Evidence for AKT-independent regulation of FOXO1 and FOXO3 in haematopoietic stem and progenitor cells
Evidence for AKT-independent regulation of FOXO1 and FOXO3 in haematopoietic stem and progenitor cells
复制标题
DOI：
10.1080/15384101.2015.1123355
复制
发表时间：
2016-03-18
期刊：
影响因子：
4.3
通讯作者：
Ghaffari, Saghi
中科院分区：
文献类型：
--
作者：
Liang, Raymond;Rimmele, Pauline;Ghaffari, Saghi
转录因子FOXO（1，3，4）是维持造血干细胞所必需的。FOXO是AKT丝氨酸苏氨酸蛋白激酶的进化保守底物，其也被除AKT之外的几种激酶磷酸化。具体地，已知AKT的磷酸化导致FOXO的胞质定位和随后的FOXO转录活性抑制。除了磷酸化，FOXO还受到许多其他翻译后修饰的调节，包括乙酰化、甲基化、氧化还原调节和泛素化，这些修饰共同决定了这些因子的输出。越来越多的证据表明，在干细胞中，包括在造血干细胞中，AKT可能不是FOXO的主要调节因子。为了更详细地解决这个问题，我们研究了基因表达，亚细胞定位，以及对AKT抑制FOXO 1和FOXO 3（HSPC（造血干细胞和祖细胞）中表达的主要FOXO）的反应。在这里，我们表明，虽然FOXO 1和FOXO 3的转录表达水平相似，内源性FOXO 3蛋白主要是核相比，在HSPC中的FOXO 1的细胞质定位。此外，抑制AKT不会增强FOXO 1或FOXO 3的核定位。尽管如此，在NAD依赖性SIRT1脱乙酰酶丧失的背景下，AKT抑制调节HSPC中FOXO 3的定位。总之，这些数据表明，FOXO 3比FOXO 1在原始造血干细胞和多能祖细胞中更活跃。此外，他们指出，除了AKT以外的上游调节因子，如SIRT1，在HSPC中维持核FOXO定位和活性。
Transcription factors FOXOs (1, 3, 4) are essential for the maintenance of haematopoietic stem cells. FOXOs are evolutionary conserved substrates of the AKT serine threonine protein kinase that are also phosphorylated by several kinases other than AKT. Specifically, phosphorylation by AKT is known to result in the cytosolic localization of FOXO and subsequent inhibition of FOXO transcriptional activity. In addition to phosphorylation, FOXOs are regulated by a number of other post-translational modifications including acetylation, methylation, redox modulation, and ubiquitination that altogether determine these factors' output. Cumulating evidence raises the possibility that in stem cells, including in haematopoietic stem cells, AKT may not be the dominant regulator of FOXO. To address this question in more detail, we examined gene expression, subcellular localization, and response to AKT inhibition of FOXO1 and FOXO3, the main FOXO expressed in HSPCs (haematopoietic stem and progenitor cells). Here we show that while FOXO1 and FOXO3 transcripts are expressed at similar levels, endogenous FOXO3 protein is mostly nuclear compared to the cytoplasmic localization of FOXO1 in HSPCs. Furthermore, inhibition of AKT does not enhance nuclear localization of FOXO1 nor FOXO3. Nonetheless AKT inhibition in the context of loss of NAD-dependent SIRT1 deacetylase modulates FOXO3 localization in HSPCs. Together, these data suggest that FOXO3 is more active than FOXO1 in primitive haematopoietic stem and multipotent progenitor cells. In addition, they indicate that upstream regulators other than AKT, such as SIRT1, maintain nuclear FOXO localization and activity in HSPCs.