Bone Cell Growth Regulation by Runx2/Cbfa1

我们已经取得了关键发现，Runx 2，成骨细胞成熟促进转录因子，控制前成骨细胞中的细胞周期进程，并且通过细胞周期的进程在三个不同的细胞周期阶段调节Runx 2活性（即，G 0/G1、G1/S和M/G1转换）。Runx 2在有丝分裂期间执行关键的表观遗传功能，并且当正常成骨细胞监测细胞外线索以启动细胞周期进程时，其在早期G1中的表达发生。我们建议，Runx 2在正常成骨细胞中的选择性蛋白水解降解对于Runx 2进入S期之前的急性下调至关重要。 我们建议的中心假设是Runx 2肽基序（特异性目标1）和Runx 2的泛素化（特异性目标2）介导其在成骨细胞周期中的G1晚期选择性降解，以防止通过激活推定的细胞周期检查点抑制细胞生长。 具体目标1将检查Runx 2肽基序，这代表了一个假定的分子中继阶段蛋白质/蛋白质相互作用的一部分，是Runx 2降解所需的。具体目标2将鉴定使Runx 2不稳定的E3泛素连接酶，并表征新的成骨细胞相关辅因子（例如，F-box蛋白）。

We have made the key discoveries that Runx2, the osteoblast maturation promoting transcription factor, controls cell cycle progression in pre-osteoblastic cells, and progression through the cell cycle modulates Runx2 activity at three different cell cycle stages (i.e., the G0/G1, G1/S and M/G1 transitions) by both transcriptional and post-transcriptional mechanisms. Runx2 performs a critical epigenetic function during mitosis and its expression in early G1 occurs when normal osteoblasts monitor extracellular cues for competency to initiate cell cycle progression. We propose that selective proteolytic degradation of Runx2 in normal osteoblasts is critical for acute downregulation of Runx2 prior to entry into S phase. The central hypothesis of our proposal is that Runx2 peptide motifs (Specific Aim 1) and ubiquitination of Runx2 (Specific Aim 2) mediate its selective degradation during late G1 in the osteoblast cell cycle to prevent cell growth suppression through activation of a putative cell cycle checkpoint. Specific Aim 1 will examine what Runx2 peptide motifs, which represent part of a putative molecular relay that stages protein/protein interactions, are required for Runx2 degradation. Specific Aim 2 will identify the E3 ubiquitin ligase that destabilizes Runx2 and characterize novel osteoblast-related co-factors (e.g., F-box proteins) that support ubiquitin ligation.