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Transport of gamma-interferon into the cell nucleus may be mediated by nuclear membrane receptors
Abstract:
Purified mouse interferon gamma (MuIFN-gamma), a lymphokine having potent antiviral, immunomodulatory, and growth inhibitory activities, is internalized (t1/2 less than 1.0 min) by mouse L929 fibroblasts via receptor-mediated endocytosis. Individual MuIFN-gamma molecules, identified by a postembedding immuno-gold technique, are then transported to the cell nucleus, perhaps through nuclear pores, into areas of dense chromatin. Purified, isolated nuclei of L929 cells bind radiolabeled MuIFN-gamma specifically and with high affinity (Kd = 2 X 10(-10) M). These nuclear membrane receptors, distinct from those for MuIFN-beta, number about 24,000/nucleus. Treatment of nuclei with trypsin prevents binding of MuIFN-gamma. The demonstration of rapid cellular uptake and transport of MuIFN-gamma into the dense chromatin, perhaps facilitated by nuclear receptors, suggests that IFN-gamma molecules, alone or bound to receptor, may directly affect genome regulation.
Insights
Mouse interferon gamma (MuIFN-gamma) rapidly enters L929 fibroblasts and travels to the cell nucleus. Nuclear receptors bind MuIFN-gamma, suggesting it may directly regulate genome activity.
Area of Science:
- Immunology
- Cell Biology
- Molecular Biology
Background:
- Interferon gamma (IFN-γ) is a key lymphokine with antiviral, immunomodulatory, and growth inhibitory functions.
- Understanding the cellular mechanisms of IFN-γ action is crucial for its therapeutic applications.
Purpose of the Study:
- To investigate the cellular uptake and intracellular transport of purified mouse interferon gamma (MuIFN-γ).
- To identify and characterize potential receptors for MuIFN-γ on the surface and within the nucleus of L929 fibroblasts.
Main Methods:
- Utilized receptor-mediated endocytosis to internalize MuIFN-γ in L929 fibroblasts.
- Employed a postembedding immuno-gold technique to track individual MuIFN-γ molecules.
- Performed radioligand binding assays on isolated L929 cell nuclei to quantify MuIFN-γ receptors.
Main Results:
- MuIFN-γ was rapidly internalized by L929 fibroblasts with a half-life under 1.0 minute.
- MuIFN-γ molecules were transported to the cell nucleus and localized within dense chromatin.
- Isolated nuclei exhibited specific, high-affinity binding of MuIFN-γ to approximately 24,000 receptors per nucleus.
- Nuclear receptors for MuIFN-γ were found to be distinct from those for MuIFN-β and sensitive to trypsin treatment.
Conclusions:
- MuIFN-γ undergoes rapid internalization and nuclear transport in L929 fibroblasts.
- Specific nuclear receptors for MuIFN-γ exist and may facilitate its entry into the nucleus.
- The nuclear localization and receptor binding suggest that IFN-γ may directly influence genome regulation.