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Infection and Immunity, October 2007, p. 4998-5003, Vol. 75, No. 10
0019-9567/07/$08.00+0     doi:10.1128/IAI.00545-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Lipopolysaccharide from Salmonella enterica Activates NF-B through both Classical and Alternative Pathways in Primary B Lymphocytes

CNRS, Institut de Biochimie Biophysique Moléculaire et Cellulaire, UMR 8619,¹ Université Paris-Sud, Laboratoire Activation Cellulaire et Transduction de Signaux, Orsay F-91405, France²

Received 16 April 2007/ Returned for modification 11 June 2007/ Accepted 29 July 2007

Lipopolysaccharides (LPS) are potent polyclonal B-lymphocyte activators. Recently, we have shown that LPS inhibits both spontaneous and drug-induced apoptosis in mature B lymphocytes, through cytosolic retention of Bax, a proapoptotic protein of the Bcl-2 family, by preventing its translocation to mitochondria. Research within the last few years has revealed that members of the NF-B transcription factor regulate cell viability by activating genes involved in mitochondrion-dependent apoptosis. In this report, we examined the effect of sustained LPS stimulation on cytosolic and nuclear proteins of the IB/NF-B family to determine which NF-B pathway, canonical (classical) or noncanonical (alternative), is activated by this agent in mature B cells. Immunoblotting analyses showed that LPS induced a time-dependent degradation of the NF-B inhibitors IBß and IB (preferentially to isoform IB), via IB kinase ß. In addition, we observed that LPS triggered the processing of NF-B p105 to p50 and that of NF-B p100 to p52 in parallel with nuclear translocation of active p50 and p52, as NF-Bp50/RelA and NF-Bp52/RelB heterodimers, respectively. These results suggest that sustained stimulation with LPS can activate NF-B through both classical and alternative pathways.

Published ahead of print on 13 August 2007.

Editor: A. Camilli