Yamamura Yasuko, Lee Wei Lin, Inoue Ken-ichi, Ida Hiroshi, Ito Yoshiaki
Oncology Research Institute, National University Medical Institutes, Institute of Molecular and Cell Biology, Graduate School for Integrative Sciences and Engineering, National University of Singapore, Singapore 117592, Singapore.
J Biol Chem. 2006 Feb 24;281(8):5267-76. doi: 10.1074/jbc.M512151200. Epub 2005 Dec 22.
The transcription factor RUNX3, which mediates apoptosis and cell growth inhibition in gastric epithelial cells, is a candidate tumor suppressor that is frequently lost in gastric cancer cells. Here, we found that restoration of RUNX3 expression in the cell line not expressing RUNX3 induced apoptosis and that it physically interacted with the Forkhead transcription factor FoxO3a/FKHRL1, known to be an important regulator of apoptosis and the cell cycle. Active unphosphorylated FoxO3a/FKHRL1 was expressed in the gastric cancer cell lines. RUNX3-induced apoptosis depended on the expression of Bim, a proapoptotic BH3-only protein, and both RUNX3 and FoxO3a/FKHRL1 were required for induction of Bim expression. Furthermore, we showed that interaction of RUNX3 and FoxO3a/FKHRL1 was also indispensable for Bim expression and apoptosis in mouse embryonic fibroblasts. In the Bim promoter, RUNX3 bound to two conserved RUNX-binding elements (RBE1 and RBE2), with RBE1 being immediately downstream of a FoxO-binding element. The physical interaction of RUNX3 and FoxO3a/FKHRL1 on the Bim promoter activated transcription of Bim. These findings show that RUNX3 cooperates with FoxO3a/FKHRL1 to participate in the induction of apoptosis by activating Bim and may play an important role in tumor suppression in gastric cancer.
转录因子RUNX3可介导胃上皮细胞的凋亡和细胞生长抑制，是一种候选肿瘤抑制因子，在胃癌细胞中常缺失。在此，我们发现，在不表达RUNX3的细胞系中恢复RUNX3表达可诱导凋亡，且它与叉头转录因子FoxO3a/FKHRL1发生物理相互作用，已知后者是凋亡和细胞周期的重要调节因子。活性未磷酸化的FoxO3a/FKHRL1在胃癌细胞系中表达。RUNX3诱导的凋亡依赖于促凋亡的仅含BH3结构域蛋白Bim的表达，且RUNX3和FoxO3a/FKHRL1对于诱导Bim表达均是必需的。此外，我们表明，RUNX3与FoxO3a/FKHRL1的相互作用对于小鼠胚胎成纤维细胞中的Bim表达和凋亡也是不可或缺的。在Bim启动子中，RUNX3与两个保守的RUNX结合元件（RBE1和RBE2）结合，其中RBE1紧邻FoxO结合元件的下游。RUNX3与FoxO3a/FKHRL1在Bim启动子上的物理相互作用激活了Bim的转录。这些发现表明，RUNX3与FoxO3a/FKHRL1协同作用，通过激活Bim参与凋亡诱导，可能在胃癌的肿瘤抑制中发挥重要作用。
