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R S Taichman

Publications and source records attributed to R S Taichman.

24 records · Page 2Linked to original sources
PubMed1996

Comparison of benzimidazole nucleosides and ganciclovir on the in vitro proliferation and colony formation of human bone marrow progenitor cells.

Recently we have shown that certain benzimidazole ribonucleosides are potent and selective inhibitors of human cytomegalovirus (HCMV) replication. Because antiviral drugs used to treat HCMV and human immunodeficiency virus (HIV) infections can suppress marrow progenitors, we have evaluated the most promising of the new benzimidazoles for their effects on human bone marrow cells in vitro. In an initial study of the bone marrow toxicity of one of the most active compounds, 100 microM 2-bromo-5,6-dichloro-1-(beta-D-ribofuranosyl)-benzimidazole (BDCRB) inhibited cell proliferation by 20% over a 10 d period compared to 52% inhibition by 100 microM ganciclovir, the drug currently most used to treat HCMV infections. The effects of these drugs and selected other benzimidazole nucleosides were evaluated more extensively in haemopoietic progenitor cell colony formation assays. Colony formation was determined at 2 weeks and scored as either burst forming units-erythroid (BFU-E), or colony forming units-granulocyte/macrophage (CFU-GM). At the highest concentration tested, 100 microM BDCRB only moderately affected BFU-E or CFU-GM formation (31% and 47% inhibition, respectively). This concentration is 10-fold higher than that required to produce a 10000-fold reduction in virus titre. Evaluation of the 2-chloro analog of BDCRB (TCRB) which is less potent against HCMV, its 5'-deoxy analog (5'-dTCRB) which is more potent, and the 2-unsubstituted compound (DRB) gave the following order of haemopoietic toxicity: DRB > TCRB > or = 5'-dTCRB > BDCRB. In contrast to the benzimidazoles, ganciclovir decreased colony formation by 84% for BFU-E and 86% for CFU-GM at 100 microM. These results establish that certain benzimidazole nucleosides are less toxic to haemopoietic progenitors than the preferred drug now being used clinically for HCMV infections. The results also establish that different structure-activity relationships exist for antiviral activity and progenitor cell toxicity, thereby suggesting that different mechanisms are involved in the two types of drug action.

Antiviral Agents↗
PubMed1996

Human osteosarcoma cell lines MG-63 and SaOS-2 produce G-CSF and GM-CSF: identification and partial characterization of cell-associated isoforms.

Bone marrow stem cells reside in close proximity to endosteal osteoblasts. To explore the potential role of osteoblasts in hematopoietic differentiation, we measured the mRNA accumulation, protein production, and secretion of hematopoietic growth factors by the nonmineralizing MG-63 and the mineralizing SaOS-2 human osteosarcoma cell lines. mRNA for the osteoblast-specific protein osteocalcin was well as granulocyte colony-stimulating factor (G-CSF), transforming growth factor-beta 1 (TGF-beta 1), and tumor necrosis factor-alpha (TNF-alpha) was produced by the MG-63 and SaOS-2 cells, like primary human cells, in the presence and absence of L-ascorbate and beta-glycerol phosphate. In contrast, both cell lines expressed c-kit ligand mRNA only in the absence of L-ascorbate and beta-glycerol phosphate induction. Granulocyte-macrophage (GM)-CSF and interleukin-6 (IL-6) mRNA appeared to develop with increasing culture age. G-CSF protein was identified in several cell-associated forms including the 28- and 32-kD species, In addition, GM-CSF was found in cell-associated form. These results suggest that osteoblasts might play a central role in the hematopoietic microenvironment as basal producers of G-CSF and GM-CSF and suggest the possibility that osteoblasts may locally present these proteins in an membrane-associated fashion

Base Sequence↗
PubMed1994

Human osteoblasts support hematopoiesis through the production of granulocyte colony-stimulating factor.

Previous attempts at identifying the constitutive source(s) of granulocyte colony-stimulating factor (G-CSF) in human bone marrow have been unsuccessful despite the fact that normal bone marrow supports abundant myelopoiesis in vivo. We hypothesized that the intimate physical association between bone and hematopoietic cells facilitates interactions between osteoblasts and hematopoietic stem cells. Here we provide the first direct evidence that human osteoblasts participate in hematopoiesis by constitutively producing G-CSF and present the protein in a membrane-associated fashion to human hematopoietic progenitors. These results suggest a direct and central role for osteoblasts in normal myelopoiesis.

