Rosenblatt Michael 
Published: May 2005

AbstractBone resorption requires the tight attachment of the bone‐resorbing cells, the osteoclasts, to the bone mineralized matric. Integrins, a class of cell surface adhesion glycoproteins, play a key role in the attachment process. Most integrins bind to their ligands via the arginyl‐glycyl‐aspartyl (R‐G‐D) tripeptide present within the ligand sequence. The interaction between integrins and ligaands results in bidirectional transfer of signals across the plasma Membrane. Tyrosine phosphorylaation occurs within cells as a result of integrin binding to ligaands and probably plays a role in the formation of the osteoclast clear zone, a specialized region of the osteoclast membraane maintained by cytoskeletal structure and involved in bone resorption.Human osteoclasts express α2β3 and αvβ3 integrins on their surface. Such signaling may also lead to “inside‐out” effects, like increased expression of integrin receptors on the cell surface, or increased affinity of the integrin to its ligand. The αvβ3 integrin, a vitronectin receptor, plays an essential role in bone resorption. Antibodies to this integrin and short synthetic RGD‐containing peptides are able to block bone resorption in vitro. Echistatin, an RGD‐containing protein from a snake venom, binds to the αvβ3 integrin and blocks bone resssorption both in vitro and in vivo. Peptides containing the RGD motif are potential competitive “antagonists” a of the osteoclast integrins and may have utility in the blockage of bone resorption. Agonists may be identified by stimulation of intracellularsignaling. In theory, tissue spacificity can be achieved by (1) introducing specific amino acids in positions adjacent to the RGD sequence, (2) identifying non‐RGD integrin binding domains, or (3) modulating the affinity of integrins for their endogenous ligands.
Growth hormone, insulin‐like growth factors, and the senescent skeleton: Ponce de Leon's fountain revisited?
Authors: Rosen Clifford J. 
Published: May 2005

AbstractAs the population ages, the prevalence of osteoporosis will continue to rise. Yet, the mechanisms leading to age‐related bone loss remain poorly defined. Furthermore, extensive logitudinal studies of bone mass, especially in the three decades beyond menopause, have not been completed. Although calciotropic hormones, growth hormone (GH), and insulin‐like growth factor‐I (IGF‐I) change with age, it is not certain if these changes are responsible for age‐related bone loss. Nor is it clear if the “sensecent” osteoblast is fully responsive to growth factor stimulation. To complicate matters further, both circulatory and skeletal IFG regulatory systems are extremely redundant. Changes in serum IFGs may lead to compensatory alterations in IGF regulatory systems are extremely redundant. Changes in serum IGFs may lead to compensatory alterations in IGF receptor number, IGF binding protein (IGFBP) synthesis, or IGFBP catabolism. What is measured in serum, maya, in the end, be either a mirror or a rirage of skeletal IGF action! Clinical trials with “replacement” doses of GH or IGF‐I are underway. But, critical efidence does not yet support the concept that a true “sommatopause” alters bone remodeling. Moreover, only scarce data exist that GH augments bone formation or prevents bone loss in the elderly. As clinicians expand the use of recombinant growth factors to elders, ethical and clinical issues surrounding administration of the new “fountain of youth” will be revisited. For basic scientists studying skeletal growth factors and their relationship to senescence, significant questions remain unanswered. New technological advances will provide clues about the basic mechanisms of skeletal aging. But, until these findings are validated, scientists and clinicians will have difficulty judging the role of growth factors in halting, or reversing, the inexorable consequences of aging.
Experimental basis of cancer combination chemotherapy with retinoids, cytokines, 1,25‐dihydroxyvitamin D3, and analogs
Authors: Bollag Werner 
Published: May 2005

