bluuebunny/crossref_metadata_2025_split huggingface dataset:
Induction of cell surface peptidase activity: A global response to cell stress correlated with apoptosis
Authors: Brown S. B. , Kluck R. M. , Ellem K. A. O. 
Published: May 2005

AbstractWe have previously characterized the stimulation of HeLa cell surface peptidase activity directed toward a nonapeptide substrate in response to low fluences of ultraviolet irradiation [Brown et al. (1993): J Cell Biochem 51:102–115]. To explore the hypothesis that this comprised a global response to cell stress featuring the interruption of DNA synthesis, a variety of agents affecting macromolecular synthesis were applied to HeLa cell cultures. Actinomycin D, 5,6‐dichloro‐1 β‐ribofuranosyl benzimadazole, mitomycin C, ultraviolet light, and cycloheximide at doses which inhibited cell growth, but fell short of increasing the proportion of cells which had lost cell membrane impermeability to trypan blue, resulted in the concentration dependent increase in both amino‐ and endo‐peptidase activities of intact HeLa cell cultures. γ‐Irradiation, despite inhibiting an increase in cell number over a 20‐h observation period, had no effect on the expressed level of cell surface peptidase activity nor did the accumulation of cells in S or G2 phase by thymidine parasynchronization. Some of these agents were found to increase the proportion of cells in the culture undergoing apoptosis (programmed cell death), and a strong correlation was found between the extent of apoptosis and the degree of elevation in cell surface peptidase activity. Higher concentrations of perturbants in some instances increased the percentage of cells that were nonviable and an associated release of intracellular proteases overwhelmed the linear correlation with apoptotic cells. The present data do not distinguish between a homogeneous elevation of surface peptidase activity in all cells of treated cultures or the heterogeneous increase in only preapoptotic or apoptotic cells. Since sunburn of the skin increases both the occurrence of apoptotic keratinocytes (sunburn cells) in the affected epidermis and the release of membrane bound cell activators such as transforming growth factor α, it is suggested by way of extrapolation of these in vitro results, that the increase in cell surface proteolytic activity plays an integral part in the reparative responses of the epidermal cells in vivo.
Interleukin 4 increases type 5 acid phosphatase mrna expression in murine bone marrow macrophages
Authors: Lacey D. L. , Erdmann J. M. , Tan H.‐L. 
Published: May 2005

AbstractType 5 acid phosphatase is a lysosomal enzyme expressed in cells of monocyte/macrophage lineage frequently used as a marker of osteoclastic differentiation. Oligonucleotide primers for DNA amplification were designed following sequence alignment of rat bone and human macrophage type 5 acid phosphatases. DNA (330 bp in length) obtained using these primers and reverse transcribed total cell RNA from in vitro generated murine osteoclastic cells was cloned and sequenced. DNA sequence analysis of two clones demonstrates that the amplified material was 91% and 96% identical to rat bone type 5 acid phosphatase at the nucleotide and amino acid level, respectively. Northern blots of murine tissue RNA show the presence of 1.5‐kb transcripts that are most highly expressed in the long bones. Total cell RNA from the osteoclastic cells contain a marked level of type 5 acid phosphatase mRNA when compared to the levels seen in the tissue samples. Additionally, osteoclastic cell RNA contains two additional transcripts of 2.5 and 5 kb. Bone marrow macrophages grown in the presence of M‐CSF express low levels of the 1.5‐kb transcript with no signal observed for either of the two larger transcripts that were seen in the osteoclastic RNA samples. Importantly, bone marrow macrophage 1.5‐kb type 5 acid phosphatase transcript levels are increased by interleukin 4 treatment in both a time and concentration‐dependent manner. These findings indicate that type 5 acid phosphatase, while a cytochemical marker for osteoclasts, can be induced in macrophages by agents that block in vitro osteoclastic differentiation. Increased type 5 acid phosphatase may play a role in interleukin 4‐stimulated monocyte activities.
Posttranscriptional regulation of thymidylate synthase gene expression
Authors: Johnson Lee F. 
Published: May 2005

