1. ¹Department of Dermatology, University of Muenster, Muenster, Germany
2. ²Department of Dermatology, University of Kiel, Kiel, Germany
3. ³Department of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany

Correspondence: Dr D Kulms, Institute of Cell Biology and Immunology, University of Stuttgart, Allmandring 31, D-70569 Stuttgart, Germany. E-mail: Dagmar.Kulms@izi.uni-stuttgart.de

Received 21 November 2005; Revised 21 February 2006; Accepted 30 March 2006; Published online 15 May 2006.

Abstract

The transcription factor nuclear factor kappa-B (NF-B) is generally regarded as an antiapoptotic factor. Accordingly, NF-B activation inhibits death ligand-induced apoptosis. In contrast, ultraviolet light B (UVB)-induced apoptosis is not inhibited but even enhanced upon NF-B activation by interleukin-1 (IL-1). This study was performed to identify the molecular mechanisms underlying this switch of NF-B. Enhancement of UVB-induced apoptosis was always associated with increased release of tumour necrosis factor- (TNF-), which was dependent on NF-B activation. The same was observed when UVA and cisplatin were used, which like UVB induce base modifications. In contrast, apoptosis caused by DNA strand breaks was not enhanced by IL-1, indicating that the type of DNA damage is critical for switching the effect of NF-B on apoptosis. Surprisingly, activated NF-B induced TNF- mRNA expression in the presence of all DNA damage-inducing agents. However, in the presence of DNA strand breaks, there was no release of the TNF- protein, which is so crucial for enhancing apoptosis. Together, this indicates that induction of DNA damage may have a significant impact on biological effects but it is the type of DNA damage that determines the final outcome. This may have implications for the role of NF-B in carcinogenesis and for the application of NF-B inhibitors in anticancer therapy.