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  • 1
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Bone marrow stromal cells (BMSCs) are a heterogeneous population of cells derived from colony-forming units-fibroblastic (CFU-Fs). These cells reside in the bone marrow cavity and are capable of differentiating into several cell phenotypes including osteoblasts, chondroblasts, hematopoiesis-supporting stromal cells, and adipocytes. However, the factors that regulate the proliferation and differentiation of the BMSC population are for the most part unknown. Since many members of the receptor tyrosine kinase (RTK) family have been shown to participate in growth control of various mesenchymal cell populations, in this study we examined the expression and function of RTKs in the BMSC population. Degenerate oligonucleotides corresponding to two conserved catalytic domains of the RTK family and RT-PCR were used initially to determine which RTKs are expressed in the human BMSC (hBMSC) system. After subcloning the amplification product generated from mRNA of a multicolony-derived hBMSC strain, PDGF receptor (β), EGF receptor, FGF receptor 1, and Axl were identified by DNA sequencing of 26 bacterial colonies. Furthermore, PDGF and EGF were found to enhance BMSC growth in a dose-dependent manner and to induce tyrosine phosphorylation of intracellular molecules, including the PDGF and EGF receptors themselves, demonstrating the functionality of these receptors. On the other hand, bFGF was found to have little effect on proliferation or tyrosine phosphorylation. Since single colony-derived hBMSC strains are known to vary from one colony to another in colony habit (growth rate and colony structure) and the ability to form bone in vivo, the expression levels of these RTKs were determined in 18 hBMSC clonal strains by semiquantitative RT-PCR and were found to vary from one clonal strain to another. While not absolutely predictive of the osteogenic capacity of individual clonal strains, on average, relatively high levels of PDGF-receptor were found in bone-forming strains, while on average, nonbone-forming strains had relatively high levels of EGF-receptor. Taken together, these results indicate that RTKs play a role in the control of hBMSC proliferation, and that the differential pattern of RTK expression may be useful in correlating the biochemical properties of individual clonal strains with their ability to produce bone in vivo. J. Cell. Physiol. 177:426-438, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0021-9541
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The effects of cell surface heparan sulfate proteoglycan (HSPG) prepared from log and confluent monolayers of a rat hepatoma cell line on hepatoma cell growth were studied. When HSPG isolated from confluent cells was added exogenously to log phase cells, it was internalized and free heparan sulfate (HS) chains appeared transiently in the nucleus. Concurrently, the growth of the treated cells was inhibited, but the cells resumed logarithmic growth as the level of nuclear HS fell, and the cells grew to confluence and became contact inhibited. When HSPG prepared from log-phase hepatoma cells was added exogenously to log phase cells, it was internalized but very little of the internalized HS appeared in the nucleus, and there was no change in the rate of cell growth. However, when the rate of cell growth was reduced by culture of the cells in serum- and insulin-deficient medium, HSPG prepared from log-phase cells stimulated the growth rate of these slow-growing cells. The cell cycle dependency of HSPG uptake and growth inhibition was studied in cultures synchronized by a thymidine/aphidicolin double block. When [35SO4]HSPG from confluent cells was added to synchronized cells just as they were released from the second block, a portion of the [35SO4]HSPG was internalized and [35SO4]HS appeared in the nucleus. However, at mitosis the [35SO4]HS disappeared almost completely from all of the cellular pools, and after mitosis, more of the [35SO4]HSPG was taken up and [35SO4]HS reappeared in the nucleus and remained in the nucleus until the cells divided again. When cultures were released from the aphidicolin block, both control and HSPG-treated cells progressed through the S, the G2, and the M phases of the cell cycle. However, the length of the G1 phase of the cycle was increased in the HSPG-treated cells. The treated cultures then progressed through the second S, G2, and M phases. Thus, the inhibition of cell division occurred in the G1, phase of the cell cycle, prior to the G1,/S boundary. Addition of the HSPG to the synchronized cultures just after the first mitosis resulted in an immediate arrest of the cell cycle in G1, These results support the earlier suggestion (M. Ishihara, N.S. Fedarko, and H.E. Conrad 1987 J. Biol. Chem. 262:4708-4716; M. Ishihara and H.E. Conrad (1989) J. Cell Physiol., in press) that the HSPG formed by confluent hepatocytes plays a role in the prevention of cell division, whereas the HSPG formed by exponentially growing cells plays a role in the stimulation of cell division. The inhibition of cell growth results from a block in the G1, phase of the cell cycle prior to the G1,/S boundary.
    Additional Material: 6 Ill.
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  • 3
    Publication Date: 1990-08-01
    Print ISSN: 0003-2697
    Electronic ISSN: 1096-0309
    Topics: Biology , Chemistry and Pharmacology
    Published by Elsevier
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