Jansson Anna M, Csiszar Agnes, Maier Joachim, Nyström Ann-Christin, Ax Elisabeth, Johansson Patrik, Schiavone Lovisa Holmberg
From the Reagents and Assay Development Division, Discovery Sciences Department.
the Institute of Cancer Research, Department of Medicine I, Medical University of Vienna, Borschkegasse 8a, A-1090 Vienna, Austria.
J Biol Chem. 2017 Sep 15;292(37):15501-15511. doi: 10.1074/jbc.M117.782904. Epub 2017 Jul 27.
Production and secretion of pro-metastatic proteins is a feature of many tumor cells. The FAM3C interleukin-like epithelial-to-mesenchymal-transition (EMT) inducer (ILEI) has been shown to be strongly up-regulated in several cancers and to be essential for tumor formation and metastasis in epithelial cells, correlating with a significant decrease in overall survival in colon and breast cancer patients. ILEI has been seen to interact with the γ-secretase presenilin 1 subunit (PS1). However, not much is known about the mechanism-of-action or the detailed ILEI structure. We present here the crystal structures of FAM3C ILEI and show that it exists as monomers but also as covalent dimers. The observed ILEI β-β-α fold confirmed previous indications that the FAM3C proteins do not form classical four-helix-bundle structures as was initially predicted. This provides the first experimental evidence that the interleukin-like EMT inducers are not evolutionarily related to the interleukins. However, more surprisingly, the ILEI dimer structure was found to feature a -linked domain swap, converting an intramolecular disulfide to intermolecular. Interestingly, dimeric but not monomeric ILEI was subsequently found to cause a dose-dependent increase in EpRas cell invasiveness comparable with TGF-β, indicating that the dimer might be the active ILEI species. This is in line with a parallel study showing that covalent oligomerization of ILEI is essential for EMT and tumor progression The structures and the activity data give some first insight into the relationship between dimerization and ILEI function as well as indicate an intriguing link between ILEI, the PS1-protease, TGF-β, and the TGF-β receptor 1.
促转移蛋白的产生和分泌是许多肿瘤细胞的一个特征。FAM3C白细胞介素样上皮-间质转化（EMT）诱导剂（ILEI）已被证明在几种癌症中强烈上调，并且对于上皮细胞中的肿瘤形成和转移至关重要，这与结肠癌和乳腺癌患者的总生存率显著降低相关。已观察到ILEI与γ-分泌酶早老素1亚基（PS1）相互作用。然而，关于其作用机制或ILEI的详细结构知之甚少。我们在此展示了FAM3C ILEI的晶体结构，并表明它以单体形式存在，也以共价二聚体形式存在。观察到的ILEIβ-β-α折叠证实了先前的迹象，即FAM3C蛋白不会形成最初预测的经典四螺旋束结构。这提供了首个实验证据，表明白细胞介素样EMT诱导剂与白细胞介素在进化上无关。然而，更令人惊讶的是，发现ILEI二聚体结构具有一个连接域交换，将分子内二硫键转化为分子间二硫键。有趣的是，随后发现二聚体而非单体ILEI会导致EpRas细胞侵袭性呈剂量依赖性增加，与TGF-β相当，表明二聚体可能是活性ILEI物种。这与一项平行研究一致，该研究表明ILEI的共价寡聚化对于EMT和肿瘤进展至关重要。这些结构和活性数据首次对二聚化与ILEI功能之间的关系提供了一些见解，同时也表明ILEI、PS1蛋白酶、TGF-β和TGF-β受体1之间存在有趣的联系。
