Section of Endocrinology and Diabetes, St. Christopher's Hospital for Children, Drexel University College of Medicine, Philadelphia, Pennsylvania 19134, USA.
J Biol Chem. 2011 Jul 15;286(28):24726-34. doi: 10.1074/jbc.M110.175364. Epub 2011 May 18.
Growth hormone (GH) stimulates growth plate chondrogenesis and longitudinal bone growth with its stimulatory effects primarily mediated by insulin-like growth factor-1 (IGF-1) both systemically and locally in the growth plate. It has been shown that the transcription factor Stat5b mediates the GH promoting effect on IGF-1 expression and on chondrogenesis, yet it is not known whether other signaling molecules are activated by GH in growth plate chondrocytes. We have previously demonstrated that nuclear factor-κB p65 is a transcription factor expressed in growth plate chondrocytes where it facilitates chondrogenesis. We have also shown that fibroblasts isolated from a patient with growth failure and a heterozygous mutation of inhibitor-κBα (IκB; component of the nuclear factor-κB (NF-κB) signaling pathway) exhibit GH insensitivity. In this study, we cultured rat metatarsal bones in the presence of GH and/or pyrrolidine dithiocarbamate (PDTC), a known NF-κB inhibitor. The GH-mediated stimulation of metatarsal longitudinal growth and growth plate chondrogenesis was neutralized by PDTC. In cultured chondrocytes isolated from rat metatarsal growth plates, GH induced NF-κB-DNA binding and chondrocyte proliferation and differentiation and prevented chondrocyte apoptosis. The inhibition of NF-κB p65 expression and activity (by NF-κB p65 siRNA and PDTC, respectively) in chondrocytes reversed the GH-mediated effects on chondrocyte proliferation, differentiation, and apoptosis. Lastly, the inhibition of Stat5b expression in chondrocytes prevented the GH promoting effects on NF-κB-DNA binding, whereas the inhibition of NF-κB p65 expression or activity prevented the GH-dependent activation of IGF-1 and bone morphogenetic protein-2 expression.
生长激素 (GH) 通过胰岛素样生长因子-1 (IGF-1) 系统和局部在生长板中发挥刺激作用，刺激生长板软骨细胞分化和长骨生长。已经表明转录因子 Stat5b 介导 GH 对 IGF-1 表达和软骨细胞分化的促进作用，但尚不清楚 GH 是否在生长板软骨细胞中激活其他信号分子。我们之前已经证明，核因子-κB p65 是一种在生长板软骨细胞中表达的转录因子，在那里它促进软骨细胞分化。我们还表明，来自生长障碍和 IκB （核因子-κB (NF-κB) 信号通路的组成部分）杂合突变的患者的成纤维细胞对 GH 不敏感。在这项研究中，我们在 GH 和/或吡咯烷二硫代氨基甲酸酯 (PDTC) 的存在下培养大鼠跖骨，PDTC 是一种已知的 NF-κB 抑制剂。PDTC 中和了 GH 介导的跖骨纵向生长和生长板软骨细胞分化的刺激作用。在从大鼠跖骨生长板分离的培养软骨细胞中，GH 诱导 NF-κB-DNA 结合以及软骨细胞增殖和分化，并防止软骨细胞凋亡。NF-κB p65 表达和活性的抑制（分别通过 NF-κB p65 siRNA 和 PDTC）在软骨细胞中逆转了 GH 对软骨细胞增殖、分化和凋亡的介导作用。最后，抑制软骨细胞中的 Stat5b 表达阻止了 GH 对 NF-κB-DNA 结合的促进作用，而抑制 NF-κB p65 表达或活性阻止了 GH 对 IGF-1 和骨形态发生蛋白-2 表达的依赖激活。
