I-KAPPA-B-ALPHA DEGRADATION IS NOT A REQUIREMENT FOR THE X-RAY-INDUCED ACTIVATION OF NUCLEAR FACTOR KAPPA-B IN NORMAL RAT ASTROCYTES AND HUMAN BRAIN-TUMOR CELLS

Purpose: To investigate the mechanism of NF kappa B activation by X-ra ys in normal primary rat astrocytes. Materials and methods: Primary cu ltures of type I astrocytes generated from the cortex of neonatal rats were exposed to X-rays with and without various kinase inhibitors and a protease inhibitor. The nuclear or cytoplasmic protein extracts wer e collected at specified times after treatment and analysed for NF kap pa B-DNA binding activity and I kappa B protein levels. Results: The N F kappa B-DNA binding activity was induced by X-rays in a dose- and ti me-dependent manner in the absence of I kappa B protein degradation in astrocytes as well as in the human glioma cell line U-373MG. Whereas a protease inhibitor (calpain inhibitor 1) and a protein kinase C inhi bitor (CGP-41251) did not affect X-ray-induced NF kappa B-DNA binding, treatment of astrocytes with the tyrosine kinase inhibitor (erbstatin ) completely prevented the increase in NF kappa B activity after irrad iation. Erbstatin also reduced the phosphorylation of I kappa B alpha after X-ray exposure. Conclusions: These results indicate that, in con trast with the more frequently investigated activators of NF kappa B, radiation-induced activation of this transcription factor proceeds in the absence of I kappa B alpha degradation and requires tyrosine phosp horylation.