Glycogen synthase kinase-3-mediated phosphorylation of serine 73 targets sterol response element binding protein-1c (SREBP-1c) for proteasomal degradation.
Glycogen synthase kinase-3-mediated phosphorylation of serine 73 targets sterol response element binding protein-1c (SREBP-1c) for proteasomal degradation.
复制标题
DOI：
10.1042/bsr20150234
复制
发表时间：
2015-11-20
影响因子：
4
通讯作者：
Raghow R
中科院分区：
文献类型：
--
作者：
Dong Q;Giorgianni F;Beranova-Giorgianni S;Deng X;O'Meally RN;Bridges D;Park EA;Cole RN;Elam MB;Raghow R
我们发现丝氨酸73是SREBP-1c上的一个新的GSK-3β位点，它改变了它与SCAP的亲和力，并改变了蛋白酶体的降解。GSK-3β在饥饿期间对丝氨酸73的磷酸化(胰岛素耗竭状态)可能导致SREBP-1c水平降低；相反，该位点的去磷酸化可能参与胰岛素稳定SREBP-1c(通过阻断GSK-3β作用)。这个部位的功能作用需要在体内得到证实。固醇调节元件结合蛋白-1c(SREBP-1c)是一种关键的转录因子，调节参与从头合成和糖酵解途径的基因。SREBP-1c的结构、周转和反式激活潜能是由大量营养素和激素通过一系列信号通路调节的。我们用MS鉴定了丝氨酸73是从MCA-RH7777肝癌细胞中提纯的大鼠SREBP-1c中一个新的糖原合成酶激酶-3(GSK-3)磷酸化位点。我们的定点突变策略表明，SREBP-1c包含野生型、磷酸零(丝氨酸到丙氨酸)或磷酸模拟(丝氨酸到天冬氨酸)替换，其周转受到不同的调节。我们发现，pSREBP-1c的S73D突变体模拟了一种结构性的磷酸化状态，更容易从SREBP-1c-SCAP复合体中解离出来，并通过SCFFbw7泛素连接酶途径经历GSK-3依赖的蛋白酶体降解。药物抑制GSK-3或siRNA抑制GSK-3可阻止SREBP-1c的加速降解。MS证明，SREBP-1c在体外被丝氨酸73位的GSK-3β磷酸化。丝氨酸73的磷酸化也发生在完整的肝脏中。我们认为，GSK-3介导的大鼠SREBP-1c丝氨酸73的磷酸化及其伴随的失稳是抑制肝脏从头合成脂质的一种新机制。
We have identified Serine 73 as a novel GSK-3β site on SREBP-1c that alters its affinity for SCAP, and proteasomal degradation. Phosphorylation of Serine 73 by GSK-3β during starvation (insulin-depleted stat) may lead to lower levels of SREBP-1c; conversely, de-phosphorylation of this site may be involved in stabilizing SREBP-1c by insulin (by blocking GSK-3β action). A functional role of this site needs to be corroborated in vivo. Sterol regulatory element binding protein-1c (SREBP-1c) is a key transcription factor that regulates genes involved in the de novo lipid synthesis and glycolysis pathways. The structure, turnover and transactivation potential of SREBP-1c are regulated by macronutrients and hormones via a cascade of signalling kinases. Using MS, we have identified serine 73 as a novel glycogen synthase kinase-3 (GSK-3) phosphorylation site in the rat SREBP-1c purified from McA-RH7777 hepatoma cells. Our site-specific mutagenesis strategy revealed that the turnover of SREBP-1c, containing wild type, phospho-null (serine to alanine) or phospho-mimetic (serine to aspartic acid) substitutions, was differentially regulated. We show that the S73D mutant of pSREBP-1c, that mimicked a state of constitutive phosphorylation, dissociated from the SREBP-1c–SCAP complex more readily and underwent GSK-3-dependent proteasomal degradation via SCFFbw7 ubiquitin ligase pathway. Pharmacologic inhibition of GSK-3 or knockdown of GSK-3 by siRNA prevented accelerated degradation of SREBP-1c. As demonstrated by MS, SREBP-1c was phosphorylated in vitro by GSK-3β at serine 73. Phosphorylation of serine 73 also occurs in the intact liver. We propose that GSK-3-mediated phosphorylation of serine 73 in the rat SREBP-1c and its concomitant destabilization represents a novel mechanism involved in the inhibition of de novo lipid synthesis in the liver.