Leng Yumei, Cao Cheng, Ren Jian, Huang Lei, Chen Dongshu, Ito Masaki, Kufe Donald
Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA.
J Biol Chem. 2007 Jul 6;282(27):19321-30. doi: 10.1074/jbc.M703222200. Epub 2007 May 11.
The MUC1 heterodimeric transmembrane protein is aberrantly overexpressed by most human carcinomas. The MUC1 C-terminal subunit (MUC1-C) is devoid of a classical nuclear localization signal and is targeted to the nucleus by an unknown mechanism. The present results demonstrate that MUC1-C associates with importin beta and not importin alpha. The results also show that, like importin beta, MUC1-C binds to Nup62 (nucleoporin p62). MUC1-C binds directly to the Nup62 central domain and indirectly to the Nup62 C-terminal alpha-helical coiled-coil domain. We demonstrate that MUC1-C forms oligomers and that oligomerization is necessary for binding to Nup62. The MUC1-C cytoplasmic domain contains a CQC motif that when mutated to AQA abrogates oligomerization and binding to Nup62. Stable expression of MUC1 with the CQC --> AQA mutations was associated with targeting to the cell membrane and cytosol and attenuation of nuclear localization. The results further show that expression of MUC1(CQC-AQA) attenuates MUC1-induced (i) transcriptional coactivation, (ii) anchorage-independent growth, and (iii) tumorigenicity. These findings indicate that the MUC1-C oncoprotein is imported to the nucleus by a pathway involving Nup62.
MUC1异二聚体跨膜蛋白在大多数人类癌症中异常过度表达。MUC1 C末端亚基（MUC1-C）缺乏经典的核定位信号，通过未知机制靶向细胞核。目前的结果表明，MUC1-C与输入蛋白β而非输入蛋白α相关联。结果还表明，与输入蛋白β一样，MUC1-C与核孔蛋白62（Nup62）结合。MUC1-C直接与Nup62中央结构域结合，并间接与Nup62 C末端α螺旋卷曲螺旋结构域结合。我们证明MUC1-C形成寡聚体，并且寡聚化对于与Nup62结合是必需的。MUC1-C胞质结构域包含一个CQC基序，当突变为AQA时，会消除寡聚化并与Nup62的结合。具有CQC→AQA突变的MUC1的稳定表达与靶向细胞膜和细胞质以及核定位的减弱有关。结果进一步表明，MUC1（CQC-AQA）的表达减弱了MUC1诱导的（i）转录共激活、（ii）不依赖贴壁生长和（iii）致瘤性。这些发现表明，MUC1-C癌蛋白通过涉及Nup62的途径被导入细胞核。
