Increased nuclear suppressor of cytokine signaling 1 in asthmatic bronchial epithelium suppresses rhinovirus induction of innate interferons.
Bottom Line: SOCS1 levels were also correlated with asthma-related clinical outcomes.Suppression of virus-induced interferon levels was dependent on SOCS1 nuclear translocation but independent of proteasomal degradation of transcription factors.Nuclear SOCS1 levels were also increased in BECs from asthmatic patients.
Affiliation: Airway Disease Infection Section, National Heart and Lung Institute, Imperial College London, London, United Kingdom; MRC & Asthma UK Centre in Allergic Mechanisms of Asthma, London, United Kingdom; Centre for Respiratory Infection, Imperial College London, London, United Kingdom.Show MeSH
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Mentions: SOCS1 can prevent nuclear factor κB (NF-κB) signaling by entering the nucleus through a C-terminal proximal nuclear localization sequence (NLS) and targeting NF-κB p65 for proteasomal degradation through the C-terminal SOCS box.32 Therefore we hypothesized that SOCS1 might suppress rhinovirus-induced interferon induction by translocating into the nucleus and initiating proteasomal degradation of transcription factors required for interferon induction. To investigate the role of nuclear translocation of SOCS1 and of the SOCS box, we used vectors expressing green fluorescent protein (GFP)–tagged full-length wild-type human SOCS1 (SOCS1wt) and 2 mutants. The mutants included SOCS1 truncations with both the NLS and the SOCS box deleted (Q108X) or with a deleted SOCS box alone, leaving the NLS intact (R172X; Fig 5, A).32 We found that the SOCS1 mutant that lacked the NLS (Q108X) was indeed unable to translocate to the nucleus; however, both SOCS1wt and R172X, which had a deleted SOCS box but intact NLS, were able to translocate to the nucleus (Fig 5, A). We then tested the ability of these constructs to suppress rhinovirus induction of interferons in BEAS-2B cells and found that the construct lacking the NLS (Q108X) had lost its ability to suppress rhinovirus-induced IFN-β and IFN-λ promoter activation, whereas fully intact SOCS1 (SOCS1wt containing both the NLS and the SOCS box) and R172X (containing the NLS but lacking the SOCS box) were still suppressive (Fig 5, B). Furthermore, SOCS1wt, but neither Q108X nor R172X, suppressed interferon-induced ISRE promoter activation. This definitively proves that SOCS1-mediated suppression of rhinovirus-induced interferon is NLS dependent but SOCS box independent and therefore distinct from interferon-induced ISRE activation, which is dependent on both the NLS and the SOCS box (Fig 5, B). Furthermore, the requirement for nuclear localization for both rhinovirus- and interferon-induced responses was supported with a full-length SOCS1 construct containing mutated NLS residues (Δ6RA), which was impaired in its ability to enter the nucleus and exhibited a less suppressive effect on interferon induction when compared with SOCS1wt (see Fig E6, B-D, in this article's Online Repository at www.jacionline.org). SOCS1wt, R172X, and Q108X proteins were expressed at similar levels, as determined by using Western blotting (see Fig E6, A).
Affiliation: Airway Disease Infection Section, National Heart and Lung Institute, Imperial College London, London, United Kingdom; MRC & Asthma UK Centre in Allergic Mechanisms of Asthma, London, United Kingdom; Centre for Respiratory Infection, Imperial College London, London, United Kingdom.