AbstractRetinoids, cytokines as well as 1,25‐dihydroxyvitamin D3 [1,25(OH)2D3] and analogs possess properties known to contribute potentially to cancer chemopreventive and chemotherapeutic effects. They induce cell differentiation, inhibit cell prolifeation, suppress expression of viral oncogenes, and inhibit angiogenesis nexessary for tumor growth. Since clinical combination chemotherapy of cytotoxic agents has proven superior to monotherapy, This moddality might also be useful for other classes of antitumor drugs. A series of retinoids, such as all‐trans‐, 13‐cis‐, 9‐cis retinoic acid, and acitreti, cytokines, 1,25(OH)2D3, and analogs have been investigated in mocdel systems of defferentiation, proliferation, viral oncogenes, and angiogenesis. The three classes of compounds have common effects but nevertheless show a variance depending on the particular representative of each class. Combination of compounds of the different classes led in the various models to a hegher efficacy compared with the compounds given alone. Cytokines such as IFNα, IFNγ, G‐CSF, TNFα, IL‐1, and IL‐4 markedly potentiate the differentiation‐inducing effect of retinoids. Cytokines as well as retinoids combined with 1,25(OH)2D3 and analogs synergistically enhanced differentiation induction in human transformed hemopoietic cell lines. On a series of human transformed epithelial cell lines a panel of cytokies, such as IFNα, IFNβ, TNFα, TGFβ, and EGF acted synergistically with retinoies on inhibition of proliferation. This was also observed by combining retinoids with 1,25(OH)2D3 and analogs. Retinoids as well as interferons α and γ have the capacity to suppress the capacity to supperess the oncogene expression of human papilloma viruses which are involved in induction and growth of certain malignancies such as cervical cancer. All‐trans‐, 13‐cis‐, 9‐cis retinoic acid, and acitretin as well as IFNα inhinited the formation of newly formed blood vessels induced by injection of HPV harboring, tumorigenic cell lines into Balb/C mice. The combination of retinoids with IFNα was more efficacious in inhibition angiogenesis than a retinoid or IFNα given alone. Since there is evidence that cell differentiationl, cell proliferation, viral oncogene expression as well as angiogenesis play a role in tumor induction and/or progression of tumor growth, retinoids, cytokines, as well as 1,25(OH)2D3 and analogs may be useful in chemoprevention and chemotherapy of neoplasms. based on the superior effect of combinations compared with administration of single compounds of these three classes under experimental conditions there is hope that also clinical application of combination treatment might bring as a step forward in chemopreventio and chemotherapy of cancer. This has already been proven in a very limited number of very limited numberr of clinical trials.
Modulation of diethylnitrosamine carcinogenesis in rat liver and oesophagus
Authors: Balansky Roumen M. , Blagoeva Penka M. , Mircheva Zwetanka I. , De Flora Silvio 
Published: May 2005

AbstractA series of 16 experiments, using a total of 2,000 BD6 rats, was designed in order to assess the ability of 8 individual agents or their combinations to modulate the liver and oesophageal carcinogenesis induced by multiple doses of diethylnitrosamine (DEN). Of the antioxidants tested, sodium selenite, ascorbic acid, and butylated hydroxytoluence generally exhibited protective effects on both types of tumors. In contrast, retinoic acid behaved as a promoter of DEN hepatocarcinogenesis, but this effect could be eliminated by its combination with either selenite or butylated hydroxytoluene. Caffeine and theophyline, when individually assayed, were devoid of significant protective effects, and the later methylxanthine stimulated oesophageal tumorigenesis when administered afer exposure to the carcinogen. Caffeine tended to decrease tje multiplicityof tumors and potentiated the inhibitory effect of selenite in the liver. Irrespective of combination with caffeine, treatment with phwnobarbital before each DEN injection tended to reduce the multiplicity of both liver and oesophageal tumors. On the other hand, the metabolic inhibitoe diethyldithiocarbamate, given after each DEN injection, dramatically enhancedd the incidence and multiplicity of oesophageal tumors. Thus, on the whole, modulation of DEN carcinogenesis varied depending on test agents, their conbinations, dosages, treatment schedules, and target organ.
Increased expression of basic fibroblast growth factor in hyperoxic‐injured mouse lung
Authors: Powers Michael R. , Planck Stephen T. , Berger John , Wall Michael A. , Rosenbaum James T. 
Published: May 2005

