Guller S, Sonenberg M, Wu K Y, Szabo P, Corin R E
Memorial Sloan-Kettering Cancer Center, New York, New York 10021.
Endocrinology. 1989 Nov;125(5):2360-7. doi: 10.1210/endo-125-5-2360.
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, approximately 0.2 nM) decrease (40-60%) in de nova 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 exposure. 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 microM) 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 refractory 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.
在无血清培养基中，生长激素（GH）是诱导3T3 - F442A成纤维细胞脂肪分化所必需的，但并不充分。在无血清培养基中，用人类（h）生长激素（2 nM）处理3T3 - F442A细胞，可导致从头蛋白质合成呈时间依赖性（48 - 72小时达到最大值）和剂量依赖性（半数有效浓度[EC50]约为0.2 nM）降低（40 - 60%）。胰岛素样生长因子 - I（IGF - I；17 nM）、催乳素（PRL；2 nM）和胰高血糖素（20 nM）不会降低从头蛋白质合成，而牛生长激素与hGH具有同等效力。对于在无血清培养基中分别培养3天且未添加或添加了hGH（2 nM）的3T3 - F442A细胞，其35S标记蛋白质的半衰期分别为21小时和57小时。与仅在无血清培养基中的细胞相比，在hGH（2 nM）中培养1 - 4天的细胞总蛋白质含量未受影响。用IGF - I（17 nM）处理细胞4天，与无血清培养基中的对照值相比，细胞蛋白质含量增加了一倍。用hGH（2 nM）对细胞进行1 - 4天的预处理对总RNA合成没有影响。与在无血清培养基中培养的对照细胞相比，用hGH（2 nM）而非IGF - I（17 nM）处理（3天）导致细胞胞质18S rRNA含量（通过DNA - RNA杂交测定）降低了7倍。当3T3 - F442A细胞转移至无血清培养基时，DNA合成逐渐减少。hGH的存在提高了3T3 - F442A细胞DNA合成减少的速率。在暴露于IGF - I 2天和3天后，IGF - I（17 nM）使DNA合成增加了6倍和8倍。在无血清培养基中培养3天的3T3 - F442A细胞，在添加血小板衍生生长因子（2 U/ml）和胰岛素（1.6 microM）后，24小时后检测到DNA合成增加了56倍。在添加血小板衍生生长因子和胰岛素之前，先用hGH（2 nM）处理3T3 - F442A细胞3天，其DNA合成反应减弱，表明暴露于GH的细胞对有丝分裂刺激部分不应答。GH对3T3 - C2细胞（脂肪生成频率较低）的大分子合成的任何方面均无影响。基于这些结果，提出了一个关于GH在3T3 - F442A细胞脂肪分化中作用的细胞周期模型。
