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Infection and Immunity, February 2008, p. 664-670, Vol. 76, No. 2
0019-9567/08/$08.00+0     doi:10.1128/IAI.00948-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Elucidating the Function of an Ancient NF-B p100 Homologue, CrRelish, in Antibacterial Defense ^,

Ze Hua Fan,^1, Xiao Wei Wang,^1, Jinhua Lu,^2, Bow Ho,^2, and Jeak Ling Ding^1,*

Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Singapore,¹ Department of Microbiology, National University of Singapore, 5 Science Drive 2, Singapore 117597, Singapore²

Received 12 July 2007/ Returned for modification 27 August 2007/ Accepted 9 November 2007

The family of NF-B transcription factors essentially regulates immune-related gene expression. Recently, we isolated and characterized the classical NF-B/inhibitor B (IB) homologues from a "living fossil," the horseshoe crab, Carcinoscorpius rotundicauda. Interestingly, this ancient species also harbors another class I NF-B p100 homologue, C. rotundicauda Relish (CrRelish). Similar to Drosophila Relish and the mammalian p100, CrRelish contains both the Rel-homology domains (RHD) and the IB-like domain. In this study, we found that the RHD of CrRelish can recognize horseshoe crab and human B response elements and activate the downstream reporter in vitro, thereby suggesting the evolutionary conservation of this molecule. Pseudomonas aeruginosa infection transcriptionally upregulates CrRelish, which exhibits a dynamic protein profile over the time course of infection. Surprisingly, secondary infection reinduced an upsurge in CrRelish protein expression to a level which overrode the protein degradation at 12 h postinfection. These observations strongly suggest the involvement of CrRelish in antibacterial defense. Secondary infection causes (i) the maintenance of a favorable expression-competent sequence context of the CrRelish gene and/or (ii) the derepression or stabilization of the CrRelish transcript resulting from the primary infection to enable the more rapid expression and accumulation of the CrRelish protein, reflecting apparent signal/immune priming in a repeated infection.

Published ahead of print on 26 November 2007.

Supplemental material for this article may be found at http://iai.asm.org/.

Editor: F. C. Fang

These two authors share equal first authorship.

Cosenior authors.