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A cytoplasmic structure resembling large protein aggregates induced by interferons
A Meyerdierks1, B Denecke, M Rohde
1Institut für Medizinische Mikrobiologie Medizinische Hochschule Hannover, Hannover, Germany.
Summary
Interferon-stimulated gene 15 (ISG15)-associated protein 35 (IFP 35) forms unique cytoplasmic aggregates in response to interferon treatment. These structures are distinct from known organelles, indicating a novel cellular organization.
Area of Science:
- Cell Biology
- Molecular Biology
- Immunology
Background:
- Interferon (IFN)-regulated proteins play crucial roles in cellular responses to viral infections and immune modulation.
- IFP 35 is an IFN-stimulated leucine zipper protein found in various cell types, including monocytes, epithelial cells, and fibroblasts.
- Understanding the subcellular localization and interactions of IFP 35 is key to elucidating its function.
Purpose of the Study:
- To investigate the subcellular localization and structural associations of IFP 35 in interferon-treated cells.
- To determine if IFP 35 interacts with known cellular organelles or structures.
- To characterize the nature of the cytoplasmic structures formed by IFP 35.
Main Methods:
- Immunofluorescence microscopy and confocal laser scanning microscopy were used to visualize IFP 35 localization.
- Co-localization experiments were performed with markers for various organelles and cellular components.
- Subcellular fractionation and gel filtration were employed to assess protein complex formation and molecular mass.
- Electron microscopy provided ultrastructural details of IFP 35 aggregates.
- Immunoprecipitation studies were conducted using transfected cells expressing tagged IFP 35.
Main Results:
- IFP 35 localizes to punctate cytoplasmic structures following IFN treatment.
- IFP 35 did not co-localize with mitochondria, peroxisomes, endoplasmic reticulum, lysosomes, endosomes, Golgi complex, ribosomes, or actin filaments.
- Subcellular fractionation confirmed IFP 35's cytoplasmic localization.
- Gel filtration indicated IFP 35 exists in large protein complexes (200-440 kD).
- Electron microscopy revealed membrane-less cytoplasmic clusters of IFP 35 aggregates.
- Endogenous and transfected IFP 35 were shown to form complexes and co-localize.
Conclusions:
- IFP 35 forms unique, non-membranous cytoplasmic structures in response to IFN.
- These structures are distinct from conventional organelles and appear to be large protein aggregates.
- IFP 35 self-associates and potentially interacts with other proteins within these novel cellular compartments.