Ionizing radiation induces expression and binding activity of the nuclear factor kappa B

Area of Science:

• Cellular Biology
• Radiation Biology
• Molecular Biology

Background:

• Ionizing radiation (IR) triggers gene expression in mammalian cells.
• Signal transduction pathways activated by IR are not fully understood.
• Previous work indicated IR induces specific genes transcriptionally.

Purpose of the Study:

• To investigate the effect of ionizing radiation on the transcription factor NF-kappa B (NF-κB).
• To determine the dose-dependent and time-course of NF-κB activation by IR.
• To elucidate the mechanism of NF-κB activation by IR, specifically whether it involves de novo protein synthesis.

Main Methods:

• Mammalian cell treatment with varying doses of ionizing radiation (2-20 Gy).
• Assessment of NF-κB DNA binding activity using electrophoretic mobility shift assays.
• Measurement of NF-κB mRNA levels.
• Experiments conducted in the presence of cycloheximide to inhibit protein synthesis.

Main Results:

• Ionizing radiation significantly increased NF-κB DNA binding activity, detectable at 2 Gy and peaking at 5-20 Gy.
• Maximal NF-κB binding activity occurred 2-4 hours post-irradiation at 20 Gy, then decreased.
• Ionizing radiation caused a transient increase in NF-κB mRNA levels.
• NF-κB DNA binding was induced by IR even when protein synthesis was inhibited (cycloheximide treatment), indicating activation of pre-existing NF-κB protein.

Conclusions:

• Ionizing radiation activates the transcription factor NF-κB in mammalian cells.
• Activation of NF-κB by IR is dose-dependent and time-dependent.
• IR-induced NF-κB activation occurs through post-translational modification of pre-existing cytoplasmic NF-κB protein, involving cytoplasmic signaling events, rather than de novo synthesis.