Base Sequence↗
PubMed1992

Effects of interleukin-1 beta and tumor necrosis factor-alpha on osteoblastic expression of osteocalcin and mineralized extracellular matrix in vitro.

Osteoblasts play a pivotal role during the bioresponse of bone to agents that stimulate bone resorption and/or inhibit bone formation including hormones, polypeptide growth factors, and cytokines. We examined the cytokines interleukin-1-beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) for their effects on osteoblastic proliferation and development and expression of alkaline phosphate and the osteoblast-specific protein osteocalcin in a mineralizing environment. Primary rat osteoblast-like cells (ROB) and osteoblastic cell lines derived from rat (ROS 17/2.8) and human (MG-63) osteosarcomas were studied. IL-1 beta and TNF-alpha were chosen because of their critical importance during the host response to local inflammatory stimuli. Qualitatively similar two- to threefold inhibition of osteocalcin synthesis by IL-1 beta and TNF-alpha were observed in all three postconfluent bone-forming model systems. Because of the readily measurable concentrations of osteocalcin produced in our culture protocol, it was not necessary to enhance osteoblastic synthesis of osteocalcin by supplementation with 1,25(OH)2-vitamin D3, a treatment which exerts pleiotropic effects on osteoblasts. Under the constraints of our protocol, where alkaline phosphatase and mineralization were already elevated at the 14-day onset of treatment, neither of these phenotypic properties was sensitive to a three-day cytokine exposure. Differences were noted in proliferation, where only TNF-alpha stimulated DNA synthesis in ROB cells, while both cytokines stimulated MG-63 cells. IL-1 beta and TNF-alpha failed to alter ROS 17/2.8 DNA synthesis except at the highest doses (25 pM IL-1 beta and 1 nM TNF-alpha) where inhibition was observed. These results further support the view that cytokine-mediated osteoblastic regulation can be relatively selective.

Alkaline Phosphatase↗
PubMed1992

Gene transfer investigations of p56-LCK function in IL-2-dependent T-cell lines: implications for mechanisms of IL-2-signal transduction.

Recently, the SRC-like non-receptor protein tyrosine kinase p56-LCK has been shown to physically associate with the interleukin-2 receptor (IL-2-R) complex and to undergo rapid elevations in its tyrosine kinase activity upon stimulation of T lymphocytes with IL-2. The functional significance of p56-LCK kinase activation for IL-2-mediated lymphocyte responses, however, has never been directly assessed. Using gene transfer approaches, we have achieved markedly elevated levels of p56-LCK kinase activity in the IL-2-dependent cytolytic T-cell line CTLL-2 and the helper line HT-2. CTLL-2 and HT-2 cells that were stably transfected with expression plasmids encoding either the normal human p56-LCK or a constitutively active version of the mouse p56-LCK kinase (LCK[Y505]) contained striking elevations in the levels of tyrosine phosphorylation on several proteins (34-36, 50-60, 62-68, 77-78, 104-110 kDa), as determined by immunoblot analysis using anti-phosphotyrosine antibodies. CTLL-2 and HT-2 LCK- and LCK(Y505F)-transfected cells remained dependent on IL-2 for their growth and survival in culture despite the findings that (i) IL-2 specifically stimulated elevations in the activity of the endogenous p56-LCK in untransfected CTLL-2 cells without affecting the activities of the other SRC-like kinases in these cells (p59-FYN, p62-YES) and that (ii) IL-2-mediated regulation of p56-LCK correlated with IL-2-driven proliferation of these T cells. Specifically, no elevation in the proliferation (DNA synthesis) or growth of these T cells was found at any of the concentrations of IL-2 examined (0.01-25 U/ml), relative to untransfected and control transfected cells. Furthermore, when cultured in the absence of IL-2, transfected T cells whose relative levels of p56-LCK activity were elevated by approximately 20-50-fold died with the same kinetics as control cells and underwent apoptosis, as defined by uptake of trypan blue dye and DNA fragmentation assays, respectively. Taken together, these data indicate that while IL-2 can up-regulate the enzymatic activity of p56-LCK, elevated levels of p56-LCK tyrosine kinase activity are insufficient to stimulate IL-2-mediated pathways required for T-cell growth and survival. These findings thus imply the existence of other signal-transducing molecules, besides p56-LCK, that physically participate in IL-2R complexes and that are necessary for initiation of the biochemical events ultimately responsible for IL-2's pleiotropic actions on lymphocytes.

Animals↗