Jacobs Frank M J, van der Heide Lars P, Wijchers Patrick J E C, Burbach J Peter H, Hoekman Marco F M, Smidt Marten P
Rudolf Magnus Institute of Neuroscience, Department of Pharmacology and Anatomy, University Medical Center, Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.
J Biol Chem. 2003 Sep 19;278(38):35959-67. doi: 10.1074/jbc.M302804200. Epub 2003 Jul 11.
Forkhead transcription factors of the FoxO-group are associated with cellular processes like cell cycle progression and DNA-repair. FoxO function is regulated by protein kinase B (PKB) via the phosphatidylinositol 3-kinase/PKB survival pathway. Phosphorylation of serine and threonine residues in specific PKB phosphorylation motifs leads to exclusion of FoxO-proteins from the nucleus, which excludes them from exerting transactivating activity. Members of the FoxO-group have three highly conserved regions containing a PKB phosphorylation motif. This study describes the cloning and characterization of a novel forkhead domain gene from mouse that appeared to be highly related to the FoxO group of transcription factors and was therefore designated FoxO6. The FoxO6 gene was mapped in region D1 on mouse chromosome 4. In humans, FOXO6 is located on chromosomal region 1p34.1. Embryonic expression of FoxO6 is most apparent in the developing brain, and FoxO6 is expressed in a specific temporal and spatial pattern. Therefore it is probably involved in regulation of specific cellular differentiation. In the adult animal FoxO6 expression is maintained in areas of the nucleus accumbens, cingulate cortex, parts of the amygdala, and in the hippocampus. Structure function analysis of FoxO6 compared with its group members shows that the overall homology is high, but surprisingly a highly conserved region containing multiple phosphorylation sites is lacking. In transfection studies, FoxO6 coupled to GFP showed an unexpected high nuclear localization after stimulation with growth factors, in contrast to the predominant cytosolic localization of FoxO1 and FoxO3. We also show that nuclear export of FoxO6 is mediated through the phosphatidylinositol 3-kinase/PKB pathway. Furthermore, we show using a chimeric approach that we can fully restore the ability of FoxO6 to shuttle between nucleus and cytosol. In conclusion, the data presented here gives a new view on regulation of FoxO-function through multiple phosphorylation events and other mechanisms involved in the nuclear exclusion of FoxO-proteins.
FoxO 家族的叉头转录因子与细胞周期进程和 DNA 修复等细胞过程相关。FoxO 的功能通过磷脂酰肌醇 3 -激酶/蛋白激酶 B（PKB）生存途径由蛋白激酶 B（PKB）调节。特定 PKB 磷酸化基序中丝氨酸和苏氨酸残基的磷酸化导致 FoxO 蛋白从细胞核中排出，从而使其无法发挥反式激活活性。FoxO 家族成员有三个包含 PKB 磷酸化基序的高度保守区域。本研究描述了从小鼠中克隆和鉴定的一个新的叉头结构域基因，它似乎与 FoxO 转录因子家族高度相关，因此被命名为 FoxO6。FoxO6 基因定位于小鼠 4 号染色体的 D1 区域。在人类中，FOXO6 位于染色体区域 1p34.1。FoxO6 在胚胎期的表达在发育中的大脑中最为明显，并且以特定的时间和空间模式表达。因此它可能参与特定细胞分化的调节。在成年动物中，FoxO6 在伏隔核、扣带回皮质、杏仁核部分区域以及海马体中持续表达。与该家族其他成员相比，对 FoxO6 的结构功能分析表明总体同源性较高，但令人惊讶的是，它缺乏一个包含多个磷酸化位点的高度保守区域。在转染实验中，与绿色荧光蛋白（GFP）偶联的 FoxO6 在生长因子刺激后显示出意外的高核定位，这与 FoxO1 和 FoxO3 主要定位于细胞质形成对比。我们还表明，FoxO6 的核输出是通过磷脂酰肌醇 3 -激酶/PKB 途径介导的。此外，我们通过嵌合方法表明，我们可以完全恢复 FoxO6 在细胞核和细胞质之间穿梭的能力。总之，本文所呈现的数据为通过多种磷酸化事件以及其他参与 FoxO 蛋白核排除的机制对 FoxO 功能的调节提供了新的视角。
