ISG15 in Interferon-mediated signaling

ISG15 ubiquitin-like modifier (ISG15) functions intracellularly as a Ubiquitin homologue and a cytokine. ISG15 induces production of IFN-gamma and augments NK/lymphokine-activated killer cell proliferation and function. Secreted from monocytes and lymphocytes, low levels of ISG15 are present constitutively in PBMCs. Interestingly, a dose-dependent ISG15 synthesis has been observed in response to IFN-alpha or IFN-beta, but not IFN-gamma.

Western Blot with Anti-Human ISG15 MAb Mouse Monoclonal Antibody against Human ISG15, Clone 2.1 Catalog No. 09321900-1

Control (C) and Treated (T) 40 μg lysate samples from A549, Ovcar and HeLa cells were run alongside 50 ng recombinant ISG15 and 100 μg ubiquitin. Cells were either untreated (C) or treated (T) with 1000 U/ml of Human IFN beta 1a (Cat. No. 09311410-2) and lysed with protease inhibitors on ice, then centrifuged to obtain supernatants. No cross-reactivity was observed with ubiquitin at tested concentrations up to 100 μg. The antibody (Cat. No. 09321900-1) was additionally tested on Daudi and U937 cell lysates (data not shown).

For instance, ISG15 is secreted in response to IFN-beta treatment in vitro in healthy volunteers, as seen by measuring ISG15 serum levels (1). A process mediated by ISG15, ISGylation, has been described to have a role in immunomodulation after bacterial infection (2). HCV also induces ISG15 expression (3).

Briefly, ISG15 expression seems to regulate, at least in part, Type I interferon signaling, translation, chromatin remodeling, cell motility, protein trafficking, and protein conjugation (ISGylation). Still, the complete spectrum of ISG15-dependent biological sequelae re-mains to be fully elucidated.

Further characterization of new ISG15 target proteins and the role of free ISG15 may offer new insights into mechanistic and immuno-therapeutic approaches to human diseases.

Tools to detect ISG15 should be able to detect both bound and free-ISG15, and have no cross-reactivity with ubiquitin (e.g. anti-human ISG15, clone 2.1), as this may hinder the interpretation of results found with biological samples.

References

  1. D’Cunha, J. et al.  Journal of Immunology, 1996, 157:4100.
  2. Dieterich, C. & Relman, D.A. PLoS ONE 6(11): e27535. doi:10.1371/journal.pone.0027535.
  3. Arnaud, N. et al. PLoS Pathog, 2011, 7(10): e1002289. doi: 10.1371/journal.ppat.1002289.

Studying the role of ISG15 in your experimental model?

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