New functions of Suppressor of Cytokine Signalling-1 (SOCS1) dependent on its nuclear localization
Immunology
Final Report Abstract
Suppressor of cytokine signaling 1 (SOCS1) is a negative feedback inhibitor of cytoplasmic Janus kinase (JAK) and signal transducer and activator of transcription (STAT) signaling. In 2008, we could show that SOCS1 also contains a bipartite nuclear localization sequence (NLS) resulting in translocation of the protein into the cell nucleus. The exact function of SOCS1 in the cell nucleus remained largely unknown at that time. Subsequent in vitro studies revealed a function of nuclear SOCS to limit nuclear NFκB activity by acting as E3 ubiquitin ligase, mediating proteasomal degradation. To elucidate the in vivo role of SOCS1 in the cell nucleus, within this funding period a transgenic mouse model was established using a bacterial artificial chromosome (BAC) containing a mutated Socs1 locus (Socs1∆NLS) that fails to translocate in the cell nucleus (MGLtg mice). Those mice were characterized in detail during this working period resulting in one major publication in Frontiers in Immunology and one thesis. The main findings were as follows: Whereas mice fully deficient for SOCS1 die within the first three weeks due to excessive interferon signaling and multiorgan inflammation, mice expressing only non-nuclear Socs1∆NLS (Socs1-/-MGLtg mice, back-crosses of MGLtg mice on a SOCS1 deficient background) were rescued from lethality. In those mice, NFκB signaling was prolonged, yet canonical IFNγ signaling as examined by Western Blot, flow cytometry, quantitative real-time PCR and whole-genome expression analysis was functional. Whole genome expression analysis showed that besides altered NFκB regulated genes a subset of nonclassical IFNγ target genes was also differentially regulated in Socs1-/-MGLtg mice. Moreover, in vitro, nuclear SOCS1 was involved in regulation of the cell cycle. The most obvious phenotypical observation was that Socs1-/-MGLtg mice spontaneously developed low-grade inflammation in the lung. This was associated with increased production of Th2-type cytokines and elevated serum IgE levels. In an ovalbumin sensitization and challenge model as well as upon direct administration of IL-13, airway eosinophilia was increased in Socs1-/-MGLtg mice. We observed a reduced epithelial cell barrier integrity by the detection of albumin in BAL and in vitro by measuring transepithelial electrical resistance (TER) in primary trachea epithelial cells from Socs1-/-MGLtg mice. Latest results using bone marrow chimera revealed that the phenotype was due to loss of nuclear SOCS1 within the radiation-resistant cells. In a methodological side project, we established and used µCT for a more detailed analysis of lung lesions and to correlate histological changes with radiological changes. Attempts to generate antibodies for immunohistochemistry of endogenous SOCS1 distribution unfortunately failed. Taken together, the results indicate that nuclear SOCS1 plays a specific role in regulating local immunity in the lung and thus unravels a so far unrecognized function for SOCS1 in the cell nucleus.
Publications
- (2015): Increased nuclear SOCS1 in asthmatic bronchial epithelium suppresses rhinovirus induction of innate interferons. J Allergy Clin Immunol. 136 (1): 177–188.e11
Gielen V, Sykes A, Zhu J, Chan B, Macintyre J, Regamey N, Kieninger E, Gupta A, Shoemark A, Bossley C, Davies J, Saglani S, Walker P, Nicholson SE, Dalpke AH, Kon OM, Bush A, Johnston SL and Edwards MR
(See online at https://doi.org/10.1016/j.jaci.2014.11.039) - (2016): Endoplasmic Reticulum Stress Is a Danger Signal Promoting Innate Inflammatory Responses in Bronchial Epithelial Cells. J Innate Immun; 8(5):464-78
Mijošek V, Lasitschka F, Warth A, Zabeck H, Dalpke AH, Michael Weitnauer
(See online at https://doi.org/10.1159/000447668) - (2016): Nuclear localization of Suppressor of Cytokine Signaling (SOCS)-1 regulates local immunity in the lung. Front. Immunol. 7: 514
Zimmer J, Weitnauer M, Boutin S, Küblbeck G, Thiele S, Walker P, Lasitschka F, Lunding L, Orinska Z, Vock V, Arnold B, Wegmann M and Dalpke A
(See online at https://doi.org/10.3389/fimmu.2016.00514)
