Regular Article

British Journal of Cancer (2000) 82, 28–33. doi:10.1054/bjoc.1999.0872 www.bjcancer.com
Published online 10 December 1999

Inhibition of IkappaB-alpha phosphorylation at serine and tyrosine acts independently on sensitization to DNA damaging agents in human glioma cells

J Miyakoshi1 and K Yagi2

  1. 1Department of Radiation Genetics, Graduate School of Medicine Yoshida-Konoe-cho, Sakyo-ku, 606-8501, Japan
  2. 2Department of Zoology, Graduate School of Science, Kyoto University, Yoshida-Konoe-cho, Sakyo-ku, 606-8501, Japan

Received 14 January 1999; Revised 17 June 1999; Accepted 21 June 1999.

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Abstract

Molecular mechanisms and/or intrinsic factors controlling cellular radiosensitivity are not fully understood in mammalian cells. The recent studies have suggested that nuclear factor kappaB (NF-kappaB) is one of such factors. The activation and regulation of NF-kappaB are tightly controlled by IkappaB-alpha, a cellular inhibitory protein of NF-kappaB. Most importantly, phosphorylation regulates activity of the inhibitor IkappaB-alpha, which sequesters NF-kappaB in the cytosol. Two different pathways for the phosphorylation of IkappaB-alpha are demonstrated, such as serine (at residues 32 and 36) and tyrosine (at residue 42) phosphorylations. To assess a role of the transcription factor, NF-kappaB, on cellular sensitivity to DNA damaging agents, we constructed three different types of expression plasmids, i.e. S-IkappaB (mutations at residues 32 and 36), Y-IkappaB (mutation at residue 42) and SY-IkappaB (mutations at residues 32, 36 and 42). The cell clones expressing S-IkappaB and Y-IkappaB proteins became sensitive to X-rays as compared with the parental and vector-transfected cells. The cell clones expressing SY-IkappaB were further radiosensitive. By the treatment with herbimycin A, an inhibitor of phosphorylation, the X-ray sensitivity of cells expressing SY-IkappaB did not change, while that of the cells expressing S-IkappaB and Y-IkappaB and the parental cells was enhanced. Change in the sensitivity to adriamycin and UV in those clones was very similar to that in the X-ray sensitivity. The inhibition of IkappaB-alpha phosphorylation at serine and tyrosine acts independently on the sensitization to X-rays, adriamycin and UV. These findings suggest that the transcriptional activation induced by NF-kappaB may play a role in the DNA damage repair. The present study proposes a possibility that the inactivation of NF-kappaB by inhibition of both serine and tyrosine phosphorylations may be useful for the treatment of cancer in radio- and chemotherapies. © 2000 Cancer Research Campaign

Keywords:

IkappaB-alpha, NF-kappaB, phosphorylation, DNA damaging agents, human glioma cells

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