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Published on: March 2, 2011
Evidence for an intracellular activation loop in the IL-1 system
R Hofmeister1, D N Männel, W Falk
1Department of Internal Medicine I, University of Regensburg, Germany.
Journal of Inflammation
|January 1, 1995
Summary
Interleukin-1 (IL-1) exhibits intracellular activity, bypassing its cell surface receptor. This finding reveals a novel mechanism for IL-1 action and suggests a role for intracellular IL-1 receptor antagonists.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- The precise mechanism of action for the pleiotropic cytokine interleukin-1 (IL-1) remains incompletely understood.
- IL-1's unique ability to be internalized and translocated to the nuclear area in a nondegraded form suggests potential intracellular functions.
- Understanding these intracellular activities is crucial for a comprehensive grasp of IL-1 signaling.
Purpose of the Study:
- To investigate the intracellular activities of interleukin-1 (IL-1).
- To determine if IL-1 can exert biological effects independent of its canonical cell surface receptor, IL-1RI.
- To explore a novel modality of IL-1 action.
Main Methods:
- Transfection of EL4 thymoma cells, expressing IL-1 receptor type I (IL-1RI), with plasmids for intracellular FLAG-IL-1 alpha fusion peptide expression.
- Assessment of IL-2 mRNA expression and IL-2 protein production following intracellular IL-1 delivery.
- Analysis of cell activation and membrane IL-1RI expression in response to intracellular IL-1.
Main Results:
- Intracellular delivery of IL-1 stimulated both IL-2 mRNA expression and IL-2 protein production.
- These intracellular effects were independent of the plasma membrane IL-1RI.
- Cells with functional IL-1RI showed abrogated membrane IL-1RI appearance, indicating IL-1 can bypass and potentially replace the cell surface receptor.
- Evidence suggests the existence of an as-yet-undefined intracellular receptor for IL-1.
Conclusions:
- Intracellularly delivered IL-1 can mediate biological responses, bypassing the need for plasma membrane IL-1RI.
- This represents a novel mechanism of IL-1 action, distinct from canonical signaling pathways.
- The findings support a potential role for intracellular IL-1 receptor antagonists (icIL-IRa) in modulating these newly identified IL-1 activities.
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