AbstractThymidylate synthase (TS) is an essential enzyme that catalyzes the formation of thymidylic acid in the de novo biosynthetic pathway and is the target enzyme for a variety of chemotherapeutic agents. The TS gene is expressed at a much higher level in proliferating cells than in quiescent cells. Control is primarily exerted at the posttranscriptional level. Studies with chimeric TS minigenes have shown that regulation of TS mRNA content in growth‐stimulated mouse fibroblasts requires the presence of sequences located upstream of the essential promoter elements. In addition, an efficiently spliced intron must be present within the transcript. Neither sequence by itself is sufficient for proper regulation, suggesting that the upstream and downstream sequences may communicate to effect regulation. A possible mechanism by which the upstream sequences influence the efficiency of splicing of TS transcripts in a cell cycle specific manner is described.Expression of the human TS gene is also controlled at the translational level. The TS enzyme is able to block the translation of its own mRNA by binding to the message in the vicinity of the AUG start codon. The translational block is relieved in the presence of substrates or inhibitors of the enzyme. The autogenous translational regulation of TS mRNA is likely to be responsible for the rapid increase in TS enzyme level that occurs when cells are exposed to certain TS inhibitors. Elucidation of the mechanism by which the translational control is exerted may lead to the design of more effective TS inhibitors.
Control of fibroblast senescence and activation of programmed cell death
Authors: Wang Eugenia , Lee Menq‐Jer , Pandey Siyaram 
Published: May 2005

AbstractWe have characterized a nuclear phosphoprotein of 57 kda, statin, found only in nonproliferating cells of both quiescent and senescent natures. Emerging results suggest that statin may function as a sequester to block the early G1 phase phosphorylation for the RB protein. A second protein, terminin, undergoes senescence‐specific posttranslational modification from 90 to 60 kda, and further death‐specific conversion from 60 to 30 kda. We also found that apoptotic mouse 3T3 fibroblasts express c‐fos, c‐myc, c‐jun, and cdc2, as well as the upregulation of RB phosphorylation and BrdU incorporation, just before final DNA fragmentation and death. It seems that en route to death, cells re‐enter the cell‐cycle traverse and experience early G1 and part of S Phase; however, this cycling event is an abortive one. In contrast, senescent fibroblasts are resistant to the initiation of the death program, since they are unable to enter cell cycle traverse. Long‐term serial passaging of normal human fibroblasts may be inadvertently selecting those, while termed as senescent, are also specialized survivors, and thus a good culture model to study both the control of permanent departure from cell cycle traverse and the mechanism underlying the survival or antideath cellular program.
Cell cycle control and cancer chemotherapy
Authors: Kohn Kurt W. , Jackman Joany , O'Connor Patrick M. 
Published: May 2005

AbstractAs detailed information accumulates about how cell cycle events are regulated, we can expect new opportunities for application to cancer therapy. The altered expression of oncogenes and tumor suppressor genes that commonly occurs in human cancers may impair the ability of the cells to respond to metabolic perturbations or stress. Impaired cell cycle regulation would make cells vulnerable to pharmacologic intervention by drug regimens tailored to the defects existing in particular tumors. Recent findings that may become applicable to therapy are reviewed, and the possible form of new therapeutic stratagems is considered.
Cell density‐dependent regulation of cell surface expression of two types of human tumor necrosis factor receptors and its effect on cellular response
Authors: Pocsik Eva , Mihalik Rudolf , Ali‐Osman Francis , Aggarwal Bharat B. 
Published: May 2005

