| Abstract: |
GH is necessary but not sufficient to induce adipose differentiation of 3T3-F442A fibroblasts in serum-free medium. Human (h) GH (2 nM) treatment of 3T3-F442A cells in serum-free medium caused a time-dependent (maximal at 48-72 h) and dose-dependent (EC50, 0.2 nM) decrease (40–60%) inde nouo protein synthesis. Insulin-like growth factor-I (IGF-I;17 nM), PRL (2 nM), and glucagon (20 nM) did not decrease de novo protein synthesis, whereas bovine GH was equipotent with hGH. The half-lives of 35S-labeled proteins of 3T3-F442A cells were 21 and 57 h for cells maintained in serum-free medium for 3 days without or with hGH (2 nM), respectively. The total protein content of cells maintained in hGH (2 nM) for 1–4 days was unaffected compared to cells in serum-free medium alone. IGF-I (17 nM) treatment of cells for 4 days doubled the protein content of cells compared to control values in serum-free medium. hGH (2 nM) pretreatment of cells for 1–4 days had no effect on total RNA synthesis. hGH (2 nM) but not IGF-I (17 nM) treatment (3 days) resulted in a 7-fold decrease in cytoplasmic 18S rRNA content (as measured by DNA-RNA hybridization) of cells compared to that of control cells maintained in serum-free medium. When 3T3-F442A cells were transferred to serum-free medium there was a progressive decrease in DNA synthesis. The presence of hGH enhanced the rate at which DNA synthesis decreased for 3T3-F442A cells. IGF-I (17 nM) increased DNA synthesis by 6- and 8-fold after 2 and 3 days of IGF-I e posure. 3T3-F442A cells maintained in serum-free medium for 3 days responded to the addition of platelet-derived growth factor (2 U/ml) and insulin (1.6 μM) with a 56-fold increase in DNA synthesis, assayed 24 h later. 3T3-F442A cells treated with hGH (2 nM) for 3 days before platelet-derived growth factor and insulin addition exhibited a diminished DNA synthetic response, demonstrating that GH-exposed cells were partially efractory to mitogenic stimulation. GH had no effect on any aspect of macromolecular synthesis in 3T3-C2 cells,which have a low frequency of adipogenesis. Based upon these results a cell cycle model for the role of GH in the adipose differentiation of 3T3-F442A cells was proposed. © 1989 by The Endocrine Society. |
| Keywords: |
nonhuman; proteins; animal cell; mouse; animal; mice; cells, cultured; cell differentiation; growth hormone; rna; dna; kinetics; cell culture; fibroblast; fibroblasts; somatomedin c; radioisotope; rna, ribosomal; cell strain 3t3; adipose tissue; differentiation; macromolecule; adipocyte; priority journal; support, non-u.s. gov't; support, u.s. gov't, p.h.s.; somatrem
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