Somatomedin-C Binding to Cultured Human Fibroblasts is Dependent onDonor Age and Culture Density*

Clemmons, David R.; Elgin, Robert G.; James, Paul E.

doi:10.1210/jcem-63-4-996

Cited by 16 publications

(9 citation statements)

References 25 publications

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“…IGF-I1 binding was 5-10 times greater than IGF-I binding and 300 times that of insulin binding. These binding results are similar to those reported previously for IGF-I binding to fetal human fibroblast monolayers (Conover et al, 1986a;Clemmons et al, 1986), and IGF-I, IGF-11, and insulin binding to postnatal fibroblast monolayers (Thorrson et al, 1985;Conover et al, 1986b). natal fibroblast cultures.…”

Section: Insulin Binding Assayssupporting

confidence: 91%

Insulin‐like growth factor II binding and action in human fetal fibroblasts

Conover

Rosenfeld

Hintz

1987

Journal Cellular Physiology

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To investigate the role of insulin-like growth factor II (IGF-II) in human prenatal growth, IGF-II binding and biological action were studied in four lines of fetal and three lines of postnatal human fibroblasts. Specific binding of IGF-II was similar in both groups: 15.7% and 14.9% for fetal and postnatal fibroblasts, respectively. This was 5-10 times the amount of IGF-I binding found in these cells. IGF-I and IGF-II caused dose-dependent increases in [14C]aminoisobutyric acid (AIB) uptake. IGF-II was sevenfold less potent than IGF-I in stimulating this metabolic response in both fetal and postnatal fibroblasts. The maximal effect of IGF-II in stimulating [14C]AIB uptake approach that of IGF-I. Similar results were obtained when IGF-I and IGF-II stimulation of [3H]thymidine incorporation was compared in fetal and postnatal fibroblasts. Incubation in the presence of alpha IR-3, a monoclonal antibody to the type I IGF receptor, inhibited the ability of both IGF-I and IGF-II to stimulate [14C]AIB uptake and [3H]thymidine incorporation in fetal and postnatal cells. A monoclonal antibody to the insulin receptor did not affect IGF action. These data indicate that IGF-II is a potent metabolic and mitogenic stimulus for human fetal fibroblasts. However, despite the presence of abundant type II IGF receptors on both fetal and postnatal human fibroblasts, IGF-II stimulation of amino acid transport and DNA synthesis appears to be mediated through the type I rather than through its own type II IGF receptor.

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Section: Insulin Binding Assayssupporting

confidence: 91%

Insulin‐like growth factor II binding and action in human fetal fibroblasts

Conover

Rosenfeld

Hintz

1987

Journal Cellular Physiology

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“…Fibroblasts explanted from old donors (74 to 96 years old) had nearly five times the number of IGF-I receptors found in the fetalnewborn group (Clemmons et al, 1986). In addition, there was a gradual loss of high-affinity receptors and a concomitant increase of low-affinity receptors with increasing donor age.…”

Section: Discussionmentioning

confidence: 93%

Altered cell cycle responses to insulin‐like growth factor I, but not platelet‐derived growth factor and epidermal growth factor, in senescing human fibroblasts

Chen

Rabinovitch

1990

Journal Cellular Physiology

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Human diploid fibroblasts (HDF) were used to study aging-related changes in the proliferative response to platelet-derived growth factor (PDGF), epidermal growth factor (EGF), and insulin-like growth factor I (IGF-I, somatomedin-C) in serum-free, chemically defined culture medium. Cell cycle kinetic parameters were determined by using 5-bromodeoxyuridine incorporation and flow cytometric analysis with the DNA stain Hoechst 33258. This allowed analysis of the growth factor response to be focussed exclusively upon of the cycling faction of cells within the culture, even in senescent cell cultures which contained predominantly nondividing cells. PDGF and EGF exert their primary effect upon regulation of the proportion of cycling cells in the culture. The doses of PDGF and EGF that produced a half-maximal cycling fraction, analogous to Km, showed no large or consistent difference between young- and old-passage cells. In contrast, IGF-I primarily affects the rate of transition of cells from G1 into S phase, and the dose of IGF-I which produced a half-maximal rate of G1 exit increased up to 130-fold in older-passage cells. Unexpectedly, supraphysiologic concentrations of IGF-I were found to increase the G1 exit rate of the dividing subpopulation of cells in older-passage cultures to rates higher than those seen in young cultures. In summary, among cells capable of cycling in aging cultures, there were few changes in the regulation of the growth fraction by PDGF and EGF, but there was a greatly increased dependence on IGF-I for regulation of the rate of entry into S phase. The slower growth of the dividing population of cells in aging cultures may be related to a requirement for IGF-I at levels which are greatly above those usually supplied.

