Wei Fang, Schöler Hans R, Atchison Michael L
Department of Animal Biology, Mari Lowe Center for Comparative Oncology, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
J Biol Chem. 2007 Jul 20;282(29):21551-60. doi: 10.1074/jbc.M611041200. Epub 2007 May 24.
Transcription factor Oct4 is a master regulator affecting the fate of pluripotent stem cells and germ cell precursors. Oct4 expression is tightly regulated, and small changes in expression level can have dramatic effects on differentiation or oncogenesis. Post-translational modifications including phosphorylation and ubiquitination have been reported to regulate Oct4 transcriptional activity. Here we show that Oct4 is a target for small ubiquitin-related modifier (SUMO)-1 modification in vivo and in vitro. Sumoylation of Oct4 occurs at a single lysine, Lys(118), located at the end of the amino-terminal transactivation domain and next to the Pit1-Oct-Unc86 (POU) DNA binding domain. SUMO-1 and Oct4 colocalize at several promoter sequences in vivo, and a fraction of Oct4 molecules colocalized with SUMO-1 in nuclear aggregates. Sumoylation of Oct4 led to significantly increased Oct4 stability and increased DNA binding. In addition, SUMO-1 cotransfection led to augmented Oct4 transactivation potential that was reduced when the Oct4 sumoylation target site was mutated. Therefore, sumoylation of Oct4 results in increased stability, DNA binding, and transactivation and provides an important mechanism to regulate Oct4 activity.
转录因子Oct4是影响多能干细胞和生殖细胞前体命运的主要调节因子。Oct4的表达受到严格调控，表达水平的微小变化会对分化或肿瘤发生产生显著影响。据报道，包括磷酸化和泛素化在内的翻译后修饰可调节Oct4的转录活性。在此，我们证明Oct4在体内和体外都是小泛素相关修饰物（SUMO）-1修饰的靶点。Oct4的SUMO化发生在单个赖氨酸残基Lys(118)上，该残基位于氨基末端反式激活结构域的末端，紧邻Pit1-Oct-Unc86（POU）DNA结合结构域。SUMO-1和Oct4在体内的几个启动子序列处共定位，并且一部分Oct4分子与SUMO-1在核聚集体中共定位。Oct4的SUMO化导致Oct4稳定性显著增加和DNA结合能力增强。此外，共转染SUMO-1导致Oct4反式激活潜能增强，而当Oct4 SUMO化靶点位点发生突变时，该潜能降低。因此，Oct4的SUMO化导致稳定性、DNA结合能力和反式激活能力增加，并提供了一种调节Oct4活性的重要机制。
