Xpo7 is a broad-spectrum exportin and a nuclear import receptor

Abstract

Exportins bind cargo molecules in a RanGTP-dependent manner inside nuclei and transport them through nuclear pores to the cytoplasm. CRM1/Xpo1 is the best-characterized exportin because specific inhibitors such as leptomycin B allow straightforward cargo validations in vivo. The analysis of other exportins lagged far behind, foremost because no such inhibitors had been available for them. In this study, we explored the cargo spectrum of exportin 7/Xpo7 in depth and identified not only ∼200 potential export cargoes but also, surprisingly, ∼30 nuclear import substrates. Moreover, we developed anti-Xpo7 nanobodies that acutely block Xpo7 function when transfected into cultured cells. The inhibition is pathway specific, mislocalizes export cargoes of Xpo7 to the nucleus and import substrates to the cytoplasm, and allowed validation of numerous tested cargo candidates. This establishes Xpo7 as a broad-spectrum bidirectional transporter and paves the way for a much deeper analysis of exportin and importin function in the future.

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© 2018 Aksu et al. This article is available under a Creative Commons License (Attribution 4.0 International, as described at https://creativecommons.org/licenses/by/4.0/). Submitted: December 4, 2017. Revision received April 9, 2018. Accepted: April 24, 2018. Published May 10, 2018. We thank J. Krull, R. Rees, G. Hawlitschek, and U. Plessmann for excellent technical assistance; U. Teichmann and R. Rümenapf for animal care and immunizations; the group of R. Lührmann for the HeLa cell extract; and Alpaca Ramona for sharing her immune repertoire. This work was supported by the Max-Planck-Gesellschaft and the Deutsche Forschungsgemeinschaft (project B3/SFB 860 to D. Görlich, Z02/SFB 1190 to H. Urlaub, and P14/SFB 1190 to M.T. Bohnsack) for funding. Author contributions: M. Aksu, T. Pleiner, M.T. Bohnsack, and D. Görlich designed experiments; M. Aksu, T. Pleiner, S. Karaca, H.-J. Dehne, M.T. Bohnsack, and D. Görlich performed experiments; M. Aksu, T. Pleiner, S. Karaca, C. Kappert, H. Urlaub, M.T. Bohnsack, and D. Görlich analyzed and interpreted data; K. Seibel contributed reagents; M. Aksu and D. Görlich wrote the paper; T. Pleiner and M.T. Bohnsack contributed to writing; and all authors approved the manuscript. The authors declare no competing financial interests.

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