Department of Chemistry and Molecular Biology, University of Gothenburg, 40530 Gothenburg, Sweden.
Department of Chemistry and Molecular Biology, University of Gothenburg, 40530 Gothenburg, Sweden.
J Mol Biol. 2021 Jun 25;433(13):166958. doi: 10.1016/j.jmb.2021.166958. Epub 2021 Mar 24.
Chaperonin Containing Tailless complex polypeptide 1 (CCT) is an essential molecular chaperone required for the folding of the abundant proteins actin and tubulin. The CCT oligomer also folds a range of other proteins and participates in non-folding activities such as providing assembly support for complexes of the von Hippel Lindau tumor suppressor protein and elongins. Here we show that the oncogenic transcription factor STAT3 binds to the CCT oligomer, but does not display the early binding upon translation in rabbit reticulocyte lysate typical of an obligate CCT folding substrate. Consistent with this, depletion of each of the CCT subunits by siRNA targeting indicates that loss of CCT oligomer does not suppress the activation steps of STAT3 upon stimulation with IL-6: phosphorylation, dimerisation and nuclear translocation. Furthermore, the transcriptional activity of STAT3 is not negatively affected by reduction in CCT levels. Instead, loss of CCT oligomer in MCF7 cells leads to an enhancement of STAT3 phosphorylation at Tyr705, implicating a role for the CCT oligomer in the sequestration of non-phosphorylated STAT3. Thus, as CCT is dynamic oligomer, the assembly state and also abundance of CCT oligomer may provide a means to modulate STAT3 phosphorylation.
无尾复合物多肽 1（CCT）的伴侣蛋白是一种必需的分子伴侣，对于肌动蛋白和微管蛋白等丰富蛋白质的折叠是必需的。CCT 寡聚体还折叠一系列其他蛋白质，并参与非折叠活性，如为 von Hippel Lindau 肿瘤抑制蛋白和 elongins 复合物提供组装支持。在这里，我们表明致癌转录因子 STAT3 与 CCT 寡聚体结合，但在兔网织红细胞裂解物中翻译时不显示早期结合，这是一种必需的 CCT 折叠底物的典型特征。与此一致的是，通过 siRNA 靶向每个 CCT 亚基的耗尽表明，在受到 IL-6 刺激时，CCT 寡聚体的缺失不会抑制 STAT3 的激活步骤：磷酸化、二聚化和核易位。此外，CCT 水平降低不会对 STAT3 的转录活性产生负面影响。相反，在 MCF7 细胞中失去 CCT 寡聚体导致 STAT3 在 Tyr705 处的磷酸化增强，表明 CCT 寡聚体在隔离非磷酸化 STAT3 中起作用。因此，由于 CCT 是动态寡聚体，CCT 寡聚体的组装状态和丰度可能提供一种调节 STAT3 磷酸化的方法。
