Nucleolin Responds to DNA Damage

Abstract

Stimuli that damage DNA activate stress-signaling pathways that include the activation of the tumor suppressor p53. Daniely et al. report that ionizing radiation (IR) or the drug camptothecin produce a transient p53-dependent redistribution of nucleolin from nucleoli to the nucleoplasm. This redistribution did not occur in cells lacking p53 or in cells in which p53 expression was inhibited through a tetracycline-repressible system. Nucleolin and p53 were coprecipitable, and the formation of the complex was stimulated by IR or camptothecin. Not all stresses that stimulated phosphorylation of p53, such as ultraviolet radiation, also stimulated the formation of the nucleolin-p53 complex. Although p53 was required for the redistribution of nucleolin, analysis of cells expressing mutant versions of p53 showed that transcriptional activity of p53 was not required. However, cells expressing a COOH-terminally truncated version of p53 did not redistribute nucleolin in response to IR, nor was a complex detectable between the p53 COOH-terminal truncation mutant and nucleolin. Nucleolin when present in nucleoli is important for processing of precursor ribosomal RNA. Once released from the nucleoli into the nucleoplasm, nucleolin may inhibit DNA replication through interactions with replication protein A and may stimulate DNA annealing, which would promote DNA repair. Y. Daniely, D. D. Dimitrova, J. A. Borowiec, Stress-dependent nucleolin mobilization mediated by p53-nucleolin complex formation. Mol. Cell. Biol. 22 , 6014-6022 (2002). [Abstract] [Full Text]