Ito Y, Zhang Y W
Department of Viral Oncology, Institute for Virus Research, Kyoto University, Japan.
J Bone Miner Metab. 2001;19(3):188-94. doi: 10.1007/s007740170041.
Cleidocranial dysplasia (CCD), an autosomal dominant human bone disease, is thought to be caused by heterozygous mutations in RUNX2/PEBP2alphaA/CBFA1. To understand the mechanism underlying the pathogenesis of CCD, we studied a novel mutant of RUNX2, namely CCDalphaA376, originally identified in a CCD patient. The nonsense mutation, which resulted in a truncated RUNX2 protein, severely impaired RUNX2 transactivation activity. We showed that signal transducers of transforming growth factor (TGF)-beta and bone morphogenetic protein (BMP) receptors, Smads, interact with RUNX2 in vivo and in vitro and enhance transactivation ability. The truncated RUNX2 protein failed to interact with Smads, and was unable to induce the osteoblast-like phenotype in C2C12 myoblasts following stimulation with BMP. Exogenous expression of Smads 1 and 4 in C2C12 cells stably expressing RUNX2 showed alkaline phosphatase (ALP) activity, suggesting a possible link between Smads and RUNX2, while in C2C12 stably expressing CCDalphaA376, a detectable level of ALP activity failed to be induced. The results suggest that CCDalphaA376 inhibited RUNX2 function in a dominant negative fashion.
锁骨颅骨发育不全（CCD）是一种常染色体显性人类骨骼疾病，被认为是由RUNX2/PEBP2alphaA/CBFA1中的杂合突变引起的。为了了解CCD发病机制的潜在机制，我们研究了一种新的RUNX2突变体，即最初在一名CCD患者中发现的CCDalphaA376。这种无义突变导致RUNX2蛋白截短，严重损害了RUNX2的反式激活活性。我们发现，转化生长因子（TGF）-β和骨形态发生蛋白（BMP）受体的信号转导分子Smads在体内和体外均与RUNX2相互作用，并增强反式激活能力。截短的RUNX2蛋白无法与Smads相互作用，并且在BMP刺激后无法在C2C12成肌细胞中诱导成骨细胞样表型。在稳定表达RUNX2的C2C12细胞中外源表达Smads 1和4显示出碱性磷酸酶（ALP）活性，这表明Smads和RUNX2之间可能存在联系，而在稳定表达CCDalphaA376的C2C12细胞中，未能诱导出可检测水平的ALP活性。结果表明，CCDalphaA376以显性负性方式抑制RUNX2功能。