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“…This would imply changes in IGF receptor presence or in post-receptor mechanisms. Clemmons, Elgin & James (1986) reported that sparse cultures of human fetal fibroblasts exhibited a greatly increased receptor binding affinity compared with cells of similar density from aged donors, which declined by 70% as the fibroblasts approached confluency, but receptor number per cell showed little change with cell density. These changes in receptor behaviour may be linked to the quantities of endogenously released IGF-I and -II in the culture medium, which will be greater in total in nearconfluent cultures.…”

Section: Discussionmentioning

confidence: 99%

Insulin-like growth factor (IGF)-binding protein release by human fetal fibroblasts: dependency on cell density and IGF peptides

Hill

Camacho‐Hübner

Rashid

et al. 1989

Journal of Endocrinology

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Insulin-like growth factors (IGFs) are bound to specific binding proteins in extracellular fluids in vivo and when released by cells in vitro. One class of binding protein (IGF-BP), a peptide of 26 kDa purified from amniotic fluid, has been shown to modulate IGF bioactivity on isolated human fibroblasts. We have determined the factors that control release of IGF-BP from monolayers of human fetal fibroblasts using a radioimmunoassay, and have compared this with the effects of these factors on the release of IGF-I and -II. Separation of cell-conditioned cultured medium on SDS-PAGE, and subsequent immunoblotting with antibody against IGF-BP showed that fibroblasts released a single species of immunoreactive protein of an estimated molecular weight of 30 kDa. This was not the predominant binding protein released by cells since major bands of approximately 42 kDa and 39 kDa were visualized following separation by SDS-PAGE and ligand blotting with 125I-labelled IGF-I. The 30 kDa IGF-BP was released in parallel with radioimmunoassayable IGF-I and -II over 48 h. However, a significant inverse correlation was found between the release of IGF-BP, IGF-I, IGF-II and cell density. The exposure of fibroblasts to 1.3 nmol/l or greater of IGF-I or -II caused a significant release of IGF-BP. Maximum release was seen in sparse cultures with little or no release from confluent cultures. IGF-I and -II were approximately equipotent with a fourfold increase in IGF-BP release at 19.7 nmol/l. Insulin caused a release of IGF-BP and IGF-I and -II from fibroblasts at supraphysiological concentrations (16.7 nmol/l) which again was maximal on sparse cell cultures. Increases in IGF-BP, IGF-I and -II release were also found in the presence of human placental lactogen (23.3 nmol/l), but human GH, epidermal growth factor, fibroblast growth factor and platelet-derived growth factor were without effect. The results show that human fetal fibroblasts released an IGF-BP immunologically similar to that seen in amniotic fluid together with IGF-I and -II, that IGF-BP release was enhanced by exogenous addition of IGF peptides, and that the release of all three peptides was a property of sparsely plated, rapidly growing cells. These findings strengthen the hypothesis that the cellular expression of IGF-binding proteins may represent an important level of control in IGF physiology.

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Somatomedin-C Binding to Cultured Human Fibroblasts is Dependent onDonor Age and Culture Density*

Cited by 16 publications

References 25 publications

Insulin‐like growth factor II binding and action in human fetal fibroblasts

Insulin‐like growth factor II binding and action in human fetal fibroblasts

Altered cell cycle responses to insulin‐like growth factor I, but not platelet‐derived growth factor and epidermal growth factor, in senescing human fibroblasts

Insulin-like growth factor (IGF)-binding protein release by human fetal fibroblasts: dependency on cell density and IGF peptides

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