Kassem M, Okazaki R, Harris S A, Spelsberg T C, Conover C A, Riggs B L
Endocrine Research Unit, Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Clinic and Mayo Foundation, 200 First Street SW, North 6 Plummer, Rochester, Minnesota 55905, USA.
Calcif Tissue Int. 1998 Jan;62(1):60-6. doi: 10.1007/s002239900395.
Insulin-like growth factors (IGF)-I and IGF-II are produced by osteoblasts and are important paracrine/autocrine regulators of osteoblast proliferation and differentiation. Estrogen has been reported to increase gene expression of IGF-I in rodent osteoblasts. However, because species differences have been demonstrated in expression of various aspects of the IGF system in bone cells, it is not known whether this action also occurs in human osteoblasts. Thus, we assessed the effects of estrogen treatment on IGF-I and IGF-II gene expression in vitro in a recently developed human fetal osteoblast cell line that has high levels of estrogen receptors. As assessed by a quantitative reverse transcriptase-polymerase chain reaction method, treatment of hFOB/ER9 cells with 17beta-estradiol (E2) increased steady state levels of IGF-I mRNA in a time- and dose- dependent fashion with a maximal increase of 319% +/- 33% (P < 0.01) of control occurring after treatment with 10(-7) M E2 for 48 hours. In contrast, E2 did not alter steady state levels of IGF-II mRNA. The pure (type 2) antiestrogens ICI 182,780 (10(-7) M) and ICI 164,384 (10(-6) M) blocked the E2- induced increase in IGF-I mRNA levels. Interestingly, 4-hydroxytamoxifen (10(-7) M), a documented pure antiestrogen in reproductive tissues, also increased IGF-I mRNA to levels similar to those observed in E2-treated cells. Since E2 was shown to mediate its effects on some target genes through a cAMP-dependent pathway, we studied the interaction between E2 and agents that are known to increase intracellular cAMP. Forskolin (10(-8) M) and dibutyryl cAMP (10(-3) M) increased IGF-I mRNA levels sixfold, and cotreatment with E2 did not affect these changes, consistent with a possible mediation of the estrogen effect on IGF-I gene expression by cAMP. We conclude that in human osteoblastic cells, the IGF-I gene is a target for estrogen action, suggesting that IGF-I may mediate part of the effects of estrogen in human bone.
胰岛素样生长因子（IGF）-I和IGF-II由成骨细胞产生，是成骨细胞增殖和分化的重要旁分泌/自分泌调节因子。据报道，雌激素可增加啮齿动物成骨细胞中IGF-I的基因表达。然而，由于已证实在骨细胞中IGF系统各方面的表达存在物种差异，因此尚不清楚这种作用是否也发生在人成骨细胞中。因此，我们在一种新建立的、具有高水平雌激素受体的人胎儿成骨细胞系中，评估了雌激素处理对体外IGF-I和IGF-II基因表达的影响。通过定量逆转录-聚合酶链反应方法评估，用17β-雌二醇（E2）处理hFOB/ER9细胞，可使IGF-I mRNA的稳态水平呈时间和剂量依赖性增加，在用10^(-7) M E2处理48小时后，最大增加量为对照的319%±33%（P<0.01）。相比之下，E2并未改变IGF-II mRNA的稳态水平。纯（2型）抗雌激素ICI 182,780（10^(-7) M）和ICI 164,384（10^(-6) M）可阻断E2诱导的IGF-I mRNA水平升高。有趣的是，4-羟基他莫昔芬（10^(-7) M），一种在生殖组织中有记载的纯抗雌激素，也可使IGF-I mRNA水平升高至与E2处理细胞中观察到的水平相似。由于已表明E2通过cAMP依赖性途径介导其对某些靶基因的作用，我们研究了E2与已知可增加细胞内cAMP的试剂之间的相互作用。福斯可林（10^(-8) M）和二丁酰cAMP（10^(-3) M）可使IGF-I mRNA水平增加6倍，与E2共同处理并不影响这些变化，这与cAMP可能介导雌激素对IGF-I基因表达的作用一致。我们得出结论，在人成骨细胞中，IGF-I基因是雌激素作用的靶点，提示IGF-I可能介导雌激素在人骨骼中的部分作用。
