Murine interferon-beta receptor-mediated endocytosis and nuclear membrane binding

Area of Science:

• Cellular and Molecular Biology
• Immunology
• Biochemistry

Background:

• Interferons (IFNs) are crucial cytokines involved in immune responses.
• Understanding the cellular mechanisms of IFN-beta action is vital for therapeutic applications.
• Specific receptor interactions and cellular trafficking pathways of IFNs are not fully elucidated.

Purpose of the Study:

• To investigate the binding characteristics and cellular uptake of mouse interferon-beta (MuIFN-beta) in L929 fibroblasts.
• To determine the affinity and receptor density of MuIFN-beta on both the plasma membrane and isolated nuclei.
• To explore the potential intracellular sites of action for MuIFN-beta.

Main Methods:

• Radioiodination of MuIFN-beta for binding assays.
• Saturation binding studies on L929 fibroblasts and isolated nuclei.
• Competition assays using unlabeled MuIFN-beta and MuIFN-gamma.
• Internalization studies at varying temperatures.
• Immunoferritin labeling, fluorescence, and electron microscopy for localization.

Main Results:

• 125I-MuIFN-beta bound to L929 cell plasma membranes with high affinity (Kd = 9.8 x 10(-10) M) and saturable binding.
• MuIFN-beta was rapidly internalized via receptor-mediated endocytosis upon warming to 37°C (t 1/2 = 1.5 min).
• Isolated nuclei exhibited higher affinity (Kd = 1.4 x 10(-10) M) and density for MuIFN-beta, with binding inhibited by MuIFN-beta but not MuIFN-gamma.
• Nuclear binding was reduced by trypsin, suggesting proteinaceous receptors.

Conclusions:

• Receptor-mediated endocytosis is a significant pathway for MuIFN-beta cellular processing.
• The high-affinity binding of MuIFN-beta to nuclear membranes suggests the nucleus as a potential intracellular site for IFN action.
• These findings contribute to understanding the molecular mechanisms underlying interferon signaling and cellular responses.