Tørring O, Firek A F, Heath H, Conover C A
Endocrine Research Unit, Mayo Clinic, Rochester, Minnesota 55905.
Endocrinology. 1991 Feb;128(2):1006-14. doi: 10.1210/endo-128-2-1006.
Specific insulin-like growth factor-binding proteins (IGFBPs) that may enhance or inhibit insulin-like growth factor (IGF) action are produced in various tissues. In the present study we demonstrated that IGFBPs are synthesized and secreted by rat osteoblast-like cells (UMR 106-01). PTH and PTH-related peptide (PTHrP) were potent stimuli for IGFBP production by UMR cells, whereas GH, IGF-I, insulin, epidermal growth factor, and T3 had little or no effect. A maximal 8- to 30-fold increase in IGFBP production was attained at 10(-7)-10(-6) M PTH and PTHrP, with a half-maximal effect at approximately 10(-9) M. By Western blot analysis, PTH and PTHrP markedly and selectively increased the production of 29,000 mol wt (Mr) and, to a lesser extent, 24,000 Mr IGFBPs. Agents that elevate intracellular cAMP by different mechanisms [(Bu)2cAMP, forskolin, and isobutylmethylxanthine] mimicked the effect of PTH and PTHrP on IGFBP synthesis. In comparison, PTH did not stimulate IGFBP production in fibroblasts and ROS 17/2.8 cells, which secrete IGFBPs of 42,000, 38,000, 34,000, 28,000, and 24,000 Mr, but not of 29,000 Mr. The PTH-responsive IGFBPs from UMR cells were nonglycosylated proteins with preferential affinity for IGF-I over IGF-II. These IGFBPs were not immunoprecipitated with antisera against rat IGFBP-2 or human IGFBP-1. Thus, PTH and PTHrP increase the production in UMR 106-01 cells of discrete IGFBP forms with Mr of 29,000 and 24,000 through a cAMP-mediated mechanism, independent of IGF-I synthesis. Taken with the known effects of PTH on IGF production in bone cells, the data suggest that PTH and PTHrP may modulate local IGF action in bone through the regulation of specific IGFBP availability.
多种组织可产生特异性的胰岛素样生长因子结合蛋白（IGFBPs），它们可能增强或抑制胰岛素样生长因子（IGF）的作用。在本研究中，我们证明了IGFBPs由大鼠成骨样细胞（UMR 106 - 01）合成并分泌。甲状旁腺激素（PTH）和甲状旁腺激素相关肽（PTHrP）是UMR细胞产生IGFBP的有效刺激物，而生长激素（GH）、IGF - I、胰岛素、表皮生长因子和三碘甲状腺原氨酸（T3）的作用很小或无作用。在10⁻⁷ - 10⁻⁶ M的PTH和PTHrP作用下，IGFBP产量最大可增加8至30倍，半最大效应浓度约为10⁻⁹ M。通过蛋白质免疫印迹分析，PTH和PTHrP显著且选择性地增加了分子量为29,000道尔顿（Mr）的IGFBP的产生，在较小程度上也增加了分子量为24,000 Mr的IGFBP的产生。通过不同机制升高细胞内cAMP的试剂[双丁酰环磷腺苷（(Bu)₂cAMP）、福斯可林和异丁基甲基黄嘌呤]模拟了PTH和PTHrP对IGFBP合成的作用。相比之下，PTH对成纤维细胞和ROS 17/2.8细胞的IGFBP产生无刺激作用，这些细胞分泌分子量为42,000、38,000、34,000、28,000和24,000 Mr的IGFBP，但不分泌分子量为29,000 Mr的IGFBP。UMR细胞中对PTH有反应的IGFBP是非糖基化蛋白，对IGF - I的亲和力高于IGF - II。这些IGFBP不能用抗大鼠IGFBP - 2或抗人IGFBP - 1的抗血清进行免疫沉淀。因此，PTH和PTHrP通过cAMP介导的机制，独立于IGF - I的合成，增加了UMR 106 - 01细胞中分子量为29,000和24,000的离散IGFBP形式的产生。结合PTH对骨细胞中IGF产生的已知作用，这些数据表明PTH和PTHrP可能通过调节特定IGFBP的可利用性来调节骨局部的IGF作用。