AbstractBasic fibroblast growth factor (bFGF) is a mitogenic polypeptide for a wide variety of cell types and has been immunolocalized in the rodent and human lung. We investigated the mRNA and protein expression of bFGF in hyperoxic‐injured adult mouse lungs using northern blot analysis and immunohistochemistry. Mece (6–8weeks) were continuously exposed to 80% osygen up to 4 days. Levels of bFGF mRNA were increased from room air control on days 3 and 4 of hyperoxia. mRNA levels of acidic fibroblast growth factor (aFGF), fibronectin, and transin/stromelysin were also examined in this injury model. Similar to bFGF, the fibronectin and transin/stromelysin mRNA levels were increased after 3 days of hyperoxia. In contrast, the aFGF mRNA levels were gradually reduced on each day of hyperoxia. A rabbit polyclonal anti‐bFGF antibody was used to determine the distribution and levels of expression in the hyperoxic‐injured lungs. The room air control and day 1 hyperoxic‐exposed lungs exhibited staining for bFGF in the basement membranes of the blood vessels, airways, and alveoli. Patchy but intense alveolar staining was prominent on day 4 of hyperoxia. The bFGF immunoreactivity of blood vessels and airways unaffected by the hyperoxia exposure. These results suggest that bFGF may play a role in the alveolar response to hyperoxic‐induced injury by virtye of the altered mRNA levels and protein distribution in this injury model.
Evidence for a regulatory element controlling amino aced transport system L in Chinese hamster ovary cells
Authors: Collarini Ellen J. , Campbell George S. , Oxender Dale L. 
Published: May 2005

AbstractWe have used the technique of somatic cell hybridization to study the regulation of the neutral amino acid transport system L in Chinese hamster ovary (CHO) cells. The cell line CHO–;tsO25C1 has a temperature‐sinsitive mutationin leucyl‐tRNA synthetase. At the nonpermissive temperature of 39oC, CHO–tsO25C1 cells are unable to charge leucyl‐tRNA and behave as though starved for leucine by increasing their system L transport activity two‐ to fourfold. From the temperature‐sensitive cell line, we have isolated a regulatory mutant cell, CHO–C11B6, that has constitutively elevated system L transport activity. The CHO–C11B6 cell line retains the temperature‐sensitive leucyl‐tRNA synthetase mutation, but growth of this cell line is temperature resistant because its increased system L transport activity leads of increased intracellular leucine levels, which compensate for the defective. Hybrid cells formed by fusion of the temperature‐sensitive CHO–;tsO25C1 cells the temperature‐resistant CHO–C11B6 cells show temperature‐sensitive growth and temperature‐dependent regulation of leucine transport activity. These data suggest that the system L activity of CHO cells is regulated by a dominant‐acting element that is defective or absent in the regulatory mutant CHO–C11B6 cell line.
Tumor promoter phorbol ester reversibly modulates tyrosine dephosphorylatioin/ inactivation of protein kinase FA/GSK‐3α in A431 cells
Authors: Yang Shiaw‐Der , Yu Jau‐Song , Wen Zin‐Der 
Published: May 2005

AbstractThe signal transducrion mechanism of protein kinase FA/GSK‐3α by tyrosine phosphorylation in A431 cells was investigated. Kinase FA/GSK‐3α was found to exist in a highly tyrosine‐phosphorylated/activated state in resting cells but could be tyrosine‐dephosphorylated and inactivated to ∼60% of the control level when cells were acutely treated with 1 μM tumor phorbol ester (TPA) at 37oC for 30 min, as demonstrated by metabolic32P‐labeling the cells, followed by immunoprecipitation and two‐dimensional phosphoamino acid analysis and by immunodetection in an antikinase FA/GSK‐3α immunoprecipitate kinase assay. Conversely, when cells were chronically treated with 1 μM TPA at 37°C for 24 h and processed under identical condetions, kinase FA/GSK‐3α was found to be rephosphorylated on tyrosine residue and reactivated to ∼130% of the original control level. Taken together, the results provide initial evidence that the phosphotyrosine content and cellular activity of kinase FA/GSK‐3α can be modulated in a reversible manner by short‐term and long‐term exposure of A431 cells to TPA. Since acute exposure of cells to TPA causes up‐regulation of cellular protein kinase C (PKC) activity and prolonged exposure to TPA causes down‐regulation of PKC, the results further suggest that the TPA‐mediated modulation of PKC may play a role in the regulation of tyrosine phosphorylation and concurrent activation of kinase FA/GSK‐3α in cells, representing a new mode of signal transduction pathway for the regulation of this multisubstrate/multifunctional protein kinase in cells.
Dual mechanism of protein‐tyrosine phosphorylation in concanavalin A‐stimulated platelets
Authors: Torti Mauro , Ramaschi Giuseppe , Sinigaglia Fabiola , Balduini Cesare 
Published: May 2005