AbstractTumor necrosis factor (TNF) is a multipotential cytokine known to regulate the growth of a wide variety of normal and tumor cells. It has been shown that the density of cells in culture can modulate the growth regulatory activities of TNF, the mechanism of which, however, is not understood. In this report, we investigated the effect of cell density on the expression of TNF receptors. The receptors were examined on epithelial cells (e.g., HeLa), which primarily express the p60 form, and on myeloid cells (e.g., HL‐60) known to express mainly the p80 form. We observed that binding of TNF to both cell lines decreased with increase in cell density. Scatchard analysis of binding on HeLa and HL‐60 cells revealed a 4‐ to 5‐fold reduction in the number of TNF receptors without any significant change in receptor affinity in both cell types at high density. The decrease in TNF receptor numbers at high cell density was also observed in several other epithelial and myeloid cell lines. The downmodulation at high cell density was unique to TNF receptors, since minimum change in other cell surface proteins was observed as revealed by fluorescent activated cell sorter analysis. Neutralization of binding with antibodies specific to each type of the receptors revealed that both the p60 and p80 forms of the TNF receptor were equally downmodulated.A decrease in leucine incorporation into proteins was observed with increase in cell density, suggesting a reduction in protein synthesis. Since inhibition of protein synthesis by cycloheximide also leads to a decrease in TNF receptors, it is possible that the density‐dependent reduction in TNF receptor number is due to an overall decrease in protein synthesis. The density‐dependent decrease in TNF receptors was accompanied by a decrease in intracellular reduced glutathione levels. A reduction in the number of receptors on TNF sensitive tumor cells induced by cell‐density correlated with increase in resistance to the cytokine.
Nuclear architecture supports integration of physiological regulatory signals for transcription of cell growth and tissue‐specific genes during osteoblast differentiation
Authors: Stein Gary S. , van Wijnen André J. , Stein Janet L. , Lian Jane B. , Bidwell Joseph P. , Montecino Martin 
Published: May 2005

AbstractDuring the past several years it has become increasingly evident that the three‐dimensional organization of the nucleus plays a critical role in transcriptional control. The principal theme of this prospect will be the contribution of nuclear structure to the regulation of gene expression as functionally related to development and maintenance of the osteoblast phenotype during establishment of bone tissue‐like organization. The contributions of nuclear structure as it regulates and is regulated by the progressive developmental expression of cell growth and bone cell related genes will be examined. We will consider signalling mechanisms that integrate the complex and interdependent responsiveness to physiological mediators of osteoblast proliferation and differentiation. The focus will be on the involvement of the nuclear matrix, chromatin structure, and nucleosome organization in transcriptional control of cell growth and bone cell related genes. Findings are presented which are consistent with involvement of nuclear structure in gene regulatory mechanisms which support osteoblast differentiation by addressing four principal questions: (1) Does the representation of nuclear matrix proteins reflect the developmental stage‐specific requirements for modifications in transcription during osteoblast differentiation? (2) Are developmental stage‐specific transcription factors components of nuclear matrix proteins? (3) Can the nuclear matrix facilitate interrelationships between physiological regulatory signals that control transcription and the integration of activities of multiple promoter regulatory elements? (4) Are alterations in gene expression and cell phenotypic properties in transformed osteoblasts and osteosarcoma cells reflected by modifications in nuclear matrix proteins? There is a striking representation of nuclear matrix proteins unique to cells, tissues as well as developmental stages of differentiation, and tissue organization. Together with selective association of regulatory molecules with the nuclear matrix in a growth and differentiation‐specific manner, there is a potential for application of nuclear matrix proteins in tumor diagnosis, assessment of tumor progression, and prognosis of therapies where properties of the transformed state of cells is modified. It is realistic to consider the utilization of nuclear matrix proteins for targeting regions of cell nuclei and specific genomic domains on the basis of developmental phenotypic properties or tissue pathology. © 1994 Wiley‐Liss, Inc.
Conformational information in DNA: Its role in the interaction with DNA topoisomerase I and nucleosomes
Authors: Caserta Micaela , Venditti Patrizia , Mauro Ernesto Di , Camilloni Giorgio , Venditti Sabrina 
Published: May 2005

AbstractInformation in DNA is not limited to sequence information. Both local and global conformational parameters are pivotal to the interaction with a number of relevant proteins. The function of the major components of the transcription machinery (RNA polymerase II, DNA topoisomerase I, nucleosomes, the TATA‐binding factor) is dependent on the topological status of the substrate DNA molecule. The topological requirements and the conformational consensus that dictate the rules for localization of nucleosomes and define the active sites for DNA topoisomerase I have been established; the reaction of DNA topoisomerase I is regulated by a topological feedback mechanism. The integrating function of the free energy of supercoiling in the transcription process and the regulatory role of DNA topoisomerase I are discussed. © 1994 Wiley‐Liss, Inc.
Role of vascular endothelial cells in bone biology
Authors: Collin‐Osdoby Patricia 
Published: May 2005

