Slootweg M C, Ohlsson C, Salles J P, de Vries C P, Netelenbos J C
Research Institute for Endocrinology, Free University Hospital, Amsterdam, The Netherlands.
Endocrinology. 1995 Oct;136(10):4210-7. doi: 10.1210/endo.136.10.7545101.
GH exerts its biological actions on osteoblasts through a specific high affinity receptor expressed on these cells. GH receptor binding is positively modulated by a number of factors, including retinoic acid and dexamethasone, whereas fetal calf serum strongly decreases the binding. To identify responsible factors in serum, components of serum, the insulin-like growth factors (IGFs)-I and -II, and IGF binding proteins (IGFBPs)-2 and -3 were tested for a possible negative modulatory role. IGF-I and -II decreased [125I]hGH binding at an optimal concentration of 30 ng/ml for IGF-I and 100 ng/ml IGF-II, reducing the binding to 51% and 55%, respectively, of control values. A stimulation of [125I]hGH binding was observed with IGFBP-2 as well as IGFBP-3, inducing an increase to 148% and 151% of control binding at an optimal concentration of 3000 ng/ml for both peptides. The effects of all peptides were dependent on the incubation time, being significantly increased after 8 h of incubation and reaching the full effect thereafter. The effects were declined at 24 h compared with 16 h for IGFBP-2 and -3 but not for IGF-I and -II. Coincubation of the cells with IGF-I and -II and IGFBP-2 and -3 neutralized the effects of the factors alone. In conclusion, these results show that IGF-I and -II on the one hand and IGFBP-2 and -3 on the other hand exert opposite actions on [125I]hGH binding, IGFBP-2 and -3 exerting probably an IGF-independent effect. Further, IGF-I and -II decreased GH receptor messenger RNA (mRNA) levels, as quantified by a solution hybridization ribonuclease protection assay, from 8.65 +/- 1.78 attomoles (amol)/microgram DNA (control) to 2.4 +/- 0.68 and 2.16 +/- 0.92 amol/microgram DNA, respectively. IGFBP-2 increased GH receptor mRNA levels from 5.26 +/- 1.17 (control) to 13.19 +/- 3.48. Incubation with IGFBP-3 did not result in stimulation of GH receptor mRNA levels (8.59 +/- 2.91 amol/microgram DNA). This shows that the mechanism of regulation of the GH receptor is, except for IGFBP-3, at least in part on the mRNA level. Lastly, IGFBP-2 and IGFBP-3 are mitogenic for UMR-106.01 rat osteosarcoma cells, inducing an increase in cell number to 125% and 142% of control cell counts after 48 h of incubation with 1000 ng/ml IGFBP-2 and -3, whereas IGF-I, IGF-II and Long R3 IGF-I did not stimulate proliferation. IGFBP-2 and -3 potentiate hGH induced mitogenesis at low hGH concentrations of both factors, whereas at higher concentrations no such effect is observed.(ABSTRACT TRUNCATED AT 400 WORDS)
生长激素（GH）通过这些细胞上表达的一种特定高亲和力受体对成骨细胞发挥其生物学作用。生长激素受体结合受到多种因素的正向调节，包括视黄酸和地塞米松，而胎牛血清则强烈降低这种结合。为了确定血清中的相关因素，对血清成分、胰岛素样生长因子（IGF）-I和-II以及IGF结合蛋白（IGFBP）-2和-3进行了测试，以探究其可能的负向调节作用。IGF-I和-II在IGF-I的最佳浓度为30 ng/ml和IGF-II的最佳浓度为100 ng/ml时降低了[125I]hGH结合，分别将结合降低至对照值的51%和55%。观察到IGFBP-2以及IGFBP-3对[125I]hGH结合有刺激作用，在两种肽的最佳浓度为3000 ng/ml时，诱导结合增加至对照结合的148%和151%。所有肽的作用均依赖于孵育时间，孵育8小时后显著增加，此后达到最大效应。与16小时相比，IGFBP-2和-3在24小时时作用减弱，但IGF-I和-II没有。细胞与IGF-I和-II以及IGFBP-2和-3共同孵育可中和这些因子单独的作用。总之，这些结果表明，一方面IGF-I和-II，另一方面IGFBP-2和-3对[125I]hGH结合发挥相反作用，IGFBP-2和-3可能发挥不依赖IGF的作用。此外，通过溶液杂交核糖核酸酶保护测定法量化，IGF-I和-II降低了生长激素受体信使核糖核酸（mRNA）水平，从8.65±1.78阿托摩尔（amol）/微克DNA（对照）分别降至2.4±0.68和2.16±0.92 amol/微克DNA。IGFBP-2将生长激素受体mRNA水平从5.26±1.17（对照）提高到13.19±3.48。与IGFBP-3孵育未导致生长激素受体mRNA水平的刺激（8.59±2.91 amol/微克DNA）。这表明，除了IGFBP-3外，生长激素受体的调节机制至少部分在mRNA水平上。最后，IGFBP-2和IGFBP-3对UMR-106.01大鼠骨肉瘤细胞有促有丝分裂作用，与1000 ng/ml IGFBP-2和-3孵育48小时后，细胞数量增加至对照细胞计数的125%和142%，而IGF-I、IGF-II和长效R3 IGF-I未刺激增殖。在两种因子的低生长激素浓度下，IGFBP-2和-3增强生长激素诱导的有丝分裂，而在较高浓度下未观察到这种效应。（摘要截断于400字）