AbstractTreatment of human platelets with the lectin Concanavalin A (Con A) resulted in the tyrosine phosphorylation of several proteins with molecular masses 65, 80, 85, 95, 120, 135, and 150 kDa. These proteins were divided in two groups: the first group included the 65‐, 85‐, 95‐, and 120‐kDa bands, which were tyrosine phosphorylated also in thrombin‐stimulated platelets; the second group (80‐, 135‐, and 150‐kDa bands) included proteins whose tyrosine phosphorylation was exclusively promoted by Con A, but not by thrombin. Members of the second group were rapidly dephosphorylated when the lectin was displaced from the cell surface by methyl α‐D‐mannopyranoside. Pretreatment of intact platelets with the prostacyclin analog iloprost, inhibited Con A‐induced tyrosine phosphorylation of the first group of proteins, but had no effect on the tyrosine phosphorylation of the proteins of the second group. Succinyl‐Con A, a dimeric derivative of the lectin, which binds to the platelet surface but does not promote clustering of the receptor, did not induce tyrosine phosphorylation of the second group of proteins, although phosphorylation of some members of the first group was observed. Our results demonstrate the presence of two different mechanisms leading to protein‐tyrosine phosphorylation in Con A‐stimulated platelets, and identify a new signal transduction pathway, promoted by the clustering of membrane glycoproteins, that produces tyrosine phosphorylation of specific substrates. This new pathway may be activated by platelet interaction with multivalent ligands, such as adhesive proteins, during adhesion, spreading, and aggregation.
Tyrosine kinase regulates phospholipase D activation at a point downstream from protein kinase C in osteoblast‐like cells
Authors: Kozawa Osamu , Suzuki Atsushi , Oiso Yutaka 
Published: May 2005

AbstractIt has recently been shown that the activation of protein kinase C (PKC) induces protein tyrosine phosphorylation in osteoblast‐like MC3T3‐E1 cells. We previously reported that the activation of PKC stimulates phosphatidylcholine‐hydrolyzing phospholipase D in these cells. In this study, we examined whether protein tyrosine kinase is involved in the PKC‐induced activation of phospholipase D in MC3T3‐E1 cells. Genistein, an inhibitor of protein tyrosine kinases, which by itself had little effect on choline formation, significantly suppressed the formation of choline induced by 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA), an activator of PKC, in a dose‐dependent manner. Tyrphostin, an inhibitor of protein tyrosine kinases chemically distinct from genistein, also dose‐dependently suppressed the TPA‐induced formation of choline. Sodium orthovandate, an inhibitor of protein tyrosine phosphatases, significantly enhanced the TPA‐induced formation of choline in a dose‐dependent manner. These results strongly suggest that protein tyrosine kinase regulates phospholipase D activity at a point downstream from PKC in osteoblast‐like cells.
Estrogen modulation of osteoclast lysosomal enzyme secretion
Authors: Kremer M. , Judd J. , Rifkin B. , Auszmann J. , Oursler M. J. 
Published: May 2005

