前 言
S6K1是一种丝氨酸/苏氨酸蛋白激酶,因能介导核糖体蛋白S6磷酸化而得名。众所周知,胞内蛋白磷酸化在多种生理及病理过程中发挥重要作用,并与癌症的发生发展关系密切。除此之外,S6K1还有控制体型的功能,下文我们将详细描述。
S6K1概述
S6K1(Ribosomal protein S6 kinase beta-1)主要由三个结构域组成,分别是N端结构域(NTD)、中间激酶结构域(KD)和C端自抑制结构域(CTD)(如图1)。S6K1具有两种形式:p70和p85,两者的区别是p70相较于p85缺失N端的23个氨基酸的核定位序列(NLS),其余序列完全一致,所以S6K1的WB结果往往呈现双条带的显影。
S6K1结构示意图(源自参考文献:http://dx.doi.org/10.1016/j.lfs.2015.03.001)
S6K1介导核糖体蛋白S6的磷酸化,发挥调节转录、细胞周期及维持细胞生成等作用,在癌症的发生发展中具有重要作用。S6K1是雷帕霉素靶蛋白(mTOR)下游的一个重要效应器,同时也是一个前沿的药物靶点。根据药融云数据显示,全球在研的S6K1靶点药物共有26个,大部分处于药物发现阶段,其中走在最前列的是默克公司的DIACC-3010(临床Ⅲ期),靶向多种肿瘤。
S6K1调控体型研究
S6K1的激活是一个多步骤调控的过程。静息状态下,S6K1的C端自抑制结构域与N端结合,不展现激酶活性。但是当C端多位点磷酸化之后,S6K1转变为开放构象,暴露出389位的苏氨酸位点(p70 S6K1的T389对应p85 S6K1的T412),并被mTORC1复合物磷酸化,进而展示激酶活性。S6K1磷酸化S6的位点有Ser235、Ser236、Ser240、Ser244、Ser247等。
在细胞模型中,如果将S6五个磷酸化位点(Ser235、Ser236、Ser240、Ser244、Ser247)进行丙氨酸(Ala)替换,导致S6K1无法磷酸化S6,则MEF、胰岛β细胞会增强蛋白合成、加快细胞分裂速度,造成细胞体型明显变小。细胞生长和增殖的速率与蛋白质合成的速率成正比。在正常细胞过程中,当生长因子和营养物质存在时,S6K1会刺激蛋白质合成。
在小鼠模型中,同样在高脂肪饮食喂养的情况下,S6K1基因缺陷小鼠体重相比野生型少30%以上,且主要是脂肪积累减少。结果表明氧化磷酸化途径的上调和胰岛素敏感性的提高,S6K1基因缺陷小鼠可避免高脂肪饮食引起的肥胖,且负向调节胰岛素信号。因此,S6K1和S6不仅能够调控细胞的体型大小,还能够调控机体的体型大小。
高脂肪饮食喂养4个月的小鼠体重变化(源自参考文献:https://doi.org/10.1038/nature02866)
磷酸化抗体验证数据
Recombinant Phospho-p70 S6 Kinase 1 (Thr389) Antibody, Rabbit Monoclonal, Cat: 110396-R0001
特异性验证:磷酸酶处理
Western blot analysis of extracts from serum-starved MCF7, untreated (line A); treated with IGF-1 (Cat: 10598-HNAE) (100 ng/mL, 30 min; +) (line B); treated with IGF-1 and λ-phosphatase (line C) using Phospho-S6K1 (Thr389) rabbit monoclonal Antibody (Cat: 110396-R0001) at 1:5000 dilution(upper), or Anti-RPS6KB1 rabbit polyclonal antibody (Cat: 10099-T38) (lower) at 1:5000 dilution.
特异性验证:磷酸化多肽竞争
Western blot analysis of extracts from serum-starved MCF7, untreated (line A); treated with IGF-1 (Cat: 10598-HNAE) (100 ng/mL, 30 min), without peptide (line B) or antigen-specific phosphopeptide (line C) or antigen-specific peptide (line D) using Phospho-S6K1 (Thr389) rabbit monoclonal Antibody (Cat: 110396-R0001) at 1:5000 dilution.
超高稀释度(1:200000)
Western blot analysis of extracts from serum-starved MCF7, treated with IGF-1 (Cat: 10598-HNAE) (100 ng/mL, 30 min), using Phospho-S6K1 (Thr389) rabbit monoclonal Antibody (Cat: 110396-R0001) (Sino) and other brands’ antibodies (company C, company P) at dilution of 1:1000, 1:10000 and 1:200000.
Phospho-S6 Ribosomal Protein (Ser240, 244) Antibody, Rabbit Mab, Cat: 110571-R0018
Western blot analysis of extracts from serum-starved HEK293, untreated (-) or treated with 20% FBS, using Phospho-S6 Ribosomal Protein (Ser240, 244) Antibody, Rabbit MAb (upper), or Anti-RPS6 Antibody, Rabbit Polyclonal (Cat: 100676-T32) (lower) at 1:1000 dilution.
Phospho-S6 Ribosomal Protein (Ser235, 236) Antibody, Rabbit MAb, Cat: 110595-R0044
Western blot analysis of extracts from serum-starved Hek293, untreated (-) or treated with IGF1 (100ng/ml, 15min; +), using Phospho-S6 Ribosomal Protein (Ser235, 236) rabbit Monoclonal Antibody at 1:1000 dilution (upper) or anti-S6 Ribosomal Protein antibody (Cat: 100676-T32) (lower) at 1:1000 dilution.
【参考文献】
1. Jastrzebski, K., et al. Coordinate regulation of ribosome biogenesis and function by the ribosomal protein S6 kinase, a key mediator of mTOR function. Growth Factors, 2007. https://doi.org/10.1080/08977190701779101
2. Ruvinsky, I., et al. Ribosomal protein S6 phosphorylation is a determinant of cell size and glucose homeostasis. Genes Dev, 2005. https://doi.org/10.1101/gad.351605
3. Tavares, M. R., et al. The S6K protein family in health and disease. Life Sci, 2015. https://doi.org/10.1016/j.lfs.2015.03.001
Um, S. H., et al. Absence of S6K1 protects against age- and diet-induced obesity while enhancing insulin sensitivity. Nature, 2004. https://doi.org/10.1038/nature02866
4. Yamashita, D., et al. hDREF regulates cell proliferation and expression of ribosomal protein genes. Mol Cell Biol, 2007. https://doi.org/10.1128/mcb.01462-06
5. Mariana, et al. The S6K protein family in health and disease. Life Sciences, 2015. http://dx.doi.org/10.1016/j.lfs.2015.03.001