Cytokine-induced nuclear translocation of STAT1 via a non-transferable NLS

Kumar, P.; Cavey, J. R.; Yang, R.; White, O.; Begitt, A.; He, L.; Suinn, S. S.; Bellis, N. F.; Lokareddy, R. K.; Vinkemeier, U.; Cingolani, G.

doi:10.64898/2026.09.28.754937

bioRxiv · 10.64898/2026.09.28.754937

Cytokine-induced nuclear translocation of STAT1 via a non-transferable NLS

Kumar, P.·Cavey, J. R.·Yang, R.·White, O.·Begitt, A.·He, L.·Suinn, S. S.·Bellis, N. F.·Lokareddy, R. K.·Vinkemeier, U.·Cingolani, G.

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Abstract

The targeting function of nuclear localization signals (NLSs) is generally considered independent of a protein's native sequence or fold and is readily transferable to heterologous cargos. Contrary to this paradigm, rapid nuclear translocation of phosphorylated STAT1 (pSTAT1) following cytokine stimulation requires importin {beta}, Ran-GTP, and the importin 5 isoform, which recognizes a non-transferable NLS. Here, we present cryo-EM structures of pSTAT1 bound to importin 5, revealing an asymmetric 2:1 complex that diverges from canonical NLS-mediated cargo recognition. Importin 5 occupies the DNA-binding groove of the pSTAT1 dimer, with a single STAT1 N-terminal domain positioning the C-terminal Armadillo repeats 9-10 (S1B domain) orthogonal to the DNA-binding interface. This interface is also targeted by the Ebola virus protein VP24, an antagonist of interferon signaling. We further show that Ran-GTP alone is insufficient to trigger nuclear release of pSTAT1, which additionally requires the exportin CAS. A cryo-EM reconstruction of the CAS-Ran-GTP-5 complex, supported by in vitro competition assays, demonstrates that CAS and pSTAT1 are mutually exclusive ligands for importin 5. Together, these findings define the molecular choreography of cytokine-induced STAT1 nuclear translocation and release, establishing a general paradigm for STAT family signaling.

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Kumar, P., Cavey, J. R., Yang, R., White, O., Begitt, A., He, L., Suinn, S. S., Bellis, N. F., Lokareddy, R. K., Vinkemeier, U., Cingolani, G.. 2026-09-29. Cytokine-induced nuclear translocation of STAT1 via a non-transferable NLS. https://doi.org/10.64898/2026.09.28.754937

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