AbstractOsteoclast‐mediated bone resorption is accomplished by secretion of lysosomal proteases into an acidic extracellular compartment. We have previously demonstrated that avian osteoclasts and human osteoclast‐like giant cell tumor cells respond in vitro to treatment with 17β‐estradiol (17β‐E2) by decreased bone resorption activity. To better understand the mechanism by which this is accomplished, we have investigated the effects of 17β‐E2 treatment on lysosomal enzyme production and secretion by isolated avian osteoclasts and multinucleated cells from human giant cell tumors in vitro. Isolated cells were cultured with bone particles in the presence of either vehicle or steroid. The conditioned media and cells were harvested, and the levels of cathepsin B, cathepsin L, β‐glucuronidase, lysozyme, and tartrate‐resistant acid phosphatase (TRAP) activities were determined. There was a steroid dose‐dependent decrease in secreted levels of these enzymes. Cell‐associated levels of cathepsin L, β‐glucuronidase, and lysozyme decreased, whereas cell‐associated levels of cathepsin B and TRAP increased. These changes were measurable at 10−10 M and maximal at 10−8 M 17β‐E2. The changes were detectable at 4–18 h of treatment and increased through 24 h of treatment. The response was steroid specific, since the inactive estrogen isomer, 17β‐E2, failed to alter the activity levels. Moreover, the effects of 17β‐E2 were blocked when the cells were treated simultaneously with the estrogen antagonist ICI182–780 in conjunction with 17β‐E2. Human osteoclast‐like cells obtained from giant cell tumors of bone responded similarly to estrogen with respect to cathepsin B, cathepsin L, and TRAP activities. However, secretion of β‐glucuronidase and lysozyme were not altered by treatment with 10−8 M 17β‐E2. These data indicate that estrogen effects on osteoclast resorption activity may be mediated by decreasing the secretion of cathepsin B, cathepsin L, and TRAP.
MAPKAP kinase 2 is activated by heat shock and TNF‐α: In vivo phosphorylation of small heat shock protein results from stimulation of the MAP kinase cascade
Authors: Engel Katrin , Ahlers Annette , Brach Marion A. , Herrmann Friedhelm , Gaestel Matthias 
Published: May 2005

AbstractThe activation of MAPKAP kinase 2 was investigated under heat‐shock conditions in mouse Ehrlich ascites tumor cells and after treatment of human MO7 cells with tumor necrosis factor‐α (TNF‐α). MAPKAP kinase 2 activity was determined using the small heat‐shock proteins (sHsps) Hsp25 and Hsp27 as substrates. In both cell types, about a threefold increase in MAPKAP kinase 2 activity could be detected in a time interval of about 10–15 min after stimulation either by heat shock or TNF‐α. Phosphorylation of MAPKAP kinase 2, but not the level of MAPKAP kinase 2 mRNA, was increased after heat shock in EAT cells. It is further shown that activation of MAPKAP kinase 2 in MO7 cells is accompanied by increased MAP kinase activity. These data strongly suggest that increased phosphorylation of the sHsps after heat shock or TNF‐α treatment results from phosphorylation by MAPKAP kinase 2, which itself is activated by phosphorylation through MAP kinases. Hence, we demonstrate that MAPKAP kinase 2 is responsible not only for phosphorylation of sHsps in vitro but also in vivo. The findings link sHsp phosphorylation to the MAP kinase cascade, explaining the early phosphorylation of sHsp that is stimulated by a variety of inducers such as mitogens, phorbol esters, thrombin, calcium ionophores, and heat shock.
Cortisol downregulates osteoblast α1(I) procollagen mRNA by transcriptional and posttranscriptional mechanisms
Authors: Delany Anne M. , Gabbitas Bari Y. , Canalis Ernesto 
Published: May 2005

AbstractGlucocorticoids decrease osteoblast proliferation and type I collagen production, and this may play a role in the development of glucocorticoid‐induced osteoporosis. Osteoblast‐enriched cultures derived from fetal rat calvaria were used to determine the mechanisms by which cortisol decreases α1(I) procollagen expression in bone cells. A 24 h treatment with cortisol decreased collagen synthesis in these cultures in a dose‐dependent manner. Cortisol decreased α1(I) procollagen transcripts in a dose‐ and time‐dependent manner as well. Repression of α1(I) procollagen transcripts was evident as early as 2 h of treatment and was maximal after 48 h of treatment. Nuclear run‐off assays showed that cortisol downregulated transcription of the α1(I) procollagen gene. In addition, pretreatment with cortisol decreased the stability of α1(I) procollagen mRNA in transcription‐arrested osteoblast cultures. The ability of cortisol to downregulate α1(I) procollagen transcripts was sensitive to cycloheximide treatment, suggesting that the gene is under “secondary control” by glucocorticoids. Since cortisol decreases α1(I) procollagen gene transcription in osteoblasts but does not affect α1(I) procollagen gene transcription in fibroblasts, we suggest that the mechanisms controlling glucocorticoid repression of collagen expression are cell‐type specific.