Hormonal Control of Immunoreactive Somatomedin Production by Cultured Human Fibroblasts

Abstract

A B S T R A C T Human growth hormone (hGH) is known to be a potent stimulator of somatomedin secretion in vivo. The induction of somatomedin by growth hormone has been difficult to study in vitro, however, because no organ containing a high concentration of sQmatomedin has been identified. Because fetal mouse explants have been shown to produce somatomedin in vitro, we have undertaken studies to determine whether postnatal human fibroblast monolayers also produce somatomedin, and if so, whether its production is regulated by other hormones. Quiescent human fibroblasts were exposed to serumfree minimum essential medium, and the medium was assayed for somatomedin concentration using a specific radioimmunoassay for somatomedin-C. A progressive rise in immunoreactive somatomedin to 0.08 U/ml per 105 cells per 24 h was observed over 72 h of incubation. This was an underestimation of the actual concentration of immunoreactive somatomedin since the amount measured following acid treatment was at least fourfold higher than in the untreated medium. Growth hormone stimulated immunoreactive somatomedin production in a dose-dependent manner: 5 ng hGH/ml = 0.1 U/ml per 105 cells; 50 ng hGH/ml = 0.25 U/ml per 105 cells. Platelet-derived growth factor and fibroblast growth factor were also stimulatory, but epidermal growth factor, thyroxine, or cortisol had no effect. Media that had been exposed to human fibroblasts stimulated DNA synthesis in BALB/c 3T3 fibroblasts (a cell type that does not produce somatomedin). Medium-derived immunoreactive somatomedin eluted from Sephacryl S-200 in two major peaks (150,000 and 8,000 mol wt).

Stromal influences on breast cancer cell growth

“…The stimulation of tumour cell growth in conditioned medium is consistent with the secretion of stimulatory fibroblast derived growth factors and/or the inability to produce active growth inhibitory factors (Clemmons et al, 1981;Clemmons, 1984;Story et al, 1989;Yee et al, 1988). We have also shown a high proliferation effect of human skin tissue derived fibroblast C-SFM on MCF-7 cells.…”

“…We have also shown a high proliferation effect of human skin tissue derived fibroblast C-SFM on MCF-7 cells. This could be due to the production of insulin-like growth factor (IGF-I) which was shown to be produced by skin fibroblasts (Clemmons et al, 1981;Clemmons, 1984). Skin fibroblasts have also been shown to express high levels of IGF II mRNA (Yee et al, 1988).…”

Structural and functional characterization of the human T lymphocyte receptor for insulin-like growth factor I in vitro.

“…The IGF-I receptor is found in numerous tissues as well and the mitogenic actions of IGF-I upon multiple tissues (1, 3) support a more extensive role for this ligand-receptor system. In addition, fibroblasts both synthesize IGF-I (4,49,50) and bear IGF-I receptors on their surfaces (51,52); the cellular production of "somatomedin-like peptides" has been suggested as an example of the autocrine model of growth regulation (53). Because T lymphocytes are frequently involved with fibrotic tissue reactions the link between the chemotactic and growth factor activity ofIGF-I may be important in the recruitment to and activation of effector lymphocytes at sites of fibroblast activation.…”

“…It circulates as a high molecular weight complex bound to a specific carrier protein. IGF-I has been shown to be identical to somatomedin C and appears to be synthesized in many mammalian tissues (2)(3)(4)(5)(6). Receptors for IGF-I have been identified in numerous tissues including placenta (7), fibroblasts (8), neuronal tissue (9), skeletal muscle (10), Leydig cells (1 1), mononuclear cells (12), and B lymphocytes (13).…”

Cell-Free Synthesis of Rat Insulin-like Growth Factor II

“…9 Synthesis of insulin-like growth factors also has been reported from several other cell and organ culture systems. These include explants of fetal rat liver, 6 chick embryo liver, 19 and diverse fetal mouse organs; 20 fibroblasts from human skin 21 ' 22 and rat embryos; 7 and a human fibrosarcoma. 23 In general, these IGF-like peptides have a Mr of 7000-9000.…”