Role of IκBα and IκBβ in the biphasic nuclear translocation of NF‐κB in TNFα‐stimulated astrocytes and in neuroblastoma cells

Abstract

In infectious diseases of the central nervous system astrocytes respond to inflammatory cytokines like tumor necrosis factor α (TNFα) by activation of the transcription factor NF-κB, mediated by the proteolysis of its inhibitors IκBα and IκBβ. We studied the kinetics of NF-κB induction by TNFα in primary astrocytes, and in the neuroblastoma cell line Neuro2A, and compared it to fibroblasts. In the latter, NF-κB DNA binding activity was induced at 30 min and remained constant up to 4 h. In contrast, in astrocytes and in Neuro2A cells NF-κB DNA binding activity followed a biphasic pattern: it was induced after 30 min (early phase), declined after 1 h, and increased again at 2 to 4 h (late phase). The early phase was due to rapid degradation of IκBα. After 1 h IκBα was resynthesized to levels exceeding the amounts present in unstimulated cells. This paralleled the low levels of nuclear NF-κB binding activity. The decrease was not observed when IκBα resynthesis was inhibited by cycloheximide. Degradation of both IκBα and IκBβ contributed to the late phase of induction. However, the second peak occurred also in the absence of IκBβ proteolysis, demonstrating the importance of IκBα in the formation of the biphasic nuclear translocation of NF-κB. GLIA 26:212–220, 1999. © 1999 Wiley-Liss, Inc.