Nuclear Import of the MUC1-C Oncoprotein Is Mediated by Nucleoporin Nup62

Yumei Leng,Cheng Cao,Jian Ren,Lei Huang,Dongshu Chen,Masaki Ito,Donald Kufe

doi:10.1074/jbc.m703222200

Yumei Leng, Cheng Cao + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m703222200

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Abstract

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.

Highlights

Amino acid transmembrane domain, and a 72-amino acid cytoplasmic tail [7]
We demonstrate that MUC1 forms oligomers through a CQC motif in the MUC1 cytoplasmic domain and that MUC1 oligomerization is necessary for nuclear import
MUC1 C-terminal subunit (MUC1-C) Associates with nucleoporin p62 (Nup62)—To investigate mechanisms responsible for nuclear import of MUC1-C, we first asked if MUC1-C associates with importins in MUC1-positive and, as a control, MUC1-negative ZR-75-1 cells

Summary

Introduction

Amino acid transmembrane domain, and a 72-amino acid cytoplasmic tail [7]. Aberrant overexpression of MUC1, as found in most human carcinomas [1], confers anchorageindependent growth and tumorigenicity (8 –11). MUC1-N is shed from the cell surface [19], leaving MUC1-C to function as a transducer of environmental stress signals to the interior of the cell In this regard, MUC1-C forms cell surface complexes with members of the ErbB receptor family, and MUC1-C is targeted to the nucleus in the response to heregulin stimulation [20, 21]. Proteins containing a classical nuclear localization signal (NLS) are imported into the nucleus by first binding to importin ␣ and in turn, importin ␤ [27, 28]. Certain proteins containing nonclassical NLSs are transported through the nuclear pore by binding directly to importin ␤ [30]. The present studies demonstrate that MUC1 is imported into the nucleus by a mechanism involving binding to Nup. Input of the GST proteins was assessed by Coomassie Blue staining

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