AbstractBone development and remodeling depend on complex interactions between bone‐forming osteoblasts, bone‐degrading osteoclasts, and other cells present within the bone microenvironment. Balanced control of bone formative and degradative processes is normally carefully maintained in the adult skeleton but becomes uncoupled in the course of aging or in various pathological disease states. Systemic regulators of bone metabolism and local mediators, including matrix molecules, cytokines, prostaglandins, leukotrienes, and other autocrine or paracrine factors, regulate the recruitment, differentiation, and function of cells participating in bone formation and turnover. Although some of these interactions are now understood, many yet remain to be elucidated. Recent studies have begun exploring in detail how vascular endothelial cells and their products function in bone physiology. The findings are revealing that bone vascular endothelial cells may be members of a complex communication network in bone which operates between endothelial cells, osteoblasts, osteoclasts, macrophages, stromal cells, and perhaps other cell types found in bone as well. Therefore, multiple systemic and locally produced signals may be received, transduced, and integrated by individual cells and then propagated by the release from these cells of further signals targeted to other members of the bone cell network. In this manner, bone cell activities may be continuously coordinated to afford concerted actions and rapid responses to physiological changes. The bone microvasculature may play a pivotal role in these processes, both in linking circulatory and local signals with cells of the bone microenvironment and in actively contributing itself to the regulation of bone cell physiology. Thus, skeletal homeostasis and the coupling observed between bone resorption and bone formation during normal bone remodeling may be manifestations of this dynamic interactive communication network, operating via diverse signals not only between osteoblasts and osteoclasts but between many cell types residing within bone. © 1994 Wiley‐Liss, Inc.
Signal transduction pathways mediating parathyroid hormone regulation of osteoblastic gene expression
Authors: Partridge Nicola C. , Bloch Sharon R. , Pearman A. Terrece 
Published: May 2005

AbstractParathyroid hormone (PTH) plays a central role in regulation of calcium metabolism. For example, excessive or inappropriate production of PTH or the related hormone, parathyroid hormone related protein (PTHrP), accounts for the majority of the causes of hypercalcemia. Both hormones act through the same receptor on the osteoblast to elicit enhanced bone resorption by the osteoclast. Thus, the osteoblast mediates the effect of PTH in the resorption process. In this process, PTH causes a change in the function and phenotype of the osteoblast from a cell involved in bone formation to one directing the process of bone resorption. In response to PTH, the osteoblast decreases collagen, alkaline phosphatase, and osteopntin expression and increases production of osteocalcin, cytokines, and neutral proteases. Many of these changes have been shown to be due to effects on mRNA abundance through either transcriptional or post‐transcriptional mechanisms. However, the signal transduction pathway for the hormone to cause these changes is not completely elucidated in any case. Binding of PTH and PTHrP to their common receptor has been shown to result in activation of protein kinases A and C and increases in intracellular calcium. The latter has not been implicated in any changes in mRNA of osteoblastic genes. On the other hand activation of PKA can mimic all the effects of PTH; protein kinase C may be involved in some responses. We will discuss possible mechanisms linking PKA and PKC activation to changes in gene expression, particularly at the nuclear level. © 1994 Wiley‐Liss, Inc.
Dual role of osteoblastic proenkephalin derived peptides in skeletal tissues
Authors: Rosen Haim , Bar‐Shavit Zvi 
Published: May 2005

