Department of Periodontics and Oral Medicine, University of Michigan School of Dentistry, Ann Arbor, Michigan 48109-1245, USA.
J Cell Biochem. 2012 Jan;113(1):70-9. doi: 10.1002/jcb.23329.
Parathyroid hormone (PTH) is an essential regulator of endochondral bone formation and an important anabolic agent for the reversal of bone loss. PTH mediates its functions in part by regulating binding of the bone-related activating transcription factor 4 (ATF4) to the osteoblast-specific gene, osteocalcin. The basic helix-loop-helix (bHLH) factors Twist1 and Twist2 also regulate osteocalcin transcription in part through the interaction of the C-terminal "box" domain in these factors and Runx2. In this study, we discovered a novel function of PTH: its ability to dramatically decrease Twist1 transcription. Since ATF4 is a major regulator of the PTH response in osteoblasts, we assessed the mutual regulation between these factors and determined that Twist proteins and ATF4 physically interact in a manner that affects ATF4 DNA binding function. We mapped the interaction domain of Twist proteins to the C-terminal "box" domain and of ATF4, to the N-terminus. Furthermore, we demonstrate that Twist1 overexpression in osteoblasts attenuates ATF4 binding to the osteocalcin promoter in response to PTH. This study thus identifies Twist proteins as novel inhibitory binding partners of ATF4 and explores the functional significance of this interaction.
甲状旁腺激素（PTH）是调节软骨内骨形成的重要调节因子，也是逆转骨丢失的重要合成代谢剂。PTH 通过调节与骨相关的激活转录因子 4（ATF4）与成骨细胞特异性基因骨钙蛋白的结合来发挥其功能。碱性螺旋-环-螺旋（bHLH）因子 Twist1 和 Twist2 也通过这些因子的 C 末端“盒”结构域与 Runx2 的相互作用部分调节骨钙蛋白转录。在这项研究中，我们发现了 PTH 的一个新功能：其显著降低 Twist1 转录的能力。由于 ATF4 是成骨细胞中 PTH 反应的主要调节因子，我们评估了这些因子之间的相互调节关系，并确定 Twist 蛋白和 ATF4 以影响 ATF4 DNA 结合功能的方式相互作用。我们将 Twist 蛋白的相互作用结构域映射到 C 末端“盒”结构域，将 ATF4 的相互作用结构域映射到 N 末端。此外，我们证明成骨细胞中 Twist1 的过表达可减弱 PTH 对骨钙蛋白启动子的 ATF4 结合。因此，本研究鉴定 Twist 蛋白为 ATF4 的新型抑制性结合伴侣，并探讨了这种相互作用的功能意义。