AbstractProenkephalin encodes a group of small peptides with opiate‐like activity, the endogenous opioids, known to function as neurohormones, neuromodulators, and neurotransmitters. Recently, we have demonstrated that in addition to its abundance in fetal brain tissue, proenkephalin is highly expressed in nondifferentiated mesodermal cells of developing fetuses. We identified the skeletal tissues, bone, and cartilage as major sites of proenkephalin expression. To examine the possibility that proenkephalin is involved in bone development we have studied the expression of this gene in bone‐derived cells, its modulation by bone active hormones, and the effects of enkephalin‐derived peptides on osteoblastic phenotype. Our studies revealed that osteoblastic cells synthesize high levels of proenkephalin mRNA which are translated, and the derived peptides are secreted. Reciprocal interrelationships between osteoblast maturation and proenkephalin expression were established. These results together with our observations demonstrating inhibitory effects of proenkephalin‐derived peptides on osteoblastic alkaline phosphatase activity, strongly support the notion that proenkephalin is involved in bone development. A different direction of research by other investigators has established the capability of the opioid system in the periphery to participate in the control of pain. On the basis of these two lines of observation, we would like to present the following hypothesis: The potential of embryonic skeletal tissue to synthesize proenkephalin‐derived peptides is retained in the adult in small defined undifferentiated cell populations. This potential is realized in certain situations requiring rapid growth, such as remodeling or fracture repair. We suggest that in these processes, similarly to the situation in the embryo, the undifferentiated dividing cells produce the endogenous opioids. In the adult these peptides may have a dual function, namely participating in the control of tissue regeneration and in the control of pain. © 1994 Wiley‐Liss, Inc.
Role of colony‐stimulating factor‐1 in bone metabolism
Authors: Felix Rolf , Hofstetter Willy , Wetterwald Antoinette , Cecchini Marco G. , Fleisch Herbert 
Published: May 2005

AbstractColony‐stimulating factor‐1 (CSF‐1) is a cytokine required for proliferation, differentiation, activity, and survival of cells of the mononuclear phagocytic system. The growth factor is synthesized as a soluble, matrix, or membrane associated molecule. The specific functions of these forms are not clear. However, some data suggest a dependence of the development of various populations of tissue macrophages on the locally expressed and presented cytokine. Deficiency in CSF‐1, as is the case in the murine mutant strain op/op, results in low numbers of macrophages and monocytes and, most striking, leads to osteopetrosis due to a virtual absence of osteoclasts. Using the op/op mutation as a model, CSF‐1 was established as one of the growth factors for osteoclasts. The expression of CSF‐1 receptors, encoded by the proto‐oncogene c‐fms, by osteoclast precursors and osteoclasts, suggested an effect of this cytokine not only during osteoclast formation but also on the mature cells. In fact, CSF‐1 was shown to inhibit the resorbing activity, to stimulate migration, and to support survival of isolated osteoclasts in vitro. By these actions on cells of the osteoclast lineage, CSF‐1 induces recruitment of new osteoclasts, leading to a net increase of bone resorption, and might govern the spatial distribution of resorption sites within the bone. During these processes, locally expressed and presented forms of the growth factor may play a crucial role, as will be discussed in this article. © 1994 Wiley‐Liss, Inc.
Prostaglandin F2α activates phospholipase D independently from activation of protein kinase C in osteoblast‐like cells
Authors: Kozawa Osamu , Suzuki Atsushi , Kotoyori Jun , Tokuda Haruhiko , Watanabe Yasuko , Ito Yoshiaki , Oiso Yutaka 
Published: May 2005

AbstractWe previously reported that prostaglandin F2α (PGF2α) receptor is coupled to pertussis toxin (PTX)–sensitive GTP‐binding protein (G protein) in osteoblast‐like MC3T3‐E1 cells [Miwa et al. (1990): Biochem Biophys Res Commun 171:1229–1235]. In the present study, we examined the effect of PGF2α on the activation of phosphatidylcholine‐hydrolyzing phospholipase D in MC3T3‐E1 cells. PGF2α stimulated the formation of choline in a dose‐dependent manner in the range between 10 nM and 10 μM. The formation of choline was stimulated by 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA), a protein kinase C (PKC)–activating phorbol ester. 4α‐Phorbol 12,13‐didecanoate, a PKC‐nonactivating phorbol ester, had little effect on choline formation. The formation of choline stimulated by a combination of PGF2α and TPA was additive. Staurosporine, an inhibitor for protein kinases, which inhibited the effect of TPA on choline formation, dose‐dependently enhanced the formation of choline induced by PGF2α. NaF, an activator of G protein, stimulated the formation of choline. The formation of choline stimulated by a combination of PGF2α and NaF was not additive. NaF‐induced formation of choline was dose‐dependently enhanced by staurosporine. PTX dose‐dependently inhibited the PGF2α‐induced formation of choline. These results strongly suggest that PGF2α activates phospholipase D independently from the activation of PKC in osteoblast‐like cells and PTX‐sensitive G protein is involved in the PGF2α‐induced phospholipase D activation. © 1994 Wiley‐Liss, Inc.